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Knowledge of Didelphidae taxonomy and diversity has increased steadily over the last decades, mainly due to increasing collection efforts and revisionary works. Yet, especially for mouse opossums, a proper appraisal of morphological variation is still incipient. Thylamys karimii occurs in the Brazilian biomes of Caatinga and Cerrado, and specimens with two different shades of dorsal coloration (brown and gray) were recently documented in sympatry in the Parque Nacional (PARNA) do Catimbau (Caatinga biome). We used qualitative and morphometric data from skulls and skins (n = 7 from PARNA Catimbau and n = 26 from other localities) to compare these two coat color morphotypes and characterize the morphological diversity and taxonomic status of the Caatinga populations. We used Student's t-tests to compare sexes and morphotypes' measurements. We found at least three well-defined coat color morphotypes distinguishable by dorsal and ventral coloration and not restricted to PARNA Catimbau. Variation of the other morphological traits suggests that these morphotypes are more likely a case of intraspecific variation in the Brazilian northeastern region. Morphometric differences, particularly between coat color morphotypes, might be better elucidated in larger samples. Additionally, these specimens represent an important extension of the species' known distribution reaching the Atlantic Forest borders. [ABSTRACT FROM AUTHOR]

\nIntroduction: In many mammals, the testes descend from its abdominal position on the mesonephric kidney and are housed in the scrotum. It has been speculated that metatherians and eutherians might have acquired the scrotal testis independently because metatherians have the scrotum cranially to the phallus, while eutherians, such as humans and mice, possess it caudally. Rather, recent studies based on sequence comparisons of testis-descent-related genes indicate that the metatherian-eutherian common ancestor might already possess the descent mechanisms. To further elucidate the path of scrotal testis evolution, it is informative to compare the processes of the descent and scrotum development between metatherian and eutherian model animals. Methods: In this study, we histologically and molecularly compare these processes in gray short-tailed opossum (Monodelphis domestica), the most commonly used metatherian experimental model, and compare them with those in mouse. Results: Our observations indicate that, while transabdominal phase of the descent appears to be largely similar, scrotal phase differs due to their distinct scrotum positions. Our cell-labeling analyses and dynamic expression of Gsc1 reveal extensive cell/tissue rearrangements in murine scrotal development. In contrast, Gsc1 is not expressed in the developing genitalia and scrotal primordium of the opossum. Conclusion: Our results suggest recruitment of new regulatory pathways for the scrotum development and the scrotal phase of the testis descent during the evolution of eutherian mammals. In many mammals, the testes are housed into the scrotum. While marsupials, such as kangaroo and opossum, have the scrotum cranially to the phallus, placentals, such as human and mouse, have it caudally. In this study, we compare the process of testis descent and scrotum development in opossum and mouse. We show extensive cell/tissue rearrangements in the mouse scrotal development. Our results suggest recruitment of new regulatory pathways for the scrotum development and the testis descent during the evolution of placental mammals. [ABSTRACT FROM AUTHOR]

Background: The common opossum (Didelphis marsupialis) is a generalist species that hosts several parasites. Nevertheless, no information is available on the specific parasites that this species may host when it inhabits urban areas. Objective: To evaluate the presence and frequency of gastrointestinal parasites of urban opossums in the Aburrá Valley, Antioquia, Colombia. Methods: A total of 70 opossums were captured in six protected urban areas using Tomahawk traps during six months. From these animals we obtained 65 fecal samples which were fixed wit SAF solution and analyzed with direct smear and sedimentation techniques. Results: Sixty-one samples were positive for, at least, one parasite (93.9%) and 60 were positive for two or more parasites, averaging five parasites per animal. We observed nematodes in 58 samples (89.2%), protozoa in 46 samples (70.7%), acanthocephalans in 29 samples (44.6%), and cestodes in eight samples (12.3%). The most frequent parasite was Aspidodera spp. in 80% of the samples. In addition, this is the first study reporting the presence of eggs of Toxocara spp., Hymenolepis spp., an Oxyuridae parasite, and coccidians Eimeria didelphidis, E. caluromydis, and E. marmosopos in D. marsupialis. The latter is also reported in Colombia for the first time. Toxacara spp. is common to dogs and cats, while Hymenolepis and Oxiuridae are common to rodents. We found no association between parasites and sex or life stage of opossums, nor to the urban area of origin. Conclusions: Urban opossums in the Aburrá Valley host a high frequency and diversity of gastrointestinal parasites compared to other areas in Latin America. Some parasites are reported here for the first time. [ABSTRACT FROM AUTHOR]

Opossums (marsupials of the Didelphidae family) retain a generalized masticatory apparatus and tribosphenic molars, often used as models to understand the evolution of mastication in early therian mammals. Like all marsupials, their growth goes through a stage when pups complete their development while permanently attached to the mother's teats before weaning and starting feeding on their own. Yet, while the masticatory muscles of adults are known, as is the ontogeny of the cranium and mandible, the ontogenetic changes in the masticatory muscles remain unknown. Here we describe for the first time the changes in the masticatory muscles observed in lactating pups, and weaned juveniles, subadults, and adults in the White‐eared opossum, Didelphis albiventris, through dissection of 25 specimens and quantification of relative muscle masses, lines of actions and mechanical advantages whenever possible. We also assessed the scaling patterns of muscle masses and mechanical advantages through ontogeny. The main changes, as expected, were found between suckling and weaned specimens, although some changes still occurred from juveniles to adults. The adult adductor musculature is similar to the other Didelphis species already known, with a dominant m. temporalis that originates on the lateral wall of the skull, up to the sagittal and nuchal crests, and fills the zygomatic arch when inserting into the lateral and medial surfaces of the coronoid process, respectively through the pars superficialis and pars profunda. The m. masseter is also subdivided in superficial and deep bundles which originate posteriorly in the maxilla and zygomatic arch, and insert into the angular process and masseteric fossa in the mandible. The m. pterygoideus medialis originates from the palatine, the pterygoid bone and the alisphenoid, and it inserts on the angular process medially. Suckling pups showed muscles with more restricted attachments, reduced muscle lines of action, and less diversity in the fiber orientation. The absence of the postorbital constriction also resulted in a distinct morphology of the m. temporalis pars profunda, through two bundles, one anterior and one posterior, which insert more inferiorly into the mandible. These major changes can be related to the onset of mastication and to size‐related changes in growing weaned age classes. In general, all adductor muscles grew with positive allometry, and increased their fixation areas through, in part, the development of specific regions of the cranium and mandible. Their lines of action also increase and diversify along ontogeny. These changes can be related to the functional requirements for fixation during lactation, which shift to adduction and mastication movements after weaning. [ABSTRACT FROM AUTHOR]

