African swine fever virus
|African swine fever virus|
|Electron micrograph of a virus particle|
African swine fever virus
African swine fever virus (ASFV) is the causative agent of African swine fever (ASF). The virus causes a haemorrhagic fever with high mortality rates in pigs, but persistently infects its natural hosts, warthogs, bushpigs, and soft ticks of the genus Ornithodoros, which likely act as a vector with no disease signs.
ASFV is the only known virus with a double-stranded DNA genome transmitted by arthropods. The virus causes a lethal haemorraghic disease in domestic pigs. Some isolates can cause death of animals as quickly as a week after infection. In all other species, the virus causes no obvious disease. 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 is a large, icosahedral, double-stranded DNA virus with a linear genome containing at least 150 genes. The number of genes differs slightly among different isolates of the virus. ASFV has similarities to the other large DNA viruses, e.g., poxvirus, iridovirus, and mimivirus. In common with other viral hemorrhagic fevers, the main target cells for replication are those of monocyte, macrophage lineage. Entry of the virus into the host cell is receptor-mediated, but the precise mechanism of endocytosis is presently unclear.
The virus encodes enzymes required for replication and transcription of its genome, including elements of a base excision repair system, structural proteins, and many proteins that are not essential for replication in cells, but instead have roles in virus survival and transmission in its hosts. Virus replication takes place in perinuclear factory areas. It is a highly orchestrated process with at least four stages of transcription—immediate-early, early, intermediate, and late. The majority of replication and assembly occurs in discrete, perinuclear regions of the cell called virus factories, and finally progeny virions are transported to the plasma membrane along microtubules where they bud out or are propelled away along actin projections to infect new cells. As the virus progresses through its lifecycle, most if not all of the host cell's organelles are modified, adapted, or in some cases destroyed.
Assembly of the icosahedral capsid occurs on modified membranes from the endoplasmic reticulum. Products from proteolytically processed polyproteins form the core shell between the internal membrane and the nucleoprotein core. An additional outer membrane is gained as particles bud from the plasma membrane. The virus encodes proteins that inhibit signalling pathways in infected macrophages and thus modulate transcriptional activation of immune response genes. In addition, the virus encodes proteins which inhibit apoptosis of infected cells to facilitate production of progeny virions. Viral membrane proteins with similarity to cellular adhesion proteins modulate interaction of virus-infected cells and extracellular virions with host components.
Based on sequence variation in the C-terminal region of the B646L gene encoding the major capsid protein p72, 22 ASFV genotypes (I–XXIII) have been identified. All ASFV p72 genotypes have been circulating in eastern and southern Africa. Genotype I has been circulating in Europe, South America, the Caribbean, and western Africa. Genotype VIII is confined to four East African countries.
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.
Signs and symptoms
In the acute form of the disease caused by highly virulent strains, pigs may develop a high fever, but show no other noticeable symptoms for the first few days. They then gradually lose their appetites and become depressed. In white-skinned pigs, the extremities turn blueish-purple and hemorrhages become apparent on the ears and abdomen. Groups of infected pigs lie huddled together shivering, breathing abnormally, and sometimes coughing. If forced to stand, they appear unsteady on their legs. Within a few days of infection, they enter a comatose state and then die. In pregnant sows, spontaneous abortions occur. In milder infections, affected pigs lose weight, becoming thin, and develop signs of pneumonia, skin ulcers, and swollen joints.
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 or isolation of the virus from either the blood, lymph nodes, spleen, or serum of an infected pig.
The first outbreak was retrospectively recognized as having occurred in 1907 after ASF was first described in 1921 in Kenya. The disease remained restricted to Africa until 1957, when it was reported in Lisbon, Portugal. A further outbreak occurred in Portugal in 1960. Subsequent to these initial introductions, the disease became established in the Iberian peninsula, and sporadic outbreaks occurred in France, Belgium, and other European countries during the 1980s. Both Spain and Portugal had managed to eradicate the disease by the mid-1990s through a slaughter policy.
