Roundworms, also called "ascarids," are large, unsegmented internal parasites. They are the most common internal parasites found in companion dogs and cats. Most puppies, even those in well-bred, well-raised, healthy litters, will develop some degree of roundworm infection early in life. Breeders typically de-worm their puppies several times before sending them to their new homes, to eliminate or at least reduce the load of intestinal parasites. Adult roundworms spend most of their lives in a dog's small intestine, which is the part of the gastrointestinal tract that connects the stomach to the large intestine, or colon. Roundworm larvae sometimes migrate out of the small intestine and invade the liver, lungs, kidneys and other organs. This can be fatal, especially in young puppies.
People can also become infected by roundworms, through what is called a "fecal-oral" route. This happens when a person comes into contact with feces from an infected dog, and somehow gets some of that fecal matter into his or her mouth. If roundworm eggs are present, the person probably will become infected. Because humans are not the normal host for canine roundworms, the life cycle of the parasites is abnormal in people. The eggs will hatch in the person's stomach and small intestine, but from there the larvae will migrate elsewhere. This condition is called "visceral larva migrans." Roundworm larvae often migrate into people's eyes and brain, which can be extremely painful, dangerous, damaging and even deadly.
Causes of Roundworms
The two most common species of roundworms found in domestic dogs are Toxocara canis and Toxascaris leonina. A related roundworm that usually infects raccoons, called Baylisascaris, can also infect dogs if they lick or eat raccoon fecal matter containing roundworm eggs. Adult roundworms live and reproduce mainly in the stomach and small intestines of dogs. They can become quite large, growing up to 6 or 7 inches in length. Adult females can lay several hundreds of thousands of eggs in a single day, which ultimately are passed out in the dog's stool. Roundworm eggs are protected by a hard, shell-like substance that enables them to survive for months or even years in the environment, after they are excreted in an infected dog's feces. Dogs of any age, and even people, can become infected by ingesting roundworm eggs or larvae from the soil or contaminated fecal matter. Dogs can also develop roundworm infection if they eat the carcass of an infected animal, which typically is a mouse, rat or other small rodent.
Unborn puppies can become infected with migrating roundworm larvae that pass through their mother's placenta. In fact, this is probably the most common route of infection. Puppies that become infected with large numbers of these larvae transplacentally often die before or shortly after they are born. Newborns can also become infected by ingesting roundworm eggs or larvae through their mother's milk. When a young dog becomes infected with roundworms through whatever route, the eggs usually hatch in its stomach. From there, the larvae migrate through the puppy's digestive and circulatory tracts, ultimately lodging in tiny blood vessels of the lungs, called "capillaries." The larvae are coughed up, or crawl up, the inside of the puppy's windpipe (trachea) into its throat. Once they arrive there, the larvae are swallowed and return to the puppy's stomach and small intestines, where they mature into adults. After this, the cycle begins again.
After about 6 months of age, most dogs develop some degree of resistance to roundworms. The larval parasites tend to form cysts in the tissues of older puppies and adult dogs, rather than completing their normal life cycle. In the encysted form, roundworms are fairly immune to most de-worming medications and, for the most part, cannot be detected or removed by the dog's immune system. They also do not cause clinical symptoms when they are in the cyst form. However, encysted roundworm larvae become activated in pregnant females, where they migrate to and through the placenta and into the mammary milk glands. This is how most puppies become infected.
Prevention of Roundworms
One of the best ways to prevent roundworm infection in puppies is to de-worm the bitch before breeding her, and again several times after day 40 of her pregnancy. Unfortunately, some encysted larvae probably will escape these treatments and will infect the puppies either across the placenta or in the mother's milk. Once the puppies are born, they can be de-wormed starting at about 3 weeks, under current veterinary recommendations. A number of medications are safe and effective at killing roundworms and other internal parasites, even in young dogs. Some of the canine de-worming medications that owners may have heard of are pyrantel pamoate (Strongid or Nemex), Drontol Plus, Telmintic, Panacur, Interceptor, Heartgard Plus and Vercom, among others. Some de-wormers are tablets, while others come in liquid or paste forms. Because each medication is effective against a different parasite or combination of parasites, a dog's owner should consult with a veterinarian for the best de-worming protocol. Most roundworm preventions for puppies involve giving a series of dosages over several weeks, to increase the chances of killing all adults and also killing the migrating and maturing larvae. A general rule of thumb is to de-worm puppies at 3, 6 and 8 weeks of age, and to continue treatment if a fecal examination shows that internal parasites are still present.
