Now that summer has ended, cooler weather promises farmers and ranchers in the Southwest relief from at least two serious animal viruses, vesicular stomatitis (VS), which has plagued both Texas and Colorado over the summer months, and West Nile Virus (WNV), which continues to be troubling in parts of New Mexico and Texas.

Animal health officials warn, however, that while cooler temperatures will help to curtail the movement and activity of black flies and gnats, the primary insects known to vector VS in horses and cattle, mosquito activity in areas that received excessive rainfall in recent weeks may continue to promote the spread of West Nile Virus among humans and livestock.

Areas most at risk from West Nile Virus include large parts of New Mexico and isolated areas of Texas that have received abundant rainfall in recent weeks.

The Eddy County Emergency Operations Center (EOC) in New Mexico initiated a mosquito collection program recently after torrential rains flooded widespread areas of the county and as far away as Carlsbad. EOC officials called in extra manpower to initiate the collection process in an effort to control mosquito populations that have exploded in numbers thanks to standing water from flooding.

Mosquitoes collected were turned over to the New Mexico Department of Health for testing and state officials have since confirmed many of the mosquito samples were carriers of West Nile Virus. WNV has become endemic across southern states and the Southwest since the late 1900s. Significant rain over the last several weeks that left standing water in fields created what health officials say are prime conditions for mosquito breeding.

Many areas in New Mexico received record or near-record rainfall over the last several weeks. Because of severe drought conditions across most of the Southwest, recent rains are a welcome site for farmers and ranchers. But with the heavy rains come heightened concerns over WNV in both animals and humans.

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Fourteen cases of human WNV have been confirmed across New Mexico this year in San Juan County, De Baca County, Quay County, Dona Ana County, Grant County and Sandoval County. The New Mexico Department of Health confirmed the first West Nile Virus death of 2014 in late September when an 89-year-old Lea County man died from encephalitis, the more severe clinical form of the West Nile Virus.

In Texas, 212 cases of human West Nile illness has been confirmed this year, including three deaths—in Montgomery, Midland and Tom Green counties.

West Nile is a mosquito-borne virus. There are two forms of the illness, West Nile neuroinvasive disease (WNND) and West Nile fever (WN fever). The symptoms of severe infection from West Nile neuroinvasive disease include headache, high fever, neck stiffness, stupor, disorientation, coma, tremors, convulsions, muscle weakness and paralysis. Symptoms of West Nile fever, the milder form of the illness, include fever, headache, body aches, and occasionally a skin rash on the trunk of the body and swollen lymph glands.

Officials say one of the most effective ways to minimize risk of infection with WNV for both human and non-human cases, in addition to wearing long, loose fitting clothing and using repellants, is to eliminate as many water-holding containers as possible.

Bad year for VSV

Texas and Colorado livestock industries have had a particularly bad year for VS outbreaks. Health officials in both states are hoping for cooler weather to help control what was becoming a moderate to intense outbreak of VS over the summer months.

VS, a virus with symptoms very similar to the more serious and greatly dreaded hoof and mouth disease, is a naturally occurring animal illness that crops up every five years or so across the American Southwest, possibly wintering in northern Mexico just south of the Texas and New Mexico border.

Texas Animal Health Commission (TAHC) officials released the last of quarantined premises for Vesicular Stomatitis last week. The last premises released included one in Bastrop County and another in Travis County.

The first case of VS in Texas was uncovered in Kinney County on May 28. Subsequent to that incident, TAHC had quarantined a total of 62 premises in 13 Texas counties. The counties included Bastrop, Guadalupe, Jim Wells, Falls, Hidalgo, Kinney, Lee, McLennan, Nueces, San Patricio, Travis, Val Verde and Williamson.

Texas livestock affected by the virus were limited to equine and cattle. However, other susceptible livestock include sheep, pigs, deer and other cloven-hooved animals.   

Though quarantines have been lifted, several states and countries may still impose enhanced entry requirements on VS susceptible livestock coming from Texas and Colorado. Producers are encouraged to contact the state of destination for official requirements. Currently, California, Georgia, New Mexico, and North Dakota have required entry requirements.

TAHC advises livestock owners to continue practicing VS preventive measures by minimizing livestock exposure to sand flies and black flies, which are known to transport the virus through biting.

While both VS and West Nile Virus have been problematic in parts of the Southwest this year, health officials say with cooler temperatures they expect to see fewer problems from the two viral pathogens.