As autumn and winter arrive, the pressure to prevent and control African swine fever rises sharply. In 2025, the global ASF epidemic showed a clear upward trend. A cumulative total of 8181 outbreaks were reported from 1-9, affecting nearly 38.2 ten thousand pigs. Outbreaks remained frequent from 10-11. Although the overall situation in China is under control, the risk of transmission in autumn and winter must not be overlooked. More troublingly, currently circulating attenuated strains cause atypical clinical symptoms, making visual identification virtually impossible. Many pig farms experience sudden outbreaks when “everything seems normal.”
Preventing and controlling ASF in autumn and winter is not about relying on a single technique or a particular drug. It depends on systematic capabilities across the entire chain—from disinfection to biosecurity, and from herd management to monitoring and early warning. No link in the chain can be allowed to fail.
I. First, understand: Why is autumn and winter a “high-risk window” for ASF?
The winter peak in African swine fever cases is no coincidence; it results from the combined effects of viral characteristics, herd condition, and environmental management.
The virus “survives longer” at low temperatures. African swine fever virus is highly tolerant of low temperatures and can survive for 60 to 1000 days in materials such as soil, feed, and transport equipment. Low temperatures further extend its survival time. This means that once contamination occurs in winter, the risk of the virus persisting for an extended period around the farm increases significantly.
Cold weather “takes a toll on the herd’s resistance.” Prolonged cold stress places a heavy burden on pigs. They need to use a large amount of energy to maintain their body temperature, leaving relatively fewer nutrients available to the immune system. As a result, their overall resistance declines, leaving them in a more susceptible, “subclinical” state.
The conflict between insulation and ventilation creates gaps in prevention and control. In winter, pig farms generally increase enclosure to retain heat. However, poor ventilation raises ammonia and dust concentrations inside the barns, continuously damaging the pigs’ respiratory mucosal barrier and further weakening local immunity. Meanwhile, low temperatures also make routine disinfection more difficult in practice: disinfection pools may freeze and disinfectants may become less effective. If management is lax, it is easy for blind spots to remain.
Disinfection efficacy falls off a cliff at low temperatures. Studies show that when the temperature drops from 20℃ to 0℃, the bactericidal efficacy of most disinfectants decreases by more than 50%. If a pig farm is still using its summer disinfection protocol, it is effectively “disinfecting in name only.”
II. Disinfection: The First Critical Line of Defense in Winter
Winter disinfection is the most critical—and also the most error-prone—part of African swine fever prevention and control. The core principle is to select disinfectants based on temperature and disinfection methods based on the situation.
Select disinfectants by area. When the temperature outside the housing is above -6℃, a 0.5% glutaraldehyde aqueous solution may be used for disinfection. When the temperature is below -6℃, switch to a disinfectant formulated for low temperatures, such as 0.2%–0.3% sodium dichloroisocyanurate or 0.2%–0.5% potassium peroxymonosulfate compound. For disinfection of the indoor environment, a 0.2%–0.5% potassium peroxymonosulfate compound may be used, but disinfection with pigs present is not recommended in winter and spring.
Prepare disinfectant with warm water. Diluting disinfectant with warm water at 20–30°C not only increases its solubility but also enhances its activity. When the air temperature is below 0°C, add 1%–3% sodium chloride or calcium chloride to the disinfectant solution as an antifreeze to prevent it from freezing.
Choose the right time to disinfect. In winter, disinfect on sunny days between 10 a.m. and 3 p.m., when the temperature is relatively high and conditions are favorable for the disinfectant to work.
Emergency “whitewashing” disinfection. During periods of high epidemic risk, carry out a comprehensive “whitewashing” disinfection once a week, with no areas left untreated. Prepare a suspension using 15%–20% lime milk and 2%–3% caustic soda solution. This makes it possible to visually identify missed areas while also extending the disinfectant’s contact time.
Do not skip disinfecting supplies. Once supplies arrive, allow them to return to room temperature before disinfection. Give priority to drying disinfection (maintain at 60–70°C for 30 minutes). For supplies that cannot be dried, prepare disinfectant with 25°C warm water and soak them for at least 30 minutes.
Three. Biosecurity: Keep the Virus Out
The ironclad rule for African swine fever prevention and control is: no contact, no infection. In winter, the four checkpoints—people, vehicles, items, and pigs—must be strictly controlled.
Personnel management is the top priority. For 3 days before entering the facility, personnel must not visit high-biosecurity-risk locations such as pig farms, slaughterhouses, or farmers’ markets. On-site personnel should have fixed duties and minimize movement between pig houses. Essential outside personnel must follow a three-stage showering procedure—change clothes once, shower, then change clothes again—with dedicated supervision throughout and restricted movement within the facility after entry. Personal items such as mobile phones may be brought in only after being wiped with 75% alcohol.
Vehicle management follows a closed-loop control process. Transport vehicles are dedicated to specific uses and may only be used after coarse washing, soap washing, thorough washing, draining, disinfection, drying, and passing inspection. In cold weather, switch to a low-temperature disinfectant. Feed-delivery vehicles unload at designated points outside the site. Loading and unloading of pigs leaving the site take place outside the site at a dedicated pig-loading platform. All outside vehicles are prohibited from entering the site.
