University investigates acute horse disease

University of Adelaide researchers are investigating the potential causes of a mystery illness which suddenly struck down 14 horses across South Australia last year, eight of them fatally.

The horses became suddenly ill over the winter months of 2014 with acute signs of sweating, rapid breathing, muscle trembling, weakness and sometimes loss of coordination. Some horses died very rapidly while others fully recovered. The 14 known cases were in 10 different locations across South Australia.

The researchers are searching for common factors between the cases and aim to establish a protocol which can be used to examine future cases.

One suspect is the weed marshmallow, Malva parviflora or small-flowered mallow.

"Marshmallow is a naturalised plant in southern Australia, commonly invading pasture that has been made bare by drought or heavy grazing," says project leader Dr Lidwien Verdegaal, Senior Lecturer in Equine Medicine in the University's School of Animal and Veterinary Sciences.

"Although there haven't to date been any confirmed fatal cases of marshmallow poisoning of horses in Australia, the plant has been implicated as the cause of poisoning cases in horses, cattle and sheep in rare incidences. Usually it is unpalatable but, as it's a common weed of horse pastures, it should be considered a potential risk.

"We think that for some reason the plant sometimes tastes sweeter and some horses will eat it. When it has rained a lot, it grows rapidly and it's possible that if there is nothing much else in the paddock, a horse may eat it."

The researchers have collected information on the cases including diet and clinical signs of the disease from the owners of the affected horses.

"We are trying to identify the common factors between the cases and the common pathology," says Dr Verdegaal.

"We'll then seek to establish a protocol including registration of clinical signs, blood and urine testing and a post-mortem for the investigation of such cases so we can learn lessons and prevent these cases in the future."