Worm Watch - Professor Jacqui Matthews

Jacqui Matthews graduated from Glasgow University Veterinary School and has devoted her career to the study of roundworms (nematodes) of horses and ruminants. Initial research focussed on vaccine development for a cattle worm, but expanded into the neglected area of horse nematodes in the 1990’s. Since then, her research group has led in development of tools to study these important worms, especially in the design of tools to investigate them at the DNA level. During this time, however, the key aims have never strayed from the applied, the main objectives of which are to investigate how dewormer (anthelmintic) resistance develops and to see if more sensitive tests can be developed to detect resistance. Having raised in excess of £3.5 million for the research, the group has published over 65 peer-reviewed research papers in this area. Jacqui is currently a member of several committees whose focus is drug resistance control. Having taught at the Glasgow and Liverpool Schools, Jacqui is now Moredun Professor of Immunobiology at the Royal (Dick) School of Veterinary Studies (Edinburgh), where she divides her time between the School and the nearby Moredun Research Institute. The equine worms that her group works on are the cyathostomins (small strongyles). These are the most important parasites of horses - in terms of their frequency and their ability to cause disease. Controlling cyathostomins is becoming more and more difficult as they have the ability to acquire resistance to all drug types developed for use against them. As no new types are appearing on the horizon, it is important that the efficacy of the currently available drugs is retained for as long as possible.

Research indicates that drug resistance develops within worm populations because these populations are extremely large (up to 1,000,000s of worms per group of horses) and because, at the DNA level, these pathogens are very diverse. This means that worms can respond to, and adapt, under ‘selection pressure’; as you would expect from Darwin’s theory of evolution. When powerful drug treatments are applied, these act as a very powerful trigger for adaptation so that even if one in 1,000,000 worms initially has a mutation that allows it to ‘resist’ the drug, it can survive – this effect builds up over time so that if the same drug type is administered frequently over time, a significant part of the population will consist of resistant types of worms. At this stage, the drug becomes ineffective – this is either seen as an inability to reduce faecal egg counts after treatment (to levels described when the drug was first licensed) or as parasite-associated clinical disease in a group of horses which have a ‘good worming history’.

It’s therefore important to use anthelmintic drugs rationally by treating horses at the appropriate time of year with the correct time of wormer. Also, at certain times of they year, to target horses carrying high burdens of worms and leave those with lower burdens untreated. It is important to remember that not all horses carry similar sizes of burdens: a reasonable rule of thumb is that 20% of horses harbour 80% of the burden. This means that worm control strategies can based on targeted treatments of individual animals taking into account level of burden. Faecal egg counts at an appropriate time of year (in the UK, spring and summer) can be used to identify which horses to treat to reduce contamination onto pasture. Remember that encysted cyathostomins in the gut wall, usually at highest levels in autumn and winter, cannot be detected via faecal egg counts, and these should be treated at these times of year using an appropriate treatment that kills encysted larvae.

The Faecal Egg Count Reduction Test (FECRT) can be used to assess sensitivity of worms in to a particular drug. At the moment this is a rather crude assay and requires updating and refinement. The Edinburgh group has just started a project (funded by the Horserace Betting Levy Board) that will allow further development of this test so that better recommendations can be made in the field. We are currently looking for Thoroughbred studs to participate in this project. This will involve completing a questionnaire on parasite management strategies as well as a free FECRT using ivermectin (the active ingredient in products such as Eqvalan or Equimax). Please contact Dr Val Relf (Valerie.Relf@moredun.ac.uk) if you’d like to get involved in this project.

In future horse owners need to be more aware of the possibility of drug resistance in worms and should consider targeting horses for treatment in the spring and summer months. They should also think about undertaking tests to see if the worms on their premises are sensitive to the drugs they are using - this can be done in conjunction with their attending veterinary surgeon.

For further information about the research at Moredun click here