The HPAI subtype H5N8 virus very probably originated in China, where the virus was already isolated in 2009-2010 as part of a monitoring programme among evidently healthy ducks in live poultry markets (Zhao et al., 2013). Pathogenicity studies showed that the virus was highly virulent for chickens, but mildly to moderately virulent for wild ducks.
HPAI subtype H5N8 uitbraken in de wereld
Phylogenetic research demonstrated that the virus was the product of various reassortment events: the hereditary material (RNA) of the virus consists of segments that come from other influenza viruses. The backbone of the HPAI subtype H5N8 virus is formed by parts of the Asian HPAI subtype H5N1 virus that has already circulated in China since 1997 and, since 2004, has spread widely to South-East Asia, the Middle East, parts of Africa and also to Europe.
According to the most recent data of the World Health Organization (27 July 2014), the H5N1 virus infected 667 people in 16 countries, ultimately resulting in 393 fatalities (source: WHO).
From January 2014 the HPAI subtype H5N8 virus spread very rapidly in South Korea, initially mainly among farm ducks. At the time of the first outbreaks among farm ducks, a large number of dead Baikal teals (Anas formosa) – a species of migratory ducks – were found near the affected farms, leading to the hypothesis that the infection may have been carried by the migratory ducks (a spill-over in the opposite direction cannot be ruled out: wild ducks were infected by a massive circulation of the virus among farm poultry). Genetic sequence analysis indicated that isolates of infected farm ducks in South Korea and dead Baikal teals in the surrounding area strongly resembled the earlier Chinese isolates (Lee et al., 2014), whilst it was also noted that the isolates of the HPAI subtype H5N8 virus in South Korea is a product of reassortment of A/duck/Jiangsu/k1203/2010 (H5N8) and other avian influenza virus subtypes that co-circulated in birds in East Asia from 2009 to 2012 (Gu et al., 2013).
In the summer and extending into September 2014, outbreaks of the HPAI subtype H5N8 virus among farm poultry were reported in South Korea. Kang et al. (2014) very recently demonstrated in a pathogenicity study into various HPAI subtype H5N8 viruses that the virus was moderately virulent in infection trials with wild ducks (Anas platyrhynchos) and Baikal teals (Anas formosa): no mortality and no serious disease. Virus replication and virus excretion was higher in H5N8-infected ducks than in H5N1-infected ducks ((Anas platyrhynchos). Domesticated ducks (Pekin duck) did become seriously ill and some animals died.
Recent phylogenetic studies into HPAI subtype H5H8 viruses isolated among infected poultry and caught from wild birds in 2014 in South Korea indicate that migrating birds played a key role in the introduction and spreading of the virus in the initial phase of the 2014 outbreak (Jeong et al., 2014).
In mid-April 2014 the presence of the HPAI subtype H5N8 virus was demonstrated at a poultry farm in Japan, where the alarm was raised after a strong rise in mortality rates was noted. Virus introduction hypothesis: migratory waterfowl from South Korea. The outbreak was rapidly brought under control.
During a monitoring operation early in November 2014, faecal samples of migrating Bewick’s Tundra swans (Cygnus columbianus bewickii) tested positive for the HPAI subtype H5N8 virus. Bewick’s Tundra swans are usually found in the Palaearctic habitat zone, such as in Asia, Europe, North Africa and the Arabian Peninsula. This swan breeds in Siberia and flies in September to its wintering grounds, including the British Isles, Denmark and the Netherlands (source: http://www.animalspot.net/).
In late October 2014 China reported several positive HPAI subtype H5N8 virus isolates in samples obtained for monitoring purposes (ProMed, 2014).
On 6 November 2014 Germany reported an outbreak of the HPAI subtype H5N8 virus in turkeys. One of the 5 stalls at a meat turkey farm was hit by exponentially rising mortality rates, after which the alarm was raised. Genetic testing of the virus by the German Friedrich Loeffler Institute indicated that this H5N8 virus showed a strong similarity with viruses isolated earlier in 2014 in South Korea, China and Japan.
Gu M, Zhao G, Zhao K, Zhong L, Huang J, Wan H, et al. Novel variants of clade 2.3.4 highly pathogenic avian influenza A(H5N1) viruses, China. Emerg Infect Dis. 2013;19:2021-2024.
Jeong J, Kang H-M, Lee E-K, Song B-M, et al. Highly pathogenic avian influenza virus (H5N8) in domestic poultry and its relationship with migratory birds in South Korea during 2014. Vet Microbiol 2014; 173: 249-257. http://dx.doi.org/10.1016/j.vetmic.2014.08.002
Kang HM, Lee EK, Song BM, Jeong J, Choi JG, et al. Novel reassortant influenza A(H5N8) viruses among domestic and wild ducks, South Korea. Emerg Infect Dis. ahead of print, February 2015 [accessed 16 Nov 2014) http://dx.doi.org/10.3201/eid2102.141268
Lee YJ, Kang HM, Lee EK, Song BM, Jeong J, Kwon YK, et al. Novel reassortant influenza A(H5N8) viruses, South Korea, 2014. Emerg Infect Dis 2014; 20(6): 1087-1089. http://wwwnc.cdc.gov/eid/article/20/6/14-0233_article
ProMED-mail. Avian influenza (78): China, poultry, HPAI H5N3, H5N8, H5N1, OIE. ProMED-mail 2014; 26 Oct: 20141026.2898069 http://www.promedmail.org. Accessed 16 November 2014.
Zhao K, Gu M, Zhong L, Duan Z, Zhang Y, Zhu Y, et al. Characterization of 3 H5N5 and one H5N8 highly pathogenic avian influenza viruses in China. Vet Microbiol. 2013; 163(3-4):351-7. http://dx.doi.org/10.1016/j.vetmic.2012.12.025