Angiostrongylus vasorum, the French heartworm, is a parasitic nematode that has dogs and other carnivores (e.g. foxes, wolves, coyotes, badgers) as final hosts.
Angiostrongylus vasorum is native to Western Europe (France, Spain, Germany, Great Britain, etc.) but it is clearly spreading to other European countries.
It has been also found in North America, and some Asiatic and African regions. There are even some reports from South America.
Studies in some European countries showed that up to 7.5 % of dogs with undefined pulmonary symptoms were infected with this parasite. Other studies showed that up to 25% of the foxes in a population may be infected. It seems that there is a correlation between incidence in foxes and in dogs, suggesting that foxes are the main reservoir in many regions.
Angiostrongylus vasorum does not affect cats, livestock (cattle, sheep, goats, swine), horses or poultry.
The disease caused by this roundworm is called angiostrongyliasis, or angiostrongylosis.
Are dogs infected with Angiostrongylus vasorum contagious for humans?
- NO. The reason is that this worm is not a human parasite.
A related species, Angiostrongylus cantonensis is a human parasite found in Southeast Asia and the Pacific. Angiostrongylus costaricensis is another related human parasite found in Central and South America.
Final location of Angiostrongylus vasorum
Predilection sites of adult Angiostrongylus vasorum are the pulmonary arteries and the right ventricle of the heart.
Anatomy of Angiostrongylus vasorum
Adults of Angiostrongylus vasorum are medium size roundworms, up to 2 cm long, and <0.4 mm thick. They have a pink color. The worm's body is covered with a cuticle, which is flexible but rather tough. The worms have no external signs of segmentation.
They have a tubular digestive system with two openings. Characteristic of Angiostrongylus worms is that the reddish intestine (filled with blood) spirals around the whitish ovaries, which looks like a barber's pole and remember the similar aspect of Haemonchus spp. a parasite of cattle sheep and other ruminants. They also have a nervous system but no excretory organs and no circulatory system, i.e. neither a heart nor blood vessels. Males have long and thin chitinous spicules for attaching to the female during copulation.
No eggs are shed but already hatched L1 larvae that are ~0.4 mm long and 15 micrometers thick. Their tail is typically curved, with a dorsal spine.
Angiostrongylus vasorum has an indirect life cycle, with dogs and other carnivores as final hosts, and snails (Achatina, Bradybaena, Helix, etc.), slugs (Limax, Deroceras, etc.) or other freshwater mollusks (Biomphalaria, Physa, etc.) as intermediate hosts. Several small vertebrates can act as transport hosts (= paratenic hosts), e.g. frogs, lizards, rats, etc. The worms do not complete development in these transport hosts, but remain encysted until a suitable final host eats them or their carcasses.
Adult females in the lung arteries or the heart lay eggs that reach the lung capillaries through the blood stream. There they hatch to L1-larvae. These larvae cross the alveolar wall and reach the lumen of the lung alveoli. Coughing, sneezing or exudations bring these larvae to the mouth. They are swallowed and subsequently passed with the feces.
These shed L1-larvae are not very resistant to adverse environmental conditions. But they can penetrate actively into snails, slugs and other freshwater mollusks, where they continue development to L3-larvae. Intermediate hosts such as frogs or lizards, or final hosts eat the infected snails or other materials contaminated with their slime and the L3-larvae are released in their stomach. In the case of the paratenic hosts these L3-larvae encyst in their tissues until a final hosts eats them or their carcasses.
In dogs or other final hosts, released L3-larvae penetrate the intestinal wall and continue development in the lymph nodules of the intestinal cavity. Later thy migrate to the portal vein, the liver, the right ventricle and the pulmonary artery, where they complete development to adult worms and reproduce.
The time between infection and shedding of first larvae (prepatent period) is 1 to 2 months.
Harm caused by Angiostrongylus vasorum, symptoms and diagnosis
Angiostrongylus vasorum is quite harmful to dogs. Migration of L1-larvae through the lung tissues can cause interstitial pneumonia, bleedings and subsequent granulomas (accumulation of immune cells that try to neutralize the foreign organisms). Chronic infections can cause fibrosis in the affected tissues (i.e. substitution of the damaged original tissue by connective tissue). Adult worms in the heart and the pulmonary artery can disturb coagulation, and cause anemia and even heart failure. Occasionally larvae may reach the left ventricle and be transported to unusual organs (e.g. eyes, brain, kidneys, etc.) by the arterial blood system.
Clinical signs are variable in time and intensity. Progressive cardio-respiratory signs are often observed: chronic cough, difficult breathing, suffocation, loss of appetite, chronic fatigue, weight loss, etc. Sometimes skin hematomas, ascites (accumulation of fluid in the peritoneal cavity) and vomits are observed. Nervous symptoms (loss of muscle coordination, slight paralysis, impaired vision, seizures, etc.) can occur if the central nervous system (CNS) is affected. There are also reports on fatalities due to acute infection, mainly in young dogs, and also on death due to obstruction of the pulmonary artery, rupture of the femoral artery and heart failure.
Diagnosis is not trivial. It is based on clinical signs and history. Larvae can be detected in the feces (Baermann technique), but shedding being intermittent false negatives are possible. Consequently the tests must be repeated. When shed, up 300'000 larvae per gram of excrements can be found. Radiographic examination and hematological tests are not specific but can be indicative. Direct echographic visualization of the worms (as with Dirofilaria infections) is not possible because Angiostrongylus vasorum worms are much smaller.
Prevention and control of Angiostrongylus vasorum infections
Best prevention is to keep dogs away from potentially infected preys (frogs, lizards, rodents, etc.) but this is often not feasible for sheepdogs, hunting dogs, and generally for dogs in rural regions.
A few dog wormers are approved in some countries for the control of Angiostrongylus vasorum (e.g. emodepside, fenbendazole, ivermectin, levamisole, milbemycin oxime, moxidectin). But they often require a special treatment regime to be determined by the veterinary doctor. It is not always clear at which extent they are effective against adult worms (i.e. for curing established infections) or against larvae (i.e. for preventing infections).
In any case precautions must be taken, because killing too many worms too quickly can cause a rapid release of antigens in the treated dog, which can lead to anaphylactic reactions, to some extent comparable to those that can happen with Dirofilaria infections. Such post-treatment reactions (e.g. serious difficult breathing and ascites) often require a supportive medication.
There are no vaccines against Angiostrongylus vasorum. To learn more about vaccines against parasites of livestock and pets >click here.
Biological control of Angiostrongylus vasorum (i.e. using its natural enemies) is so far not feasible.
You may be interested in an article in this site on medicinal plants against external and internal parasites.
Resistance of Angiostrongylus vasorum to anthelmintics
So far there are no reports on resistance of Angiostrongylus vasorum to anthelmintics.
This means that if an anthelmintic fails to achieve the expected efficacy, chance is very high that either the product was unsuited for the control of Angiostrongylus vasorum, or it was used incorrectly.
Ask your veterinary doctor! If available, follow more specific national or regional recommendations for Angiostrongylus vasorum control.