Pig herd management should focus on “building resilience and screening early.” Introduced pigs must undergo three tests (before introduction, 1 weeks; after arrival, 1 weeks; before joining the herd, 1 weeks). In northern regions, it is recommended to introduce a sufficient number of replacement pigs in a single batch before month 11 each year, and not to introduce any more pigs from 3 to 4 of the following year, thereby minimizing the risks associated with introducing pigs. For feeding, adjust the diet to increase energy intake, mix feed with warm water and provide warm drinking water, and do not feed moldy feed.
The handling of pigs that die or are euthanized due to illness must be carried out properly. They must be placed immediately in a refrigerated, sealed temporary storage area that prevents seepage and leakage. Dedicated vehicles operated by a qualified harmless-treatment facility must be contracted to transport them off-site. After treatment, thoroughly disinfect the site and tools. Selling or arbitrarily discarding them is strictly prohibited.
Four. Monitoring and Early Warning: A New Challenge in the Era of Low-Virulence Strains
The greatest challenge in African swine fever prevention and control today is no longer highly lethal, virulent strains, but the covert spread of low-virulence variants. Infection with low-virulence strains causes atypical clinical symptoms. Pregnant sows may show only recurrent fever and loss of appetite, while finishing pigs show almost no obvious symptoms in the absence of stress. Detecting an outbreak through visual inspections alone is extremely difficult.
This means pig farms must establish an active surveillance system centered on laboratory testing.
Optimize the surveillance plan. Use nucleic acid and antibody testing in combination, conduct regular environmental testing outside the farm, and test high-risk points inside the farm—such as door handles, fans, and feed troughs—for viral nucleic acid every week. Regularly sample and monitor viral antibody levels in sow and finishing pig groups. During high-risk periods, consider antibody monitoring across the entire sow herd.
Collect samples scientifically. Combining deep pharyngeal swabs with pooled blood samples from the tail base, or combining oral and nasal swabs with pooled samples from inguinal lymph node punctures, can improve pathogen detection rates. Use polypropylene swabs for sampling and avoid cotton products.
Use technology where possible. Farms with the necessary resources can use an infrared body-temperature monitoring system to monitor the temperature of all pigs daily and promptly collect samples for testing if any abnormalities are detected. The minimally invasive sampler and supporting testing method developed by the team led by Li Xiaowen at Liaocheng University can provide an early warning of an outbreak 3 days in advance and accurately identify positive individuals. This “precision culling” technology has been included in the Ministry of Agriculture and Rural Affairs’ Technical Guidelines for the Normalized Prevention and Control of African Swine Fever.
Establish a rapid response mechanism. If a suspected outbreak is detected, immediately report it to the competent authorities and isolate the abnormal pigs at the same time. They must never be housed together with healthy pigs. Once the outbreak is confirmed, take measures as required by the Emergency Implementation Plan for African Swine Fever Outbreaks to prevent the outbreak from spreading.
Five. Herd health: Give pigs the “confidence” to withstand challenges on their own
All preventive measures ultimately depend on the pigs’ overall health. Pigs with strong immunity may avoid infection or develop symptoms later, even if a small amount of virus enters the herd.
Ensure adequate nutrition. Add an appropriate amount of energy to the feed and supplement it with vitamins and probiotics to help the herd cope with stress. Use warm water to mix the feed and provide drinking water, avoiding irritation to the gastrointestinal tract from cold water.
Balance heat retention and ventilation. In winter, pig houses need to strike a balance between retaining heat and ventilation. Suckling piglets and nursery pigs need additional heating equipment, such as infrared lamps and hot-air furnaces, but the pig house must not be completely sealed off for the sake of heat retention. The core approach is “low-volume, continuous ventilation,” using variable-frequency ventilation technology to adjust the airflow in real time according to the ammonia concentration and temperature inside the pig house. Keep the ammonia concentration below 15ppm and the day-to-night temperature difference within 5℃.
Ensure routine immunization. Vaccinate against common diseases such as classical swine fever and pseudorabies according to the established schedule to improve the herd’s baseline health. A healthier herd will also have greater resistance to African swine fever.
Summary
The key to ASF prevention and control in autumn and winter is to build a comprehensive prevention and control system: adapt disinfection to low temperatures, control the movement of people and materials through biosecurity measures, take a proactive approach to monitoring, and maintain the health of the pig herd. In the era of attenuated strains, the greatest challenge is the “invisible enemy.” The naked eye is no longer enough; laboratory testing and the ability to precisely identify and remove infected animals must be established.
With no vaccine yet on the market, biosecurity remains the only effective weapon. Farms need to firmly reject fake vaccines, provide training on prevention and control, and raise all employees’ awareness of disease prevention. Only by controlling the environment, keeping testing up to date, and maintaining the health of the pig herd can farms get through this winter smoothly.