Parasitic pneumonia, also known as hoose or husk, is an economically important disease in cattle caused by the lungworm Dictyocaulus viviparus.
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 cattle submitted for post-mortem examination at AFBI laboratories during the current grazing season.
Whilst warm and moist conditions are required for a build-up of lungworm contamination on pasture, cases are occurring despite this summer’s dry conditions and lungworm should be considered as a possible reason for cattle coughing. With recent rain in a number of areas, lungworm burdens on pasture are expected to increase further.
Lungworm infection is acquired by the ingestion of larvae from pasture and calves in their first grazing season, such as dairy calves and autumn born suckler calves, are most at risk of being affected. Animals exposed to infection develop a degree of immunity which provides a level of resistance to re-infection in previously exposed animals.
The persistence of this immunity is however dependent on further exposure, otherwise immunity tends to wane over time. Current long-acting anthelmintics, which are used to prevent or treat parasitic gastroenteritis are highly effective but can have the effect of reducing the exposure of young animals to low levels of lungworm infection, which is required to ensure the development of protective immunity. 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 result in difficulty in breathing and death. Faecal testing for lungworm larvae is also a useful diagnostic aid but negative results are possible, particularly in early infections.
Effective treatment options are available involving the administration of anthelmintic products. Veterinary advice and treatment should be sought for affected animals.