Search

We detected 2 natural, asymptomatic Plasmodium inui monoinfections in humans in Malaysia by using nested PCR on concentrated high-volume blood samples. We found a P. inui-positive Anopheles cracens mosquito in the same site as the human infections. Investigators should use ultrasensitive detection methods to identify simian malaria parasite transmission in humans.

We detected the simian malaria parasites Plasmodium knowlesi, P. cynomolgi, P. inui, P. coatneyi, P. inui–like, and P. simiovale among forest fringe–living indigenous communities from various locations in Malaysia. Our findings underscore the importance of using molecular tools to identify newly emergent malaria parasites in humans.

To monitor the incidence of Plasmodium knowlesi infections and determine whether other simian malaria parasites are being transmitted to humans, we examined 1,047 blood samples from patients with malaria at Kapit Hospital in Kapit, Malaysia, during June 24, 2013–December 31, 2017. Using nested PCR assays, we found 845 (80.6%) patients had either P. knowlesi monoinfection (n = 815) or co-infection with other Plasmodium species (n = 30). We noted the annual number of these zoonotic infections increased greatly in 2017 (n = 284). We identified 6 patients, 17–65 years of age, with P. cynomolgi and P. knowlesi co-infections, confirmed by phylogenetic analyses of the Plasmodium cytochrome c oxidase subunit 1 gene sequences. P. knowlesi continues to be a public health concern in the Kapit Division of Sarawak, Malaysian Borneo. In addition, another simian malaria parasite, P. cynomolgi, also is an emerging cause of malaria in humans.

Plasmodium cynomolgi is a simian malaria parasite that has been a central model parasite since it was first described in 1907. Recently it has made the zoonotic jump and started naturally infecting humans. In this paper, the interactions between Plasmodium cynomolgi and humans, the environment and the non-human animal intermediates or definitive host will be discussed, with a particular focus on the clinical implications of infection and approaches to management of this novel zoonotic parasite.

Made available in DSpace on 2019-10-06T16:00:21Z (GMT). No. of bitstreams: 0 Previous issue date: 2018-07-01. Added 1 bitstream(s) on 2019-10-09T18:35:04Z : No. of bitstreams: 1 S1984-29612018000300363.pdf: 2770381 bytes, checksum: c15ec391d851104f6d38492a03ad8099 (MD5) Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) Instituto Brasileiro do Meio Ambiente e dos Recursos Naturais Renováveis The aim of this study was to identify Plasmodium spp. in blood samples from nonhuman primates (NHPs) in the state of Maranhão, using classical and alternative techniques for examination of human malaria. A total of 161 blood samples from NHPs were analyzed: 141 from captive animals at a Wildlife Screening Center (CETAS) and 20 from free-living animals in a private reserve. The techniques used were microscopy, rapid diagnostic test (RDT), Indirect fluorescent antibody test (IFAT) and molecular techniques (semi-nested PCR, quantitative real-time PCR and LAMP). Two serological methods (dot-ELISA and indirect ELISA) were also standardized with rhoptry protein-soluble antigen of P. falciparum and P. berghei. Trophozoite forms of Plasmodium sp. were identified on slides from five different animals. No samples were positive through RDT and LAMP. Four samples were seropositive for P. malariae through IFAT. The samples showed low reactivity to ELISA. Plasmodium sp. was detected in 34.16% (55/161) of the samples using qPCR based on the 18S rRNA gene. After sequencing, two samples showed 100% identityl to P. malariae, one showed 97% identity to Plasmodium sp. ZOOBH and one showed 99% identity to P. falciparum. PCR was shown to be the most sensitive technique for diagnosing Plasmodium in NHP samples. Laboratório de Parasitologia Animal Curso de Medicina Veterinária Universidade Federal de Rondônia – UNIR Centro de Estudos da Malária Superintendência de Controle de Endemias – SUCEN Departamento de Saúde do Estado de São Paulo Instituto de Medicina Tropical de São Paulo – IMTSP Universidade de São Paulo – USP Laboratório de Patologia Veterinária Curso de Medicina Veterinária Universidade Federal de Rondônia – UNIR Laboratório de Imunoparasitologia Faculdade de Ciências Agrárias e Veterinárias – FCAV Universidade Estadual Paulista – UNESP Laboratório de Imunoparasitologia Faculdade de Ciências Agrárias e Veterinárias – FCAV Universidade Estadual Paulista – UNESP FAPESP: 10/12820-4 FAPESP: 12/03961-9

