Cases Of Grass Sickness Research Articles

Update on the equine grass sickness biobank, database and research project.

Beth Wells, equine grass sickness project lead at the Moredun Research Institute, encourages vets to report any equine grass sickness cases they encounter and explains how case reports and samples are being used to support research into this complex disease.

Chilean Patagonia: Equine grass sickness cases

Chilean Patagonia: Equine grass sickness cases

Bodyweight change aids prediction of survival in chronic equine grass sickness.

Objective criteria for predicting survival of chronic grass sickness cases are currently lacking. To determine whether the rate and/or magnitude of bodyweight change during hospitalisation of chronic grass sickness cases can provide an objective predictor of survival to discharge from hospital. Clinicians' recorded indication(s) for euthanasia were also reviewed. Single centre retrospective observational study. Case records of all horses admitted for management of chronic grass sickness to The Dick Vet Equine Hospital between 1998 and 2013 were analysed. Case background, survival to hospital discharge, indication(s) for euthanasia, disease duration at admission and bodyweight changes during the hospitalisation period were analysed, and data for survivors and nonsurvivors compared. Percentage weight change was calculated for 7 day intervals up to 28 days (0-7, 7-14, 14-21, 21-28 days) and for entire periods from the first weight recorded (0-7, 0-14, 0-21, 0-28 days). These results were used to estimate survival probability conditional on weight change. The study sample comprised 213 horses, with 114 survivors (53.5%) and 99 (46.5%) nonsurvivors. Compared with nonsurvivors, survivors had significantly lower median maximum bodyweight loss as a percentage of first weight (survivors 5.9%, interquartile range 1.8-13.5; nonsurvivors 12.7%, 6.4-17.3). Throughout all time periods analysed, survivors had significantly lower median bodyweight loss than nonsurvivors, but no specific time period was more predictive of survival. Highest percentages of total bodyweight loss for individual horses were comparable for survivors (36%) and nonsurvivors (37%). Survival prediction curves reporting percentage survival rates for all time periods analysed provided data to aid prediction of chronic grass sickness survival. Overall, nonsurvivors had greater bodyweight loss than survivors. Rapidity and magnitude of bodyweight loss were equally predictive of outcome. Percentage survival prediction curves provide objective data to aid discussion of prognosis, but greater predictive specificity with associated sensitivity is required for clinical decision making in individual cases.

Edaphic and Phytochemical Factors as Predictors of Equine Grass Sickness Cases in the UK

Background: Equine dysautonomia or equine grass sickness (EGS), as it is more commonly known, is a usually fatal disease of equids of uncertain etiology, although associated with grazing, that affects the autonomic and enteric nervous system. Lowered gastrointestinal motility, leading to paralysis of the gut, is one of the main symptoms of EGS. Previous studies have implicated anaerobic bacteria, notably Clostridium botulinum, but what triggers the severe bacterial infestations remains enigmatic. We hypothesized that a detailed comparison of soil mineral and botanical composition of EGS and control sites would yield new insights into the causation of the disease. Results: Between March 2007 and September 2008, soil, plant, and water samples from a total of 23 EGS sites and 11 control sites were studied. Metal and non-metal element levels of the soil and herbage samples were assessed. Significantly, EGS sites had higher levels of soil nitrogen, and significantly higher levels of iron, lead, arsenic, and chromium in the herbage. Toxic Ranunculus spp. (buttercups) were found in abundance at every EGS site, making ingestion plausible. Conversely, neurotoxin-producing cyanobacteria were not found in any of the water samples analyzed. Conclusions: The significantly higher levels of iron and heavy metals found in herbage growing in EGS sites, in addition to toxic Ranunculus species, suggest that previously unknown triggers are involved in a multi-factorial EGS etiology. Our results also show that cyanobacteria on the other hand, are unlikely to be a factor in EGS. Consequently, the concomitant presence of two (or more) factors could be the trigger for an outbreak of EGS.

