Dictyocaulus viviparus

Introduction

Dictyocaulus viviparus is the bovine lungworm (a member of the Trichostrongyloidea). They are white thread-like worms, less than 8cm long, which are found in the trachea and larger bronchi and are responsible for parasitic bronchitis (syn. Bovine dictyocauliosis, husk, hoose). There has been an increase in the incidence of husk in recent years; first season calves are particularly affected, although yearling and adult cattle may also succumb to the disease. Lungworm is responsible for reduced weight-gain and deaths in calves and yearlings and lowered milk-yield in dairy cows. A closely-related species is also responsible for one of the most important diseases of farmed deer. The parasite is of welfare importance if clinically affected animals are left untreated.

Life-Cycle

1. Adult worms in tracheae and larger bronchi – females lay embryonated eggs
2. Embryonated eggs are coughed up and swallowed
3. Eggs hatch during passage through the intestine
4. First stage larvae passed in fresh faeces (as D. viviparus is not a metastrongyloid, the larvae do not have an S-shaped tail like other lungworms)
5. Development to second and third (infective) stage larvae in dungpat on pasture
6. Ingestion of infective larvae at grazing
7. Infective larvae swallowed, pass through alimentary tract, penetrate wall of intestine and migrate via lymphatics → blood circulation → lungs
8. Ascend respiratory tree and mature to adult lungworms. Prepatent period 3 and a half weeks

• Dictyocaulus viviparus causes parasitic bronchitis