Keeping your dog worm-free

Keeping your dog worm-free – includes related article

Dori Stehlin


Parasitic worms are a problem that most dog owners have to face at some point in their dogs’ lives. While they all are equally repulsive, they are not all the same. There are actually many different worms that can infect dogs, and they can cause a wide variety of symptoms. What they are, what they do, and how to get rid of them and then prevent reinfection are important things for every dog owner to know.

Heartworm (Dirofilaria immitis)

Adult heartworms, which can grow as long as 12 inches, can cause severe heart, lung and liver damage in dogs. Signs of infection include weight loss (despite a healthy appetite), coughing, difficult or painful breathing, a swollen abdomen and legs, and lethargy. Unfortunately, symptoms do not develop until the disease is well advanced.

Mosquitoes transmit heartworm disease. They pick up the larvae when they bite an infected dog and then deposit the larvae on the next dog they bite. The larvae penetrate the dog’s skin through the mosquito bite. In infected dogs, heartworms are usually found in the right ventricle of the heart and pulmonary artery, and adjacent blood vessels.

To prevent infections with heartworm, veterinarians will do a blood test to detect the presence of the heartworm larvae. In areas where mosquitoes are only a problem in the summer, this test is usually done right before the warm weather starts.

For dogs that are not infected, preventive medicine can keep them that way. The prescription drug diethylcarbamazine (DEC), which is given orally, kills the larvae before they can reach the heart and mature. DEC must be given daily beginning before and continuing for two months after the mosquito season. It may have to be given all year long in areas where the climate is always warm and mosquitoes are always active.

Another drug, ivermectin, also effectively kills the larvae. However, unlike DEC, treatment with ivermectin is only needed once a month during the mosquito season.

FDA approved ivermectin in 1987 for use in dogs to prevent heartworms. FDA regulates veterinary drugs to ensure safety and effectiveness.

Neither of these drugs should be given to dogs with established populations of adult worms and large numbers of larvae. The death of all the heartworms in a badly infected dog could cause shock and even death.

To kill adult worms, treatment with the drug arsenamide is effective. The drug is highly toxic, however, and pneumonia may occur within the first two weeks as the adults die and their fragments lodge in the terminal branches of the pulmonary artery. Because of these adverse effects, dogs treated with arsenamide must be closely observed during their recovery.

In addition to arsenamide, surgery to remove the adult worms is also possible. Of course, any treatment to kill the adult worms should be followed by preventive drugs to prevent reinfection.

Hookworm (Ancylostoma canimum)

Hookworms are small–between one-quarter and three-quarters of an inch long. Adult worms live in the intestines and suck blood from the intestinal wall.

Infection with hookworms can occur if a dog ingests larvae–which infected dogs shed in their stool. Infected mothers can also pass the worms to their unborn puppies across the placenta and to newborns through their milk. In addition, hookworms can penetrate a dog’s skin.

The most serious cases of hookworm disease occur in puppies younger than 4 months. As few as 50 to 100 hookworms can consume a puppy’s blood faster than the bone marrow can make it, leading to severe anemia and death within a month.

Hookworms are not as serious a problem in adult dogs, and a mature, well-nourished dog can be infected without showing any signs. However, these dogs need to be treated; otherwise they can be a source of infection for puppies.

Bloody diarrhea usually accompanies severe infections. Dermatitis can occur when the worms penetrate the skin.

There are several oral drugs that will effectively kill adult worms. Treatment must be repeated in 10 to 14 days to remove any worms that were still larvae when the first dose was given. Besides drug treatment, the dog may require blood transfusions to replace lost blood and a special diet–high in protein, iron and vitamins–to help the animal regain its strength.

Controlling hookworm should begin by insuring that females are free of the parasites before breeding and kept out of contaminated areas during pregnancy. Infection can be prevented with daily doses of both diethylcarbamazine (used to prevent heartworm disease) and styrylpyridinium.

Good sanitation is also essential to prevent infection in both dogs and people. Although canine hookworms can’t mature in people, the larvae can migrate through the skin and subcutaneous tissue, causing serious skin lesions. Paved kennel runs can be sanitized with a solution that contains one cup detergent, one cup sodium borate, one gallon bleach, and approximately four gallons of water.

Roundworms (Toxascaris leonina and Toxocara canis)

Roundworms are tough creatures. Roundworm eggs can withstand freezing and are resistant to most common disinfectants. The eggs are also sticky. They tend to adhere to paws and hair and become mixed with soil.

