Angiostrongylus vasorum is a small roundworm known colloquially as French heartworm with a somewhat complicated life cycle. It has been common in Europe for some time, but this parasite seems to be spreading throughout the world. Most dogs who suffer from the symptoms of angiostrongylosis make significant recovery within just a few days. Dogs who contract angiostrongylosis generally remain predisposed to new outbreaks. Angiostrongylosis is a dangerous condition which can be fatal without prompt medical treatment.

Angiostrongylosis, also known as French heartworm, is caused by an infestation of a tiny roundworm with the scientific name of Angiostrongylus vasorum.

The incubation period for the Angiostrongylus vasorum averages between one and three weeks from the ingestion of the parasite.

This Angiostrongylus vasorum parasite is known as the French heartworm, but there are a few parasites which are similar and may cause some confusion:

Dirofilaria immitis - This is the more commonly seen version of heartworm. It is spread by mosquito rather than by snails or slugs and can affect dogs, cats, or ferrets. Domestic animals in areas where Dirofilaria immitis is found are often given monthly medication to prevent infestation by this parasite.

Angiostrongylus cantonensis - This parasite is very closely related to French heartworm, but the final life stage of these parasites usually occurs in rodents rather than dogs and other canids. For this reason, it is called rat lungworm.

The life cycle of the French heartworm is a somewhat complicated one. For dogs, the most likely vector for infection is the ingestion of infected slugs or snails. Once the infected snail or slug is eaten, the Angiostrongylus larvae travel out of the gastrointestinal tract and into to the lymph nodes. After developing in the lymph nodes, the parasites take up residence on the right side of the heart. Eggs from the mature females in the heart pass into the dog’s stool, where they encounter the snails and slugs they need for the next part of their lifecycle.

It is more common for angiostrongylosis to become a problem for younger dogs than older, although it can be contracted at any age. Diagnosis is originally based on the clinical signs and the animal’s health history. Because the signs and symptoms can vary greatly in time and intensity, it can be difficult to get a diagnosis based on this information. The larvae can often be found in the stools. The stools would be tested using multiple techniques and the tests may be repeated if no parasites were found the first time. 

A smear of the sample will be examined microscopically, while the remainder of the specimen is tested using a fecal flotation technique. This technique involves floating the fecal matter in a solution that allows any eggs to float to the top of the container while debris sinks to the bottom. Because the larvae are only released sporadically, most veterinarians will check multiple samples over a few days to ensure that they don’t base the diagnosis on a false negative reading. Although fecal float tests are the most common diagnostic technique for this disease, new advances have been made in serological rapid testing for these parasites.

Dogs that are exhibiting the more critical symptoms will get supportive treatment such as supplemental oxygen and IV fluids right away to alleviate the symptoms. Dogs who are experiencing breathing difficulties should be kept in a small area to minimize heavy exercise, and may be given oxygen enriched air and bronchodilators. There are several medications that can be utilized to remove the infestation by this variety of roundworm. Some common medications prescribed to kill roundworms like Angiostrongylosis might include Pyrantel Pamoate, Fenbendazole, and Moxidectin. Fenbendazole seems to be most effective in clearing up problems with this particular variety of roundworm, but medicated topical ointments (using Moxidectin) may also be used to help eradicate the problem and are also quite effective in preventing new outbreaks. 

Some veterinarians may choose to administer corticosteroids for their immunosuppressive properties, which help to prevent post-treatment anaphylaxis. Dogs can develop complications after treatment which may require antibiotics to clear up. It is important not to kill too many of the worms at once as it can cause a dangerous amount of antigens to be produced and anaphylactic shock occurs.

The prognosis for angiostrongylosis is largely dependent on how severe the neurological symptoms become, and how quickly treatment is sought. While most canines recover completely with appropriate treatment, it can sometimes become lethal. The usual causes of fatality are related to neurological damage that has become irreversible, failure of the respiratory system, or massive hemorrhaging due to clotting issues. A calm and quiet environment should be provided for the recovering patient when you return home, as your pet may be confused and disoriented. Plenty of fresh water should be made available, and extra bathroom breaks should be planned for while both the toxins and the medications make their way through the dog’s digestive system.