The putative haemobartonella that influences Plasmodium falciparum parasitaemia in squirrel monkeys is a haemotrophic mycoplasma

Splenectomised squirrel monkeys (Saimiri sciureus) are increasingly being used as an experimental host for human malaria studies, notably for the assessment of candidate vaccines against Plasmodium falciparum blood-stage infection. Recently, S. sciureus monkeys in our primate-breeding colony were reported to be asymptomatic carriers of a putative Haemobartonella species. Patent haemobartonella infection is frequently activated following splenectomy, and may interfere with studies on the course of P. falciparum parasitaemia in these animals. Here, we show by 16S rRNA gene sequence analysis that this wall-less bacterium is not a rickettsia but, instead, is a haemotrophic mycoplasma. Haemotrophic mycoplasmas are a newly identified group of mycoplasmas that parasitise the surfaces of erythrocytes of a wide variety of vertebrate hosts.     

Haemobartonellosis in squirrel monkeys (Saimiri sciureus): antagonism between Haemobartonella sp. and experimental Plasmodium falciparum malaria

A hemotropic parasite of the genus Haemo bartonella (rickettsial parasite of the Family Anaplasmataceae) is responsible for latent asymptomatic infection in colony-born Saimiri monkeys. Indeed, many of these animals develop a patent Haemobartonella infection following splenectomy. Such patent parasitism is characterized by an intense Haemobartonella parasitemia which peaks between days 12 and 14 after removal of the spleen and then decreases to become undetectable between days 25 and 30. During the resolving phase of parasitemia, a moderate anemia associated with monocytosis and erythrophagocytosis is observed. In certain Saimiri monkeys, Haemobartonella parasitemia remains latent following removal of the spleen. This indicates that the spleen plays a role but is not necessary to maintain latent Haemobartonella parasitism. It also suggests the existence of heterogeneity in the host immune reactivity to the parasite. Latent or patent haemobartonellosis might raise a problem when Saimiri monkeys are used as experimental hosts of Plasmodium falciparum asexual blood stages, as already noticed with "rodent malaria." Thus we investigated the relationship between Haemobartonella and P. falci parum in splenectomized monkeys. When animals harboring latent Haemobartonella sp. were infected with P. falciparum, the former remained latent and exerted no influence on the course of the P. falciparum parasitemia. In constrast, when P. falciparum was initiated in animals which were in the process of developing patent haemobarto nellosis, the course of the former was protracted and either the animal resisted longer, or it self-cleared the P. falciparum infection. Conversely, patent haemobartonellosis was delayed when splenectomy was performed at different times after initiation of P. falciparum infection in intact monkeys. Our results do not allow us to draw conclusions as to the mechanism(s) of the antagonism between the two parasites, but they emphasize the need to monitor the presence of Haemobartonella when splenectomized Saimiri monkeys are used as experimentals hosts for P. falciparum parasitism.     

Malaria diagnosis by enzyme-linked immunosorbent assays.

Enzyme-linked immunosorbent assays (ELISA) for detecting malarial parasites in blood were tested on uninfected monkeys and in monkeys infected with Plasmodium falciparum. A double antibody sandwich ELISA detected one malarial cell per 10(3) uninfected cells, and an inhibition ELISA detected on infected cell per 10(4) uninfected erythrocytes. These methods are not yet as sensitive as conventional blood-film examinations, in which a well-trained microscopist might be expected to detect one malarial cell per 10(6) erythrocytes. Nevertheless, ELISA offers an objective means of detecting malaria and is particularly advantageous since up to 100 samples may be processed simultaneously.     

Disparate Data Sets Resolve Squirrel Monkey (Saimiri) Taxonomy: Implications for Behavioral Ecology and Biomedical Usage

Squirrel monkeys (Saimiri spp.) are the most commonly used neotropical (platyrrhine) monkeys in biomedical research; however, no consensus exists as to the phylogenetic relationships amongst geographic variants or whether these variants represent species or subspecies. Here we report a strongly supported squirrel monkey phylogeny, congruent across multiple data sets, including new field data and the first molecular (mtDNA) cladogram. These data support species-level classification for the three major groups in this study. Approximately the same amount of molecular divergence exists among Saimiri oerstedii, S. sciureus, and S. boliviensis. The S. sciureus/S. oerstedii ancestor diverged from S. boliviensis and shortly thereafter S. sciureus and S. oerstedii diverged. Until now, lack of a robust taxonomy has hindered exploitation of the massive potential of Saimiri for comparative studies. No other primate genus displays such widely divergent, genetically-based social behaviors. Our taxonomy also provides robust support for previous warnings against the widespread use of hybrid squirrel monkeys as research models.     

