Infection with Angiostrongylus vasorum was first described in the 19th century in southern France, which is where the name “French heartworm” comes from. It commonly affects foxes and, less frequently, dogs, and is transmitted through the ingestion of snails. In Germany, French heartworm has only recently come under increased scrutiny, as the consequences of infection can be severe.
Foxes or dogs infected with Angiostrongylus vasorum shed larvae (Stage 1) in their feces. These are ingested by snails, where they develop into infectious Stage 3 larvae. Foxes and dogs then become infected in turn by eating infected snails. Dogs that eat grass or actively feed on snails are therefore at increased risk. Dogs under one year of age are particularly susceptible to infection. The infection cannot be transmitted directly from dog to dog.
In dogs, the larvae migrate through the intestinal wall into the blood and lymph vessels and then into the pulmonary arteries. The worms that develop there are much smaller—about 2.5 centimeters long—than the large heartworm associated with dirofilariasis (see the corresponding article). Angiostrongylus vasorum therefore settles in the smaller pulmonary arteries and damages the vessel walls. The adult worms can remain in the blood vessels of the lungs for years. Sexually mature female worms lay their eggs there. These develop into Larva 1, which then migrates into the alveoli. They are then coughed up, swallowed along with mucus, and finally excreted in the feces.
Inflammation in the lungs and pulmonary blood vessels causes the following symptoms:
In addition, coagulation disorders (see related article) occur in the form of delayed clotting with bleeding into various organs. This may lead to anemia (see related article).
If the right side of the heart is infested, this can lead to right-sided heart failure. In cases of massive infestation, sudden death may occur.
In rare cases, the larvae migrate to other tissues and cause neurological deficits, lameness, pain, or even visual disturbances.
After a general examination that includes a thorough assessment of the cardiovascular and respiratory systems, your veterinarian will perform various blood tests. This allows for an evaluation of changes in the blood count and coagulation parameters. Nowadays, an antigen test can quickly and reliably detect the parasite’s proteins in the blood, thereby confirming an Angiostrongylus vasorum infection. Alternatively, your veterinarian will perform a fecal examination, ideally using fecal samples collected over three consecutive days. This allows them to directly detect the live larvae.
Treatment is carried out using a deworming medication effective against the French heartworm. This can be administered as a spot-on treatment (applied directly to the skin) or as tablets. The spot-on treatment is applied once, with a possible repeat dose after four weeks. You must give the tablets four times at weekly intervals. If your dog has severe clinical symptoms, your veterinarian will also treat your dog with a glucocorticoid (“cortisone”). If secondary infections are present, an antibiotic is necessary.
Keep your dog calm for the first three days of treatment. Exercise increases blood flow, which can cause clumped, dead worms and larvae to lead to embolisms (= blockage of a blood vessel).
Three to seven weeks after treatment, an antigen test should be performed again to confirm the success of the therapy.
The prognosis is very good with early diagnosis and treatment. However, if left untreated or diagnosed too late, the infection can cause severe organ damage and be fatal.
The most important preventive measure is regular deworming with a deworming medication effective against French heartworm. In high-risk areas, this should be done monthly. Also, if possible, prevent your dog from eating snails.
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