New research project to look at role of pasture fungi in EGS
By Dr Scott Pirie
New research project to look at role of pasture fungi in EGS Dr Scott Pirie Researchers from the Food and Environment Research Agency (FERA) and the Royal (Dick) School of Veterinary Studies have teamed up to further explore the potential causal role of pasture fungi in Equine Grass Sickness (EGS). The Equine Grass Sickness Fund have provided funding for this collaborative effort to revisit this route of investigation which was a major focus in the 1990s, predominantly through the work of Dr Jean Robb. Although this earlier work revealed a high detection rate of Fusarium on EGS pastures, this did not prove a causal role for this pasture living fungus in disease induction, despite it demonstrating “nerve damaging” properties when added to isolated nerve cells grown in the laboratory. Although no further advances were made on this route of investigation, it is likely that the nerve damage resulted from certain toxic components released from the fungus, termed mycotoxins. However, the study of mycotoxins and their effects on plants and animals is an inherently difficult area of investigation and at the time of this work being conducted, the laboratory tools to further investigate this phenomenon were not readily available. Fortunately, recent years have seen significant advances in the development and availability of appropriate tools to study the role of mycotoxins in a variety of diseases. The state-of-the-art laboratory techniques required to advance this route of investigation are available at only selected institutes, including FERA which is the UK National Reference Laboratory for Mycotoxins in Food.
Both researchers from FERA and the Dick Vet Equine Hospital were independently revisiting the “fungal hypothesis”, initially unaware of their common route of investigation. However, upon realisation of their mutual goals, they quickly joined their collaborative efforts in what is hoped will be a productive and synergistic partnership. The researchers from FERA will provide an unparalleled range of expertise in the field of mycotoxicology with the researchers from the Dick Vet providing an extensive knowledge of the clinical, pathological and epidemiological aspects of the disease.
Dr Judith Turner and her team at FERA have recently conducted a pilot study, the results of which have supported an association between EGS occurrence on a pasture and the detection of high levels of Fusarium on the same pasture. Furthermore, they have identified certain mycotoxins to be present in these pastures in very high concentrations. The levels of toxins present in grass were several orders of magnitude higher than those commonly found in harvested wheat grain samples, a major host for Fusarium infection. Despite the previously published association between Fusarium growth and EGS occurrence on a particular pasture, these data on mycotoxin detection are extremely novel and of considerably greater significance with regard to any efforts to establish a link between Fusaria and EGS. Without the detection of mycotoxins and/or confirmation of the Fusarium’s capability to produce them, any proposed link between fungal pasture contamination and disease-inducing potential remains (and will likely remain) highly speculative.
The current study aims to further confirm this association by analysing a larger dataset, incorporating appropriate control pasture analysis and to screen for an extensive array of mycotoxins (around 50) on EGS-affected pastures using advances laboratory techniques. Furthermore, although the proposed sample number has been selected to provide only “pilot data”, full case histories, details of field agronomy and meteorological data will be collected for each case and control location. This will allow these data to be incorporated into a larger scale study, should initial results warrant a subsequent funding application. In addition, soil samples and, where possible, faecal and urine samples (from horses co-grazing with the EGS case at the time of disease onset) will be collected to facilitate both mycotoxin analysis and analysis for toxin break-down products. Finally, FERA are currently in the process of analysing samples of archived cat food obtained from “outbreaks” of feline dysautonomia to determine whether mycotoxin ingestion may also be associated with this closely related disease. If a link is established between EGS and field exposure to both Fusarium species and certain mycotoxins, followon studies are planned to further investigate whether these toxins are capable of either triggering and/or causing EGS.
The investigative team, which includes researchers from FERA (Dr. Judith Turner, Dr. Susan McDonald, Dr. Phil Jennings) and the Dick Vet Equine Hospital (Dr Scott Pirie, Prof. Bruce McGorum), are well placed, in their respective roles, to shed significantly more light on the potential role of pasture fungi in EGS. Should such a role be discovered, then appropriate and targeted management strategies could be developed to significantly reduce the incidence of the disease.
The researchers will continually liaise with the Equine Grass Sickness Fund to remain informed about the occurrence of cases, thus facilitating early access to pasture and co-grazer samples. Therefore, we would ask that readers continue to inform the Fund about any confirmed EGS cases.