Detection and diagnosis of dog lungworm larvae and eggs

Recent expansion of the lungworm Angiostrongylus vasorum from well known endemic areas of the UK and elsewhere (Morgan et al, 2009), along with the severity of clinical signs associated with infection in some dogs, has caused concern among the practising veterinary profession (Helm et al, 2010) and increased interest in parasitological diagnosis. However, it is easy to forget that besides Angiostrongylus vasorum, a number of other, less common lungworms can infect dogs namely Crenosoma vulpis, Filaroides osleri, F. hirthi and Eucoleus aerophilus. The life cycles of these parasites, their pathogenicity, and the risk factors for infection and reinfection are complex and varied and in many cases unclear, but knowing which species are involved in a clinical case can be very valuable, not least because specific veterinary advice and treatment is required.

Diagnosis may, in general, be indicated by radiography, bronchoscopy, clinical signs and haematology, and, in the case of A. vasorum, from an understanding and experience of local prevalence. But in order to make a definitive diagnosis, the parasite must be recovered and identified to species level. Until recently, this relied exclusively on microscopic examination of larvae and eggs. The advent of highly specific laboratory tests using the polymerase chain reaction (PCR) and antigen capture enzyme-linked immunosorbent assay (ELISA) has increased options for laboratory diagnosis of A. vasorum (Verzberger-Epshtein et al, 2008; Jefferies et al, 2009, 2011; Schnyder et al, 2011). This includes diagnosis using blood samples. However, diagnosis by larval recovery and microscopic identification still has a place in veterinary practice: it can achieve similar levels of sensitivity and specificity to more recent complex tests, can yield results more quickly if conducted in house, and unlike highly specific laboratory tests will detect the full range of lungworms that might be implicated in disease. Parasites can be recovered from faeces and in some cases by broncho-alveolar lavage (BAL) and from sputum, and the equipment and training requirements are modest. This article aims to review methods for the recovery of eggs and larvae of lungworms of dogs from clinical samples, which are suitable for the practice laboratory. Issues relevant to diagnosis using these methods are illustrated through a series of example cases.