R. W. Barrette et al. discuss evidence that Reston ebolavirus (REBOV) has been circulating in Philippino pigs, possibly spilling over from bats ("Discovery of swine as a host for the Reston ebolavirus," Reports, 10 July 2009, p. 204). We hypothesize that this has implications for the health of livestock and humans in sub-Saharan Africa, particularly if large pig herds increase in number there. Many viruses circulate among African bat populations, including filoviruses with high human pathogenicity (1). There are also concerns that the passage of REBOV through swine may alter its pathogenicity, perhaps through "epidemic enhancement" (2). According to this theory, if a pathogen is introduced into a population containing individuals with acquired immunity, the resultant epidemics will likely be longer in duration and/or larger in size than in a population where pathogens are introduced to naïve populations. If true, transmission to humans is more likely from contact with animals housed in concentrated animal feeding operations (CAFO) than from more isolated animals, as postulated to explain the emergence of Nipah virus in Malaysia, another virus transmitted to humans from bats by way of pigs (2, 3).
Few, if any, pig CAFOs are currently located between South Africa and the Sahel (4). Increasing globalization and population growth is likely to intensify pig farming in sub-Saharan Africa. Although lowering the economic and health burden of cysticercosis (4), this change may enhance viral livestock epidemics. To reduce this risk, we suggest that CAFOs in sub-Saharan Africa be located and designed in ways that minimize interaction with populations of bats, particularly those that harbor filoviruses. Until the viral dynamics among bat populations are better understood, we suggest that areas that are ecologically similar to sites of known filoviral outbreaks among humans or primates be classed as unsuitable locations. Reducing deforestation and other practices that have been hypothesized to stress and displace bats, leading to viral spillover is also desirable (5), as is surveillance (6).
Colin D. Butler and Haylee J. Weaver
National Centre for Epidemiology and Population Health, The Australian National University, Canberra 0200, Australia.
References
1. E. M. Leroy et al., Nature 438, 575 (2005)
2. J. R. C. Pulliam, J. G. Dushoff, S. A. Levin, A. P. Dobson, PLoS ONE e165, (2007).
3. K. B. Chua et al., Science 288, 1432 (2000).
4. R. Krecek et al., Vet. Parasitol. 154, 38 (2008).
5. R. K. Plowright et al., Proc. R. Soc. London Ser. B 275, 861 (2008).
6. Editorial, Nature 459, 889 (2009).
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