Cellular DNA is subject to damage from a multitude of sources and repair or bypass of sites of damage utilize an array of context or cell cycle dependent systems. The recognition and removal of oxidatively damaged bases is the task of DNA glycosylases from the base excision repair pathway utilizing two structural families that excise base lesions in a wide range of DNA contexts including duplex, single-stranded and bubble structures arising during transcription. The mammalian NEIL2 glycosylase of the Fpg/Nei family excises lesions from each of these DNA contexts favoring the latter two with a preference for oxidized cytosine products and abasic sites. We have determined the first liganded crystal structure of mammalian NEIL2 in complex with an abasic site analog containing DNA duplex at 2.08 Å resolution. Comparison to the unliganded structure revealed a large interdomain conformational shift upon binding the DNA substrate accompanied by local conformational changes in the C-terminal domain zinc finger and N-terminal domain void-filling loop necessary to position the enzyme on the DNA. The detailed biochemical analysis of NEIL2 with an array of oxidized base lesions indicates a significant preference for its lyase activity likely to be paramount when interpreting the biological consequences of variants.

Bat‐pollinated plants feature open flowers, facilitating easy access to their abundant nectar for various animal groups. The Caatinga, a Brazilian Seasonally Tropical Dry Forest, stands out globally as a hotspot for bat‐pollinated plants. This study presents the first documentation of the opossum Didelphis albiventris (Marsupialia) engaging in the consumption of nectar on flowers of Hymenaea cangaceira (Fabaceae), a bat‐pollinated tree species within the Caatinga. The observation spanned five nights and occurred unexpectedly during an experiment involving bagged flowers to assess nectar dynamics. Initially, torn bags were discovered containing flowers, which nectar had been consumed. Subsequent nights revealed the opossum actively exploring bagged flowers, likely guided by the fragrant nectar of H. cangaceira, and unmanipulated flowers located in the canopy's upper reaches. Given the opossum's contact with reproductive structures during these visits, it emerges as a potential pollinator. Following this observation, a comprehensive literature review on Didelphis interactions with other plants was conducted, leading to the construction of a meta network. This network unequivocally illustrates that the majority of plants visited by Didelphis indeed have bats as their primary pollinators. Owing to the nocturnal, arboreal and stealthy nature of opossums, documenting their interactions with flowers proves highly challenging. Consequently, our record highlights significant knowledge gaps in comprehending the interplay between opossums and chiropterophilous flowers. These gaps include the under‐sampling of this process in the Caatinga, the role of olfactory signalling and the broader consequences of this unique interaction. [ABSTRACT FROM AUTHOR]

The bushy-tailed opossum Glironia venusta is a rare marsupial from Amazonia, with most of the known records obtained through scant visualization/photography events or by few captures/deposit of specimens in scientific collections. This study presents unusual records for the species: the first record of individuals dead due to vehicle collision, and a specimen opportunistically trapped into a mistnet. The data presented herein provide additional morphometrical data and ecological insights about G. venusta. Although this species is considered essentially arboreal, our records indicate that movements on ground are part of its habits. [ABSTRACT FROM AUTHOR]

The non-indigenous mysid Neomysis americana (S.I. Smith, 1873) is reported here, for the first time, along the Bay of Biscay in the Loire estuary, France in 2021. This species, originating from North-American estuaries, was initially discovered in Europe in 2010 (Wadden Sea) and first reported in France in 2017 (Seine estuary). The absence of long-term monitoring makes it impossible to know precisely the arrival of this non-indigenous species in the Loire estuary. However, this species is present in high abundance, suggesting an arrival prior to 2021. Its introduction might even be prior to or concomitant to the Seine estuary discovery, suggesting an introduction via the ballast water of the commercial vessels. [ABSTRACT FROM AUTHOR]

Parasites are key players in ecosystems, influencing population sizes and food webs, yet the impact of environmental factors on their diversity is not well understood. The Atlantic rainforest in Brazil, particularly the Parque Estadual das Fontes do Ipiranga (PEFI), exemplifies a biodiversity hotspot facing significant deforestation, housing diverse animal species such as the synanthropic Brazilian common opossum (Didelphis aurita), which serves as a reservoir for multiple zoonotic pathogens. In this study, we investigated parasite diversity, abundance, prevalence, and richness in free-living D. aurita in the PEFI, São Paulo, Brazil. From January 2015 to January 2017, 101 fecal samples of D. aurita were collected in two areas of PEFI, at the Instituto de Pesquisas Ambientais (IPA) and the Parque de Ciência e Tecnologia (Cientec), and analyzed using three different parasitological methods. In total, 99% of the samples were positive for at least one parasite. The most prevalent parasite belonged to the order Strongylida (82%), followed by Cruzia sp. (77%), the latter having a significantly higher prevalence at IPA. In contrast, Acanthocephala showed greater prevalence at Cientec. Co-infections were common, with some individuals harboring up to seven different parasites. Our findings reveal significant parasite diversity in the D. aurita population at PEFI, including both helminths and protozoan trophozoites, some of which are reported for the first time in this host species. Further research is essential for accurate species identification of the observed parasites. [ABSTRACT FROM AUTHOR]

Didelphid marsupials are considered a morphologically unspecialized group with a generalist diet that includes vertebrates, invertebrates, and plant matter. While cranium and scapula variation has already been examined within Didelphidae, variation in mandible shape, usually associated with diet or phylogeny in other mammalian groups, has not yet been properly assessed in the family. We evaluated the variation in mandible shape and size of didelphids (2470 specimens belonging to 94 species) using 2D geometric morphometrics. We classified the diet of the didelphids into four broad categories to assess whether morphospace ordination relates to dietary habits. We also provided the most comprehensive phylogeny for the family (123 out of the 126 living species) using 10 nuclear and mitochondrial genes. We then mapped mandible size and shape onto that phylogeny for 93 selected taxa and ancestral size and shapes were reconstructed by parsimony. We found phylogenetically structured variation in mandible morphology between didelphid groups, and our results indicate that they have a significant phylogenetic signal. The main axis of shape variation is poorly related to size, but the second is strongly allometric, indicating that allometry is not the main factor in shaping morphological diversity on their mandibles. Our results indicate that the shape and size of the ancestral mandible of didelphids would be similar to that of the current species of the genus Marmosa. [ABSTRACT FROM AUTHOR]

