December 7, 2022

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Vaccine Trial For Killer Elephant Virus Begins

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“She’s our wonder baby!” says elephant keeper Katie Morrison, smiling broadly.

Katie points to five-year-old Indali, an elephant survivor of an often deadly virus, which has killed seven calves at Chester Zoo.

Now, the zoo, with scientists at the University of Surrey, is embarking on a world first – a trial, in elephants, of a potentially life-saving vaccine.

The disease, called elephant endotheliotrophic herpes virus (EEHV), has a mortality rate of up to 85%.

“We’ve lost elephants usually between the ages of 18 months and three years,” Katie explains. “When we see symptoms – lethargy, mouth lesions – it’s usually too late”.

The virus was discovered in 1990 and formally characterised in 1999 by researchers at the Smithsonian Zoo in Washington DC. They linked 10 cases of a “highly fatal haemorrhagic disease” in young Asian and African elephants in zoos. In each case, they found “herpes virus-like particles” in cells of dead elephants’ hearts, livers and tongues.

Since then, the virus has been a zoo’s worst nightmare. A recent study, led by Berlin-based veterinary scientist Sonia Jesus Fontes, calculated that it had caused 52% of the deaths of Asian elephants in European zoos since 1985. In North American zoos, it accounted for 50% of deaths since 1980.

It has now been detected in sanctuaries, safari parks and, more worryingly, in wild elephant herds in nine countries.

Cruelly, it usually affects the youngest animals. Since 2010, Chester Zoo has had just one calf survive to five years of age – Indali. All the others died of EEHV.

In 2018, it claimed three-year-old Nandita and 18-month-old Aayu in the course of a single day. “It’s so tough – you do everything you can, and it’s not enough,” says Katie.

Groups of researchers around the world study EEHV, but Chester Zoo is now taking an important step with the vaccine trial, as the lead scientist behind its development, Prof Falko Steinbach from the University of Surrey, explains.

“We know it’s almost impossible to prevent infection – we’re trying to prevent serious disease and death,” he tells BBC News.

Much about how the virus causes such severe disease is still unknown, but it’s believed to be passed from older elephants to calves – possibly when a calf is being weaned and the antibodies from the mother’s milk decline. At this stage, a calf’s immune system is in a “delicate balance” with the virus and can become overwhelmed.

“Our aim is to give them a prime before infection,” explains Prof Steinbach. “So the elephant’s immune system knows the virus and is on the front foot.”

The team – of immunologists, zoo vets and keepers – is able to move ahead with the trial now because the new vaccine is built on a tried and tested “scaffold”. Essentially, the backbone of this vaccine is identical to one routinely used to immunise elephants against a virus called cowpox.

The scientists have “seeded” this tried and tested vaccine backbone with proteins from EEHV – bits of the virus for the elephant’s immune system to recognise and respond to.

“We’re using established, safe processes,” says Prof Steinbach. “And it’s important to move ahead with a trial in elephants, because there is no other animal we can test this in.”

Elephant co-operation

The trial itself is only possible because the zoo elephants take part.

In their battle against the virus, vets at Chester test the elephants regularly, so the animals are used to health checks and to provide blood samples.

“We build a mutual respect between us and them,” explains Katie. “It’s all based around a positivity and food rewards.

“We encourage them to interact with us. But if they don’t want to, that’s fine. We’ll leave them to it and try later.”

When we’re invited behind the scenes to watch the process, the big male elephant Aung Bo seems to be feeling quite co-operative.

With expert coaxing from Katie and from Richard Fraser, Chester’s elephant team manager – and with the aid of a huge pouch of high-fibre elephant biscuits – Aung Bo positions himself so his wonderfully flappy ear is up against a small elephant-ear-sized door in the bars of his training enclosure.

Javier Lopez, Chester Zoo’s vet, then climbs up a small stepladder to take a blood sample from the elephant’s ear vein. This will be the process for the vaccine trial – each animal rewarded for participating with biscuits and encouraging words from their trusted keepers.

Prof Steinbach is hopeful there will be “significant progress” towards a vaccine within five years. Until then, tests and blood donations from the herd have enabled Chester’s vets to diagnose the virus before symptoms appear.

When Indali tested positive, the team spent two weeks intensively treating her with anti-virals, immune boosters and blood plasma transfusions (donated by Aung Bo).

“Then we were in uncharted territory,” recalls Katie. “We’d never got that far – usually we lost calves within 24 hours.”

Mike Jordan, director of animals at the zoo, says the ability to develop this treatment in a captive setting is “hugely important” for all Asian elephants.

“The more we look for this disease in the wild, the more we find it – it’s clearly an important threat in a whole suite of threats they face,” he says.

“All these things combined are what drive species to extinction.”

Katie adds that, for the zoo, “a vaccine would give our calves a fighting chance right from the beginning.

“And any way that we can support the wild population would be fantastic.”

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