Squirrel monkeys support replication of BK virus more efficiently than simian virus 40: an animal model for human BK virus infection

We performed experiments to test the suitability of squirrel monkeys (Saimiri sciureus) as an experimental model for BK virus (BKV) and simian virus 40 (SV40) infection. Four squirrel monkeys received intravenous inoculation with BKV Gardner strain, and six squirrel monkeys received intravenous inoculation with SV40 777 strain. Eight of 10 monkeys received immunosuppression therapy, namely, cyclophosphamide subcutaneously either before or both before and after viral inoculation. The presence of viral infection was assessed by quantitative real-time PCR amplification of viral DNA from blood, urine, and 10 tissues. We found that squirrel monkeys were susceptible to infection with BKV, with high viral copy number detected in blood and viral genome detected in all tissues examined. BKV genome was detected in urine from only one monkey, while three monkeys manifested focal interstitial nephritis. BKV T antigen was expressed in renal peritubular capillary endothelial cells. By contrast, SV40 was detected at very low copy numbers in only a few tissues and was not detected in blood. We conclude that the squirrel monkey is a suitable animal for studies of experimental BKV infection and may facilitate studies of viral entry, pathogenesis, and therapy.     

Development of a polymorphic strain of Plasmodium vivax in monkeys.

A strain of Plasmodium vivax from Thailand with a polymorphic repeat unit of the circumsporozoite protein was established in Saimiri sciureus boliviensis and 3 species of Aotus monkeys. All 11 attempts to transmit infection via sporozoite inoculation, 4 times to splenectomized S. sciureus boliviensis, 2 times to splenectomized Aotus nancymai, and 5 times to intact Saimiri monkeys, were successful. Anopheles freeborni, Anopheles stephensi, Anopheles dirus, and Anopheles gambiae mosquitoes were infected by feeding on parasitemic blood from a chimpanzee and an Aotus azarae boliviensis monkey. Our results indicate that this strain may be useful in antisporozoite vaccine trials.     

以恒河猴为模型的DNA疫苗的免疫保护作用研究

研究了以霍乱毒素B亚基（CTB）为载体的重组疟疾多价抗原（AWTE）表位的DNA疫苗在恒河猴中的免疫原性及对相应疟原虫感染的免疫保护作用。结果表明DNA疫苗组免疫2次后即产生了较高水平的细胞免疫和体液免疫,免疫后91天用1.25×10     

Severe anemia affects both splenectomized and non-splenectomized Plasmodium falciparum-infected Aotus infulatus monkeys

Severe anemia is the earliest and a frequently fatal complication of Plasmodium falciparum infection. Here we describe Aotus infulatus as a primate model suitable to study this malaria complication. Both non-splenectomized and splenectomized monkeys receiving different inocula of P. falciparum FVO strain presented large (> 50%) decreases in hematocrit values during infection. Non-splenectomized animals were able to control parasite growth (parasitemia did not exceed 4%), but they had to be treated because of severe anemia. Three of 4 splenectomized monkeys did not control parasitemia and were treated, but developed severe anemia after treatment when presenting a negative blood film. Destruction of parasitized red blood cells alone cannot account for the degree of anemia. Non-splenectomized monkeys repeatedly infected with homologous parasites became rapidly and progressively resistant to reinfection and to the development of severe anemia. The data presented here point to A. infulatus as a suitable model for studying the pathogenesis of severe malarial infection.     

