Angiostrongylus vasorum:

where is it, and what are the risks?

Angiostrongylus vasorum:

where is it, and what are the risks?

Ian Wright, BVMS, BSc, MSc, MRCVS
Ian Wright, BVMS, BSc, MSc, MRCVS
Photo by Alexas Fotos / Pexels

Abstract

Angiostrongylus vasorum, commonly referred to as “lungworm” or “French heartworm,” is a nematode parasite that infects the heart and pulmonary arteries of dogs and wild canids, primarily affecting lung tissue. Dogs become infected by ingesting gastropods containing infective third-stage larvae. The infection predominantly causes respiratory disease, leading to coughing and dyspnoea. Severe cases can involve chronic fatigue, anorexia and coagulation disorders.

Canine angiostrongylosis is a focal disease with varied epidemiology based largely on the wildlife reservoir species, lifestyle factors, and the abundance and distribution of the gastropod molluscs.

In the UK, A vasorum has spread from initial hotspots in the south-east and south-west to the north of England, Scotland and Northern Ireland. The spread of lungworm is thought to be influenced by factors such as climate change and the movement of infected animals. A vasorum poses a significant health risk to dogs in the UK, especially in areas where the parasite is endemic, including south-east England, west midlands and south Wales.

Awareness among pet owners and veterinarians is crucial for early detection, treatment and prevention of infection in dogs. Recognising and diagnosing lungworms can be challenging, necessitating vigilance.

Management of canine angiostrongylosis focuses on prophylactic and therapeutic treatment using anthelmintics and minimising dogs’ exposure to slugs or snails. In this article, the current knowledge on the distribution and risks of A vasorum infection in the UK is discussed.

Contents

Dog lungworm A vasorum has become an increasingly significant parasitic infection affecting dogs in various regions, including the UK.

This roundworm primarily targets the cardiovascular and respiratory systems, leading to potentially severe health issues.

A vasorum has been spreading across the UK. Initially reported in localised areas in south-eastern England and south Wales, it is now found in various regions, including central and northern England (Kirk et al, 2014). The aim of this article is to provide an update on A vasorum, highlighting its impact on dogs, and outlining the necessary measures for prevention, diagnosis and treatment.

Furthermore, the article emphasises the increasing prevalence and distribution of A vasorum, explores the factors contributing to its spread and underscores the critical need for ongoing research and improved awareness to mitigate its impact on canine health.

Life cycle and transmission dynamics

A vasorum has a multi-host, multi-stage, indirect life cycle that involves dogs as the definitive host, gastropod molluscs (slugs and snails) as intermediate hosts and wild canids, such as red foxes, as reservoirs. Dogs get infected by accidental or intentional ingestion of third-stage larvae from these intermediate hosts or from slime trails and paratenic hosts such as frogs. Larger slugs, active in autumn, pose a higher risk, while smaller slugs are active year-round. Slugs and snails are prominent intermediate hosts, though other gastropod species may also play a role.

The type of habitat is a major factor determining the opportunities of dogs encountering gastropods. Gastropods are drawn to complex vegetated areas because they offer better food sources, moisture retention and ease of movement.

As a result, dogs are more likely to encounter gastropods in these vegetated environments and less likely on hard surfaces. High-risk gastropod species are especially common in the evening and when humidity is high (Tolhurst et al, 2021).

A vasorum prevalence in gastropods can vary geographically within the UK, influenced by timing and environmental factors. Gastropod species composition, abundance and activity, influenced by climate and potentially invasive species, can significantly impact A vasorum transmission dynamics.

Climate change is expected to alter gastropod community dynamics and A vasorum transmission, with species such as the “Spanish slug” being particularly affected by humidity and temperature (Tolhurst et al, 2021).

Image © ginasanders / Depositphotos.com

Geographic spread

A vasorum is increasingly found in domestic dogs across the UK. Initially confined to small endemic areas in Cornwall and south Wales, it is now present in south-east England, the midlands and as far north as Glasgow.

The spread is facilitated by dog movements and the presence of foxes and slugs. Data indicate that foxes, the main wildlife reservoir hosts for lungworm, have shown an increase in prevalence from 7.3% in 2005 (Morgan et al, 2008) to 18.3% in 2014 (Taylor et al, 2015), spreading to previously unaffected regions.

Slugs are active in mild, moist conditions. Warmer and wetter climates enhance parasite survival rates, affecting companion animals. Hence, climate change, resulting in milder winters and summers, may increase year-round exposure to slugs.

