March 2005

West Nile Virus Still Defies Research

Educating yourself and consulting your local veterinarian remain your best defenses.

Caution must be used whenever you vaccinate breeding stock for anything.

As of the beginning of December 2004, 3,523 horses in Mexico had been tested for West Nile virus (WNV) antibodies. Of those, 29% (1,023) were positive, but none had displayed any symptoms of West Nile Virus infection. What’s up?

Prior exposure to a closely related virus, St. Louis Encephalitis virus (SLE), is known to cross protect against West Nile infection, and positive titers for this virus are commonly found in Mexican horses in some areas. However, previous large surveys of horses in Mexico that checked for antibodies to both viruses found similar fairly high exposure rates with West Nile, but none of those horses were positive for SLE so there’s more…