Background
Various lungworms can affect dogs and cats in the UK. Dogs can be infected with Crenosoma vulpis(‘ fox lungworm’), Oslerus osleri( formerly known as Filaroides osleri) and less commonly Filaroides hirthi, Ecoleus species and Capillaria aerophila, while Aelurostrongylus abstrusus is the most common lungworm found in the cat. However, it is Angiostrongylus vasorum that is often of particular interest to the veterinary community.
This parasite is of note due to its epidemiology and spread, the vast array of clinical signs of infection( including problems with bleeding) and the fact that infections can be life-threatening, yet are preventable. Clinical vigilance and knowledge are key to recognising disease and protecting dogs against this important parasite. Therefore, this article will focus on A. vasorum.
A. vasorum is a metastrongyloid nematode parasite with an indirect life cycle, which is dependent on the infection of the final host( a dog or related Canidae) following ingestion of an intermediate host( a slug or snail) or a paratenic host( for example, a frog) [ 1 ]. The adult parasite inhabits the pulmonary arteries and right ventricle of the heart in the dog and has a pre-patent period of 35 – 60 days. The pre-patent period is the time between a host getting infected by a parasite and the parasite( or its eggs / larvae) first becoming detectable in the host ' s body or being able to be transmitted. The L1 larvae are shed in the faeces of an affected animal; these larvae then mature to the L3 form within the obligate intermediate hosts before they can infect the final host once again( Figure 1). Dogs have been known to excrete larvae for up to 5 years post infection.
A. vasorum is now recognised as having a global distribution. It was first identified in the UK in 1973 in an imported greyhound, after which numerous cases were reported in southern England and Wales, as well as Ireland. Over the past 10 – 15 years, however, the parasite has expanded its range northwards to include areas such as Scotland. As a result, much of the UK is now considered to be at risk of exposure.
Epidemiology and risk of disease
A. vasorum is maintained in a wildlife cycle, with foxes as reservoir hosts, and cycling through slugs and snails. Within the UK, there are plentiful slugs and snails and abundant fox populations to sustain the life cycle of this parasite. Additionally, there is some evidence that suburban areas of the UK are particularly suitable as an environment to maintain the parasite [ 2 ].
Once A. vasorum becomes established within fox populations in an area, further spread occurs as foxes disperse and contaminate new gastropod hosts with larvae, leading to the formation of additional endemic areas. Of note, the prevalence in foxes in Great Britain, by region, roughly doubled between 2008 and 2015 [ 3 ]. While this local expansion tends to be gradual, more rapid parasite spread can occur through longdistance movement events. Such events may include the transportation of foxes via wildlife rehabilitation programmes, or the inadvertent transport of infected gastropods on plants, soil or other materials moved between locations. However, the most significant contributor to long-range spread is possibly through the movement of dogs. Dogs that relocate with their owners, or those that travel for various other reasons, can introduce A. vasorum to previously unaffected areas.
Figure 1. Schematic illustration of the life cycle of Angiostrongylus vasorum. Courtesy of Zoetis UK.
20 Veterinary Nursing Journal