My comments on the spreading of African Swine Fever in Asian countries have largely been on the market perspective – what the virus means for the global pork supply, consumer prices, etc. But I have noticed that some readers were concerned about the human health implication of this virus. Although I had, from time-to-time, heard from the folks in the pork industry and researchers that it poses no risk as best as I can tell from the evidence, I’m no expert on this matter.

So, I decided to ask Dr Peter Evans, a veterinarian and animal production specialist, to paint for us a basic picture of the African Swine Fever, guided by these questions:

  • What is the African Swine Fever?
  • Does it present any health risk to humans?
  • How does it spread, specifically in South Africa?

Here are Peter’s viewpoints undiluted:


SALIENT FACTS: African Swine Fever

Written By: Dr Peter Evans.

Introduction

African Swine Fever (ASF) is a severe, highly contagious haemorrhagic disease of pigs, caused by a DNA virus for which there is no vaccine or treatment. ASF occurs in most Asian countries, Sub-saharan African countries, Sardinia, Eastern Europe and Belgium (Central Europe).

For many years the occurrence of African Swine Fever in the RSA was limited to a control zone in the Northern parts of South Africa (includes Limpopo Province, the northern area of North West province and Mpumalanga, roughly following a line of latitude running through Bela Bela). Unfortunately, isolated cases of ASF have occurred outside of the control zone, namely:

  • 2012 in Western Mpumalanga /Eastern Gauteng;
  • 2016 in North West Province, 2017/8 in Freestate / Northern Cape
  • and in 2019 re-occurrence in Western Mpumalanga, Gauteng including the Eastern Freestate.

Primarily the cases were found in communal farming set-ups and some individual farmers who had bought pigs at auction yards. There have been no cases on commercial pig farms related to these mini-outbreaks.

Public Health

African Swine Fever does not affect humans at all. Meat from infected pigs will cause no harm or disease to humans.

All pigs are inspected at registered abattoirs and any animals showing signs of fever or other diseases will not be passed fit for human consumption.

Transmission /Epidemiology

Transmission of ASF to pigs in RSA is from warthogs in the control zone. The infection occurs either via tampans (soft ticks) which become infected when they feed on, especially young, warthogs who are infected with ASF virus and then pass it onto the next warthog or domestic pig at their next feed; or domestic pigs can become infected by being fed meat or offal from infected warthogs and/or other pigs that have died from ASF. The transmission cycle through wild pigs is commonly known as the sylvatic cycle.

In some parts of the world a “Domestic cycle” occurs where domestic pigs become carriers of the disease and become the reservoir. At present, there is no evidence that there is a domestic cycle within the borders of South Africa.

What is evident though in South Africa is that the “uncontrolled” movement of pigs including the trading through auctions is a major transmission risk.

ASF virus is resistant to a wide range of pH’s, resistant to freeze/thaw cycles and can remain infective for many months at room temperature. ASF virus in body fluids can only be inactivated if heated to 60°C for more than 30 minutes but in infected meat need to heat to 70°C for more than 30 minutes. The survivability of the ASF virus means that all tissue, fluids, faeces or any other fomites can easily transmit the disease long after all ASF infected pigs have died. Biosecurity and proper disinfection are required to prevent spreading the infection from an infected site to new sites.

Clinical findings

Acute disease is characterised by a short incubation period of 5-7 days followed by high fever and death within 7 to 10 days. Gross symptoms include loss of appetite, depression and recumbency. Often reddening of the skin and bleeding from nose or anus may be seen. Post mortem findings include haemorrhages in most organs including lymph nodes.

Mortality ranges from 30% for some less virulent genotypes to 100%. In outbreaks and especially where a domestic cycle does not exist generally mortalities are 100%.

Control and Prevention

Due to the persistence of the ASF virus, successful eradication procedures include culling, appropriate disposal of the carcasses and thorough decontamination (=cleaning and disinfection) of the infected premises.

All measures need to be taken to ensure that infection is not spread by contaminated clothing, vehicles or equipment.

 

References

  1. National Centre Biotechnology Information:
    https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5454416/
  2. Merck Veterinary Manual (10th Edition) Pages 645-647.
  3. World Organisation for Animal Health (OIE): –
    http://www.oie.int/en/animal-health-in-the-world/animal-diseases/african-swine-fever/#A
  4. Penrith ML, Vosloo W: REVIEW OF AFRICAN SWINE FEVER: TRANSMISSION, SPREAD AND CONTROL

Follow me on Twitter (@WandileSihlobo). E-mail: wandile@agbiz.co.za

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