Health Professionals

Clinical Updates

10 August 2012

Risk of mosquito-borne disease: advice for travellers to the United States (with updated information on West Nile virus)

This updates the Clinical Update of 1 August, 2012

Government health departments in the United States (US) provide advice for residents and visitors regarding the prevention of mosquito borne diseases that occur throughout the country [1-3]. 

There are several mosquito-borne diseases in the US, including West Nile Virus (WNV), Eastern equine encephalitis virus (EEEV) and dengue [4].

West Nile virus

Since being introduced into the US in 1999, WNV has been reported from almost every continental state; in 2011 a total of 721 cases were reported from 43 states and the District of Columbia [5, 6]. During 2012 as of 7 August, 527 cases of human WNV have been reported to the US Centers for Disease Control [6].  The Department of State Health Services, Texas, have reported a higher than usual number of human WNV cases in 2012, and the highest number for an individual US state this year. As of 9 August, 301 cases in 35 of the counties of Texas have been reported, with most cases residing in Dallas, Collin, Tarrant and Denton counties [7, 8].  Nine WNV related deaths have been confirmed in Dallas County, Texas [9]. In 2011, there were 27 reported cases with 2 deaths; the highest number of human cases  in Texas was recorded in 2006 (454 cases with 33 deaths) [10].

 

Eastern equine encephalitis

EEEV is a rare disease in humans. Most cases are reported from Florida, southeastern Georgia, southern Alabama, and the Carolinas [11].  In 2012, there has been one case reported in Florida [12].

Dengue

The first cases of dengue occurred in Florida in 2009 after an absence of several decades. In 2010, 66 cases of locally acquired dengue were reported from Key West, Florida [13, 14]. No outbreaks of dengue have been reported in the US in 2011 and 2012 [15].

 

Advice for travellers

There is a very low risk of contracting these mosquito-transmitted viruses during travel to the US. The risk depends upon destination, season, length of exposure, and the intensity of disease transmission at time of travel. Certain groups are at increased risk; individuals over 50 years of age are at highest risk of developing severe WNV and those under 15 years and over 50 years are at increased risk of severe EEEV [4].

During travel to risk areas of the US, individuals should be aware of the risk and take appropriate mosquito bite avoidance measures. There are no vaccines that prevent WNV, EEEV or dengue.

Health professionals who see travellers with a characteristic febrile illness, who have returned from the US, should be alert to the possibility of mosquito borne disease. Relevant samples for testing together with a full clinical and travel history should be submitted to the Health Protection Agency Rare and Imported Pathogens Laboratory.

References

1. Centers for Disease Control and Prevention. West Nile Virus. Fight the bite. [Accessed 10 August, 2012]. Available at: http://www.cdc.gov/ncidod/dvbid/westnile/index.htm

2. Centers for Disease Control and Prevention.  Eastern Equine Encephalitis: Prevention. [Accessed 10 August 2012]. Available at: http://www.cdc.gov/EasternEquineEncephalitis/gen/pre.html

3. Centers for Disease Control and Prevention. Dengue:Prevention. [Accessed 10 August 2012]. Available at: http://www.cdc.gov/dengue/prevention/index.html

4. Centers for Disease Control and Prevention. National Centre for Infectious Diseases. Insect and Arthropod Diseases. [Accessed 10, August 2012]. Available at: http://www.cdc.gov/ncidod/diseases/insects/diseases.htm

5. Centers for Disease Control and Prevention. West Nile Virus Disease and Other Arboviral Diseases — United States, 2011. MMWR. 61:510-514. [Accessed 10 August 2012]. Available at: http://www.cdc.gov/mmwr/pdf/wk/mm6030.pdf

6. Centers for Disease Control and Prevention. West Nile Virus (WNV) activity reported to ArboNET, by state, United States, 2012. as of August 7, 2012). [Accessed 10 August 2012]. Available at: http://www.cdc.gov/ncidod/dvbid/westnile/Mapsactivity/surv

&control12MapsAnybyState.htm

7. Texas Department of State Health Services. West Nile Virus in Texas. [Accessed 10 August 2012] Available at: http://www.dshs.state.tx.us/idcu/disease/arboviral/westNile/

8. Texas Department of State Health Services. DSHS Urges Precautions to Reduce West Nile Exposure

News ReleaseJuly 27, 2012. [Accessed 10 August 2012] Available at: http://www.dshs.state.tx.us/news/releases/20120727.aspx

9. Dallas County, Department of Human Health and Services (DCHHS) Office of Public Information. DCHHS confirms 9th West Nile Virus related death in Dallas County. [Accessed 10 August, 2012]. Available at: http://www.dallas-cms.org/epulsearticles/WNV080912.pdf

10. Texas Department of State Health Services. Human West Nile Virus cases Texas 2002-2011. [Accessed 10 August 2012] Available at: http://www.dshs.state.tx.us/idcu/disease/arboviral/wes

Nile/human/

11. Centers for Disease Control and Prevention. Eastern Equine Encephalitis: epidemiology and geographic distribution. [Accessed 10 August 2012]. Available at: http://www.cdc.gov/easternequineencephalitis/tech/epi.html

12. Florida Department of Health. Florida Arbovirus Surveillance. July29 – August 4, 2012. [Accessed 10 August 2012]. Available at: http://www.doh.state.fl.us/Environment/medicine/arboviral/

pdfs/2012/2012Week31ArbovirusReport_08-04-2012.pdf

13. Florida Department of Health.Dengue Fever in Key West. [Accessed 10 August 2012]. Available at: http://www.myfloridaeh.com/medicine/arboviral/Dengue_

FloridaKeys.html

14. NaTHNaC Clinical Update. Locally acquired dengue: Key West, Monroe County, Florida, USA. 11 June 2010. [Accessed 10 August 2012]. Available at: http://www.nathnac.org/pro/clinical_updates/dengue_usa_

15. Centers for Disease Control and Prevention. Dengue: Epidemiology. [Accessed 10 August 2012]. Available at: http://www.cdc.gov/Dengue/epidemiology/index.html

Links

Health Protection Agency: Rare and Imported Pathogens Laboratory

NaTHNaC Health Information Sheet: Insect bite avoidance