The African green monkey (Cercopithecus aethiops) as a laboratory model for cyclosporiasis

Abstract

Cyclospora cayetanensis, a coccidian protozoan parasite, that causes diarrhoea in immunocompetent as well as immunocompromised individuals with or without international travel., The biology and epidemiology of C. cayetanensis has been complicated by lack of information on the pathogen’s origins and if animal reservoirs do exist for this parasite. Morphological and molecular characterization of three new Cyclospora spp isolated from East African non-human primates that are very similar to C. cayetanensis that infects humans, offer an opportunity to study the biology and pathogenesis of Cyclospora species. This study was conducted at the Institute of Primate Research (IPR), Nairobi with a view to developing and testing the suitability of African green monkey (AGM) as a laboratory model for cyclosporiasis in humans. Pabio anubis and Cercopithecus aethiops collected from the wild by trapping, underwent clinical and parasitological evaluation. Multiple individual faecal samples were collected and processed using the standard formalin ethyl acetate concentration technique. Faecal smear slides were stained with modified Ziehl Neelsen and hot safranin stains, then examined by light microscopy for the presence of Cyclospora oocysts and other gastrointestinal parasites. The Cyclospora oocysts isolated were used to establish experimental infections in four AGM for pathological evaluation and demonstration of the life cycle stages of Cyclospora species. Efficacy of Trimethoprim- Sulphamethoxazole (TMP-SMX) was evaluated in monkeys with natural Cyclospora infections.. Hematological analyses were carried out using venipuncture blood from the animals. The Enzyme linked immunosorbent assay was used to probe sera for simian immunodeficiency virus infections and Cyclospora specific antibody responses in the study animals. Nested polymerase chain reaction was used to confirm the identity of isolated Cyclospora oocysts from infected non-human primates. Data generated were analysed using Statistical Analysis System where the prevalence of intestinal parasites was computed as the proportion of number of positive observations and the Chi-square statistics was used to determine the associations between parasite species and Cyclospora and p values of < 0.05 considered significant. The prevalence of Cyclospora infections in non-human primates collected from the wild was 6.2% for the baboons and 64.1% for the monkeys with significantly higher prevalence in adult animals than in juveniles (p value = 0.0310). SIV infection was detected in adult animals, with a prevalence of 30% recorded for baboons, and 64.1% for monkeys (50% in male, 71.5% in female AGM. Cyclospora-SIV co-infections occurred in 10% of the baboons and in 30% of the monkeys, though the animals were asymptomatic at the time of faecal sample collection. Experimental Cyclospora infections were successfully established in four monkeys. On gross pathology, the juvenile animals had minimal changes at 49 days post-infection, while the adult males showed more severe pathology, with haemorrhages in the stomach and intestine, mildly enlarged and prominent lymph nodes, and the livers had moderate pitting of the surface which was widespread. Histopathology indicated that the stomach and intestines had mild disruptions of the mucosal wall, lymphocytic infiltration, with intracellular parasite vacuoles in the luminal end of the enterocytes. The livers showed periportal lymphocytic infiltration with formation of granulomas in the liver. The mesenteric lymph nodes were hyperplastic with extensive proliferation of the lymphocytes. TMP-SMX therapy was effective for treatment of Cyclospora in AGM. Recurrent asymptomatic Cyclospora infection occurred in 33% of the cases which responded to second treatment with TMP-SMX. DNA analysis confirmed the oocysts identified in natural infection used in experimental inoculation study to be Cyclospora species with a PCR product of 294 base pairs. In conclusion, and based from this study the Cyclospora infections in African green monkey produced pathological lesions similar to those reported in humans with cyclosporiasis. Response to treatment with TMP-SMX was similar to what has been reported for human cases. It appears that the current study has developed the African green monkey as an appropriate model to study cyclosporiasis