Parascariasis

ASCARIDS:
A Growing Problem
PA R AS I T E P R I M E R — PA R T 3
n the world of internal parasites, ascarids get no respect. Unlike strongyles, they aren’t a high-drama threat to your horse’s health, and they aren’t a “hot topic” parasite like the tapeworm. But that doesn’t mean they should be overlooked or discounted in your war on worms. Ascarids, or roundworms, wreak their havoc largely onyoung horses with naïve immune systems, and that can set your youngster up for depression, stunted growth, and potentially fatal colic.

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BY KAREN BRIGGS, WITH CRAIG REINEMEYER, DVM, PHD; DENNIS FRENCH, DVM, MS, DIPL. ABVP; AND RAY KAPLAN, DVM, PHD

What Are They?
Ascarid is a general term referring to a large family of closely related parasites that infect a variety of vertebrates,including dogs, cats, horses, cattle, swine, birds, skunks, raccoons, and even humans. Most species of ascarids are host-specific, meaning they will grow to adults and reproduce in only a single type of host animal. So the ascarid of equids, Parascaris equorum, occurs in horses, donkeys, and zebras, but is not capable of infecting pigs or dogs.

ARND BRONKHORST

Ascarids, which are usuallyproblematic only for horses up to 15 months of age, were some of the first internal parasites to be recognized by man.

March 2004

THE HORSE

www.TheHorse.com

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Encysted Strongyle

QUEST AND QUEST PLUS CONTROL DEADLY ENCYSTED STRONGYLES IN ONE DOSE.
Nearly all horses and pastures are infected with encysted strongyles – parasites that live and grow inside the intestinal lining. Whenhundreds of encysted strongyles emerge at once, they can cause diarrhea, colic or even death. Moxidectin, the active ingredient in QUEST® and QUEST PLUS, can kill deadly encysted strongyles in a single dose – along with many other harmful parasites. So ask your Fort Dodge equine health supplier for QUEST today. It’s the simple solution for encysted strongyles.

World Equine Leaders
©2007 Fort DodgeAnimal Health, a division of Wyeth. fortdodgelivestock.com

PARASITE PRIMER PART 3—ASCARIDS: A GROWING PROBLEM
Most ascarids are comparatively large parasites, ranging in width from one to two millimeters (imagine a pencil lead) to three-eighths of an inch, and in length from one to 14 inches. Their large size meant ascarids were some of the first internal parasites to be recognized by man.Adult specimens of P. equorum, by far the largest of the common species to infect horses, are approximately the dimensions of a pencil. Ascarids are easily observed in the manure of infected horses, especially after treatment with an effective anthelmintic. Unlike the tapeworms discussed last month, ascarids have a relatively conventional sex life, developing as separate sexes, males and females.Like most other parasitic nematodes (a phylum of elongated cylindrical worms), the femalesare much larger than the males because they are the egg factories and have a more critical role in propagating the species. The female ascarid is a prolific egg layer, producing hundreds of thousands of eggs per day, each with a thick, multilayered shell that makes them resistant to desiccation (drying) andfreezing. They’re also equipped with a sticky protein coating that enables them to adhere to any surface they come into contact with, once they pass into the environment with the manure. The usual route of transmission for most species of ascarids is through ingestion of infective eggs. Some ascarid species, however, have very complex life cycles. The common ascarid of dogs (Toxocara canis), forinstance, can be transmitted from the bitch to the pups before they are born, and its counterpart in cats (Toxocara cati) can infect suckling kittens through the milk. In addition, each of these species can survive in the tissues of small mammals, and dogs or cats are infected when they exercise their predatory instincts. the small intestine. But like a racehorse, they have to go around the track...