Epidemiological study of selected viral pathogens and assessment of responses to polio vaccines in semi- captive chimpanzees in Uganda.

Abstract

The high influx of non-human primates (NHP) including apes into sanctuaries that have increased in numbers in the last two decades across Africa’s equatorial region is of great concern. There were no studies conducted previously to establish the health status of NHP including the potential viral pathogens of zoonotic concern in these sanctuaries. The main goal of this study was therefore to screen the chimpanzees for the main viral pathogens, characterize them at molecular level and establish phylogenetic relationship with strains from other primates to generate baseline data on these pathogens important for monitoring the health of the chimpanzees in the sanctuary and as basis for reviewing of standard operating procedures. The study also evaluated effectiveness of vaccination of chimpanzees against measles and polio virus. In order to achieve this, blood and fecal samples were collected from 42 wild-born captive chimpanzees on Ngamba Island Chimpanzee Sanctuary (NIC) during annual health checks in 2007 and 2008. Retrospective samples from previous health checks were included in the analyses. Serum was subjected to enzyme-linked immunoassays for detection of antibodies directed against simian/human immunodeficiency virus (SIV/HIV), human T-lymphotropic virus types 1 and 2 (HTLV-1 and HTLV-2) and Hepatitis B Virus (HBV). Nucleic acids (DNA and RNA) were extracted from all samples and amplified by Polymerase Chain Reaction (PCR) and genotyped for specific viral pathogens. Viruses were characterized by phylogenetic analysis. The study has revealed that chimpanzees NIC sanctuary are infected with multiple viral pathogens with zoonotic potential. The viral infection prevalence in chimpanzees were 85.7%, 73%, 60.5% and 32.4% for the Adenoviruses, Simian Foamy virus (SFV), gammaherpesviruses and Hepatitis B Virus (HBV), respectively. They were also screened for simian/human immunodeficiency virus (SIV/HIV), human T-lymphotropic virus types 1 and 2 (HTLV-1 and HTLV-2) antibodies, Hepatitis C virus (HCV), Hepatitis E Virus (HEV), Flavivirus, human metapnuemovirus, and Chikungunya viruses but were negative for all these parameters. Phylogenetic analysis of the herpersviruses found that chimpanzees were infected with members of the Gammaherpesvirinae with one novel herpesvirus in the same family tentatively named Pan troglodytes rhadinovirus 3 (PtroRHV-3) in two chimpanzees that fell into a clade of primate rhadinoviruses and Kaposi sarcoma herpesvirus (human herpesvirus 8). SFV sequences obtained in this study formed four sub clusters within the specific SFV P. t. schweinfurthii clade with significant variability among the newly described SFVs strains. This gives evidence for an on-going SFV transmission among chimpanzees within the sanctuary most likely through horizontal routes leading to co-infection of individuals with more than one strain. PCR amplification of chimpanzee samples positive for antibodies to hepatitis B (core) antigen (ant-HBc) detected chHBV DNA in one captive wild born (Mika) and one wild chimpanzee (Kiiza). The HBV clustered closely with HBV isolate FG published previously for P.t.schweinfurthii. Retrospective analysis of samples from Mika for HBV genome provided evidence of persistence HBV infection with high viral load in the infected chimpanzee and proves that HBV circulates naturally in chimpanzees. Analysis of the nearly complete HBV genomes indentified from Mika and Kiiza for recombination with human HBV subtype C, as earlier reported for the FG isolate there was no recombination with human HBV subtypes or strains from other sub species. Adenovirus infection was widely spread in chimpanzees with 85.7% prevalence and this is most probably shed as infectious virions in substantial quantities in feces in apparently healthy population. This poses the risks of intra-species transmission and intra-species recombination of adenoviruses. This study also presents applicability of using some of the established non-invasive methods in detection of some of viral pathogens as evidenced by the detection of viral DNA by PCR for adenoviruses, herpespesviruses and hepatitis B virus in feces of chimpanzees. This is a very valuable tool especially for health monitoring of wild ape populations. This study also shows that chimpanzees vaccinated against poliomyelitis using oral polio vaccine (OPV) had neutralizing antibodies against polio virus type 1, 2 and 3 nine years post vaccination. Conversely only a few chimpanzees vaccinated against measles had detectable protective titers. This shows that preventive measures employed in sanctuaries especially vaccinations need to be monitored and evaluated for effectiveness over time. OPV mounts protection among vaccinated chimpanzees but its continued use should be evaluated along the global eradication program following the established WHO global action for laboratory containment of wild polioviruses. Findings of these viral pathogens coupled with the close phylogenetic relationship between chimpanzees and humans plus high levels of interactions during sanctuary operations, presents a high potential for pathogen exchange. Some of the viral pathogens are shed in body fluids in large quantities like SFV in saliva and adenovirus in feces which presents high risk for zoonotic transmission to animal keepers in sanctuaries coming into contact with chimpanzee fecal matter and other body fluids while cleaning housing facilities. Results of this study give insights onto implications of management of primates in sanctuaries and cautions for the improvement of occupational health and safety protocols to minimize risks of pathogen exchange.