Knowledge regarding the influence of individual traits on interaction patterns in nature can help understand the topological role of individuals within a network of intrapopulation interactions. We tested hypotheses on the relationships between individuals' positions within networks (specialization and centrality) of 4 populations of the mouse opossum Gracilinanus agilis and their traits (i.e. body length, body condition, tail length relative to body length, sex, reproductive condition, and botfly parasitism) and also seasonal effects in the Brazilian savanna. Individuals with lower body length, better body condition, and relatively shorter tail were more specialized (i.e. less connected within the network). Individuals were also more specialized and less connected during the warm-wet season. The relationship between individuals' position in the network and body traits, however, was independent of season. We propose that specialization may arise not only as a result of preferred feeding strategies by more capable individuals (i.e. those with better body condition and potentially prone to defend and access high-quality food resources) but also because of morphological constraints. Smaller/younger individuals (consequently with less experience in foraging) and short-tailed individuals (less skilled to explore the vertical strata of the vegetation) would feed only on a subset of the available food resources and consequently become more specialized. Moreover, individuals are more specialized during the warm-wet season because of high competition (population-dense period) and higher ecological opportunities (resource-rich period). Therefore, our study reveals the relevance of individual traits in shaping interaction patterns and specialization in populations. [ABSTRACT FROM AUTHOR]

ABSTRACT Canopy mammals constitute a diverse and widely distributed group. However, these species have not been widely studied, and there are currently many gaps in our knowledge of their ecology, behaviour, distribution, and conservation status. We identified crucial trends and omissions in terms of research effort on research themes, taxonomic groups, countries, and protected areas (PAs) and geographic information biases. A systematic review was conducted by consulting two electronic databases (Web of Science and Scopus), including research conducted within neotropical countries (from central Mexico to northern Argentina) until the end of the first half of 2021. All the references obtained were reviewed and categorised, and the geographical location of each study was extracted to evaluate geographical gaps. We found that two orders (Carnivora and Didelphimorphia) and three families (Didelphidae, Felidae, and Cricetidae) were the most studied taxa, and were featured in more than 50% of cases. Brazil had the highest number of studies. Topics concerning diseases (19% of cases), distribution (14%), and ecology (14%) were the most frequently addressed; only 4.6% of the studies focused on anthropogenic disturbances, and less than 30% of the studies were conducted within PAs. We found that one of the largest and most important geographical biases in knowledge was in the northern Amazon region, where the number of studies was low or null. This study lays the groundwork for future research on these understudied mammals, to develop better research that can allow us to design more appropriate conservation strategies. [ABSTRACT FROM AUTHOR]

Background: Although urban wildlife has increased during the last years, the effects of urbanization on wildlife are poorly understood. Common opossum (Didelphis marsupialis) is a frequent dweller of the Metropolitan Area of Valle del Aburrá (AMVA) in the Antioquia province (Colombia) where opossum-human conflicts result in large numbers of injured or dead opossums. Objective: To evaluate the effects of urban and rural habitats on the morphometry and reproductive output (litter size in marsupium) of opossums. Methods: A total of 131 opossums were captured: 94 in the AMVA, and 37 in rural areas of Antioquia. Opossums were weighed, measured, sexed, clinically inspected, and photographed. Results: Urban opossums were heavier and larger than rural individuals, regardless of sex, and no differences were observed in terms of reproductive output between both habitats. Additionally, urban opossums were more abundant than rural opossums, possibly explained by the fact that cities favor survival -through higher food availability-but not reproduction. Alternatively, bigger animals could also be explained by inadequate diets rich in carbohydrates which may also have deleterious health effects. We observed sexual size dimorphism in head and tail length but not in body length of opossums. Conclusion: We confirm that urban environments have a significant effect on body mass and size of opossums; however, it is unknown whether this is beneficial or detrimental for these animals. Finally, we report the lowest litter size for the species, with no difference between rural and urban habitats. [ABSTRACT FROM AUTHOR]

The Andean white ear opossum (Didelphis pernigra, Allen 1900) is one of the three species of the genus Didelphis reported in Colombia. Here we present a systematic review of D. pernigra in Colombia, with a geographical and altitudinal distribution hypothesis from the country. We reported geographic records and scientific available information of D. pernigra in 40 studies, 55.26 % of the available literature corresponded to local and regional inventories; 23.68 % of other documents were studies about mammal assemblages, while 21.05 % were specific studies about the species and the genus Didelphis in Colombia. We classified literature according to the following subcategories: natural history, diet, inventories, threats, reproduction, uses and perceptions. Most of the literature corresponded to detection in inventories (55.26 %), followed by natural history information (21.05 %) and threats (7.89 %). Research about diet, uses, perception and reproduction, had the lowest proportion with 5.26 %. Regarding distribution, geographic records ranged between 1060 and 3740 m across the three Andean ranges of Colombia. In general, little is known about the ecology or natural history of the species, efforts should be focused on filling the information gaps about natural history, and surveys should fill the distribution gaps along the Western and Central ranges of Colombia. [ABSTRACT FROM AUTHOR]

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Macropodid alphaherpesvirus 2 (MaAHV2) is best described in macropods and has been implicated in outbreaks among captive marsupial populations in Australia. Natural disease caused by herpesviruses has not been reported previously in opossum species, to our knowledge. One Virginia opossum (Didelphis virginiana) and 1 water opossum (Chironectes minimus) were submitted for postmortem examination from a zoo that housed 6 opossums, all of which died within several weeks. Red kangaroos (Macropus rufus) and red-necked wallabies (Macropus rufogriseus) were also present at the facility. Liver samples from both opossums were submitted for transmission electron microscopy and whole-genome sequencing. Microscopically, both opossums had multifocal necrosis in the liver and lung, with intranuclear inclusion bodies within hepatocytes and pneumocytes. Another significant finding in the Virginia opossum was sepsis, with isolation of Streptococcus didelphis from various organs. Ultrastructural analysis of formalin-fixed liver tissue identified herpesviral replication complexes in both opossums; negative-stain electron microscopy of unfixed liver tissue repeatedly yielded a negative result. The herpesvirus had >99% nucleotide identity with MaAHV2. These 2 cases indicate that both opossum species are susceptible to MaAHV2 infection, and the outbreak has implications for mixed-species facilities that house macropods. [ABSTRACT FROM AUTHOR]