Blood infection by the simian parasite, Plasmodium simium, was identified in captive (n = 45, 4.4%) and in wild Alouatta clamitans monkeys (n = 20, 35%) from the Atlantic Forest of southern Brazil. A single malaria infection was symptomatic and the monkey presented clinical and haematological alterations. A high frequency of Plasmodium vivax-specific antibodies was detected among these monkeys, with 87% of the monkeys testing positive against P. vivax antigens. These findings highlight the possibility of malaria as a zoonosis in the remaining Atlantic Forest and its impact on the epidemiology of the disease.

SUMMARYPlasmodium knowlesiis a simian malaria of primarily the macaque species of South East Asia. While it was known that human infections could be induced during the years of malariotherapy, naturally occurringP. knowlesihuman infections were thought to be rare. However, in 2004, knowlesi infections became recognized as an important infection amongst human populations in Sarawak, Malaysian Borneo. Since then, it has become recognized as a disease affecting people living and visiting endemic areas across South East Asia. Over the last 12 years, clinical studies have improved our understanding of this potentially fatal disease. In this review article the current literature is reviewed to give a comprehensive description of the disease and treatment.

Background In recent years, the primate malaria Plasmodium knowlesi has emerged in human populations throughout South East Asia, with the largest hotspot being in Sabah, Malaysian Borneo. Control efforts are hindered by limited knowledge of where and when people get exposed to mosquito vectors. It is assumed that exposure occurs primarily when people are working in forest areas, but the role of other potential exposure routes (including domestic or peri-domestic transmission) has not been thoroughly investigated. Methodology/Principal Findings We integrated entomological surveillance within a comprehensive case-control study occurring within a large hotspot of transmission in Sabah, Malaysia. Mosquitoes were collected at 28 pairs households composed of one where an occupant had a confirmed P. knowlesi infection within the preceding 3 weeks (“case”) and an associated “control” where no infection was reported. Human landing catches were conducted to measure the number and diversity of mosquitoes host seeking inside houses and in the surrounding peri-domestic (outdoors but around the household) areas. The predominant malaria vector species was Anopheles balabacensis, most of which were caught outdoors in the early evening (6pm - 9pm). It was significantly more abundant in the peri-domestic area than inside houses (5.5-fold), and also higher at case than control households (0.28±0.194 vs 0.17±0.127, p, Author Summary The primate knowlesi malaria has now emerged in human populations throughout South East Asia. Our limited knowledge of where and when people get exposed to the vector (Anopheles balabacensis) has resulted in poor control measures, although it is assumed that exposure occurs primarily when people are working in forest areas. We investigated the role of peri-domestic (outdoors but around the household) and domestic transmission. Mosquitoes were collected at 28 pairs households composed of one where an occupant had a confirmed knowlesi malaria infection and an associated “control” where no infection was reported. Most of the vectors were caught outdoors from 6pm - 9pm. The vectors were also significantly more abundant in the peri-domestic area than inside houses (5.5-fold), and also higher at case than control households. Ten Anopheles (out of 641) were found positive for primate malaria parasites. This study shows that humans can be exposed to knowlesi infection around their homes. Given the vectors are mainly outdoor biters, interventions using insecticide treated bednets inside households may have relatively little impact. A paradigm shift in control methods is required to reduce infection of this primate malaria.

