African swine fever (ASF) is a devastating and economically significant infectious disease that has caused enormous losses in the commercial pig sector in China since 2018. The primary transmission routes of the African swine fever virus (ASFV), the causative agent of ASF, are direct pig-to-pig contact or indirect contact with virus-contaminated objects. While aerosol transmission of ASFV has been previously reported under experimental conditions, no reports have described it under field conditions. In this case study, aerosol-associated samples were collected over a monitoring period of 24 days in an ASFV-positive farm. A complete and clear chain of ASFV transmission through aerosols was observed: pigs in Room A on Day 0-aerosol in Room A on Day 6-dust of air outlets in Room A on Day 9-outdoor aerosols on Day 9-dust of air inlets in Room B on Day 15-aerosols/pigs in Room B on Day 21. Furthermore, a fluorescent powder experiment confirmed the transmission of dust from Room A to Room B. This study represents the first report providing evidence of aerosol transmission of ASFV under field conditions. Further research is needed to study the laws of aerosol transmission in ASFV and develop effective strategies such as air filtration or disinfection to create a low-risk environment with fresh air for pig herds.

IntroductionPorcine circovirus type 2 (PCV2) is the primary etiological agent of porcine circovirus diseases (PCVD), which are widespread in most pig herds, causing huge economic losses in the global pig industry. Therefore, it is critical to assess the infection characteristics of PCV2 in different swine herds to develop effective strategies against PCVD.MethodsIn this study, routine diagnostic and monitoring protocols were used to collect 12,714 samples from intensive farms in China, and PCV2 was tested for by qPCR to determine positivity rates and viral loads in samples from different herds and materials.ResultsPCV2 was found to be prevalent throughout China, and fattening farms had higher positivity rates than breeding farms. The PCV2 positivity rates in breeding farms in Southern China were higher than those in Northern China. Growing–finishing pigs demonstrated the highest positivity rate in the tested samples, while pre-weaning piglets and adult sows had the lowest. Meanwhile, samples with viral loads exceeding 106 copies/mL in growing–finishing pigs had 27.2% positivity, compared to 1.9% and 3.3% in sows and piglets, respectively. The results of the viral loads in the serum samples followed a similar trend.DiscussionThe findings reveal that PCV2 circulates in different herds from intensive farms, with positivity increasing from pre-weaning to growing–finishing herds. It is urgent to develop effective strategies to reduce PCV2 positivity in growing–finishing herds and prevent viral circulation among pigs.

BackgroundAfrican swine fever (ASF) is a devastating and economically significant infectious disease and has caused huge losses in the commercial pig sector in China since 2018. The major transmission route of African swine fever virus (ASFV), the causative agent of ASF, is direct pig-to-pig contact or indirect contact with virus-contaminated objects. Although aerosol transmission route of ASFV has been reported under experimental conditions previously, whereas no reports described under field conditions.Case presentationIn the three ASFV-positive piggeries, environmental samples, including floors, aerosols, dusts and air outlets, tested positive in the monitoring period. Aerosol and floor samples always tested positive firstly at the same time. ASFV-positive aerosols were associated with live ASFV-positive pigs in piggeries. Dust and air outlet samples remained positive for several days after all positive pigs were eliminated, and the times of positive and persistent positive of dust and air outlet samples were always close.ConclusionsThis is the first report to provide some evidence of airborne transmission route of ASFV in field piggeries, and more research is needed to study aerosol-spread laws of ASFV under field conditions, assess the risk of ASFV aerosol transmission, and develop effective strategies for air disinfection to create low-risk fresh air for pig herds.

Background Since the first report of ASFV in China in 2018, conventional whole herd depopulation method to control ASF has proved unwieldly because of high production intensity and complex trade network. To provide an alternative to conventional methods, we evaluated the feasibility of implementating an extensive sampling method and qPCR tests to determine the status of ASFV in herds, with a rapid response to identified outbreaks. Case presentations By assessing and applying these methods without whole herd depopulation, we successfully controlled ASF and eliminated the virus from 4 large swine herds. The time to negative herd was 19, 28, 14, and 1 days in farms 1-4 respectively. Retention rates of pigs of farm 1 to farm 4 was 69.7% , 65%, 99.4% and 99.72% respectively.Conclusions We anticipated that this innovative method would replace the conventional stamping out one and greatly facilitate the control and eradication of ASFV in China and worldwide.