Vesicular Stomatitis V. S

W. C. PATTERSON AND L. O. MOTT.

VESICULAR stomatitis is a damaging disease, but its special importance derives from the fact that its clinical picture is like that of foot-and-mouth disease.

Vesicular stomatitis (V. S.) is characterized chiefly by the formation of vesicles, or blisters, in the mouth of cattle and horses and on the snout and feet of swine. One can tell it from foot-and-mouth disease only after inoculations or laboratory tests.

Vesicular stomatitis as a disease of horses and mules was initially reported in South Africa in 1897. The disease had probably occurred among horses used in the Civil War, but the first established report in the United States was in 1916, when horses with V. S. were seen in the Denver stockyards. That year the disease spread through remount stations across the Great Plains to Chicago and Virginia.

Cattle in Richmond, Ind., were diagnosed as having vesicular stomatitis in 1925. The organism that caused it was preserved and now is known as vesicular stomatitis Indiana type. The next year a serious outbreak of vesicular stomatitis in New Jersey was diagnosed as being caused by an organism that was immunologically different from the one isolated in Indiana. It was identified as vesicular stomatitis New Jersey type. All later outbreaks have been found to be of one of these two types.

Severe outbreaks occurred in Texas and Louisiana in 1941, and in Colorado in 1942, 1943, and 1944. The Indiana-type organism was isolated from the 1942 outbreak in Colorado.

That type has not been diagnosed in the United States since then.

An outbreak in California in 1945 had additional importance because a second vesicular disease (vesicular exanthema) was present in that State at the same time. Small, sporadic outbreaks in cattle occurred the following years. In 1949 V. S. swept across the United States from Mexico to Canada and from the Rockies to the Appalachians. Large numbers of animals were involved in the Southeastern States, the upper Mississippi Valley, and the Rocky Mountain States.

No vesicular stomatitis was reported in the United States in 1950 or 1951. Vesicular stomatitis was diagnosed in Georgia in 1952; in Georgia, New Jersey, Oklahoma, North Carolina, Virginia, Maryland, and West Virginia in 1953; in Florida, Louisiana, North Carolina, and Georgia in 1954; and in Georgia, Louisiana, North Carolina, and South Carolina in 1955.

An outbreak of V. S. occurred in swine in a hog cholera serum plant in Missouri in 1943. Fifty percent of 1,500 swine were involved. It was diagnosed as of the New Jersey type. This was the first time that V. S. had been diagnosed officially in swine. It is still not known how the virus got into the plant.

The first natural outbreak of V. S. in swine on a farm was diagnosed by Department of Agriculture veterinarians in Georgia in May 1952. V. S. in swine was diagnosed in Georgia and North Carolina in 1953; in Florida, Louisiana, and North Carolina in 1954; and in Georgia, Louisiana, North Carolina, and South Carolina in 1955. Those outbreaks occurred in May, June, July, and August. Information collected from veterinarians, livestock owners, and game wardens during the 1952 outbreak in Georgia indicates that V. S. may have occurred in swine there for at least 15 years.

THE CAUSE of vesicular stomatitis is a virus that is concentrated in the blisters and the blister coverings formed during the course of the disease. The virus is also found in the blood during the fever stage of the disease and for a short period afterwards.

The virus, as seen under an electron microscope, is rod shaped, about 0.000008 inch long, and about one-fourth as wide--125,000 of the organisms would measure 1 inch.

The virus remains active for several days at body temperature (98.6 F.). Infectivity is retained for several months in the refrigerator at 42 to 46 F. The virus retains its infectivity for years when it is frozen at 94 . It is affected considerably by caustic chemicals like acids, lye, and lime, which can make the virus noninfectious if they are used in the proper strength. Sunlight and ultraviolet light rapidly destroy the virus. A temperature of 130 destroys its viability in 15 minutes.

One of the two types of virus (Indiana and New Jersey) does not immunize against the other type, and an animal recovering from one type might suffer a fresh attack of the disease by the other type. Animals immune to either type of V. S. have not been found to demonstrate any immunity to foot-and-mouth disease or vesicular exanthema.

During the past 25 years V. S. has been mainly a disease of cattle. Early reports were that it was found primarily in horses. Since 1952, the number of infected swine has increased. It is believed that many outbreaks in swine go undiagnosed each year. Only since the great outbreak of vesicular exanthema in 1952 has a close check on all suspicious swine been made.

The disease occurs seldom in sheep and goats. The infection has been reported in deer and dogs. Mice, rats, guinea pigs, chinchillas, hamsters, ferrets, chickens, and chicken embryos are rather easily infected. Man also is somewhat susceptible to the disease. According to R. P. Hanson and his coworkers at the University of Wisconsin, the disease appears to be confined entirely to persons who come in close contact with it in their work.

The disease is not usually found in cattle and horses less than 1 year old. Only one 6-month-old animal was reported in the 1949 outbreak in Wisconsin, which involved 11,380 head of cattle. V. S. has been reported in suckling pigs.

The first symptoms usually noted in cattle and horses are salivation and a softening and tearing off of the mucous membrane of the tongue, lips, hard palate, and gums. A sick animal shows an acute temperature rise 2 to 5 days after exposure. Temperatures in cattle rise to 105 F., but are seldom observed in the field because this stage of the disease has passed before the farmer is aware of an abnormal condition in his cattle.

In cows and horses there is a patchy reddening of the oral mucous membranes, especially the tongue. Small areas start swelling. The swellings develop into vesicles, which may be as small as a dime or as big as a dollar.

The vesicles often join together to form large vesicles. The fully developed vesicle contains a clear, straw-colored fluid, which has a high virus content. The vesicles usually rupture in a few hours and therefore are not often seen in the field.