ANGIOSTRONGYLUS VASORUM: INFECTION AND PREVENTION

Transcription

1 Vet Times The website for the veterinary profession ANGIOSTRONGYLUS VASORUM: INFECTION AND PREVENTION Author : Gayle Simpson Categories : Vets Date : February 1, 2010 Gayle Simpson BSc (Hons), RVN, describes this parasite s life cycle and apparent increasing significance for the UK s dog population A VASORUM (or French heartworm) is an endoparasite that is considered to be affecting the health of our domestic dog population with escalating frequency. Originally described in 1866 by Baillet, this metastrongyloid nematode (roundworm) was, for many years, considered only a problem in the UK in wet and temperate areas, such as Cornwall and Wales ( Figure 1a, 1b and 1c ). By the 1990s, A vasorum infection in dogs and foxes had been reported in south-east England and London, and there is evidence to suggest that the reservoir of infection is moving northwards 1. Why are we worried about it? With the climate seemingly becoming milder, conditions allowing survival of the intermediate host species for the larval stages of this parasite have increased. Slugs and snails are intermediate hosts for first-stage larvae (L1) of A vasorum. Infected dogs and foxes expel these larvae on to the ground via their faeces. The larvae are taken up by slugs and snails, and develop into further larval stages inside these hosts bodies and are then transferred to the alimentary canal of the dog or fox when the slug or snail is eaten. The larvae migrate into the dog s pulmonary artery where, as adult worms, they lay eggs that migrate into the lungs via the bloodstream and form tissue nodules. From here, the eggs develop 1 / 5

2 into L1 larvae and move into the alveoli. They are then coughed up into the larynx, swallowed and then excreted through the alimentary canal. It is known that slugs and snails act as intermediate hosts in the A vasorum life cycle ( Figure 2 ), but it is not yet certain whether these hosts have to be ingested by the canid (fox or dog) or whether ingestion of their mucus is sufficient to infect the dog 2. If the latter is true, dogs may pick up the infective larvae by rummaging through the undergrowth, eating grass, drinking out of puddles or outdoor water bowls, or playing with toys left outdoors. Therefore, dogs that have access to the great outdoors, particularly those that run off the lead or live in an area with a dense fox population, are at risk of picking up the parasite. All ages and breeds can be infected, although younger dogs may be more prone to picking up the parasite. Life cycle and development stages Once the worms reach the pulmonary artery, which takes about 10 days post-infection, they cause an inflammatory response involving the surrounding lung tissue and lead to foci of interstitial pneumonia. When larvae migrate into the lung airspaces, pneumonia and pulmonary haemorrhage can occur and granulomas can develop in response to the eggs and larvae. Emphysema can develop, as can thromboarteritis and intimal proliferation that leads to pulmonary hypertension and, potentially, right-sided congestive heart failure. Coagulopathies commonly occur. Symptoms include anaemia, melaena, subcutaneous haematomas, and haemoptysis 3. Infection can, therefore, result in a number of different symptoms. Some dogs don t initially show outward signs of lungworm infection. Often, the symptoms are mild at first and worsen progressively into bleeding disorders, coughing, vomiting, weight loss, collapse and neurological signs. Sometimes, the symptoms can be confusing, particularly once the worms have migrated, sometimes extensively, through the circulation. Case study: Petal Petal was a two-yearold female spayed beagle that was referred for an internal medicine work-up after she had remained inappetent, lethargic and haematuric for several weeks after a post-spay bleed was rectified by surgical intervention. Petal was losing bodyweight and, approximately one month after blood was found in her urine, her owners noticed that her right eye had an increased ocular discharge and was partially closed. The owners could not recall any traumatic events that could have caused this. On clinical examination, Petal had increased ventral airway sounds, a palpable mid-abdominal mass, mild lymphadenopathy and bilateral episcleral and conjunctival vessel hyperaemia, the latter being particularly marked in the right eye. 2 / 5