In 1971 an outbreak of the disease occurred in Cuba, resulting in the slaughter of 500,000 pigs to prevent a nationwide animal epidemic. The outbreak was labeled the "most alarming event" of 1971 by the United Nations Food and Agricultural Organization.
Six years after the event, the newspaper Newsday, citing untraceable sources, claimed that anti-Castro saboteurs, with at least the tacit backing of U.S. Central Intelligence Agency officials, allegedly introduced African swine fever virus into Cuba six weeks before the outbreak in 1971, to destabilize the Cuban economy and encourage domestic opposition to Fidel Castro. The virus was allegedly delivered to the operatives from an army base in the Panama Canal Zone by an unnamed U.S. intelligence source.
ASFV crossed the Atlantic Ocean, and outbreaks were reported in some Caribbean islands, including Hispaniola (Dominican Republic). Major outbreaks of ASF in Africa are regularly reported to the World Organisation for Animal Health (previously called L'office international des épizooties).
Eastern and Northern Europe
ASFV first occurred in Europe in 1957, when it was introduced in Portugal. From there, it spread to Spain and France. Although concerted efforts to eradicate ASFV were undertaken, such as widespread culling and the construction of modern farming facilities, the disease was only eradicated in the 1990s.
Outside Africa, an outbreak occurred at the beginning of 2007 in Georgia, and subsequently spread to Armenia, Azerbaijan, Iran, Russia, and Belarus, raising concerns that ASFV may spread further geographically and have negative economic effects on the swine industry.
African swine fever had become 'endemic' in the Russian Federation since spreading into the North Caucasus 'in November 2007, most likely through movements of infected wild boar from Georgia to Chechnya, said a 2013 report by the Food and Agriculture Organization, a United Nations agency. The report showed how the disease had spread north from the Caucasus to other parts of the country where pig production was more concentrated the Central Federal District (home to 28.8% of Russia's pigs) and the Volga Federal District (with 25.4% of the national herd) and northwest towards Ukraine, Belarus, Poland and the Baltic nations. In Russia, the report added, the disease was 'on its way to becoming endemic in Tver oblast' (about 106 km north of Moscow—and about 500 km east of Russia's littoral neighbours on the Baltic. Among the vectors for the spread in Russia of African swine fever virus was the 'distribution' of 'infected pig products' outside affected (quarantined and trade restricted) areas, travelling large distances (thousands of kilometers) within the country.
'Wholesale buyers, particularly the military food supply system, hav[ing] been implicated multiple times in the illegal distribution of contaminated meat' were vectors for the virus's spread, said the Food and Agriculture Organization report—and evidence of that was 'repeated outbreaks in Leningrad oblast'.  The report warned that 'countries immediately bordering the Russian Federation, particularly Ukraine, Moldova, Kazakhstan, and Latvia, are most vulnerable to [African swine fever] introduction and endemic establishment, largely because the biosecurity of their pig sector is predominantly low. Preventing the spread of [African swine fever] into Ukraine is particularly critical for the whole pig production sector in Europe. Given the worrisome developments in the Russian Federation, European countries have to be alert. They must be ready to prevent and to react effectively to [African swine fever] introductions into their territories for many years to come'...To stop the virus's spread, 'the current scenario in the Russian Federation suggests that [prevention] should be particularly stressed at the often informal backyard level and should involve not just pig keepers, but all actors along the whole value chain—butchers, middlemen, slaughterhouses, etc. … They need to be aware of how to prevent and recognize the disease, and must understand the importance of reporting outbreaks to the national authorities … It is particularly important that [African swine fever]-free areas remain free by preventing the [re]introduction of the disease and by swiftly responding to it when it occurs'.
Estonia in July 2015 recorded its first case of African swine fever in farmed pigs in Valgamaa on the country's border with Latvia. Another case was reported same day in Viljandi county, which also borders Latvia. All the pigs were culled and their carcasses incinerated. Less than a month later, almost 15,000 farmed pigs had been culled and the country was 'struggling to get rid of hundreds of tons of carcasses'. The death toll was 'expected to rise'.
