Abstract
ABSTRACT African swine fever (ASF) entered China in August 2018 and rapidly spread across the entire country, severely threatening the Chinese domestic pig population, which accounts for more than 50% of the pig population worldwide. In this study, an ASFV isolate, Pig/Heilongjiang/2018 (Pig/HLJ/18), was isolated in primary porcine alveolar macrophages (PAMs) from a pig sample from an ASF outbreak farm. The isolate was characterized by using the haemadsorption (HAD) test, Western blotting and immunofluorescence, and electronic microscopy. Phylogenetic analysis of the viral p72 gene revealed that Pig/HLJ/18 belongs to Genotype II. Infectious titres of virus propagated in primary PAMs and pig marrow macrophages were as high as 107.2 HAD50/ml. Specific-pathogen-free pigs intramuscularly inoculated with different virus dosages at 103.5–106.5 HAD50 showed acute disease with fever and haemorrhagic signs. The incubation periods were 3–5 days for virus-inoculated pigs and 9 days for contact pigs. All virus-inoculated pigs died between 6–9 days post-inoculation (p.i.), and the contact pigs died between 13–14 days post-contact (p.c.). Viremia started on day 2 p.i. in inoculated pigs and on day 9 p.c. in contact pigs. Viral genomic DNA started to be detected from oral and rectal swab samples on 2–5 days p.i. in virus-inoculated pigs, and 6–10 days p.c. in contact pigs. These results indicate that Pig/HLJ/18 is highly virulent and transmissible in domestic pigs. Our study demonstrates the threat of ASFV and emphasizes the need to control and eradicate ASF in China.
Highlights
African swine fever (ASF) is one of the most serious viral diseases affecting pigs
To assess the viral growth dynamics, primary porcine alveolar macrophages (PAMs) were infected at a multiplicity of infection (MOI) of 0.2, and the cell supernatants were collected at different times post-infection for viral genome quantification by quantitative PCR (qPCR) targeting the p72 gene [10]
The virus belongs to Genotype II and is genetically close to African swine fever virus (ASFV) prevalent in Eastern Europe; it replicated efficiently in primary PAMs and its viral titre reached
Summary
African swine fever (ASF) is one of the most serious viral diseases affecting pigs. It is listed as a “notifiable disease” by the World Organization for Animal Health (OIE), in part because of its high mortality rate. ASF is caused by African swine fever virus (ASFV), which belongs to the genus Asfivirus within the Asfarviridae family [2,3]. In the 1950s, ASFV rapidly spread throughout Europe, including Spain, Portugal, Italy, and France, and was eradicated from these countries, with the exception of Sardinia, by the mid-1990s [6]. The virus has continued to spread worldwide, and has been reported in 37 countries or regions. In 2018, at least four countries, including Hungary, Bulgaria, Belgium, and China, reported their first ever ASF outbreaks to the OIE (http://www.oie.int/)
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