The relationship between meteorological features and equine grass sickness (dysautonomia)

Local weather patterns associated with 15 outbreaks of equine grass sickness in eastern Scotland were studied. The majority showed a trend toward cooler drier weather associated with irregular ground frosts. This would not preclude the hypothesis that fungi might be connected with the aetiology of grass sickness.     

Acute phase proteins in grass sickness (equine dysautonomia)

Four acute phase proteins were assayed in the serum of normal horses and those with acute, subacute and chronic grass sickness, colic and inflammatory conditions, in order to investigate their diagnostic value in grass sickness. The grass sickness and inflammation group had a significantly increased haptoglobin concentration (P less than 0.01-P less than 0.001). Orosomucoid was elevated in acute, subacute and chronic grass sickness and inflammation (P less than 0.001, P less than 0.001, P less than 0.05 and P less than 0.05, respectively). Highest concentrations of haptoglobin and orosomucoid were recorded in subacute grass sickness. Ceruloplasmin was significantly higher in acute grass sickness cases than all other groups except the colic group (P less than 0.05-P less than 0.01). alpha 2-macroglobulin was significantly higher in acute grass sickness than normal, colic and chronic grass sickness cases (P less than 0.01, P less than 0.05 and P less than 0.05). The time scale of changes suggests that the stimulus to haptoglobin and orosomucoid synthesis occurs at the onset of clinical signs whereas the increase in ceruloplasmin and alpha 2-macroglobulin is more likely to reflect haemoconcentration.     

Small intestine and small colon neuropathy in equine dysautonomia (grass sickness)

The number of neurons in the coeliacomesenteric ganglia and the myenteric and submucosal plexuses of the jejunum, ileum and small colon, and the pathological changes induced in them, were studied in various types of equine dysautonomia. In all forms of dysautonomia, severe and extensive neuron loss and damage occurred in the ileum. In acute and subacute dysautonomia, jejunal neuron loss and damage were severe, but in chronic cases significantly less loss or damage occurred. The damage followed the same pattern in the small colon but it was always less obvious than in the jejunum. The distribution of the damage was uniform within a segment of the intestine. In fatal cases of dysautonomia, the clinical severity and duration of illness seems, in most instances, to be related to the amount of neuronal disruption occurring in the jejunum. Severe disruption results in acute/subacute dysautonomia, while milder damage leads to the chronic form.No case of dysautonomia was encountered in which enteric neuron loss and damage occurred without significant neuronal disruption also occurring in the coeliacomesenteric ganglia.Ileal neuronal damage and loss are not invariably worse than that in the jejunum, and the possible reasons for this, together with the relationship between neuronal damage and possible causes of dysautonomia, are discussed.Abbreviations H&E haematoxylin and eosin Deceased. Formerly of the Moredun Research Institute, 408 Gilmerton Road, Edinburgh, EH17 7JH, UK     

Analysis of peritoneal fluid as a diagnostic aid in grass sickness (equine dysautonomia)

The analysis of peritoneal fluid is of value in the differential diagnosis of equine colic but its characteristics have not been evaluated in grass sickness. Peritoneal fluid was collected from 15 normal horses and from 11 cases of medical colic, 11 cases of surgical colic, 20 cases of acute grass sickness and 13 cases of subacute grass sickness. The fluid was analysed for its appearance, total and differential white cell count, specific gravity, total protein concentration and total and intestinal alkaline phosphatase activity. Fluid from cases of medical colic was normal in these respects. Surgical cases were unique in having bloodstained fluid with a high alkaline phosphatase activity. Grass sickness cases had a higher specific gravity and protein content than the cases of medical colic although the appearance of the fluid was similar. Grass sickness cases were distinguishable from cases of surgical colic on the basis of the appearance of the fluid and its lower alkaline phosphatase activity.     

Functional and histopathological evidence of cardiac parasympathetic dysautonomia in equine grass sickness

The parasympathetic terminal cardiac ganglia were examined in three normal horses and in five horses with grass sickness. Histopathological changes, consistent with those observed in other ganglia of horses with grass sickness, were identified in the terminal cardiac ganglia of the affected horses. A functional analysis of cardiac autonomic control by time domain analysis (TDA) of heart rate variability was applied to eight horses with grass sickness, and double-paired to 16 normal horses on the basis of their age, sex and breed, and the time of day at which the electrocardiographs were obtained. There were statistically significant differences between the normal and the affected horses in terms of the triangular index (P=0.01), a geometric method of TDA, the sNN100 index (P=0.009), a statistical method of TDA, and the R to R interval (P<0.0005). These results indicate that there is a pathological and functional parasympathetic decentralisation to the heart in equine grass sickness.     

A comparative study of normal equine populations and those with grass sickness (dysautonomia) in eastern Scotland

A retrospective survey was made of premises in eastern Scotland on which at least two cases of grass sickness had occurred between 1970 and 1987. For comparison, a further survey of 49 equine establishments, on which no grass sickness had been recorded, was conducted from 1986 to 1988. The results indicated that younger animals are more susceptible, especially those in good physical condition grazing full-time in the spring or early summer. Movement to new grazing increases the risk of grass sickness and identifiable stress may contribute. The nature of the establishment governed the animals' condition during the summer, but it did not appear to influence the prevalence of grass sickness. However, riding schools and livery establishments which experienced the disease kept, on average, significantly more animals than unaffected premises of the same type. No relationship was found between supplementary feeding or stage of pasture growth and grass sickness. The results of the survey support the hypothesis that the causal agent of grass sickness is associated with grazing but multiple factors may influence the expression of illness.     

