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Pomacea canaliculata is one of the most dangerous invasive species. Morphological and molecular analyses have revealed that a digenean species belonging to the family Echinostomatidae parasitizes this snail at two sites in Buenos Aires Province, Argentina, South America. Molecular results confirmed that the species belongs to a genus closely related to Patagifer. Analysis of the 28S rDNA showed that the sequences of the rediae and metacercariae are identical, indicating that the apple snail acts as the first and second intermediate host. The cercariae may encyst as metacercaria inside the redia and also emerge and re-infect the same snail or another snail. The prevalence of digeneans was higher in one of the sampling locations (15.1% vs. 0.72%), probably because the bird species that acts as the definitive host is more abundant in that area. Histopathological examination showed that the parasite quickly invades multiple host organs (gills, intestines, albumen gland, lung, kidney, and mantle border) besides the gonad and digestive gland, as is usual in digeneans. In addition, the partial or total castration of snails was observed in cases of moderate and high infection intensity. In males, there was loss of integrity in testicular tubules, while in females, the replacement of ovarian tissue by rediae was found

Histopathology associated with the apicomplexan Aggregata valdessensis in the wild population of Octopus tehuelchus was studied. Moreover, to analyze the impact of the prevalence and infection intensity on the dorsal mantle length, sex, maturity stages, condition index and total hemocyte counts on wild O. tehuelchus, Generalized Linear Models (GLMs) were applied. Kruskal–Wallis (KW) test was used to compare growth parameter (RNA/DNA ratios) in infected and uninfected octopuses. Lesions including hypertrophy of host cells and destruction of the tissue organ architecture as well as the replacement of host tissue by parasites were associated with infection. The infection caused an inflammatory defensive response in form of hemocytic infiltration.. The prevalence of apicomplexan increased with octopus dorsal mantle length (GLM, t = 2.68; p = 0.007). Infection intensity was significantly higher in male octopus (GLM, t = 2.69; p = 0.009) and decreased at higher temperatures in both sexes (GLM, t = -2.42; p = 0.018). The digestive gland condition index did not significantly vary with infection intensity, and no significant relationship between total hemocyte counts and coccidian infection was found (Lineal Model, t = 0.46; p = 0.64). The acid nucleic ratio was significantly lower in octopuses infected by A. valdessensis (Kruskal Wallis test, H = 4.8; p = 0.02), suggesting a detrimental effect on O. tehuelchus growth caused by the coccidian

Transmissible cancers, in which cancer cells themselves act as an infectious agent, have been identified in Tasmanian devils, dogs, and four bivalves. We investigated a disseminated neoplasia affecting geographically distant populations of two species of mussels (Mytilus chilensis in South America and M. edulis in Europe). Sequencing alleles from four loci (two nuclear and two mitochondrial) provided evidence of transmissible cancer in both species. Phylogenetic analysis of cancer-associated alleles and analysis of diagnostic SNPs showed that cancers in both species likely arose in a third species of mussel (M. trossulus), but these cancer cells are independent from the previously identified transmissible cancer in M. trossulus from Canada. Unexpectedly, cancers from M. chilensis and M. edulis are nearly identical, showing that the same cancer lineage affects both. Thus, a single transmissible cancer lineage has crossed into two new host species and has been transferred across the Atlantic and Pacific Oceans and between the Northern and Southern hemispheres.

