Acute equine grass sickness in a two-year old Warmblood stallion in Germany

Abstract

Equine grass sickness (EGS) is a frequently fatal disease with a mortality rate of 85% and more, which can affect all members of the equine family (equidae). The disease results in severe and extensive damage of neurons in both the central and the peripheral nervous system. The gastrointestinal tract is particularly affected although some of the signs of the disease are related to nerve damage in other parts of the body. Much of the characteristic neuronal cell degeneration is found in the nervous system that controls involuntary functions, the autonomic nervous system, hence an alternative name for the disease is 'equine dysautonomia'. In the United Kingdom (UK) this disease is prevalent with the highest incidence worldwide. However, in the rest of Europe it is still a rare disease and there are only very few cases reported in Germany. Many studies tried to discover meteorological and signalement-related risk factors. There are three main forms: acute, subacute and chronic EGS. Each form has different clinical signs. Acute cases present with signs of colic, beginning weight loss and difficulty swallowing. Often large amounts of gastrointestinal reflux and tachycardia are characteristic findings during the initial clinical examination. Horses can also show bilateral ptosis, patchy sweating and muscle fasciculations in all forms. The subacute form is similar to the acute form, only a little bit slower in onset and usually without reflux. In chronic cases massive weight loss and the typical "tucked up" silhouette are predominant. This report presents the case of a two-year old Warmblood stallion in Germany. The horse was referred to the hospital with a suspect neurological disorder. Upon presentation primary neurological signs were not remarkable, but the horse was in bad body condition. It was somnolent, tachycardic and dysphagic, showed signs of colic, and naso-gastric intubation revealed large amounts of nasogastric reflux. Bloodwork revealed marked azotemia. The horse received supportive care including fluids and antiinflammatory drugs. After two days there was no significant clinical improvement and only little fecal output. EGS was suspected and confirmed by a positive phenylephrine-test. Due to lack of clinical improvement, the high certainty of EGS and a bad prognosis, it was decided to euthanize the horse. Postmortem a sample of the ileum was taken for histopathological examination. Upon histopathology, a nearly complete loss of neurons in the ganglia of the enteric autonomic nervous system was apparent. Thus, the case was initially classified as an acute form of equine grass sickness. This case report discusses a horse suffering from EGS and displaying signs of acute, subacute and chronic disease. However, the main purpose of this case report is to raise awareness that grass sickness, although rare, does exist outside of the UK. Additionally, the authors want to draw attention towards the easy to perform phenylephrine-test. Conclusively, Equine grass sickness is a differential diagnosis in horses with colic and gastrointestinal hypomotility, weight loss and dysphagia, even in Germany.