Pleistocene diversification of living squirrel monkeys (Saimiri spp.) inferred from complete mitochondrial genome sequences

In order to enhance our understanding of the evolutionary history of squirrel monkeys (Saimiri spp.), we newly sequenced and analyzed data from seven complete mitochondrial genomes representing six squirrel monkey taxa. While previous studies have lent insights into the taxonomy and phylogeny of the genus, phylogenetic relationships and divergence date estimates among major squirrel monkey clades remain unclear. Using maximum likelihood and Bayesian procedures, we inferred a highly resolved phylogenetic tree with strong support for a sister relationship between Saimiri boliviensis and all other Saimiri, for monophyly of Saimiri oerstedii and Saimiri sciureus sciureus, and for Saimiri sciureus macrodon as the sister lineage to the S. oerstedii/S. s. sciureus clade. We inferred that crown lineages for extant squirrel monkeys diverged around 1.5 million years ago (MYA) in the Pleistocene Epoch, with other major clades diverging between 0.9 and 1.1 MYA. Our results suggest a relatively recent timeline of squirrel monkey evolution and challenge previous conceptions about the diversification of the genus and its expansion into Central America.     

Aotus infulatus monkey is susceptible to Plasmodium falciparum infection and may constitute an alternative experimental model for malaria

Aotus is one of the WHO-recommended primate models for studies in malaria, and several species can be infected with Plasmodium falciparum or P. vivax. Here we describe the successful infection of the species A. infulatus from eastern Amazon with blood stages of P. falciparum. Both intact and splenectomized animals were susceptible to infection; the intact ones were able to keep parasitemias at lower levels for several days, but developed complications such as severe anemia; splenectomized monkeys developed higher parasitemias but no major complications. We conclude that A. infulatus is susceptible to P. falciparum infection and may represent an alternative model for studies in malaria.     

Reproducible infection of intact Aotus lemurinus griseimembra monkeys by Plasmodium falciparum sporozoite inoculation

Aotus lemurinus griseimembra is considered one of the best nonhuman primate species for malarial studies because of its susceptibility to infection by Plasmodium falciparum asexual blood stages. However, reproducible transmission of infective P. falciparum sporozoites by mosquito inoculation has been difficult to achieve even in splenectomized monkeys. Characterization of an Aotus-P. falciparum cyclical transmission model has become a top priority as a result of the significant progress toward the development of preerythrocytic malaria vaccines. Herein, we describe a reproducible model developed using intact A. lemurinus griseimembra monkeys intravenously inoculated with sporozoites from a monkey-adapted P. falciparum (Santa Lucia) strain and a wild Falciparum-Cali-Colombia-4 (FCC-4) strain. Sporozoites were obtained by salivary gland dissection of laboratory-reared Anopheles albimanus mosquitoes. Parasitemia was monitored by thick-smear microscopy, parasite lactate dehydrogenase (pLDH) determination, and mosquito xenodiagnosis. The last method proved to be the most sensitive method for monitoring parasitemias. Infection with the Santa Lucia strain showed a mean prepatent period of 16 days (range 6-21 days), whereas infection with the wild FCC-4 strain resulted in a 24-day prepatent period. Mean peak parasite density was approximately 900 parasites/microliter for both parasite strains. The prepatent period, the peak of parasitemia, and the duration of patency were independent of the size of the sporozoite inoculum and the presence of spleen in the host. This model is being successfully used to test the protective efficacy of P. falciparum preerythrocytic vaccine candidates.     

Blood typing in Saimiri sciureus monkeys: influence of anti-red blood cell alloantibodies on Plasmodium falciparum parasitaemia in vivo

The Saimiri sciureus monkey is a well-established host for experimental studies with human malaria parasites. During the course of iterative inoculations with Plasmodium falciparum parasitised red blood cells (RBC), anti-RBC alloantibodies were detected in the sera of two of eight Saimiri monkeys. These anti-RBC antibodies were further used to investigate RBC phenotypes in 35 colony-reared Saimiri monkeys by flow cytometry. Three RBC phenotypes (named I-III) were observed. Their distribution was I (86%), II (11%) and III (3%). Using the Palo Alto FUP-2 strain, a variant P. falciparum line insensitive to hyperimmune serum and the passive transfer of anti-RBC alloantibodies, a dramatic drop in parasite growth was documented in an incompatible monkey.     

