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Canine Intestinal Parasites

Canine parasites exist internally and externally. Many are species specific and exist only on the dog. Intestinal parasitism exists in all ages of dogs with the greatest frequency in puppies. Types and incidence of parasitism varies with geographic regions. Additionally, age and immune status are significant factors influencing gastrointestinal (GI) parasitism. This article concerns itself with canine GI parasites of North America.

Most parasites are diagnosed by a microscopic fecal examination using various chemicals to help concentrate the population of parasite eggs. Some parasites are visible to the naked eye although, they are not consistently shed into the feces. Some tapeworms shed packages (segments) of eggs consistently into the feces and are easily spotted by the owner. Certain GI parasites consist only of one cell such as, the protozoans; i.e., coccidia, giardia, and cryptosporidium.

Common intestinal parasites: Coccidia are one celled protozoans that are intracellular parasites of the lining of the small intestine that occur with some frequency. Eimeria and Isospora are the two most common coccidia of the dog. Infection occurs upon ingestion of contaminated feces or food. Upon ingestion, the parasite colonizes the lining of the small intestine and reproduction begins. As reproduction progresses, the new coccidia are shed through the feces to the environment. Shedding of the protozoan can be asymptomatic or associated with signs of diarrhea and bloody stools. Puppies are most commonly affected. Most infections are not apparent and resolve on their own by self immunization. Occasionally, signs will occur and can be quite severe in heavily compromised pups. Adult dogs usually display significant immunity. Treatment for coccidia consists of antimicrobials that are bacteriostatic. These drugs stop the growth of coccidia and then the hostıs immune system responds to rid the intestine of the parasite. Sulfas are frequently employed as a coccidiastat. In kennel environments, prevention is essential. Usually good steam cleaning of kennels will eliminate the infestation of the environment. When the environment is difficult to control, coccidiastats can be added in the feed or water for late stage pregnant bitches or young pups 3-6 weeks of age. Coccidia of the dog are not a zoonotic threat.

Cryptosporidium is a tiny coccidia that is can be difficult to confirm on routine microscopic fecal exams. Special stains are required. The organism infects man, cats and dogs. Puppies are primarily at risk. The disease produces voluminous watery diarrhea that varies with the severity of the organism and the health of the host. Immunocompromised dogs are at severe risk. In most dogs, the disease is usually asymptomatic or self limiting. Puppies are most likely to show signs. No treatment is available for eliminating the organism although coccidiastats have been used with questionable success. Antibiotics may have some effect. Treatment is primarily symptomatic to combat fluid loss.

Giardia is another protozoan intestinal parasite that infects many mammals including man. It probably is a zoonotic. The parasite is one of several flagellates (mobile tails attached to the single cell) that infect mammals. The disease produced is variable depending on the individual and age. Young puppies are most often affected. Signs usually occur 1-2 weeks after infection and often the disease goes unnoticed or is self limiting after a bout of diarrhea. It can produce severe diarrhea and fluid loss. Most cases that show signs are mild with minimal depression. The parasite is passed in the feces and is consumed directly by the next host. Giardia is very hardy and can remain in the environment for a number of months waiting for a suitable host. In addition, contaminated water is a frequent source of the flagellate. Diagnosing giardia can be demanding and may require frequent microscopic fecal examinations. Recently immunodiagnostics have been researched with some success. Giardia responds very well to treatment. Metronidazole, an oral antibiotic, is the drug of choice given daily for 5 days. However, because of resistance, other drugs are being tried and may possibly replace metronidazole.

Tapeworms in dogs are less common than in the cat, probably because of their feeding habits and environmental restrictions. They represent a minority of the parasites seen in the dog but do occur regularly. They apparently do not stimulate any immunity by the host. The common tapeworms of dogs pose no threat to humans. However, Echinococcus, an uncommon tapeworm but increasing in frequency, is potentially fatal to humans.

Dipylidium caninum and Taenia pisiformis are the common tapeworms of dogs. They are passed to the dog by ingestion of the intermediate host of the tapeworm. The flea is the intermediate host of Dipylidium and rabbits and rodents are the intermediate host for Taenia. Dogs ingest the intermediate host and release the intermediate stage of the tapeworm into the GI of the final canine host where the parasite matures to an adult in the small bowel. Eggs are shed to the environment from the GI of the dog in small segments that look like small pieces of rice. These segments can often be seen in fresh feces or attached to the adjacent tissues of the dogıs anus. As the segments desiccate they release microscopic eggs into the environment for the cycle to begin again. Mature adult Dipylidium and Taenia reach 50cm. or more in length. Signs of Dipylidium and Taenia infestation are unapparent. These parasites seem to be innocuous in the dog. Their only threat is their repugnancy and the potential to further debilitate a compromised pet. Treatment for these two tapeworms is either oral or by injection under the skin. Several drugs are available. They include praziquantel, epsiprantel, fenbendazole and mebendazole. Prevention of Dipylidium consists of good flea control. Prevention of Taenia is difficult if your dog is a good rodent and rabbit hunter and may require prophylactic tape worming several times a year.