The genus Gracilinanus ranges from savannas to dense forests in South America, yet its systematics have never been thoroughly investigated across its wide distributional range. We assessed Gracilinanus phylogenetic relationships, species boundaries, and geographical limits using mtDNA sequences. Our analysis confirmed the distinctiveness of the six recognized species (G. aceramarcae, G. agilis, G. emiliae, G. marica, G. microtarsus, and G. peruanus), with a mean p-distance for interspecific nucleotide sequence divergences ranging from 13–16.2% and robust phylogenetic support (BPP > 0.95; BS > 75%). Refined species delimitation approaches (GMYC, PTP, ASAP) revealed potential cryptic diversity, suggesting up to 20 candidate species. Three geographically structured and divergent lineages (4.1–4.8% sequence divergence) were identified within G. agilis, extending its Cerrado range. Within G. emiliae, we found divergence values ranging from 4.7–5.7% and the first known record for the northeastern Atlantic Forest. Three divergent clades were recovered within G. microtarsus (9.0–9.8% sequence divergence), including a new lineage for the northern Atlantic Forest. For G. peruanus, we found two divergent lineages (7.2%) and the first documented occurrence for Amazonian lowland forest. This comprehensive sampling revealed greater genetic diversity in Gracilinanus, extending its geographic limits. Here we propose nine putative new species, emphasizing a hidden diversity that warrants formal description and further increases the taxonomic diversity of this genus. These newly identified lineages underscore the urgency of inventorying and conserving the threatened ecosystems of the Cerrado and Atlantic Forest hotspots. [ABSTRACT FROM AUTHOR]

The Peruvian gracile mouse opossum (Gracilinanus peruanus) is known from scattered localities. Very little information is available on its natural history, habitat requirements and geographic distribution. Also, its conservation status has never been evaluated. We provide a new hypothesis on its distribution limits using species distribution models (SDM), and evaluate for the first time the conservation status of the species. The SDM suggested high suitability for G. peruanus in the Brazilian Shield, indicating continuous suitable areas for the species between the disjunct areas of western Brazil and Bolivia/Peru. Voucher records show that Teles Pires River is not a geographic barrier and the eastern limits still need to be delimited. To the south, the species appears to be limited by the Pantanal wetlands and the Chaco biome, and to the west by the Andes mountains. We suggest that G. peruanus should be globally classified as 'Least Concern.' Nevertheless, the species may be considered as Near Threatened in a near future in Brazil, mainly because it occurs in an area with high rates of deforestation and habitat loss in the Cerrado of western Brazil, thus reinforcing the importance of protecting gallery forests to forest dweller species. [ABSTRACT FROM AUTHOR]

In Mexico opossums are difficult to find, and much of their natural history, ecology, and behavior are unknown. Through photographic and visual records, we obtained data on the presence of two species of marsupials in southern Mexico. We report new municipal records of Derby's woolly opossum, Caluromys derbianus in Veracruz, and new municipal records of the Gray four-eyed opossumPhilander opossum for Oaxaca, Veracruz, and Chiapas. Local mammal records are crucial for understanding the biology and ecology of species, as well as identifying its threats. [ABSTRACT FROM AUTHOR]

Ticks are hematophagous arthropods and, during feeding, may transmit pathogens to vertebrate hosts, including humans. This study aimed to investigate the presence of Rickettsia spp. in ticks collected between 2010 and 2013 from free-ranging capybaras (Hydrochoerus hydrochaeris) and opossums (Didelphis albiventris) that inhabit Sabiá Park in Uberlândia, Brazil. Overall, 1,860 ticks were collected: 1,272 (68.4%) from capybaras (487 of the species Amblyomma sculptum, 475 adults and 12 nymphs; 778 Amblyomma dubitatum, 727 adults and 51 nymphs; and seven larva clusters of the genus Amblyomma); and 588 (31.6%) from opossums (21 A. sculptum, one adult and 20 nymphs; 79 A. dubitatum, all nymphs; 15 Ixodes loricatus, 12 adults and three nymphs; 457 Amblyomma sp. larva clusters; 15 Ixodes sp. larva clusters; and one Argasidae larva cluster). Out of 201 DNA samples tested for the presence of Rickettsia spp. DNA using polymerase chain reaction (PCR) 12 showed amplification of a gtlA gene segment that was specific to Rickettsia bellii, a bacterium non-pathogenic to humans. As there has been a report showing serological evidence of infections caused by Rickettsia species of the spotted fever group (SFG) in capybaras and opossums in the park, including Rickettsia rickettsii, the etiological agent of Brazilian spotted fever, and considering the presence of A. sculptum ticks, which are aggressive to humans, as well as these vertebrate hosts, which are amplifiers of R. rickettsii, it is important to monitor the presence of SFG rickettsiae in the Sabiá Park, which is visited daily by thousands of people. [ABSTRACT FROM AUTHOR]

Introduction: The gray short-tailed opossum, Monodelhis domestica (M. domestica), is a widely used marsupial model species that presents unique advantages for neurodevelopmental studies. Notably their extremely altricial birth allows manipulation of postnatal pups at timepoints equivalent to embryonic stages of placental mammals. A robust literature exists on the development of short-tailed opossums, but many researchers working in the more conventional model species of mice and rats may find it daunting to identify the appropriate age at which to conduct experiments. Methods: Here, we present detailed staging diagrams taken from photographic observations of 40 individual pups, in 6 litters, over 25 timepoints across postnatal development. We also present a comparative neurodevelopmental timeline of short-tailed opossums (M. domestica), the house mouse (Mus musculus), and the laboratory rat (Rattus norvegicus) during embryonic as well as postnatal development, using timepoints taken from this study and a review of existing literature, and use this dataset to present statistical models comparing the opossum to the rat and mouse. Results: One aim of this research was to aid in testing the generalizability of results found in rodents to other mammalian brains, such as the more distantly related metatherians. However, this broad dataset also allows the identification of potential heterochronies in opossum development compared to rats and mice. In contrast to previous work, we found broad similarity between the pace of opossum neural development with that of rats and mice. We also found that development of some systems was accelerated in the opossum, such as the forelimb motor plant, oral motor control, and some aspects of the olfactory system, while the development of the cortex, some aspects of the retina, and other aspects of the olfactory system are delayed compared to the rat and mouse. Discussion: The pace of opossum development is broadly similar to that of mice and rats, which underscores the usefulness of this species as a compliment to the more commonly used rodents. Many features that differ the most between opossums and rats and mice were either clustered around the day of birth and were features that have functional importance for the pup immediately after or during birth, or were features that have reduced functional importance for the pup until later in postnatal development, given that it is initially attached to the mother. [ABSTRACT FROM AUTHOR]

