A horse with grass sickness.
With a mortality rate of more than 90 per cent, researchers are desperate to find a way of stopping the illness, first identified in Scotland more than 100 years ago.
The Animal Health Trust says there is still a desperate lack of basic knowledge about the disease, which is different to staggers.
It occurs throughout northern Europe, but particularly in Great Britain.
The trust's scientists, along with others from the Universities of Edinburgh and Liverpool and the Equine Grass Sickness Fund, are involved in a nationawide surveillance scheme, set up in 2006.
The information gathered is being used to analyse trends revealing where and when cases occur across Britain, as well as giving an accurate picture of the true welfare impact of EGS.
Georgette Kluiters, grass sickness research assistant at the Animal Health trust, said: "April to June is predominantly the time when the number of equine grass sickness cases peak in the UK.
"We had notification of just five cases in the first quarter of 2009, but the number of cases in the second quarter has shown a sharp 10-fold increase, with more than 50 reports so far.
"We're appealing to owners whose horses have suffered with the illness, or vets who have treated horses with the illness at any time throughout the year, to let us know. It is never too late to submit a case - your information is vital."
Scientists suspect that the bacteria that causes botulism could be the culprit.
In the acute form of the disease, affected animals show signs of depression and high heart rate.
The increase in heart rate is usually higher than expected for the amount of pain the horse shows. No gut sounds are audible. Horses show patchy sweating, and have difficulty eating and swallowing. Affected animals die within 1-2 days.
In the subacute form, affected animals show less dramatic signs and survive for 2-7 days.
Almost all cases are fatal, although some less severely affected animals may survive with intensive nursing.
Grass sickness results from damage to the nerves responsible for gut motility. The severity of the signs is related to the degree of damage.
The cause has not been confirmed but it looks likely that toxins from the soil-dwelling bacterium Clostridium botulinum may be involved. If so, it may be possible to produce an effective vaccine.