By Dr. Molly Bellefeuille
Nineteen equine West Nile Virus (WNV) cases have been reported this year in Texas. Counties affected include Houston, Atascosa, Jefferson, Roberts, Sterling, Parker, Randall, Liberty, Scurry, Hutchinson, Taylor, Nolan, Trinity, Robertson, Midland, Orange, Harris and Victoria. The majority of the affected horses were not previously vaccinated against WNV. WNV was first detected in the United States in 1999; however, it is now considered endemic to North America. Since 1999 over 25,000 cases of WNV have been reported in U.S. horses. The virus has been detected in all of the continental United States, most of Canada and Mexico.
The virus is maintained through the transmission cycle between the mosquitoes and wild birds. The virus uses the bird as a reservoir host (area of virus expansion and amplification) and the mosquitoes as a vector host (mode of transportation). Thus the horse is infected with WNV predominantly through the mosquito. To date there is no evidence of horse-to-horse or horse-to-human transmission. To read more puck up the November 2015 issue of NTFR.