Internal Parasites

Most animals have worms and other parasites that live inside their bodies. Most worm infections are relatively easy to control. If they are not controlled, they weaken the host dog to the point that other medical problems occur. Roundworm infection can kill puppies and cause severe problems in adults, as the hatched larvae travel to the lungs and trachea through the bloodstream.


The roundworms that infect dogs are known scientifically as Toxocara canis. They live in the dog's intestines and shed eggs continually. It has been estimated that the dog produces about 6 or more ounces of feces every day. Each ounce of feces averages hundreds of thousands of roundworm eggs. There are no known areas in which dogs roam that do not contain roundworm eggs. The greatest danger of roundworms is that they infect people, too. It is wise to have your dog tested regularly for roundworms. In young puppies, roundworms cause bloated bellies, diarrhea, coughing and vomiting, and are transmitted from the dam (through blood or milk). Affected puppies will not appear as animated as normal puppies. The worms appear spaghetti-like, measuring as long as 6 inches. Adult dogs can acquire roundworms through coprophagia (eating contaminated feces) or by killing rodents that carry roundworms. Cleanliness is the best preventive for roundworms. Always pick up after your dog and dispose feces in appropriate receptacles.


In the United States, dog owners have to be concerned about 4 different species of hookworm, the most common and most serious of which is Ancylostoma caninum, which prefers warm climates. The other are Ancylostoma braziliense, Ancylostoma tubaeforme and Uncinaria stenocephala, the latter of which is a concern to dogs living in the Northern U.S. and Canada, as this species prefers cold climates. Hookworms are dangerous to humans as well as to dogs and cats, and can be the cause of severe anemia due to iron deficiency. The worm uses its teeth to attach itself to the dog's intestines and changes the site of its attachment about 6 times per day. Each time the worm repositions itself, the dog loses blood and become anemic. Ancylostoma caninum is the most likely of the 4 species to cause anemia in the dog. Symptoms of hookworm infection include dark stools, weight loss, general weakness, pale coloration and anemia, as well as possible skin problems. Fortunately, hookworms are easily purged from the affected dog with a number of medications that have proven effective. Most heartworm preventives include hookworm insecticide as well. As a preventive, use disposable gloves or a "poop-scoop" to pick up your dog's droppings and prevent your dog (or neighborhood cats) from defecating in children's play areas.

Owners also must be aware that hookworms can infect humans, who can acquire the larvae through exposure to contaminated feces. Since the worms cannot complete their life cycle on a human, the worms simply infest the skin and cause irritation. This condition is known as cutaneous larva migrans syndrome.


There are many species of tapeworm, all of which are carried by fleas. The most common tapeworm affecting dogs is known as Dipylidium caninum. The dog eats the flea and starts the tapeworm cycle. Humans can also be infected with tapeworms. Fleas are so small that your dog can pass them onto your hands, your plate or your food and thus make it possible for you to digest a flea that is carrying tapeworm eggs. While tapeworm infection is not life-threatening in dogs, it can be the cause of a very serious liver disease for humans. Effective flea control and good sanitation practices will keep you and your family free from tapeworm infections.


In North America, whipworms are counted among the most common parasitic worms in dogs. The whipworm's scientific name is Trichuris vulpis. These worms attach themselves in the lower parts of the intestine, where they feed. Affected dogs may only experience upset stomach, colic and diarrhea. These worms, however, can live for months or years in the dog, beginning their larval stage in the small intestine, spending their adult stages in the large intestine and finally passing infective eggs through the dog's feces. The only way to detect whipworms is through a fecal examination, though this is not always foolproof. Treatment for whipworms is tricky, due to the worm's unusual life cycle pattern, and very often dogs are reinfected due to exposure to infective eggs on the ground. The whipworm eggs can survive in the environment for as long as 5 years; thus, cleaning up dropping in your own backyard as well as in the public places is absolutely essential for sanitation purposes and the health of your dog and others.


Though less common than roundworms, hookworms and tapeworms, threadworms concern dog owners in the Southwestern U.S. and Gulf Coast area where the climate is hot and humid. Living in the small intestine of the dog, this worm measures a mere 2 millimeters and is round in shape. Like that of the whipworm, the threadworm's life cycle is very complex and the eggs and larvae are passed through the feces. A deadly disease in humans, Strongyloides readily infects people, and the handling of feces is the most common means of transmission. Threadworms are most often seen in young puppies with bloody diarrhea and pneumonia. Sick puppies must be isolated and treated immediately; vets recommend a follow up treatment one month later.


