Blog: The race for a vaccine

At Chester Zoo a new stage of research has begun in the race to tackle Elephant Endotheliotropic Herpesvirus (EEHV), a highly potent disease that threatens the future of elephant conservation. Science has led the zoo to a pilot study of a potential vaccine - a real milestone on its journey to finding a solution to this deadly virus, which affects Asian elephants globally.
 

EEHV is a major threat to the long-term survival of the Asian elephant, of which just 40,000 now remain. Reports of wild elephant fatalities at the hands of the disease are on the rise in India, Nepal, Myanmar and Thailand, while cases have been recorded in five further countries across its native range, as well as in zoo conservation breeding programmes worldwide.

Asian elephants are listed as endangered on the International Union for the Conservation of Nature’s (IUCN) Red List of Threatened Species. A vaccine that can protect this amazing species is widely viewed as the best hope for tackling the virus.

Conservation scientists at Chester Zoo have been researching EEHV for more than 10 years and, along with its partners at the University of Surrey and the Animal & Plant Health Agency, are leading efforts on behalf of the international conservation community to research and understand the disease, and develop treatments that may ultimately save lives. Thanks to support through its Never Forget fundraising campaign, we have made great progress in tackling this deadly virus. Now, thanks to this continued support, we have together developed the first vaccine of its kind to ever enter a pilot study, anywhere in the world.

The virus
Like every other virus, EEHV is a tiny particle that simply aims to reproduce. But it can’t do this on its own – it needs to hijack the cells of a living being, turning them into factories that churn out new copies of the virus at an incredible rate. All animals have a defence system to protect us from a virus threat, the immune system, but this does not always protect from an invader. Some viruses, like EEHV, are particularly good at spreading and are incredibly damaging once spread. They can overwhelm the developing immune system of a young elephant before it has the chance to mount a full-scale defence.

Developing a vaccine
Since our research first began, technology has advanced and so too has our knowledge of how this particularly potent pathogen functions. This has got us to this landmark stage where we have now begun a vaccine pilot study.

Vaccines work by giving our immune system a practice run at fighting a disease in a safe environment, equipping its long-term memory with the knowledge of how to fight the real infection.

There are many ways to develop a vaccine, and our partnership has been working on two in particular.

The MVA Vaccine
An MVA vaccine has saved countless human lives by tricking our immune system. Developed nearly 50 years ago, this vaccine can change how a virus is seen by our natural defences.

By removing the DNA that makes EEHV look like EEHV to the immune system, and placing it into a harmless form of a different virus, called ‘vaccinia’, we have a way to trick the elephant’s immune system. It quickly wipes out the vaccinia, and in the process learns what EEHV looks like should the real virus surface.
 

Protein Vaccines
With this vaccine, we’re simply exposing the elephant’s defences to the specific proteins that cells would create when infected with EEHV, and examining if it responds. If all goes to plan, the immune system will form a long-term memory that will one day instruct a rapid response to these proteins when they’re detected in the body – not because we’ve put them there, but because an EEHV infection is beginning to destroy live cells.

How close are these vaccines to completion?
We’ve reached a significant point on our journey but it’s still early days. This great collaboration of researchers has got us to the point where we have two vaccine prototypes that we can test in a pilot study. We need to confirm that they can reliably, and repeatedly, stimulate an immune response.

So far, in this pilot we’ve given the vaccines to the Hi-Way herd’s bull elephant, Aung Bo, and tested small amounts of his blood for an immune system reaction. After vaccination, if we expose Aung Bo’s white blood cells to the markers of EEHV, we’d expect to see a rapid and strong immune reaction. We were encouraged to see some signs of this in the test, but at the moment it’s too early to tell if this means the vaccine would prevent a full-scale infection.

A larger trial awaits us now to build on this knowledge, where, in-time, we’ll learn whether this research is successful in protecting young elephants from EEHV both in the wild and in breeding programmes around the world.

This is a landmark moment on a long road, and one to celebrate. Stay with us on this journey to find out how these trials progress.

Read more about Chester Zoo’s EEHV research right here: https://www.chesterzoo.org/what-you-can-do/campaigns/never-forget/

By Mike Jordan, Animal & Plant Director, Chester Zoo
& Dr Simon Dowell, Conservation Science & Policy Director, Chester Zoo

All blogs reflect the views of their author and are not a reflection of BIAZA's positions.