Four human deaths caused by Plasmodium knowlesi, a simian malaria species, are stimulating a surge of public health interest and clinical vigilance in vulnerable areas of Southeast Asia. We, and other colleagues, emphasize that these cases, identified in Malaysia, are a clear warning that health facilities and clinicians must rethink the diagnosis and treatment of malaria cases presumed to be caused by a less virulent human malaria species, Plasmodium malariae.

First attack, Borneo 1956 I contracted malaria during a student expedition from Cambridge to British North Borneo (now Sabah, Malaysia) in 1956. It was diagnosed at the time at the Hospital for Tropical Diseases in London as P. vivax. (Published: 8 February 2016) Citation: Infection Ecology and Epidemiology 2016, 6: 30139 - http://dx.doi.org/10.3402/iee.v6.30139

International audience; Two cases of Plasmodium knowlesi infection in humans were identified in Cambodia by 3 molecular detection assays and sequencing. This finding confirms the widespread distribution of P. knowlesi malaria in humans in Southeast Asia. Further wide-scale studies are required to assess the public health relevance of this zoonotic malaria parasite.

Plasmodium knowlesi has a relatively broad host range extending to humans, in whom it causes zoonotic malaria. Recent studies have shown that human infection with P. knowlesi is widely distributed in forested areas of Southeast Asia. In the present study, we evaluated commercial rapid diagnostic tests (RDTs) for human malaria to assess their reactivity and sensitivity in detecting P. knowlesi parasites using blood samples obtained from infected monkeys. The blood samples were assayed using two commercial RDTs based on immunochromatographic assays: (i) the OptiMAL-IT, designed to detect parasite lactate dehydrogenase (pLDH) of both P. falciparum and other plasmodia, and (ii) the Entebe Malaria Cassette (MC), designed to detect P. falciparum-specific histidine-rich protein 2 (PfHRP2) and P. vivax-specific pLDH. Interestingly, when the P. knowlesi-infected blood samples were examined with the RDTs, OptiMAL test results were interpreted as falciparum malaria-positive, while Entebe MC test results were interpreted as vivax malaria-positive. The sensitivities of both tests in detecting P. knowlesi parasite were similar to those for P. falciparum and higher than P. vivax. Thus, commercial RDTs based on detection of pLDH should be used with great caution, and should not replace conventional microscopy in the diagnosis of suspected cases of P. knowlesi malaria.

Naturally Acquired Human Plasmodium knowlesi Infection, Singapore, We report a case of naturally acquired Plasmodium knowlesi in Singapore, a malaria-free country. Diagnosis was confirmed by PCR with validated species-specific primers. In industrialized countries, free-ranging primates are a potential source of P. knowlesi human infection. P. knowlesi infection is a differential diagnosis of febrile illness acquired in Singapore.

Human Infections with Plasmodium knowlesi, the Philippines, Five human cases of infection with the simian malaria parasite Plasmodium knowlesi from Palawan, the Philippines, were confirmed by nested PCR. This study suggests that this zoonotic infection is found across a relatively wide area in Palawan and documents autochthonous cases in the country.

