Rift Valley Fever: Epidemiology of Human Disease

1. Rift Valley Fever:Epidemiology of Human Disease Rebecca Shultz, MPH Bureau of Environmental Public Health Medicine Florida Department of Health

2. Transmission routes • Majority - tissue or body fluids of infected animals • Aborted fetuses • Slaughter • Necropsy • Veterinary procedures • Carcass disposal • Aerosol • Slaughter • Laboratory

3. Vector transmission • Arthropod vector • Mosquitoes • Aedes • Anopheles • Culex • Others • Mosquito species in the U.S. could serve as vectors • Biting flies are possible vectors Center for Food Security and Public Health Iowa State University - 2003

4. Additional transmission routes • Some evidence of infection from consuming uncooked/unpasteurized milk from infected animals • No direct person-to-person transmission • No evidence of transmission in health care settings with infection control measures in place

5. Human Disease • Incubation period: 2-6 days • Infections range from asymptomatic to severe • Overall fatality less than 1% • Mild disease • Flu-like signs • Fever, headache, joint and/or muscle pain • Stiff neck, photophobia, anorexia, vomiting • Recovery in 4-7 days

6. Severe Disease • Retinopathy (0.5 - 2% of cases) • 1-3 weeks after onset of symptoms • Blurred or decreased vision • Photophobia • Can resolve in 10-12 weeks without treatment • Can lead to permanent vision loss • 50% in those with macular lesions • Death is uncommon

7. Severe disease – cont’d • Encephalitis (less than 1%) • Onset 1-4 weeks after initial symptoms • Memory loss • Confusion • Disorientation • Lethargy • Coma • Neurologic complications >60 days later • Low mortality, lasting neurologic damage

8. Severe disease – cont’d • Hemorrhagic fever (less than 1%) • Onset 2-4 days after initial symptoms • Liver impairment – jaundice • Hemorrhage – gums, skin, nose, blood in stool • Case fatality ratio ~ 50% • Death usually occurs 3-6 days after hemorrhagic symptoms appear

9. Diagnosis and Treatment • Diagnosis • ELISA, human blood • Demonstration of viral antigen • Treatment and vaccine • May not be needed • Symptomatic and supportive therapy • No commercially available vaccine Center for Food Security and Public Health Iowa State University - 2003

10. Important Outbreaks • Senegal, Africa, 1987 • Differed from other outbreaks • Not associated with rainfall • Kenya, 1997-1998 • Est. 89,000 humans cases • 478 deaths • Saudi Arabia, 2000 • First outbreak outside of Africa • Egypt, 2003 • 45 cases, 17 deaths Center for Food Security and Public Health Iowa State University - 2003

11. Kenya, 2006-2007 • Associated with heavy rainfall/flooding • Spread to Tanzania and Somalia • ~1,000 cases with 300 deaths • Case fatality 23%-45% Courtesy of CDC

12. Risk factors associated with human disease • Studies done during different outbreaks • Male gender • Close contact with animals • Drinking raw milk • Housing animals indoors • Living <100m from a swamp RVF distribution map, courtesy of CDC

13. Vector information • Dominant vector species varies between regions • Female mosquitoes can transmit virus transovarially • Outbreaks associated with heavy rainfall • Humans develop enough viremia to infect mosquitoes

14. Prevention and control • Risk reduction! • Avoid close contact with infected blood or tissues • Wear appropriate PPE • Thoroughly cook all animal products before consumption • Vector control • Protection from mosquito bites • Personal insect repellent • Avoid being outdoors during peak feeding • Wear long shirts and pants • Larvicide identified vector breeding sites

15. Prediction by modeling • Outbreaks associated with above-average rainfall • Remote Sensing Satellite Imagery can measure response of vegetation to increased rainfall • Heavy rainfall occurs during warm phase of El Nino/Southern Oscillation (ENSO) phenomenon • Development of forecasting models and early warning systems • Predictions can be made up to 5 months in advance in East Africa (Linthicum, 1999)

16. In the United States • Could this happen here? • RVF as a bioterrorism agent • Aerosol or droplets • 50kg could cause ~10,000 illnesses and 100 deaths • International tourism and trade • More than 1600 flights arrive in the U.S. each day from foreign countries • Animals as sentinels

17. Response in Florida • DOH response • Support DACS: responder health • Surveillance for human illness • Diagnostics • Investigate human cases • Identify risk factors • Communicate prevention messages • Serosurvey

18. References • World Health Organization. Rift Valley fever Fact Sheet. Rev. 9/07. www.who.int/mediacentre/factsheets/fs207/en/print.html. Accessed 10/3/08. • CDC. Rift Valley fever outbreak –Kenya, November 2006-January 2007. MMWR 2007; 56:73-76. • Madani TA, Al-Mazrou YY, Al-Jeffri MH, et al. Rift Valley fever epidemic in Saudi Arabia: epidemiological, clinical, and laboratory characteristics. Clin Infect Dis 2003;37:1084--92. • CDC. Outbreak of Rift Valley fever---Yemen, August--October 2000. MMWR 2000;49:1065--6. • Linthicum KJ, Anyamba A, Tucker CJ, Kelley PW, Myers PF, Peters CJ. Climate and satellite indicators to forecast Rift Valley fever epidemics in Kenya. Science 1999;285:397--400. • CDC. Rift Valley fever webpage. Accessed 10/3/08. http://www.cdc.gov/ncidod/dvrd/spb/mnpages/dispages/rvf.htm. • Rift Valley fever. Center for Food Security and Public Health at Iowa State University. http://www.cfsph.iastate.edu/factsheets/pdfs/rift_valley_fever.pdf.

19. Questions