Potentially – Zoonotic Viruses in the Straw-Colored Fruit Bat (Eidolon Helvum) in Ghana_2015

Abstract

Bats are reservoirs for many emerging zoonotic RNA viruses, including rabies virus (RABV), SARS-like coronavirus, henipaviruses and filoviruses. Several bat species have been associated with Lagos bat virus (LBV) infection. They include Wahlberg‟s epauletted fruit bat (Epomorphorus wahlbergi), the straw-colored fruit bat (Eidolon helvum), the Egyptian fruit bat (Rousettus aegyptiacus), and an insectivorous bat, the Gambian slit-faced bat (Nycteris gambiensis). Bats are important for the maintenance and transmission of zoonotic viruses. The role of bats in the maintenance and evolution of lyssaviruses is complex and poorly understood. Fruit eating bats, including E. helvum, often inhabit and feed in agricultural areas, and this brings them into closer contact with humans and domesticated animals. LBV and other non-rabies lyssaviruses have not been well studied and the risk for humans and animals in Ghana is uncertain. Lyssavirus epidemiology is influenced by the host species distribution, abundance, demographics, behavioral ecology, dispersal, and interactions with humans. E. helvum occur in cities and rural areas of Ghana. The species is comestible and hugely harvested for bushmeat by both urban and rural folk. E. helvum feeds on fruits from farm plantations and roosts within or near residential areas. The species thus has close interaction with people. The pathobiology and route of transmission of LBV is not known in E. helvum bats. This study is one of the few studies of LBV in fruit bats in Ghana and the experimental infection study is the first conducted on LBV in one of its natural reservoir species. Using E. helvum as a model, we hypothesize that there is endemic circulation of LBV in this bat species in Ghana. The circulation of Lagos bat virus in the bat population is facilitated by certain pathobiology of the infection including susceptibility to the virus, incubation and clinical periods for different doses and routes of LBV infection, behavioral changes of rabid bats, virus occurrence in various bat tissues and excreta. Inoculation of LBV will result in clinical disease (rabies), although not all inoculated bats will develop the disease, especially when inoculated peripherally. The aim of this PhD study was dual. Firstly, it investigated infection dynamics of LBV in E. helvum in free ranging populations at the 37-Military hospital in Accra and Tano Sacred grove and in a captive population of E. helvum kept at the Achimota Forest. Secondly, the study conducted experimental investigation of the pathogenesis of Lagos bat virus, in E. helvum in captivity at the Achimota Forest in Accra, Ghana. To evaluate these hypotheses, E. helvum bats were repeatedly sampled from two major roost locations in Ghana from 2012 - 2014. Longitudinal sampling was also undertaken quarterly on captive bats at the Achimota Forest. Dead bats were collected from the roost sites and predetermined tissues collected at necropsy. Serum samples were subjected to virus neutralization tests against LBV. Tissues from dead bats were tested by FAT and PCR for LBV antigen and RNA respectively. To investigate the pathobiology of LBV in fruit bats, we conducted experimental intracranial (i.c) and peripheral (i.m) inoculation in captive bred straw-colored fruit bats (Eidolon helvum) which were seronegative for LBV, in Accra, Ghana. The study found high seroprevalence (0.447; CI=0.391-0.503) against LBV in Ghanaian E. helvum bats. There was, however, clear seasonal variation with a higher proportion of bats testing negative during the rainy season (Wild caught bats p-value = 1.06). None of the brain samples from bats found moribund or dead in this study showed presence of lyssavirus antigen or RNA. The experimental study confirmed that LBV can cause disease in E. helvum. Bats that were infected by either route of inoculation showed clinical signs similar to animals infected with RABV, though with some variation between isolates in the IC inoculation experiment. There was detection of virus in the brain, salivary gland and saliva. There was seroconversion in peripherally inoculated bats. A high seroprevalence against LBV is reported in E. helvum and other African megacheroptera. No published infection study exists of LBV in one of its reservoir hosts, such as the straw-colored fruit bat, with a gap in scientific knowledge of the disease. This study demonstrated that LBV is endemic and circulates among E. helvum in Ghana. The experimental study confirms that LBV is pathogenic to E. helvum by IC and peripheral inoculation and that there is seroconversion in bats before death and in surviving bats. This is the first ever experimental infection study of LBV in E. helvum bats. It is concluded that E. helvum is a suitable animal model for studies of the pathobiology of lyssaviruses. The species is abundant and widely distributed and adapts well to captivity. Comparative studies should be initiated with other LBV host species and viral isolates to compare the influence of viral origin, dose and route of inoculation, host demographics, and environmental conditions on infection dynamics. This will develop further our understanding of the dynamics of pathogen adaptation and host responses, as well as help to identify public health risk factors for emerging infections among the Chiroptera.