3 A standard biochemistry screen revealed raised kidney parameters, globulin and total protein levels, and raised ALT, CK and amylase. Haematology screening showed a mild thrombocytopaenia and clotting profiles revealed elevated clotting times and elevated fibrinogen degradation products by D-dimers. These results were consistent with disseminated intravascular coagulopathy. The use of Multistix and sediment urinalysis confirmed blood and protein in the urine. Ophthalmic examination confirmed secondary uveitis affecting both eyes, mostly in the posterior segment of the eyes. The right eye had developed a secondary retinal detachment and glaucoma, with increased ocular pressure of 34 mmhg. The pain from this condition could have induced the inappetence, lethargy and weight loss described in this patient. Digital radiography of the thorax revealed multiple solid nodules throughout the caudodorsal lobes and diffuse interstitial pattern throughout the rest of the lung ( Figure 3a and 3b ). Abdominal ultrasound revealed a thin-walled cystic mass in the mid-ventral abdomen and an ovoid mass in the caudal pole of the right kidney. These findings were suspicious of recent haemorrhages. Baermann testing of faecal samples confirmed the presence of A vasorum on the basis of L1 larval morphology. How is infection diagnosed? If a patient is displaying clinical symptoms suggestive of A vasorum infection there are simple tests that can be performed in-house to narrow the field of diagnostic suspicion. Firstly, a direct faecal smear can be examined microscopically. Fresh faeces (which can be taken directly from the rectum) is mixed with saline on a microscope slide and then examined under a magnification. It will not be possible to identify the exact species, but any lungworms present should be recognisable from their tapered, coiled form ( Figure 4 ). Precise identification of A vasorum will require faecal testing using the Baermann technique, which normally involves sending samples to an external laboratory. As the larvae are intermittently shed in the faeces, they may not be present in one given stool sample, despite the dog being infected. Therefore, it is wise to submit at least three fresh, consecutive faecal samples for testing. Adult worms can be seen in a brochoalveolar lavage sample of an infected patient, and adult worms have been seen in the cerebrospinal fluid of an infected puppy with ataxia 4. The A vasorum research group at the University of Bristol is developing new diagnostic tests (polymerase chain reaction [PCR] and serological testing) to improve on current methods of detecting infection by the parasite. How is an infection treated? 3 / 5

4 Moxidectin is licensed for use in the treatment of A vasorum infection. A seven-day (minimum) course of fenbendazole can also be used, but it is not licensed and is, thus, further down the veterinary medicines cascade. The death of a heavy worm burden can itself be fatal to the patient. Thromboembolic disease and anaphylactic reactions can occur, typically three to four days into the recommended treatment programme as the worms start to die off. An infected dog will incur costs of hospitalisation, diagnostic work-up, laboratory services, medical support for symptoms of dehydration, fatigue and anorexia, plus any other complications, as well as the cost of a treatment programme. The worst cost of all is the potential loss of a much-loved pet. The threat of A vasorum infection should not, in my view, be taken lightly by owners or veterinary staff. Raising awareness and compliance Several veterinary practices have included a page on their websites that introduces A vasorum and its implications if your dog becomes infected with it. By supplying real-life case histories on these pages, the threat becomes much more of a reality to the owners and they are provided with information about what they should ask for when they contact their vet. Not only do such web pages further public awareness about the parasite, but they also encourage people into their veterinary practices. Once there, other concerns may be discussed and it is common for this to lead to further investigation of the pet, increased sales of flea treatments and wormers, and a better practiceowner relationship. It is also useful to be able to reassure the public that A vasorum does not infect humans, nor is it thought to infect cats. However, it is worth noting that cats can be infected with a different lungworm (Aelurostrongylus abstrusus). All members of the veterinary practice team that deal with the public should be aware of the increase of A vasorum infections and be ready to speak to clients about it directly. All enquiries by clients asking for wormers could be used to discuss the increased incidence of this parasite, together with options to go towards protecting against it. No product yet has a licenced claim to prevent infection with A vasorum, but owners should be encouraged to ensure their dog is receiving regular worming treatments at the dose and frequency recommended by their veterinarian. The nurse should also stress that the key to successful treatment of a dog with suspected infection by the worm is early action. Good husbandry should be promoted advise clients to keep their garden and surrounding areas free of dog faeces. This will reduce the worm burden in the environment, not just of Angiostrongylus, but of other parasites harmful to humans and pets. It may be worthwhile reminding owners with infected or suspected infected dogs that other dogs they may own will be at risk if they share the same surroundings. It should also be noted that the diagnosis of Angiostrongylus vasorum infection, the treatments 4 / 5

5 Powered by TCPDF ( used and their dose rates and timings, are the responsibility of the vet in charge of the case. References and further reading 1. Morgan E R, Tomlinson A, Hunter, S, Nichols T, Roberts E, Fox M T and Taylor M A (2008). Angiostrongylus vasorum and Eucoleus aerophilus in foxes (Vulpes vulpes) in Great Britain. Veterinary Parasitology 154:(1-2), p Personal communication: Dr Ryan Jefferies, Angiostrongylus vasorum research group, University of Bristol. 3. Conboy G A (2000). Canine Angiostrongylosis (French Heartworm). In: Companion and Exotic Animal Parasitology, Bowman D D (ed). /conboy_angiostrongylosis/ivi s.pdf 4. Personal communication: Barbara Glanemann, Dr VetMed Dip ECVIM-CA / 5