Distribution of chromosomal polymorphisms in three subspecies of squirrel monkeys (genus Saimiri)

The presence of nucleolar organizer regions (NORs) and C-band polymorphisms has been examined in three subspecies of squirrel monkeys, Saimiri sciureus sciureus, S. boliviensis boliviensis, and S. boliviensis peruviensis. Pericentric inversions in chromosomes 15 and 16 were also examined in the three groups. Chromosome 15 was acrocentric in S. s. sciureus and submetacentric in S.b. boliviensis and S.b. peruviensis. Chromosome 16 was acrocentric in S.s. sciureus and S.b. boliviensis while being submetacentric in S.b. peruviensis. There was a significant difference in the distribution of the C-band polymorphisms on chromosomes 5 and 14 in the three groups, as determined by Chi-square analysis, while no difference was observed in the distribution of the NOR polymorphism on chromosome 2. The NOR polymorphism and the interstitial C-band polymorphism of chromosome 14 were found in all three groups; the C-band polymorphism of chromosome 5 was found only in S.s. sciureus. Twelve pedigreed families were examined. Pedigree analyses were consistent with codominant inheritance of each polymorphism. The results of these cytogenetic studies in squirrel monkeys are pertinent to genetic management and research protocols.     

Experimental Plasmodium falciparum cerebral malaria in the squirrel monkey Saimiri sciureus.

Infection of the squirrel monkey, Saimiri sciureus, with several strains of Plasmodium falciparum leads in a proportion of animals to neurological symptoms with a fatal outcome. This first simian model for human cerebral malaria was studied with three strains of parasites, the uncloned Palo Alto(FUP-1) strain, the Palo AltoPLF3 clone MHB11, and the recently monkey-adapted P. falciparum strain IPC/RAY. Cerebral malaria could develop during primo infection of monkeys, whether the animals had been splenectomized or not. It did not occur in all animals and the appearance of neurological symptoms could not be predicted, as it was not related to the degree of parasitemia or duration of parasite infections.     

重组霍乱毒素B亚基与疟原虫多表位融合蛋白的免疫保护作用研究

对以霍乱毒素B亚基为载体蛋白的重组疟疾多价抗原在小鼠及恒河猴中的免疫原性及对相应疟原虫感染的免疫保护作用进行了研究。结果表明：该抗原免疫小鼠后,对约氏疟子孢子攻击的保护率在50%左右;恒河猴免疫后用1×10⁸食蟹疟裂殖子攻击,对照组2只动物在攻击后4d感染,感染持续30d以上;免疫组2只动物中,两只动物在感染6～7d后完全恢复,且1只推迟3d感染,说明该抗原具有免疫保护作用。     

Downregulation of p56(lck) tyrosine kinase activity in T cells of squirrel monkeys (Saimiri sciureus) correlates with the nontransforming and apathogenic properties of herpesvirus saimiri in its natural host

Herpesvirus saimiri is capable of transforming T lymphocytes of various primate species to stable growth in culture. The interaction of the T-cellular tyrosine kinase p56(lck) with the transformation-associated viral protein Tip has been shown before to activate the kinase and provides one model for the T-cell-specific transformation by herpesvirus saimiri subgroup C strains. In contrast to other primate species, squirrel monkeys (Saimiri sciureus) are naturally infected with the virus without signs of lymphoma or other disease. Although the endogenous virus was regularly recovered from peripheral blood cells from squirrel monkeys, we observed that the T cells lost the virus genomes in culture. Superinfection with virus strain C488 did not induce growth transformation, in contrast to parallel experiments with T cells of other primate species. Surprisingly, p56(lck) was enzymatically inactive in primary T-cell lines derived from different squirrel monkeys, although the T cells reacted appropriately to stimulatory signals. The cDNA sequence revealed minor point mutations only, and transfections in COS-7 cells demonstrated that the S. sciureus lck gene codes for a functional enzyme. In S. sciureus, the tyrosine kinase p56(lck) was not activated after T-cell stimulation and enzymatic activity could not be induced by Tip of herpesvirus saimiri C488. However, the suppression of p56(lck) was partially released after administration of the phosphatase inhibitor pervanadate. This argues for unique species-specific conditions in T cells of S. sciureus which may interfere with the transforming activity and pathogenicity of herpesvirus saimiri subgroup C strains in their natural host.     

Immune responses during helminth-malaria co-infection: a pilot study in Ghanaian school children

Malaria and helminth infections have a shared geographical distribution and therefore co-infections are frequent in tropical areas of the world. Human populations of helminth and malaria co-infection have shown contradictory results for the course of malarial infection and disease, possibly depending on the type of helminth studied, the intensity of helminth infection and the age of the study population. Although immunological studies might clarify the underlying mechanisms of protection or increased susceptibility, there are very few studies that have looked at immunological parameters in helminth and malaria co-infection. After discussing the available immunological data on co-infection, we describe a pilot study performed in Ghanaian school children where we compare anti-malarial responses in children living in an urban area, where the prevalence of helminth and Plasmodium falciparum infections was low, with that of children living in a rural area with high prevalence of helminth and Plasmodium falciparum infections.     

