Health risks linked to human/wildlife overlap
There are a number of parasites and pathogens that humans share with other animals and these represent a health risk to both parties. For example humans exposed to dog faeces may become infected with eggs from tapeworms residing in the dog and consequently suffer from hydatid disease. Toxoplasma gondii which is normally a parasite of cats and rodents is known to cause many human birth defects. In the case of humans and baboons, the concern is valid in both directions. As humans and non-human primates may potentially share a variety of pathogens, humans that cross paths with baboons could transfer pathogens to the baboons, and vice versa (especially if baboons and humans share food sources or come into physical contact with one another).
www.pringlebay.info
From a conservation point of view, interaction between humans and wildlife in general is therefore thought to have negative effects on the wildlife in question. This was evident in 2007, when a Peninsula baboon was diagnosed with Mycobacterium tuberculosis, or human tuberculosis (TB). Scientists feared the worst for the Peninsula baboon population as this disease can decimate whole groups of primates in short time periods. Fortunately this was not the case in the Peninsula. Because of the invasive nature of the methodology normally used to test individuals for TB (eyelid test, sputum sample or x-ray of chest) only a handful of baboons have been tested for TB since. However, none of these animals were found to be infected with TB. However, due to the high prevalence of human TB in the Western Cape all baboon that come into to contact with human waste are potentially at risk.
In recent times, the study of diseases in primates specifically has become a central issue in conservation. Increased contact between human and non-human primates increases the possibility of parasite transmission in both directions and of sharing infectious diseases. More than 100 parasite species are shared between wild primates and humans. It is thus highly probable that the baboons of the Cape Peninsula are at high risk of infection by parasites and other infectious diseases from their neighbouring human reservoir. It is therefore of great importance to ascertain what diseases are found in the Cape Peninsula baboons as this knowledge may have profound implications for management of both baboons and humans on the Peninsula.
What do we know about diseases in the Cape Peninsula baboons?
Our current knowledge on the viruses and bacteria infecting the Cape Peninsula baboons is virtually non-existent. This is due to the fact that the tracking of most viruses and bacteria in a host require the collection of blood samples, which can only be achieved by anaesthetising the animals. This is not the case for gastrointestinal parasites, protozoa and helminths (worms) that could infect the Cape Peninsula baboons.
BRU member Damiana Ravasi collected data on gastrointestinal protozoa and helminths (worms) between 2006 and 2008 in an attempt to understand how parasite infection dynamics in baboons are being affected by urbanization. Worms live in the host gut and excrete infectious stages (eggs) in the faeces of the host. Protozoa emit cysts as infective stages. These stages are then dispersed in the environment and will infect new hosts via soil ingestion or other modes of transmission. While we cannot see the worm inside the animal, the infective stages can be easily collected without using invasive techniques, i.e. by collecting the faeces.
What knowledge are we trying to gain by studying parasites?
- First of all, we want to establish baseline data on the gastrointestinal parasite fauna in the Cape Peninsula baboons.
- Once this knowledge has been obtained, we will compare the parasite infections of the Cape Peninsula baboon population with other baboon populations across South Africa and find out if there is variation in infection rates.
- We also wish to compare parasite infections between troops in the Cape Peninsula with varying degrees of human contact, and analyse potential causes of variation in parasite infections.
- Finally, we want to ascertain whether nematode (round worms) species found in both the baboon and human Peninsula population are the result of cross-contamination between baboons and humans
- If this study successfully demonstrates a clear link between parasite prevalence and proximity of baboons to humans then it provides conservation authorities and town planners alike with the necessary information to restrict overlap between the two primate populations.
What gastrointestinal parasites have we found in Cape Peninsula baboons?
With the aid of all BRU members and field assistants, we were able to collect more than 600 faecal samples from six baboon troops. All these samples were processed for the extraction of parasite infective stages and analyzed one by one under the microscope for parasite identification. The following microscope images show a few examples of what stages we found in baboon faeces. Each stage type corresponds to a different parasite species (worm or protozoan).
Egg of nematode Trichuris sp. (whipworms). Scale bar = 25 µm.
This type of nematode occurs in the large intestine of humans and primates throughout the world. Heavy infections with Trichuris sp. may result in severe enteritis, with diarrhoea, and even death. We do not know with certainty if the Trichuris found in baboons can be shared with humans. The human whipworm (Trichuris trichiura) has been well-documented in the clinics of the Cape Peninsula.
Egg of nematode Oesophagostomum sp. (nodular worms). Scale bar = 25 µm.
Primates are susceptible to infection with multiple species of Oesophagostomum. This nematode is very common in Old World monkeys and apes and has the capacity to cause substantial pathology and death. Heavy infections of Oesophagostomum have been associated with mucosal inflammation, ulceration, dysentery, weight loss, and death in primates.
Cyst of protozoan Balantidium coli. Scale bar = 25 µm.
Infections with this protozoan are common in nonhuman primates. B. coli is usually not considered pathogenic in primates. However, heavy infections are associated with diarrhoea and ulcerative enteritis.
More information about cross-transmission
If we want to confirm cross-transmission between humans and nonhuman primates, the parasites must be identified to the species level. Due to the limited morphological characters of parasites, delimiting their species using microscopy can be difficult. Molecular techniques are increasingly used as a main tool in the identification of species. For example, molecular methods have been used to study genetic variation within Oesophagostomum bifurcum in humans and nonhuman primates in Ghana (remember that Oesophagostomum sp. was also found in Cape Peninsula baboons). Using molecular tools, researchers have shown that Oesophagostomum bifurcum found in humans is genetically distinct from that infecting some non-human primates and thus that nonhuman primates are unlikely to be a source of human oesophagostomiasis. More research must therefore be done to confirm cross-transmission of parasites between humans and baboons.
Are there concerns for Cape Peninsula residents?
Currently there is no evidence for transmission of human parasites to baboons or vice versa in the Peninsula but we are investigating this possibility in our study and will be sure to keep the public informed as the results become available. We strongly suggest that people avoid contact with baboons and their faeces. However, to put this risk in perspective we need to be aware that a similar warning could be made for human contact with the faeces of domestic animals that are far more prevalent within our community and whose faeces are more abundant within public areas and private gardens.
References
Cogswell, F. 2007. Parasites of Non-human Primates. In: Flynn’s parasites of laboratory animals, (ed.) R. J. Flynn & D. G. Baker. Blackwell Pub.: Ames, Iowa, pp. 693 – 743.
Gasser, R. B., De Gruijter, J. M., and Polderman A. M. 2006. Insights into the epidemiology and genetic make-up of Oesophagostomum bifurcum from human and non-human primates using molecular tools. Parasitology 132: 453 – 460.
Pedersen, A. B., Altizer, S., POSS, M., Cunningham, A. A, and Nunn, C. L. 2005. Patterns of host specificity and transmission among parasites of wild primates. International Journal for Parasitology 35 (6): 647 – 657.
