Lungworm or Heartworm?
Dog owners may have recently become aware of a relatively new disease which has been diagnosed more frequently over the last twelve months or so throughout the country, and, from my personal experience as a vet, locally as well.
Angiostrongylus vasorum (Lungworm/ French heartworm)
This parasite can be known either as lungworm infection or French Heartworm. The adult worms live within the pulmonary artery and right ventricle of the heart of the dog. The eggs hatch in the lungs and the young larvae eventually pass out in microscopic form in the faeces. If these larvae are then ingested by slugs and snails and the infected slugs and snails are then eaten by other dogs, (perhaps deliberately, perhaps unintentionally whilst eating grass), the now infective larvae migrate through the intestinal wall and make their way back to the heart to start the life cycle again.
This used to be a very rare disease and until last year was not thought to occur in this area. However we have had several cases recently so it is on the increase. The main problem with this disease is that symptoms can be very vague and not what you might expect. Because the eggs and larvae occur in the lungs, they can produce chest problems and a cough which initially can be very similar to the dreaded "kennel cough", for which it could be mistaken in the early stages. The adult worms can affect the ability of the blood to clot causing haemorrhage or bleeding disorders including nose bleeds, or excessive bruising. Large numbers of worms in the heart could cause problems with the circulation causing lethargy. In some cases there has been haemorrhage into the brain and spinal cord causing odd neurological episodes or collapse. Diagnosis depends on finding larval stages of the worm in fresh faecal samples but because they do not continuously produce larvae several samples may need to be tested before a dog could be considered either affected or clear. Treatment is relatively straightforward once diagnosis has been made and there are different products that are effective and your vet would advise you as to which is most appropriate if necessary. There is no effective prevention except discouraging your dog from ingesting slugs and snails. Spread of the disease is probably though infected dogs and foxes and via slugs and snails which have been plentiful this year
Filaroides osleri or Oslerus osleri (lungworm)
This is a true lungworm in that the adult form of this parasitic worm lives and breeds in the bronchi within the lungs. The adults are visible within the lungs when using a scope and also cause nodular changes within the tissue of the airway. Unlike the Angiostrongylus worms, they can transmit infective larvae directly either in saliva and sputum or via the larvae in their faeces. Infection is either via direct contact between dogs or from infective larvae on the ground passed from either dogs or foxes. Infected animals may develop a chronic cough which may again be easily mistaken for kennel cough initially. Not all affected animals show symptoms but any dog with a persistent cough, especially in younger animals, should be tested. Diagnosis is either by direct bronchoscopy to look for adults which are 1 to 1.5 cm long , or by faecal examination for larval form of the worm. Medication is different to that of the French Heartworm above and needs to be discussed with your veterinary surgeon but is straightforward. There is no specific preventative treatment.
This is canine heartworm, thankfully a disease not yet found in the UK. The adult worms are again found within the right ventricles of the heart but with this worm the larvae or microfilariae are found within the bloodstream. They are transmitted by the mosquito and mature within this tiny host for a couple of weeks before they become infective. At this point they travel to the mouthparts of the mosquito to be transmitted into a new dog where they migrate via the blood stream to the heart and the cycle starts again. This disease is widespread in the United States and warmer parts of Europe and could pose a threat if it is brought in by dogs travelling into the UK on the Pets Passport scheme, especially in areas like the New Forest where there is an abundant mosquito population. Because it lives mainly within the heart and the blood vessels, it causes problems with circulation and the heart, commonly lethargy and heart failure. It can be prevented in areas where the disease is common by regular treatment similar to anti malarial medication and it is treatable using similar products. The main thing is that at the moment you only need to worry about this parasitic disease if you take your dog abroad. I have mentioned it mainly because of the confusion that arises because of the similarity of the names of these different parasitic diseases.
French heartworm/Lungworm – spread by slugs and snails, uncommon but increasing, causes a variety of conditions including cough, haemorrhage and nervous signs
Typical Lungworm – spread directly or indirectly between foxes and dogs, relatively uncommon in the New Forest, causes chest problems and coughing.
Heartworm – not present in the UK, causes heart problems
Please try not to worry too much about these parasites as they are still uncommon, but if you have any concerns please ask your veterinary surgeon.