Risk factors for the spread of African Swine Fever in China: A systematic review of Chinese-language literature.

African Swine Fever Virus (ASFV) is a contagious pathogen that can cause severe acute haemorrhagic fever in pigs. The first occurrence of an ASF outbreak in Asia was reported in China in August 2018. The devastating impacts caused by ASF on the pig industry have strongly focused research on risk factors for the spread of ASFV. The purpose of this systematic review was to identify the potential knowledge gap in the English literature on risk factors for the spread of ASFV in outbreaks that occurred in China, 2018-2020. China National Knowledge Infrastructure (CNKI) was searched as the primary database. Sixty-four records were screened, and 31 (48%) records were included in data extraction. These records were also assessed for quality of evidence. Frequency tables for reported risks were created, considering quality of evidence. A narrative summary of mortality rate and case fatality rate reported in a small number of records was made. Mortality rate was reported in seven studies, ranging from 3.7% to 84.0% (median 11.9%). Case fatality rate was reported in six studies, ranging from 20.6% to 100% (median 63.3%). Based on 31 reviewed records, live pig transport, swill feeding and vehicles were the three most important risks for spread contributing to the ASF epidemic in China. Bites of infected Ornithodoros ticks was stated in 12 low level of evidence records but only 1 high level of evidence record as a risk factor for transmission. Direct contact with wild pigs was reported to be a risk factor in 8 records with low level of evidence, and 1 record from the high level of evidence group. However, limited evidence was provided to support the tick-domestic pig or wild pig-domestic pig transmission routes in China. Lack of resources to obtain veterinary assistance and to improve husbandry and biosecurity was mentioned four times in the 31 records, especially in remote rural areas. In conclusion, to effectively control the spread of ASF, it is very important to reduce mechanical dissemination of ASFV by vehicles and live pig transport involved in the production cycle and to ensure that transported pigs are always subject to inspection and quarantine. Additionally, despite strict implementation of prohibition on swill feeding often being impractical or nearly impossible, ensuring the safety of pig feed can greatly contribute to disease prevention. Improvement in biosecurity management, specifically environment disinfection, carcass disposal, and decontamination of vehicles and personnel will be most effective in reducing the risk of infection in small-scale pig farms.