Roundworms in Dogs

Roundworms, nematodes or ascarid worms are intestinal parasites that live freely in the intestine, obtaining their nutriment from the partially digested intestinal contents. The name is derived from their round bodies to differentiate them from tapeworms that have flattened bodies.

Two are important in the dog, Toxocara canis and Toxascaris leonina. The former has greater capability for producing disease and also is important because it can be transmitted to people on rare occasions.

How did my dog pick up roundworms?

Microcscopic eggs are passed from infected dogs in the faeces. These are picked up by susceptible dogs during their habit of sniffing one anothers stools (faeces). They are also picked up by other susceptible animals including rodents and birds. In these they do not mature to adults but if this “paratenic” host is eaten by a dog, completion of the life cycle will take place and the dog can become infected with the nematode.

In the dog the worm undergoes a complicated life cyle before mature roundworms are found in the bowel. This involves several stages and also migration through various tissues. Roundworm larvae (immature worms) can encyst in the host’s tissues. This is important in the bitch because under the influence of the hormones in pregnancy these encysted larvae will start to develop and ultimately cross the placenta into the unborn puppy. Thus puppies can be born with worms and can be passing fertile eggs from adult worms in their bowels by the time they are approximately eleven days old. 

Similarly other larvae will enter the mother’s mammary glands and are another source of infection to the suckling puppy.

Are roundworms much of a problem to my dog?

The main problems occur in puppies.  Up to twelve day old puppies may show signs of noisy breathing accompanied by a nasal discharge especially when suckling. There is often retarded growth. From two weeks of age onwards vomiting and abdominal discomfort, diarrhoea and lack of growth may be seen. From approximately six weeks old there may be chronic diarrhoea and a distended abdomen, the so called “pot belly.”

However sometimes quite heavy infestations in puppies will show no clinical signs until ultimately it is realised that the puppy is not as well grown as some of the litter mates. On rare occasions, the worms may cause a physical intestinal obstruction and sever clinical signs will be seen.

The life cycle of Toxocara canis is more complicated than that of other nematode worms  found in dogs. Adult dogs swallowing infected larvae may result in the majority of the larvae encysting in the dog’s tissues. Few worms will actually mature in the bowel.  Consequently few eggs are passed in the stool thus leading to difficulty in definitive diagnosis.

How is the condition diagnosed?

In puppies clinical signs – stunted growth, pot belly, recurrent diarrhoea are a good indication but definitive diagnosis is by microscopic examination of the dog’s faeces. Since in the majority of infestations only a moderate number of eggs are passed, do not be surprised if you are requested to submit more than one sample!

Is it true that children can pick up roundworm infections?

If the infected eggs of Toxocara canis are swallowed by people the larvae can invade the tissues and become encysted in various organs. Humans thus act like any other paratenic host. If a large number of infected eggs are ingested then clinical disease may become apparent. This is particularly important if children are involved.

"If the infected eggs of Toxocara canis are swallowed by people the larvae can invade the tissues and become encysted in various organs."

Very rarely liver problems may be caused and even less commonly the larvae can migrate to the eye where they can cause blindness. However the risk is really extremely low.

What is the treatment?

Treatment is simple, relatively inexpensive and very effective provided it is carried out conscientiously. There are many safe and effective preparations available to kill roundworms in the intestine. With some the worms are passed whole but dead. Other preparations kill the worms which are then digested so that no worms are passed to show that the preparation has been effective.

In addition some of the spot-on preparations used for flea, other ectoparasite control or monthly heartworm tablets may also be effective against roundworms.

However the majority of preparations available today, both over-the-counter and on prescription, kill only the adult worms and do not affect migrating or encysting larvae. It is therefore important that repeated treatments are carried out and it is for this reason that we suggest worming puppies every two weeks until at least eight weeks of age and then at a regular basis thereafter.

What about eggs passed in the environment?

When first passed the eggs are not infective but after a period of time which may vary from weeks to months depending on temperature and conditions, the eggs develop into infective larvae (L.2). Optimally this takes approximately four weeks. These can remain viable within the environment for a considerable time and are particularly resistant.

Removal of the dog’s faeces as soon as passed, since when any eggs are not then infective, is by far the best method of control.

What is the most effective strategy I can employ to control infection in my dogs, protect my family and reduce contamination of the environment?

1.  In addition to any previous worming pregnant bitches must be de-wormed in late pregnancy, (after the 42nd day). This will help to reduce potential contamination of the environment for new born puppies.

2.  Puppies should be treated from about two weeks of age and this must be repeated regularly. Today there are many safe preparations available. Please contact us for advice.

3.  Adult dogs remain susceptible to reinfection with roundworms throughout their lives and therefore regular deworming is important. This should be carried out at least twice yearly and more frequently in high risk situations, e.g. exercise in a local park frequented by a lot of dogs, attendance at training classes, shows etc.

4.  Rodent control is important since rodents can serve as a source of infection for dogs that catch them.

5.  Dogs should be restrained from entering children’s play areas and there should be prompt disposal of all dog faeces, especially in gardens, playgrounds and public parks.

6.  Practice strict hygiene particularly with children. Do not allow them to play in potentially contaminated environments.