The 'invincible' virus -African swine fever is ravaging China's pig sector and eliminating it could take decades

 

Meat sweats: Pedestrians walk past a shuttered meat store in Hong Kong, China last week. Hong Kong spotted a second case of African Swine Fever, despite the city’s effort to prevent the spread of the disease that has scuppered China’s pork supply, according to local media reports. Photo: Paul Yeung/Bloomberg
Meat sweats: Pedestrians walk past a shuttered meat store in Hong Kong, China last week. Hong Kong spotted a second case of African Swine Fever, despite the city’s effort to prevent the spread of the disease that has scuppered China’s pork supply, according to local media reports. Photo: Paul Yeung/Bloomberg
Pork cuts: Buyers inspect pig carcasses hanging from a conveyor at a pork wholesale market on Shanghai’s outskirts. Photo: Qilai Shen/Bloomberg

The deadly pig virus that jumped from Africa to Europe is now ravaging China's €113bn pork industry and spreading to other Asian countries; an unprecedented disaster that has prompted Beijing to slaughter millions of pigs. But stopping African swine fever isn't so easy.

The virus that causes the disease is highly virulent and tenacious, and spreads in multiple ways. There's no safe and effective vaccine to prevent infection, nor anything to treat it.

The widespread presence in China means it's now being amplified across a country with 440m pigs - half the planet's total - with vast trading networks, permeable land borders and farms with little or no ability to stop animal diseases.

The number of pigs China will fatten this year is predicted to fall by 134m, or 20pc, from 2018 - the worst annual slump since the US Department of Agriculture (USDA)began counting China's pigs in the mid-1970s. While the pig virus doesn't harm humans even if they eat tainted pork, the fatality rate in pigs means it could destroy the region's pork industry.

Sanitary measures

Spain's experience with the disease suggests that a cull alone won't be enough to solve the problem. The country implemented strict sanitary measures and industrialised its pig production system but it took 35 years and help from the EU before the disease was eradicated in 1995. The Italian island of Sardinia has been trying unsuccessfully to get rid of the virus for four decades, and its pig population is a fraction of China's.

Scientists say the virus may have arrived in China the same way it entered Europe in early 2007. A United Nations report suggests some food-waste containing pork was dumped from a ship visiting the port of Poti on the Georgian Black Sea and then eaten by one of the local pigs that are allowed to scavenge on garbage.

Waste disposal units

Within weeks, 30,000 pigs had died and 80pc of Georgia's districts were thought to be infected. Pigs and their feral wild-boar cousins are quintessential waste disposal units, guzzling on protein from a wide variety of sources, including kitchen scraps, manure and dead hogs.

While the omnivorous nature of the animals makes them low-cost nutrient converters, it's also a key reason that African swine fever spreads easily.

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A review of outbreaks showed that almost half were caused by the spread of virus material on vehicles and on non-disinfected workers, with feeding pigs contaminated swill or food scraps the second-biggest source.

Feeding raw swill to pigs has been outlawed in China because of the risk of disease transmission, but clandestine use of non-heat-treated restaurant and household waste is reported to persist among suburban and smallholder farmers.

So far, government efforts to halt the spread through quarantining and sanitising infected farms, culling vulnerable pigs, closing markets and restricting animal movements have been insufficient, and the disease has become entrenched across the country.

Identifying outbreaks early is critical for mitigating their spread. The Chinese government has pledged to pay a subsidy of 1,200 yuan (€150) per pig to compensate farms for losses, but some local governments are reported to be withholding payments - removing an incentive for farmers to report the disease. In some instances, individuals have even been punished for publicising outbreaks. A pig-farm manager in Shandong province was allegedly arrested for reporting infected pigs to the national government after his efforts to alert local officials were ignored.

Saturated blood

The virus, though, doesn't need travelling swine to spread. A single drop from an acutely infected pig can contain 50m virus particles, and just one of those particles ingested in contaminated drinking water may be enough to transfer the disease to another pig.

Infected blood, or fluids from urine, saliva or faeces, can be carried on truck tyres and shoes, allowing the disease to travel hundreds of miles quite rapidly. Tens of thousands of swine have been infected in China and their carcasses represent an enormous environmental risk, requiring careful handling and disposal.

In Romania, the contamination of the Danube River from dead hogs was implicated in the virus's spread to a 140,000-pig farm.

Fifty years on, the quest for a vaccine continues

After 50 years of research, scientists haven't managed to develop a vaccine that's safe and effective against African swine fever, and even if recent research proves fruitful, it could be years before an effective shot becomes commercially available.

One of the earliest attempts - based on a live, weakened form of the virus - was abandoned after it was found the vaccine gave pigs a debilitating and disfiguring disease.

Studies have found that the animals which recover from an initial African swine fever infection are resistant to some other strains, but scientists aren't sure what exactly confers that protection or how best to evaluate the potential efficacy of candidate vaccines.

One of their difficulties is that the large, complex DNA virus that causes African swine fever has some 170 genes and 80 proteins, many of them specialised in evading different aspects of the pig immune system.

More recent attempts to produce an immunisation using viruses that lack key disease-causing genes appear to be safe.

Still, researchers are yet to carry out large field trials to demonstrate effectiveness in commercial farms - a necessary step for gaining regulatory approval. That may delay the availability of game-changing vaccines for years.

With a tough virus to eradicate and no vaccine on the horizon, the best way China can protect its domestic pork industry from African swine fever is to carefully monitor and control the germs on every pig, person and product entering and leaving farms.

That would mean turning China's 26 million piggeries into veritable biocontainment facilities.

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