An acute outbreak of equine dysautonomia (equine grass sickness) in a group of eight Przewalski's horses (Equus ferus [caballus] przewalskii)

Equine grass sickness (EGS) is a neurodegenerative disease affecting grazing equids of which a single case of the chronic clinical presentation has previously been reported in a Przewalski's horse (Equus ferus [caballus] przewalskii). A group of 8 Przewalski's horses were moved to a new enclosure, recently vacated by a group of 4 Eastern kiang (Equus kiang holdereri) that showed no evidence of disease. After 23 days the first Przewalski's horse showed clinical signs of acute EGS including flank sweating, belly kicking, rapid loss of body condition, cessation of faecal passage, nasogastric reflux and mouthing water. It was subjected to euthanasia within 48 h due to lack of therapeutic response. Within 24 h of this first case developing clinical signs, a further 5 Przewalski's horses showed similar clinical signs of acute EGS and were subjected to euthanasia. Post mortem examinations confirmed acute EGS, with all animals demonstrating typical chromatolysis, cytoplasmic hypereosinophilia, cellular swelling, vacuolation, pyknosis and loss of nuclei in approximately 90% of neurones in the cranial cervical and cranial mesenteric ganglia and myenteric and submucosal plexi of the ileum. Two Przewalski's horses within the group showed no clinical signs of disease. No single pathogen was identified as the causal agent, but the epidemiological pattern of the outbreak was typical for that previously reported for acute EGS in domestic equids. All affected animals and the 2 surviving Przewalski's horses had low antibody titres to Clostridium botulinum type C. This is the first report of acute EGS in a herd of Przewalski's horses.     

Development of a clinical prediction score for detection of suspected cases of equine grass sickness (dysautonomia) in France

Equine grass sickness (EGS) (equine dysautonomia) is a neurodegenerative condition of grazing equines. Pre-mortem diagnosis of EGS is a challenge for practitioners as definitive diagnosis requires ileal/myenteric lymph node biopsies. This study aimed to develop a clinical score that could be used by practitioners to improve the detection of acute or subacute EGS cases in the field. Suspected EGS cases were declared by veterinary practitioners. A case was classified as confirmed positive if ileal or rectal biopsy samples showed neuronal degeneration typical of EGS. A semi-quantitative scoring system, including epidemiological and clinical data, was created to attempt to classify suspected EGS horses into confirmed positive or negative cases. Each variable was weighted based on a boosted regression trees model, while taking into account its clinical relevance. Twenty-eight EGS cases were confirmed by biopsy during the entire study period. The best cut-off value for the score to have a high sensitivity while maximizing specificity was 8, with a sensitivity of 100% and a specificity of 53%. In our dataset, 77% of animals would be correctly classified with this cut-off value of 8. Highest sensitivity was chosen in order to detect the highest number of potential cases. Our score represents an inexpensive and useful tool to aid in the identification of suspected EGS cases in the field and selection for further diagnostics procedures to confirm or rule out the disease. Application of the score to larger populations of animals would be required to further adapt and refine the score.     

An epidemiological study of risk factors associated with the recurrence of equine grass sickness (dysautonomia) on previously affected premises

REASONS FOR PERFORMING STUDY: The reasons why equine grass sickness (EGS) recurs on premises are unknown and, consequently, practical methods for reducing the risk of recurrence are not available. OBJECTIVES: To identify risk factors associated with recurrence of EGS on premises and to gain possible insights into the pathogenesis of the disease. METHODS: Data on disease history and risk factors were collected by postal questionnaire from premises with EGS cases between 1st January 1997 and 31st December 2001. Data on variation in rates of recurrence of EGS for different risk factors were analysed using Poisson regression analysis. RESULTS: Of 509 premises contacted, 305 (60%) returned useable questionnaires and 100 of these (33%) were classified as 'recurrent' premises. An overall median incidence rate for EGS of 2.1 EGS incidents/100 horses/premises/year was recorded. There was an increased rate of recurrence with higher numbers of horses, presence of younger animals, stud farms and livery/riding establishments, loam and sand soils, rearing of domestic birds and mechanical droppings removal. The rate of recurrence decreased with chalk soil, cograzing ruminants, grass cutting on pastures and removal of droppings by hand. Several statistically significant interactions were identified. CONCLUSIONS: Many of the findings are consistent with the theory that EGS is a toxico-infectious form of botulism. Several of the significant factors identified may directly or indirectly relate to soil disturbance and consequent soil contamination of grass, thereby increasing the rate of exposure of grazing horses to Clostridium botulinum, which resides in soil. Potential relevance: Identification of potentially modifiable risk factors may, ideally following validation in appropriately designed, controlled and randomised intervention studies, lead to practical measures to reduce the incidence of EGS on previously affected premises.     

Outbreaks of equine grass sickness in Hungary

Equine grass sickness (EGS) occurs mainly in Great Britain, but has once been reported in Hungary. The stud which was affected by EGS in 2001 had no new cases until 2009/10, when 11 of 60 and five of 12 one- to three-year-old colts died or were euthanased due to EGS. Following a few hours in the high-risk field during the winter of 2010/11 further four cases of acute EGS were noted among these horses. The affected horses showed somewhat different clinical signs compared with the cases reported in Great Britain. Histopathological findings in these horses were consistent with EGS. In most examined cases carbofuran, a carbamate was found in the liver by toxicological examination, and it is postulated that carbofuran may influence the immune system and therefore predispose the horses to develop EGS. Carbamates are thought to cause a delayed neurotoxicity in human beings. Further studies are needed to clarify the potential role of carbamates in EGS.