Location: Foreign Arthropod Borne Animal Disease Research
Project Number: 3022-32000-025-012-S
Project Type: Non-Assistance Cooperative Agreement
Start Date: Sep 1, 2022
End Date: Aug 31, 2025
The fundamental objective of this project is to expand the understanding of the ecology, host range and pathogenesis of infection by Japanese encephalitis viruses (JEV). Japanese encephalitis is one of the most serious and prevalent mosquito-borne infections in the world. This virus is endemic in numerous Asian countries, and periodic outbreaks occur in adjacent areas such as Australia. Incursion of JEV into the United States would have significant negative impacts on animal agriculture and public health and expanding the understanding of host range and aspects of pathogenesis such as persistent infection will support management of the disease if such an incursion occurs. JEV is a flavivirus closely related to West Nile virus (WNV). It is transmitted by Culex mosquitoes and the major recognized amplifying hosts are pigs and wading birds. Infected humans can suffer serious and fatal disease, but are considered dead-end hosts, as they do not develop a high enough level of virus in blood for feeding mosquitoes to become infected. This project will address two major knowledge gaps concerning JEV that may be important in formulating plans for surveillance and control should this virus be introduced into North America: 1) Are there non-classical amplifying or maintenance hosts for JEV that may be epidemiologically important? Birds are clearly the major amplifying hosts for WNV, but previous work performed by the Cooperator demonstrated that alligators and snakes can also play that role and may be important in maintaining the virus in relevant ecosystems. The ectothermic nature of reptiles and amphibians raises the intriguing possibility that they could become infected during warm weather, harbor the virus for prolonged periods during periods of cool temperature or hibernation, and then provide a source of virus to mosquitoes as the weather warms. 2) Five genotypes of JEV are currently recognized, all belonging to a single serogroup. However, virtually nothing is known about the comparative pathogenesis of these different genotypes in pigs or birds, which again could have high impact in the face of an incursion. Specific objectives include: 1) Evaluate the pathogenesis of multiple genotypes of JEV infection in at least one species of alligators, snakes, and/or frogs. 2) Evaluate the pathogenesis of multiple genotypes of JEV infection in North American bats to ascertain their potential importance as amplifying or overwintering hosts. 3) Determine the duration and magnitude of JEV viremia in feral pigs and two species of wild avian hosts (pigeons and house sparrows) following infection with contemporary isolates of each of the five genotypes. 4) Characterize the potential role of ectothermic vertebrates and feral swine (wild boar) as amplifying and maintenance hosts for JEV in Cambodia, a country with endemic JEV infection.
A number of critical gaps remain in the understanding of the ecology and host range of JEV, particularly with regard to a potential incursion into North America. This project will address several of these knowledge gaps with an overlying mindset of preparing for introduction of JEV into the new world. Aim 1. Evaluate the pathogenesis of multiple genotypes of JEV infection in at least one species of alligators, snakes, toads and/or frogs. Major outcomes will be to characterize the magnitude and duration of viremia under both warm temperature and following a warm-cool transition. The basic pathogenesis of JEV infection will be determined in these species and the duration of infection will be evaluated following induced hypothermia and renormalization of environmental temperature to determine whether these animals might be capable of serving as overwintering hosts for JEV. Aim 2. Evaluate the pathogenesis of multiple genotypes of JEV infection in North American bats to ascertain their potential importance as amplifying or overwintering hosts. Susceptibility of three species of North American bats to infection with the two dominant genotypes of JEV will be evaluated. Aim 3. Evaluate the duration and magnitude of JEV viremia in feral pigs and two species of wild avian hosts (pigeons and house sparrows) following infection with one or two contemporary isolates of each of the five genotypes. The Cooperator has previously demonstrated that a variety of birds are susceptible to JEV infection and infection results in viremia that has the potential to infect mosquitoes. Evaluating the susceptibility of feral swine is also highly important considering the huge problem that they pose in the southern US. The susceptibility of swine and birds in the transmission cycle of JEV will also be exploited to determine, for the first time, whether there are significant differences in pathogenesis and viremia profiles after infection of these animals with the five known genotypes of JEV. Aim 4. Characterize the potential role of ectothermic vertebrates and bats as amplifying and maintenance hosts for JEV in Cambodia, a country with endemic JEV infection. JEV occurs commonly in large regions of Asia, and it is important to evaluate whether the results obtained from experimental infection of ectotherms and bats are congruent with a real-world situation where JEV circulates continually. Cambodia is such a JEV-endemic country, and serosurveillance studies involving capture-release of snakes, toads, frogs, lizards and multiple species of bats will be conducted there. Additionally, materials from Aims 1, 2, and 3, will be used to investigate potential influences of the same virus replicating in different hosts on population-level changes in the viral genetics.