WORMS DOGS GET
What are intestinal parasites? What kind of worms do dogs get? Can I catch my dog's worms? Will my children get dog worms? How can I tell if my dog has worms?
Dog Worms: A to Z
by Fred Lanting, Breeder/Judge/Organic Chemist
First, you need to know what kinds of worms animals get, how worms develop, and how to keep your pets free from intestinal parasites.
Most worms (nematodes) settle and grow in the small intestine, though some species are found in the cecum, heart, lung, and other tissues in various stages of development. The intestinal nematodes produce eggs, which are carried with the digestive products to exit in the feces. But since the egg-laying does not always coincide with the dog’s bowel movements, stool samples may not show the presence of worms. A 5 day sampling will probably reveal some eggs if hookworms or roundworms are present, but tapeworms or whipworms may still escape detection. For this reason, many breeders rely instead on outward signs of poor coat, flatulence and/or diarrhea, loss of weight, and an abnormal look or smell to the stool.
In many breeds, the topcoat should lie flat, straight, and smooth, giving a water resistant thatch over the softer undercoat and skin. If these coarse, straight guard hairs stand up and out, or if the ends curl out away from the body, it may be a temporarily “open” condition due to worms. Lustre and texture also is gone, and the feel is rough and dry, the natural lubrications being lost when worms take their tariff from the intestinal lining’s rich supply of blood vessels, or otherwise interfere with normal absorption of nutrients. In this article you will see the word anthelmintics, which is the more accurate word for “wormer,” “worm medicine,” etc.
Roundworm — This is the most widespread of parasitic worms in dogs, cats, and many other animals. They are present in almost all newborn pups, having passed in larval stage through the placenta into the fetus’s liver. After birth, these larvae are carried by the blood to the heart, then to the lungs. Irritation of the bronchial passages causes the dog to gag and cough the larvae up, then swallow them. This enables the larvae to reach the intestines where they latch onto the walls with lamprey-like tenacity, and in as few as ten days can be found to have matured into identifiable roundworms of egg laying capacity. (fig. 1 click chart to ENLARGE)
Older pups that get worms a second time usually do so by ingesting worm eggs from stool or stool-¬contaminated surfaces. Pups (and adults) may also pick up roundworms from cat stools, which present a tremendous attraction. Larvae have also been detected in bitch’s milk. Swallowed roundworm eggs hatch in the intestine where the liberated larvae penetrate the wall and are carried in the lymph system to the veins. They, too, take the liver heart--lungs route, molt, and start laying eggs of their own four weeks after being ingested. So, it’s a good idea to repeat initial worming a couple weeks later, whether it’s a new litter or a dog you have just obtained but aren’t sure of its worming history (such as may be the case with some imports).
Adults and half grown dogs tend to trap some roundworm larvae in body tissues in an encapsulated or encysted condition, where they do no further harm. Pregnant bitches, however, undergo a hormone change about three weeks before whelping that releases the encysted larvae, freeing them to migrate to the placenta and affect the fetuses as the bitch herself was affected when she was a growing embryo. This dormant stage of roundworm larvae can also exist in transient or intermediate hosts such as rodents, and if mice are eaten, the process of digestion will release the larvae in the dog’s intestine, where they will not migrate (because they are in a different form), but develop into roundworms. Dogs that catch and eat beetles, cockroaches, mice, even earthworms, all of which may be hosts for roundworms, should periodically be given anthelmintics (wormers) as a routine control measure. Pyrantel pamoate (Strongid™, Nemex™) is an excellent anthelmintic for the youngest puppies because it is considered non-toxic and very safe even if rather overdosed accidentally; it is highly effective against round and hookworms. A good routine is to administer 2 weeks after birth, and then again 10 days after that. The next worming can be with ivermectin, but if you have a very small breed, you might want to dilute that. More on this anthelmintic drug later. (Part 2 will cover effective worming treatments)
Hookworm — Hookworms are much smaller than roundworms and cannot be seen outside the dog, but as in the case of roundworms, eggs can be detected in fecal matter under the microscope. (fig. 2 click chart to ENLARGE) “Hook,” as dog fanciers often call it, is a debilitating disease in adults and a frequent killer of pups. It is possibly the leading cause of death in puppies over two or three weeks of age. In chewing their way to blood vessels serving the intestinal walls, hookworms inflame the lining and make the organ less efficient. As a result, the dog becomes malnourished as well as anemic. Bloody stool, diarrhea, anemia, weakness, and dehydration are symptom of hookworm infestation, in addition to the sign of poor coat condition. There are a number of good anthelmintics, but the one I find most convenient, safe, and effective is ivermectin, good not only for heartworm prevention, but also for preventing and treating for round, hook, whip, and even ticks. Milbemycin is another heartworm “medicine” that gets many of these parasites. Since all wormers are potentially dangerous especially to debilitated pups, follow your veterinarian’s orders when worming sick or very weak pups. Hookworm can commonly be picked up at dog shows, veterinarians’ lawns and lobbies, city sidewalks, and parks where dogs defecate. The eggs can live a long time in the soil, but sunlight helps to kill them, and full strength chlorine bleach can destroy or force them to hatch and thus be susceptible to attack by products available from your veterinarian.
Whipworm — Whipworm infestation is usually less of a problem since it is not so widespread, but it’s harder to detect and eradicate. Eggs are extremely resistant to the environment, and larvae can exist for several years in the soil or cracks in basement floors. Whipworms don’t lay as many eggs, or as often, as other worms, so they are more difficult to detect. Take several days’ stool samples (in one mixture) to the vet. Whipworm Symptoms are similar to those of hook, and repeated doses with specific whipcides are quite effective when strict sanitation is an adjunct. Generally, anything that will kill hookworms or whipworms will also kill roundworms. Febantel™ has generally replaced the old dichlorvos as the wormer of choice because this latter was a bit risky for the youngest pups or dogs with liver or kidney insufficiency or heartworm, or if absorbed along with other cholinesterase inhibitors.
