Responsible dog owners are committed to keeping their much-loved pets healthy and an important part of this is preventing worm infestation. Worms are hidden parasites; they’re inside the body so their presence is often only detected when symptoms appear. Rather than waiting until their dog is unwell, it’s better for owners to avoid infestation in the first place. This requires an understanding of which worms affect dogs and how they can be prevented. Worm control is also important in keeping people healthy because some species can infect humans, causing serious illness (1).
There are four types of worms that affect dogs
Roundworms are a common cause of diarrhoea in young pups. Sometimes pups will bring up an adult worm in their vomit, which looks very much like a thick white strand of spaghetti. Other effects of a heavy roundworm infection include a pot-bellied appearance, general ill-thrift (the inability to put on or maintain weight) and possibly an intestinal obstruction. Roundworm larvae can infect people and migrate through the brain, eyes and liver. One study found that over 5% of dogs in one region of England had roundworm, which means they are a significant human health hazard (2).
Hookworms are blood suckers. They live in a dogs’ small intestine and drink blood, leading to anaemia. Puppies are particularly susceptible to their effects because they’re working hard to produce enough blood to help them grow, yet they’re effectively losing blood because of hookworm. Affected pups are pale, weak and lethargic. They may have diarrhoea and, if they do, it is often black and tarry. Hookworm can be fatal in puppies.
Whipworms are found in the canine large intestine where they cause inflammation, leading to diarrhoea, often with blood and mucus. The diarrhoea can be very difficult to control and may persist for quite some time.
Tapeworms are perhaps the easiest intestinal worm to spot in dogs. They can be seen as small, white, wriggling worm segments in a dog’s droppings, or on the hair around their bottom; they look like grains of rice. These are the least harmful worms in dogs and really only cause an itchy bottom. Affected dogs will drag their bottom on the ground to try and get some relief.
How dogs get worms
It’s not difficult for a dog to pick up worms. There are a number of sources of infection. Pups can acquire roundworm and hookworm while still in the uterus, or when drinking infected milk from their mother. This means they already have a tummy full of worms when they’re born, giving them a very poor start in life.
Another source of roundworm infection is eggs that have been deposited in the soil in the stools of infected dogs. Dogs can swallow these eggs as they lick and groom themselves. The eggs then hatch and develop into adults in their intestine. Rodents and other intermediate hosts can also swallow these eggs and, if a dog then eats these animals, they too will become infected.
Dogs acquire hookworm in similar ways, except the eggs hatch into larvae in the ground. These larvae are swallowed by dogs (or rodents which become intermediaries) and find their way into a dog’s intestine in the same way as roundworms. The larvae can also penetrate the dog’s skin, by burrowing through the skin of their feet as they stand on contaminated soil, for example.
Whipworm eggs are swallowed by dogs and develop into adults in their large intestine.
Tapeworms are spread by fleas, so if your dog has a few of these little parasites, it’s likely that they’ll have tapeworms too.
Preventing worm infestation in dogs
It’s not always possible to tell if your dog has worms. Unless they are showing symptoms, vomiting up roundworm, or scratching their bottom due to tapeworm, there are no obvious external signs until they’re unwell. Similarly, faecal tests can identify worm eggs, but only if there are eggs in that particular stool sample. Whipworms are notorious for laying eggs periodically, so a dog can be infected but not have eggs in their droppings.
For this reason, regular deworming is the best way to keep your pooch healthy. Because puppies can be infected with worms before they’re born, it’s safer to assume all pups have worms and treat accordingly. Puppies require a more frequent worming schedule than adult dogs because of this and also because they’re more susceptible to the adverse effects of intestinal worms.
Other ways of controlling worms in dogs include treating a pregnant dog before she gives birth to her puppies to prevent transmission of roundworm and hookworm, and keeping fleas under control to stop the spread of tapeworm.
Cleaning the environment can also play a role in preventing worm infestation in dogs. Whipworm and roundworm eggs are very resilient and can survive in the environment for a long time. Hookworm eggs are less sturdy and are usually dead within months. Cleaning up faeces regularly and controlling intermediate hosts, such as rodents, will remove a major source of infection.
When dog owners learn the effects worms can have on dogs, it’s understandable that they can become worried. However, worms can be controlled and dogs can be protected from their harmful effects. Regularly using a reliable worm treatment can ensure our companions are safe from worms and give us, as owners, valuable peace of mind.
1 Luzio, A., Belmar, P., Troncoso, I., Luzio, P., Jara, A. and Fernandez, I. (2015). Parasites of zoonotic importance in dog feces collected in parks and public squares of the city of Los Angeles, Bío-Bío, Chile. [Article in Spanish]. Rev Chilena Infectol., 32(4), pp.403-7. 2 Wright, I., Stafford, K. and Coles, G. (2016). The prevalence of intestinal nematodes in cats and dogs from Lancashire, north-west England. J Small Anim Pract.
Author info: Dr Audrey Harvey is a graduate of the University of Queensland, Australia, and has worked in small animal practices for 25 years. She is particularly interested in obesity management and the role of exercise in resolving behaviour problems in dogs.