Today we know that the toxin responsible for atypical myopathy is a toxin present in the seeds of some Maples such as the common Sycamore. For outbreaks occurring in spring, the assumption is that the germinating seeds of the maple & sycamore trees contain the toxin. With the current climatic conditions, these seeds have begun to germinate and it is therefore imperative that, if possible, horses avoid ingesting them. It is important to inspect your grass to make sure it does not contain these seedlings but if that is the case, you may try to mow or burn them.
From the retrospective studies of large clinical series throughout Europe, we have learned that when a large number of cases of atypical myopathy were recorded in autumn, many new cases are encountered in the following spring. In spring 2014 it is anticipated that a large number of deaths due to atypical myopathy may occur.
From Irish Equine Centre's update Spring 2014
Inherent dangers (risk/benefit) in treating Rhodococcus equi
Rhodococcus equi can cause respiratory and or enteric / intestinal disease in foals. This disease varied in prevalence among Irish Studfarms during the economic boom years. It was sporadic / seldom seen with just one or two cases occurring on some farms, outbreaks involving multiple cases on others and epidemics involving 60% or more of foals were also, but more rarely, seen. The economic downturn resulted in a sharp decline in R. equi cases. However, the disease has not gone away and there is a suspicion that the incidence of R. equi disease may once more, be slightly increasing.
The diagnosis of R. equi is not an easy task and may require the use of multiple diagnostic tools including specialised blood samples, ultrasound examination and attempts at recovering the causal organism from affected foals, to reach a definitive diagnosis.
This multiple tool approach, wherever it is feasible is important, because guessing can be dangerously misleading and can lead to initiation of R. equi treatment, for foals that do not have this condition. Even where a diagnosis is confirmed, using these criteria, highly experienced equine clinicians recognise that foals are capable of making a spontaneous recovery and they will make judgement calls on which do or do not require treatment. These judgement calls can be backed up by serial evaluations.
Inappropriate or excessive use of the very specific (macrolide) antibiotics that are the only effective treatment, can lead to the creation of an R equi population on the farm that is resistant to these antibiotics. If this happens, as it has in other countries, then there is no effective alternative treatment available.
Furthermore, these antibiotics are not “user friendly” and can create significant bowel / intestinal upsets and rarely, can lead to gut ulceration and even bleeding into the gut. This adverse effect is seen more frequently in warmer weather, of the type that Ireland has been experiencing recently. Intestinal bleeding can lead to very significant changes in the bacterial population of the gut, including the overgrowth of Clostridial and Salmonella species, which are once again, difficult to treat and potentially very serious complications.
There are other dangers too, if mares ingest faeces/ droppings from foals on macrolide antibiotic treatment, the antibiotic contaminated foal faeces can precipitate a potentially fatal colitis in the mare.
In conclusion, although most foals that are treated for R equi disease make an uneventful recovery, the diagnosis is not a casual exercise and the evaluation of the risks versus the benefits of treatment and monitoring of response to it, are very important considerations.
D.P.Leadon MA, MVB, MSc, FRCVS, DipECEIM, European College & RCVS Registered Consultant / Specialist in Equine Medicine, Irish Equine Centre, Johnstown, Naas, Co Kildare.