What Is a Vesicular Lesion?

Swine Vesicular Disease (SVD), also known as swine infectious vesicular disease, is a viral infectious disease. ^[1] It is characterized by the formation of blisters or rotten skin between the skin of the hoof or nasal end of the pig and the mucosa of the mouth and tongue Macular, the clinical symptoms cannot be distinguished from foot and mouth disease (FMD), vesicular stomatitis (VS) and swine vesicular rash (VES).

Swine vesicular disease

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Swine Vesicular Disease (SVD), also known as porcine infectious vesicular disease, is a

The disease was first discovered in 1966. It is a relatively new infectious disease in pigs. It is a contagious virus disease caused by swine vesicular virus. The epidemic is non-seasonal and occurs frequently in humid and sweltering seasons. ^[2]

In October 1966, a swine disease that was clinically indistinguishable from FMD occurred in Lombardy, Italy, and the pathogen was identified as enterovirus in 1968. In the 1970s, Hong Kong and Japan in Asia, as well as many countries in Europe, successively developed this disease. In 1973, the 20th Session of the European Food and Disease Control Committee of the Food and Agriculture Organization of the United Nations and the 41st General Conference of the International Organisation for Animal Diseases (OIE) confirmed that this was a new disease and was named "pig vesicular disease". The disease is mainly concentrated in Europe and Asia. The popularity peaked in the early 1970s, and gradually eased afterwards. By the end of the 1980s, there were only a few outbreaks, but in the 1990s it seems that SVD has a tendency to rise again. The OIE epidemic report and summary data published by some countries (as of March 1995) are summarized in Table 5-10 to show the epidemic history and geographical distribution of SVD.

Epidemic history and theoretical distribution of swine vesicular disease

Countries and regions with outbreaks in years (number of times *)

1966 Italy (2)

1971 Hong Kong (repeatedly)

1972 Italy (70), United Kingdom (multiple times), Austria (18), Poland (2), France (100)

1973 Italy (41), United Kingdom (multiple times), France (102), Belgium (1), Switzerland (1), former West Germany (2), Japan (15)

1974 Italy (6), United Kingdom (276), France (100), Austria (7), former West Germany (1)

1975 Italy (8), United Kingdom (17), France (1), former West Germany (12), Netherlands, Japan, Malta (1), Austria (1)

1976 Italy, United Kingdom (3), Austria (6)

1977 Italy (26), United Kingdom (9), former West Germany (1)

1978 Italy (7), United Kingdom (1), former West Germany (1)

1979 Italy (9) United Kingdom (43), Belgium (6), Greece (1), Australia (?)

1980 United Kingdom (60)

1981/1982 Italy (15), United Kingdom (26), France (1), former West Germany (2)

1983 Italy (1), France (1)

1984 Italy (1)

1985 Former West Germany (1)

1988 Italy (1), Hong Kong

1989 Italy (1)

1991 Italy (6)

1992 Italy (25), Netherlands (15), Belgium (1)

1993 Italy (11), Belgium (1), Spain (3)

1994 Italy (28), Pays-Bas (3)

1995 Italy (12)

Note: * The number of outbreaks is for reference only. Unknown national data is unknown.

? Australia had a vesicular disease outbreak in 1979. After testing for non-foot-and-mouth disease, it may be SVD. It did not happen after culling.

The economic losses caused by SVD include fall off, stunted growth, extended fattening period (average 20%), sow abortion, piglet death, and quarantine and disinfection costs. If culling measures are taken, the one-time loss will be greater, but it will help to eliminate the epidemic. From 1972 to 1979, there were 446 SVD outbreaks in the UK, and the losses from slaughter alone amounted to nearly 10 million pounds. SVD is a major disease in the pig industry and one of the Class A animal infectious diseases specified by OIE. Both at home and abroad require the occurrence of any vesicular disease to be reported to the national veterinary authority, and preventive measures equivalent to FMD should be taken. For example, the first SVD epidemic occurred in Japan on November 23, 1973. On December 8, the same year, the Japanese government issued a cabinet decree to control SVD and formulated a set of quarantine and handling measures. Countries have strict requirements on the import and export quarantine of pigs and pork products, so SVD has a great impact on international trade. On the other hand, the outbreak of SVD cannot rule out the possibility of infecting workers. ^[2]

The cause of porcine vesicular disease is porcine vesicular disease virus (SVDV). According to the Fifteenth Report of the International Commission for Classification of Viruses (ICTV) (1991), SVDV is classified as the Picornaviridae family (Picornaviridae)

SVD diseased pigs and pork products and live pigs and pork products in the SVD incubation period are the most important sources of infection. After mixing cattle and sheep with pigs infected with SVDV, SVDV can be isolated from their oral cavity, milk and feces, and SVDV proliferation can occur in sheep, but they do not have any clinical symptoms. Whether cattle and sheep can be the source of infection and their role in transmission is inconclusive, but mechanical transmission is possible.