Echinococcus multilocularis is a small tapeworm that lives in the arctic fox, wolf, domestic cat and dog as the final host. Diagnosis in the dog is primarily by microscopic fecal exam. The intermediate host is the rodent; such as moles, shrews and field mice. The range of this parasite is moving south and is found in some of the northern tier states of the US. The zoonotic threat comes from the ingestion of fruit, food or water, contaminated by the feces of the fox, cat or sled dog. The increase in camping has exposed more humans and their pets to the potential of Echinococcus. Once the eggs of Echinococcus are ingested by man they form a large cyst in the liver. The only treatment is surgical removal. Unfortunately, the prognosis is guarded because the cyst itself is very fragile and can rupture with manipulation resulting in death. Treatment for Echinococcus in the dog is the same drugs used for other tapeworms.

Diphyllobothrium latum (DL) is the largest tapeworm of the dog. It is uncommon except in remote areas of the northern US and Canada where dogs, humans and wildlife may come in contact. The final host in addition to the dog is primarily man, but it also exists in the cat, fox, and bear. The worm enters the final host by ingesting raw or under cooked trout, pike, fresh water salmon and perch. DL can grow to an amazing 20 meters in the intestine. Eggs are shed directly into the feces. If shed into water small crustaceans swallow the egg which are then consumed by fresh water fish and ultimately the final host. With each intermediate host, DL matures to infect the final host when eaten. The worm is asymptomatic in the dog, but in man can produce severe anemia. Treatment is no different than other tapeworms in the dog. Diagnosis is primarily by microscopic fecal exam.

Roundworms (Toxocara) are very common. It has been speculated that 85% of puppies are infected with roundworms. Toxocara canis (TC) and Toxocara leonina (TL) are the two roundworms of the dog, with the former being far more prominent. Both worms are large, around 3 inches. Both are diagnosed by standard microscopic fecal exams. False negatives occur when no eggs have been shed into the sample presented. Infection occurs in both TC and TL by ingestion of eggs when contaminated feces are shed into the environment. However, the vast majority of TC infection occurs by transplacental migration from the bitch to the pup. Immature larvae from either method of transmission of TC undergo migration from the gut into various tissues. The majority of the larvae migrate through the liver, diaphragm, lungs and up the major airways. As they move up the trachea, occasionally several worms will be coughed up by the pup and discovered in the expectorant. Most of TC will continue their migration and be swallowed, moving down the esophagus, into the stomach and back into the small intestine where they reach adult status and begin shedding eggs. Some of the migrating larvae become encysted in tissues as migration occurs. They remain there without consequence during the dogıs life. Infection by TL does not produce this larval migration. Most dogs develop some immunity to reinfection of TC and TL. Reinfection can add to the existing burden of encysted immature larvae but usually does not result in intestinal infection. Adult infection is estimated to be around 10-15% in the US. Encysted larvae return to the intestine when severe stress occurs to the host. The best example is the pregnant bitch which regularly passes TC via the placenta to its offspring. As a consequence almost all puppies are positive for roundworms. TC does have a serious zoonotic threat when larval migration enters vital tissue of man, in particular the eye. Children are at the greatest risk because they tend to put their fingers into their mouth without proper hygiene. The high incidence of TC and the serious health concern in children make a cogent argument for vigorous round worming schedules in puppies.

Signs of roundworms can be serious in puppies producing abdominal pain, bloating, dull coat, diarrhea and occasionally fatal small bowel obstruction. Migration can cause respiratory signs that mimic upper respiratory infections. Occasionally, serious pneumonia results. Adult dogs rarely show GI signs but can compromise their overall condition, especially if other diseases are active.

Treatment of roundworms in puppies consists of oral medication at 4, 6 and 8 weeks, followed by a microscopic fecal exam at 11-12 weeks. In adults, annual fecal exams are recommended to remove asymptomatic infections. Monthly heartworm preventive drugs contain good round wormers and effectively worm the dog each month during the heartworm season. There are many good round wormers on the market. Pyrantel pamoate is one the more common effective inexpensive wormers. Other wormers include dichlorvos, febantel, fenbendazole, ivermectim and piperazine.