Since 1960, a total of seven species of monkey malaria have been reported as transmissible to man by mosquito bite: Plasmodium cynomolgi, Plasmodium brasilianum, Plasmodium eylesi, Plasmodium knowlesi, Plasmodium inui, Plasmodium schwetzi and Plasmodium simium. With the exception of P. knowlesi, none of the other species has been found to infect humans in nature. In this report, it is described the first known case of a naturally acquired P. cynomolgi malaria in humans.The patient was a 39-year-old woman from a malaria-free area with no previous history of malaria or travel to endemic areas. Initially, malaria was diagnosed and identified as Plasmodium malariae/P. knowlesi by microscopy in the Terengganu State Health Department. Thick and thin blood films stained with 10% Giemsa were performed for microscopy examination. Molecular species identification was performed at the Institute for Medical Research (IMR, Malaysia) and in the Malaria & Emerging Parasitic Diseases Laboratory (MAPELAB, Spain) using different nested PCR methods.Microscopic re-examination in the IMR showed characteristics of Plasmodium vivax and was confirmed by a nested PCR assay developed by Snounou et al. Instead, a different PCR assay plus sequencing performed at the MAPELAB confirmed that the patient was infected with P. cynomolgi and not with P. vivax.This is the first report of human P. cynomolgi infection acquired in a natural way, but there might be more undiagnosed or misdiagnosed cases, since P. cynomolgi is morphologically indistinguishable from P. vivax, and one of the most used PCR methods for malaria infection detection may identify a P. cynomolgi infection as P. vivax.Simian Plasmodium species may routinely infect humans in Southeast Asia. New diagnostic methods are necessary to distinguish between the human and monkey malaria species. Further epidemiological studies, incriminating also the mosquito vector(s), must be performed to know the relevance of cynomolgi malaria and its implication on human public health and in the control of human malaria.The zoonotic malaria cannot be ignored in view of increasing interactions between man and wild animals in the process of urbanization. This work was supported by the Interuniversity Cooperation Programme (AECID grant and A1/035539/11) and IMR/NIH Project NMRR-11-410-9622. THT was financed by a fellowship from the Instituto de Salud Carlos III. Sí

Simian malaria parasites were first reported in Malayan monkeys by Daniels in 1908 [1]. It had been assumed for a long time that transmission of simian malaria to humans would not be possible. However, an accidental infection of scientists in Atlanta, USA by mosquito bites in the laboratory proved that a simian malaria species– Plasmodium cynomolgi can be transmitted to humans [2, 3]. In 1965 the first natural infection in human was reported in an American surveyor who was infected in the jungles of Pahang, Malaysia [4]. Fortunately he returned to USA and was detected first as Plasmodium falciparum and later revised to Plasmodium malariae due to the band form of the parasite. Further examination proved that it was actually Plasmo‐ dium knowlesi [4].

We describe a case of naturally acquired infection with Plasmodium knowlesi in Thailand. Diagnosis was confirmed by the small subunit ribosomal RNA and the mitochondrial cytochrome b sequences. The occurrence of simian malaria in human has signified the roles of wild primate populations in disease transmission in some malaria-endemic areas., Emerging Infectious Diseases 10(12), pp.2211-2213; 2004

Plasmodium knowlesi is an emerging malaria parasite in humans and is unique to Southeast Asia. Since most countries in Southeast Asia are working towards elimination of malaria, it is important to have knowledge on this emerging simian malaria parasite affecting humans. The first case of simian malaria was reported in Malaysia in 1965. At that time extensive work conducted did not reveal other simian malaria cases in humans. However, in 2004, a large focus of P. knowlesi was reported from Sarawak, Malaysian Borneo and that led to many studies and cases being reported from most countries in Southeast Asia. In this chapter, the history, epidemiology, diagnosis, vectors and role of simian host are discussed. Malaria is now a zoonosis and the challenges facing the countries of Southeast in tackling the knowlesi malaria situation and the way forward have been documented.

The parasite that causes simian malaria in the Brazilian Amazon, Plasmodium brasilianum, is infective to man. In this region, where humans live within and in close proximity to the forest, it was suspected that this parasite could be the cause of a zoonosis. A study was performed in the areas surrounding two hydroelectric plants in the Amazon, Balbina and Samuel, aiming at determining the zoonotic potential of this parasite. P. brasilianum was detected in, respectively, 15.8% and 9.9% of 126 and 252 primates belonging to seven and eight species examined from Balbina and Samuel. The highest malaria infection rates were found among the red-howler monkey Alouatta seniculus straminea (32.3%), the bearded-saki Chiropotes satanas chiropotes (50%) and the spider-monkey Ateles paniscus paniscus (2[1+]) from Balbina and in the squirrel-monkey Saimiri ustus (21%) and the black-faced-spider-monkey Ateles paniscus chamek (28.6%) from Samuel.