The incubation period for SVD is 2-6 days, the incubation period for exposure to infection is 4-6 days, and the incubation period for feeding infected pork products is 2 days. Typical lesions can appear 36 hours after intradermal vaccination. Generally, the results of intracutaneous and intravenous vaccination are relatively regular. Latent pigs already have high titers of virus in their skin and muscle. The swine virus that came into contact with sick pigs appeared in the nasal mucosa within 24 hours, appeared in the rectum and pharyngeal cavity in 48 hours, was in a viremia state on the 4th day, appeared initial blisters on the 5th day, and collapsed after 2-3 days. A large number of detox sources are blisters and blisters. Viral titers are still high in ruptured skin over 10 days of age. Followed by detoxification via feces and secretions. After infection, detoxifying the nasal cavity for 7-10 days, detoxifying the oral cavity for 7-8 days, detoxifying the pharyngeal cavity for 8-12 days, and detoxifying the rectum for 6-12 days. Due to the viremia process, all tissues can be a source of infection.

Almost all SVDs are related to feeding contaminated food (such as swill water, meat washing water), contacting the contaminated site, using live vehicles to transport live pigs, or introducing sick pigs. Only a few outbreaks have unknown causes. There were 446 SVD outbreaks in Britain from 1972 to 1979, 66 of which were caused by contaminated transport facilities, 74 were caused by the transfer of live pigs from contaminated sites, and 66 were caused by the feeding of contaminated lame feed. Secondly, it is caused by personnel flow, horizontal transmission and secondary recurrence. Experiments have shown that SVD is different from foot-and-mouth disease, and the possibility of airborne transmission is small. Infected sows are likely to infect piglets through the placenta, because it has been found that SVD can occur as early as 5 hours after birth in recovered sows, which is clearly within the incubation period. However, embryo transfer does not cause SVD transmission. Even eggs and embryos from infected sows will not cause infection in recipient pigs, and piglets born to recipient pigs are also negative for SVD. However, artificially contaminating eggs or embryos with SVDV, even if treated with protease or antiserum and repeated washing, can not completely eliminate SVDV.

It is generally believed that the skin is the most sensitive part of SVDV, and small wounds or abrasions may be the main route of infection. Followed by the digestive tract epithelial mucosa. The respiratory mucosa appears to be less sensitive.

SVD outbreaks have no obvious seasonality and are generally less frequent in summer. Occurs in places where pigs are concentrated. Pigs of different breeds and ages are susceptible, and generally have less FMD transmission and lower incidence than FMD. ^[2]

The first observation was the lameness of individual pigs in the herd. It is more obvious to walk on hard ground, and often walk on the back of the arch, have painful reactions, or can't lie on the ground. Body temperature generally rises 2-4 ° C. Injuries generally occur in the crown of the hoof and between the hoofs. The disease may be single hoof or multihoof. The skin appears blisters and ulceration, and can spread to the bottom of the hoof, some with loose or even shelling. Blisters and secondary ulcers may also occur on the nose, oral epithelium, tongue, and nipples. In general, primary blisters appear in the incubation period of 2-4 days after exposure, and secondary blisters appear in 5-6 days. Onset of infection within 2 days of vaccination. Pigs usually return to normal in 3 weeks. Incidence rates vary widely between different outbreaks, some not exceeding 10%, but others reaching 100%. Mortality is generally low. Experimental infection of lactating sows has a high morbidity and mortality in the piglets they feed. Infected pigs with clinical symptoms and pigs in contact with them can produce high titers of neutralizing antibodies, which can be maintained for at least 4 months. ^[2]

Vesicular injury is the most typical and representative pathological change of SVD. The appearance and microscopic observation of vesicular lesions were not different from those of FMD. Other pathological changes, such as brain injury, were not characteristic.

It is generally believed that the infection mainly passes through two ways. One is to directly invade the epithelial tissue from the contaminated site through the traumatized skin, and the proliferated virus reaches the other susceptible sites through the blood circulation to cause lesions. Another way is to enter the digestive tract through the mouth, invade the virus through the epithelium and mucosa of the digestive tract, and reach the susceptible site through the blood circulation, resulting in lesions such as blister injury and non-purulent encephalomyelitis. ^[2]

1.Prohibit unboiled simmer water to feed pigs

2. Vaccination

2.1 Attenuated vaccine against porcine vesicular renal cell-derived cells; used for vaccination. For large and small fat pigs, 2 ml can be injected into the deep femoral muscle. 3 to 5 days after the injection, strong immunity can be produced. The immune period is temporarily 6 Months.

2.2. Swine vesicular cytotoxic crystal violet vaccine; 2 ml intramuscularly can be injected into healthy weaned pigs and fattened pigs, and the immunization period is 9 months.