Hydatid disease is caused by the Echinococcus granulosus, a tapeworm of dogs. Eggs laid by the tapeworm in the dog's intestine are passed in the dog's faeces and contaminate grass, garden vegetables and other areas and can then be eaten by grazing cattle and sheep. Each egg then hatches in the intestine of the sheep/cow and the early stage of the parasite is carried by the blood stream to various parts of the body - liver, lungs, brain etc., where they slowly develop into hydatid cysts.
Hydatid cysts can grow quite large and contain many young tapeworms floating in clear fluid. If a dog is fed or allowed to scavange on infected carcasses, then the young tapeworms are released from the cysts and grow inside the dog's intestine. These, in turn, produce more eggs and cause futher spread of infection.
Humans can pick up the infection from infected dogs. People, especially children, become infected by ingesting eggs through hand to mouth transfer of eggs after contact with infected dogs. It may also occur through ingestion of food, water or soil that has been contaminated with infected dog faeces. Eggs so ingested can hatch in the intestine and release the early stage of the parasite which can travel in the body and form a hydatid cyst somewhere. Symptoms experienced relate to where the cyst forms ..... if it is in the brain it can cause symptoms similar to a brain tumour.
The only treatment for Hydatid Disease in humans is the surgical removal of the cysts.... this can be extremely difficult and dangerous because of the site of the cyst (eg. brain). Rupture of the cyst during surgery can cause acute shock and also releases thousands of worm heads into the body. There are no effective drug treatments against Hydatid disease in humans.
Thankfully, there have only been a very small number of cases of hydatid disease in the UK in recent years, but there are hotspots of infection especially in Wales namely Powys, Monmouthshire and areas in the Brecon Beacons and Black Mountains.
In order to kill the adult tapeworm in the dog, a drug called Praziquantel must be used. This is found only in certain wormers available from vets, for example Milbemax or Drontal. In areas of risk dogs should be wormed every 6 weeks with a wormer that contains Praziquantel. If you visit Wales with your dog is is advisable to worm your dog both before and after your visit.
For further information on worming your dog please ask your vet and for more general information visit www.wales.gov.uk/animaldiseases
Other Worms That Can Cause Human Disease
Toxocara Canis is a roundworm of dogs. Puppies in particular can have heavy life-threatening infections. Humans can act as an accidental host for the migrating larval form with children being especially at risk. Toxocara eggs are very resistant and remain infective for a long time in the environment eg. parks and gardens. The eggs are sticky and may stick to the dog's fur. Humans then become infected by contact with areas contaminated with dog faeces or from ingestion of eggs from the dog's fur. Toxocara larvae can be found in any organ of the body, commonly they migrate to the liver and lungs casusing fever and disease. The most serious condition results from the migration of the worm larvae through the retina and this can cause blindness.
Dipylidium caninum is a tapeworm of both dogs and cats and has the flea as its intermediate host. Dogs and cats become infected when they groom and swallow infected fleas. This is a relatively common and usually harmless tapeworm but it has been shown on occasion to infect children who accidentally swallow fleas when playing with dogs or cats. This can be prevented by regular worming and flea treatment.