Gert van der Hoek
In Memoriam - Editor, Senior Moderator
ASFv mutation in China: What does it mean on-farm?
How does China’s pig industry deal with the aftermath of African Swine Fever? Although most messages appear to be overly positive, there is also reason to remain vigilant. ASF virus appears to be popping up in a mutated form. Dr E. Wayne Johnson, veterinarian in Beijing, describes what he sees happening on farms.
Most messages about China’s pig industry in 2020 and early 2021 are very positive. Even though the African Swine Fever (ASF) outbreaks of 2019 led to the estimated disappearance of at least 40% of the country’s sow herd, the shortage brought on record prices and profits. A country on the rebound, now swine facilities are built everywhere.
For instance, early December 2020 news agency Reuters sent out an impressive article covering a huge 21 multi-storey building swine farm by Muyuan in Henan province, eventually to be housing 84,000 sows. Yet, does that mean that ASF is something of the past? Officially, it does not seem to be a huge problem. In January 2021, the Chinese Ministry of Agriculture and Rural Affairs (MARA) reported 1 infected farm in Guangdong province with 1,015 pigs. The report before that dates from October 2020.
Variant ASF cases on farms
There are plenty of reasons to believe that the ASF epidemic is far from over in China, that is, if the virus will ever completely disappear. Mid-January, Reuters reported that various variant ASF viruses had been found in China and attributed that to illegal ASF vaccines (see Box). Dr E. Wayne Johnson is a US pig veterinary consultant in Beijing and he confirms coming across one of these variants.
In a correspondence with Pig Progress, he writes: “The ‘new virus’ circulating in China is the double-gene deleted vaccine virus. It lacks safety and its efficacy is not clear. This vaccine has deletions in the MGF360 locus and the CD2v locus which weakens the virus, but does not render it innocuous. It just produces a milder form of the disease.”
Dr Johnson compares the vaccine to a barrow “which has had 2 important things removed”, but can still eat and eat.
Effects of the new virus seen on-farm
According to Dr Johnson, the double gene deleted vaccine produces a PRRS-like viral reproductive syndrome in vaccinated sows, with stillbirths, mummifications, embryonic deaths, infertility, and abortion. He adds there is some apparent mortality as well as transient fever from the vaccine virus itself, but that vaccine-induced mortality is rather low.
Live-born pigs, he says, may be born weak with reduced viability. “Pigs that survive into the grow-finish period appear to shed the vaccine virus and pass it to other pigs. Chronic atypical ASF is the result with chronic blood vessel and immune system disease. Infarcts and thrombi with active zones of necrosis and haemorrhage and chronic lesions with fibrosis are seen in multiple organs microscopically and visibly particularly in the lymph nodes and the kidneys.”
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How does China’s pig industry deal with the aftermath of African Swine Fever? Although most messages appear to be overly positive, there is also reason to remain vigilant. ASF virus appears to be popping up in a mutated form. Dr E. Wayne Johnson, veterinarian in Beijing, describes what he sees happening on farms.
Most messages about China’s pig industry in 2020 and early 2021 are very positive. Even though the African Swine Fever (ASF) outbreaks of 2019 led to the estimated disappearance of at least 40% of the country’s sow herd, the shortage brought on record prices and profits. A country on the rebound, now swine facilities are built everywhere.
For instance, early December 2020 news agency Reuters sent out an impressive article covering a huge 21 multi-storey building swine farm by Muyuan in Henan province, eventually to be housing 84,000 sows. Yet, does that mean that ASF is something of the past? Officially, it does not seem to be a huge problem. In January 2021, the Chinese Ministry of Agriculture and Rural Affairs (MARA) reported 1 infected farm in Guangdong province with 1,015 pigs. The report before that dates from October 2020.
Variant ASF cases on farms
There are plenty of reasons to believe that the ASF epidemic is far from over in China, that is, if the virus will ever completely disappear. Mid-January, Reuters reported that various variant ASF viruses had been found in China and attributed that to illegal ASF vaccines (see Box). Dr E. Wayne Johnson is a US pig veterinary consultant in Beijing and he confirms coming across one of these variants.
In a correspondence with Pig Progress, he writes: “The ‘new virus’ circulating in China is the double-gene deleted vaccine virus. It lacks safety and its efficacy is not clear. This vaccine has deletions in the MGF360 locus and the CD2v locus which weakens the virus, but does not render it innocuous. It just produces a milder form of the disease.”
Dr Johnson compares the vaccine to a barrow “which has had 2 important things removed”, but can still eat and eat.
Effects of the new virus seen on-farm
According to Dr Johnson, the double gene deleted vaccine produces a PRRS-like viral reproductive syndrome in vaccinated sows, with stillbirths, mummifications, embryonic deaths, infertility, and abortion. He adds there is some apparent mortality as well as transient fever from the vaccine virus itself, but that vaccine-induced mortality is rather low.
Live-born pigs, he says, may be born weak with reduced viability. “Pigs that survive into the grow-finish period appear to shed the vaccine virus and pass it to other pigs. Chronic atypical ASF is the result with chronic blood vessel and immune system disease. Infarcts and thrombi with active zones of necrosis and haemorrhage and chronic lesions with fibrosis are seen in multiple organs microscopically and visibly particularly in the lymph nodes and the kidneys.”
READ MORE
