Sleeping Sickness Wakes Again

Sleeping sickness of horses was, as reeentiy as the IQSO's, the most devastating livestock disease in the United States. Horses died by the hundreds of thousands in the Midwestern United States, in California, and along the Atlantic seaboard at a period which coincided with the beginning of the sharp decline in the use of horses on the farm. Losses were so severe in some areas that the inevitable process of farm mechanization, particularly the use of tractors, was accelerated. Today, the owners of horses, ponies, mules, and burros can take steps to protect their animals from this continuing disease threat. As used in this chapter, sleeping sickness refers to equine encephalitis, a virus disease of American horses. It should not be confused with African sleeping sickness of human beings which is caused by a blood parasite and spread by bites of tsetse flies. While severe outbreaks of equine encephalitis had been observed during early periods of American history, the most significant milestones weren't reached until the 1930's in determining its cause, in witnessing its most devastating effects, and in developing control methods. Credit for recognizing equine encephalitis as a virus disease, and one that is transmitted to horses by mosquitoes, belongs to veterinarians, physicians, and entomologists serving in the U.S. Department of Agriculture and various biomédical research institutions. Among those who figured prominently were K. F. Meyer, formerly of the University of California and presently Director Emeritus of the Hooper Foundation. USD A veterinarians who contributed to early research on equine encephalitis included H. W. Schoening, M. S. Shahan, and L. T. Giltner. Investigators soon found that equine encephalitis was due to two diflferent viruses, both producing a similar disease. They were designated as the eastern and western strains of virus. The western virus afí'ects horses generally west of the Appalachians. The eastern attacks horses along the Atlantic seaboard and in the Gulf States. Subsequently, it was found that the two viruses and the disease they produce overlap considerably in their geographic distribution. Another type of equine encephalitis, afí*ecting horses in South and Central America, is Venezuelan equine encephalitis. However, this disease has not been recognized in horses in the United States. Meyer was also the first to speculate that the virus causing equine sleeping sickness might also cause encephalitis in human beings. His theories proved out, as it was soon established that