Describe the epidemiology of endemic arboviral infections affecting humans in the United States

Describe the epidemiology of endemic arboviral infections affecting humans in the United States

• 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

Arthropod-borne virus

• 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

Transmission intensity coincides with activity of vector

• 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.)

Clinical spectrum varies widely

• 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

Western equine encephalitis virus (WEE)

• 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)

Family: Togaviridae (genus: Alphavirus)

• 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)

Family: Togaviridae (genus: Alphavirus)

• 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

Family: Flaviviridae (genus: Flavivirus)

• 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

Family: Flaviviridae (genus: Flavivirus)

• Family: Flaviviridae (genus: Flavivirus)

• First isolated in 1958 (human, Canada)
• Transmitted by a tick (primarily Ixodes cookei)

• 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

Family: Flaviviridae (genus: Flavivirus)

• 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

Family: Bunyaviridae (genus: Bunyavirus, California)

• 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

1/3 of the global population lives in endemic countries

• 1/3 of the global population lives in endemic countries

• WHO estimates up to 100 million cases/year
• 20,000 deaths (mostly children)

436 travel-associated cases reported in U.S. in 2010 (most from PR)

• 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)

Chikungunya

• 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

Outbreaks

• Outbreaks

• Infrequent
• Unpredictable

• Geographic distribution knowledge

• Surveillance

• Prevention/control

• Treatment

Be aware of peak mosquito hours

• 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.

Arboviral infections result from viruses maintained in nature between arthropods and vertebrate hosts

• 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