Could This Vaccine For Deer Hold Out Hope For Humans?

CWD, CJD And (Maybe) More

Unless you're involved in parkland management or neuroscience, or you're a poacher who really does their research, there's no reason for you to know, but a disease has been ravaging the deer populations of the United States and elsewhere. It's a brain-based wasting disease that bears a close resemblance, both in its effects and in its epidemiology, to "mad cow disease" (BSE), and the human equivalent, Creutzfeldt–Jakob Disease (CJD). That means it's a wasting disease characterized by progressive, degenerative neurological damage. In humans, CJD begins with progressive dementia, hallucinations and loss of cognitive function. In cows and deer, it's a little harder to track some of the more subtle neurological symptoms, but much of the physical wasting is caused by the animals forgetting to eat.

When their brains are autopsied, all three diseases show a common factor: BSE is called bovine spongiform encephalopathy because it occurs in cows and affects the brain, but also because it makes the brain take on a sponge-like appearance, with many small holes. The human and deer equivalents work the same way.

What's happening is that a complex protein, called a prion, is made wrongly, and it folds in on itself. The next thing that happens is that these misformed prions communicate their misshape to the proteins either side. Whole areas of the brain fold in on themselves and die, and the resulting spongy appearance (under a microscope) gives the whole group of diseases their name, transmissible spongiform encephalopathies. In deer, it's called chronic wasting disease (CWD) and it's spreading at an alarming rate across the deer population of the USA.

Now Scientists Think They May Have Found An Effective Vaccine

In a study published in the December 21 edition of Vaccine, the team will show that they have been able to halt the spread of cervid (deer-like animals, including elk and caribou) CWD with a vaccine. Senior study investigator and neurologist Thomas Wisniewski, MD, a professor at NYU Langone, said:

Until now, it's been impossible to halt the spread of TSEs without culling. In outbreaks of "mad cow disease", it was necessary to cull whole herds, decimating local beef industries. As many as 100 percent of captive deer in the USA are infected with CWD, making the prospect of culling a major concern. It's also worrisome because while cervid CWD can spread to other cervids like elk and caribou, BSE and its sheep equivalent, scrapie, have been shown to be transmissible to humans, causing vCJD, variant Creutzfeldt-Jakob Disease. An infected herd doesn't just hurt the meat industry, and CJD is incurable and quickly fatal, killing most of its victims in the first year and 85 percent in the first six months.

See Also: Prions Similar To The Proteins That Cause Mad-Cow Disease May Be Essential In Brain Development

It's Small Sample, But It's Promising

The vaccine works by infecting the animals' guts with salmonella. CWD is spread by deer eating infected food or feces during natural feeeding, and Salmonella easily enters the gut. These salmonella bacteria were "attenuated" — no longer dangerous. They had a prion-like protein inserted into their genome. It's thought that the vaccine works by triggering the production of anti-prion antibodies.

A Human TSE Vaccine?

If we could have a usable vaccine for cervid TSEs and nothing else came of this research, that would be a fantastic result, but there's more on the table. It might be possible to use the same principles to create vaccines for other TSEs, in cows, sheep and even in humans. We could halt the spread of CJD between humans via infected tissue and blood, which is currently a major worry. Because prions aren't actually alive they can't be killed, so autoclaving and other once-sufficient procedures for sterilizing surgical equipment didn't work.

The WHO recommended that surgical equipment used on prion-infected patients be incinerated, until an alternative cleaning strategy that breaks prions down chemically was developed. That's great for surgical equipment, but not so wonderful for blood, for instance, which obviously can't be chemically cleaned. As a result, the USA has strict restrictions on who can give blood, based on their probable exposure to TSEs in Europe and the UK. 

Add in the fact that we don't know how many people were exposed to TSEs during the 90s "mad cow" scare. Because TSEs can have incubation periods up to 40 years, we don't know how many cattle were carriers, or how many infected people have yet to show symptoms.

Again, that would in itself be fantastic news. But CJD, horrible though it is, is relatively rare in human beings. It occurs at a rate of about one case per million people per year. But there are diseases that cause similar symptoms and are much more common. And they largely proceed by similar processes. 

Hope For Alzheimer's?

Alzheimer's disease kills about half a million people every year, and affects about six percent of people over 65. It's a major killer but an even more major drain of quality of life. There's no really effective drug therapy - some things  work a little but nothing really halts or even significantly slows he progress of the disease, which is characterised by brain shrinkage and the presence of amyloid plaques in the brain.

The development of amyloid plaques has been suggested as the underlying cause for Alzheimer's. But amyloid plaques show up in the brains of people and animals with TSEs too.

It's possible. The vaccine works by controlling the entry of prions into the body via the gut, though, rather than addressing the issue of amyloid plaques directly. And these aren't fully proven to be the cause of Alzheimer's in any case — it could be a case of "post hoc ergo proctor hoc" ("after it, therefore because of it"). No-one has yet proven a cause for Alzheimer's.

See Also: New Alzheimer's Disease Treatment: The Search Is On

Vaccines based on the amyloid plaque hypothesis have been tried in mice and humans with disappointing results, while vaccines based on tau theory have also not produced good results, with one trial having to be abandoned. Until we have a vaccine that acts directly on the cause of degenerate neurological diseases, we don't have a solution, sadly.