Parasitic pneumonia, also known as hoose or husk, is an economically important disease in cattle caused by the lungworm Dictyocaulus viviparous. Lungworm can result in severe financial losses due to loss of performance and fatalities in growing cattle, and drop in milk yield and fatalities in lactating cows.
Outbreaks of parasitic pneumonia are usually observed from July to October with occasional outbreaks occurring either earlier in the summer or after October. AFBI would like to alert cattle farmers that we are now in the high risk period for parasitic pneumonia, and fatal cases of hoose have already been diagnosed in calves examined at AFBI laboratories during the current grazing season.
Warm and moist conditions are required for a build up of lungworm contamination on pasture. With the good weather experienced in May followed by the wetter weather in June lungworm burdens on pasture may now potentially be high and may increase further.
Infections are acquired by ingestion of infective larvae from pasture, and calves in their first grazing season are chiefly affected by lungworm. Thereafter immunity may develop and is important in developing resistance to re-infection in previously exposed calves. Dairy calves and autumn born suckler calves are very susceptible to infection.
Persistence of immunity is dependent on further exposure, and in the absence of exposure immunity may wane over time. Cases of parasitic pneumonia are now commonly diagnosed by AFBI in older calves and in adult cattle in which immunity to lungworm has waned due to lack of exposure in the intervening period or in animals which were not exposed to lungworm in previous seasons.
Clinical signs of lungworm infection include respiratory signs, panting and harsh persistent cough. Growth rates may be affected. Severe infections may result difficulty in breathing and death.
Lungworm infection should be considered whenever batches of calves grazing permanent or semi permanent pasture are affected by respiratory signs and coughing. Faecal testing for lungworm larvae is also a useful diagnostic aid but it should be remembered that negative results are possible particularly early in infections.
Effective treatment options are available involving the administration of anthelmintic products. Veterinary advice and treatment should be sought for severely affected animals.
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