Determining the risk

Various demographic and lifestyle risk factors for A vasorum infection in dogs are important to highlight.
  • Age and breed. Dogs below two years, particularly puppies, face a higher risk, although certain breeds (cavalier King Charles spaniels, cocker spaniels, Jack Russell terriers, springer spaniels, and Staffordshire bull terriers) may be more susceptible. Evidence on this remains inconclusive, though (Blehaut et al, 2014).
  • Lack of recent treatment. Dogs that have not received anthelmintic treatment are at a higher risk.
  • Ingestion of contaminated items. Dogs can become infected by intentionally ingesting gastropods or paratenic hosts such as frogs (Elsheikha et al, 2014). Unintentional ingestion via contaminated food, scavenging or grass-chewing is also a significant risk. Food-borne transmission can occur via contaminated gastropods or paratenic hosts like chickens. However, cooking or freezing the meat would likely reduce this risk.
  • Environmental exposure. Opportunities for contact with infected gastropods increase the risk of infection. Third-stage larvae released from gastropods into water can infect dogs through contaminated water or food, although this has not been detected under field conditions. Natural habitats increase the probability of encounters, especially in woodland and grassland.

To determine the risk, assessment should encompass lifestyle factors such as consumption of molluscs and drinking from puddles, as well as geographic factors, prevalence maps of foxes and local diagnoses.

Regular testing and sharing of results among veterinary practices are crucial for accurately gauging local risks. Surveillance initiatives such as SAVSNET and real-time mapping can help track the spread and prevalence of A vasorum, though biases and data collection challenges exist.

A lungworm map is available for vets to add data, along with resources to help educate pet owners.

Risk of disease in dogs

A vasorum is highly pathogenic in dogs, carrying a mortality rate of 2% to 13% even with treatment.

In dogs, infection primarily induces respiratory disease characterised by inflammation around first-stage larvae as they invade lung alveoli, resulting in coughing and dyspnoea.

Severe cases may manifest additional signs, including anorexia, chronic fatigue and syncope. Furthermore, impaired coagulation functions are commonly observed, leading to life-threatening conditions such as anaemia, hematomas and prolonged bleeding.

Rarely, larvae may migrate to unusual locations, causing issues in organs such as kidneys, heart muscle and eyes. Neurological signs may result from central nervous system haemorrhages or aberrant larval migrations.

Diagnosis

Confirmation of infection includes various serological, molecular assays and conventional parasitology methods:
  • Baermann faecal analysis. This is cost-effective and highly specific, but requires fresh samples across three consecutive days.
  • AngioDetect (antigen-based ELISA). A point-of-care blood test, this has a 84.6% sensitivity and 100% specificity.
  • Antibody-based ELISA. This is sensitive and specific, but not yet widely available.
  • Bronchoalveolar lavage (BAL). It detects larvae in infected dogs, but carries some risk in those with respiratory conditions.
  • qPCR testing. This test detects worm DNA with high precision, and is useful for blood and faecal samples.
  • Coagulation tests. Thromboelastometry and buccal mucosa bleeding time assess bleeding risk.
  • Imaging. Thoracic radiographs and CT scans can reveal lung changes indicative of infection.

Treatment

Common anthelmintics for lungworm include fenbendazole, milbemycin oxime and moxidectin (Elsheikha et al, 2014). Fenbendazole, though not licensed for lungworms, is used at 25mg/kg for 20 days (91% efficacy) or 50mg/kg daily for several days, with slower-acting treatments preferred for severe cases.

Tablet products, for example containing milbemycin oxime, are is effective at 0.5mg/kg, administered four times weekly.

It significantly reduces the level of lungworm burden with immature adult (L5) and adult stages and is sometimes combined with praziquantel. Spot-on products containing moxidectin have shown 85% efficacy with one treatment and nearly 100% with two treatments a month apart, making it suitable for mild to moderate cases.

Severe cases may need supportive treatment with antibiotics, glucocorticoids and blood substitutes, with at least 2-3 days of rest.

Post-treatment follow-up and managing complications

Post-treatment, dead worms may be destroyed by macrophages, encapsulated or expelled through coughing. Radiographic improvements typically occur over several months.

Pre-treatment with glucocorticoids (for example, prednisolone) can reduce the immune response to dead worms, but evidence is mixed, and their use is case-specific.

Managing coagulopathy includes addressing hyperfibrinolysis and hypofibrinogenaemia using tranexamic acid at a dosage of 10 mg/kg to 20mg/kg administered every 6 to 8 hours, along with fresh frozen plasma given at a rate of 20mL/kg.

Pulmonary hypertension occurs in up to 15% of cases, treated with sildenafil at 1mg/kg to 3mg/kg every 8 to 12 hours, starting at lower doses and monitoring the response.

Monitoring treatment success involves observing reductions in clinical signs, radiographic resolution and normalisation of bleeding responses.

Repeat treatments and faecal larval counts may be needed in some cases, and BAL and faecal PCR are useful tools for assessment.

Prevention and control

Preventive measures are crucial due to the potentially fatal outcomes if infections are left untreated. To minimise exposure, it is advisable to prevent dogs from feeding outdoors, walking in damp environments and keeping dog toys indoors.

Regular cleaning of outdoor water dishes and promptly removing dog faeces are crucial measures. Anthelmintic treatments containing moxidectin or milbemycin oxime are effective for preventing established infections and reducing environmental contamination.

