George Charbonneau from South West Ontario Veterinary Services, ASFV : Surviving In The Forest

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African swine fever (ASF) is highly contagious and virulent disease with very high mortality in both domestic pigs and wild boar. Normally having a fast onset of disease with high mortality in infected animals is not a great recipe for virus survival in a population. If the virus kills off its hosts too quickly it will normally have fewer places to survive and propagate. One trick that ASF has is its incredible ability to survive in the environment. The virus is infectious for up to 11 days in faeces, 15 weeks in chilled meat, > 15 weeks in frozen meat and 3 to 6 months in cured hams that have not reached high-temperature during processing. Not a great trick, however, to survive in a fridge or a freezer. Would ASF fair as well in more natural conditions in a forest? To answer this question researchers first needed to determine if live pigs would be interested in the rotting carcass of ASF affected mortalities. A group of researchers placed wild boar carcasses in the forest and monitored the decomposing carcasses over time to see if cannibalism by other pigs occurred. Direct contact occurred in 81% of the recorded visits and cannibalism was observed in 9.8% of all recorded visits. Cannibalism was not detected until the carcasses had been in place for 70 days. (Yucky but not necessarily surprising!) Pigs apparently are very interested in these rotting carcasses. This group of researchers wanted to evaluate the survivability of ASF virus (ASFV) in tissues and body fluids from experimentally infected domestic pigs and wild boar, which were stored in different tissues and at different temperatures. Samples were analysed at regular intervals for viral genome and infectious virus. How long would ASFV survive in various tissues?

The researchers found that ASFV could survive for different times based on tissues and temperature:

• In bones
o at -20 °C infectious virus was detected for up to three months
o at 4 °C for up to one month
o at room temperature (RT), no infectious virus could be recovered after one week.
• In skin
o at -20 °C infectious for three months
o at 4 °C infectious for six months
o at RT remained infectious for up to three months.
• In urine and faeces
o no infectious virus was recovered after one week
Take Home Messages:
• ASFV can persist in skin of dead carcasses for three or more months depending on temperature
• Live pigs will be very interested in having direct contact with these carcasses and perhaps consuming some of the carcass.
• Removing the dead pigs from the environment is a very important part of reducing the spread of ASFV.

Submitted by Dr. George Charbonneau

Ref : Melina Fischer , Jane Hühr , Sandra Blome , Franz J Conraths , Carolina Probst Stability of African Swine Fever Virus in Carcasses of Domestic Pigs and Wild Boar Experimentally Infected with the ASFV “Estonia 2014” Isolate Viruses. 2020 Oct 1;12(10):E1118. doi: 10.3390/v12101118.