Detection of hypoglycin A in the seeds of sycamore (Acer pseudoplatanus) and box elder (A. negundo) in New Zealand; the toxin associated with cases of equine atypical myopathy

An ongoing concern: 20 years of research on equine atypical myopathy

Anne-Christine François, Benoît Renaud, Caroline-Julia Kruse, Christel Marcillaud-Pitel and Dominique-Marie Votion of the Atypical Myopathy Alert Group discuss insights from 20 years of research and surveillance on equine atypical myopathy.

Hypoglycin A in Acer genus plants

Hypoglycin A (HGA) is an amino acid occuring in the Sapindaceae family. Ingestion of certain Acer genus plants belonging to this family has been connected with atypical myopathy (AM) or seasonal pasture myopathy (SPM). To date, all cases of AM/SPM have been associated with sycamore (Acer pseudoplatanus) and boxelder maple (Acer negundo). The aim of this work was to determine and compare HGA in sycamore, boxelder and silver maple (Acer saccharinum), the trees known for HGA content, whose occurence is quite common in the Czech Republic. In sycamore and boxelder maple the effect of location, weather condition and sampling season was evaluated. The other aim was screening for presence of HGA in 12 other species of Acer genus which are grown as ornamental trees in Europe. The determination of HGA was conducted using ultra - high performance liquid chromatography - tandem mass spectrometry (LC/MS). HGA was detected in all samples of sycamore, boxelder and silver maple except for eight leave samples of boxelder maple. In the case of sycamore maple, the highest concentrations of HGA (median) were found in seedlings (770 mg/kg) followed by samaras (130 mg/kg) and by leaves (48 mg/kg) and inflorescences (24 mg/kg). In boxelder maple, significantly higher concentrations of HGA (median) were found in seedlings (550 mg/kg) compared with samaras (45 mg/kg), leaves (14 mg/kg) and inflorescences (24 mg/kg). According to the results the seedlings could pose a significant risk of poisoning, although other factors such as accessibility and palatability of other parts, especially samaras, should be considered. No significant differences of HGA concentrations in silver maple (56 mg/kg) were found between samaras, leaves and inflorescences. HGA was also identified in sugar maple (Acer saccharum), Japanese maple (Acer palmatum), trident maple (Acer buergerianum), paperbark maple (Acer griseum) and Himalayan maple (Acer oblongum). Although silver maple and other ornamental maples have not been reported to cause AM/SPM, the possibility of intoxication in animals can not be excluded.

Detection of Hypoglycin A and MCPrG Metabolites in the Milk and Urine of Pasture Dairy Cows after Intake of Sycamore Seedlings

Hypoglycin A (HGA), methylenecyclopropylglycine (MCPrG), hypoglycin B (HGB), and γ-glutamyl-α-(methylenecyclopropyl) glycine (γ-glutamyl-MCPrG) are secondary plant metabolites occurring in sycamore maple (Acer pseudoplatanus) as well as several other Sapindaceae (e.g., Blighia sapida). By interfering with energy metabolism, they may cause severe intoxication in humans and other species. However, to date, there is not enough data available concerning the intake, metabolism, or excretion of sycamore maple toxins in dairy cows. In May 2022, five cows were observed over four days, when they had first access to a pasture with two sycamore maples. Grazing of their seedlings that grew numerously in between the pasture plants was monitored by direct observation. Milk samples were drawn both from individual cows and from the bulk tank. Spontaneous urine samples were collected from all cows on day 3 after access to the pasture. Seedlings (100 g) were sampled on the pasture and analyzed, together with milk and urine samples, for sycamore toxins and their metabolites using liquid chromatography-tandem mass spectrometry and liquid chromatography-high-resolution mass spectrometry. Cows ingested sycamore seedlings while grazing. Values of HGA in milk were below the limit of quantification. However, metabolites of HGA and MCPrG were detected in individual milk samples already at the end of the first day of grazing. Urine samples of all five cows showed higher concentrations of conjugated HGA and MCPrG metabolites than in milk. Observations suggest that dairy cows may have a low susceptibility toward sycamore maple toxins. However, whether this could be attributed to foregut fermenting species in general requires further elucidation.

Grazing Mares on Pasture with Sycamore Maples: A Potential Threat to Suckling Foals and Food Safety through Milk Contamination

Simple Summary

Equine atypical myopathy is seasonal poisoning resulting from the ingestion of seeds and seedlings of the sycamore maple that contains toxins. Literature mentions several cases of intoxication among gravid mares and in unweaned foals. The objective of this study was to determine whether the toxins responsible for atypical myopathy could pass to the foal via suckling. Four mares that were pasturing with sycamore in the vicinity were milked. Analysis revealed the presence of toxins in milk. This unprecedented observation could partially explain cases of unweaned foals suffering from atypical myopathy. However, a transplacental transfer of the toxin cannot be excluded for newborn cases. Besides being a source of contamination for offspring, milk contamination by toxins from fruits of trees of the Sapindaceae family might constitute a potential risk for food safety regarding other species’ raw milk or dairy products.

Abstract

Equine atypical myopathy (AM) is seasonal intoxication resulting from the ingestion of seeds and seedlings of the sycamore maple (Acer pseudoplatanus) that contain toxins, among them, hypoglycin A (HGA). Literature mentions several cases of AM among gravid mares and in unweaned foals. The objective of this study was to determine whether HGA and/or its metabolite are present in milk from grazing mares exposed to sycamore maple trees as confirmed by detection of HGA and its metabolite in their blood. Four mare/foal couples were included in the study. Both HGA and its metabolite were detectable in all but one of the milk samples. To our knowledge, this is the first study describing transfer of HGA to the milk. This unprecedented observation could partially explain cases of unweaned foals suffering from AM. However, a transplacental transfer of the toxin cannot be excluded for newborn foals. Besides being a source of contamination for offspring, milk contamination by toxins from fruits of trees of the Sapindaceae family might constitute a potential risk for food safety regarding other species’ raw milk or dairy products.

