African swine fever: Forgotten contagion

Viruses, it seems, are at war with life forms. While the world is struggling with the novel coronavirus, another one has been killing pigs, decimating the global pork and animal feed trade. African swine fever, a century-old disease that infects pigs and wild boars with a near 100 per cent fatality rate, has claimed a third of the world’s pigs since 2018. Its latest victim is India, where cases have been reported since May 2020 but have exploded in the past couple of months. Since there is no cure or vaccine, the infected animal has to be culled. With most piggeries in Asia being small-scale and the spread of the virus showing no signs of abating, what are the implications for pig farmers and the global trade of the world’s primary source of protein? 

India’s northeastern states account for nearly 47 per cent of the country’s over 9 million pig population. In 2021, African swine fever cases have been reported in Meghalaya, Mizoram, Manipur, Nagaland, Arunachal Pradesh and Assam (Illustrations: Ritika Bohra)

“A BULLET TO the forehead.” In the past few months, pig farmers in Mizoram have come to dread hearing this sentence. But Thanliana and his three sons had little choice. Having lost 308 of their 500-odd pigs to a “fever” since April, they finally informed the state’s Animal Husbandry and Veterinary Department, whose officials visited their piggery in Sateek village, on the outskirts of state capital Aizawl, on June 18. They were accompanied by two armed policemen dressed in personal protective equipment or PPE.

Read: Every Mizoram district feared swept by African swine fever

Veterinary officer Esther Lalzoliani had already identified the pigs’ symptoms as African swine fever (ASF), a viral haemorrhagic disease that is known to infect pigs and wild boars, with a near 100 per cent fatality rate. The infected animals develop fever and their skin turns purple, with watery discharge from the eyes and severe, bloody diarrhoea before death.

With no cure or vaccine, isolation or culling are the only ways to curb the spread of this highly contagious disease which transmits through direct contact with sick animals or from anything contaminated — water, soil, feed, objects like shoes, vehicles and farm equipment, live or dead pigs or even pork products.

That day, at Thanliana’s piggery, 42 pigs were culled by the police, who used a pistol for the smaller animals and a rifle for the bigger ones. “A third of the dead are sows that were part of the breeding stock and half of the lot culled was ready to be sold to the slaughterhouse,” says Thanliana, adding that he has borrowed heavily to set up and expand the pig farm.

“Every week for the past two months, we have been burying pigs by the dozen around the farm. I called the officials to save the rest of the stock,” says PC Ramchullova, the eldest son of Thanliana. That day, too, the family dug trenches to help the team bury the animals, but had to hire an earth-mover to dig since the number of culled animals was quite high.

Lalhmingthanga, joint director of the animal husbandry department and nodal officer for monitoring the outbreak in Mizoram, who was accompanying the team, estimated the loss at Rs 10.3 lakh. “It is a rudimentary estimate,” he says, “the overall loss would be higher, accounting for person-days lost looking after the pigs, the cost of medicines and the earth-mover, among others.”

Esther and Lalhmingthanga have become used to culling-burial-loss estimation process as ASF sweeps across India’s northeastern states, which account for nearly 47 per cent of the country’s 9.06 million pig population and where pigs are a major source of livelihood and a significant part of the local diet and culture.

India does not have a history of ASF, though the disease was first described almost a century ago (more on this later). It reported its first outbreak to the World Organisation for Animal Health (OIE) in May 2020, with cases reported from Arunachal Pradesh and then Assam. A few months later, on June 24, 2020, the Centre intimated the state governments about the Department of Animal Husbandry and Dairying’s “National Action Plan for control, containment and eradication of ASF” and asked them to take “suitable action”.

Read: Illegal pig import may be behind African swine fever outbreak in Manipur, say officials

Cases started to rise again this year, with Lungsen village in Mizoram’s Lunglei district reporting a pig death from an unknown disease on March 21. On April 15, the National Institute of High Security Animal Disease, Bhopal, confirmed it as the first case of ASF in the state.

