Vesicular Exanthema

F. J. MULHERN AND W. C. PATTERSON.

VESICULAR EXANTHEMA of the swine became a national problem in the summer of 1952. The disease suddenly escaped from California, where it had been confined for more than 20 years, and within 6 weeks it spread to 18 States. By September of 1953 it had appeared in 42 States.

Vesicular exanthema causes weight losses in mature hogs, slower gains in the feeder pigs and runts, and sometimes death in the suckling pigs. Because it resembles foot-and-mouth disease, vesicular exanthema creates fear, which depresses hog prices whenever it appears in auction and sales markets and stockyards.

A VESICULAR DISEASE that affected only swine and looked like foot-and-mouth disease was discovered in swine fed on raw garbage in Orange County, Calif., in April 1932. It spread to Los Angeles and San Bernardino Counties and was diagnosed as foot-and-mouth disease. All animals involved in the outbreak were killed and buried.

The lesions of vesicular exanthema--commonly called V. E. consist of vesicles (blisters), that develop on the feet and snouts of infected hogs and rupture quite rapidly. The name given to the disease tends to describe the lesions presented. Vesicular refers to the vesicles, or blisters, while exanthema refers to the eruption of them. These lesions are identical with the lesions produced by foot-and-mouth disease and vesicular stomatitis in swine.

When a suspected case is reported, animal inoculation tests or laboratory tests are needed to determine whether the infection is vesicular exanthema, vesicular stomatitis, or foot-and-mouth disease.

A similar disease in hogs that were fed raw garbage occurred in San Diego County in March 1933. It also was confined to swine. When test animals were inoculated, swine and horses developed lesions, but cattle and guinea pigs did not. Opposite results are produced when test animals are inoculated with tissue infected with foot-and-mouth disease virus. All cloven-footed animals, including cattle and swine, and guinea pigs are susceptible to foot-and-mouth disease. Horses are not susceptible. Therefore, because of the findings of those tests, no official diagnosis was made, but all animals involved were slaughtered, and indemnities were paid.

A new disease of swine was described in 1934. by Jacob Traum, of the University of California, as the cause of the 1933 outbreak. Dr. Traum reported that the agent that caused the disease was different both from that of foot-and-mouth disease and vesicular stomatitis. Animals that recovered from it were not immune to those two diseases. Dr. Traum also considered the 1932 outbreak to have been caused by this new agent, for which he suggested the name vesicular exanthema.

The vesicular exanthema that occurred in 1934 was found only on premises where raw garbage was fed. A strict quarantine was imposed until no other animals in that vicinity were reported as having the disease. Mild outbreaks occurred, however, in 1935 and 1936. Then 42 months passed before it was reported again. When it did reappear, it was for a more serious disease than it was previously considered to be.

A serious outbreak started in 1939 in San Mateo County. One-fourth of the hogs in California were involved within 6 months. The disease subsequently appeared each year there.

Vesicular exanthema appeared at a plant manufacturing biologicals in Grand Island, Nebr., in June 1952. That was the first time the disease had been detected outside California. The source of the infection was traced to swine near Cheyenne, Wyo., which had been fed garbage from transcontinental trains whose point of origin was California.

Before the disease was detected, hogs from Grand Island had been shipped to the stockyards in Omaha, Nebr., and moved out to various parts of the country. In slightly more than a month, 18 States were under Federal quarantine because of vesicular exanthema. The Secretary of Agriculture declared a state of emergency on August 1, 1952 an action that provided funds for an eradication program.

VESICULAR EXANTHEMA is caused by a virus, which is concentrated in the fluid in the blisters as well as in the tissue that makes up the cover of the blister. The blisters, vesicles, are formed during the fever stage. The virus also is present in the blood during the fever stage and for a short period thereafter. The virus is said to be 0.000002 inch in diameter.

The virus can remain infective for 2.5 years at 45 F. in unground vesicle coverings stored in a 50-percent glycerine phosphate buffer.

Meat scraps from infected pigs can remain infectious after storage at 45 for at least 4 weeks and for a much longer time when they are frozen. Hams infected with vesicular exanthema virus are inactivated (made noninfectious) when the internal temperature of the meat is held at 150 for 30 minutes. A fresh 2-percent lye solution (caustic soda) kills the virus.