After discovery of malaria parasites and their transmission by Anophelines, until recently, malaria was antroponotic disease caused by four Plasmodium species. These parasites were circulated among humans by different vectors around the world. Coatney [1] reported the first known case of naturally infected simian malaria, Plasmodium knowlesi, in human [1,2]. Near to half of century later that discovery, with applying molecular techniques, detection and identification of simian malaria, especially P. knowlesi, was renewed [3]. Recently, Baird [4] revised the biology and medicine of zoonoses malaria [4]. CoxSingh [5] indicated the role of other simian malaria, P. inui and P. synomology, in human infection at Southeast Asia [5].

The schizont maturation assay for in vitro drug sensitivity tests has been a standard method employed in the global baseline assessment and monitoring of drug response in Plasmodium falciparum. This test is limited in its application to synchronous plasmodial infections because it evaluates the effect of drug on the maturation of parasite especially from ring to schizont stage and therefore synchronized P. falciparum cultures are required. On the other hand, P. knowlesi, a simian malaria parasite has a unique 24-h periodicity and maintains high natural synchronicity in monkeys. The present report presents the results of a comparative study on the course of in vitro maturation of sorbitol synchronized P. falciparum and naturally synchronous P. knowlesi. Ring stage parasites were incubated in RPMI medium supplemented with 10-15% pooled homologous serum in flat-bottomed 96-well micro plates using a candle jar at 37 degrees C. The results suggest that the ideal time for harvesting the micro-assay plates for in vitro drug sensitivity test for sorbitol-synchronized P. falciparum and naturally synchronous P. knowlesi are from 26 to 30 h and from 22 to 25 h, respectively. The advantages of using P. knowlesi in chemotherapeutic studies are discussed.

The simian malaria parasite Plasmodium knowlesi is transmitted in the forests of Southeast Asia. Symptomatic zoonotic knowlesi malaria in humans is widespread in the region and is associated with a history of spending time in the jungle. However, there are many settings where knowlesi transmission to humans would be expected but is not found. A recent report on the Ra-glai population of southern central Vietnam is taken as an example to help explain why this may be so.

Several questions on public health impact have arisen from the discovery of a large focus of the simian malaria parasite, Plasmodium knowlesi, in the human population. P. knowlesi malaria is not newly emergent and was overlooked until molecular tools to distinguish between P. knowlesi and the morphologically similar Plasmodium malariae became available. Knowlesi malaria is a zoonosis that is widely distributed in Southeast Asia and can be fatal. Information on knowlesi malaria should be included in medical and public health guidelines to encourage the accurate diagnosis and treatment of patients, and monitor the incidence and distribution of cases. A complete emergence of P. knowlesi into the human population could be overwhelming and, although challenging, the prevention of this situation deserves serious consideration.

Background Simian malaria is still an open question concerning the species of Plasmodium parasites and species of New World monkeys susceptible to the parasites. In addition, the lingering question as to whether these animals are reservoirs for human malaria might become important especially in a scenario of eradication of the disease. To aid in the answers to these questions, monkeys were surveyed for malaria parasite natural infection in the Amazonian state of Rondônia, Brazil, a state with intense environmental alterations due to human activities, which facilitated sampling of the animals. Methods Parasites were detected and identified in DNA from blood of monkeys, by PCR with primers for the 18S rRNA, CSP and MSP1 genes and sequencing of the amplified fragments. Multiplex PCR primers for the 18S rRNA genes were designed for the parasite species Plasmodium falciparum and Plasmodium vivax, Plasmodium malariae/Plasmodium brasilianum and Plasmodium simium. Results An overall infection rate of 10.9% was observed or 20 out 184 monkey specimens surveyed, mostly by P. brasilianum. However, four specimens of monkeys were found infected with P. falciparum, two of them doubly infected with P. brasilianum and P. falciparum. In addition, a species of monkey of the family Aotidae, Aotus nigriceps, is firstly reported here naturally infected with P. brasilianum. None of the monkeys surveyed was found infected with P. simium/P. vivax. Conclusion The rate of natural Plasmodium infection in monkeys in the Brazilian state of Rondônia is in line with previous surveys of simian malaria in the Amazon region. The fact that a monkey species was found that had not previously been described to harbour malaria parasites indicates that the list of monkey species susceptible to Plasmodium infection is yet to be completed. Furthermore, finding monkeys in the region infected with P. falciparum clearly indicates parasite transfer from humans to the animals. Whether this parasite can be transferred back to humans and how persistent the parasite is in monkeys in the wild so to be efficient reservoirs of the disease, is yet to be evaluated. Finding different species of monkeys infected with this parasite species suggests indeed that these animals can act as reservoirs of human malaria.

