Latest science advances included in makeover of equine parasite handbook

This image of a horse's caecum - the first portion of the large bowel - shows the damage that can be caused by encysted strongyles, also known as cyathostomins. Encysted strongyles are very resilient.
This image of a horse’s caecum – the first portion of the large bowel – shows the damage that can be caused by encysted strongyles, also known as cyathostomins. Encysted strongyles are very resilient. © Martin Nielsen

Martin Nielsen and Craig Reinemeyer have stepped up to the plate for another swing in the dizzying world of equine parasitology, updating their Handbook of Equine Parasite Control for a second edition.

They are among the biggest names you will find in this specialist field, and their handbook, first published in 2013, filled an important niche in the field’s literary microbiome.

It is interesting to read the original preface to the first edition, and what the pair have to say in their preface to the second edition.

Nielsen and Reinemeyer explained in 2013 that their book was conceived through their realization that equine practitioners were not likely to achieve competence in evidence-based parasite control by reading journal-length articles or by attending a few hours of continuing education.

Evidence-based parasite control was a relatively new development in equine medicine back then, and their new book was intended to help upskill veterinarians in this new strategy.

The pair, along with other veterinary parasitologists, had been pushing the approach, but equine practitioners had been unreceptive at first. By the time the 2013 book was published, many had embraced the important principles behind the strategy and understood the need to preserve the effectiveness of existing drugs against a steadily rising tide of resistance.

As they pointed out, evidence-based worming is about overturning four decades of tradition, and what they described as competing recommendations from the marketing people at drug companies.

So, how have things fared over the past five years?

Their latest preface provides a succinct summary. Some people, it transpires, still consider parasite control confusing, with many different opinions abounding.

Questions are common, and proved to be the main reasons why Nielsen and Reinemeyer wrote the book in the first place.

They acknowledge that equine parasitology is a research field with only a limited number of scientists involved.

Despite this, substantial new knowledge has been generated since the first edition, helped in particular by advance in gene-based technologies. Remarkable advances have been made on the diagnostic front, they note – a chapter which has grown more than any other in the book.

“A parasitologist cannot imagine a world without our beloved fecal egg counts, and despite their old-school nature, we can conclude that they are here to stay,” they say.

“In fact, they remain the foundation of good evidence-based parasite control.”

An entire chapter is now devoted to resistance to wormers. “We continue to see more and more resistance across the world.”

The pair said computer modeling has in recent years proved invaluable in predicting the dynamics of equine parasite infections and anthelmintic resistance development.

The authors have added to their clinical case scenarios at the end of the book, all based on actual cases they have encountered.

Further illustrations have been added, and the pair have expanded the scientific reference list for those keen to read the original sources. Expanding the references helped them weed out a few observations in the original text that perhaps had not stood closer scrutiny years after it was originally written.

“Yes,” they said, “we are also guilty of making unsubstantiated assumptions.”

The book remains an important and some might say innovative effort to address interest in the field by offering practical advice and logical recommendations, based on the latest science.

The authors themselves admit the book might appear somewhat academic to some, but in my view the volume walks an admirable line, first and foremost informing veterinary professionals, while at the same time using, in the most part, straightforward language that horse enthusiasts with an interest in parasites can follow.

Nielsen and Reinemeyer acknowledge that change does not come easily when it comes to parasite control, and their book lays out an eloquent case for change to challenge those who still adhere solely to a calendar-based worming program.

Progress, they admit, is measured one practitioner and one horse owner at a time.

The pair certainly cannot be accused of impatience.

The new edition is some 20 pages longer than the first. Their fundamental objectives are still well and truly met, having distilled a significant and ever-growing body of material into 230 pages, in a mix of science and practical advice.

The first section delves into internal parasites and factors affecting their transmission, neatly summarizing the likes of their biology, life cycles, environmental factors, and aspects of the host and the parasite that affect transmission.

The second section explains the principles of parasite control, dealing not only with anthelmintic use, but non-chemical means of parasite control, such as pasture hygiene and quarantine practices.

The importance of management measures such as picking up manure are stressed in the handbook.
The importance of management measures such as picking up manure are stressed in the handbook.

The third section delves into diagnosing and assessing parasitologic information, the tests for assessing worm burdens and the use of fecal egg counts to detect resistance to anthelminitics.

Section four comprises an expanded series of interesting case histories which show, among other things, the challenges of worm control.

As the authors point out, evidence-based parasite control is more complicated than most pragmatists suspect, relying on diagnostic testing before applying the strategic use of the right anthelmintics to minimize the risk of parasitic disease, reduce infection pressure and minimize the advance of resistance.

The book is logically structured and lays out what veterinarians, technicians and others with an interest in worm control need to know to put together a parasite control program using modern-day principles.

It was touching to see that Nielsen and Reinemeyer dedicated this latest edition to Dr Eugene Lyons and his career-long assistant, Sharon Tolliver, who both died shortly before the book went to print.

Lyons was a towering figure in equine parasitology who published more than 300 research articles. Tolliver was one of the world’s few experts on identifying equine helminths and contributed to more than 200 seminal publications in equine parasitology.

As Nielsen and Reinemeyer point out, their passing marked the end of an era.

What is important is that others step up to continue to advance our understanding of equine parasites, and in this regard I have no doubt the late pair would have been impressed by the efforts of Nielsen and Reinemeyer.

Their handbook is an important contribution that fills an important niche.

“We realize that we just represent another opinion about parasitology; we might even be adding to the confusion about these topics,” they write.

“Nonetheless, our ambition is the exact opposite, and our opinions at least are based on the best possible evidence available at this time.”

Handbook of Equine Parasite Control
by Craig R Reinemeyer and Martin K Nielsen
Hardcover, 230pp, Wiley-Blackwell, 2018.
ISBN 9780470658710; RRP $A77.23
Available from Amazon (US), Amazon (UK), and from Wiley. Also available as an e-book. An excerpt of chapter 1 is available here.

Martin K. Nielsen is an Associate Professor in the Department of Veterinary Science of the Maxwell H. Gluck Equine Research Center at the University of Kentucky. He has a doctorate from the University of Copenhagen, and was a faculty member there for four years before moving to Kentucky. His research interests include endoparasite infections of horses, clinical and molecular diagnosis, epidemiology, surveillance, and control.

Craig R. Reinemeyer graduated from the Ohio State University College of Veterinary Medicine in 1976, and spent 5 years in mixed animal practice before returning to OSU to pursue a PhD in veterinary parasitology. He was a faculty member of the University of Tennessee College of Veterinary Medicine from 1984 to 1998, and served as the President of the American Association of Veterinary Parasitologists from 2003 to 2004. In 1997, Dr. Reinemeyer founded East Tennessee Clinical Research, a contract research organization that conducts pharmaceutical studies to facilitate the development of new veterinary drugs. ETCR’s efforts have contributed to the approval of several currently marketed anthelmintics for horses, cattle, and pets.


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