Most roundworm eggs are extremely hardy and highly resistant to environmental factors. They can survive outside of their host and remain infective for years. It is almost impossible to remove roundworm eggs from soil that is heavily contaminated.
Roundworm larvae can cause a very serious condition in people called "visceral larva migrans," which is particularly dangerous to young children. Visceral larva migrans develops when a person ingests roundworm eggs, particularly those of Toxocara canis or the raccoon roundworm, Baylisascaris. People can also become infected when the parasites penetrate their skin directly. Infants and toddlers most commonly develop this condition from poor hygiene, eating dirt and/or walking barefoot in areas where dogs, raccoons or other mammals frequently defecate, such as on soil, in grassy areas and in sandboxes in rural areas or city parks.
When taken in by a person, roundworm eggs hatch and develop into larvae in the stomach and small intestine, as they would in their canine host. However, they do not mature into adults there, as they normally would in a dog. Instead, they migrate out of the digestive tract by tunneling through the intestinal wall. They can end up in any number of places, including the liver, kidneys, spleen, heart, lungs, skin, eyes and/or brain. In infants and toddlers, roundworm larvae often migrate to the eyes and brain, causing blindness. Affected eyes may need to be removed surgically, through a procedure known as "enucleation".
How Roundworms Affect Dogs
Roundworms can affect dogs of all ages, but they are particularly hazardous to young puppies. Newborns are at the greatest risk of developing severe disease or even dying from these parasites. Puppies between 2 and 6 months of age may have mild signs from roundworms, including abdominal pain (belly-aches), diarrhea and general ill-thrift. Adults and adolescents over 6 months of age rarely develop detectable symptoms when they are infected with roundworms.
Symptoms of Roundworms
Newborn puppies get roundworms either through the placenta before they are born (in utero), or through their mother's milk. In very young dogs, the typical symptoms of roundworm infection include one or more of the following:
Vomiting (mild to severe; with or without visible worms in the vomitus that look like moving strands of spaghetti)
Diarrhea (mild to severe; with or without visible worms in the feces that look like moving strands of spaghetti)
Dull hair coat
Poor skin condition
Distended abdomen ("pot-bellied" appearance)
Abdominal pain (crying; whimpering; biting at belly)
Loss of appetite (inappetence; anorexia)
Ill thrift (chronic and often dramatic)
In severe cases, roundworms cause anemia, which is an abnormally low level of red blood cells in circulation. Anemia often causes:
Respiratory distress (difficulty breathing; dyspnea)
Puppies with an especially large burden of roundworm larvae can develop severe parasitic pneumonia. Their lungs and liver are commonly damaged by the maturing parasites. Unfortunately, when this happens, the puppies often die, especially during the first week or two of life. Adult roundworms can become tangled in the digestive tract of older puppies and cause death due to intestinal obstruction or rupture, although this is uncommon.
Dogs at Increased Risk
Very young puppies – especially those whose mother was not vaccinated before and during pregnancy – have a highly increased chance of becoming infected with roundworms. Older dogs with compromised immune systems also are at increased risk of developing roundworm infections. These parasites do not discriminate between genders or breeds; dogs of either sex and of any breed or mix of breeds are equally susceptible to infection.
How Roundworms in Dogs are Diagnosed
Roundworms are extremely common in domestic dogs, especially in newborns. Fortunately, they are not particularly difficult to diagnose. A veterinarian presented with a puppy showing signs of internal parasites will take a history from the owner and perform a thorough physical examination. He probably will also take a blood sample to run routine blood work, including a complete blood count and a serum biochemistry panel. A urine sample may also be taken for a urinalysis, which is another common test performed as part of an initial work-up. The results of these tests may suggest that the puppy has an internal parasite infection. For example, the puppy may be anemic (have low levels of circulating red blood cells), have liver enzyme abnormalities, or have abnormal numbers of circulating white blood cells, which can reflect a mounting immune response to internal parasites.
The best way to diagnose roundworms is to analyze the dog's feces. The simplest way to do this is through a fecal flotation. This test is performed on a small, fresh fecal sample, which usually is taken manually at the veterinary clinic. It can also be done on a fresh stool sample brought in by the dog's owner. The fecal sample will be mixed with a solution that has specific chemical properties which enable parasite eggs and cysts to float to its surface. After the solution and the feces are mixed in a glass beaker, the mixture will be strained into a test tube. A thin glass coverslip will be placed on top of the full test tube, coming into direct contact with the mixture. The contents of the tube will then be mixed mechanically in a centrifuge, at a set speed for a defined period of time. After being spun, the tube will be allowed to sit, so that any parasite eggs and cysts can float to the surface. In theory, after this process, the eggs and cysts will rise to the surface and stick to the glass coverslip, which will be in direct contact with the mixture.
