The incidence of West Nile virus cases in North Texas has reached epidemic proportions as the virus claimed its first recorded death nationally of 2012 in Dallas, officials said Tuesday.
Physicians and hospitals have reported that 16 cases of West Nile virus have occurred in Tarrant County this year, according to the Tarrant County public health department.
Nine of those West Nile virus cases have been the more serious neuro-invasive form of the virus, while seven cases have been diagnosed as West Nile fever, said Sandra Parker, Tarrant County public health medical director and health authority. In its neuro-invasive form, the virus attacks the body's nervous system, Parker said.
Dallas County public health officials on Monday reported the death of a man in his 60s who resided north of downtown Dallas. The death has been attributed to the West Nile virus. The Centers of Disease Control and Prevention report that no other deaths caused by the West Nile virus have been reported anywhere else in the country as of July 10.
As of Monday Dallas County officials reported 16 human cases of West Nile in Dallas County. Two are West Nile fever and 14 are neuro-invasive.
No deaths attributable to the virus have been reported in Tarrant County but five of the 16 people who have contracted the virus required hospitalization, Parker said.
"This fits the definition of an epidemic," Parker said. "The most important thing I think the numbers say is that we need to do what we can to prevent the illness."
This is the worst West Nile virus season in Tarrant County since 2009, when there were three deaths and 32 human cases reported, Parker said. In 2010, there were no West Nile virus cases reported in Tarrant County and in 2011, there were two cases, Parker said.
"The illnesses are occurring earlier, " Parker said. "Sometimes, the disease can start in its milder form and then progress into the neuro-invasive form if it is not treated."
Some species of animals can also get the disease, and people need to learn if their pets are at risk, Parker said. Horses are the animals most susceptible to the disease.
The Denton County public health department reported 10 human cases of the West Nile virus, four that are neuro-invasive and six from West Nile fever, according to its website.
The Culex species of mosquito that spreads the West Nile virus typically only lives for around two weeks; however, new mosquitoes can be born every day. These new mosquitoes would first have to bite an infected bird in order to transfer the virus to a human.
This mosquito is highly active around dawn and dusk, and typically prefers to bite around the ankles.
The majority of people, 80 percent, show no symptoms of the disease and the body fights off the virus. People over 50 or with compromised immune systems are at a higher risk of displaying symptoms from the disease.
Paying for a warm winter and spring
A warmer than average winter which helped the adult population survive and a warm spring which allowed for fast mosquito population growth could be contributing factors to the West Nile virus outbreak in North Texas, said Mike Merchant, an urban entomologist with the Texas AgriLife Extension Service.
The area was 2.6 degrees above normal in February, 4.5 degrees in January and .5 degrees above normal in December, said Matt Bishop, a meteorologist in the Fort Worth office of the National Weather Service.
The principal ways that people can protect themselves against mosquitoes is to interrupt their breeding cycles by emptying containers of standing water and by finding a good mosquito repellant and sticking with it, Merchant said.
"Everyone needs to go in their backyards and look for small containers that can fill with water," Merchant said. "A half a cup of water is all it takes for mosquitoes to breed. Overturned garbage can lids, toys, buckets, it's usually things you're not looking for."
This story contains material from the Star-Telegram archives.
Mitch Mitchell, 817-390-7752