August 5, 2010 - Mosquito season is here, meaning farmers and ranchers need to be prepared to protect themselves and their livestock from mosquito-borne diseases like West Nile Virus.
"Basically, mosquitoes carry West Nile by biting infected birds and then the virus can be passed to humans when the mosquito bites a human," said Christine DeLoma, assistant press officer for the Department of State Health Services. "As the warmer weather continues, mosquitoes definitely multiply across the state. West Nile Virus generally begins in late spring, peaks in August and continues into the fall."
Despite a peaking season, those in Texas have a relatively low chance of contracting the virus, according to the DSHS, since only one out of 100 mosquitoes are carriers of the virus. Those who become infected may not even realize it.
"About 80 percent of people that are infected with West Nile Virus have no symptoms at all," DeLoma said. "If they don't have symptoms they usually recover on their own. But the virus can cause serious illnesses."
Sometimes the virus can have long-term effects on an individual, including memory loss, depression and confusion. There are two forms of WNV including West Nile neuroinvasive disease, which is the more severe form the disease caused by the WNV which incorporates the central nervous system, and West Nile fever, the form of the disease caused by WNV that shows no evidence of neuroinvasion
While Texas sees its fair share of the virus, the state is not one of the more highly-affected.
"For West Nile activity in 2008, Texas had about 54 cases of West Nile virus infection in humans and in California, for example, there was 445 cases, so we are definitely not in the top of the pack with that," DeLoma explained.
Though chances of contracting the virus may be relatively low, individuals should still protect themselves and their livestock.
"Basically the number one thing people can do to protect themselves against mosquito-borne illnesses, such as West Nile, is use insect repellent," Deloma Said. "Other precautions other than spraying yourself with insect repellent when you go outdoors, we encourage people to drain standing water regularly and that is usually in the back yard, such as emptying cans or buckets or tires, rain gutters, (and) the saucers that are under your potted plants. Because mosquitoes breed and hatch in water."
The Department of State Health Services regularly tests mosquito populations in various parts of the state. In 2010, so far, they have had 15 positive mosquito pulls.
"So, it is hard to tell if we will see an increase in incidents in West Nile Virus this year," she said. "So far, we have only gotten one A-symptomatic blood donor. Basically, the person gave blood and the virus was detected, but there were no symptoms in the person that had West Nile virus."
Symptoms of WNV can be mild or severe. Mild symptoms include fever, severe headaches, muscle or bone aches, nausea or drowsiness. The more serious forms of WNV can cause a stiff neck, visual problems, altered taste, body tremors, mental confusion, memory loss and seizures.
WNV has been detected in several forms of livestock -- horses being the most prevalent. Weems and Stephens veterinarian Dr. Nancy Aronoff of Aubrey explained that vaccinating is the best defense against WNV and any other mosquito-borne diseases for livestock.
""Dying birds usually precede the equine outbreaks," she explained. "Five percent to 10 percent of infected horses usually display clinical signs, with 90 percent of cases being greater than 1 year of age, and most of your cases being over 3 years of age."
Symptoms in horses are affected by WNV parallel those in humans, including stiff muscles and aches.
"Symptoms can be ataxia, which is neurological, more severe in the rear legs; twitching of the facial or the neck muscles; hyperesthesia, with is being real reactive to everything; more hyper-excitability; sometimes fever, sometimes blindness, sometimes temper, or not eating, lethargy and then sometimes in a small number of cases, they become recumbent," Dr. Aronoff said.
Whether or not an unvaccinated horse can survive a WNV infection depends highly on how the horse's body reacts.
"If the horse has been exposed to it before, it may have some protective antibodies," Aronoff explained. "The best way to prevent this is to vaccinate. It has been proven when it hit Florida, the vaccines are very safe. There has been a lot of stuff on the Internet saying that there is problems with the vaccine, and that has not been proven. The best way to avoid it here in a big mosquito area is to vaccinate."
Many veterinarians will suggest WNV vaccines be added to horse owner's yearly vaccines to protect their animals.
"They say if you are in a heavy mosquito area, or an area that has been known to see West Nile, that sometimes it is better to do it twice a year," Aronoff said. "The best thing for people to do is to get with their veterinarian. Along with the West Nile, they probably need to do the other mosquito-borne (vaccinations) which is the Eastern and Western encephalitis. It is the same thing -- it is going to protect them against the virus.
"Bottom line, there are certain vaccines that we consider core vaccines and Eastern and Western encephalitis and West Nile are some of those things," she continued. "It is very important to vaccinate. If people get on the Internet and listen to the rumors and stuff, really the vaccines are safe. They need to vaccinate their horse or risk them contracting the disease."
According to Texas A&M University Agricultural and Environmental Safety's 2009 WNV activity case breakdown, there were 106 cases of WNV in humans and 23 reported cases in horses in the state. To find out more about WNV in each Texas county, visit http://www-aes.tamu.edu/.