After an appropriate resting period, the coverslip will be carefully removed, placed sample-side down onto a regular glass slide and examined under a microscope. The eggs of many different internal parasites, including roundworms, can be identified in this fashion. Most parasite eggs look different depending upon their species. Because roundworm eggs are excreted sporadically in the feces of an infected dog, a single negative result from a fecal flotation test does not necessarily mean that the dog is free from these parasites. However, a positive test, especially if lots of eggs are identified, is always diagnostic.
Another way to diagnose roundworms is by examining a fecal smear. The stool sample for this test is taken directly from the dog's anus with a cotton swab, smeared on a glass slide, sometimes stained with certain dyes and then examined under a microscope for bacteria, parasite eggs and other abnormalities. This test is less specific and less commonly used for internal parasites than is the fecal floatation.
Sometimes, adult roundworms (or pieces of adult worms) can be seen in the vomitus or feces of infected dogs. This is not especially common, which probably is a good thing because adult roundworms are quite large and usually are disturbing to owners who see them.
Most veterinarians can easily perform an in-house fecal floatation on a fresh stool sample. The results will be available in short order. Roundworm infections are common and potentially dangerous to young puppies. Owners should be sure that their puppies are de-wormed appropriately from birth, and they should follow an appropriate de-worming protocol according to the puppy's veterinarian.
Treatment for roundworms involves supportive care, administration of de-worming medications, appropriate follow-up and prevention of future infection with a regular de-worming protocol. A number of anti-parasitic drugs are available to treat parasites in dogs. Medical and common names that owners may recognize for some of these medications include Interceptor, Sentinel, Milbemycin, Selamectin, Pyrantel, Revolution, Drontal, Nemex, Heartguard, Ivermectin, Fenbendazole, Panacur, Dichlorvos, Task Tabs, Happy Jack and Filaribits. There are others, as well. Some of these are heartworm preventatives that a dog may already be receiving. De-worming recommendations are made by veterinary professionals not only for the health of the animals involved, but also to reduce the risk of human infection by managing the parasite burden in the environment.
De-wormers, or anti-parasitic medicines, are called "anthelmintics." Unfortunately, most anthelmintics will not eliminate all of the sequestered larval or encysted forms of roundworms, especially in fetuses that become infected inside the uterus after day 40 of the mother's pregnancy. Roundworm larvae can migrate widely throughout infected dogs. They often become encapsulated, or sequestered, in skeletal muscle and the tissue of the lungs, kidneys and other organs. Most effective roundworm treatment protocols involve giving a series of doses over a matter of weeks, to increase the chances of killing all adults and migrating larvae as they mature. Current veterinary recommendations are that puppies should be de-wormed at least 3 or 4 times, starting at about 3 weeks of age and continuing at two-week intervals thereafter. Adults usually are given one or two treatments, depending on the medication used and the preferred protocol suggested by the dog's veterinarian. Daily treatments may be recommended as well, depending upon the type of anthelmintic medication used.
Puppies that are severely debilitated by roundworm infestation may require in-patient supportive care, including intravenous fluids and appropriate nutritional support, while anti-parasitic drugs are administered. Puppies that are suffering from pneumonia caused by migration of parasites into their lungs may develop a severe reaction to parasiticidal drugs, because the bodies of dead roundworms can accumulate in their lungs and bloodstream. If this happens, steroids may be recommended to help manage the inflammatory response. Depending upon the situation, the veterinarian may also suggest that pregnant females be treated with de-wormers from about the 40th day of pregnancy until a week or so after whelping, to improve their puppies' chances of being born ascarid-free.
If a dog is diagnosed with roundworms, all potentially contaminated areas should be cleaned and disinfected thoroughly. Consider using a high-pressure water washer along with a mixture of bleach and water. While this will not kill roundworm eggs, it can help to loosen them up from environmental surfaces, especially in kennels or other high-traffic areas. This is particularly important for owners who have young puppies and/or children. All fecal material should be removed from yards, dog runs and kennel areas as soon as possible. Infected dogs' blankets and bedding should be washed in hot water with a detergent that contains bleach.
The prognosis for dogs with roundworms is usually very good, as long as their infection is treated appropriately. Owners who are considering breeding their bitch should discuss with their veterinarian how best to ensure that she is properly treated for roundworm infection before and during her pregnancy. Owners of new puppies should discuss appropriate de-worming protocols with the breeder and with their puppy's veterinarian. They should start (or hopefully continue) a sound de-worming regimen.