Evaluation of Synaptophysin as an Immunohistochemical Marker for Equine Grass Sickness

It has been proposed that synaptophysin, an abundant integral membrane protein of synaptic vesicles, is an immunohistochemical marker for degenerating neurons in equine grass sickness (GS). In the present study, a statistically generated decision tree based on assessment of synaptophysin-immunolabelled ileal sections facilitated correct differentiation of all 20 cases of GS and 24 cases of non-GS disease (comprising eight horses with colic, six with neuroparalytic botulism and 10 controls). This technique also facilitated correct diagnosis of GS in all three cases that had been erroneously classified as having non-GS disease based on conventional interpretation of haematoxylin and eosin-stained cryostat sections of ileal surgical biopsies. Further prospective studies involving larger numbers of horses are required to fully validate this decision tree. In contrast to GS, botulism did not alter ileal neuron density or synaptophysin labelling, indicating that different mechanisms cause neuronal damage and/or dysfunction in GS and botulism.

Clustering of equine grass sickness cases in the United Kingdom: a study considering the effect of position-dependent reporting on the space–time K-function

Equine grass sickness (EGS) is a largely fatal, pasture-associated dysautonomia. Although the aetiology of this disease is unknown, there is increasing evidence that Clostridium botulinum type C plays an important role in this condition. The disease is widespread in the United Kingdom, with the highest incidence believed to occur in Scotland. EGS also shows strong seasonal variation (most cases are reported between April and July). Data from histologically confirmed cases of EGS from England and Wales in 1999 and 2000 were collected from UK veterinary diagnostic centres. The data did not represent a complete census of cases, and the proportion of all cases reported to the centres would have varied in space and, independently, in time. We consider the variable reporting of this condition and the appropriateness of the space-time K-function when exploring the spatial-temporal properties of a 'thinned' point process. We conclude that such position-dependent under-reporting of EGS does not invalidate the Monte Carlo test for space-time interaction, and find strong evidence for space time clustering of EGS cases (P < 0.001). This may be attributed to contagious or other spatially and temporally localized processes such as local climate and/or pasture management practices.

Long-term survival of equine surgical colic cases. Part 1: patterns of mortality and morbidity.

Postoperative complications and mortality can occur many weeks or months after colic surgery. We are interested in the long-term outcome of these cases. This study documents patterns of mortality and morbidity among 341 horses that recovered from colic surgery March 1998-August 2000. The progress of each horse was rigorously followed by periodic telephone and postal questionnaires. Event time data were recorded for each animal and a total of 321 horse years of survival, together with death from all causes, colic-related death and various postoperative complications. Postoperative survival (of all horses excluding grass sickness cases) was triphasic over the first 600 days and there was marked mortality in the first 10 days postoperatively. The probability of survival postoperatively decreased to 0.87 by 10 days, 0.82 by 100 days and declined slowly to 0.75 at 600 days. Horses suffering from epiploic foramen entrapment had a significantly reduced probability of postoperative survival (RR = 2.1, P = 0.033). The causes of death for 104 horses that died postoperatively and the prevalence of postoperative complications are recorded for the study population. Postoperative colic was the most prevalent complication with 100 horses (29%) suffering one or more episodes. However, only 16 horses (4.6%) suffered 3 or more episodes. The incidence of postoperative colic was 0.55 episodes/horse year at risk. This study provides data that will inform the prognosis for postoperative colic cases and identifies epiploic foramen entrapment as carrying a worse prognosis for survival than other strangulating lesions.

Presence of in vitro electrical activity in the ileum of horses with enteric nervous system pathology: equine dysautonomia (grass sickness)

