Predicting disease dynamics in African lion populations

Abstract

In 1994, one-third of Serengeti lions died from canine distemper virus (CDV). I estimated the epidemiological network structure of the Serengeti lion population using long-term data. I found that the lion population is a mix of local pride-to-pride contacts (driven by territory adjacencies) and transient nomad-to-pride contacts (driven by gamma variance process). When canine distemper virus (CDV) was introduced into the network, I found that although nomads are numerous, travel long distances, and are likely candidates to be considered "superconnectors" (connecting distant parts of a network), their impacts on CDV disease dynamics were surprisingly low. Analysis of the data-driven, Levins-type network model demonstrates that the epidemic probably was not propagated solely by within-species transmission but rather involved multiple introductions from other carnivore species, such as jackals and hyenas. The social network model further suggests that the epidemiological observations from the 2000 km2 Serengeti study area may not have reflected the larger-scale dynamics because the sample was (1) located at the periphery of the pride-pride contact network and (2) confined to a small region relative to the scale of the ecosystem. If lions could not produce the observed CDV outbreak, and other wild carnivores were repeatedly involved in transmission to the lion population, could a multi-host spatial model account for the patchy pattern of CDV spread seen in lions in 1994? A stochastic susceptible-infected-recovered model was constructed which allowed transmission between a highly territorial species, like lions, and 1-2 more gregarious hosts, such as hyenas and jackals. When other gregarious species were coupled with lions with low interspecific contact rates, the erratic patterns of CDV spatial spread were similar to those seen in lions in 1994. The results of both the network and the multi-host models suggest that lions are a non-maintenance population for canine distemper virus, and more broadly address issues of spatial disease ecology and multi-host pathogens in complex ecosystems.