African swine fever

Context:

An outbreak of suspected African swine fever (ASF) has killed 276 domestic pigs in Lunglei district of Mizoram.

• As a part of the preventive measures, the local authorities have restricted the procurement and supply of pigs from and to the affected area and the district beyond.

About African Swine Fever (ASF):

• African swine fever virus (ASFV) is a large, double-stranded DNA virus in the Asfarviridae family.
• It is the causative agent of African swine fever (ASF). The virus causes a hemorrhagic fever with high mortality rates in domestic pigs; some isolates can cause death of animals as quickly as a week after infection.
• It persistently infects its natural hosts, warthogs, bushpigs, and soft ticks of the genus Ornithodoros, which likely act as a vector, with no disease signs.
• It does not cause disease in humans.
•  ASFV is endemic to sub-Saharan Africa and exists in the wild through a cycle of infection between ticks and wild pigs, bushpigs, and warthogs.
• The disease was first described after European settlers brought pigs into areas endemic with ASFV, and as such, is an example of an emerging infectious disease.
• ASFV replicates in the cytoplasm of infected cells.
• It is the only virus with a double-stranded DNA genome known to be transmitted by arthropods.
• The mortality is close to 100 per cent, and since the fever has no cure, the only way to stop it spreading is by culling the animals

The virus is thought to be derived from a virus of soft tick (genus Ornithodoros) that infects wild swine, including giant forest hogs (Hylochoerus meinertzhageni), warthogs (Phacochoerus africanus), and bushpigs (Potamochoerus porcus). In these wild hosts, infection is generally asymptomatic. This virus appears to have evolved around 1700 AD.

This date is corroborated by the historical record. Pigs were initially domesticated in North Africa and Eurasia. They were introduced into southern Africa from Europe and the Far East by the Portuguese (300 years ago) and Chinese (600 years ago), respectively. At the end of the 19th century, the extensive pig industry in the native region of ASFV (Kenya) started after massive losses of cattle due to a rinderpest outbreak. Pigs were imported on a massive scale for breeding by colonizers from Seychelles in 1904 and from England in 1905. Pig farming was free-range at that time. The first outbreak of ASF was reported in 1907.

Diagnosis

The clinical symptoms of ASFV infection are very similar to classical swine fever, and the two diseases normally have to be distinguished by laboratory diagnosis. This diagnosis is usually performed by an ELISA, real time PCR or isolation of the virus from either the blood, lymph nodes, spleen, or serum of an infected pig