Ascaridae infection in dogs: causes, symptoms and treatment


Roundworms are the most common canine internal parasites. Adult roundworms spend most of their life in the stomach and small intestine. Females lay hundreds of thousands of eggs per day, which are excreted in the stool and survive in the environment for years.

The dog contracts the infection when he ingests the eggs of this parasite or eats infected rodents. Roundworms cause abdominal pain, vomiting, diarrhea, coughing, insufficient weight gain or inappropriate weight loss. Infected dogs develop coat opacity, abdominal distension and stunted growth. If the animal exhibits one or more of these symptoms, it is advisable to go to the vet as soon as possible. Furthermore, roundworms can also infect humans.


The two most common species of roundworms found in domestic dogs are Toxocara canis is Toxascaris leonina. There is also an ascarid, which usually infects raccoons, called Baylisascaris, which can also infect dogs if they lick or ingest raccoon fecal matter containing the parasite’s eggs.

Adult roundworms live and reproduce mainly in the stomach and small intestine of the infected dog. Their length can reach 15-17 centimeters. Adult females can lay several hundred thousand eggs in a single day, which are eventually expelled into the dog’s stool. Roundworm eggs are protected by a hard and resistant substance that allows them to survive for months or even years in the environment after being excreted in the feces of an infected dog.

Dogs of any age, and also people, can contract the infection by ingesting the eggs or larvae of this parasite present in the soil or contaminated faecal material. Dogs can develop an ascarid infection as a result of ingesting the carcass of an infected animal, typically a mouse or other small rodent.

The unborn puppies can become infected due to the migration of the larvae through the mother’s placenta. This is probably the most common way of transmitting the infection. Puppies who contract the infection by transplacental transmission, due to a high quantity of larvae, often die before or shortly after birth. Even newborn puppies can become infected by ingesting the parasite’s eggs or larvae through breast milk.

Regardless of how the infection is transmitted, when a young dog becomes infected, eggs generally hatch in the animal’s stomach. From here, the larvae migrate through the puppy’s digestive and circulatory systems, settling in the small pulmonary blood vessels, called “capillaries”. The larvae are sputum coughed or crawl up the inside of the puppy’s trachea reaching the throat. Once here, the larvae are ingested and return to the puppy’s stomach and small intestine where they mature to adults. Thereafter, the cycle begins again.

After about 6 months of age, most dogs develop some degree of resistance to roundworms. Larval parasites tend to form cysts in the tissues of larger puppies and adult dogs, rather than completing their normal life cycle. In the encysted form, ascarids are quite immune to most deworming drugs and difficult to detect or remove from the dog’s immune system. However, the roundworm larvae encysted in pregnant females, where they migrate to and through the placenta and mammary glands. This is how most puppies get infected.


Roundworms can affect dogs of all ages, but are especially dangerous for young puppies. Newborn puppies have an increased risk of developing a severe form of the disease or even of dying from these parasites. Puppies between 2 and 6 months of age may exhibit mild signs, including abdominal pain, diarrhea and stunted growth. Adult and adolescent dogs over the age of 6 months rarely develop detectable symptoms when they contract the infection.

As mentioned above, newborn puppies can contract the infection through the placenta before being born (in utero) or through breast milk. In very young dogs, the typical symptoms of ascaridiasis include one or more of the following:

  • Vomizione (mild to severe, with or without visible worms in vomiting)
  • Diarrhea (mild to severe, with or without visible worms in the stool)
  • Vomiting (intermittent)

In severe cases, roundworms cause anemia, which is an abnormally low level of circulating red blood cells. Anemia often causes:

  • Respiratory distress (difficulty in breathing, wheezing)

Puppies with particularly large numbers of larvae can develop severe parasitic pneumonia. Lungs and liver are commonly damaged by ripening parasites. Unfortunately, when this happens, puppies often die, especially during the first or first two weeks of life. Adult roundworms can take root in the digestive system of older puppies and cause death due to intestinal occlusion or rupture, although this is rare.


Dogs most at risk

Very young puppies, especially those whose mother has not been vaccinated before and during pregnancy, are more likely to get infected. Older dogs with compromised immune systems also have a higher risk of developing roundworm infection. These parasites do not have a particular preference for gender or race. It follows that any dog ​​can be susceptible to infection.


Roundworms are extremely common in domestic dogs, particularly in newborn puppies. Fortunately, they are not particularly difficult to diagnose.

The vet will review the dog’s medical history and conduct a careful physical examination. Probably, it will also pick up a blood sample which will be subjected to a subsequent analysis, inclusive of complete blood count and biochemical panel of the serum. You may also decide to collect a urine sample to perform a urine test, another common test that is typically done as part of an initial diagnostic protocol. The results of these tests may suggest the presence of an infection with internal parasites. For example, the puppy may be anemic, have abnormal liver enzymes or abnormal amounts of circulating white blood cells, which may reflect a growing immune response to internal parasites.

The best way to diagnose the presence of roundworms is to analyze the dog’s stool. The easiest way is by faecal flotation. This test is conducted on a small fresh stool sample, which is usually collected manually at the veterinary clinic. It can also be performed on a fresh stool sample brought by the owner of the animal. The faecal sample will be mixed inside a glass beaker with a solution characterized by specific chemical properties that will allow the parasite’s eggs and cysts, if present, to rise to the surface. Then the mixture will be transferred to a test tube. A coverslip will be applied on the upper part of the latter (adhesion slide) which will be in direct contact with the mixture. The contents of the mixture will subsequently be centrifuged. Once this operation is finished, the test tube will be left to rest so that any eggs and cysts rise to the surface. In theory, after this process, the eggs and the surface-raised cysts will adhere to the coverslip. The latter will then be carefully removed and positioned, with the part relating to the sample facing downwards, on a slide and examined under a microscope.