Unusual colorations are rare in Didelphis, but records are important to understand genetic aspects of the species. Albino individuals have a total absence of pigmentation throughout the body (skin and hair) and have eyes without traces of pigmentation, but with a red or pink color. We draw attention to the first two confirmed records of albinism in white-eared opossum (Didelphis albiventris) and their karyotype. This is the first record of albinism in D. albiventris in Northeastern Brazil. This calls attention to develop future research on the genetic diversity and the risk of inbreeding and consanguinity in populations of this region. [ABSTRACT FROM AUTHOR]

Marsupials are born with structurally immature lungs when compared to eutherian mammals. The gray short-tailed opossum (Monodelphis domestica) is born at the late canalicular stage of lung development. Despite the high degree of immaturity, the lung is functioning as respiratory organ, however supported by the skin for gas exchange during the first postnatal days. Consequently, the majority of lung development takes place in ventilated functioning state during the postnatal period. Microcomputed tomography (μCT) was used to three-dimensionally reconstruct the terminal air spaces in order to reveal the timeline of lung morphogenesis. In addition, lung and air space volume as well as surface area were determined to assess the functional relevance of the structural changes in the developing lung. The development of the terminal air spaces was examined in 35 animals from embryonic day 13, during the postnatal period (neonate to 57 days) and in adults. At birth, the lung of Monodelphis domestica consists of few large terminal air spaces, which are poorly subdivided and open directly from short lobar bronchioles. During the first postnatal week the number of smaller terminal air spaces increases and numerous septal ridges indicate a process of subdivision, attaining the saccular stage by 7 postnatal days. The 3D reconstructions of the terminal air spaces demonstrated massive increases in air sac number and architectural complexity during the postnatal period. Between 28 and 35 postnatal days alveolarization started. Respiratory bronchioles, alveolar ducts and a typical acinus developed. The volume of the air spaces and the surface area for gas exchange increased markedly with alveolarization. The structural transformation from large terminal sacs to the final alveolar lung in the gray short-tailed opossum follows similar patterns as described in other marsupial and placental mammals. The processes involved in sacculation and alveolarization during lung development seem to be highly conservative within mammalian evolution. [ABSTRACT FROM AUTHOR]

Angiostrongylus costaricensis is a metastrongyloid nematode that primarily infects themesenteric arteries of wild rodents. This parasite is endemic in several regions of the American continent, and in humans, causes a disease known as abdominal angiostrongyliasis. Despite the important health implications of this nematode, there are limited studies investigating the involvement of wild animals in its life cycle. In this study, we present the clinical manifestations, pathologic findings, and molecular diagnosis, to the best of our current knowledge, of the first documented onset of cerebral angiostrongyliasis because of A. costaricensis infection in a juvenile free-ranging opossum (Didelphis marsupialis). Histopathological findings stress the presence of eosinophilic meningoencephalitis with nematodes present within the lesions, and PCR was positive for cox1 and ITS1 reactions. The obtained sequences for a 279 bp fragment of ITS1 were 100% identical to A. costaricensis from Costa Rica. This case highlights the substantial difficulties in diagnosing neuroangiostrongyliasis, yet underscores the importance of considering A. costaricensis as a potential culprit behind neurological conditions in wild marsupials. It acts as an urgent call to action to improve surveillance programs tracking infectious and parasitic diseases causing mortality in wildlife populations. [ABSTRACT FROM AUTHOR]

Climate change is one of the main threats to biodiversity in the 21st century. However, the effects that it may have on different mammal species are unknown, making it difficult to implement conservation strategies. In this paper, we used species distribution models (SDM) to assess the effect of global climate change on the potential distribution of the 8 of the 9 marsupial species in Mexico, and analyzed their distribution in the current system of natural protected areas (NPAs). We used presence records for each species and bioclimatic variables from the present and the future (2050 and 2080) with 2 contrasting possible scenarios (representative concentration pathways RCP 4.5 and 8.5). We found that Tlacuatzin canescens would have the most stable potential range under any climate change scenario, while the remaining species (Caluromys derbianus, Chironectes minimus, Didelphis marsupialis, D. virginiana, Philander opossum, Marmosa mexicana , and Metachirus nudicaudatus) would undergo notable range losses in the future, though there would not only be losses—according to our SDMs, for all species there would be some range gain under the different climate scenarios, assuming the vegetation cover remained. The current system of NPAs in Mexico currently protects and under the 2 future scenarios would protect less than 20% of the potential range of marsupials, so a reevaluation of their areas beyond the NPAs is highly recommended for the long-term conservation of this group. Our results provide relevant information on the estimated effects of global climate change on marsupials, allowing us to design more effective methodologies for the protection of this portion of the mammalian fauna in Mexico. [ABSTRACT FROM AUTHOR]

In marsupials, upper-layer cortical neurons derived from the progenitors of the subventricular zone of the lateral ventricle (SVZ) mature morphologically and send their axons to form interhemispheric connections through the anterior commissure. In contrast, eutherians have evolved a new extra callosal pathway, the corpus callosum, that interconnects both hemispheres. In this study, we aimed to examine neurogenesis during the formation of cortical upper layers, including their morphological maturation in a marsupial species, namely the opossum (Monodelphis domestica). Furthermore, we studied how the axons of upper layers neurons pass through the anterior commissure of the opossum, which connects neocortical areas. We showed that upper-layer II/III neurons were generated within at least seven days in the opossum neocortex. Surprisingly, these neurons expressed special AT-rich sequence binding protein 2 (Satb2) and neuropilin 1 interacting protein (Nrp1), which are proteins known to be essential for the formation of the corpus callosum in eutherians. This indicates that extrinsic, but not intrinsic, cues could be key players in guiding the axons of newly generated cortical neurons in the opossum. Although oligodendrocyte precursor cells were present in the neocortex and anterior commissure, newly generated upper-layer neurons sent unmyelinated axons to the anterior commissure. We also found numerous GFAP-expressing progenitor cells in both brain structures, the neocortex and the anterior commissure. However, at P12–P17 in the opossums, a small population of astrocytes was observed only in the midline area of the anterior commissure. We postulate that in the opossum, midline astrocytes allow neocortical axons to be guided to cross the midline, as this structure resembles the glial wedge required by fibers to cross the midline area of the corpus callosum in the rodent. [ABSTRACT FROM AUTHOR]