In some cases, they are also tough to get rid of once a dog is infected. While the larvae of one of the two common roundworm. species–Toxocara canis–may not mature or cause any symptoms in puppies over 6 months and adults, in newborn pups these worms can cause bronchitis, pneumonia and death. In adults, T. canis larvae can migrate throughout the body where they lie dormant in the muscles, connective tissue, kidneys, and many other tissues. These dormant larvae, which are almost impossible to get rid of, become a problem if a dog has puppies. During pregnancy, these larvae again become active and migrate into the developing fetus.

Because of this problem with dormant larvae, most puppies are considered to be infected even if they don’t have symptoms. According to the Merck Veterinary Manual, puppies should be treated as early as 2 weeks of age, and the mothers should be treated at the same time. Repeat treatments are necessary if eggs appear in the feces.

The other roundworm species, Toxascaris leonina does mature in the intestines of adult dogs. Infected dogs may have dull hair and pot bellies. In puppies, more serious symptoms such as vomiting, diarrhea, bronchitis and pneumonia can occur.

There are several drugs available that will eliminate an active roundworm infection, including an over-the-counter product–piperazine salts. Preventing reinfection requires good sanitation. This includes control of rodents and cockroaches because they can be intermediate hosts

In addition, children should be kept away from lactating mothers and young puppies until successful treatment is complete. Although roundworms will not mature in humans, the larvae can migrate through internal organs and cause tissue damage. In rare cases serious damage, such as blindness, may occur.

Whipworms (Trichuris vulpis)

Whipworms are 2 to 3 inches long and can live in a dog’s large intestine for up to 16 months. Eggs, which are passed in an infected dog’s stool, can remain alive for up to five years in a warm, moist environment.

Most dogs infected with whipworms show no sign of disease. Symptoms such as diarrhea and weight loss occur only in the most severe cases.

While there are several prescription drugs available to treat whipworms, both the larvae and the adult whipworms are notoriously resistant to medication, according to Dr. Sandra Woods, a veterinarian with FDA’s Center for Veterinary Medicine. “Elimination may require several treatments over a period of many months and reinfections from a contaminated environment are common,” she said.

Because treatment is so difficult, preventing infection in the first place is important. Because the eggs cannot survive without warmth and moisture, cleanliness and eliminating moist areas can considerably reduce reinfection.

Tapeworms (Dipylidium caninum)

All parasites need a host. But for tapeworms–like many other parasites–one isn’t enough. Before it can infect a dog, it has to infect an intermediate host. While small mammals are the intermediate hosts for some tapeworms, Dipylidium caninum makes its temporary home in the flea. This flea-transmitted tapeworm is the most common one to infect urban dogs, who rarely eat anything but prepared foods.

Tapeworms, which can grow as long as 20 inches, rarely cause serious disease. According to the Merck Veterinary Manual, symptoms can vary from failure to thrive, malaise, irritability, erratic appetite, and shaggy coat to colic, mild diarrhea, emaciation, and seizures.

There are several prescription medications used to eliminate tapeworms, but unless the worm is destroyed completely, the remaining segments can regenerate whole worms in just a few weeks. Because of this potential for the worms to grow again, the stool of dogs being treated for tapeworm must be carefully checked for eggs a few weeks after treatment starts. To prevent reinfection, fleas must be eliminated.

While worms may seem inevitable, they can be prevented in many cases. All puppies should be treated by a veterinarian for hookworm and roundworm whether or not they have symptoms.

Adult dogs should be seen by a vet two or three times a year, according to FDA veterinarian Sandra Woods. “A healthy dog might not have symptoms, but that doesn’t mean harm isn’t being done,” she said.

Determining which worm a dog is infected with requires microscopic examination of blood or fecal samples. For this reason and the fact that many effective medications for worms require a prescription, dog owners should not attempt to diagnose or treat their pets by themselves.

Finally, many of the symptoms caused by worms can also be caused by other diseases. The only way to be sure is to see a veterinarian.

PHOTO : Adult heartworms live in the heart and pulmonary arteries, causing inflammation, roughening of the artery walls, reducing or blocking blood flow. They also cause damage to the lungs, liver and kidneys, as well as the heart.

COPYRIGHT 1988 U.S. Government Printing Office

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