Epidemiology of West Nile Virus in Georgia

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Epidemiology of West Nile Virus in Georgia. What is West Nile Virus?. Member of the genus Flavivirus Genus includes Yellow Fever, Dengue, and Hepatitis C viruses Japanese Encephalitis Serocomplex within genus
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Epidemiology of West Nile Virus in Georgia 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)
  • 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?
  • 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)
  • 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)
  • 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
  • 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
  • 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)
  • 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)
  • 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.
  • 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. (1) WNV in the U.S. (2) 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
  • 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 (1) WNV in Georgia (2) WNV in Georgia (3) 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)
  • Human Arboviral Infections Surveillance
  • Avian Mortality Surveillance
  • Equine Surveillance
  • Mosquito Surveillance
  • 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
  • Public health asks the public to report dead birds with no obvious cause of death
  • Birds were tested for WNV until 2012
  • 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)
  • 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 (2) WNV in Georgia (3) 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 (2) WNV in Georgia (3) 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 (2) WNV in Georgia (3) 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
  • 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
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