(1) Background: Central nervous system (CNS) development is characterized by dynamic changes in cell proliferation and differentiation. Key regulators of these transitions are the transcription factors such as SOX2 and SOX9. SOX2 is involved in the maintenance of progenitor cell state and neural stem cell multipotency, while SOX9, expressed in neurogenic niches, plays an important role in neuron/glia switch with predominant expression in astrocytes in the adult brain. (2) Methods: To validate SOX2 and SOX9 expression patterns in developing opossum (Monodelphis domestica) cortex, we used immunohistochemistry (IHC) and the isotropic fractionator method on fixed cortical tissue from comparable postnatal ages, as well as dissociated primary neuronal cultures. (3) Results: Neurons positive for both neuronal (TUJ1 or NeuN) and stem cell (SOX2) markers were identified, and their presence was confirmed with all methods and postnatal age groups (P4-6, P6-18, and P30) analyzed. SOX9 showed exclusive staining in non-neuronal cells, and it was coexpressed with SOX2. (4) Conclusions: The persistence of SOX2 expression in developing cortical neurons of M. domestica during the first postnatal month implies the functional role of SOX2 during neuronal differentiation and maturation, which was not previously reported in opossums. [ABSTRACT FROM AUTHOR]

The white‐eared opossum (Didelphis albiventris) is a Neotropical marsupial that occurs in the Brazilian territory. The larynx is an important organ of vocalization in mammals, although, other laryngeal functions are more fundamental for survival of mammals than phonation. The anatomical knowledge of respiratory structures is pivotal for a better understanding of the species. Thus, this study aimed to examine the larynx of the white‐eared opossum by gross anatomy, computed tomography and histological description. For this, 10 adult (six females and four males) white‐eared opossums (D. albiventris) were used. The white‐eared opossum larynx was formed by epiglottis, thyroid, cricoids and arytenoid cartilages and a corniculate process. There is a similarity between the larynx of this marsupial and those reported in other wild mammals, regarding the number of cartilages and their location. Histologically, the epiglottis consisted of elastic cartilage and thyroid, cricoid and arytenoid cartilages were composed of hyaline cartilage. The epiglottis protruded rostrally into the nasal part of the pharynx, above the soft palate, and this is probably a marsupial characteristic as the fact that the thyroid and cricoid cartilages were ventrally fused. The hyoid apparatus was similar to that of other animals, with the same bony constitution, but with a greatly reduced stylohyoid bone. Histologically, the larynx was similar to those of other species such as koala, armadillo, crab‐eating foxes and giant anteaters. The knowledge of the larynx morphology is important for the anatomical features of the species and clinical and surgical procedures, such as endotracheal intubation. [ABSTRACT FROM AUTHOR]

Wildlife is a potential source for emerging and re-emerging zoonotic diseases. Trichinella spiralis is the major etiological agent that causes Trichinella spp. infection in humans and domestic pigs, but other Trichinella species are also involved. Pigs are the most important source of Trichinella spp. infection worldwide, being their outdoor breeding, waste feeding, their exposure to wildlife and carcasses, the documented risk factors for pig production, food security, and health. Early Trichinella spp. detection and the study of their reservoir’s competence are needed to prevent and control Trichinella spp. infection. The aims of this study were to analyze the occurrence of Trichinella spp. infection in in synanthropic and non-synanthropic wild and domestic animals in rural areas and compare Trichinella spp. infection in synanthropic and non-synanthropic wild small mammals on intensive and extensive piggeries. This is a two-year study in an endemic area of the disease. To evaluate parasite infection, we included samples from animals captured in 18 intensive and extensive piggeries and from road-killed vertebrates collected lengthwise 882 km within 13 counties along eight consecutive seasons. Trichinella spp. infection association to small mammals’ infestation levels and community composition and structure was analyzed. From a total of 697 wild and domestic animals analyzed, infected Rattus norvegicus and Didelphis albiventris individuals were found in two extensive piggeries. The parasite was not found outside piggeries. Infections were identified as T. spiralis by a Nested-Multiplex PCR. These findings showed some evidence that supports the idea that extensive farming has a higher risk of transmission of T. spiralis than intensive farming. [ABSTRACT FROM AUTHOR]

The white-eared opossum (Didelphis albiventris) is a neotropical marsupial that inhabits various ecoregions and highly modified environments. However, there is limited research on host-parasite interactions and the structure of helminth communities in D. albiventris. Therefore, the aim of this study is to investigate the intestinal helminths of D. albiventris inhabiting a rural area in Buenos Aires, Argentina, and assess the relationship between host age and sex and helminth community structure. Opposums were captured in 2004 and intestines were examined to detect helminths. By analyzing 22 intestines, we identified a total of 8 978 helminths, including Cruzia tentaculata, Turgida turgida, Rhopalias coronatus, Brachylaima sp., individuals of the family Diplostomidae, and a single specimen of a cestode. Among these, C. tentaculata and R. coronatus were the most prevalent species, with C. tentaculata exhibiting the highest levels of abundance, mean intensity, and aggregation index. To assess the influence of host sex and age on parasite abundance and probability of occurrence, we conducted Generalized Linear Models. The results revealed that host juveniles had lower helminth prevalence and abundance compared to other age categories. Host sex was only significant in interaction with host age for parasite abundance in C. tentaculata and R. coronatus. Most captured juveniles relied on maternal feeding, potentially reducing exposure to consuming infected intermediate hosts with indirect life cycles. Understanding the parasite ecology of this opossum species in modified environments provides valuable information about their role at the wildlife-human interface in anthropogenic areas. [ABSTRACT FROM AUTHOR]

The brown-eared woolly opossum (Caluromys lanatus) is an elusive frugivorous Neotropical canopy specialist marsupial considered primarily arboreal, but here we report the first records of individuals from this species captured on the ground in the Cerrado. We hypothesize two main reasons to explain this behavior: first related to canopy openness, which would force the animals to the ground to keep moving across the landscape; and the second related with search for food on the ground during periods of food scarcity due to increased canopy gaps. Our findings can have important implications for the species conservation and understanding forest ecological dynamics. [ABSTRACT FROM AUTHOR]

Understanding the predatory behavior of a species is critical to its ecological role. Little is known about the predatory behavior of the marsupial Didelphis aurita. Here, we present two cases to shed light on its opportunistic nature: an opossum struggling to locate and attack an immobile juvenile bird, indicating olfactory detection and visual constraints, and an opossum carrying a weakened rat that was host of four blowfly larvae. These events reinforce D. aurita's opportunistic behavior in attacking debilitated vertebrates. [ABSTRACT FROM AUTHOR]

