Dictyocaulus viviparus

 

Life Cycle:
The adult worms live in the bronchi of the lungs. Eggs are laid in the lungs and may hatch there or in the intestine (after being coughed up and swallowed). First stage larva emerge from the cow in the feces. The larvae reach the ensheathed infectious third-stage (L3) by about 4 days. L3 are either washed out of the fecal pads or expelled from the fecal pad when they happen to be on a sporangium of the fungus Pilobolus which explodes to release its spores. On pasture the L3 will migrate up grass blades and be eaten by the cow. The L3 exsheath in the small intestine, penetrate the bowel wall and molt to L4 in the mesenteric lymph nodes. They then migrate to the lungs via the thoracic duct. They reach the lungs about 2 weeks after they were ingested. They molt to the adult stage at about 15 days of infection and begin laying eggs around 22 days post-infection (PI). The adult worms begin to be expelled at about 50 days PI, and most are gone by 70 days PI. A few adults or late stage larvae may over winter in the lungs of an infected animal and L3 may over winter on pasture by migrating down into the root mat and soil.

 

 Life Cycle Dictyocaulus viviparus

Clinical Signs
In heavy infections: During the first 25 days of infection there may be tachypnea and coughing. During days 25 to 55 the lung signs increase in intensity with harsh lung sounds (ronchi and emphysematous crackling) being heard.
In mild infections the disease may be asymptomatic.

Diagnostic
The first stage larva (0.3 to 0.36 mm) is found in the fresh feces

Treatment