African Swine Fever: ASF
General Information
African Swine Fever (ASF), a highly virulent viral disease exclusive to the Suidae family, which encompasses both domestic and wild pig populations, is characterized by severe hemorrhagic disease across all age classes, often resulting in mortality rates reaching up to 100% in affected domestic pigs and wild boar. Its etiology stems from the African swine fever virus (ASFV), an entity classified within the Asfarviridae family. ASFV represents a DNA virus within the genus Asfivirus. Notably, ASFV stands as the exclusive member within this familial classification. ASFV demonstrates remarkable resistance to low temperatures, enduring viability for prolonged periods within blood, fecal matter, tissues, and carcasses, particularly within infected, improperly cooked, or raw pork products, even within various environmental conditions. Additionally, it possesses the capability to proliferate within vectors, notably soft ticks in Ornithodoros spp.
Transmission
ASFV transmission occurs through direct contact between infected and susceptible animals, as well as indirect exposure to contaminated materials or feed, notably through the consumption of swill-feeding contaminated pig products. Furthermore, inanimate objects such as clothing, vehicles, and veterinary equipment may serve as potential sources of infection. Concurrently, arthropod vectors, particularly soft ticks, have been identified as competent transmitters of the virus. Reported instances of discarded pig carcasses are observed along roadways and the peripheries of forests, rendering them susceptible to scavenging by free-roaming domestic pigs or wild boar, thereby posing a potential risk for viral transmission.
Disease Outbreak
African Swine Fever (ASF) was first recorded in Kenya, Africa, in 1921 and later emerged in various European countries, beginning with a notable outbreak in a Portuguese pig farm in 1957, persisting in Europe until 1995. In 2007, ASF virus reappeared in Georgia and subsequently disseminated to other Caucasian and Eastern European nations. The initial outbreak in Asia occurred in August 2018, with the disease subsequently reaching China, the world’s leading pig producer, and presently extending its presence across multiple Asian countries, including the Southeast Asian region.
In Thailand, the initial notification of the outbreak was officially conveyed by the Department of Livestock Development (DLD) in January 2022. By December 2022, there had been 114 recorded cases of the outbreak across 35 out of the country’s 77 provinces, affecting the domestic pig industry.
ASF in wild boar
Bushpigs (Potamochoerus spp.) and warthogs (Phacochoerus spp.) native to Africa are acknowledged natural reservoirs for the ASFV, with Ornithodoros ticks playing a significant role as vectors in disease transmission. The epidemiological landscape of ASF has undergone notable shifts since 2007, particularly evident in Eurasia, where Eurasian wild boar (Sus scrofa) infections have emerged as a prominent feature. This trend is mirrored in other regions, notably in Europe, where wild boar species have also been identified as critical reservoirs for ASFV. The frequent interaction among live wild boar, free-ranging domestic pigs, and contaminated carcasses or pig products has perpetuated ASF transmission independently of domestic pig populations, leading to its gradual diffusion across eastern Europe. Consequently, persistent challenges persist in effectively controlling ASF within affected regions.
In Asia, the prevalence of ASF has been predominantly noted among domestic pig populations, with sporadic occurrences reported in wild boars. Notably, specific Asian nations like Far East Russia and South Korea have instituted ASF surveillance protocols targeting wild populations. However, a significant development emerged in 2020 with the initial confirmation of ASF in carcasses of free-wild boar in Southeast Asian countries, specifically Laos and Vietnam. Despite this milestone, comprehensive documentation of ASF cases in wild boars remains limited in other affected nations in the region, such as Thailand. This underscores the importance of expanding surveillance efforts to better comprehend the extent and dynamics of ASF transmission within both domestic and wild swine populations across Asia.
Choenkwan Pabutta
The Monitoring and Surveillance Center
for Zoonotic Diseases in Wildlife and Exotic Animals (MoZWE)
Faculty of Veterinary Science, Mahidol University