Latvia in January 2017 declared African swine fever emergency in relation to outbreaks in three regions, including a pig farm in Krimulda region, that resulted in a cull of around 5,000 sows and piglets by using gas. In February another massive pig cull was required, after an industrial scale farm of the same company in Salaspils region was found infected, leading to a cull of about 10,000 pigs.
In June 2017, the Czech Republic recorded its historically first case of African swine fever. The Czech Republic in Zlin, through a measure of the relevant veterinary administration, by introducing a regulation that prevented the spread of the ASF infection by removing the contaminated zone via odor fences. Odor fences with a total length of 44.5 km were able to keep the wild boar in the health zone.
In May 2019, European Council announced that the Czech Republis is the first country on the world, where the ASFV were eliminated.
In 2018, Romania experienced a nation wide African swine fever pandemic which prompted the slaughter of most of farm pigs.
In September 2018, an outbreak occurred in wild boars in Southern Belgium. Professional observers suspected importation of wild boars from Eastern European countries by game hunters being the origin of the virus. By the 4th of October, 32 wild boars had tested positive for the virus. For control of the outbreak, 4,000 domestic pigs were slaughtered preventively in the Gaume region, and the forest was declared off-limits for recreation.
Since approximately 2007 to August 31, 2018, 1367 cases of ASF of domestic pigs or wild pigs were reported by veterinary department of the Rosselkhoznadzor (Russian: Россельхознадзор), a Russian federal agency that supervises over agriculture) and state media. According to official report the central and south districts were among most affected by the disease (with several occasions on the east). Many regions effectively established local quarantines some of which was ended later.
In August 2018, China reported the first African swine fever outbreak in Liaoning province, which was also the first reported case in East Asia. As of September 1, 2018[update], the country has culled more than 38,000 hogs. Since the week of September 10, 2018, China has blocked transports of live pigs and pig products in a large part of the country to avoid further spread beyond the 6 provinces where the virus is currently confirmed. By the end of 2018, the outbreaks has been reported in 23 provinces and municipalities across China.
Ze Chen and Shan Gao et. al. from Nankai University detected African swine fever virus (ASFV) in Dermacentor (hard ticks) from sheep and bovines using small RNA sequencing. This 235-bp segment had an identity of 99% to a 235-bp DNA segment of ASFV and contained three single nucleotide mutations (C38T, C76T and A108C). C38T, resulting in a single amino acid mutation G66D, suggests the existence of a new ASFV strain, which is different from all reported ASFV strains in the NCBI GenBank database and the ASFV strain (GenBank: MH713612.1) reported in China in 2018.
The appearance of ASF outside Africa at about the same time as the emergence of AIDS led to some interest in whether the two were related, and a report appeared in The Lancet supporting this in 1986. However, the realization that the human immunodeficiency virus (HIV) causes AIDS discredited any potential connection with ASF.
In September 2018, the outbreak of the African swine fever was recorded in Belgium.
- Denyer, M. S.; Wilkinson, P. J. (1998). "African Swine Fever". Encyclopedia of Immunology. p. 54. doi:10.1006/rwei.1999.0015. ISBN 9780122267659.
- Dixon; et al. (2008). "African Swine Fever Virus". Animal Viruses: Molecular Biology. Caister Academic Press. ISBN 978-1-904455-22-6.
- Dixon, L.K.; Chapman, D.A.G.; Netherton, C.L.; Upton, C. (2013). "African swine fever virus replication and genomics". Virus Research. 173 (1): 3–14. doi:10.1016/j.virusres.2012.10.020. PMID 23142553.
- Netherton, C.L.; Wileman, T.E. (2013). "African swine fever virus organelle rearrangements". Virus Research. 173 (1): 76–86. doi:10.1016/j.virusres.2012.12.014. PMID 23291273.
- Leblanc, N.; Cortey, M.; Fernandez Pinero, J.; Gallardo, C.; Masembe, C.; Okurut, A. R.; Heath, L.; Van Heerden, J.; Sánchez-Vizcaino, J. M.; Ståhl, K.; Belák, S. (2012). "Development of a Suspension Microarray for the Genotyping of African Swine Fever Virus Targeting the SNPs in the C-Terminal End of the p72 Gene Region of the Genome". Transboundary and Emerging Diseases. 60 (4): 378–383. doi:10.1111/j.1865-1682.2012.01359.x. PMID 22776009.
