Pimelea trichostachya poisoning (St George disease) in horses.

This study details an incident wherein a plant known as Pimelea trichostachya, also known as St. George disease, poisoned a group of horses in Queensland, Australia. The research presents the characteristics of the poisoning, including the clinical symptoms in the horses and the pathological findings.

Pimelea trichostachya and St George disease

• The research focuses on an instance of poisoning attributed to the Pimelea trichostachya plants, a species from the Thymelaeaceae family. This instance took place in inland Queensland, Australia, in the months of October and November in 2005.
• The plant, also known for causing St George Disease, was found in densities ranging from 2 to 45 g wet weight per square meter, with an average density of 16g/m2. In terms of plant numbers, densities ranged from 5 to 69 plants/m2 with an average of about 38 plants/m2.
• These plants comprised between 3% and 20% of the pasture volume, with an average of 9%.

Impacts on the Horse Population

• Out of a group of thirty-five horses, compromising mares, fillies, and geldings, ten were affected by the Pimelea poisoning.
• Noticeable clinical signs of the poisoning included loss of body weight, lethargy, nasal discharges, severe diarrhea, and oedema, which is swelling caused by excess fluid, in the chin, chest, and abdominal areas.

Pathological Findings

• Examinations showed various pathological conditions such as anemia, leucocytopenia, which is low white blood cell count, hypoproteinaemia or decreased protein in the blood, and symptoms related to the heart and liver.
• There were also indications of alimentary mucosal hyperaemia, which is an increased blood flow to the mucous membranes, and swelling of mesenteric lymph nodes, which are lymph nodes in the abdomen.
• Cattle that were grazed on the same pasture as the horses suffered from Pimelea poisoning as well. However, when both the horses and cattle were moved to pastures free of Pimelea plants, recovery ensued.

Comparison to Past Incidents

• This case draws similarity to another incident of this syndrome, which was recognized only in cattle in Australia until it occurred in horses in South Australia in 2002. In that instance, the poisoning was also due to exposure to a dense population of a Pimelea species, specifically Pimelea simplex.