Dogs at high risk of exposure due to lifestyle factors (for example, snail or slug eaters) or in endemic areas should receive monthly preventive treatment.

The exact impact monthly anthelmintic treatments have on the prevalence of A vasorum in endemic regions remains to be investigated. In uncertain areas, testing prior to surgery, in suspected cases, and annual testing of young dogs helps determine endemic status and inform risk-based advice.

Raising awareness

Awareness of A vasorum risks and the appropriate use of diagnostic methods is crucial to prevent delayed diagnosis.

Also, better understanding of the life cycle and ecology of A vasorum could help dog owners make informed decisions to prevent infection.

Sharing case occurrences via social media and local press, along with national publicity campaigns, can effectively raise awareness about lungworm risks. Studies are needed to investigate how different public awareness and education campaigns affect owner compliance with preventive measures for A vasorum.

Large-scale citizen science studies are also needed for comprehending national trends and assessing the efficacy of treatments and preventive measures.

Advice and information sharing

Collaboration and vigilance among veterinary professionals are crucial, especially in areas with emerging cases.

Practitioners should share local risk information with colleagues, and voluntary case reporting helps map high-prevalence areas.

Small animal practices should communicate the most appropriate preventive approach for dogs to their clients. ESCCAP UK and Ireland offers a free query service, frequently addressing questions about angiostrongylosis prevention.

Annual screening of pets in areas with known lungworm presence should be part of wellness plans to ensure treatment efficacy and compliance.

Ensuring owner compliance with treatment is crucial to achieve effective lungworm prevention (Elsheikha, 2016a; 2016b).

Conclusion

The prevalence and geographical distribution of angiostrongylosis caused by A vasorum are increasing, posing a serious threat to dogs’ health.

Factors such as climate change, urbanisation of foxes and invasion of exotic snail species contribute to the spread of A vasorum.

Climate change may accelerate larval development within gastropod intermediate hosts, though its overall impact on the availability of infective larvae remains uncertain.

The risk of disease from A vasorum infection in dogs involves a combination of age, seasonal factors, lack of preventive treatment and environmental exposure to infected gastropods or paratenic hosts like frogs and chickens. Young dogs are particularly susceptible, especially if they have not received recent anthelmintic treatment.

Understanding these risk factors is crucial for developing effective prevention and control strategies.

The main approach to managing angiostrongylosis involves administering anthelmintics to prevent the establishment of infection and related health complications.

Further research is crucial for gaining a comprehensive understanding of the dynamic distribution and prevalence trends of A vasorum across various geographical regions, encompassing both domestic and wild carnivore populations.

Key points

  • A vasorum has spread from endemic areas in Wales and southern England to nearly the entire UK.
  • Despite variable risks across the UK, the presence of A vasorum poses a significant threat to dogs.
  • Factors contributing to the parasite’s spread include increased dog movement, urbanisation of foxes and favourable climatic conditions for slug and snail activity.
  • The AngioDetect blood test offers rapid, reliable results and is useful for suspect cases and pre-operative screening.
  • Some canine lungworm cases require immediate intervention for severe symptoms, while others are less urgent.
  • Advances in understanding bleeding disorders in infected dogs suggest treatments like tranexamic acid and plasma transfusions.
  • Control of canine lungworm is too complex to be addressed by a single approach. Proactive prevention and targeted treatment are crucial in managing this potentially deadly nematode.

Top tips

  • In the UK, while the risk of transmission to dogs peaks during the autumn months, it can occur year-round, though at a significantly reduced rate during colder winters.
  • The spread of lungworm is facilitated by dog movements and the presence of foxes and slugs.
  • Relying solely on treatment response is insufficient for accurately assessing A vasorum prevalence.
  • A vasorum should be considered in a wide range of clinical presentations, including cough, dyspnoea, tachypnoea, exercise intolerance, anaemia, haematomas and neurological defects.
  • Traditional detection methods, such as Baermann technique, are insensitive.
  • Testing for A vasorum using AngioDetect is advised before surgery to prevent perioperative haemorrhage.
  • Recognise that no test is infallible; a single negative result does not rule out infection.
  • Anthelmintic treatment is essential for prevention and slowing the parasite’s spread, as lungworms cannot be eradicated once established thanks to wildlife reservoirs.
  • Monthly treatments with macrocyclic lactone-based anthelmintics (moxidectin or milbemycin oxime) are recommended in endemic areas for preventing angiostrongylosis.
  • Hypocoagulability is common, and tranexamic acid is recommended for its anti-fibrinolytic properties. Plasma transfusions may also be beneficial.
  • Preventive treatment is advised, as there is no immunity after initial infection.
  • Preventing dogs from ingesting slugs, especially during their peak activity times (after dusk), is crucial.
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  • Tolhurst BA, Overall ADJ, King PJ, Morgan ER and Baker RJ (2021). Co-occurrence of domestic dogs and gastropod molluscs in public dog-walking spaces and implications for infection with Angiostrongylus vasorum: a preliminary study, Animals 11(9): 2,577.

Further reading