Research may hold clues about Alzheimer’s Disease

By Margaret Evans

Horses, as mammals, share common ground with humans when it comes to suffering similar conditions. They can get allergies, cancer, blood disorders, cystitis, heart disease, skin tumours, and a variety of other ailments. 

But scientists at the University of Edinburgh’s Roslin Institute and Royal (Dick) School of Veterinary Studies are finding new information about a fatal horse condition known as equine grass sickness that may hold clues to better understanding Alzheimer’s disease.

Equine grass sickness damages parts of the nervous system which control the involuntary functions resulting in gut paralysis and muscle tremors. The condition can kill a horse or pony within days.

The cause of the disease is unknown despite the fact that there has been almost a century of investigation. The first case was reported in eastern Scotland about 1907. There are three forms of grass sickness – acute (in which horses die within 48 hours), subacute (in which animals may only live seven days), and chronic (in which some animals may survive with intense nursing).

As to the cause, all kinds of poisonous plants, chemicals, bacteria, viruses, insects and metabolic connections have been examined and the current theory being explored is a soil bacterium. Yet, there have also been a few cases of animals getting the disease that have not had access to grazing. The disease does not appear to be contagious and the type of nervous system damage done suggests some kind of toxic substance.

Symptoms are sudden, severe, and are associated with paralysis of the digestive system from the esophagus on down. It may first present as colic, but the animal also has difficulty swallowing and will drool saliva. The stomach can become distended with a foul-smelling fluid pouring down the nose. Constipation occurs but if the horse does pass dung, it will be small and hard with a mucus coating that looks cheesy. Other signs are loss of appetite, rapid weight loss, sweating and tremors. But not all affected horses exhibit all the symptoms, making it hard for vets to isolate the disease from other causes of colic.

In trying to throw more light on the cause of this dire condition, the scientists studied the nerve tissue of six horses that had died from grass sickness. But in a serendipitous clinical analysis, they found that the tissue contained proteins commonly seen in the brains of Alzheimer’s patients, such as the build-up of amyloid proteins.

Alzheimer’s is the most common form of dementia and a hallmark of the disease is the accumulation of amyloid plaques between nerve cells in the brain.  

In total, the researchers discovered 506 different proteins had been altered in nerve tissue from the horses that had died from grass sickness compared to equines that had died from other causes. The promising result from the study is that the new knowledge could help develop tests to quickly detect the condition, which is currently so hard to diagnose and often only confirmed at autopsy. 

While the disease is extremely rare in North America, some two percent of horses die from grass sickness each year in the UK, and horses also succumb to it in some European countries. It is most often seen in young horses between two and seven years of age and during spring growth season or during the fall.

Like all research, new discoveries can open up promising pathways to faster diagnosis, more effective treatment, and applications to other conditions. And perhaps, in the process, this research may benefit both horses with grass sickness and humans with Alzheimer’s disease.

To learn more about equine grass sickness, visit: www.grasssickness.org.uk.

Photo: The outlook for horses with grass sickness is bleak. Credit: Shutterstock/Otmar Smit