In Brazil simian malaria is widely spread, being frequent in the Amazon region (10% of primates infected) and even more in the forested coastal mountains of the Southeastern and Southern regions (35% and 18% infected, respectively), but absent in the semi-arid Northeast. Only two species of plasmodia have been found: the quartan-like Plasmodium brasilianum and the tertian-like P. simium, but the possible presence of other species is not excluded. P. brasilianum is found in all enzootic foci, but P. simium was detected only on the coast of the Southeastern and Southern regions, between paralles 20 degrees S and 30 degrees S. Nearly all hosts are monkeys (family Cebidae, 28 species harbouring plasmodia out of 46 examined), and very rarely marmosets or tamarins (family Callitrichidae, 1 especies out of 16). P. brasilianum was present in all infected species, P. simium in only two. The natural vector in the Southeastern and Southern regions was found to be Anopheles cruzi, but has not been conclusively identified in the Amazon. One natural, accidental human infection due to P. simium was observed. There is no evidence of the relation of simian to human malaria in the Southeastern and Southern regions, where human malaria was eradicated in spite of the high rates of monkeys infected, but in the Amazon recent serological studies by other workers, revealing high positivity for P. brasilianum/P. malariae antibodies in local indians, would suggest that among them malaria might possibly be regarded as a zoonosis.

Background Since a large focus of human infection with Plasmodium knowlesi, a simian malaria parasite naturally found in long-tailed and pig tailed macaques, was reported in Sarawak, Malaysian Borneo, it was pertinent to study the situation in peninsular Malaysia. A study was thus initiated to screen human cases of Plasmodium malariae using molecular techniques, to determine the presence of P. knowlesi in non- human primates and to elucidate its vectors. Methods Nested polymerase chain reaction (PCR) was used to identify all Plasmodium species present in the human blood samples sent to the Parasitology laboratory of Institute for Medical Research. At the same time, non-human primates were also screened for malaria parasites and nested PCR was carried out to determine the presence of P. knowlesi. Mosquitoes were collected from Pahang by human landing collection and monkey-baited-traps situated on three different levels. All mosquitoes were identified and salivary glands and midguts of anopheline mosquitoes were dissected to determine the presence of malaria parasites and nested PCR was carried out on positive glands. Sequencing of the csp genes were carried on P. knowlesi samples from humans, monkeys and mosquitoes, positive by PCR. Results and Discussion Plasmodium knowlesi was detected in 77 (69.37%) of the 111 human samples, 10 (6.90%) of the 145 monkey blood and in 2 (1.7%) Anopheles cracens. Sequence of the csp gene clustered with other P. knowlesi isolates. Conclusion Human infection with Plasmodium knowlesi is occurring in most states of peninsular Malaysia. An. cracens is the main vector. Economic exploitation of the forest is perhaps bringing monkeys, mosquitoes and humans into increased contact. A single bite from a mosquito infected with P. knowlesi is sufficient to introduce the parasite to humans. Thus, this zoonotic transmission has to be considered in the future planning of malaria control.

