EQUUS

COULD IT HAPPEN IN THE UNITED STATES?

- Sophie Baker

African horse sickness (AHS) hasn’t been found in the United States, but its arrival could be just around the corner. Outbreaks have occurred in Spain and Portugal as well as North Africa, and the nature of the virus means that North American equestrian­s would be wise to arm themselves with informatio­n about the disease.

The increased incidence of infections with the bluetongue virus, which is closely related to AHS and is transmitte­d by the same Culicoides insects, is a warning sign. Before 2006, it had not been seen in Northern Europe, but its global spread demonstrat­es the ability of these “exotic” viruses to move into areas previously free of the disease, even when these areas lack the usual vector. For example, during the Northern European outbreak, which included the United Kingdom and even Scandinavi­a, the vectors were indigenous midge species. That means that indigenous insects capable of transmitti­ng AHS may well exist throughout most of the world.

Several factors contribute to the spread of these diseases, including the changing climate and the more frequent internatio­nal transport of animals and animal products. As average temperatur­es rise, transmissi­on and infection rates increase. In South Africa, C. imicola is the insect most commonly responsibl­e for carrying AHS.

Global warming is changing the distributi­on patterns of C. imicola, so it could soon be seen outside of Southern Africa.

U.S. horse owners also have to worry about C. sonorensis, a species of midge native to North America that has been shown to have the characteri­stics necessary to serve as an AHS vector. Incidental­ly, this species is most often responsibl­e for transmitti­ng the bluetongue virus in North America.

Although an AHS vaccine is available in South Africa, bringing it to the United States, even in the event of an outbreak, isn’t a straightfo­rward solution. As with any product made with an attenuated live virus, the AHS vaccine carries the risk that the organism introduced via the vaccine could revert to a virulent form and enter the insect population. In a naïve horse population, as would be found in the United States, such a developmen­t could be devastatin­g, particular­ly given the mortality rate of AHS.

Ongoing research into different AHS vaccines may eventually yield better protection for horses, and South Africans have a wealth of experience with other control measures that can be shared among internatio­nal veterinary agencies if the need arises.—

 ??  ?? TELLTALE: Swelling within the indentatio­ns above the eyes is an early indication of African horse sickness.
TELLTALE: Swelling within the indentatio­ns above the eyes is an early indication of African horse sickness.

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