Equine dysautonomia (grass sickness) is a frequently fatal disease of horses characterised by intestinal stasis. Interstitial cells of Cajal (ICC) are the pacemakers and mediators of neurotransmission in the gastrointestinal tract. Impaired ICC-mediated control of motility has been implicated in intestinal disorders in laboratory mammals, humans and in equine grass sickness. The aim of this study was to compare the in vitro electrical properties of ileum from grass sickness cases with horses free from gastrointestinal disease. Intracellular microelectrode recordings were made from smooth muscle cells in cross-sectional preparations of equine ileum, superfused in vitro. Samples were taken from six horses with grass sickness and from eight horses free from gastrointestinal disease, all euthanised on humane grounds. Ileal tissues were processed for haematoxylin and eosin histology, and c-Kit immunohistochemistry. Membrane potential oscillations were recorded in the ileal preparations from four of the six horses with grass sickness and from all of the normal horses. A waxing and waning pattern of the membrane potential oscillation activity was noted in some cells. In comparison to the normal horses, the membrane potential oscillations in grass sickness horses had a significantly reduced frequency ( P=0.0001) and increased duration ( P=0.0002). Immunohistochemistry revealed the presence but reduction of ICC in grass sickness. Histological assessment of the same tissues used for analysis of the ICC showed the depletion and pathology of the enteric neurons in grass sickness. Therefore, the majority of ileal preparations from grass sickness-affected horses exhibited prominent membrane potential oscillation activity suggesting that, although the neural elements are damaged severely, the ICC-mediated pacemaker function remains intact.

Liver and biliary system pathology in equine dysautonomia (grass sickness).

Hepatocellular and hepatobiliary damage was assessed in equine acute, subacute and chronic grass sickness cases (AGS, SAGS, CGS). Histopathological analysis showed that even in some early AGS cases enlarged hepatocytes, hepatocyte vacuolation indicative of lipid accumulation (steatosis), intrahepatocyte, canalicular and periportal deposition of pigments, frequent leucocyte infiltration and cholangitis occurred. Analysis of serum indicated significantly increased levels of unconjugated bilirubin in all groups and conjugated bilirubin in AGS and SAGS groups, increased levels of bile acids in some individuals from each group and significantly increased levels of glutamate dehydrogenase (GLDH) in AGS and SAGS cases. Conjugated bilirubin was significantly elevated in urine of AGS and SAGS cases. The evidence suggests that abnormal liver function involving moderate hepatocellular pathology in conjunction with steatosis and cholestasis may contribute to the pathogenesis of GS.

Phenylephrine eyedrops as a diagnostic test in equine grass sickness

The effect of an ocular administration of the α-1 adrenergic agonist phenylephrine was studied in 23 cases of grass sickness and 12 control horses. In the horses with grass sickness...

Investigation of the susceptibility of equine autonomic neuronal cell lines, clonally derived from the same paravertebral ganglion, to toxic plasma from equine dysautonomia (grass sickness) cases

In the autonomic nervous system (ANS) of equine grass sickness (GS) cases, some neurones show abnormal changes while neighbouring neurones are unaffected. To test whether noradrenergic neurones showed variable susceptibility to the GS toxin in culture, clonally-derived populations isolated from the same fetal thoracic sympathetic chain ganglion were challenged with plasma from GS cases previously shown to induce ANS damage when injected into normal horses. During the early stages of exposure to toxic plasma, cells within a clonal population showed variable susceptibility ranging from no obvious effect to characteristic patterns of pathology. However, after 3 days of exposure to toxic plasma all cells were killed. Dose response analysis on selected clonal populations showed no significant difference in TD 50 values.

Establishment and characterization of equine autonomic ganglion cell lines to enable direct testing of candidate toxins involved in equine dysautonomia (grass sickness).

To enable direct testing of a range of potential toxins or pathogens that might be involved in grass sickness, equine thoracic sympathetic chain ganglion cell lines were established from primary cell cultures by retroviral-mediated transduction of the temperature-sensitive mutant of the establishment oncogene encoding SV40 large T antigen. Morphological and behavioral features, temperature dependence, and immunocytochemical characteristics of the cell lines were investigated. The majority of cells were noradrenergic neurons in which dopamine-beta-hydroxylase, the enzyme that catalyzes norepinephrine synthesis, and neuropeptide Y coexisted. Cells treated with plasma from grass sickness cases that had previously been shown to induce autonomic nervous system damage when injected into normal horses showed significantly decreased mitochondrial function after 1 day. After 3 days exposure most cells showed severe degeneration in contrast to those treated with normal plasma. Liver and lung cell lines were also susceptible to plasma, suggesting that the toxin is not specifically neurotoxic.

