Angiostrongylus vasorum (also known as French heartworm) is a parasitic nematode that affects the heart and pulmonary arteries of wild and domestic canids (Di Cesare and Traversa, 2014).
The life cycle of the parasite is indirect, with slugs and snails acting as intermediate hosts and dogs becoming infected when they ingest an infected mollusc (Di Cesare and Traversa, 2014; Wright, 2024).
The prevalence and geographical distribution of A. vasorum in both dogs and foxes has increased in the UK in recent years, with 20 percent of veterinary practices reporting seeing at least one case over a year in a 2014 survey (Kirk et al., 2014; Taylor et al., 2015).
Pathology
A. vasorum lives in the right side of the heart and pulmonary arteries, and can cause a range of clinical signs in dogs, in particular severe cardiopulmonary disease and haemostatic aberrations such as bleeding diathesis (Thomsen et al., 2024; Wright, 2024).
Although bleeding diathesis is a fairly common complication in dogs infected with A. vasorum, previous research has found no difference in survival in dogs with or without bleeding diathesis
The severity and clinical presentation of infection varies considerably, from dogs that are asymptomatic to those that present as an emergency with a fatal outcome. Although bleeding diathesis is a fairly common complication in dogs infected with A. vasorum, previous research has found no difference in survival in dogs with or without bleeding diathesis (Sigrist et al., 2017).
What did the latest study investigate?
A new study by Dr AaseThomsen and colleagues, published in the Journal of Small Animal Practice, investigated clinical and laboratory haemostatic differences in dogs infected with A. vasorum with and without signs of bleeding, examining the impact of bleeding diathesis on survival (Thomsen et al., 2024).
The retrospective cohort study searched the patient records database of the University Hospital for Companion Animals at the University of Copenhagen for dogs diagnosed with a documented A. vasorum infection between January 2005 and April 2019. Diagnosis was achieved by either a positive Baermann method, faeces smear, Angio Detect rapid assay or microscopic larvae identification at necropsy.
For A. vasorum-positive dogs, the demographics, method of diagnosis, type of clinical bleeding, treatment received (if any) and survival were recorded, along with various laboratory parameters. The latter included haematocrit, platelet count, activated partial thromboplastin time, prothrombin time, fibrinogen concentration, d-dimer and thromboelastography (TEG). All parameters were compared between dogs with and without signs of bleeding using univariable analyses.
A total of 180 A. vasorum-positive dogs were included in the study. Dogs were generally young, with a median age at diagnosis of 1.2 years, but ranging from 3 months to 13 years 11 months. Most affected dogs were purebred, with large mixed breeds and Labrador Retrievers the most prevalent breeds.
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What were the findings?
Clinical signs of bleeding diathesis were found in 36 percent of dogs and varied significantly in type and severity, with gingival/cutaneous and mucosal bleeding diathesis in several anatomical localisations revealed as the most common clinical findings. Neurological signs associated with intracranial and intraspinal bleeding were recorded in 30 percent of dogs; three of these dogs did not have any other clinical signs of bleeding diathesis but did present with either seizure or hindlimb paresis.
Half of the dogs with A. vasorum were detected as hypercoagulable, regardless of whether bleeding diathesis was detected
Several haemostatic aberrations were identified in A. vasorum-positive dogs with bleeding diathesis. Haematocrit, platelet count, thromboelastographic angle (α), maximum amplitude (MA), global clot strength (G), maximum rate of thrombin generation (MRTG) and total thrombin generation (TG) were all decreased in bleeding dogs, while prothrombin time was significantly prolonged. In dogs in which TEG was measured, those with clinical bleeding diathesis had decreased α, MA, G, MRTG and TG compared to those without bleeding. Half of the dogs with A. vasorum were detected as hypercoagulable, regardless of whether bleeding diathesis was detected. A quarter of infected dogs were hypocoagulable, and these dogs had significantly increased odds of bleeding diathesis compared to dogs with normocoagulability and hypercoagulability TEG profiles. There was no significant difference between dogs with normocoagulability and hypercoagulability.
Of dogs that received non-steroidal anti-inflammatory drugs (NSAIDs) within a month before diagnosis, 10 percent had significantly increased odds of clinical bleeding diathesis compared to those that had not received NSAIDs, anthelmintics or corticosteroids. There were no differences identified regarding bleeding state between dogs that received anthelmintic treatment or corticosteroids, or dogs not receiving either of these treatments.
A. vasorum-positive dogs with clinical signs of bleeding diathesis were 4.3 times more likely to die or be euthanised during hospitalisation compared to dogs without bleeding
In the study, 3 percent of dogs died spontaneously due to A. vasorum, and 11 percent were euthanised due to poor prognosis, financial constraints and/or emotional stress. A. vasorum-positive dogs with clinical signs of bleeding diathesis were 4.3 times more likely to die or be euthanised during hospitalisation compared to dogs without bleeding. The survival rate of bleeding dogs was also lower one month after diagnosis (66 percent) than in dogs without signs of bleeding (90 percent). Therefore, bleeding dogs had decreased odds of surviving discharge. This finding contrasts with that of a previous study, which found that the survival of A. vasorum-positive dogs with bleeding diathesis did not differ from those without bleeding (Sigrist et al., 2017).
Were there limiting factors?
Due to its retrospective nature, the study was limited by the variation in laboratory analyses and a lack of a full haemostatic panel for all dogs. Furthermore, the exact cause of death was not registered for all dogs, which could have obscured the true survival rate.
Take-home message
Bleeding diathesis is an important negative prognostic indicator in A. vasorum infections, with almost a quarter (23 percent) of affected dogs with bleeding not surviving to hospital discharge
The diagnostic and prognostic information presented in this study is pertinent and valuable for client communication regarding A. vasorum-positive dogs. The findings confirm that bleeding diathesis is an important negative prognostic indicator in A. vasorum infections, with almost a quarter (23 percent) of affected dogs with bleeding not surviving to hospital discharge.
The most common clinical signs of bleeding diathesis that presented were cutaneous or mucosal bleeding. Affected dogs had confirmed laboratory haemostatic aberrations, leading to a prolonged prothrombin time and thromboelastographic parameters statistically indicative of less-firm blood clot formation.
As some dogs presented with neurological signs, A. vasorum infection should be considered a major differential diagnosis in any dog with either unexplained coagulopathy or neurological signs in A. vasorum endemic areas.
