Strong biosecurity can mitigate African Swine Fever Virus

The recent discovery and subsequent spread of African Swine Fever (ASF) in one of largest swine operations in Romania (a 140,000 swine complex) is opening the eyes of epidemiologists in terms of the potential routes of contamination and spread of this virus.

It’s known that there are two most-common ways for viruses to spread. The first is direct contact with infected animals or the consumption of contaminated food. The latter most often happens because using by-products as an ingredient in feed is a common practice in swine backyard operations. These happened with a 1978 ASF index case occurring in Brazil, in which food waste from a Portuguese airline was used to feed pigs on a farm near the airport in Rio de Janeiro.

The second common cause is when raw swine products that have not been temperature-treated or even cooked hit the market.

Indirect transmission can happen when garbage containing infected meat is introduced to food or feed; through fomites like premises, vehicles, implements, and clothes; or through biological vectors such as soft ticks. The sources of the virus are blood, tissues, secretions and excretions of sick and dead animals; carrier animals (especially African wild swine and domestic pigs in enzootic areas) and soft ticks.

As with any pathogen, biosecurity and careful sanitation is key to preventing the spread. The ASF virus is susceptible to 2% citric acid (ideal over high porous surfaces), 2,000 parts per million (ppm) sodium hypochlorite and 1% Ca(OH)2 with 30 minutes of exposure. The virus is highly resistant to inactivation in the environment in the presence of organic matter. It persists for long periods of time in infected material and tissues: up to 15 weeks in putrefied blood, up to 11 days in feces kept at room temperature and up to 1,000 days in frozen meat.

This virus can remain in the environment for long periods of time. Critical components of its dissemination are dead animals, carcasses of infected pigs, and cooked or cured pork from endemic areas. The disposal of these potential virus sources is critical. Disposal is best performed by following specific standard operating procedures for incineration, under watertight well-structured pits that can prevent contamination and provide appropriate coverage. People involved should wear personal protective equipment.

Even though there are ASF virus strains with high virulence and high levels of contamination, past outbreaks in large commercial operations have indicated that some strains could have low to moderate pathogenicity, even if a farm is in close proximity to potential exposure points, like wild boars or employees hunting over areas where wild boars may be present. Veterinarians should rule out the ASF virus with any abnormal rise of mortality and clinical signs that may correspond to any other fever-causing bacteria or systemic viruses associated with hemorrhages on the skin.

Feed ingredients have not been associated in the past with any index case for ASF, but based on preliminary studies, we can say that a risk may exist. In one study, transit conditions of overseas feed shipments were reproduced in a laboratory, meant to mimic shipments of ingredients that are regularly imported to the U.S. from current ASF-endemic countries. These ingredients were spiked with a known amount of ASF virus, which was able to survive the simulated transport conditions, which included changes in temperature and humidity.

Biosecurity at the farm level remains a key component to reduce and prevent the exposure of commercial animals to the normal virus ecologies that persist in populations of wild boars and soft ticks. When farmers, swine farm workers or swine veterinarians travel to farms in endemic areas, they must take extra precautions; such as wearing unique shoes (like Crocs, etc.) during transport from, for example, a hotel to a farm, with those shoes remaining in the endemic country and not being brought back in luggage. People are the most critical component of virus dissemination in endemic areas, and the virus persists much better with the help of organic matter.

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