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Dr. Alisa E. Kubala, DVM, MVS (Conservation Medicine), MRCVS
A PhD Thesis
Health and Conservation of Eastern Gorillas: A One-Health Study of Blood-Borne Parasites and Retroviral Infections
- Dr Kristin Warren
- Dr Carly Holyoake
- Dr Lian Yeap
- Professor Ian Robertson
- Professor Una Ryan
- Dr Mike Cranfield
Eastern gorillas comprise two subspecies, Grauer’s (G. beringei graueri) and mountain (G. beringei beringei), which are endangered and critically endangered (n~8,000 and n~880) respectively. Mountain gorillas exist in the Virunga Conservation Area straddling Rwanda, Uganda and Democratic Republic of Congo (DRC), and in Bwindi Impenetrable National Forest, Uganda, ranging in altitude from 1,400 to 3,800m. Grauer’s gorillas exist solely in DRC, and range in altitude from 600 to 2,900m. The region in which these populations exist is prone historically to political conflicts and warfare, and is comprised of some of the highest human densities found on the African continent. Local economies are agriculture-based and extremely poor. Attempts by local humans to meet their subsistence needs, lead directly to anthropogenic disturbances which threaten gorilla survival. Such disturbances include agricultural conversion, illegal extraction of resources (snare setting for smaller mammals which entraps young gorillas), and animal trafficking (trapping of infants for the black market, a process which results in the deaths of group members and often disintegration of the group). These pressures, along with the threat of infectious disease circulating among gorillas, humans and their livestock, represent the greatest threats to the survival of eastern gorillas and the integrity of their habitats.
Humans and gorillas share 98.5% of their genetic makeup, rendering them susceptible to many of the same infectious diseases. However, whilst humans have acquired resistance to many pathogens from around the globe, eastern gorillas have remained in relative isolation, leaving them immunologically naïve and at greater risk of acquiring a new infection when the two species come into contact with each other.
Malaria, microfilaria and retroviruses are endemic in eastern gorilla host countries, where they are leading causes of morbidity and mortality. Co-infection may lead to increased parasite/viral loads, faster disease progression and increased disease transmission. Whilst malaria has traditionally been endemic at lower altitudes (<1,500m), highland epidemics (>1,500m) are increasing in frequency, where they can cause overwhelming fatalities among humans lacking immunity. This may be attributed in part to increasing temperature and rainfall leading to increasing parasite and vector development and distribution, raising concerns about the effects that climate change may have on malaria distribution at altitudes hosting immunologically naïve eastern gorillas. Molecular techniques have recently uncovered a multitude of Plasmodium species infecting great apes across Africa, several of which were previously thought to be human specific. This, and the finding of parasites very closely related to P. falciparum in gorillas, emphasise the risk of cross-species transmission. While it has been confirmed that wild apes carry these strains of malaria, it is not yet known how pathogenic they are, nor to what extent spillover from human malaria poses a threat to them.
Human immunodeficiency virus (HIV) is prevalent among humans living near to eastern gorilla habitats, and predisposes them to infections such as tuberculosis and other respiratory and faecal-oral pathogens prevalent in the region. Likewise, eastern gorillas may harbour retroviruses such as simian immunodeficiency virus (SIV), which has been shown to cause increased mortality and AIDS-like immunopathology in chimpanzees, and which could predispose gorillas to common and harmful infections.
Multiple species of blood-borne microfilariae including Loa loa, Oncocerca volvulus and Mansonella perstans, are prevalent among humans living near eastern gorillas. In addition to causing clinical illness, microfilaria may also interfere with the host’s immune mechanisms, and influence the outcome of other infections such as malaria, tuberculosis and HIV. The significance of microfilaria to eastern gorilla health is unknown at this time.
Haematological and biochemical reference intervals have not been described for eastern gorillas, nor has blood cell morphology. Previous studies in western gorillas reported that great ape blood cell morphology is similar to that of humans, with the exception of hypersegmented granulocyte nuclei. This difference is more prominent in eastern than in western gorillas, representing either a normal variant or, concerningly, possible nutrient deficiencies resulting from habitat loss.
My research will focus on the malarial, retroviral and microfilarial status of eastern gorillas, other local primate species and local humans. My work will determine whether cross-species disease transmission is occurring in these eastern gorilla habitats, and determine which vector species are responsible for blood parasite transmission. The research will also involve establishment of haematology and biochemistry reference intervals to enable rapid health assessments of eastern gorillas, and nutrient assays will be incorporated to rule out deficiencies as a cause of the eastern gorilla’s unique blood cell morphology. As a result of this study, the overall health status of eastern gorilla populations will be better understood; malaria, microfilaria and retroviruses in and around eastern gorilla habitats will be described; and malarial and microfilarial vector control guidelines will be created for the mutual benefit of both gorillas and humans.
- To determine whether eastern gorillas, other local primate species and the local human population are infected with Plasmodium, and if so, identify the species of Plasmodium present
- To determine what vector species are responsible for malaria transmission in eastern gorilla habitats
- To validate the use of ape and human faecal samples for non-invasive PCR diagnostic screening for Plasmodium infection
- To determine whether eastern gorillas and other local primate species are infected with retroviruses, including SIV and STLV, and if so, the clinical significance of these infections
- To determine whether eastern gorillas, other local primate species and the local human population are infected with microfilaria, and if so, the clinical significance of these infections
- To determine what vector species are responsible for microfilaria transmission in eastern gorilla habitats
- To create haematology and biochemistry reference intervals for eastern gorillas to enable determination of health status of individuals and detection of disease
- To describe the normal cell morphology for eastern gorillas, including investigating the possibility that nutrient deficiencies may be a cause of the prominent hypersegmentation of granulocyte nuclei observed in this species
This research involves collaboration between Gorilla Doctors™, University of Pennsylvania Perelman School of Medicine, Temple University, Chester Zoo, Cleveland Zoo, Congolese Institute for the Conservation of Nature (DRC), Lwiro Primate Sanctuary (DRC), Kahuzi-Biéga National Park (DRC), and Virunga National Park (DRC).
This project is funded by the School of Veterinary and Life Sciences, Murdoch University, and by Dr. Kubala’s Murdoch University International Postgraduate Scholarship.
Photos by Alisa E. Kubala