Serious form of tapeworm infestation, which occurs at a particular developmental stage of the tapeworm. The larval worm develops from the ovum (egg) of the tapeworm. The ova of the tapeworm are actually encysted larvae, surrounded by a casing formed by the larvae themselves. They can live for up to six months, even under unfavourable conditions such as drought. The ova are passed with the faeces and can be eaten by cattle, pigs or human beings, depending on the kind of tapeworm. The animal (or man) then functions as intermediate host; larvae can develop into fully-grown tapeworms only in the definitive host. One small tapeworm, Echinoccus granulosus, occurs in dogs, and its larval form can develop in sheep or in man. The illness in human beings is known as echinococcosis. The larva from the egg taken in via the mouth usually develops into a larval worm in the liver and sometimes in the lungs. (The larval worm can become a fully-grown tapeworm only in the dog.) This larval worm in the liver or lungs of man can lead to stomach pain, coughing and constriction. Echinococcosis is usually treated by removal of the worm by surgery. It is possible to prevent infestation by good hygiene.