Dogs become infected following ingestion of rat lung worm larvae within infected snails/ slugs. They do not necessarily need to eat the slug itself to become infected; ingestion of larvae can also occur from the ‘’snail trial’’ produced by the snails' movement over surfaces and vegetation.
Once rat lung worm larvae are ingested, they penetrate the wall of the gastrointestinal tract and make their way to the spinal cord. Migration within the spinal cord results in severe inflammation (eosinophilic) as the body reacts to a ‘’foreign object’’ resulting in eosinophilic meningoencephalomyelitis or inflammation of the meninges, spinal cord and in some cases brain tissue. Direct damage to the spinal cord also occurs by the migration of the larvae themselves.
What is rat lung worm disease?
Canine neural angiostrongyliasis is a clinical syndrome of eosinophilic meningoencephalomyelitis caused by accidental infection with larval forms of Angiostrongylus cantonensis which is a lung worm affecting rats. This disease is more generally referred to as ‘rat lung worm disease ’. Neural angiostrongyliasis also affects people and is endemic in south Asia, the Pacific island, Australia and the Caribbean islands.
Who is affected by rat lung worm disease?
Dogs of any age group can be affected however due to the inquisitive nature of puppies, this disease is most commonly seen in puppies less than 6 months of age (range 7 weeks to 14 years).
The majority of cases reported that occured in late Autumn – early winter (March – July) as this corresponds to the highest activity and number of snails/ slugs.
Rat lug worm disease in Australia is isolated to the East coast and has been reported as far north as Townsville and south as Jervis Bay.
Signs of Rat lung worm disease
The classical presentation of rat lung worm disease in puppies is an ascending weakness initially affecting the back legs and pain. This may present as;
- Hind limb weakness, wobbliness, walking with swaying back legs or as if drunk
- Tendency to sit more, unable to support their weight in the back legs
- Inability to wag the tails, flaccid tail
- Pain on patting or gentle palpation of the spine
- Rigid low neck carriage
- Urinary and faecal incontinence
In some animals, the brain may become affected and result in other clinical signs such as dull mentation or seizures.
Rat lung worm disease diagnosis
Classic clinical presentation in young dogs is sufficient to raise suspicions amongst experienced veterinarians. Diagnostic investigation recommended would include;
- Complete blood count and serum biochemistry- approximately 80% of affected dogs will have an increased number of blood eosinophils. This is not definitive for a diagnosis of rat lung worm disease as this can also occur with gastrointestinal worms, allergic skin disease and some endocrine disorders.
- Serology testing for other infectious disease such as cryptococcus, toxoplasma and neospora
- Cerebrospinal fluid(CSF) collection – demonstrates a mild to marked increase in inflammatory cell, with the majority eosinophils
- Antibody testing or PCR on the CSF – a positive result is considered definitive for a Angiostrongylus canonentsis.
- Identification of larvae within the CSF sample – also considered definitive however very rare in veterinary medicine
- Advanced imaging such as MRI of the spinal cord or brain may be considered in patients that do not have classical clinical signs or prior to CSF collection
Rat lung worm disease Treatment
Treatment of rat lung worm disease is with supportive care, anti-inflammatories and in some cases, treatment with deworming products.
The mainstay of treatment is corticosteroids (prednisolone) to treat the body’s inflammatory response to the presence of the worms. The inflammatory response is accountable for the majority of clinical signs seen, especially pain. Pain relief with opioid analgesia is often required initially.
There is no consensus on treatment directly aimed at killing the larvae in people or in dogs. Whilst it sounds intuitive, treatment aimed at killing larvae given immediately can result in a catastrophic inflammation in response to the dead and dying worms and as such is generally avoided. Deworming may be considered following control and improvement of clinical signs.
The majority of dogs respond well to treatment with corticosteroids however some will suffer long term complications with abnormal gait or urinary incontinence. Very uncommonly, animals can succumb to rat lung worm disease.
There are 3 things that are essential to developing rat lung worm disease: rats, slugs/snails and your beloved pooch.
Rat and snail/slug control can help prevent exposure of your dog (and family) to the infectious larvae and other disease such as leptospirosis in the case of rats. Extreme care should be taken to ensure that this does not place your dog at further risk of toxicity from rat or snail bait – both of which can be fatal.
Routine heartworm prevention can help to reduce the risk of larvae survival and development of disease. If you witness your dog eating a snail or slug, a preventative course of a broad spectrum all wormer (fenbendazole) can be considered with care in consultation with your veterinarian.
- Lee R et al (2020). Further studies of neuroangiostrongyliasis (rat lungworm disease) in Australian dogs: 92 new cases (2010–2020) and results for a novel, highly sensitive qPCR assay. Parasitology 1–9. https://doi.org/10.1017/S0031182020001572