Atypical myopathy in Père David's deer (Elaphurus davidianus) associated with ingestion of hypoglycin A

From 2004 until 2016, 21 Père David's deer (Elaphurus davidianus) have died for unknown reason at Zoo Duisburg. These deer, also known as milu, have succumbed from a myopathy that occurred seasonally in autumn and in spring. The clinical signs shown by the animals closely resembles those of a disease called equine atypical myopathy (EAM), which is formerly known in horses. The cause for EAM in Europe was found in the ingestion of hypoglycin A, contained in samaras and seedlings of the sycamore maple tree (Acer pseudoplatanus). To test the hypothesis that the mortality of milus was caused by ingestion of hypoglycin A, 79 sera from all zoos and wildlife parks that have kept milus in Germany and Austria, including 19 diseased and 60 healthy animals, were used. Selected biochemical values and additionally hypoglycin A, methylenecyclopropyl acetic acid-carnitine (MCPA-carnitine), and acylcarnitines, which have been found in horses suffering from EAM, were determined. The results showed greater values of serum activities of creatine kinase (P < 0.001) and aspartate aminotransferase (P < 0.001) in diseased milus comparing to healthy ones confirming a myopathy in affected animals. Moreover, hypoglycin A and MCPA-carnitine were found in the blood of Père David's deer and thus, hypoglycin A intoxication was considered to be a potential cause for the myopathies by ingestion of sycamore maple samaras that were present in the enclosure of the affected animals. Hypoglycin A values were greater in diseased animals (P < 0.01) as well as MCPA-carnitine levels (P < 0.05). Additionally, affected milus showed greater C5-OH-carnitine (P < 0.01) and C6-carnitine (P < 0.001) values. Until now hypoglycin A intoxication was only known in the family of Equidae, in humans, and in laboratory rats, and it has not been previously described in other zoological families. Comparing to horses, ruminants do have a different digestive tract and it will need further investigation to find out if several factors are involved to trigger an outbreak in ruminants.

An epidemiological investigation of an idiopathic myopathy in hunting dogs in New Zealand

AIM

To conduct an epidemiological investigation of an idiopathic myopathy, known as "Go Slow" (GSM), which was initially recognised in dogs used for pig hunting. A secondary aim was to describe the hunting activities, diet and health of dogs used for pig hunting in New Zealand.

METHODS

A retrospective cohort study was conducted between June 2014-June 2017. Cases of GSM in dogs were diagnosed by veterinarians using a combination of clinical history, physical examination findings, serum biochemistry and/or skeletal muscle histology. A telephone interview was conducted with the owner or primary veterinarian to provide information regarding the dog's diet and exercise over the 7 days preceding the onset of clinical signs. In August 2015, a separate online survey of owners of dogs used for pig hunting was conducted to characterise the normal hunting activities, diet and health of these dogs.

RESULTS

A total of 86 cases of GSM were recruited, of which 58 (67%) were pig hunting dogs, 16 (19%) pet dogs and 12 (14%) working farm dogs. Cases were most commonly reported in the upper North Island, and 65 (76 (95% CI=67-85)%) were from the Northland region. Processed commercial dog food had been fed to 93 (95% CI=88-98)% of affected dogs. Ingestion of raw, frozen or cooked wild pig in the preceding week was reported for 76 (88 (95% CI=82-95)%) dogs with the myopathy. In the survey of owners of healthy pig hunting dogs, 203 eligible responses were received; pig hunting was reported to most commonly occur in Northland (20.2%), Waikato (22.3%) and Bay of Plenty (23.2%) regions. Commercial dog food was fed to 172 (85 (95% CI=80-90)%) of the dogs included in this survey, and 55 (27 (95% CI=20-33)%) had eaten wild pig in the preceding week. The most common reported health problem in pig hunting dogs was traumatic wounds.

CONCLUSIONS

Cases of GSM were most commonly recognised in dogs used for pig hunting, but also occurred in pet and working farm dogs. The disease was most frequently reported in the upper North Island of New Zealand and ingestion of wild pig was a consistent feature in cases of this myopathy.

CLINICAL RELEVANCE

To minimise the risk of dogs developing this myopathy, it would seem prudent to avoid feeding any tissues from wild pigs to dogs in areas where the disease is known to occur.

Acylcarnitines profile best predicts survival in horses with atypical myopathy

Equine atypical myopathy (AM) is caused by hypoglycin A intoxication and is characterized by a high fatality rate. Predictive estimation of survival in AM horses is necessary to prevent unnecessary suffering of animals that are unlikely to survive and to focus supportive therapy on horses with a possible favourable prognosis of survival. We hypothesized that outcome may be predicted early in the course of disease based on the assumption that the acylcarnitine profile reflects the derangement of muscle energetics. We developed a statistical model to prognosticate the risk of death of diseased animals and found that estimation of outcome may be drawn from three acylcarnitines (C2, C10:2 and C18 -carnitines) with a high sensitivity and specificity. The calculation of the prognosis of survival makes it possible to distinguish the horses that will survive from those that will die despite severe signs of acute rhabdomyolysis in both groups.