Heartworms are thin, extended worms up to 12 inches long, which live in a dog's heart and the major blood vessels surrounding it. Dogs may have up to 200 worms. Symptoms may be loss of energy, loss of appetite, coughing, pot belly and anemia. Heartworms are transmitted by mosquitoes. The mosquito drinks the blood of an infected dog and takes the larvae with the blood. The larvae, called microfilariae, develop within the body of the mosquito and are passed on to the next dog bitten after the larvae mature. It takes 2 to 3 weeks for the larvae to develop to the infective stage within the body of the mosquito. Dogs are usually treated at about 6 weeks of age and maintained on a prophylactic dose given monthly. >Blood testing for heartworms is not necessarily indicative of how seriously your dog is affected. Although this is a dangerous disease, it is not easy for a dog to be infected. Discuss the various preventives with your vet, as there are many different types now available.

Angiostrongylus vasorum (French heartworm or canine lungworm) infection in dogs is an emerging disease that has high mortality. Canids are the definitive host, slugs and frogs act as intermediate hosts. First-stage (L1) larvae hatching from the eggs enter the alveoli, pass through the tracheobronchial tree, pharynx, gastrointestinal tract, and are excreted in the feces. Dog feces are an attractive food for many gastropod molluscs in which the larvae develop to become infectious for the final host. The infections are the cause of severe cardiopulmonary diseases in dogs. The adult worm (13–21 mm) is a nematode that resides in the pulmonary arteries and right heart in dogs and other wild canids. Infected dogs may have clinical signs of verminous pneumonia, disorders of blood clotting, neurological disorders, and pulmonary hypertension. Naturally infected dogs may show clinical or internal signs of bleeding with associated complications. The infection also induces a wide range of other clinical signs, such as intracranial bleeding and gastrointestinal bleeding. Increased bleeding and partial deficiency of fibrinogen can be treated successfully with tranexamic acid and FFP transfusions.1,2 Monthly administrations of NexGard Spectra® is an effective treatment for the prevention of canine French heartworm infection.3

Diseases Caused By Drinking Contaminated Water

The diseases which are carried by water and get entry to animal body through drinking water are known as water-borne diseases. The causative agents of water-borne diseases may be viruses, bacteria, protozoa, or helminths. The diseases like viral hepatitis are caused by virus. Dysentery which is caused by the protozoan Entamoeba histolytica is spread either by drinking contaminated water or ingesting food washed in contaminated water. Other protozoal diseases such as those caused by Balantidium coli, Cryptosporidium spp. are spread in a similar way. Schistosomiasis, also known as bilharzia, is a water-borne disease caused by worms of the genus Schistosoma.

One of the parasitic diseases that animals can get from eating waterfowl infected with Alaria species of trematode parasitic worms is called alariasis. A number of species of the trematode genus, Alaria, including Alaria mustelae in mink, and A. americana and A. canis in dogs, foxes, wolves and coyotes are parasitic in domestic and wild animals. Alaria eggs are passed in the feces of mammalian hosts to which Alaria is not pathogenic. Following larval development in a snail intermediate host, a second intermediate host is infected (usually frog). Infection of dogs and cats also occurs by ingestion of infected frogs. Acute symptoms may develop within a short period of time, while findings of chronic infestation may occur after months or even years. Systemic infection produces bronchiospasms, subcutaneous nodules, and infiltration of cardiopulmonary, gastrointestinal, biliary, hepatic, and central nervous systems. Complications may include hypersensitivity vasculitis (inflammation of blood vessels), blood clots, and death.


  1. Hyperfibrinolysis and Hypofibrinogenemia Diagnosed With Rotational Thromboelastometry in Dogs Naturally Infected With Angiostrongylus vasorum. J Vet Intern Med. 2017 Jul-Aug; 31(4): 1091–1099.
  2. GIS-supported epidemiological analysis on canine Angiostrongylus vasorum and Crenosoma vulpis infections in Germany. Parasit Vectors. 2017; 10: 108.
  3. Monthly administrations of milbemycin oxime plus afoxolaner chewable tablets to prevent Angiostrongylus vasorum infection in dogs. Parasit Vectors. 2016; 9(1): 485.