Frugivory Richness Predicts Ebola Spillover in Africa

Mireya Dorado, a student at Northeastern University, worked in Dr. Patrick Stephen’s lab studying pathogen spillover

Ebola is a deadly filovirus that infects a variety of mammals including humans. Since the first documented outbreak i n 1976, there have been numerous field studies searching for the source of the spillover of Ebola. Only a few studies have directly investigated the effect of mammalian host biodiversity. These studies have been limited to the diversity of known Ebola hosts and bats. However due to Ebola’s broad host range, there has not been a systematic approach to which hosts may be important for spillover. Therefore, our goal was to determine whether and what aspects of mammalian diversity play a significant role in predicting Ebola spillover events. We calculated species richness of mammals in 50 kilometer by 50 kilometer grid cells across Africa. Statistical analyses were based on a presence absence approach, which compared species richness at sites of spillover t o pseudo-absence background locations. We used bagged logistic regression, a machine learning method, to create statistical models testing how well species richness of different mammal subgroups predicted spillover. Overall, we found that Cercopithecidae and Pteropodidae were the strongest taxonomic predictors of spillover (mean AUC=0.943 and 0.936 respectively), but diversity of frugivorous species was the best overall predictor (mean AUC=0.956). This strongly implicates a role of fruit in Ebola transmission and the significance of fruiting and masting seasons as ideal times for spread of infection.


Testing the Enemy Release Hypothesis in Ungulates (Artiodactyl and Perissodactyl) and Carnivores

Lauren Kleine, a student from Colorado State University, examined the enemy release hypothesis in a project directed by Dr. Patrick Stephens and Dr. J.P. Schmidt.

Abstract:  The Enemy Release Hypothesis (ERH) predicts that invasive species will achieve greater success in non-native ranges due in part to escape from parasites found in their native ranges. The purpose of our study was to determine whether members of mammal populations occurring outside their native ranges are generally infected by fewer parasites than those from populations of the same species within their native ranges. We used the Global Mammal Parasite Database version 2.0 to investigate 39 species with entries from both inside and outside of their native ranges. For each species, Parasite Species Richness (PSR) was calculated for each species in native and non-native ranges, as well as measures of sampling effort. We used a Generalized Additive Model (GAM) of PSR as a function of sampling effort to generate residual values of PSR. Residual values were then used to test for differences in PSR in native vs. invasive ranges. In final analyses restricted to well-studied hosts, we found a significant reduction in PSR in invasive ranges. This study highlights the importance of considering sampling effort measures when comparing species richness values, and lends support to the enemy release hypothesis.

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Host Breadth of Parasites in Ungulates and Carnivores

Emili Price, a student from Winthrop University, worked with Drs. Patrick Stephens and John Gittleman in the Odum School of Ecology to look at host breath of parasites in ungulates and carnivores.

Emili Price1, Patrick R. Stephens2, John L. Gittleman2

1. Winthrop University, Rock Hill, South Carolina

2. Odum School of Ecology, University of Georgia, Athens, Georgia

Most parasites infect multiple hosts, but few studies have focused on characteristics of hosts and parasites that may cause differences in the host breadth. We investigated two facets of host breadth: variation in the number of host species different parasite species infect and the similarity of parasite communities among host species (i.e., overlap in the parasite species that infect different pairs of host species).  We first tested for the effects of parasite transmission mode and taxonomic identity on host breadth among parasites of ungulates and carnivores using a number of definitions of host breadth, and using several methods to try and correct for differences in sampling effort among parasite species. We found that viruses and sexually transmitted parasites infect significantly more hosts than other types of parasites in ungulates regardless of the estimate of host breadth considered.  We also found that viruses and vertically transmitted parasites infect significantly more hosts than other types of parasites among ungulate parasites that infect at least two hosts.  Finally, among carnivore parasites with two or more hosts, we found that parasites transmitted via feces infect significantly more hosts than other types of parasites.  We next investigated the effect of phylogenetic distance, differences in mass, and the geographic overlap among ungulate host species on parasite community similarity. All three variables showed statistically significant correlations with parasite overlap regardless of whether Jaccard’s or the corrected Jaccard’s index was used to measure parasite overlap among hosts.  However, geographic range area overlap and phylogenetic relatedness explained much more variation than differences in body mass among hosts.  Our results were almost identical when we restricted consideration to viruses, save that mass was an even weaker predictor of overlap.  Finally, we tested to see whether carnivore species that prey on ungulates are infected by more ungulate parasites than those that do not. We found that carnivore species that prey upon ungulates were infected by on average twice as many ungulate parasites than carnivores that specialize on different prey items.

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