Lungworm of cattle

Dictyocaulus viviparus is a parasitic nematode belonging to the order Strongylida and the family Dictyocaulidae. While often discussed within agricultural contexts due to its impact on livestock productivity, it is specifically a lung-dwelling parasite that affects cattle, deer, and other ruminants, causing the condition known as parasitic bronchitis or husk.

The biological life cycle of this parasite is direct, occurring without intermediate hosts. Infected animals shed first-stage larvae in their feces onto pasture land. Under favourable humid conditions, these larvae undergo two molts to reach the infective third stage, which then moves onto blades of grass, waiting to be ingested by grazing livestock.

Once ingested, the larvae migrate from the intestinal tract to the lungs through the lymphatic and circulatory systems. Within the bronchial tree, the parasites mature into adults. Their presence stimulates the production of excessive mucus and inflammatory exudate, leading to the characteristic obstruction of the airways that defines the pathology of the disease.

The clinical impact on the herd is severe and economically significant. Affected animals exhibit respiratory distress, tachypnea, and a persistent, loud cough. Chronic infestations lead to weight loss, reduced milk yield in dairy cows, and susceptibility to fatal pneumonia, particularly in young calves that lack prior exposure and immunity.

Management and control strategies are essential for sustainable livestock production. Producers should implement effective anthelmintic treatment programs and practice strategic pasture management, such as rotating grazing areas. In regions with high prevalence, vaccination of young cattle can be a key preventive measure to ensure the health and productivity of the herd.