Epidemiology of West Nile Virus in Georgia: Epidemiology of West Nile Virus in Georgia


What is West Nile Virus?: What is West Nile Virus? Member of the genus Flavivirus Genus includes Yellow Fever, Dengue, and Hepatitis C viruses Japanese Encephalitis Serocomplex within genus Includes closely-related viruses such as Saint Louis Encephalitis virus (SLE), Japanese Encephalitis virus (JE), and Kunjin virus, among others


What is West Nile Virus? (2): What is West Nile Virus? (2) WNV is an arbovirus (arthropod-borne virus) Arboviruses are transmitted by mosquitoes or ticks Zoonotic life cycle – humans are not part of the WNV life cycle, they are incidental hosts Birds are the primary amplifier hosts, or reservoirs of West Nile Virus (WNV) Migratory birds play a role in distribution of WNV


How is WNV Spread?: How is WNV Spread? Most common mode of transmission is by bite of an infected mosquito Uninfected mosquito bites infected bird and acquires virus Virus replicates in mosquito Mosquito bites uninfected bird and transmits virus, infecting the bird Occasionally, mosquito cannot find bird to feed on and bites humans, horses, or other mammals, causing incidental infection


How is WNV Spread? (2): How is WNV Spread? (2) No direct person-to-person transmission Bite of infected mosquito (most commonly) Organ transplant / blood transfusion from infected donor Mother-to-infant during pregnancy or through breast milk Occupational exposure (laboratory workers, bird or alligator handlers)


How is WNV Spread? (3): How is WNV Spread? (3) The mosquito species Culex quinquefasciatus is the most common WNV vector in Georgia Also known as the Southern House mosquito, C. quinquefasciatus is most active at dusk and dawn


WNV History: WNV History Virus was first isolated in Uganda in 1937 Believed to cause only minor short-term illness First recorded outbreak of WNV was in Israel in the 1950s: Outbreak in Israel, 1957: First correlation between WNV infection and severe central nervous system (CNS) disease First correlation between older patients and more severe disease Soon recognized as one of the most widespread Flaviviruses in the world


WNV Infection in Humans: WNV Infection in Humans Humans are incidental hosts Not part of WNV life cycle Humans are dead-end hosts Humans do not develop high enough levels of virus in their blood to infect mosquitoes that bite them


WNV Infection in Humans (2): WNV Infection in Humans (2) 80% of people infected with WNV will not have any symptoms 20% of people infected with WNV will develop a mild, flu-like illness for a few days (“West Nile Fever”) Less than 1% of people infected with WNV will develop severe disease, such as encephalitis (“West Nile Neurologic Disease”)


WNV Infection in Humans (3): WNV Infection in Humans (3) Incubation period is 3-15 days after being bitten by an infected mosquito Case fatality rate among people with more severe disease is 3-15%


WNV in the U.S.: WNV in the U.S. First identified in New York City in 1999 WNV spread rapidly to other states, stretching from coast to coast by 2002 WNV caused an unprecedented outbreak of human meningitis/encephalitis in 2002 which more than doubled in 2003


WNV in the U.S. (2): WNV in the U.S. (2)


WNV in the U.S. (3): WNV in the U.S. (3)


How Did WNV Enter the U.S.?: How Did WNV Enter the U.S.? Exact mode of introduction unknown Possible modes of introduction: Migrating or storm-transported bird (most likely) Imported mosquito or larvae Migrating infected human Imported animal Intentional introduction


WNV in Georgia: WNV in Georgia First detected in a bird from Lowndes county in July, 2001 WNV has caused human disease each year since it arrived in Georgia WNV is now considered endemic in Georgia (meaning it can be expected to occur each year in Georgia)


WNV in Georgia (2): WNV in Georgia (2)


WNV in Georgia (3): WNV in Georgia (3)


WNV Surveillance in Georgia: WNV Surveillance in Georgia Purpose Detect the presence of WNV in Georgia Monitor the spread of WNV throughout Georgia Predict risk to human and animal populations so control measures may be implemented


WNV Surveillance in Georgia (2): WNV Surveillance in Georgia (2) Human Arboviral Infections Surveillance Avian Mortality Surveillance Equine Surveillance Mosquito Surveillance


Human WNV Surveillance in Georgia: Human WNV Surveillance in Georgia Arboviral infection is a notifiable condition Immediately report to public health Active surveillance was conducted in metro Atlanta area until 2005 Enhanced passive surveillance in other areas of Georgia Testing is available at most commercial labs as well as at the Georgia Public Health Laboratory


Avian Mortality Surveillance: Avian Mortality Surveillance Public health asks the public to report dead birds with no obvious cause of death Some birds may be collected for WNV testing All bird reports are noted for surveillance purposes, even if the bird is not picked up Useful in tracking spread of WNV Assists in predicting risk for human illness


Avian Mortality Surveillance (2): Avian Mortality Surveillance (2) High rate of birds dying from WNV in U.S. is unusual compared to other countries that experienced WNV outbreaks Crows and blue jays are especially susceptible to WNV Bird mortality rate may decrease in future due to herd immunity or host or virus adaptation


WNV in Georgia: WNV in Georgia


WNV in Georgia (2): WNV in Georgia (2)


Equine Surveillance: Equine Surveillance Testing is available for horses with clinical central nervous system disease symptoms Surveillance for WNV in horses is a sensitive tool to recognize foci of viral activity Especially useful in rural areas for surveillance There is a WNV vaccine for horses, which limits the ability to use WNV disease in horses for surveillance


WNV in Georgia: WNV in Georgia


WNV in Georgia (2): WNV in Georgia (2)


Mosquito Surveillance: Mosquito Surveillance Larval and adult mosquito surveillance assesses the populations sizes of mosquitoes Increase in mosquito populations indicates increased local human risk Some adult mosquito pools are tested to see if mosquitoes in a certain geographic area are carrying WNV Mosquito control programs are planned in response to large mosquito populations or positive mosquito pools


WNV in Georgia: WNV in Georgia


WNV in Georgia (2): WNV in Georgia (2)


Preventing West Nile Virus: Preventing West Nile Virus Avoiding mosquito bites is the best way to prevent infection with West Nile virus. Personal precautions against mosquito bites Wear long sleeves, pants, and DEET-based repellent Avoid being outdoors at dusk and dawn when mosquitoes are most active Source reduction to reduce mosquito breeding habitats Empty stagnant water around your home (flower pots, bird baths, gutters) Treat ponds with larvacide or stock with fish


Resources: Resources Georgia Division of Public Health Mosquito-Borne Diseases website: http://health.state.ga.us/epi/vbd/mosquito.asp CDC West Nile Virus website http://www.cdc.gov/ncidod/dvbid/westnile/index.htm Still have questions about West Nile Virus? Call the Georgia Division of Public Health at 404-657-2588