While global attention is currently focused on COVID-19, a disease that has jumped from animals to humans, it is important to remember that diseases that breach the species barrier also pass from people and their domestic animals to wildlife populations. And this poses a serious threat to endangered species like tigers who are already teetering on the brink of extinction.
The first episode in the Year of the Tiger series of WildCats Pawast covers the top three infectious diseases which are having an impact on tigers, including the indirect threats from African Swine Fever and Lumpy Skin Disease to the more direct impacts of Canine Distemper Virus.
One undeniable common theme between all three diseases is that the human disruption of natural systems is intensifying unnatural interactions between species and creating emerging infectious disease transmission pathways. But not only are we engaging in our natural environment in a more exploitative way, but we are also traversing it differently. The movement of people, animals and animal products has increased dramatically through international travel and trade which has effectively meant that diseases benefit from more freedom of movement than most of the human population.
Listen to the episode below
In this blog we take a deep dive into African Swine Fever
This month on WildCats Pawcast, we spoke with Dr Matthew Linkie, the Indonesia Deputy Country Director for the Wildlife Conservation Society (WCS) and the Asia Coordinator for the IUCN/SSC Wild Pig Specialist Group. He has recently led a study that investigated the spread and impact of African Swine Fever and has since been working on a joint position statement that outlines a collaborative approach to prevent the further spread of the disease and its cascading effects, such as through the loss of a key tiger prey species in wild boar.
African Swine Fever (ASF) has been around for centuries. It is endemic in Southeast Africa within common warthogs who show no signs of clinical disease, but you can get spillover events into domestic pigs where it causes 100% fatality.
Matt explained that from Africa to Europe there have been three waves of ASF. One in the 1950s to Portugal which came over on contaminated plane food and ended up being used as pig feed. Then again in 1960s, but this time it spread even further to Brazil and the Caribbean who only managed to eradicate it in the 1990s through strict control measures like biosecurity and carcass disposal. The more virulent Genotype 2 came across via a ship from southern Africa to Georgia in 2007 in contaminated waste food which ended up in pig feed. It then spread to Russia and Ukraine and for a decade was just cycling within the wild boar population.
In 2019, Genotype 2 spread to China and since then it has swept all the way down to Southeast Asia. It also made it over from mainland China to Taiwan in a cooked pork wonton. ASF spreads easily through secretions and excretions like urine, faeces, saliva and blood and can stay in a carcass for a couple of months. The record is in cured ham for over a year showing just how easily this disease can spread.
Today ASF is in around 51 countries around the world and is having major economic impacts on the domestic pork industry. China has lost over 100 million pigs, costing their economy over 100 billion dollars which is almost 1% of their GDP. Then on top of that, there is the impact of wildlife and the cascading effects.
Wild pigs are well known to be ecosystem engineers as seed dispersers and seed predators, but it is not yet known how Asia’s wild spaces will be impacted by the fall in their population numbers. What Matt Linkie was sure of is that their decline could trigger a cascade of impacts on endangered carnivores where they form one of the major prey bases. Tiger subspecies rely on different prey across Asia. In India, there is a huge variety of food for them to choose from at large densities so wild boar wouldn’t potentially be the principal prey. But for Amur and Sumatran tigers, wild boar is the number one prey species, so they are most at risk from the cascading impacts of ASF.
But what is being done to control African Swine Fever?
Strict biosecurity measures within the pork industry have helped contain the spread in Europe. But when it comes to wild boar it is a lot harder. Matt specified that we need to know where ASF is occurring by having surveillance set up. Local rudimentary early warning systems can work well where community partners report any pig die-offs or signs of tigers coming out of the forests in a declining condition. When pig die-offs are reported samples are needed and then carcasses must be disposed of responsibly. Ideally, incineration or burying deep underground in a body bag as the virus can last for at least 2 months in infected carcasses. Unfortunately, there is still no vaccine. In the US there have been 3 successful vaccine trials and the Chinese government are also working on one. If COVID-19 has shown us anything, it is how quickly we can create a vaccine when needed and there does seem to be growing support for an ASF vaccine, mainly due to the economic impact of the disease.
Based on the vaccination solution could it be inconceivable that we think about restocking some of these tiger landscapes with vaccinated pigs? Matt highlighted that they are a crop pest so didn’t think there would be much support for restocking, but emphasised that if we don’t then what are some of these tigers going to eat?
If tigers aren’t eating enough, they are forced to the edge of the forest, encountering people, getting caught accidentally in pig snares and predating upon domestic animals and livestock. Matt indicated we haven’t yet seen a rise in human-tiger conflict which we can link to ASF outbreaks, however, you can see the logic. One good pre-emptive response to this is looking into good livestock husbandry practices, penning animals in at night in predator-proof enclosures to avoid retaliatory killings of tigers by local people.
But we need to start thinking through all options and first things first, get control on the infection.
”I never thought having worked in tiger conservation for 20 years that I would be concerned about the wild boar dropping out of our landscapes, they have always been least concern on the IUCN red list. They are one of the most widespread mammal species on earth as they breed really well and are an omnivore. So the fact that now we’re really concerned about their population is in many ways just part of a broader issue. How did we get here to where all of a sudden we are worried about wild boar, what have we done to the planet we’re living in?
Dr Matthew LinkieDeputy Country Director for WCS Indonesia
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