COUNTERMEASURES TO CONTROL AND ERADICATE RIFT VALLEY FEVER (RFV)
Location: Arthropod-Borne Animal Diseases Research
Title: Rift Valley Fever Virus Control: Integration of Virus, Host and Vector Studies
Submitted to: Meeting Proceedings
Publication Type: Proceedings
Publication Acceptance Date: October 13, 2009
Publication Date: August 1, 2010
Citation: Mecham, J.O., Bennett, K.E., Drolet, B.S., Miller, M.M., Wilson, W.C. 2010. Rift Valley Fever Virus Control: Integration of Virus, Host and Vector Studies. Meeting Proceedings. 711-712.
Rift Valley fever (RVF) is a disease of animals and humans that occurs in Africa and the Arabian Peninsula. It is caused by a Phlebovirus in the family Bunyaviridae. Mosquito-borne epizootics occur during years of unusually heavy rainfall. Domestic cattle, sheep and goats are highly susceptible to infection, which can result in high mortality in young animals and increased abortion in adults. Unapparent infections are quite common in wild ruminants. Infection in humans causes influenza-like symptoms, but can lead to severe complications, including retinopathy, blindness and even death. Control of RVF in livestock requires a three-pronged approach that includes diagnosis, vaccination and vector monitoring and management. Scientists at the Arthropod-Borne Animal Disease Research Laboratory (ABADRL) conduct research to address each of these areas.
Research on vector competence of North American species of mosquitoes for RVF virus (RVFV) was conducted in collaboration with the US Army Medical Research Institute of Infectious Diseases (USAMRIID). This work showed that Culex tarsalis is highly susceptible to infection and is able to transmit the virus (competent vector). Aedes vexans from Louisiana and Florida were competent vectors of RVFV; however, Aedes vexans from California and the Rocky Mountains were only minimally competent. Other North American species of mosquitoes, such as Culex erythrothorax and Aedes dorsalis, were shown to be poor vectors for RVFV.
Collaborative research agreements for vaccine development, evaluation and validation were established with the Canadian Food Inspection Agency (Winnipeg, Canada), Onderstepoort Veterinary Institute (South Africa), Kenya Agriculture Research Institute, Colorado State University, University of North Carolina, Department of Homeland Security, and the Department of State Biosecurity Enhancement Program. Infection trials have been conducted in collaboration with the Canadian Food Inspection Agency to experimentally reproduce disease in sheep and cattle and to produce reagents for validation of diagnostic assays. In addition, experiments have been conducted at the ABADRL to examine the host immune response and to determine if competent mosquitoes can become infected from animals following vaccination with the attenuated MP-12 strain of RVFV.
Finally, ABADRL scientists are working to develop operator safe reagents and diagnostic tests for RVF. Expressed RVFV proteins and antibody reagents (rabbit, mouse and sheep) have been produced and incorporated into both competitive enzyme-linked immunosorbent assay (c-ELISA) tests and immunohistochemical (IHC) assays for detection of RVFV antibodies and antigens. Real-time PCR assays have been developed for rapid virus detection during RVF outbreaks. Collaborations have been established to facilitate both development and validation of the diagnostic assays.
In summary, studies have identified North American mosquito species that are competent vectors for RVFV; animal models have been developed to study RVFV infection in ruminants; the ability of mosquitoes to transmit a candidate vaccine strain of RVFV (MP-12) has been examined; the duration of immunity to the MP12 strain is being investigated; and operator safe reagents and diagnostic tests have been developed for RVF, and agreements are in place to validate these diagnostic tests.
Future research directions include evaluating the potential for genetic reassortment in North American mosquito species between wild-type strains and vaccine strains of RVFV, and between North American bunyaviruses and wild-type or vaccine strains of RVFV. They also include determining the effect of environmental temperature on the ability of Cx tarsalis to transmit RVFV; determining which mosquito cells/tissues support RVFV replication; understanding population differences in vector competence; and understanding vertical transmission of RVFV. In terms of vaccine discovery and validation, collaborations are in place to examine mosquito transmission of RVFV from challenged vaccinates to naïve hosts; and to evaluate and improve alphavirus replicon DNA vaccines. Agreements are also in place to field validate the c-ELISA, the IHC and the Real-Time PCR diagnostic tests. Finally, collaborative agreements are in place to develop novel procedures, such as On-Probe Pyrolysis Desorption Electrospray Ionization (DESI) Mass Spectrometry and Surface Enhanced Raman Scattering, for diagnosis of RVF.