The purpose of this study was to compare the parasites of two coexisting bivalves, the edible Puelche oyster (Ostrea puelchana) and the false oyster (Pododesmus rudis) that lives attached to O. puelchana shells, and to investigate their host specificity. Samples from wild populations, 465 O. puelchana and 131 P. rudis, were collected seasonally during two years in the San José Gulf (northern Patagonia, Argentina) and were processed using standard histological techniques. To increase the natural low prevalences of Bonamia spp. and Perkinsus spp. that are present in wild populations, an in situ experiment was performed by maintaining captive sentinel bivalves at high densities inside a plastic mesh bag to enhance parasite transmission. Polymerase chain reaction (PCR) assays were used to test for apparent Bonamia sp. infections among captive sentinel O. puelchana specimens (n = 80), and Ray’s fluid thioglycollate medium (RFTM) assays and histological immunoassays tested for apparent Perkinsus sp. infections among captive sentinel P. rudis specimens (n = 100). Despite histological observations that revealed the presence of microcells resembling Bonamia sp. infecting hemocytes of some Puelche oysters, PCR assays did not confirm that parasite identification. Among captive sentinel P. rudis that showed histological evidence of Perkinsus sp. infections, neither RFTM nor immunoassays confirmed such parasites. Ostrea puelchana from wild populations were occasional hosts for both Rickettsia-like organism (RLOs) and Urastoma-like turbellarians. In contrast, six parasite taxa infected P. rudis from coexisting populations, including RLOs, Urastoma-like turbellarians, an intracellular gregarine species, Nematopsis-like oocysts, an unidentified coccidian and a Perkinsus qugwadi-like protozoan. These results demonstrated specific infection patterns of the identified parasites in relation to their hosts

The yellow clam Amarilladesma mactroides (Deshayes, 1854) is considered a vulnerable species since the mid-1990s. Populations have experienced mass mortalities throughout their entire range of distribution (23–41°S) along exposed sandy beaches of Atlantic South America. Detrimental anthropogenic impacts have further contributed to failure of populations to make a recovery. To determine the factors involved in these events, density prior to a mortality event was calculated and live yellow clams encompassingmost of its geographic range distribution were analyzed histologically to describe parasites and pathologies. Moreover, moribund specimens were analyzed by molecular techniques to test for the presence of the virus OsHV-1. A mortality event was recorded after a maximum density of 127 clams/m2 was attained. No clear pattern was found between the prevalence and intensity of infection and localities, mortality events, or sampling season. Although OsHV-1 was not observed in any of the yellow clams tested, the possibility that another viral agent was implicated cannot be ruled out. The presence of bacteria of the genus Vibrio in combination with stress caused by a relatively high population density is suggested as the likely cause of these episodic mass mortalities.

The yellow clam Amarilladesma mactroides (Deshayes, 1854) is considered a vulnerable species since the mid-1990s. Populations have experienced mass mortalities throughout their entire range of distribution (23–41°S) along exposed sandy beaches of Atlantic South America. Detrimental anthropogenic impacts have further contributed to failure of populations to make a recovery. To determine the factors involved in these events, density prior to a mortality event was calculated and live yellow clams encompassingmost of its geographic range distribution were analyzed histologically to describe parasites and pathologies. Moreover, moribund specimens were analyzed by molecular techniques to test for the presence of the virus OsHV-1. A mortality event was recorded after a maximum density of 127 clams/m2 was attained. No clear pattern was found between the prevalence and intensity of infection and localities, mortality events, or sampling season. Although OsHV-1 was not observed in any of the yellow clams tested, the possibility that another viral agent was implicated cannot be ruled out. The presence of bacteria of the genus Vibrio in combination with stress caused by a relatively high population density is suggested as the likely cause of these episodic mass mortalities.

The yellow clam Amarilladesma mactroides (Deshayes, 1854) is considered a vulnerable species since the mid-1990s. Populations have experienced mass mortalities throughout their entire range of distribution (23–41°S) along exposed sandy beaches of Atlantic South America. Detrimental anthropogenic impacts have further contributed to failure of populations to make a recovery. To determine the factors involved in these events, density prior to a mortality event was calculated and live yellow clams encompassingmost of its geographic range distribution were analyzed histologically to describe parasites and pathologies. Moreover, moribund specimens were analyzed by molecular techniques to test for the presence of the virus OsHV-1. A mortality event was recorded after a maximum density of 127 clams/m2 was attained. No clear pattern was found between the prevalence and intensity of infection and localities, mortality events, or sampling season. Although OsHV-1 was not observed in any of the yellow clams tested, the possibility that another viral agent was implicated cannot be ruled out. The presence of bacteria of the genus Vibrio in combination with stress caused by a relatively high population density is suggested as the likely cause of these episodic mass mortalities.

