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Arbovirus Epidemiology

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Arbovirus Epidemiology

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  1. Arbovirus Epidemiology 2nd Quarter DIDE Training May 18, 2011

  2. Objectives • Describe the epidemiology of endemic arboviral infections affecting humans in the United States • Briefly review other arboviral diseases that may be reported following travel outside the United States • Discuss mosquito bite prevention

  3. Arboviruses • Arthropod-borne virus • Viruses maintained in nature through biological transmission between susceptible vertebrate hosts by blood feeding arthropods (mostly mosquitoes) • Over 130 arboviruses known to cause disease in humans • Three virus families: • Togaviridae • Flaviviridae • Bunyaviridae

  4. Arbovirus Transmission • Transmission intensity coincides with activity of vector • Late spring through early fall (for mosquitoes) • Incubation period: usually 3 to 18 days • Humans are dead-end hosts (i.e., do not become viremic) • There are exceptions • Blood transfusions • Organ transplants • Perinatal exposure • Certain viruses (e.g., chikungunya virus, dengue, etc.)

  5. Human Arboviral Infections • Clinical spectrum varies widely • Most infections are asymptomatic • Can range from mild fever to aseptic meningitis or encephalitis • Non-neuroinvasive vs. neuroinvasive • Symptomatic infections can result in complications • Hospitalization, long-term neurologic dysfunction, or even death • Vaccines, specific treatment generally not available for most arboviruses

  6. Major Arboviruses Endemic in U.S. • Western equine encephalitis virus (WEE) • Eastern equine encephalitis virus (EEE) • St. Louis encephalitis virus (SLE) • Powassan virus (POW) • West Nile virus (WNV) • California Serogroup viruses • La Crosse encephalitis virus (LAC)

  7. WEE • Family: Togaviridae (genus: Alphavirus) • First isolated in 1930 (horse, California) • No human cases in U.S. for past 10 years • Majority of cases west of Mississippi River • Vector and virus still persist in affected region • Risk groups: • rural residents of the West (particularly children <1 year)

  8. WEE Neuroinvasive Disease Cases Reported by State, 1964–2009

  9. EEE • Family: Togaviridae (genus: Alphavirus) • First isolated in 1933 (horse, Virginia) • Average of 6 cases reported per year (range: 0–20) • Atlantic and Gulf coastal areas, Great Lakes • Risk groups • Persons >50 years or <15 years are highest risk • 30% of encephalitic cases result in death

  10. EEE Neuroinvasive Disease Cases Reported by Year, 1964–2009

  11. EEE Neuroinvasive Disease Cases Reported by State, 1964–2009

  12. SLE • Family: Flaviviridae (genus: Flavivirus) • First isolated in 1933 (human, Missouri) • Average of 102 cases reported per year (range: 2–1,967) • Reported throughout U.S. • Outbreaks: Mississippi Valley and Gulf Coast • High risk • Elderly, low income

  13. SLE Neuroinvasive Disease Cases Reported by Year, 1964–2009

  14. SLE Neuroinvasive DiseaseCases Reported by State, 1964–2009

  15. POW • Family: Flaviviridae (genus: Flavivirus) • First isolated in 1958 (human, Canada) • Transmitted by a tick (primarily Ixodescookei) • Average of 3 cases reported per year (range: 0–7) • Most cases in New England, Upper Midwest • High risk • Adults that spend time in tick habitats • 10–15% result in death

  16. POW Neuroinvasive DiseaseCases Reported by State, 2001–2009

  17. WNV • Family: Flaviviridae (genus: Flavivirus) • First isolated in 1937 (human, Uganda) • Average of 2,500 cases reported per year (range: 21–9,861) • Emerged in 1999, quickly peaked in 2003 • Spread throughout continental U.S. • High risk • Persons >50 yrs of age

  18. WNV 1999

  19. WNV 2000

  20. WNV 2001

  21. WNV 2002

  22. WNV 2003

  23. WNV 2010

  24. LAC • Family: Bunyaviridae (genus: Bunyavirus, California) • First isolated in 1964 (human, Wisconsin) • Nearly all California serogroup viruses are due to LAC • Average of 78 cases reported per year (range: 29–167) • Most cases occur in Upper Midwestern, mid-Atlantic and southeastern states • High risk: • Children <16 years

  25. California Serogroup Virus Neuroinvasive Disease Cases Reported by State, 1964–2009

  26. *Haddow AD, Bixler D, Adoi, A. The spatial epidemiology and clinical features of reported cases of La Crosse Virus infection in West Virginia from 2003 to 2007. BMC Infectious Diseases 2011, 11:29

  27. Other Arboviruses - Dengue • 1/3 of the global population lives in endemic countries • WHO estimates up to 100 million cases/year • 20,000 deaths (mostly children)

  28. Dengue in the United States • 436 travel-associated cases reported in U.S. in 2010 (most from PR) • Outbreak in Hawaii in 2001–2002 • Local transmission reported in Florida beginning 2009 (53 cases in 2010)

  29. Other Arboviruses - CHIK • Chikungunya • Transmission documented in 37 countries • Primarily found in Africa and Asia • 1.4 million cases reported in 2006 • Travel-associated cases documented in U.S. • 109 cases since 1995 • Similarities with dengue • Same vectors • Humans can become reservoirs when infected

  30. Challenges • Outbreaks • Infrequent • Unpredictable • Geographic distribution knowledge • Surveillance • Prevention/control • Treatment

  31. Mosquito Bite Prevention Checklist Reduce your risk of mosquito-borne disease this summer by following these tips: • Be aware of peak mosquito hours • For many mosquitoes, peak hours are between dusk and dawn or evening and early morning. • For the mosquitoes that transmits La Crosse encephalitis virus peak hours are actually during the daytime (dawn until dusk). • Use insect repellant that contains DEET, picaridin, IR3535 or oil of lemon eucalyptus on exposed skin and clothing when outdoors. • Always follow package directions. • Apply sparingly to children, avoiding hands and face, and wash them with soap and water when they come indoors. • Permethrin is a repellant that can be applied to clothing and provide protection through multiple washes. Do not apply permethrin-containing repellants directly to skin. • Wear protective clothing such as long sleeves, pants, and socks when weather permits • Install and repair window screens as needed to keep mosquitoes out of homes • Mosquitoes can lay eggs in small amounts of water. Remove breeding sites around the home: • Empty standing water from flower pots, buckets, barrels, and tires • Change the water in pet dishes regularly • Replace water in bird baths weekly • Drill holes in tire swings so the water drains out • Empty children’s wading pools and store on their side when not in use • Empty standing water from canoes and boats

  32. Summary • Arboviral infections result from viruses maintained in nature between arthropods and vertebrate hosts • LAC continues to be the primary arbovirus of human concern in WV • Other arboviruses may result from out-of-state or international travel • Prevention efforts center around removal of breeding sites and repellant use