Platelet kinetics and other hematological profiles in experimental Plasmodium falciparum infection: a comparative study between Saimiri and Aotus monkeys.

Levels of platelets and other hematological values were monitored in 21 Saimiri and 12 Aotus monkeys over a period of three weeks post-infection with monkey-adapted Indochina CDC-1 strain of Plasmodium falciparum. In both Saimiri sciureus boliviensis and Aotus nancymai karyotype-1 monkeys the severest thrombocytopenia was observed at 14 days post-infection coinciding with peak parasitemia, neutropenia, lymphocytosis, and anemia associated with severe hemoglobinemia and elevated fibrinogen degeneration products(FDP's). MCH and MCV profiles in Aotus monkeys decreased with ascending parasitemia. In contrast, these parameters in Saimiri were characterized by a significant compensatory increase correlating with parasitemia. In general, thrombocytopenia was one of the earliest clinical manifestations of the infection with the platelets returning to normal levels shortly after peak parasitemia at 14 days. Platelet kinetics had a strong correlation with hematologic and parasitologic values in the Aotus model. No consistent associations were observed between platelet kinetics and other parameters in the Saimiri model. These data indicate that the Aotus model for malaria is more predictable than the Saimiri. Further, platelet turnover rates and recovery provide a useful prognostic parameter during malaria infection. The results are discussed in relation to the value of the two species of monkeys as models for the pathogenesis of human malaria.     

Protein electrophoretic variability in Saimiri and the question of its species status

An electrophoretic survey of 15 protein systems (22 loci) was employed to determine the genetic relationships among 9 populations (441 individuals) of South American squirrel monkeys (Saimiri sciureus sciureus, S. sciureus boliviensis, and S. sciureus ustus). Genetic markers capable of differentiating the second from the two other taxa were observed mainly in the ADA and GPI systems. Heterogeneity for ADA and CA2 between populations from opposite banks of the Jamari river was verified in S. sciureus ustus. The average heterozygosities ranged from 3% to 5%, the lowest being in S. sciureus sciureus and the highest in S. sciureus boliviensis. Low genetic distances (D = 0.001?0.057) were observed between populations within taxa or between S. sciureus sciureus and S. sciureus ustus. But both differed to a larger extent from S. sciureus boliviensis (D = 0.11 in both comparisons). There is a positive correlation between the genetic and geographic distance matrices. The three taxa are more clearly separated (D = 0.76–0.77) from the outgroup used for comparison (Cebus apella). Our data suggest that there is only one large, polytypic species of squirrel monkeys in South America, S. sciureus, forming a contiguous ring of geographical races or subspecies. Two of the most differentiated forms meet at the Peruvian Amazonia where natural hybrids and secondary intergradation have been reported. © 1993 Wiley-Liss, Inc.     

Severe malarial anemia associated with increased soluble Fas ligand (sFasL) concentrations in Gabonese children

To investigate if severe malarial anemia is associated with specific cytokine overproduction, we evaluated serum levels of soluble Fas ligand (sFasL), tumor necrosis factor (TNF-alpha) and interleukin-10 (IL-10) from three groups of young children with Plasmodium falciparum infection (asymptomatic cases, uncomplicated malaria cases and severe malarial anemia cases), in a hyperendemic area of Gabon. In uncomplicated cases, only TNF levels were significantly (p < 0.001) increased in comparison to asymptomatic cases with P. falciparum infection. High levels of sFasL, TNF-alpha and IL-10 were associated with low hemoglobin concentrations, sFasL levels were significantly higher in children with severe malarial anemia (p < 0.001) as compared to both other groups. The parasite density was positively correlated with IL-10, TNF-alpha and sFasL levels. TNF-alpha and sFasL, but not IL-10 or parasitemia, were independent predictors of hemoglobin concentrations. These results suggest that, in malaria, a specific dysregulation of the cytokine balance may lead to complications such as severe anemia.