Gametocytocidal activity of artemisinin (qinghaosu) has been demonstrated against simian malaria parasite Plasmodium cynomolgi B. Colony-bred Anopheles stephensi were allowed to feed on gametocyte-carrying rhesus monkeys and the mosquito infectivity rate and oocyst count of the infected mosquito gut were recorded on day 8-9 postinfection. Control (pretreatment) feedings of mosquito on gametocyte-carrying monkeys showed good infectivity in different batches of the mosquitoes ranging from 57.14 to 95.0%. Administration of single intramuscular injection of 5 mg/kg artemisinin (suspended in neutralised oil) resulted in complete loss of mosquito infectivity within 24 h of drug administration. This is the first report on the possible use of artemisinin to stop malaria transmission. The drug has no sporontocidal action.

Previous evaluations of the timing of developing stages in the erythrocytic cycle of the simian malaria parasite, Plasmodium cynomolgi, a frequently used model for relapsing malaria in man, have depended on procurement of blood samples at 4- or 6-hourly intervals. This brief report describes the blood cycle as determined from hourly bleedings, thus providing a more discriminating sequence usable for immunochemical or biochemical study of specific stages. The approximate timing of development for five defined stages in the asexual cycle was determined to be 12-14 hours for young trophozoites, 22-24 hours for developing trophozoites, 5-7 hours for mature trophozoites, 5-6 hours for early schizonts, and 3-5 hours for late schizonts. It was also demonstrated that the rate of erythrocytic multiple infection declined in proportion to the maturity of the parasite. Young and developing trophozoites presented the most numerous cases of multiple infection whereas very few schizonts were seen multiply infecting a host cell.

Immunity to reinfection in the simian malaria system studied was evidenced by (a) a delay in development of infections, (b) a milder course of parasitaemia, or (c) complete resistance to challenge. The immunity produced by repeated exposure to one antigenic variant was effective against subsequent challenge with heterologous variants. Populations of parasites isolated from different recrudescences of chronic P. knowlesi infections were shown to be antigenically distinct.

Summary Large, non-pigmented schizonts manifestly different from the classical schizonts found in erythrocytes have been observed in some strains of P. relictum, P. gallinaceum, P. cathemerium, P. circumflexum, and (one unconfirmed report) P. nucleophilum, but not in several other species of avian and simian malaria examined. Although human malarial infections have not yet been extensively studied, forms similar to those seen in avian malarias have been reported in infections with P. vivax and P. falciparum. The identification of infected cells has usually not been made by specialists, but infections are reported in endothelial cells and various cells of the lymphoid-macrophage system (rarely in granulocytes). In infections with P. elongatum schizonts occurring in all blood and blood-forming cells are morphologically identical; the large schizonts mentioned above have not been described. That the exo-erythrocytic schizonts are a part of the malarial life cycle and not a contaminant is indicated principally by the facts that they have not been separated from malaria nor shown to occur apart from it, that they differ characteristically in different species of malaria, and that their immunological specificity parallels that of the associated malaria. Miscellaneous other evidence supports this view. They clearly differ from both avian and mammalian types of toxoplasmas in morphology and transmissibility. The exo-erythrocytic stages are not appreciably affected by schizonticidal drugs, but their number is reduced by plasmochin. Various evidence that the sporozoite development does not occur in circulating erythrocytes, together with the fact that the exo-erythrocytic schizonts appear earlier and more numerously after sporozoite inoculation than after the injection of infected blood, suggests that the exo-erythrocytic schizonts are the early developmental stages of sporozoites. Evidence is inconclusive on this question, though exo-erythrocytic schizonts have been found 16 hours after the inoculation of sporozoites. Other ideas on the significance of the exo-erythrocytic stages include theories that they reflect an unfavorable condition of the blood as a medium, or reduced digestive activity of tissue phagocytes, and the theory that they represent stages in the evolution of sporozoa of the sub-order Haemosporidiidea into strictly erythrocytic parasites. While they indicate a closer relationship between the Plasmodidae and the Haemoproteidae, adequate criteria for the separation of these families still exist. In addition to their great biological significance, the newly discovered exo-erythrocytic stages are of vital practical importance, particularly in the study of chemotherapy of malaria.

