1.   An increased fecundity of existing adult worm populations.

2.   The expulsion of the adult worm population is considered to be the consequence of an immediate-type hypersensitivity reaction to antigens derived from the developing larvae.

3.   However, when necessary, treatment with any of the benzimidazoles, levamisole or ivermectin will remove adult worms and developing stages.

4.   Small numbers of adult worms can survive in the bronchi of infected animals, particularly yearlings, until the next grazing season.

5.   The adult worms are most often found in the small bronchi and their eggs, containing the first stage larvae, hatch soon after being passed in the faeces.

6.   In one species, T. tenuicollis, groups of adult worms are characteristically found feeding in groups.

7.   Usually the adult worms, soon after arrival at the perirenal site, are encapsulated in cysts, which may contain greenish pus.

8.   Though the adult worms are never numerous, they are very fecund, and an infected pig may pass a million eggs per day.

9.   In less severe infections the adult worms cause a haemorrhagic tracheitis with excess mucus production which leads to partial occlusion of the airways and difficulty in breathing.