Dog - Roundworms

Roundworms, known as nematodes or ascarid worms are parasites that live freely in the intestine. They obtain their 'food' from the partially digested intestinal contents. They are called roundworms because of their round bodies which differentiates them from another group of worms, cestodes or tapeworms that have flattened bodies.

Two nematodes are important in the dog, Toxocara canis and Toxascaris leonina. T.canis is more likely to cause problems for the host dog and is also important because it can occasionally be transmitted to people.

How did my dog get these worms?

Dogs infested with roundworms regularly pass microscopic eggs in their faeces. These are then transmitted to susceptible dogs during their habit of sniffing one another’s faeces (stools) They are also picked up by other susceptible animals including rodents and birds. In these animals, called 'paratenic' hosts, they do not mature but if the rodent or bird is eaten by a dog, completion of the life cycle will take place and the dog will become infected with the roundworms.

In the dog nemotodes undergo a complicated life cycle before mature roundworms are found in the bowel. The life cycle involves several stages and migration through various tissues. Sometimes the roundworm larvae (immature worms) encyst in the host’s tissues. This is important in the bitch because under the influence of the hormones of 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.

Other larvae migrate to the mother’s breast tissue and from there infect the puppy while suckling.

Are roundworms a health hazard for my dog?

The main problems occur in puppies. Up to twelve days old infected puppies may show signs of noisy breathing accompanied sometimes with a nasal discharge especially noticed when suckling. The puppy doesn't grow very much. From two weeks of age onwards vomiting and abdominal discomfort, diarrhoea and lack of growth may be seen. At approximately six weeks onwards chronic diarrhoea and a distended abdomen, the so called 'pot belly' may be obvious.

Quite heavy infestations in puppies will often show no clinical signs until it is realised that the puppy is not as well grown as other members of the litter.

Toxocara canis has a more complicated life cycle than other nematode worms found in dogs. When adult dogs swallow infected larvae often the majority of those larvae encyst in the dog’s tissues. Few worms actually mature and enter the bowel. Consequently few eggs are passed in the stools which leads to difficulties in making a definitive diagnosis.

How is the condition diagnosed?

In puppies clinical signs – stunted growth, pot belly, recurrent diarrhoea are a good indication. Definitive diagnosis is by microscopic examination of the puppy’s faeces.

In the majority of infestations only a moderate number of eggs are passed, therefore you may be 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 act like any other paratenic host. If a large number of infected eggs are ingested then clinical disease can occur and this is particularly important if children are involved.

Very rarely liver problems may be caused and even less commonly the larvae can migrate to the eye resulting in visual impairment. The risk is really very low but nevertheless regular worming of all pet dogs and clearing any faeces as soon as practicable after voiding are sensible precautions.

What is the treatment?

Treatment is simple, relatively inexpensive and very effective provided it is carried out according to instructions. 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 and other ectoparasite control will also be effective against roundworms.

Most de-worming preparations available kill only the adult worms and do not affect migrating or encysting larvae although such preparations are gradually becoming available. Therefore at the moment it is 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 on a regular basis thereafter. We will be happy to discuss this with you, taking into account the lifestyle of the pet and the local worm problem. Please contact us.

Can the eggs passed in the environment be prevented from developing?

When first passed in the faeces nematode eggs are not infective. Depending on temperature and other conditions, these eggs develop into infective larvae (L2) from weeks to months. Under optimal conditions this is usually about four weeks. These larvae remain viable within the environment for a variable time. They are particularly resistant.

The best method of control is removal of the dog’s faeces as soon as passed, when the eggs are not infective. It is for this reason that local authorities are keen to enforce `Poop Scoop’ bylaws particularly in respect of public open spaces.

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. 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 many 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 (paratenic or 'transfer' host).
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.