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. Additionaly, 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; 
ie., 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 consist of antimicrobials 
that are bacteriostatic. These drugs stop the growth of coccidia and then 
the host¹s 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 problably 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 
dog¹s anus. As the segments dessicate 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 come 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 accept 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. I f shed into 
water small crustaceans swallow the egg which are then consumed by fresh 
water fish and ultimately the final host. With each intermediated 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 dog¹s 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 result. 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 penetrate 
the bare foot of man and cause 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 carry 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 clients) 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 is 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 lung 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, reswallowed and passed in the feces. Severe infections cause chronic 
inflammation of the bronchi and trachea but, mild infections are common. 
Ivermectin may play a roll 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 poising involves supportive care including 
intravenous fluids and antibiotics. Prevention involves avoidance of raw 
freshwater fish. No therapy is recommended for infection with the fluke.