This week, the Texas A&M Veterinary Medical Diagnostic Laboratory (TVMDL) confirmed additional West Nile virus (WNV) cases. The number of WNV positive cases in Texas now total 13.
As of September 3, 2015, TVMDL can confirm horses in the following counties tested
positive for WNV.
1. Houston County
2. Atascosa County
3. Jefferson County
4. Roberts County
5. Sterling County
6. Parker County
7. Randall County
8. Liberty County
9. Scurry County
10. Hutchinson County
11. Taylor County
12. Nolan County
13. Trinity County
As with earlier reported positive cases, the majority of the affected horses were not previously vaccinated against WNV. One horse’s vaccination history was uncertain, but it exhibited classical muscle facilitation for 2-3 days before tests confirmed WNV.
The main method of WNV transmission is through mosquito bites. The virus abruptly attacks the central nervous system. In the U.S., clinical signs for WNV develop in only 10-39 percent of infected horses. The death rate among U.S. horses ranges from 30 to 40 percent for West Nile disease. Of horses that recover from the disease, up to 40 percent may exhibit neurological signs for six months or more after the initial diagnosis. Horse to human transmission is not a concern; however, mosquito control for livestock and humans is important. The Texas Department of State Health Services and the Texas Animal Health Commission have information related to WNV and mosquito control available for free download.
Though the TVMDL Serology Section has received numerous requests for Eastern Equine Encephalitis testing, the number of positive cases remains at 7 for 2015. EEE is a viral disease that also normally cycles between wild birds and mosquitoes. As the virus infection rate increases in birds it is more likely to be transmitted by an infected mosquito that bites horses and humans. The virus abruptly attacks the central nervous system. As with WNV, EEE cannot be transmitted from horse to horse, or from a horse to a human. Horses and humans are considered “dead-end” hosts, meaning if infected they cannot transmit the virus back to feeding mosquitoes.
Symptoms for other neurologic diseases can present similarly; diagnostic testing is the only method to definitively determine infection. In order to have a complete diagnostic picture, TVMDL also recommends veterinarians request additional tests including: Equine Herpesvirus-1, Western Equine Encephalitis and Venezuelan Equine Encephalitis.
For more information on TVMDL’s equine neurologic testing, visit tvmdl.tamu.edu, or contact the agency headquarters at 1.888.646.5623.