Dangerous Worm Disease: Filariasis in Dogs

Filariasis in dogs: How the various worm diseases manifest themselves, where they occur and much more can be read in this guide article.

What is Filariasis?

Filariasis is a disease caused by different types of filaria (roundworms). The pathogens are endoparasites, which means they feed and develop in their host. Depending on the type of roundworm, in the adult stage, they attack, among other things, the lymph nodes, the subcutaneous tissue (subcutis), or the peritoneal cavity (peritoneal cavity). This article focuses on five species of filaria that occur in Europe:

  • Heartworm (Dirofilaria immitis);
  • Skin worm (Dirofilaria repens);
  • Acanthocheilonema reconditum;
  • Dipetalonema dracunculoides;
  • Cercopithifilaria grassi.

Filariasis in Dogs

Possible disease carriers (vectors) for filariasis are:

  • various mosquitoes;
  • mites, dog and cat fleas;
  • lice;
  • louse flies;
  • various shield ticks such as the brown dog tick.

The way from the mosquito to the dog

When a mosquito bites an infected animal, it ingests the larvae (microfilariae). After their further development within the insect, the larvae transfer themselves to a host – for example, a dog – in a subsequent act of suckling. The microfilariae get into the bloodstream of the four-legged friend. Next, the larvae develop into adult roundworms (microfilariae) and, depending on the genus, manifest themselves in the respective target tissue. That is where the multiplication takes place.

Filariasis in Dogs: Occurrence

Rising numbers of adoptions from southern and southeastern Europe, infections during dog vacations, and global warming – all of this promotes the spread of the pathogen in Germany. As a result, it can be assumed that the parasites will increasingly pose a threat to domestic four-legged friends in the future.


The heartworm is widespread. It occurs mainly in subtropical and tropical countries as well as in the warmer regions of the temperate zone. Popular European travel destinations such as Austria, southern France, Spain, the Canary Islands, and (with particular severity) northern Italy and Tuscany are affected.

Skin worm

In addition to Africa and Asia, the skin worm (Difilaria repens) also occurs in southern, southeastern, and western Europe. Evidence of the pathogen is now available in Germany.

More filaria in Europe

The following filaria is less common and poses a health risk in some European countries:

  • Acanthocheilonema reconditum: Southern European Mediterranean countries such as Spain, Portugal, Italy, and Greece;
  • Dipetalonema dracunculoides: Spain and Portugal;
  • Cercopithifilaria grassi: Italy and Greece.

Filariae in the Dog: Symptoms


If a dog is weakly infected and has a strong immune system, it often shows no signs. In the case of severe infestation, on the other hand, heartworm disease occurs, which is initially noticeable as exhaustion, coughing, shortness of breath, and choking. Without treatment, right heart failure or failure of other organs is often the result.

Skin worm

Cutaneous dirofilariasis is often asymptomatic. Over time, however, skin lumps, swellings, bald spots, skin inflammation, and itching can occur.

Acanthocheilonema reconditum can cause itching, bald spots, skin inflammation, and restlessness. Very little is known about the clinical picture of the two other filariasis.

Filariasis: Diagnosis

There are different approaches to diagnosing filariasis in dogs.

  • A microscopic blood test, a PCR test, the Giemsa stain, and the Knott test provide evidence of microfilariae.
  • An antigen detection (ELISA) can detect adult filariae.
  • Heartworm infestation can also be detected by ultrasound cardiography.
  • Roundworms in the subcutaneous tissue can be discovered by chance during a surgical procedure.

Filariasis: Treatment of the Dog

Filariasis discovered early can be treated well. But before the vet starts treatment, there is always an evaluation of the microfilariae density. Depending on what the result looks like, the treating veterinarian starts an appropriate therapy. A combination of several drugs can be used, which the nematodes and symbiotic bacteria secrete from the body.

In the case of heartworm disease, for example, doxycycline is used in addition to an anti-parasitic agent. If the dog suffers from a severe infestation, a surgical procedure in which the worms are removed is an option.

Filariae in the Dog: Prevention

Unfortunately, there is no one hundred percent protection against filariasis in dogs. However, some measures help to keep the likelihood of illness low.

  • Dog vacation: Find out exactly what the situation is in the respective vacation country and, if necessary, consult your vet. Traveling to risk areas increases the risk of filariasis in dogs.
  • Ask your veterinarian about preventive measures. Different preparations – for example, spot-on with a protective effect and drugs that kill microfilariae – keep the risk at a low level.
  • A regular health check with the veterinarian cannot prevent filariasis. However, the controls are important in order to detect possible signs in good time and to ensure early treatment.
Alice White

Written by Alice White

Alice White, a devoted pet lover and writer, has turned her boundless affection for animals into a fulfilling career. Originally dreaming of wildlife, her limited scientific background led her to specialize in animal literature. Now she happily spends her days researching and writing about various creatures, living her dream.

Leave a Reply


Your email address will not be published. Required fields are marked *