We know of five virus types, which have been identified as A-48, B-51, C-52, D-53, and E-54. The letter indicates the order of isolation and the numbers indicate the year when they were found. Of these five types, none immunized against the other. Only B-51 has been identified as the causative agent of outbreaks outside California.

There is reason to believe there are still other types. R. A. Bankowski started this classification of types when all previously isolated types were no longer available.

Vesicular exanthema is confined almost entirely to swine. A. B. Crawford, of the Department of Agriculture, in 1937 isolated four strains of the virus, identified as A, B, C, and D. All four affected swine, but only B and D were infectious to the horse.

Of the many outbreaks reported since June 1952, only in one outbreak has a horse been reported as being susceptible, and he was used in a differentiation test. Material collected from him would not produce lesions when inoculated into a second horse. Other horses and cattle used in tests have not been susceptible.

Experimental attempts to infect sheep, goats, guinea pigs, rats, suckling and adult mice, ferrets, chickens, and chicken embryos have failed.

S. H. Madin and Dr. Traum reported that hamsters could be infected with the 194.0 A and B strains when the inoculations were made on the skin on the abdomen these strains are no longer available. Inoculations of hamsters with A-48 and B-51 virus types were negative. Dogs have been infected but not with regularity, according to R. A. Bankowski and M. Wood, of the University of California.

THE FIRST SYMPTOMS of vesicular exanthema usually noted are the formation of vesicles on the snout and lips and lameness, caused by the formation of vesicles on the feet. The lesions usually develop 24 to 72 hours after exposure to the virus. During the vesiculation period, the temperatures usually range from 104 to 106 F. and persist for 24 to 36 hours. Then they recede rapidly, but a second rise in temperature may occur 24 to 72 hours later.

Those rises in temperature coincide with two stages of the disease. The first may occur when a primary lesion forms on the snout. The virus then enters the blood stream, and secondary lesions appear on other parts of the body. The spread of virus to all parts of the body is termed generalization. It is at this time that the second rise in temperature occurs, and it is the point at which most livestock owners first observe the disease. The pain and swelling of the foot lesions cause the animal to limp or refuse to move.

Vesicles may also form on the lips and tongue and other parts of the lining of the mouth cavity and on the area around the top of the hoof in the space between the toes and the soles of the feet. Lesions have been reported on the teats of nursing sows.

As the vesicles begin to form, there is a whitening of the affected area, which then forms a blister filled with fluid and containing great amounts of virus. The blisters will pit on pressure. Slight friction or pressure will tear away the epithelium covering and leave a red, raw, eroded surface. Shreds of tissue will cling to the margins of the wounds.

The primary lesions may spread over the whole surface of the snout and lips. Foot lesions, which commonly are found after generalization has taken place, may be so severe that the entire hoof will slough off. Formation of another hoof may take 3 to 6 months. The junction of the new and old hoofs is often marked by a black line.

It is of great importance that a differential diagnosis be made of any known vesicular disease. The lameness and blisters are easily recognizable evidence of a vesicular condition. But the determination of which vesicular disease is present is made by a specially trained diagnostician through a differential diagnosis by inoculations of horses, cattle, and swine. This method is like the one used to determine the presence of foot-and-mouth disease.

THE SPREAD of vesicular exanthema comes about principally in three ways:

The feeding of raw garbage containing infected raw pork scraps; direct contact with infected swine; and contact with mechanical carriers, including people and vehicles.

Infected swine in the early stages of the disease, when they show no signs of the disease, can be marketed without being detected as being ill. Scraps of pork from such animals or from other infected and exposed or recovered swine may be thrown into the garbage of restaurants, institutions, hotels, and households. Such garbage, fed uncooked to swine, may spread the disease. In California, before most farmers cooked the garbage they fed hogs, the chances of vesicular exanthema in garbage-fed swine were a thousand times greater than in grain-fed swine.

Swine in the early stage of the disease and recovered swine might be marketed undetected as carriers of the disease. Discharges from them may infect others with which they come in contact before slaughter in markets, sales barns, and stockyards.

Hogs with fresh lesions spread the disease quite readily. Large amounts of virus are liberated when the blisters rupture, both in the fluid and tissues that make up the cover.

Human beings do not contract vesicular exanthema, but they can carry the disease to swine on their clothing, especially their shoes, if they have been walking on infected premises or have been in contact with infected swine.