So the lone Taenia, as he grows, prolongs His flatten’d form with young adherent throngs. ...Erasmus Darwin, in The Temple of Nature, before 1800
Tapeworm — A variety of tapeworms (cestodes) infest dogs and all of these flatworm parasites rely on an intermediate host in order to be transmitted from one direct host to another. Depending on the genus and species, some require an insect, others a crustacean, still others a different mammal in which they exist in a non-worm stage such as a larva, usually encysted. Eggs are seldom detected in flotation slides, but the owner may see little white crawling things on the surface of some stools. These are called proglottids, segments of the tapeworm that contain the eggs and are shed by the worm in order to propagate itself while the head and younger segments remain attached to the inside of the dog. The shed segments have been likened to rice grains, cucumber seeds, and tiny blunt arrowheads and can vary in size from those of cucumber seed dimensions down to nearly microscopic particles that can be mistaken for frost if seen on a cold morning. The stool is not necessarily soft, unless the infestation is so bad that diarrhea is around the corner. However, tapeworms should be suspected when the dog has been wormed for hook yet still has flatulence and poor coat. He must then have the specific tapeworm anthelmintic.
Dipylidium caninum, (fig. 4 click to ENLARGE) a member of one of the most common flatworm parasite groups in dogs, is transmitted by the dog flea and the cat flea. When the dog bites and eats the flea, the tapeworm larva is given access to the canine intestine where the cycle starts again. The flea’s family members, meanwhile, are waiting in the grass (or even your carpets!) to feed on the eggs in the proglottids shed by earlier tapeworms.
The genus Taenia (fig. 5 click to ENLARGE) includes several species of tapeworm, the most common of which is T. pisiformis. Most cases of infestation come about when the dog eats a rabbit or mouse in whose intestines can be found encysted Taenia larvae. Prevention of infection with Taenia includes not allowing your dog to eat raw wildlife, particularly the internal organs, and especially rodents. The best preventive measure against Dipylidium is to keep your dog from socializing with cats or visiting places where cats hang out, for our feline friends are typical intermediate hosts even though they are seldom bothered by the fleabites.
A much-used wormer called praziquantel (trade name Droncit™), is nearly 100 percent effective against both of the above types of tapeworm. It causes the tapeworm to lose resistance to digestion by the host, so you will rarely see pieces of the worm in the stool after the wormer has done its job. Other anthelmintics for hookworms, roundworms, and whipworms don’t affect either of these tapeworms. A few minor flatworms are transmitted by the eating of raw fish. Another tapeworm species, Echinococcus granulosus, is a danger to man, its intermediate host. It is found mostly in Alaska and parts of Canada. There is a tablet anthelmintic sold under the trade name “Drontal™ Plus” which combines Droncit with pyrantel pamoate—the latter paralyzes hook and round worms. There is also febantel, which interferes with the metabolic process of whipworms; in combination with praziquantel, it is useful in the control of several types of intestinal worms with one dose. Some of these can be also be administered by injection.
Heartworm — (fig. 6 click to ENLARGE) Once a southern problem, heartworm has spread rapidly since the 1960s, due to increased travel around the United States. Only mosquitoes apparently can incubate the heartworm nematode, and only certain species of mosquito seem willing to do the job; unfortunately, they seem to be everywhere. Apparently, foxes as well as coyotes can keep the problem alive in any given area, but there are enough dogs around that are not on a preventative, that they don’t need any help from wild animals to spread this disorder. A good blood test can uncover microfilariae.
An excellent preventative is the once-a-month dosage with either ivermectin (most common trademark as sold by vets—and much more expensive than the feed-store generic brands—is Heartgard™) or milbemycin (sold as Interceptor™). Ivermectin was long used by farmers as a pig and cattle wormer; they found it got rid of all worms in their dogs, too—except tapeworms. Ivermectin has long been used in Australia as a public health measure because it also kills ticks which infest the crossbred dingoes and their Aborigine owners. There it has been found that dosing every six weeks was adequate in controlling the tick problem.
The lifecycle of the heartworm begins with the mosquito feeding on an infested dog. It picks up, with the blood, some tiny heartworm embryos called microfilariae. Within minutes, the microfilariae begin to migrate from the gut to another part of the mosquito, changing into an infective form called larvae. In a couple of weeks these larvae move to the mosquito’s mouth and when the insect bites the dog they escape into the blood, fat, and mucous tissues of that victim. There they continue to develop in the fatty tissue under the dog’s skin and undergo more molts. In a few weeks they enter the veins as immature worms and reach the heart three months after entering the dog. Growing to a length of some seven inches for males and almost twice that for females, they lodge in the heart, copulate, and produce eggs that then hatch into microfilariae, and the cycle is complete.
The danger to the dog is in the heartworms’ interference with flow of blood, proper opening and closing of the heart valves, effective oxygenation of cells, and proper blood flow to the lungs, especially when the worms die and clog up the pulmonary arteries. The principal danger to the dog with an adult heartworm population being treated with arsenic is when the dead worms let go and obstruct the pulmonary arterial flow; pneumonia is then the most likely cause of death, so the dog must be kept from exercise or exertion during this treatment period.
Other worms — I have limited these suggestions to worm problems that are most common in North America. There is insufficient room or reason to describe the other, much more minor, worms that can bother dogs in this region, but if your dog exhibits typical “wormy” symptoms and a couple of routine wormings a few weeks apart don’t improve his condition, take a refrigerated 5 day stool sample to the veterinarian for a complete study.