Lungworm an internal parasite affecting cats & dogs
|Lungworm an internal parasite affecting cats & dogs|
Angiostrongylus vasorum is a member of the lungworm (metastrongyle) family of nematodes. There are many different species of lungworm that affect a range of animals, but A. vasorum only affects dogs and foxes. Whereas members of the lungworm family often cause mild to moderate disease, A.vasorum can cause a much more serious disease, and infections may be fatal. A. vasorum is present in many areas of the world, including in the UK. In the UK, the parasite was traditionally seen to cause disease in specific parts of the country, and has long been recognised in areas such as south Wales, Cornwall and Surrey, however in the past few years cases have been reported further afield, including in the north of England and Scotland, indicating that the parasite has spread beyond its previously known "hot spots".
Adult worms reside in the heart and pulmonary arteries of infected dogs and foxes. This is in contrast to the rest of the lungworm family - which mainly reside within the bronchi/bronchioles or the lung itself. (A. vasorum should not be confused with "Heartworm"- i.e. Dirofilaria immitis, which also resides in the heart; Dirofilaria is not endemic in the UK). A. vasorum worms are slender worms of around 2.5cms in length.
First stage larvae, which are passed in the faeces of infected dogs can be distinguished from other lungworm larvae by the characteristic notch at the end of the tail.
The life cycle of A. vasorum is indirect, with dogs becoming infected when they ingest the intermediate host - an infected slug or snail. The adult worm resides in the right side of the heart and pulmonary arteries of infected dogs and foxes. The female worm releases eggs, which are carried in the bloodstream to the lung, where they develop into first stage (L1) larvae.
These L1 larvae burrow through the walls of the alveoli (air sacks of the lung), and from there are eventually coughed up and swallowed, and passed out into the environment with the faeces, where they can infect slugs and snails. Further development (to the third larval stage) takes place within the mollusc.
Dogs and foxes then become infected by eating an infected mollusc. Digestion of the slug or snail releases the larvae, which penetrate the intestinal wall, develop further within the lymph nodes (to L5 larvae) and then migrate via the liver and caudal vena cava back to the right side of heart, where development into a new adult worm takes place.
The time taken from ingestion of an infected slug or snail to an adult worm being present in the dog's heart is on average 38-57 days.
Dogs become infected with A. vasorum when they eat an infected slug or snail. It is important to note that these slugs/snails can be very small, and it is not always the cases that the owner (or even the dog) is aware of ingestion. Dogs that eat grass may eat a small slug attached to the blades, slugs can fall into water bowls, or be attached to a dog toy in the garden.
Lungworm Health Risks
Angiostrongylus vasorum is a potentially life threatening parasite of dogs, and can cause significant clinical signs. These signs can be very variable, and a dog infected with A. vasorum may have none, one or a combination of symptoms. Signs can include:
* Respiratory signs such as coughing, difficulty breathing, gagging, tiring on exercise.
* Bleeding abnormalities - which may manifest in a variety of ways, including bleeding from the nose, bleeds into the eye, coughing up blood, prolonged bleeding after surgery or after an injury, and many forms of internal bleeding.
* Neurological abnormalities such as paralysis, incoordination, seizures.
* Other non-specific signs such as reluctance to eat, vomiting, diarrhoea, weight loss.
All of these symptoms can, of course, be caused by many other diseases, making it sometimes difficult to tell if an animal has lungworm from its symptoms alone.
Outcome depends partly on the severity of the initial presenting signs, and the condition can be fatal in some cases, however in many instances, where appropriate therapy is initiated early enough, dogs will go on to make a full recovery.
It is worth considering that, even after successful treatment, re-infection is possible, as the dog is returning home to the same local environment where it encountered the infected molluscs, so ongoing preventative measures should be considered.
Whilst there are species of lungworm that can infect humans, Angiostrongylus vasorum itself is not considered a risk to people.
This usually involves examining the dogs faeces for the presence of parasite larvae (L1), using the Baermann technique. The larvae can be identified by the characteristic notch in the tail. Ideally faecal samples should be collected over three consecutive days, and analysed separately, as larvae may be missed if only a single sample is examined. Not finding larvae does not completely rule out the disease, as the larvae can be difficult to find, so presumptive diagnosis and treatment may be necessary in some cases.
Blood tests to diagnose A.vasorum are in development, but are not yet commercially available.
As angiostrongylosis is potentially life threatening, it is vital to administer effective anthelmintic treatment to all cases. It should be noted that standard wormers aimed at killing intestinal parasites are not necessarily always effective against this parasite. The only licensed treatment for A. vasorum comes in a monthly spot-on preparation.
Alongside the anthelmintic treatment, supportive treatment may also be needed depending on the signs that the animal initially presented with.
The same spot-on that is licensed for treating this parasite is also the only product licensed as a preventative medication for A. vasorum, when used as a spot-on on a monthly basis. While it is impossible to stop a dog from ever eating an infected slug or snail, this product has been shown to be highly effective at killing the parasite at an early stage and thereby preventing it from completing its life cycle.
Treatments for Lungworm include Advocate, Panacur
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