[Rhinopneumonia or mycotoxin intoxication? Neurologic phenomena in horses from a riding school].

The research paper discusses a case wherein a number of riding school horses exhibited severe neurological symptoms such as uncoordinated movements, trembling, and paralysis, leading to the need for them to be euthanized. Despite suspicions that EHV1 might be the root cause, it was eventually found that the horses had been exposed to a toxic substance, known as lolitrem B mycotoxin, through their hay feed, causing a condition called ‘ryegrass-stagger syndrome.’

Observations and Initial Findings

• The research began after observing that almost all the 40 horses in a riding school developed ataxia (loss of control over bodily movements) within a few days.
• Five of those horses displayed severe ataxia and tremors, leading to paralysis and ultimately requiring euthanization.
• Eleven privately-owned horses kept in the same area did not exhibit any symptoms, intriguing the researchers – why are some affected while others aren’t?

Suspicions and Early Hypotheses

• Considering the symptoms, the scientists hypothesized the cause to be ‘neurological form of EHV1′ – a type of Equine Herpesvirus that affects horses’ nervous systems; yet the symptoms did not completely match typical presentations.

Further Developments

• A second outbreak of the disease occurred among the riding-school horses weeks later. Interestingly, one of the previously unaffected privately-owned horses also showed signs of ataxia.
• The research team then analyzed ‘paired serum samples’ and cerebrospinal fluid but found no increase in EHV1 titers, opposing their original hypothesis.

The Unexpected Cause

• Further scrutiny of the stored hay (feed used for the horses), which was delivered just before the first outbreak, revealed significantly enhanced concentrations of lolitrem B mycotoxin. This substance is usually found in ryegrass, a common feed type for horses.
• They realized in retrospect that this ryegrass hay had occasionally been fed to the horses shortly before the onset of their neurological problems.
• All these findings led the team to a new conclusion: the horses were suffering from a condition named ‘ryegrass-stagger syndrome’, a neurological disease in horses caused by ingestion of ryegrass infected with the endophytic fungus that produces the lolitrem B mycotoxin.