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Metastrongylosis

 

The nematode superfamily Metastrongyloidea contains worms that infect the airways, lungs, heart and surrounding blood vessels. In the UK these are Angiostrongylus vasorum, Crenosoma vulpis, Oslerus osleri and Filaroides hirthi in dogs and Aelurostrongylus abstrusus in cats. There is growing evidence that disease due to A. vasorum (and Crenosoma vulpis), although still rare and sporadic, is being seen more often and that these parasites are increasing their range in this country. Angiostrongylosis is a serious condition, associated with coughing, dyspnoea, exercise intolerance, vomiting, abdominal pain, weight loss, neurological signs, heart failure, bleeding diatheses and sudden death.

Angiostrongylus vasorum
Adult A. vasorum inhabit the pulmonary arteries of the dog or fox and females shed their eggs within the pulmonary capillaries. The first stage larvae (L1) penetrate the capillary and alveolar walls, are coughed up, swallowed and appear in the faeces.  L3 infective larvae develop in a gastropod molluscan intermediate host.  When ingested by the dog, the L3 larvae migrate through the intestinal wall, moulting and maturing to the final larval stage (L5) in the mesenteric lymph nodes. L5 larvae eventually migrate via the lymphatics, hepatic portal vein, liver and caudal vena cava to the right ventricle and pulmonary arteries, where they mature into the adult worms. The prepatent period is reported to range from 38 to 57 days.

This parasite has been a significant cause of disease in dogs in south west France since 1852 and is endemic in many countries with a mild wet, climate. In the UK, it was first recorded in 1975 in a greyhound imported from Ireland. Throughout the 1980s, A. vasorum (sometimes termed the “French heartworm”) was noted in “hot spots” in Cornwall and subsequently in South Wales.

Since the early to mid 1990s, however, cases of A. vasorum and C. vulpis infection have been reported in Hampshire, Surrey, Kent and Essex and Warwickshire. In the past few years, cases have occurred in the Midlands, in the Manchester area and recently in Glasgow.

Density, age, sex and seasonal dispersal of foxes are important factors in transmission but it is also suggested that movement of infected dogs may result in infection in foxes. There are some 115 species of terrestrial snails in the UK and 30 species of slugs but it is far from clear if all these species can act as intermediate hosts. Climate of course will affect the size and activity of mollusc populations and some researchers have commented that outbreaks of infection in dogs have occurred in mild, wet years in when gastropods are presumed to be abundant.

Crenosoma vulpis
This nematode is more common in foxes than in dogs but is being increasingly implicated in canine lungworm cases in the UK, due in part to increased awareness since case publications in 1994.  Adult worms are found in the trachea, bronchi and bronchioles.  Clinical signs are those of chronic respiratory infection with coughing, sneezing and nasal discharge.  Infections in dogs may mirror seasonality of infected snail populations in the vicinity of fox habitats.  The highest incidence of clinical crenosomosis is seen in autumn.

Oslerus osleri
Adult worms are found in characteristic fibrous nodules in the upper respiratory tract and coughing is the major clinical sign of infection. Although requiring general anaesthesia, bronchoscopy is a reliable diagnostic method for nodule examination and larger nodules may be seen by lateral thoracic radiography. Oslerus osleri has been recorded from many countries but there is no virtually data on prevalence and distribution in the UK. A case submitted from a veterinary practice in Manchester was seen by TEST-A-PET in 2007. Transmission is direct.

Filaroides hirthi
This species inhabits the lung parenchyma and forms small soft (sometimes coalesced) nodules. The parasite has been recorded from North America, Europe and Japan.  Infection is invariably asymptomatic but in rare heavy infections hyperpnoea may occur. The parasite has been recorded from Beagles in breeding establishments but may well be an established parasite in pet dogs the UK.  Transmission is direct.

Identification of metastrongyles
Given that there are several lungworms of caniids in the UK with different transmission characteristics and pathogenicity, accurate differential diagnosis of lungworm is vital in managing clinical situations in domestic dogs.

Definitive diagnosis of angiostrongylosis in the living animal is achieved by the recovery and identification first stage larvae from BAL or from Baemannised faecal samples. Staff at here TEST-A-PET are experienced in lungworm identification. We have a reference collection of different metastrongylid first stage larvae and are able to distinguish different species by using a combination of precise measurement and by examination of the fine architecture of the tail. 

Metastrongyloidea testing at TEST-A-PET.

Parasite detection.
At TEST-A-PET we use the Baerman technique to detect larvae in faeces.  In addition, we will also analyse sputum, bronchial lavage and Baermannised faecal fluid.  Larvae detected in dog samples will be identified to species level (Angiostrongylus vasorum, Crenosoma vulpis, Oslerus osleri and Filaroides hirthi).

We will consider requests from other species e.g. ruminants and equines.

Detection of larvae may be enhanced by examining several faecal samples collected over three consecutive days.

Sample required: 3g of fresh faeces (a larger amount should be sent if available), Sputum, Bronchial lavage, Baermannised faecal fluid.

Results are available within one working day of us receiving the sample

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Picture

Angiostrongylus vasorum first stage larvae.

 

Picture

Angiostrongylus vasorum adult worms.

 

Links
For details on submitting samples for testing, please click here.

For further advice on diagnosis and treatment, please click here.

For further reading on metastrongylyosis, please click here.