Broadly speaking the main types of worms that cause problems in the dog are:
- Intestinal roundworms: the most important example is the common intestinal roundworm Toxocara canis.
- Intestinal tapeworms: Dipylidium caninum, Taenia species and Echinococcus species are the three main examples in the UK.
- Lungworm: the most important examples are the French heartworm Angiostrongylus vasorum and the fox lungworm Crenosoma vulpis.
Roundworms are free-living within the gut. In puppies, large numbers can stunt growth, create serious digestive upsets and cause flatulence. Puppies with heavy worm burdens often have a 'pot-bellied' appearance. Roundworms spread directly from dog to dog via eggs in the faeces.
As with the intestinal roundworms, these rarely cause problems in adult dogs but in puppies tapeworms can be responsible for digestive upsets, intestinal blockages and stunted growth. The tapeworms require an 'intermediate host' in order to spread, that is, they do not spread directly from dog to dog. Dipylidium caninum, the common canine tapeworm, is spread by fleas.
Cases of lungworm are on the increase due to changes in the fox population (a major source of Crenosoma vulpis) and changes in climate and pet travel trends (Angiostrongylus vasorum was previously rare in the UK). Dogs usually become infected by eating snails or slugs (intermediate hosts); the larvae travel from the digestive tract to the lungs; eggs are subsequently coughed up and swallowed. This is why we can test for lungworm by looking for eggs in a faecal sample. The main signs of disease are coughing and shortness of breath but these worms can also cause clotting disorders and ultimately can prove fatal.
Treating for worms
Worms can affect dogs at any age and some of the worms your dog can carry cause disease in people, especially children. You should worm your dog at least every 6 months, ideally every 3 months, with a reliable worming product. Most worming products do not have any residual activity, so whilst they eliminate any worms present at the time they are given, there is nothing to stop your dog picking up another worm soon after. Speak to your vet if you wish to discuss worming protocols in more detail.