Research from Bristol University confirms that Angiostrongylus vasorum is spreading in the UK, with 16 per cent of dogs involved in a recent study testing positive for the parasite’s larvae.
The nationwide survey, funded by the RCVS Trust and Novartis Animal Health, was set up to determine the geographical distribution and typical presentation of angiostrongylosis in UK dogs and to elucidate risk factors for infection. The findings are based on examination of 630 faecal samples from dogs (500 sick and 130 healthy) around the country which presented in practice with a wide range of clinical signs for which there was no other obvious diagnosis.
"We received faecal samples from dogs with respiratory and cardiovascular disease, bleeding, neurological and gastrointestinal disorders," explained Eric Morgan, Veterinary Parasitology and Ecology Research Group, University of Bristol School of Biological Sciences. "We also received samples from a smaller number of apparently healthy dogs and examined all of them in the laboratory using the Baermann’s test. The sample was analysed alongside an accompanying questionnaire that recorded history, clinical signs and the vet’s index of suspicion that A. vasorum was the cause of the disease."
More than half (60 per cent) of the dogs that were positive displayed respiratory signs, including coughing. The next most common signs were cardiovascular (including syncope, lethargy and exercise intolerance). The most widespread combination of clinical signs was respiratory and cardiovascular. However, several dogs also presented with haemorrhagic signs and no respiratory involvement, and a wide spectrum of other signs such as diarrhoea, lameness and neurological disease.
Eric said: "Angiostrongylus vasorum is a great imitator and our research proves it can present in a wide variety of ways. Prompt diagnosis is vital but relies heavily on vets being aware of A. vasorum involvement. They should be especially suspicious of dogs that are coughing, lethargic, prone to collapse and presented in practice with unexplained bleeding."
Geographical extent Due to the survey relying on voluntary vet involvement, there was a strong bias in the regions represented, with high numbers of samples coming from South Wales and Surrey. Eric said: "Although these are known hot spots for A. vasorum, there were also positive samples from across southern England demonstrating that the parasite is much more widespread than we previously thought. It’s important that vets outside of the known endemic areas regard this disease as a real threat, to ignore it because you believe dogs outside these areas are not at risk would be a very dangerous assumption indeed. You could already be missing cases."
Risk factors The most significant risk factor was age, with younger dogs more likely to be infected although cases were found in dogs up to 11 years old. “The age profile of positive cases did not vary by region, suggesting that there is no significant build-up of immunity in the dog population,” Eric continues. "Several dogs became re-infected which also suggests that strong immunity does not develop following infection."
More than 40 breeds were represented in the survey with Staffordshire Bull Terriers and Jack Russell Terriers more commonly infected than other breeds. However, when considered alongside all the other risk factors the difference was not significant. "There are certainly no breeds which are resistant to infection, all of them can get it and are therefore at risk!"
Dogs that had not been wormed in the past six months were more likely to be positive (17 per cent of these were positive) than those dogs that had been regularly wormed (12 per cent). "It’s important to realise that even in dogs that are regularly wormed, incidence is still high," concludes Eric. "Vets should pay particularly attention to the worming regimes that they routinely recommend and ensure that the products they prescribe have some activity against A. vasorum. They should also be prepared to consider A.vasorum as a diagnosis even in dogs that are routinely wormed. What we have to remember is that this is a tough worm to get rid of and one we need to take seriously if we are to prevent its spread."
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