Rift Valley Fever: Human Health and Epidemiology

Report
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 - 2003
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 (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
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 - 2003
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
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
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.
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.
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