Internal dog parasites explained

Posted by Dr Dog. February 10th 2014.

Endoparasites are parasites where the majority of their life cycle occurs within the dog’s body. Most people associate them with gastrointestinal problems but you should be aware that a number of worms can infect other organs such as lungs, liver and even a dog’s brain. A number of these parasites’ lifecycles are not restricted to the dog and involve another host species such as fleas, snails, slugs which can have implications on their control. Also you must always keep in mind that some parasites can be transmitted to humans (zoonotic) and hence along with your dog’s health there are public health implications in not worming your dog. It is recommended that the average dog is wormed every 3 months though more is advisable in puppies and dogs with fleas.

Labrador puppy & vet

1)    Roundworm

The most common species of roundworm in dogs is Toxocara canis. They may be seen in your dog’s faeces or vomit and resemble coiled spaghetti. They are picked up when dogs eat their larvae, the adult worm develops and the eggs are passed out in the faeces. These eggs then hatch in larvae that move out on to the ground and are ingested by the dog. Children can be susceptible to some roundworm and can develop blindness if infected, so, regular worming and cleaning up of dog faeces immediately is essential. This worm is commonly seen in puppies as the bitch can transmit the worm whilst the puppies are in the womb and through her milk. Signs a dog has worms may include weight loss, dull coat, pot belly, diarrhoea or cough. The signs are generally more obvious and worse in puppies than adults.


2)    Tapeworm

Tapeworms are a common worm of dogs. The tell-tale sign that your dog has tapeworm is the presence of segments around the anus or in the faeces. These can look like grains of rice and may wiggle. They contain the eggs. Transmission is often via fleas entering the dog’s body when it grooms and swallows the flea. They can be transmitted to humans. It is advisable that any dog that has fleas is treated against tapeworm. Tapeworm may cause no other signs of problems other than an itchy bottom though sometimes diarrhoea may result.


3)    Hookworm

The hookworm is small and thin and attaches to the gut lining and feeds on blood and tissue. The larvae can be transmitted from bitch to pup and also from ingestion of the larvae from the ground or through the skin. In puppies they can cause bloody dark diarrhoea, anaemia and failure to thrive. In adults diarrhoea and/or anaemia may be seen or the dog may appear well. They are much less common than roundworm and tapeworm. Foxes are often a source of transmission.


4)    Whipworm

The whipworm looks like its name, thin front ‘whip’ end and a thicker ‘handle’ end. They are picked up from the environment. A large number of infected dogs will show no signs but it can progress to bloody ‘mucousy’ diarrhoea, weight loss and anaemia. Some animals may have a poor coat and vomit.


5)    Lungworm

The lungworm is a potentially life-threatening parasite. The adults live in the heart and major blood vessels going to the lungs. Here they can cause serious problems and if untreated are often fatal. The parasite is transmitted via slugs and snails. Note that you pet does not have to actually eat the slug just licking/drinking/eating something that the slug has made contact with can be enough. Infection can cause all kinds of very differing signs including breathing problems, coughing, blood clotting problems, behavioural or neurological changes and sometimes your dog may just seem generally unwell. These signs can be mistaken for something else so prevention is definitely better than cure with this dangerous parasite. Lungworm is common in foxes and seems to be on the increase in the UK.


6)    Heartworm

Heartworm is transmitted dog to dog via mosquito bite and is potentially life-threatening.
It is relatively rare but cases have been diagnosed in the south of England. The parasite travels through the blood stream and the adult lives in the heart and can lead, in the long term, to heart failure. Signs may take months or years to develop and will show as cough, lethargy, weight loss and weakness. Treatment is complex so prevention is definitely better than cure.

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