Hookworms are common parasites of dogs regardless of age. They are most common in warm humid climates but, exist all over North America. Ancylostoma and Uncinaria are the two hookworms found. The incidence of Ancylostoma is just under 20% in all ages of dogs. Uncinaria is found in about 1% of the dogs and is more common in Canada. Both worms are transmitted by chance skin penetration by the immature larvae or by ingestion of contaminated feces.

Hookworm is a zoonotic. Skin penetration of infective larvae penetrates the bare foot of man and causes mostly a self limiting local skin irritation for three weeks. In the dog, hookworm can be severe to unapparent. After eggs are deposited onto the ground in the feces, hot humid temperatures will precipitate the development of larvae. After skin penetration, migration of the larvae into the blood stream carries them around the body and into many tissues. Most are brought to the lungs and like roundworms are swallowed back into the intestinal tract 3 weeks later. As mature hookworms, they attach to the lining of the intestinal track and suck blood. Hookworm larvae also migrate into the gestating pup and continue to mature when the pup is born. Puppy hookworm can be profound and require strong supportive care. Severe hookworm infection can cause marked anemia, intermittent bloody diarrhea, dull dry hair coat, and weight loss. Young and adults dogs that are immunocompromised or suffer with another disease are most at risk.

Hookworm is easily diagnosed by microscopic fecal exams. Treatment involves one of many good drugs available in mild cases. In more severe cases pyrantel pamoate, intravenous therapy, blood transfusions, and good nutritional support are very important. As with roundworm the migrating larvae require several wormings given at 2-3 week intervals. Prevention can be accomplished by annual fecal exams (repeated more often in warm humid climates) or by the use of a monthly wormer in conjunction with heartworm prophylaxis. Filarabits plus, a daily heart wormer, also provides daily hookworm prevention. Prophylaxis includes regular removal of feces. Bleach can be used to disinfect cement dog runs. Treatment of lawns with a commercial larvacide may also be necessary if repeated hookworm infection occurs.

Whipworms are common but less prevalent parasites. Whipworms are found in warm humid climates and are much less prevalent in the western dry areas of North America. In addition, the difficulty in diagnosing this parasite may disguise its actual incidence. It may require several fecal samples to demonstrate the egg in a microscopic exam.

Whipworms are acquired by ingestion of the egg from contaminated feces. The egg is capable of surviving in the environment for months. Upon ingestion, the egg matures and the adult infection occurs in 2-3 months as the worm burrows into the lining of the large bowel and cecum. Clinical signs are that of colitis: straining, mucous diarrhea with occasional blood and an urge to defecate small volumes frequently.

Treatment for whipworms requires several treatments with fenbendazole or febantel for 3-5 days and repeated in 3 weeks. Severe cases of whipworms are not common but, can require surgical intervention. Prophylaxis includes careful removal of feces and bleaching dog runs regularly.

Less common parasites: Strongyloides is a less common intestinal parasite found only in warm, humid areas of the US. Signs of the disease are mainly severe diarrhea often bloody. The worm is quite serious in puppies and will cause death if untreated. The disease is diagnosed by microscopic fecal exam. Infection occurs when contaminated feces are consumed or by skin penetration. Treatment is with one of several drugs that include pyrantel pamoate, fenbendazole, thiabendazole and possibly ivermectin.

Capillaria is a roundworm that resides in the lungs of dogs and foxes. The incidence is under 1% in the US. Infection is by ingestion of contaminated feces. The developing larvae migrate directly to the lungs. Adults lay eggs in the lungs which are moved out the lungs and coughed up, re-swallowed and passed in the feces. Severe infections cause chronic inflammation of the bronchi and trachea, but mild infections are common. Ivermectin may play a role in treatment, but currently there is no recommended therapy.

Paragonimus is an infrequent parasite of the dog that exists almost exclusively in the most northern areas of the Midwest and north central Canada. The parasite is a trematode (fluke) that occurs very infrequently when dogs are exposed to the fresh waters of the north where dogs may come in contact with mink feces. Transmission is by consumption of freshwater crustaceans and snails, acting as an intermediate host. The disease is serious only when the parasite gets into the brain. There is no recommended therapy. Prevention is by eliminating the consumption of freshwater crustaceans and snails.

Nanophyetus salmincola is a small intestinal fluke acquired by dogs when they consume raw salmon from the northwest. The disease exists only in the northwest. The parasite is mostly innocuous. However, within the parasite a more serious threat lives. Many of the flukes are infected with Neorickettsia helminthoeca (salmon poising), a rickettsia which causes fever, anorexia, vomiting, diarrhea and death in up to 90% of the cases. Therapy for salmon poisoning involves supportive care including intravenous fluids and antibiotics. Prevention involves avoidance of raw freshwater fish. No therapy is recommended for infection with the fluke.




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