Thursday, March 26, 2015

Studying the ecology of disease and primates

We often think of habitat loss, hunting, and perhaps even the pet trade as serious threats to primate conservation. Disease, on the other hand, is commonly forgotten. Yet, increasingly fragmented forests create more opportunities for humans and wildlife to come into contact and potentially transfer and spread disease. Our close genetic relationship with non-human primates further increases the likelihood of spreading illness through contact, making this a topic worth paying attention to.

Cryptosporidium parvum
A study came out recently in the journal PLOS Neglected Tropical Diseases that should remind all of us not to exclude disease as a potential threat to non-human primate conservation. Parsons et al., 2015 studied chimpanzees (Pan troglodytes) and baboons (Papio anubis) in Gombe National Park (where Jane Goodall studied chimps) and found that they are exposed to a parasite called Cryptosporidium. Cryptosporidium is transmitted through food, water, and zoonotic means (from animals to humans).

Death from infectious disease is the leading cause of mortality for the three chimpanzee communities inhabiting Gombe (Lonsdorf et al., 2006; Williams et al., 2008), thus studying disease ecology should allow us to better conserve the Gombe population. While Papio anubis is not endangered, Pan troglodytes is.

Of the 131 non-human primates tested, 16% were positive for Cryptosporidium compared to 9.6% of livestock and just 4.3% of the 185 humans tested. Baboons and chimpanzees were infected at a similar rate. Three species of Cryptosporidium were detected: C. hominis, C. suis, and C. xiaoi.
Bush pig, Photo credit: Derek Keats
Half of the Cryptosporidium documented in the Kasekela community of chimpanzees are of a Cryptosporidium species (C. suis) typically associated with pigs. Surprisingly, C. suis was not detected in any of the humans, baboons, or livestock tested. The authors suggest that the transmission cycle may involve bush pigs, Potaochoerus larvatus, because domesticated pigs are not present in this area due to a mainly Muslim population. The bush pigs are found in the forest the Kasekela chimps inhabit and may serve as a reservoir for the parasite. It seems there are more details to be teased out when understanding the connection between C. suis and humans. Another species of the Cryptosporidium parasite found in this study, C. hominis, is one of two species most commonly found in humans (Chalmers and Katzer, 2013; Insulander et al., 2013). Yet C. hominis was also found in baboons and one of the chimpanzee communities, raising a red flag.

Cryptosporidium has been found in other primate species as well, including mountain gorillas, which were found to have the same species of Cryptosporidium, C. parvum, as found in nearby human populations (Nizeyi et al., 1999; Graczyk et al., 2001). Cryptosporidium has also been reported in red colobus and black and white colobus monkeys (Sayler et al., 2012). The Parsons study thus contributes to a growing body of literature on the prevalence of zoonotic diseases and their transmission. The authors stress the need to further understand the complex connections between primates, their ecology, their contact with humans, and the spread of disease so that we can better understand this relatively unexplored area of primate conservation.

This is an interesting article because Parsons and colleagues tackled a question that is poorly studied. The ecology of how diseases like Cryptosporidium spread and affect our primate relatives is not well understood, but zoonotic diseases make up the majority (60.3%) of emerging diseases worldwide (Jones et al., 2008). This is a timely and interesting paper that is worth reading or at least skimming. You can find the article posted online here. It's free and worth a look!

Links of interest:
Non-human primate biosafety from the University of Minnesota
Studying disease emergence in primates may help us understand emergence in humans
ScienceDaily article on paper

Chalmers, Rachel M., and Frank Katzer. "Looking for Cryptosporidium: the application of advances in detection and diagnosis." Trends in parasitology 29.5 (2013): 237-251.
Insulander, M., et al. "Molecular epidemiology and clinical manifestations of human cryptosporidiosis in Sweden." Epidemiology and infection 141.05 (2013): 1009-1020.
Jones KE, Patel NG, Levy MA, Storeygard A, Balk D, et al. (2008) Global trends in emerging infectious diseases. Nature 451: 990–993 doi: 10.1038/nature06536
Graczyk TK, DaSilva AJ, Cranfield MR, Nizeyi JB, Kalema G, et al. (2001) Cryptosporidium parvum Genotype 2 infections in free-ranging mountain gorillas (Gorilla gorilla beringei) of the Bwindi Impenetrable National Park, Uganda. Parasitology Research 87: 368–370. pmid:11403378 doi: 10.1007/s004360000337 
Lonsdorf EV, Travis D, Pusey AE, Goodall J (2006) Using retrospective health data from the Gombe chimpanzee study to inform future monitoring efforts. American Journal of Primatology 68: 897–908 
Parsons, M. B., et al. "Epidemiology and Molecular Characterization of Cryptosporidium spp." Humans, Wild Primates, and Domesticated Animals in the Greater Gombe Ecosystem, Tanzania. PLoS Negl Trop Dis 9.2 (2015): e0003529.
Nizeyi JB, Mwebe R, Nanteza A, Cranfield MR, Kalema G, et al. (1999) Cryptosporidium sp and Giardia sp infections in mountain gorillas (Gorilla gorilla beringei) of the Bwindi Impenetrable National Park, Uganda. Journal of Parasitology 85: 1084–1088. pmid:10647041 doi: 10.2307/3285672 
Salyer SJ, Gillespie TR, Rwego IB, Chapman CA, Goldberg TL (2012) Epidemiology and Molecular Relationships of Cryptosporidium spp. in People, Primates, and Livestock from Western Uganda. Plos Neglected Tropical Diseases 6.(4):e1597. doi: 10.1371/journal.pntd.0001597. pmid:22506085
Williams JM, Lonsdorf EV, Wilson ML, Schumacher-Stankey J, Goodall J, et al. (2008) Causes of death in the Kasekela chimpanzees of Gombe National Park, Tanzania. American Journal of Primatology 70: 766–777 doi: 10.1002/ajp.20573

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