The vivax-type simian malaria parasite Plasmodium cynomologi was cultured in vitro by both the candle jar method and the continuous flow technique, with rhesus monkey erythrocytes and RPMI 1640 medium supplemented with Hepes buffer and human serum. After 6 weeks in culture, the growth of the parasite had permitted a 5 X 10(6) cumulative dilution of the original inoculum. Cultured parasites remained infective to rhesus monkeys and exhibited a reversible decrease in the ameboid behavior of their trophozoites.

Duffy blood group negative human erythrocytes (FyFy) are resistant to infection by Plasmodium knowlesi, a simian malaria that infects Duffy positive human erythrocytes. The P. knowlesi resistance factor, Duffy negative erythrocytes, occurs in high frequency in West Africa, where the people are resistant to vivax malaria. This suggests that Duffy blood group determinants (Fya or Fyb) may be erythrocyte receptors for P. vivax.

An apparatus is described and illustrated for the continuous semi-automated cultivation of Plasmodium knowlesi, The change of medium was automated and involved six operations. Parasites were maintained for 12 weeks, at which time the experiment ended. During this period, parasite density, morphology and serological specificity were monitored. Parasites retained synchromy and normal morphology only for the first cycle in culture. The maximum degree of morphological abnormality (90%) was reached at three weeks. Lysis of infected erythrocytes seemed to occur before full maturation of the parasites. Infected cells cultured for 31 days produced a normal, fulminating infection in a rhesus monkey.

Prophylactic treatment with 0.1 mg of human gamma interferon per kg (body weight) per day completely suppressed experimental infection with Plasmodium cynomolgi B sporozoites in rhesus monkeys. Treatment with lower doses partially suppressed this infection. Prophylactic treatment with human gamma interferon, however, had no protective effect against trophozoite-induced infection, suggesting that the interferon effect was limited to the exoerythrocytic stage of parasitic development.

Publisher Summary This chapter discusses the studies conducted on simian malaria in Brazil. Two species of Plasmodium have been found in monkeys in Brazil: the quartan-like P. brasilianum in Casajao calvus from the Upper Amazon, and P. simium in Alouatta fusca in the state of Sao Paulo. The investigation was made to study the prevalence of malaria in monkeys, the seasonal variation, infectivity of the parasites to various hosts (including man) and the vectors in nature; the site was the government forest reserve—Horto Florestal da Cantareira—on the outskirts of Sao Paulo. Of 35 Alouatta examined, malaria parasites were found in 12 and malaria pigment in an additional three. A quartan like parasite was found in two monkeys; the remainder was P. simium. Two adult Alouatta were captured alive and were found to harbor P. simium in small numbers, which became greatly augmented after splenectomy, reaching a density of 225,000 parasites per cu mm.

A quotidian-type parasite, Plasmodium knowlesi, has been found as a ndtural infection in man. The infection was acquired by a white male during a short visit to peninsular Malaysia. This occurrence constitutes the first proof that simian malaria is a true zoonosis.

Dr. Cockburn is well trained and has had impressive experience with infectious diseases around the world. He describes his book as "a bird's-eye view of the relationships between host, parasite, and environment" and states that a specialist "is likely to find errors and omissions within his special knowledge."The first chapter, "The Role of Speculation in Research," notes common distrust of "speculation," as, for example, the prejudice (based partly on negative experiments) of malariologists against considering simian malaria important in human disease until the recent demonstration of mosquito transmissibility to humans of Plasmodium vivax-like simian parasites.In chapters on "Evolutionary Background," "Paleoepidemiology," "The Evolution of Infectious Diseases," and "The Species Concept in Microbiology," the author applies principles of evolution and genetics in speculating on the development of pathogenic organisms from originally "free living forms." He cites the recent discovery of Treponema zuelzerae (which contains "Reiter antigen") as an example