ARS | Publication request: Rift Valley fever Entomology, Ecology, and Outbreak Risk Factors

Submitted to: United States Animal Health Association Proceedings
Publication Type: Proceedings
Publication Acceptance Date: October 13, 2010
Publication Date: June 1, 2010
Citation: Linthicum, K., Anyamba, A., Small, J., Pak, E., Tucker, C.J., Witt, C., Chretien, J., Britch, S.C. 2010. Rift Valley fever Entomology, Ecology, and Outbreak Risk Factors. United States Animal Health Association Proceedings. p. 709-710.

Technical Abstract: Rift Valley fever (RVF) is a mosquito-borne zoonotic disease of domestic ruminants and humans in Africa. The disease is most severe in cattle, sheep, and goats, and it causes high mortality in young animals and abortion in adults. Exotic aanimal breeds from areas where RVF is not endemic tend to be more susceptible. Human infection causes significant morbidity and mortality. RVF has caused serious disease in laboratory workers and must be handled with high level biosecurity. RVF was first described in 1930 in the Rift Valley of Kenya, and the disease has since occurred irregularly in Kenya every 3 to 10 years. The disease first spread outside sub-Saharan Africa into Egypt in 1997 and resulted in large losses among the domestic animal populations and caused significant human disease. Subsequently, in 1987 a large outbreak in animals and people occurred in Sahel region of Senegal and Mauritania, and then in September 2000, a RVF outbreak occurred in Saudi Arabia and Yemen along the Red Sea Coast, representing the first Rift Valley fever cases identified outside Africa. RVF generally occurs during years of unusually heavy rainfall and when localized and widespread flooding occurs. It is thought that the flooding causes transovarially infected Aedes mosquito eggs to hatch and introduce the virus into domestic animals, thus allowing the maintenance of the virus in nature during dry non-epidemic conditions. After livestock are infected, a wide variety of mosquito species may act as the vector for transmission of RVF virus to spread the disease. There are no licensed animal or human vaccines available for use in the United States. We have developed a monitoring and risk mapping system using global sea surface temperatures and normalized difference vegetation index times series data derived from the advanced very high resolution radiometer instrument on polar orbiting national oceanographic and atmospheric administration satellites to map areas at risk for a potential outbreaks in sub-Saharan Africa, the Nile River Valley, and the Arabian Peninsula. This system is now an important tool for local, national and international organizations involved in the prevention and control of animal and human disease, permitting focused and timely implementation of disease control strategies several months before an outbreak. We are currently developing a geographic information system-based remotely sensed early warning system for potential RVF vectors in the United States. Forecasts of the potential emergence of mosquito vectors will be disseminated throughout the United States, providing several months’ warning in advance of potentially elevated mosquito populations. This would allow timely, targeted implementation of mosquito control, animal quarantine and vaccine strategies to reduce or prevent animal and human disease. Currently above normal sea surface temperatures have developed in the equatorial eastern Pacific Ocean (~ 2ºC) and also in the equatorial (~1ºC) typical of the 1997-1998 and 2006-2007 period. This warming of the ocean’s increases the likelihood of elevated rainfall in the Horn of Africa at the end of 2009 and early 2010. Since the most recent RVF outbreak occurred in this area in 2007 and the number of RVF susceptible animals is limited the elevated rainfall is unlikely to cause significant RVF disease activity during the current season but may cause focal disease introduction into isolated populations as virus infected Aedes mosquitoes are produced subsequent to flooding. We conclude that: • The threat from globalization of RVF, is real and ever present danger • RVF surveillance and control preparations are critical • Further research on RVF disease ecology, vector biology and control, genetics, vaccines, etc to is essential to react quickly and effectively control disease and limit spread • RVF vector control, quarantine and vaccine containment strategies must continually be developed and tested • Enhanced preparation will reduce human and animal health risk, and limit economic losses from RVF • Much more research, operational preparation, and agency coordination is needed to either prevent or contain RVF vector borne diseases