By June 10, the viral disease had spread to Meghalaya, Mizoram, Manipur and Nagaland, says the Food and Agriculture Organization (FAO)’s ASF Situation in Asia and Pacific Update. In Mizoram, the government data shows ASF has caused severe losses, claiming more than 8,130 pigs in 10 of the state’s 11 districts by June 29.

With every culled pig, the meat economy takes a hit. According to the Mizoram government’s Economic Survey, the state’s annual meat production rose from 13,158 tonnes in 2011-12 to 16,533 tonnes in 2019-20, of which pork accounted for almost half.

“As of now, the spread of the disease has largely remained under control because of COVID-19 lockdown restrictions. But given the virulence of the pathogen, it won’t take long before spreading to other parts of the country. This will have a disastrous impact unless stringent biosecurity measures are implemented,” warns Swaraj Rajkhowa, principal scien tist at the Indian Council of Agricultural Research-National Research Centre on Pig, Guwahati.

Such measures include thorough disinfection, proper disposal of carcasses and waste, movement control, surveillance and early detection and humane killing of animals, as per OIE, which classifies ASF as notifiable disease.

Read: The worst of Nagaland’s African swine fever outbreak may be over, say officials

The virulence of the disease stems from the fact that it is caused by a double-stranded DNA virus that is fairly large, genetically diverse and is talented at evading the immune system.

The Food and Agriculture Organization (FAO) says ASF virus, when in a suitable protein env ironment, can survive in a range of pH and extreme temperatures. It has been shown to remain stable in serum at room temperature for 18 months, in refrigera ted blood for 6 years and in blood at 37 degrees Celsius for a month.

It may also remain viable in faeces for 11 days, decomposed serum for 15 weeks and in bone marrow for months. As a result, only certain disinfectants are effective in its control, says FAO.

Studies also show that ASF virus, when in a feed ingredients, can tolerate long-distance sea transports. This allows it to be easily spread and transmitted.

This complex makeup, apart from a general lack of willingness to invest in research until recently, are the reasons scientists have not been able to develop a cure or vaccine against the disease, des pite knowing it for almost a century now.

A worker at Thanliana’s farm buries culled pigs in a trench treated with lime. Thanliana owns one of Mizoram’s largest commercial piggeries, The farm has lost over 300 pigs to African swine fever this year

Disease origin

ASF was first recognised after its introduction in domestic pigs to Kenya in 1910, according to Elsevier’s Encyclopedia of Virology. In 1921, R Eustace Montgomery, veterinary adviser to the government of Uganda, established the likely transmission of ASF from wild swine. The virus is said to have evolved around 1700 AD from a virus of soft tick that infects wild swine, including giant forest hogs, warthogs and bush pigs.

In 1957, ASF appeared for the first time outside Africa, in Portugal, and in just a few decades, spread to other countries in Africa, Europe and the Americas, even reaching the Caribbean islands of Cuba and Haiti.

It entered Asia in 2018, when China — the world’s largest producer and consumer of pork — reported the first case. That year, nations rushed to declare it a “notifiable” contagious animal disease under OIE to be managed with national and international regulations and agreements.

India, however, remained free from the disease till 2020 despite neighbours Bangladesh and Myanmar reporting ASF in 2018 and 2019. So how did the virus enter India?

Passage to India 

Understanding the source and route of the spread of a virus is important to plug the gap before it can spread to pandemic-like proportions. However, scientists have so far not managed to trace its foray into the country.

Some believe that the virus has arrived via Tibet. “In 2020, [during the first outbreak] OIE reported two epicentres in Tibet, on the border of Arunachal Pradesh. People reported big carcasses flowing in rivers criss-crossing the international border,” A Chakraborty, director of research, North Eastern Regional Disease Diagnostic Laboratory, Guwahati, tells Down To Earth (DTE).

Last year, most outbreaks were on these river banks. The carcasses might have been mauled by community dogs who then brought the virus to villages, he says. In July 2020, soon after Arunachal Pradesh and Assam reported the initial outbreaks of ASF, Rajkhowa had also told DTE that the disease could have spread from Tibet.

Tapan Kumar Dutta, professor of microbiology at the Central Agricultural University College of Veterinary Scien ces and Animal Husbandry, Aizawl, says there are several potential ways the virus might have spread to India:

It first reached China (in 2018), then Myanmar and then Bhutan. There is a possibility that our domestic animals might have contracted the infection from wild boars coming from bordering countries through forests.

