Elephant Endotheliotropic Herpesviruses in African Elephants and Detection by Saliva Sampling

Abstract

Elephant endotheliotropic herpesviruses (EEHVs) are the etiologic agents of a lethal hemorrhagic disease in Asian elephants (Elephas maximus) and African elephants (Loxodonta africana). This disease is responsible for 50 percent of all Asian elephant deaths in the United States since 1980. However, EEHVs remain enigmas because it is rare for herpesviruses, wich have typically coevolved with their host species and establish life-long, persistent infections, to cause such an acute disease in the host species. To explore the infection dynamics of EEHVs that might suggest determinants of pathogenicity, I conducted an epidemiological study of a wild population of African elephants in Samburu, Kenya and monitored the viral shedding of two asymptomatic female African elephants in New Jersey for one year using a novel saliva assay. My goals were to look at 1. the prevalence of nodules, which have been found to harbor EEHVs and are considered to be evidence of symptomatic virus reactivation or infection, in wild African elephants; 2. the effects of age, weaning, sex, and seasonal and environmental stresses on the changing landscape of selective pressures determining host immunomodulation of the infection and susceptibility to nodules or asymptomatic viral shedding in saliva; and 3. the diversity of virus populations within hosts, divergence of virus populations between elephants, and the dynamics of coinfection. I report a 20% nodule prevalence in the wild population and find that nodule frequency and severity is highest in young elephants, especially three-year-olds, suggesting that immunological naivety and stress play into host susceptibility. The detection of four different types of EEHVs and 3 types of EGHVs shed by both elephants over the sampling period reveals patterns of coinfection and seasonal shedding. Additionally, this study describes a high level of DNA polymorphism in the origin binding protein gene for the EEHV3A and EEHV3B virus populations of the two elephants and a significant amount of divergence between the virus populations of the two elephants even for the same virus sub-type. These data suggest that elephants harbor signature virus populations that evolve under changing selective pressures. Symptomatic reactivation or infection outbreaks such as nodules or even hemorrhagic disease cases could result if a virus becomes maladapted to the host or if the coinfection equilibrium is upset. This study advances the understanding of infection dynamics of EEHVs and provides paths for further research.