Rodent carcasses are a source of food and a biological hazard that can commonly be found in natural and anthropic ecosystems. Therefore, this article aims to determine which organisms consume those carcasses in an urban reserve. For this, 53 rodent carcasses were placed in front of camera traps to record their consumers. The final destiny of 41 carcasses is known: 76 % were consumed by opossums (Didelphis virginiana) and 24 % by ringtails (Bassariscus astutus). Flies and ants attempted to take advantage of the carcasses but in all cases ended up losing the competition to mammals. Opossums are the most efficient carrion consumers, as they exhibit learning as to where the carcasses are located and are able to consume old carcasses (up to 10 days old). This suggests that mid-size mammals, especially opossums, are providing an important ecological and health service for both natural ecosystems and human populations by removing rodent carcasses that otherwise could become sources of infection. [ABSTRACT FROM AUTHOR]

Abstract Background The genus Borrelia comprises pathogenic species of bacteria that pose a significant risk to public health. Borrelia spp. are emerging or reemerging infectious agents worldwide with complex transmission cycles, and many species use rodents as vertebrate reservoir hosts. Spirochetes morphologically compatible with Borrelia have been recurrently observed in opossums; however, there is currently a lack of genetic evidence confirming infection or supporting that these marsupials are hosts of Borrelia spirochetes. Methods During 2017, 53 serum samples of Didelphis marsupialis from the municipality of Colosó (department of Sucre, Colombia) were collected and allocated in a serum bank. DNA extracted from the serum samples was submitted to a Borrelia genus-specific real-time PCR targeting the 16S rRNA gene. Positive samples were subsequently derived from semi-nested PCR protocols to obtain large fragments of the 16S rRNA and flaB genes. Obtained amplicons were subjected to Sanger sequencing. One positive sample was randomly selected for next-generation sequencing (NGS). Obtained reads were mapped to genomes of Borrelia spp. and sequences of two genes used in a multilocus sequence typing scheme retrieved for taxonomic assignment and phylogenetic analyses. Results Overall, 18.8% (10/53) of the samples were positive by qPCR. Of them, 80% (8/10) and 60% (6/10) were positive for the 16S rRNA and flaB genes after semi-nested PCRs, respectively. Bioinformatic analysis of one sample sequenced with NGS yielded 22 reads of genus Borrelia with different sizes. Two housekeeping genes, rplB and pyrG, were recovered. Nucleotide pairwise comparisons and phylogenetic analyses of 16S rRNA, flaB, rplB and pyrG genes showed that the Borrelia sp. found in opossums from Colosó corresponded to Borrelia puertoricensis. Conclusions We describe the first molecular evidence to our knowledge of B. puertoricensis in Colombia, specifically in opossums, and the first detection of this spirochete in a vertebrate host since its isolation from Ornithodoros puertoricensis in Panama. This detection is also relevant because of the epidemiological importance of opossums as reservoirs of zoonotic diseases to humans. Graphical abstract

Didelphis virginiana (the Virginia opossum) is often used as an extant model for understanding feeding behaviour in Mesozoic mammaliaforms, primarily due to their morphological similarities, including an unfused mandibular symphysis and tribosphenic molars. However, the three-dimensional jaw kinematics of opossum chewing have not yet been fully quantified. We used biplanar videofluoroscopy and the X-Ray Reconstruction of Moving Morphology workflow to quantify mandibular kinematics in four wild-caught opossums feeding on hard (almonds) and soft (cheese cubes) foods. These data were used to test hypotheses regarding the importance of roll versus yaw in chewing by early mammals, and the impact of food material properties (FMPs) on jaw kinematics. The magnitude of roll exceeds that of yaw, but both are necessary for tooth-tooth or tooth-food-tooth contact between complex occlusal surfaces. We confirmed the utility of the four vertical kinematic gape cycle phases identified in tetrapods but we further defined two more in order to capture non-vertical kinematics. Statistical tests support the separation of chew cycle phases into two functional groups: occlusal and non-occlusal phases. The separation of slow close into two (occlusal) phases gives quantitative kinematic support for the long-hypothesized multifunctionality of the tribosphenic molar. This article is part of the theme issue 'Food processing and nutritional assimilation in animals'. [ABSTRACT FROM AUTHOR]

Background: The genus Borrelia comprises pathogenic species of bacteria that pose a significant risk to public health. Borrelia spp. are emerging or reemerging infectious agents worldwide with complex transmission cycles, and many species use rodents as vertebrate reservoir hosts. Spirochetes morphologically compatible with Borrelia have been recurrently observed in opossums; however, there is currently a lack of genetic evidence confirming infection or supporting that these marsupials are hosts of Borrelia spirochetes. Methods: During 2017, 53 serum samples of Didelphis marsupialis from the municipality of Colosó (department of Sucre, Colombia) were collected and allocated in a serum bank. DNA extracted from the serum samples was submitted to a Borrelia genus-specific real-time PCR targeting the 16S rRNA gene. Positive samples were subsequently derived from semi-nested PCR protocols to obtain large fragments of the 16S rRNA and flaB genes. Obtained amplicons were subjected to Sanger sequencing. One positive sample was randomly selected for next-generation sequencing (NGS). Obtained reads were mapped to genomes of Borrelia spp. and sequences of two genes used in a multilocus sequence typing scheme retrieved for taxonomic assignment and phylogenetic analyses. Results: Overall, 18.8% (10/53) of the samples were positive by qPCR. Of them, 80% (8/10) and 60% (6/10) were positive for the 16S rRNA and flaB genes after semi-nested PCRs, respectively. Bioinformatic analysis of one sample sequenced with NGS yielded 22 reads of genus Borrelia with different sizes. Two housekeeping genes, rplB and pyrG, were recovered. Nucleotide pairwise comparisons and phylogenetic analyses of 16S rRNA, flaB, rplB and pyrG genes showed that the Borrelia sp. found in opossums from Colosó corresponded to Borrelia puertoricensis. Conclusions: We describe the first molecular evidence to our knowledge of B. puertoricensis in Colombia, specifically in opossums, and the first detection of this spirochete in a vertebrate host since its isolation from Ornithodoros puertoricensis in Panama. This detection is also relevant because of the epidemiological importance of opossums as reservoirs of zoonotic diseases to humans. [ABSTRACT FROM AUTHOR]

