The genetic diversity of mammal reservoir host populations is a key factor in the emergence of rabies virus epidemics

Rabies virus (RABV) is a worldwide spread zoonotic parasite. RABV maintains successful transmission cycles within some host species of the mammalian orders Carnivora and Chiroptera, which act as reservoirs. From these reservoirs and through cross-species transmission (host jumps), RABV can transiently infect a wide range of mammals, including humans, with no onward transmission (spill-over hosts). The symptoms caused by RABV, which ultimately lead to host dead, and the difficulty to eradicate the virus from reservoir hosts make this virus an important problem for the maintenance of wild fauna, and a major concern for human health. Indeed, RABV causes 60,000 human deaths every year. Despite the importance of the virus, the factors that influence RABV evolution and the likelihood of a virus jump to a new host are still poorly understood. Identifying these factors is central to design strategies to prevent RABV epidemics. It has been proposed that the likelihood of a virus to jump to a new host is directly linked to the genetic diversity of the virus population in the reservoir host(s). However, this hypothesis has been seldom tested. A group of researchers coordinated by Dr. Israel Pagán has analyzed how different ecological factors affect the genetic diversity of RABV populations and the frequency of virus host jumps. Among these ecological factors, the study considered the genetic diversity of the host population, the average host-virus co-evolutionary time-scale, host population size and density, host adult body size, and host geographic and home ranges. Results provide evidence that greater host genetic diversity increases both RABV genetic diversity and the likelihood of a host being a donor in RABV cross-species transmission events, with the other ecological factors having a minor role. This study contributes to understand the factors that drive the emergence of RABV epidemics, and could open the possibility to develop statistical models to predict the conditions that favor RABV epidemics.