The hydatid tapeworm or Echinococcus granulosus occurs in the dog and dingo – not in the cat family. The adult tapeworm is tiny, being only about 4 to 6 millimeters long. It resides in the small intestine of the dog and causes it very little inconvenience.
Eggs are produced in the last segment of the worm which drop off approximately every two weeks and are shed in the droppings. Each mature segment contains up to one thousand eggs and if the dog is confined to a small area it can be appreciated how quickly the environment and the dog’s coat becomes contaminated.
The next stage of the life cycle depends on a suitable intermediate host swallowing an infective egg. Suitable intermediate hosts include sheep, cattle, goats, pigs, kangaroos and of course man.
Grass eating animals ingest the eggs when feeding on pasture contaminated with dog droppings or dust blowing the eggs from the contaminated area discussed above. Man becomes infected by eating or smoking after handling a dog carrying the eggs on its coat.
After being swallowed, the eggs hatch in the small intestine and penetrate small blood vessels from where they can be carried throughout the body, but most often come to rest in the liver and lungs. These then develop into fluid filled bladder-like structures or cysts.
They slowly increase in size, and after about five months produce immature tapeworms. It is from these cysts present in the liver and lungs of the intermediate host that the dog is infected. The cysts can rupture in the intermediate host producing thousands of secondary or daughter cysts.
Dogs become infected only by eating mature cysts. The most common source of infection of the dog is the careless feeding of dogs on country properties. It is still quite common for farmers to throw uncooked offal to their dogs when killing a sheep. When it is realized that as many as 50 percent of the sheep on a particular property can be infected, then the chances of the dog receiving a mature infective cyst are very high.
In cattle most cysts remain sterile. Whilst in goats 30 percent remain sterile but in pigs about 88 percent are infective. In sheep 94 percent of cysts are capable of reproducing the disease if swallowed by a dog.
The control of the disease depends mainly on breaking the link between the sheep and the dog. Dogs should be treated with an efficient anthelmintic – the most effective and easiest to use is Droncit. This should be done every six weeks in rural dogs.
Proper disposal of offal and sheep carcasses must be carried out as well as ensuring that dogs do not roam freely onto neighboring properties.
As explained, dogs do not become infected themselves by associating with other infected dogs but they can passively transmit the infective eggs on their coat if they have been in an area heavily contaminated. Encourage children not to handle strange dogs and to be sure to wash their hands before eating.
Hydatid disease is important not only because of the cause of a serious human disease but it causes vast economic loss through the condemnation of sheep products in the abattoir, in man the presence of large number of cysts in vital organs of the body can produce serious symptoms and surgical treatment is difficult where large numbers of cysts are present.