In our last post, Dog worms: what are they?, we explored the various types of worms and how strategic they can be to survive. While clever, they can also be quite dangerous to our fur friends. As part of our 3-part series, today we'll explain why you need to be aware of dog worms.

Dog worms don't only affect dogs - they can also pose a health risk for humans. Some of them can cause mild to moderate illnesses while others, if left undetected and untreated, can lead to death.

Vets and breeders are very well aware of the issue of worms, which is why they advise deworming dogs from their earliest age. It's important to know how they affect our animals so we can take the necessary measures to ensure the wellbeing of both our pets and ourselves.

With that in mind, let's look at what to be aware of when it comes to dog worms.

Dog worms: effects to health

Dog worms are a health concern for two key reasons:

1. Risk to your dog's health, even possible death (the most dangerous being nematodes)

2. Risk to public health

Of course, all worms are not on par concerning their pathogenic potential on either dogs or humans. Let’s rank them below in order of concern.


Heartworm is the most dangerous worm for both dogs and cats. It causes inflammation in the pulmonary arteries, thromboembolism, right-sided heart failure, renal failure and, if untreated, death.

Even with treatment, there is also risk of harm to our pets. Treatment of immature or adult heartworms needs to be done with caution as remnants of the destroyed worms can cause of an overreaction of the immune system, damaging the lungs.


Ancylostoma caninum (hookworm)

Among the two types of hookworm, Ancylostoma caninum is by far the most dangerous. It sucks a lot of blood, and a moderate infestation of as few as 50 worms can cause severe anemia. A larger infestation can cause death.


Toxocara canis is a major concern for puppies. Because of its large size, it is able to obstruct or even destroy young dogs’ intestines. Sometimes owners find these large worms in the faeces or vomit of the animal.


Whipworms feed on the blood of dogs. Heavy infestations cause anemia and inflammation of the intestinal wall. Large, untreated infestations may cause death.


While dogs do not tend to suffer from tapeworms, the animal should still be treated to prevent any itching and potential complications.

How do worms affect human health? (zoonosis)


Both Echinococcus granulosis and Echinococcus multilocularis can cause serious public health issues.

Echinococcus behaves in humans the same way as in any other intermediate host: it encysts in tissue. In the case of Echinococcus granulosis, the larva encysts primarily in the lungs or liver, and then very slowly grows, over many years, to form a large cyst. Until recently, the only medical treatment was surgery.

Echinococcus multilocularis is even worse. The cysts continuously proliferate and infiltrate tissue, much as cancer metastasis. It invariably proves fatal after a few years.



Once in a human's body Toxocara larvae are unable to find their way to the digestive tract so remain in tissue where they encyst. This phenomenon is called cutaneous larva migrans.

In most cases, few symptoms are detected. Young children are more susceptible to contamination as they are more likely to be exposed to the eggs when playing near the ground and dirt, and by putting various items in their mouths.

A recent study in the US showed that 13.9% of the population tested positive to Toxocara. In most cases, seropositive patients do not display any symptoms. For others, consequences are diverse, and most of the symptoms are not disease-specific. They include:

- Visceral larva migrans: gastrointestinal and intra-abdominal dysfunction, headache, weakness, lethargy, fever, coughing, asthma, pneumonia, eosinophilia

- Neural larva migrans: seizures (rare)

- Ocular larva migrans: loss of vision, eye inflammation or damage to the retina, and in some very rare cases, blindness

Ancylostoma caninum (hookworm)

Infective Ancylostoma caninum larvae penetrate directly into the body through the skin. They then encyst in tissue similar to Toxocara. Symptoms are limited to abdominal pain and eosinophilia (high levels of a certain type of white blood cells).


Heartworms can’t achieve their lifecycle in a human body. Larvae or young adults usually die before they reach the heart. Instead, they can form lesions in tissue, especially in the lungs and on the skin. While symptoms are usually not of concern, these lesions can be detected on X-rays and misinterpreted as abnormal tissue growth (neoplasia).


It's important to understand that the above information provides extensive detail about the risks to both dogs and humans. However, these days treatment is usually readily available.

When adopting your new best friend from a reputable shelter or breeder, various treatments will have already been administered. Your responsibility is to ensure that future vaccinations and treatments are provided as directed by an expert vet. They will also be able to advise on the risks associated in your region and provide the necessary precautions. This will ensure both your dog's and your personal wellbeing and health.

And always remember - if you're ever unsure about your dogs' health, or that of your own, seek expert advice for peace of mind.

In our third and final instalment of our 3-part series on dog worms, we explore the diagnostic process and how to control worm infestations in your dog.

See you there…

Source: Gilles Ventejol

Gilles Ventejol has more than 20 years' marketing experience in the animal health industry. He has launched new veterinary medicines, led prospective work on new drugs development, and organised international events in the animal health space. He has also written countless materials for vets and owners, including reports, articles, guides and brochures, and produced video content and website material.

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