Dictyocaulus viviparus is a parasitic lungworm of cattle that cause bronchitis and pneumonia ('parasitic bronchitis', 'hoose pneumonia') in cattle in temperate regions. It is one of the most important parasites in grazing cattle, and outbreaks result not only in clinical disease but also economic losses.
Although a number of other species of Dictyocaulus are recognised, only D. viviparus is known to cause disease in cattle.
Adult females lay embryonated eggs in the bronchi. These eggs hatch into first-stage larvae which are then coughed up and swallowed. First stage larva eventually emerge in the feces. In the soil, these first-stage larvae reach the ensheathed infectious third-stage (L3) after four days which are then eaten by another cow.
The infective L3 penetrate the bowel wall and molt to L4 in the mesenteric lymph nodes. They then migrate to the lungs over a two-week period via the thoracic duct and reach the lungs, where they molt to the adult stage. The adults begin laying eggs around 22 days post-infection. Adult worms survive about 50 days before being attacked by the cow's macrophages. Some L4s and adults survive within the host over winter.
Weight loss, intermittent frebrile cough and failure to thrive are common signs in early stages of the disease. In the prepatent phase, D. viviparus causes blockage of bronchioles, resulting in obstruction of the airways and collapse of alveoli distal to the block. Sudden deaths have been reported due to severe interstitial emphysema. In dairy herds, milk yield noticeably drops in affected cattle.
In chronic cases, a nonsuppurative, eosinophilic, granulomatous pneumonia is observed, complicated by interstitial emphysema, pulmonary edema, and secondary bacterial infection.
In acute cases, broad-spectrum antibiotics are recommended to minimise secondary bacterial infections.
Treatment is effective using various anthelmintic preparations. These include the benzimidazoles (fenbendazole, oxfendazole, and albendazole) and macrocyclic lactones (ivermectin, doramectin, eprinomectin, and moxidectin). Moxidectin (10%) long-acting (LA) injectable formulation has shown efficacy at preventing re-infection for <150 days.
Levamisole is used in cattle but treatment may need to be repeated 2 weeks later because it is less effective against larvae during the early stages.
Vaccination strategies are also indicated for lungworm-naïve animals when introduced into an adult herd.
Single mass-treatment before the grazing season may be useful to break a series of annual lungworm outbreaks. However, it is not a secure method to prevent parasitic bronchitis for more than one year.
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