Swine fever

Swine fever is a viral disease that afflicts swine. The disease is also known as hog cholera. A related form of the disease is called African swine fever.

The virus that causes swine fever is a member of the family Flaviviridae and the genus Pestivirus. A virus causes African swine fever from the family Iridovirisae. The virus itself is designated Asfarviridae, a name derived from "African Swine Fever and Related Viruses." The virus is so far the sole member of the newly created genus Asfivirus.

The two viruses are quite different from one another in structure and behavior. Yet, the diseases they cause are very similar with respect to their transmission and the symptoms of infection. Both viruses can be easily passed from an infected pig to a healthy pig. Contact can be direct or via body secretions or feces. The resulting infection can be mild or more severe. Also a long lasting form of infection can result. The more severe form of the infection results in a very high fever that can lead to convulsions. Often the skin appears discolored and pigs will huddle together. Death usually results a week or two weeks after the appearance of symptoms. The chronic form of the infection displays similar but less severe symptoms. The symptoms can persist for months before the swine succumbs. Finally, an infection can display few if any symptoms. However, this mild bout of the disease can caused reduce number of live births.

Swine that survive the infections can be life-long carriers of the viruses.

Distinction of swine fever from African swine fever is only possible by the direct examination of the viruses. The examinations typically involve the isolation of the virus in an appropriate cell culture and the use of fluorescent-labeled antibodies and the enzyme-linked immunosorbant assay (ELISA ).

Both viruses are easily spread from hog to hog. Pigs and related animals such as wild boar are the only natural reservoirs of Pestivirus. Asfivirus can reside in species such as ticks. The viruses can also be accidentally carried from an infected swine to a susceptible swine via humans, animals, and birds. This is in part due to the environmental persistence of the viruses. For example, Pestivirus is able to survive cold conditions, and so can survive in a refrigerated carcass during transport. As well, the virus is able to survive some forms of meat processing (e.g., curing and smoking). However, Pestivirus is susceptible to various disinfectants (e.g., sodium hydroxide, Formalin, various detergents).

Pestivirus infects the blood and virtually all body fluids of an infected animal. Furthermore, the animal can excrete the virus for months.

The adverse effects to the health of the swine, and to their economic value, has made the eradication of swine fevers a priority in many countries around the world. In the United States, for example, a concerted effort by State and Federal governments and industry over almost two decades has virtually eliminated the disease in the country. However, vigilance is necessary to maintain this record. In Great Britain, where swine fever had been eliminated by 1966, it reappeared in 2000.

Such is not the case around the world. In many countries, swine fever remains a problem. Belgium and France experienced heavy economic losses in 1997, for example. African swine fever is a major problem affecting swine in countries such s Gambia, Ghana, and Madagascar, and there have also been outbreaks in more northern countries (e.g., Italy in 1999 and Portugal in 2000).

In countries such as the United States, swine entering the country are quarantined for 90 days to ensure that the swine do not harbor the virus that has yet to be evident as an infection.

Currently there is no treatment for either swine fever, save slaughter of the infected animals. In this regard, swine fever is similar to foot and mouth disease that afflicts cattle and sheep. The use of a vaccine consisting of weakened but living virus has been an effective preventative measure for swine fever. However, unless the vaccination involves the total swine population in the target region, the prevention of infection will not be absolute.

See also Virology