Equine Encephalomyelitis
There are two types of Equine Encephalomyelitis virus, an eastern and a western, that produce the disease. The eastern type causes death in about 9 out of 10 cases, the western type usually in only 1out of 4 or 5 cases.
The symptoms in a horse or mule include fever, sleepiness, and stupor, grinding of the teeth, uncoordinated and wobbly movements, and difficulty in chewing and swallowing. Body functions become more or less paralyzed and ultimately the animal collapses, lying in stupor or delirium, and dies. In some cases, however, the disease stops with the early fever stage, and it might be thought that the animal was suffering only from some other mild illness. Both types of attack confer considerable immunity.
The disease occurs in episodic (the animal equivalent of epidemics) during the warm months is essentially confined to pastured animals, and is roost common where there is water or marshy land. Every indication points to the fact that it is spread by bloodsucking insects. Experiments have proved that several species of mosquitoes and the Rocky Mountain spotted fever tick can transmit the virus, and it has been found in the field in one species of mosquito and in the assassin bug. It has also been proved that over 20 species of birds, as well as cattle, swine, sheep, goats. dogs, cats, guinea pigs, rabbits, monkeys, rats, mice, gophers, hedgehogs, and woodchucks can be infected, and since 1938 the virus has been definitely found in cases of brain disease in human beings. In fact, so far as is known, ho other virus is capable of infecting so many different species of animals.
Diagnosis of the disease is based on clinical symptoms, postmortem examination, and sometimes inoculation of laboratory animals or a neutralization test with serum. Control measures which should be carried out by a qualified veterinarian, include:
- Vaccination before the episodic season with a vaccine prepared from artificially infected chick-embryo tissue treated with formaldehyde to destroy its ability to produce the disease. (An antiserum may be used, but the vaccine is usually preferable).
- Control of bloodsucking insects by all practicable means; in particular, protection of affected animals against these insects
- Extermination of rats, mice, and other vermin and exclusion of pigeons and stray animals from the premises.
- Prompt and thorough disposal of animal’s dead of the disease and thorough disinfection of their quarters.
Medicinal or other treatments may be used by the veterinarian to relieve certain symptoms in a sick animal. The caretaker’s job is to follow instructions and do everything possible to keep the animal comfortable.
Various other diseases, some of which affect the brain, may be confused with encephalomyelitis, including moldy corn poisoning, plant poisoning, tick paralysis, anthrax, shipping fever, swamp fever, rabies, heat stroke, brain tumors and abscesses, mechanical injuries, botulism, azoturia, and an acute, highly fatal malady called toxic hepatogenous citrus which seems to follow encephalomyelitis income areas.