The eggs of many internal parasites, including roundworms, can be identified in this way. Most parasite eggs differ in appearance depending on the specific species. Since roundworm eggs are sporadically excreted in the feces of an infected dog, a single negative outcome following faecal flotation does not necessarily mean that the dog is free of these parasites. However, a positive outcome, especially if a large quantity of eggs are detected, is always diagnostic.

Another way to diagnose roundworms is toexamination of a fecal smear. In this case, the stool sample is collected directly from the dog’s anus, lying on a slide, sometimes dyed with some dyes and then examined under a microscope for bacteria, parasite eggs and other anomalies. This test is less specific and less used for the search for internal parasites compared to faecal flotation.

Sometimes adult roundworms (or portions of adult worms) may be visible in the vomit or feces of infected dogs. This, however, is not particularly common.


Treatment includes supportive therapy, administration of deworming drugs, adequate follow-up and prevention of possible reinfection through a regular deworming protocol.

A variety of pesticide medications are available to treat canine parasites. Some common medications include Interceptor, Sentinel, Milbemycin, Selamectin, Pyrantel, Drontal, Nemex, Heartgard, Ivermectina, Fenbendazole, Panacur, Dichlorvos, Happy Jack and Filaribits. There are also others. Some of these are preventive of heartworm disease. The recommendations relating to deworming are made by the veterinarian not only for the health of the animals involved, but also to reduce the risk of human infection by managing the parasite present in the environment.

Vermifuge or antiparasitic drugs are called “anthelmintics”. Unfortunately, most anthelmintics will not eliminate all isolated larval or encysted forms of roundworms, especially in fetuses that have contracted infection inside the uterus after the mother’s 40th day of pregnancy. Roundworm larvae can migrate to various body sites. They often become encapsulated in skeletal muscle and in the tissues of the lungs, kidneys and other organs.

The most effective treatment protocols involve the administration of a series of dosages over the course of several weeks to increase the chances of killing all adult and migrating larvae in the maturing phase. The current veterinary recommendations provide for the deworming of puppies (which must be carried out at least 3 or 4 times) at the age of 3 weeks and then at intervals of 2 weeks. Adults are usually given 1 or 2 treatments, depending on the drug used and the preferable protocol suggested by the veterinarian. Daily treatments may also be recommended, depending on the type of anthelmintic drug used.

The severely debilitated puppies from infestation they may need supportive therapy in hospitalization, including intravenous fluids and adequate nutritional support, while antiparasitic drugs are administered. Puppies suffering from pneumonia, caused by the migration of parasites into the lungs, can develop a severe reaction to pesticides, as the bodies of dead roundworms can accumulate in the lungs and bloodstream. If this happens, steroids may be recommended to help manage the inflammatory response. Depending on the situation, the veterinarian may also suggest that pregnant females be treated with dewormers starting from the 40th day of pregnancy up to a week after giving birth, in order to improve the chances that the puppies will be born without roundworms.

If the dog is diagnosed with roundworms, all potentially contaminated areas should be cleaned and disinfected with care. It is possible to use a high pressure washer with a mixture of bleach and water. Although this does not kill the parasite’s eggs, it can still help reduce the amount present on environmental surfaces. This is particularly important if there are young puppies and / or children in the home environment. All faecal matter should be removed from gardens, dog spaces and kennel areas as soon as possible. Blankets from infected dogs should be washed in warm water with a bleach-containing cleaner.

The prognosis is usually very good, as long as the infection is treated appropriately.


One of the best ways to prevent roundworm infection in puppies is to deworm the mother before mating and then on the 40th day of gestation. Unfortunately, some encysted larvae are likely to resist these treatments and infect puppies through the placenta or breast milk.

Once born, puppies can be wormed once they reach 3 weeks of age, according to current veterinary recommendations. There are several safe and effective drugs capable of killing roundworms and other internal parasites, even in young dogs. Some of these drugs include Pyrantel pamoato (Strongid or Nemex), Drontol Plus, Telmintic, Panacur, Interceptor and Heartgard Plus, among others. Some deworming drugs are available in tablets, while others in liquid form or in the form of a paste. Since the effectiveness of each drug depends on the type of parasite or the combination of parasites to be treated, it is advisable to always consult the veterinarian for the formulation of the most suitable deworming protocol.

For puppies, the preventive protocol in most cases involves the administration of a series of dosages over several weeks, in order to increase the probability of killing adult roundworms and migrating or maturing larvae. In general, it is advisable to de-worm puppies at 3, 6 and 8 weeks of age and to continue treatment if the stool examination should again detect the presence of internal parasites.

Most roundworm eggs are extremely resistant to environmental factors. They can survive outside the host organism and remain infectious for years. It is almost impossible to remove the eggs of this parasite from heavily contaminated soil.

Ascarids and human being

Roundworm larvae can cause a very serious condition in humans, called Visceral larva migrans, especially dangerous for young children. The visceral larva migrans develops when an individual ingests the parasite’s eggs, especially the eggs of Toxocara canis. The human being can also contract the infection when the parasites directly penetrate the skin. Infants and children develop this condition more commonly as a result of poor hygiene, ingestion of dirt and / or walking barefoot in areas where dogs or other mammals frequently defecate, such as land and grassy areas.

When the parasite’s eggs are ingested, they hatch and develop into larvae in the stomach and small intestine, just like in dogs. However, they do not mature to adults there, as in the case of the dog. Instead, they migrate outside the digestive system by digging tunnels through the intestinal wall. They can reach various bodily sites, including the liver, kidneys, spleen, heart, lungs, skin, eyes and / or brain. In infants and young children, roundworm larvae often migrate to the eyes and brain, causing blindness. Affected eyes may need to be removed surgically by means of a procedure known as “enucleation”.

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