- Michaud, V; Randriamparany, T; Albina, E (2013). "Comprehensive phylogenetic reconstructions of African swine fever virus: proposal for a new classification and molecular dating of the virus". PLOS ONE. 8 (7): e69662. doi:10.1371/journal.pone.0069662. PMC 3723844. PMID 23936068.
- Gifford-Gonzalez, D; Hanotte, O (2011). "Domesticating Animals in Africa: Implications of Genetic and Archaeological Findings". J World Prehist. 24: 1–23. doi:10.1007/s10963-010-9042-2.
- Levathes LE (1994) When China ruled the seas: The treasure fleet of the Dragon Throne, 1405–1433. New York: Oxford University Press
- Howey; et al. (2013). "Pathogenesis of highly virulent African swine fever virus in domestic pigs exposed via intraoropharyngeal, intranasopharyngeal, and intramuscular inoculation, and by direct contact with infected pigs". Virus Research. 178 (2): 328–339. doi:10.1016/j.virusres.2013.09.024. PMID 24076499.
- "African Swine Fever (ASF)". PigSite.
- Arzt et. al. (2010). "Agricultural diseases on the move early in the third millennium". Veterinary Pathology. 47 (1): 15–27. doi:10.1177/0300985809354350. PMID 20080480.
- Costard, S.; Mur, L.; Lubroth, J.; Sanchez-Vizcaino, J.M.; Pfeiffer, D.U. (2013). "Epidemiology of African swine fever virus". Virus Research. 173 (1): 191–197. doi:10.1016/j.virusres.2012.10.030. PMID 23123296.
- Zilinskas, R. A. (1999). "Cuban Allegations of Biological Warfare by the United States: Assessing the Evidence". Critical Reviews in Microbiology. 25 (3): 173–227. doi:10.1080/10408419991299202. PMID 10524329.
- Wheelis, M. (2004). "A Short History of Biological Warfare and Weapons". The Implementation of Legally Binding Measures to Strengthen the Biological and Toxin Weapons Convention. NATO Science Series II: Mathematics, Physics and Chemistry. 150. pp. 15–68. doi:10.1007/1-4020-2098-8_3. ISBN 978-1-4020-2096-4.
- "CIA Link to Cuban Pig Virus Reported". San Francisco Chronicle. January 10, 1977.
- Zinn, Howard (1980). A People's History of the United States. United States: Harper & Row. ISBN 978-0-06-014803-4.
- Devlin, Hannah; Davies, Christian (2018-09-03). "'It's not if, it's when': the deadly pig disease spreading around the world". the Guardian. Retrieved 2018-09-03.
- Gogin, A.; Gerasimov, V.; Malogolovkin, A.; Kolbasov, D. (2013). "African swine fever in the North Caucasus region and the Russian Federation in years 2007–2012". Virus Research. 173 (1): 198–203. doi:10.1016/j.virusres.2012.12.007. PMID 23266725.
- "Ukraine reports its first outbreak of African swine fever". Bloomberg. 2012-08-02. Retrieved 2014-01-27.
- "Russia bans hogs and pork from Belarus on African swine fever". Bloomberg. 2013-07-08. Retrieved 2014-01-27.
- African swine fever in the Russian Federation: risk factors for Europe and beyond, Food and Agriculture Organization, Rome, May 2013. Retrieved: 12 August 2015.
- "«Уберечь животных вы не сможете»". Новая газета - Novayagazeta.ru (in Russian). Retrieved 2018-09-05.
- Россельхознадзор запретит ввоз свинины из Литвы из-за АЧС в ближайшее время [Rosselkhoznadzor bans the import of pigs from Lithuania immediately on account of ASF] (in Russian). Russia. ITAR-TASS. 2014-01-24. Retrieved 2014-01-26.
