UT School of Public Health Study Says
West Nile Virus
Takes Toll on Homeless
HOUSTON – (Sept. 26, 2007)–As if living on the street wasn’t dangerous enough, the homeless are more likely to contract the mosquito-borne, West Nile virus than the general population, epidemiologists from The University of Texas School of Public Health report in the October issue of the Emerging Infectious Diseases Journal.
Kristy O. Murray, D.V.M, Ph.D.
Vulnerable to the summer onslaught of the disease-carrying insects, which is particularly acute during August and early September, the homeless spend much of the day outdoors and may not utilize mosquito repellent and other preventive measures, the researchers reported.
The study led by Kristy O. Murray, D.V.M, Ph.D., assistant professor at the UT School of Public Health, involved 397 homeless people in Houston who in 2004 completed an interviewer-administered questionnaire and provided blood samples for West Nile virus antibody testing.
First identified in Uganda in 1937, West Nile virus is transmitted to humans by mosquitoes – primarily the Culex mosquito – which pick it up by feeding on infected birds. Roughly 20 percent of those infected develop mild flu-like; about 80 percent are symptom-less; and fewer than one percent develop a potentially fatal brain infection.
One of every 14 study participants tested positive for West Nile virus (WNV) compared to an estimate of 1 of every 22 in the general population, Murray said.
“Combining education with distribution of effective mosquito prevention aids such as mosquito repellent may help reduce the risk for WNV infection and other mosquito borne diseases in this high-risk population,” lead author and UT School of Public Health doctoral student Tamra E. Meyer wrote in the study.
Funded in part by the Texas Department of State Health Services and The University of Texas Health Science Center at Houston’s General Clinical Research Center, the study was conducted after an analysis of patients hospitalized with West Nile virus between 2002 and 2004 revealed that the homeless were disproportionately represented, Murray said.
Houston’s homeless population is estimated at 10,000.
Researchers found that study participants who had been homeless for more than a year or who spent more than six hours a day outdoors were at increased risk of West Nile virus infection.
They also found that mosquito precautions taken by the homeless were ineffective and, in some instances, actually increased the risk of infection. For example, many participants mistakenly thought that lighting candles and swatting at mosquitoes were effective deterrents.
Marijuana use was also found to be a predictor of West Nile virus, but researchers aren’t sure why.
West Nile virus first appeared in the United States in 1999 in New York and in Houston in 2002, when there were 97 human cases, with five deaths. Symptoms include fever, muscle pain, weakness and a rash. There is no specific treatment.
Difficult to diagnose, West Nile virus can be confused with other afflictions. “Clinicians need to be on the lookout for this illness, particularly among their homeless patients or patients with increased occupational or recreational outdoor exposures,” Murray said.
Information gleaned from these and other studies, according to Rudy Bueno Jr., Ph.D., director of the Mosquito Control Division of Harris County Public Health & Environmental Services, provides mosquito control planners with a better understanding of who is at risk. “It helps us see trends,” Bueno said. “Once we see trends happening, we are able to focus our efforts in different areas.”
Also contributing to the study were: Lara M. Bull, Ph.D., Kelly Cain Holmes, Rhia F. Pascua, Christian R. Gutierrez, Tracie Corbin and Jennifer L. Woodward, all with the UT School of Public Health; Amelia Travassos da Rosa and Robert B. Tesh, M.D., both with The University of Texas Medical Branch at Galveston; and Jeffrey P. Taylor, Texas Department of State Health Services, Austin.
The article, which is titled “West Nile Virus Among the Homeless, Houston, Texas,” is available online at http://www.cdc.gov/EID/content/13/10/1500.htm . Emerging Infectious Diseases Journal is a monthly publication of the Department of Health and Human Services Centers for Disease Control and Prevention.