Praveen Mallick, commissioner, Department of Animal Husbandry and Dairying, also attributes ASF transmission to wild boars that easily cross over the border.

However, in states like Mizoram and Nagaland, that reported ASF this year for the first time, genesis of the outbreaks are shrouded in mystery.

Intra-country spread?

Lalhmingthanga suggests that the outbreak in Mizoram’s Lungsen village could have come from Bangladesh which, surprisingly, is not currently listed among FAO’s “ASF reported administrative areas since August 2018”.

He says:

The Village Council President at Rolui (just south of Lungsen) told us about pigs dying in various villages on the Bangladesh side of the border from the beginning of February. Lungsen is a village where pigs, illegally imported from Bangladesh, are kept along with the local animals. From Lungsen, the imported pigs are then supplied to Lunglei town.

There was also an outbreak in Mizoram’s Zokhawthar village, situated along the international border. It is a major hub of trade between Myanmar’s Chin State and Mizoram. Although 250 pigs died at Zokhawthar, the outbreak was quickly contained and there have been no further reports from anywhere in the vicinity.

Could it have come from Chin then? While some officials suspect this, others say the virus may have come from within India, probably Shillong in Meghalaya, because fresh as well as smoked pork from there is a staple in Aizawl. Mizoram had banned pigs from other states as soon as ASF Arunachal Pradesh and Assam reported outbreaks. But state authorities admit it is nearly impossible to check every vehicle that crosses state boundaries.

Nagaland, too, had imposed such restrictions for nearly a year to avoid any ASF outbreak by imposing restrictions on pig movements from neighbouring states since April 2020. Five months later, it allowed pigs from Punjab and Haryana, but restrictions continued for Assam and Arunachal Pradesh. Officials are now clueless about how the disease reached the districts of Phek and Kiphire.

Researchers say the incursion of ASF into the densely distributed domestic pig population of this region, mostly reared under backyard and scavenging systems with poor biosecurity measures, is also a major threat to wild boars.

A research paper in the journal Pathogens in December 2020, written by scientists working on animal diseases in India, representing various institutions, says:

Tracking down the first outbreaks of ASF in the NE [northeastern] region of India, it was observed that the outbreaks were reported alongside the river tributaries of Brahmaputra, a trans-boundary river which flows through Tibet, India, and Bangladesh. The Brahmaputra receives a number of tributaries that flows through national parks and wildlife sanctuaries of the northeast, comprising a significant number of wild boar population.”

Outbreaks can wipe out the pig population of the entire region if not appropriately controlled, they say.

The research paper has a dire warning for the future: “From the NE pocket, the disease may further spread to eastern India and then to the mainland through the river routes and interstate movement of pigs for trade and commerce. Therefore, considering the existing high density of domestic pig population in India, there is every chance that ASF might attain an endemic status if not controlled critically.”

Global spread

India’s northeastern region is the latest geography in the world to be gripped by ASF. Overall, 26 countries have reported the viral disease this year. Over two-thirds of the outbreaks have been in Europe this year. “This is the largest animal disease outbreak in history. We’ve never had anything like it,” Dirk Pfieffer, veterinary epidemiolo gist at the City University of Hong Kong, was quoted by the Associated Press.

Currently, China is the worst affected. Shenyang, a city in northern China, reported the first case on August 3, 2018. By the end of 2019, or in just 16 months, it spread to rest of the country.

The virus slipped into China from east Europe, in all likelihood through contaminated meat or pork products that were used as feed, also called swill feed. From there, it reached Vietnam, Cambodia, North Korea, Laos, Myanmar, the Philippines, South Korea, and, most recently, East Timor and southeast Asian countries.

Just like the human-impacting virus, this animal disease also demonstrates how fast it can spread in the inter-connected world. Like in the case of the COVID-19 pandemic, this disease also has global economic impacts.

Also read: African swine fever: Ripple effect across the world

This was first published in Down To Earth’s print edition (dated 1-15 July, 2021) 

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