[...] глава ветеринарно-пищевой службы Литвы Йонас Милюс представил российской стороне факты о том, что у двух диких кабанов на территории страны был выявлен вирус АЧС, который стал причиной их гибели [...]
- "Latvia extends emergency zone for African swine fever". terradaily.com. AFP. 2014-07-22. Retrieved 2014-07-28.
[...] Latvia on Tuesday declared a state of emergency in a second area of this Baltic EU state as efforts continued to contain an outbreak of deadly African swine fever in its pig population.[...] Straujuma blamed wild boar crossing in from Russia for Latvia's first-ever outbreak of the disease, detected on June 26. In July, 3 farms discovered African swine fever in Estonia. [...]
- African swine fever spreads to farmed pigs, 500 animals to be exterminated, Estonian Public Broadcasting, Tallinn, 21 July 2015. Retrieved: 12 August 2015.
- Close to 23,000 pigs killed as African swine fever ravages Estonian farms, Estonian Public Broadcasting, Tallinn, 21 July 2015. Retrieved: 12 August 2015.
- Farms in three regions have all reported outbreaks., Pork Network, 20 January 2017. Retrieved: 21 March 2017.
- Latvia declares African swine fever emergency, Watt Ag Net, 23 January 2017. Retrieved: 21 March 2017.
- Another massive pig cull required, Public broadcasting of Latvia, 8 February 2017. Retrieved: 21 March 2017.
- ASF first time recorded in Czech republic - official report in Czech language. ASF first time recorded in Czech republic - machine translation. The most recent information about the ASF in Czech republic - Czech language
- Romania battles African swine fever outbreak, DW, 29 August 2018. Retrieved: 03 September 2018
- Bulgaria reports its first outbreak of African swine fever, Reuters, 31 August 2018
- Daily newspaper "L'Avenir du Luxembourg", 15 September 2018.
- Different testimonies on RTBF TV channel, end September 2018.
- Radio channel RTBF "La Première", 4 october 2018.
- "Эпизоотическая ситуация в Российской Федерации 2007-2018: 1367 случаев" (PDF). www.fsvps.ru.
- "Вспышки АЧС зарегистрированы в четырех регионах России". Российская газета (in Russian). 2017-12-18. Retrieved 2018-09-05.
- "В Омской области снят карантин по африканской чуме свиней". ТАСС. Retrieved 2018-09-05.
- "В Брянской области сняли карантин по АЧС | Наш Брянск·Ru". news.nashbryansk.ru (in Russian). Retrieved 2018-09-05.
- "Карантин ввели в Свердловской области из-за вируса АЧС". Известия (in Russian). 2018-08-01. Retrieved 2018-09-05.
- "Карантин по АЧС в Воронежской области отменен досрочно". 2017-10-23. Retrieved 2018-09-05.
- China culls 900 pigs after reports of first African swine fever outbreak in country.
- "China says has culled over 38,000 hogs due to African swine fever". Channel NewsAsia. Retrieved 2018-09-03.
- Pig Progress, overview of ASF outbreaks and transport bans in China.
- "African swine fever hits huge, foreign-invested Chinese farm". Reuters. 2019-01-03. Retrieved 2019-01-03.
- Ze Chen, Xiaofeng Xu, Xiaojun Yang, Weihao Dou, Xiufeng Jin, Haishuo Ji, Guangyuan Liu, Jianxun Luo, Hong Yin, Gao Shan. DNA segments of African Swine Fever Virus detected for the first time in hard ticks from sheep and bovines. bioRxiv, 2018: 485060; doi: https://doi.org/10.1101/485060
- Feorino, P.; Schable, G.; Schochetman, G.; Jaffe, H.; Curran, J.; Witte, J.; Hess, W. (1986). "Aids and African Swine Fever Virus". The Lancet. 328 (8510): 815. doi:10.1016/S0140-6736(86)90339-9.
- Europe's farmers on red alert as deadly African swine fever spreads to Belgium.
- CFIA Animal Disease Information
- European Commission
- World Organisation for Animal Health (OIE)