This article was first published as show notes for podcast Episode 2 of Monsoon.
African swine fever is a virus disease that kills 100% of domestic pigs it infects. Originally from the common warthogs in Africa, the disease has spread to Europe and then Asia. Domestic and wild pigs in Asia are encountering the virus for the first time. In Southeast Asia, eleven species of wild pigs - ten of them found nowhere else - face potential decimation, scientists warn. Decisive and effective actions must be taken to protect both domestic and wild pigs, and thus the ecological, economic and social functions they provide.
Now, imagine a pig.
The pig which we have domesticated more than 9,000 years ago is Sus scrofa. This is the same species of the animal which we often call the ‘wild boar’ or ‘babi hutan’ in Borneo. The domesticated Sus scrofa lives inside pens; the wild ones live in the forests.
The other wild pig species though subscribe to a different fashion sense. While the wild boars are “stocky”, as Matthew Linkie describes them, the Bornean bearded pigs grow beards above their noses (females have some on their jaws) and have “elegant, lean bodies with long legs”.
Don’t picture a giraffe though. All pigs stay close to the ground. They are down-to-earth in that way and many others.
Then there the warty pigs, five species found across Java island and the Philippines. In these pigs, warts are sexy and safe. Males butt heads to win over females and facial warts could have evolved to cushion the blow. It’s a case where thick warts save you from the ward…I guess.
Of the 18 species of wild pigs worldwide, eleven live in Southeast Asia. What explains this diversity? Perhaps it’s the fragmented landscape of Southeast Asia, with the thousands of islands in the Philippines and Indonesia, says Matthew.
Islands, valleys, mountain ranges (all of which are abundant across Southeast Asia) can splinter a population of pigs (or any animal for that matter) into pockets (a process called ‘vicariance’). Separated and not able to breed with other groups (‘reproductive isolation’), each pocket could change and adapt to its immediate environment.
As small changes pile up, a pocket could become so different that it eventually evolves into a new species that cannot breed with other populations, even if they meet again.
Some of the world’s oldest lineage of living pig species are found in Southeast Asia, says Sheherazade, who goes by ‘Shera’ for short. The babirusa (Babyrousa) of Sulawesi, for example, evolved more than 10 million years ago, even before the more cosmopolitan Sus genus. That makes babirusa the “oldest guy” in the pig family, Suidae, says Shera.
A key citizen
Given their long history and wide range in the region, wild pigs have played important roles in regional human cultures and communities. In Sulawesi, scientists are discovering ancient cave paintings of wild pigs. Shera mentions one that is 35,000 years old. In January, scientists reported another that is at least 45,000-years old depicting the Sulawesi warty pig.
And in some communities, such as the Dayaks in Borneo, men hunt wild pigs not just for food, but also as a rite-of-passage, says Matthew.
Our forests must have harboured huge numbers of wild pigs, perhaps up to a few decades ago. Matthew recalls stories of “trains of thousands and thousands” of wild bearded pigs migrating across Borneo. The pigs were migrating across the land, tracking the fruiting season in the rainforest. Bearded pigs still migrate, of course, but I have only heard biologists describe them as “hundreds” now, not “thousands”.
Still, hundreds of bearded pigs sprinting through the palms and trees on their lean long legs, sniffing for the scent of ripe fruits – what a sight it must be!
Southeast Asians forests would likely be poorer without wild pigs. These animals, numerous and meaty, provide crucial nutrients to indigenous communities and many predators, some endangered like the Sumatran tiger and the Javan leopard.
And by gorging on fruits and defecating some distance away, the pigs could help trees disperse their seeds too. We often hear of hornbills or elephants described as ‘gardeners of the forests’ – wild pigs might be gardeners in that sense too.
Unfortunately, many wild pig numbers are falling. Habitat loss and excessive hunting have been the main threats. Now, a new killer emerges swift and terrible.
African swine fever is a disease caused by a virus. It is specific but lethal, infecting only pigs but killing almost all domestic pigs infected.
A pig can contract the virus via direct contact with infected pigs or carcasses, or by eating virus-contaminated materials. The virus also infects some ticks which can pass it to pigs.
Wild boars in Asia, which are the same species as the domesticated pigs, are vulnerable to African swine fever. Infected wild boars were found in China and South Korea in 2018 and 2019, respectively.
Scientists like Matthew and Shera speculate that infected wild boars can transmit the disease to other wild pigs in the forests, especially those of the Sus genus.
To date, ASF has been detected in domestic pigs across Africa, Europe, and Asia. The disease appears to have eased in Africa and Europe, showing signs of the virus evolving into a less virulent strain, says Matthew.
Worse is yet to come?
But in Asia, the rampage has just begun. Since 2018, ASF has cost China an estimated USD140 billion in losses.
The World Organisation of Animal Health compiles bi-weekly reports on ASF impact through its early-warning system. In the first two weeks of February 2021, the Philippines and Indonesia lost 162,471 domestic pigs to the disease, according to the February 5-18 report.
Media reports, however, cited much higher figures at more than 400,000 pigs culled in the Philippines alone by 1 February. Industry sources estimated up to 4.7 million pigs – one-third of the country’s total – could be affected.
In Sabah, Malaysia, dozens of wild bearded pigs were found dead since December. The Sabah Department of Veterinary Services has been testing the carcasses for ASF but hasn’t publicised their results yet. The Department did not respond to my request for updates.
In their 2020 paper, Matthew, Shera, and their team assessed the vulnerability of wild pigs to ASF. They examined several factors including levels of pork consumption and pork production in the vicinity of wild pig ranges. Shera compiled the data with her colleague, Selly Surya.
They found five wild pig species to suffer particularly high risk from ASF. Of these five, Matthew is particularly worried about the Visayan warty pig (Sus cebifrons) and the Mindoro warty pig (Sus oliveri). Both species live on only three small islands in the Philippines. One bad roll of the dice could wipe the pigs out.
Act quick, act right
What should we do then? Matthew emphasises two critical steps to contain ASF in Southeast Asia. The first is to establish standard guidelines in all range states. The second is to have pig carcasses disposed of immediately and thoroughly, regardless if ASF was involved or not. Pig carcasses should either be incinerated or bagged and buried very deep.
Shera adds that pig farmers and the public need to understand ASF better. There had been instances where pig farmers protested the culling of pigs which was meant to contain the disease.
She also hopes that some of our listeners would be intrigued enough to study wild pigs. That’s a hint for science journalists like me to write more about our wildlife in Southeast Asia!