A survey of pathological conditions affecting natural beds of the most economically important bivalve species was performed for first time in the Argentinean Sea. The bivalves studied were Aequipecten tehuelchus (Pectinidae), Mytilus edulis, Aulacomya atra (Mytilidae), Protothaca (=Venus) antiqua (Veneridae), Ostrea puelchana (Ostreidae) and Pododesmus rudis (Anomiidae), all from San Jose´ gulf (42820VS, 64820VW), in northern Patagonia, Southwest Atlantic Ocean. Samples of about 30 adult individuals from each molluscan species were collected and processed by standard histological techniques. Rickettsia-like organisms were the commonest parasites found, followed by ciliates, Nematopsis-like spores, sporocysts and metacercariae of Trematoda, larval Cestoda, Turbellaria and two crustaceans (an isopod and a pea crab). A protozoan of uncertain taxonomic affinities, similar to that formerly reported as Perkinsus karlssoni in Argopecten irradians, was found in A. tehuelchus. DNA analysis demonstrated that it does not belong to a Perkinsus species. The commercially exploited bivalves here studied seem to be devoid of serious pathogens. None of the parasites appear to be a problem to future farming due either to low infestation levels or low pathological effect. Moreover, none of these parasites is OIE notifiable, although to confirm these initial results it is necessary to perform a more exhaustive survey in several beds from different seasons. In order to manage Argentinean stocks, a continuous, organized survey, satisfying international standards, is strongly recommended.

A study was conducted into the health status of natural populations of the venerid clam Pitar rostrata from Uruguay. Perkinsus sp. was detected in 22% of the clams. Severe hemocytic infiltration was detected in the tissues parasitized by this protozoan parasite. The sequencing of the ITS-5.8S gene cluster of the parasite confirmed that it belonged to the Perkinsus olseni species. Rickettsia or Chlamidia-like organisms were also found, with a prevalence of 11%, although without apparent host reaction; an unidentified species of Coccidia was found in the nephridia of 78% of the clams, with the intensity of infection ranging from moderate to high. A gregarine, Nematopsis-like organism was observed mainly in the epithelial cells of the intestine, without host response and with a prevalence of 56%. Of the metazoan parasites, trematodes were found in 11% of the individuals analyzed.

A survey of the health status of the yellow clam Mesodesma mactroides was performed to contribute to establish the causes of mass mortality episodes. A sample of 32 clams was collected from Isla del Jabalí (40°32’S- 62°21’W, Buenos Aires province, Argentina), a relict population by 1999, that two years later suffered a mass mortality. Microscopical examination of the histological sections revealed the presence of four parasitic or commensal taxa: Trichodina sp. ciliates, coccidian, gregarines and turbellaria. Specimens of Trichodina sp. were found on the gills of 58% of clams with moderate intensities without apparent cell damage. Coccidian were present in the nephridal tubules with both high prevalence (93%) and intensity of infection. Macrogamonts and meronts containing merozoites were the more frequently observed stages, obtruding the lumen of the nephridial tubules and associated with hypertrophying epithelial cells. Gregarines were observed inside the digestive epithelial cells and in the adjacent connective tissue in high intensities, with a prevalence of 64%. They were present alone or in groups of several individuals, in which case the epithelial cells were lysed. Turbellaria specimens were found inhabiting the lumen of the digestive tract, parasitising 30% of examined clams. Additionally, histological preparations from 36 dying clams from Monte Hermoso (40°32’S- 62°21’W, Buenos Aires province, Argentina, collected during mass mortality episode of November 1995) were re-examined. Despite the bad-condition of tissues, the same parasites found in Isla del Jabalí were observed, with the exception of gregarines: Trichodina sp. (100%), coccidians (100% from the five histological sections which included nephrida), turbellaria (14%). To support the hypothesis of a diseases- caused epidemic it is necessary to examine samples from other clam populations and to examine for virus infection.