[Display omitted] • Raccoon (Procyon lotor) is an intermediate host of Sarcocystis neurona in the Americas. • We describe an outbreak of clinical disease in nine raccoons with S. neurona Ag Type I. • Ten years and thousands of miles separate the two outbreaks in raccoons and marine mammals. • Diagnosis was confirmed histologically, immunohistochemically, and by bioassays in knockout mice and in cell culture. • Molecular characterization using 11 genes confirmed S. neurona infection. Here, we report the first known outbreak of clinical protozoal myeloencephalitis in naturally infected raccoons by the parasite Sarcocystis neurona. The North American opossum (Didelphis virginiana) and the South American opossum (Didelphis albiventris) are its known definitive hosts. Several other animal species are its intermediate or aberrant hosts. The raccoon (Procyon lotor) is considered the most important intermediate host for S. neurona in the USA. More than 50% of raccoons in the USA have sarcocysts in their muscles, however clinical sarcocystosis in raccoons is rare. In 2014, 38 free-living raccoons were found dead or moribund on the grounds of the Saint Louis Zoo, Missouri, USA. Moribund individuals were weak, lethargic, and mildly ataxic; several with oculo-nasal discharge. Seven raccoons were found dead and 31 were humanely euthanized. Postmortem examinations were conducted on nine raccoons. Neural lesions compatible with acute sarcocystosis were detected in eight raccoons. The predominant lesions were meningoencephalitis and perivascular mononuclear cells. Histologic evidence for the Canine Distemper Virus was found in one raccoon. Schizonts and merozoites were present in the encephalitic lesions of four raccoons. Mature sarcocysts were present within myocytes of five raccoons. In six raccoons, S. neurona schizonts and merozoites were confirmed by immunohistochemical staining with S. neurona -specific polyclonal antibodies. Viable S. neurona was isolated from the brains of two raccoons by bioassay in interferon gamma gene knockout mice and in cell cultures seeded directly with raccoon brain homogenate. Molecular characterization was based on raccoon no. 68. Molecular characterization based on multi-locus typing at five surface antigens (SnSAG1-5 - 6, SnSAG3 and SnSAG4) and the ITS-1 marker within the ssrRNA locus, using DNA isolated from bradyzoites released from sarcocysts in a naturally infected raccoon (no. 68), confirmed the presence of S. neurona antigen type I, the same genotype that caused a mass mortality event in which 40 southern sea otters stranded dead or dying within a 3 week period in April 2004 with S. neurona -associated disease. An expanded set of genotyping markers was next applied. This study reports the following new genotyping markers at 18S rRNA, 28S rRNA, COX1 , ITS-1 , RON1 , RON2 , GAPDH1 , ROP20 , SAG2 , SnSRS21 and TUBA1 markers. The identity of Sarcocystis spp. infecting raccoons is discussed. [ABSTRACT FROM AUTHOR]

As human development continues to expand, wildlife must relocate or adapt to survive. Many mammalian mesopredators, such as the Virginia opossum (Didelphis virginiana), have adapted to living alongside human development. Furthermore, top‐down predation pressure may be altered in nuanced ways within the human environment. Species such as opossums may be shielded from predation by human development or behavioral changes in predators. Understanding how dominant and subordinate mesopredators co‐exist across natural and developed areas will provide insight into how wildlife communities are structured. Our objective was to evaluate how opossum occupancy, abundance, and activity were associated with human development and the relative abundance of their predators. We used data from a nationwide camera trapping study, Snapshot USA, to estimate opossum occupancy, abundance, and activity. We related these measures to the surrounding landscape and urbanization variables. We found that opossum occupancy was positively associated with anthropogenic sound (a surrogate for human activity). Furthermore, opossums in heavily forested areas were more likely to be detected in locations with higher predicted anthropogenic sounds. In areas with a high density of human housing, opossum relative abundance increased when predator abundance increased. We also found opossums were strictly nocturnal and shifted their activity to earlier in the evening in the presence of high predator abundance. Our results suggest that humans and their urban development can have multidimensional impacts on opossum behavior and occurrence, and could facilitate changes in predator–prey dynamics. Future research should evaluate if the association of opossums with urban areas is due to human‐subsidized resources or caused by reduced mortality from altered predator–prey dynamics. [ABSTRACT FROM AUTHOR]

Streptococcus didelphis was once reported as related to severe infections in opossums. Thus, we present the first comprehensive whole-genome characterization of clinical S. didelphis strains isolated from white-eared opossums (Didelphis albiventris). Long-read whole-genome sequencing was performed using the MinION platform, which allowed the prediction of several genomic features. We observed that S. didelphis genomes harbor a cluster for streptolysin biosynthesis and a conserved genomic island with genes involved in transcriptional regulation (arlR) and transmembrane transport (bcrA). Antimicrobial resistance genes for several drug classes were found, including beta-lactam, which is the main antimicrobial class used in Streptococcus spp. infections; however, no phenotypical resistance was observed. In addition, we predicted the presence of 33 virulence factors in the analyzed genomes. High phylogenetic similarity was observed between clinical and reference strains, yet no clonality was suggested. We also proposed dnaN, gki, pros , and xpt as housekeeping candidates to be used in S. didelphis sequence typing. This is the first whole-genome characterization of S. didelphis , whose data provide important insights into its pathogenicity. [ABSTRACT FROM AUTHOR]

Murine typhus is an acute febrile illness caused by Rickettsia typhi, an obligately intracellular Gram-negative coccobacillus. Rats (Rattus species) and their fleas (Xenopsylla cheopis) serve as the reservoir and vector of R. typhi, respectively. Humans become infected when R. typhi-infected flea feces are rubbed into flea bite wounds or onto mucous membranes. The disease is endemic throughout much of the world, especially in tropical and subtropical seaboard regions where rats are common. Murine typhus is reemerging as an important cause of febrile illness in Texas and Southern California, where an alternate transmission cycle likely involves opossums (Didelphis virginiana) and cat fleas (Ctenocephalides felis). Although primarily an undifferentiated febrile illness, a range of neurologic manifestations may occur, especially when treatment is delayed. Serology is the mainstay of diagnostic testing, but confirmation usually requires demonstrating seroconversion or a fourfold increase in antibody titer from acute- and convalescent-phase sera (antibodies are seldom detectable in the first week of illness). Thus, early empiric treatment with doxycycline, the drug of choice, is imperative. The purpose of this review is to highlight murine typhus as an important emerging and reemerging infectious disease, review its neurologic manifestations, and discuss areas in need of further study. [ABSTRACT FROM AUTHOR]