A case-control study of grass sickness (equine dysautonomia) in the United Kingdom

A case-control study was performed to investigate the epidemiology of grass sickness in the United Kingdom from 1992 to 1995. Data were collected by means of postal questionnaire when cases of grass sickness were identified. Sets of three questionnaires were posted to owners of, or veterinary surgeons attending, cases of grass sickness, with a request to provide information on the case, on one healthy animal on the same premises as the case and on another healthy animal on other premises. Controls were matched to cases by date of onset. After univariate analyses, the probability of grass sickness in horses was modelled using conditional logistic regression techniques. Young animals were found to be at increased rick of grass sickness and females were less likely to become affected, as were animals that had a history of contact with previous cases of the disease. The probability of grass sickness was higher in animals that were on premises where grass sickness had previously occurred, particularly if this was recent. Animals were at particular risk of disease if they changed fields within the previous 2 weeks; the risk thereafter reduced with time. The disease had a seasonal pattern, with a peak from April to June. More than 95% of cases had access to grazing, and 66% occurred after 2 week periods of predominantly dry weather.

Evidence that the agent of equine grass sickness may reach neurons by retrograde axonal transport.

Sera from acute and chronic cases of natural grass sickness or normal horses were injected into the parotid salivary gland of ponies. This gland receives its sympathetic innervation from the ipsilateral cranial cervical ganglion. None of the ponies showed any local or systemic signs of illness. After one week the cranial cervical ganglia, stellate and coeliaco-mesenteric ganglia were removed for histological study. Pathological changes were found only in the cranial cervical ganglion ipsilateral to a parotid salivary gland which had received an injection of grass sickness serum. Four out of five batches of test sera from cases of acute natural grass sickness were associated with chromatolytic changes in neurons; the remaining batch of serum produced no abnormalities. The most severe chromatolytic changes were induced by two samples obtained from horses whose signs of grass sickness had been present for less than 12 hours. A serum sample from a chronic case of grass sickness of three weeks duration did not produce chromatolysis but was associated with a moderately severe inflammatory infiltrate and neuronophagia in the ipsilateral cranial cervical ganglion. One batch of serum was size fractionated to separate components with molecular weights above or below 30 kDa. Only the fraction containing components above 30 kDa induced chromatolytic changes.

Use of clinical measurements to predict the outcome in chronic cases of grass sickness (equine dysautonomia)

Forty-five cases of chronic grass sickness were given scores for selected clinical measurements when they were first examined, to assess their value in predicting survival. Sixteen cases survived. The clinical scores for the degree of dysphagia, appetite, colic and the degree of reduction in gut sounds were significantly lower in the survivors than in the non-survivors. In addition, only the non-survivors had severe rhinitis. Ponies were significantly less likely to survive than cob types.

Two cases of grass sickness

Two cases of 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.

Effects of detomidine on equine oesophageal function as studied by contrast radiography

The effects of sedation with detomidine on oesophageal function were assessed by contrast radiography in 10 healthy adult thoroughbred horses. Barium swallows were monitored by means of image intensification, first without sedation and then after the intravenous administration of detomidine at doses of 10 and 20 micrograms/kg bodyweight. The transit time of contrast agent to the oesophageal hiatus was recorded and each swallow was scored for markers of oesophageal dysfunction. Analysis of the data indicated that there were highly significant dose dependent increases in the transit time, the retention of barium within the longitudinal mucosal folds, and retrograde peristalsis and pooling of contrast agent within the oesophagus at both the thoracic inlet and caudal to the base of the heart. The degree of gastrooesophageal reflux was not affected at either dosage. These changes in oesophageal function were similar to those recorded from cases of grass sickness and indicate that care should be taken in the interpretation of studies of swallowing in animals that have been given detomidine before a radiographic examination.

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<0·01-P<0·001). Orosomucoid was elevated in acute, subacute and chronic grass sickness and inflammation (P<0·001, P<0·001, P<0·05 and P<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<0·05-P<0·01). α2-macroglobulin was significantly higher in acute grass sickness than normal, colic and chronic grass sickness cases (P<0·01, P<0·05 and P<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 α2-macroglobulin is more likely to reflect haemoconcentration.

Plasma histamine levels during exploratory laparotomies in suspected equine grass sickness cases

Plasma histamine levels during exploratory laparotomies in suspected equine grass sickness cases