Researchers at the National School of Tropical Medicine at Baylor College of Medicine analyzed the Texas outbreak of West Nile virus in 2012 and found the number of reported cases was more than twice than previously seen and the economic cost of the outbreak likely exceeded $47 million, demonstrating a need for ongoing surveillance in order to put into immediate effect measures to control spread of the disease.
"This shows us how unpredictable West Nile can be, and how we always need to remain vigilant in looking for it, especially early on in the season so that it can be prevented," said Dr. Kristy Murray, associate professor and associate vice chair of research in the Department of Pediatrics at BCM and director of the Laboratory of Viral and Zoonotic Diseases at Texas Children's Hospital.
Researchers examined surveillance data from all reported cases in Texas in 2012. A total of 1,868 cases were reported to the Texas Department of State Health Services, including 89 deaths. The outbreak peaked in mid-August with 225 reported cases, which is historically the same time period for the peak for all prior outbreaks of West Nile in Texas from 2002 to 2011.
The 2012 outbreak was more than two times the historic high, which occurred in 2003 with 735 cases. However, when comparing the cases to the previous 10 years of data, researchers found no difference in the severity of the disease with regards to age. They continued to find that older adults, minorities, and males to be at highest risk for developing the severe form of the disease, which is a result of the virus invading the nervous system.
Surveillance, mosquito control
"The report emphasizes the importance of surveillance and mosquito control to prevent human cases," said Murray, who led the study.
Murray and colleagues observed a three-year pattern of increases in reported human cases in Texas.
"We may be going into a cycle where we see an even larger outbreak every 10 years," said Murray.
She said that more work needs to be done to develop predictive models, but notes that the drought in the previous year and the mild winter may have been contributing factors to the 2012 outbreak.
Others who took part in the study include Melissa S. Nolan of BCM and Texas Children’s Hospital and Duke Ruktanonchai, Dawn Hesalroad and Eric Fonken of the Texas Department of State Health Services.
The project was funded by the Gillson Longenbaugh Foundation and the National Institute of Allergy and Infectious Diseases grant number 5R01AI091816-01.