‘Gumshoe Sleuthing’ in Equine Veterinary Medicine

Dr. John Madigan presented the AAEP’s 2014 Milne lecture on discoveries that changed equine and human health.
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Being in the right place at the right time is sometimes the catalyst needed to catapult a bright, inquisitive mind into a world of discovery. This is what happened to John Madigan, DVM, MS, Dipl. ACVIM, ACAW, professor and researcher in medicine and epidemiology at the University of California, Davis (UC Davis), School of Veterinary Medicine, when he began veterinary practice in Northern California back in the 1970s. There, early in his career, he was faced with the challenging situation of treating a very sick horse with a puzzling illness, with clinical signs ranging from fever, lethargy, and ataxia (incoordination) to icterus (jaundice in the eyes), and mild petechiation (blood spots on the gums). Madigan wasn’t satisfied with simply treating the horse symptomatically, so he kept looking for answers.

He described this process of discovery during his delivery of the Frank J. Milne State of the Art Lecture at the 2014 American Association of Equine Practitioners Convention, held Dec. 6-10 in Salt Lake City, Utah. The disease he ended up investigating for many years following his encounter with that sick horse is one that affects not just horses but also humans and other animals: tick fever, or granulocytic anaplasmosis, caused by Anaplasma phagocytophilum, previously known as Ehrlichia equi.

Anaplasmosis

Madigan’s sleuthing began when he pulled blood from the horse and examined it under a microscope. Being a careful observer, he noticed strange-looking inclusion bodies within the neutrophils—white blood cells that are important for clearing infection in the body. Inclusion bodies are unusual structures found in the cytoplasm or nucleus of cells that may indicate certain types of infection. This clue led him to further investigation and, finally, answers. It turned out that he was dealing with a bacterial disease caused by Ehrlichia equi and transmitted by the very same ticks that infect humans and animals with Lyme disease. In this case, one sick horse ended up leading to the discovery of significant human disease—granulocytic erhlichiosis—caused by the same bacteria; this proved instrumental in stimulating development of effective treatment protocols (e.g., tetracycline) for both horses and humans.

The process by which Madigan and others identified the vector and disease required careful work using the principles of evidence-based medicine. They used their observations made in the field to lead to more scientific inquiry and study. “Never theorize before you have data because, invariably, you’ll end up twisting facts to suit the theories instead of developing theories to suit the facts,” he said

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Written by:

Nancy S. Loving, DVM, owns Loving Equine Clinic in Boulder, Colorado, and has a special interest in managing the care of sport horses. Her book, All Horse Systems Go, is a comprehensive veterinary care and conditioning resource in full color that covers all facets of horse care. She has also authored the books Go the Distance as a resource for endurance horse owners, Conformation and Performance, and First Aid for Horse and Rider in addition to many veterinary articles for both horse owner and professional audiences.

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