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

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

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

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

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

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

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

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

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

Important Outbreaks Senegal, Africa, 1987 –Differed from other outbreaks Not associated with rainfall Kenya, –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

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

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

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

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

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)

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

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

References World Health Organization. Rift Valley fever Fact Sheet. Rev. 9/07. Accessed 10/3/08. CDC. Rift Valley fever outbreak –Kenya, November 2006-January MMWR 2007; 56: 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: CDC. Outbreak of Rift Valley fever---Yemen, August--October MMWR 2000;49: CDC. Outbreak of Rift Valley fever---Yemen, August--October MMWR 2000;49: 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: CDC. Rift Valley fever webpage. Accessed 10/3/ Rift Valley fever. Center for Food Security and Public Health at Iowa State University.

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