The scientific community and the horse industry are on alert for the next serious threat to livestock in the U.S. This one is a disease called African horse sickness and it is transmitted by a tiny biting midge. These little bugs are about a fiftieth the size of a mosquito, but they bear bad news for the equine population.
African horse disease is listed, at this point, as a Tier 3 disease. According to the USDA’s Animal and Plant Health Inspection Service (APHIS), “Tier 3 diseases and pests pose less risk and fewer consequences than those in Tiers 1 and 2, but still rise to the level of inclusion because of their potential negative impact on animal or human health.”
African horse disease leads the list of Tier 3 maladies, which also includes contagious bovine and caprine pleuropneumonia, glanders and melioidosis, henipavirus, rinderpest and peste des petites ruminants, and tropical bon tick.
Equine animals can contract the disease by being bitten by the midge. The presence of the insect is extremely difficult to assess because of its size.
According to researchers at Texas A&M and the National Bio and Agro-Defense Facility (NBADF), the symptoms for the problem are much the same as those that indicate respiratory and circulatory impairment. NBADF says: “At the first signs of the disease, owners are advised to eliminate affected horses and vaccinate noninfected horses with polyvalent vaccine; then let them rest for two weeks.”
African Horse Disease has a 90% mortality rate of those infected. Mules and donkeys are also susceptible. NBADF and Texas A&M labs have been tracking the virus and the movement of the vectors that carry it.
“African donkeys and zebras very rarely display clinical symptoms, despite high virus titers in blood, and are thought to be the natural reservoir of the virus. Thus, it is thought the virus was transported to Thailand through asymptomatic zebras,” an NBADF spokesman said.
The midges are vectors that are an eighth of an inch or less in size. The immature stages of the bug are associated with wet environments, such as lakes, bogs, river edges, swamps and such.
Pete Teel of Texas A&M said the risk of the disease coming to the US is very real. “If it gets here, we have other insects that could also become effective vectors of the virus,” he said.
African horse disease, coupled with the already present equine encephalitis, blue tongue and epizootic hemorrhagic disease, could be devastating to the horse population in this country.
There is a vaccine for the disease, but it is problematic since it contains a live pathogen and can sicken horses.
“With horses, it might mean keeping them stalled in areas where biting midges are a problem and using insecticides to keep the midges off them,” said Kay Ledbetter of Texas A&M. “But this might not be as possible with wild horses or horses in pastures that may not be able to be handled or stabled.”
There have been no known cases of African horse disease in the U.S. so far.