Lungworm is a growing animal health and economic concern for farms and understanding the lifecycle of the parasite is necessary for management and control. Mild winters allow larvae to survive within the faecal path and persist as a source of infection for the herd in the spring. Older cows can also present a source of infection for others as they can act as carrier cows. These carrier cows have dormant larvae in their lungs which can mature and spread on pasture to other cows, presenting a significant year-on-year source of infection in some herds. A cow first ingests immature, infective larvae (L3) from pasture. L3 larvae enter the gut and penetrate through the intestinal wall into the lymphatic system.  In the lymph nodes, they molt into L4 larvae.

L4 larvae then travel through the lymph and blood to the lungs, where they break out of capillaries about 1 week post infection into the alveoli. The mature larvae cause inflammation and irritation as they move up the airways into the bronchi, where they moult to L5 becoming mature adults 4 weeks post infection.  The adult lungworms are now able to mate and produce eggs. The eggs are then coughed up with mucous and swallowed by the cow. These eggs then hatch to L1 in intestines and larvae are shed in faeces which completes the lungworm’s lifecycle inside the animal.

The free-living parasitic phase involves the maturation of L1 to L3 within the faecal pat on pasture.  This takes approximately 7 days in optimal conditions.  In cold or dry conditions, the larvae will remain within the faecal path, where it is moist and warm, until favourable conditions arise. Once L3 are exposed to optimal conditions such as mild temperatures and rain, they will migrate away from the faecal pat.  Larval dissemination is often assisted by cows walking through the dung, airborne spread through Philobolus fungus or earthworm and wildlife transfer.

Lungworm can persist in the environment and within carrier cows, making management difficult for farmers.  Treating your herd with Eprecis, the only available injectable anthelmintic with zero milk withdrawal, can give you confidence you are effectively treating each animal with a precise dose that will act quickly to treat lungworm infections.

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