West Nile virus outbreaks are likely to flare up in the coming years, spurred on by warmer, longer mosquito seasons coupled with cuts in disease-control funding that leave authorities unprepared, according to two new studies.
After an all-time high in 2003 with nearly 10,000 cases and 264 dead, the virus backed off gradually for the remainder of the decade — until last year. In 2012, there were 5,674 cases and 286 deaths, almost twice the 2003 mortality rate.
This strong resurgence is suggestive of “unpredictable local and regional outbreaks” to come, according to a study by the Centers for Disease Control and Prevention. Even when the number of infections dies down, the virus remains in circulation with an ever-
present danger of periodic recurrences.
“Every once in a while, you will have the right conditions to have it build up in the mosquito and bird populations, and spill over to humans,” said Stephen M. Ostroff, formerly of the CDC, who wrote an editorial in the Journal of the American Medical Association (JAMA) that accompanied the studies.
“Our sense of urgency and the degree of attention paid to West Nile virus has diminished considerably and so, too, have the necessary resources to prevent another outbreak,” Ostroff said.
Two studies — a review of the West Nile virus from the CDC and an investigation of a 2012 West Nile epidemic in Dallas from Dallas County Health and Human Services — were published online Tuesday in JAMA, along with the editorial by Ostroff. The Dallas investigation studied 173 cases of West Nile neuroinvasive disease, 225 cases of West Nile fever and 19 deaths in the latter half of 2012.
Transmitted mostly by mosquitoes that have bitten infected birds, the virus made its first U.S. appearance in 1999.
The Dallas study cites the combined effect of a mild winter, the early arrival of spring and summer heat, and lots of rain that caused mosquitoes to hang around for longer than usual, allowing more infection to spread.
Meanwhile, funding toward prevention and control has fallen. The CDC’s Epidemiology and Laboratory Capacity for Infectious Diseases program — which distributes money to states and large cities for use against mosquito-borne diseases — saw its funding drop from nearly $35 million in the early 2000s to less than $10 million by 2012.
Ostroff, the former deputy director of the CDC’s National Center for Infectious Diseases, believes it is a result of growing apathy toward the West Nile virus.
“It seemed like the problem had gone away, and it was an easy place to cut,” he said.
Complacency arises from a belief that a disease is on its way out, but that attitude can be dangerous because some diseases follow more of a boom-and-bust pattern. For instance, experts in the late 1980s thought that tuberculosis could be virtually eliminated from the United States by 2010. An unexpected resurgence of TB a few years later, largely fueled by the onset of the HIV epidemic, hit hard — particularly since funding and TB control programs had been eliminated.
While many states keep an eye out for West Nile infections in humans, the CDC study stresses that early detection in the carriers themselves is key. To wait for people to become exposed to the virus, have it manifest as an infection or illness, visit a doctor and test positive for West Nile virus could cause authorities to lose weeks in the war against an outbreak.
On the other hand, mosquito traps and tests are inexpensive and certainly cheaper than some of the last-resort measures eventually used to bandage up situations such as the Dallas outbreak. The study cited costs of $1.6 million for aerial pesticide spraying and $8 million in estimated West Nile-related health-care costs.
By cutting funding for mosquito surveillance, “we’re being penny-wise and dollar-foolish,” Ostroff said.
If an infection problem is identified early, authorities can try to prevent swarms of mosquitoes from reaching human hosts by draining blocked streams, introducing predatory fish and applying larvicides to prevent spring hatching.
No human vaccine or specific treatment exists. Wearing bug spray does reduce one’s risk of West Nile virus, but the CDC study said people are unlikely to put on repellant regularly, even during well-publicized outbreaks. Advice to wear long pants and sleeves is also unlikely to be followed, especially in the sweltering heat of peak mosquito season.