Reinfection of yearling calves with Ascaris suum.

Naturally occuring outbreaks of Ascaris suum infection in calves have usually beeen found in animals nine to 12 months of age. The circumstances surrounding these outbreaks suggest that yearling calves are either particularly susceptible to a primary exposure to A. suum or react strongly to A. summ after sensitization early in life to this or some related ascarid. To determine the effect of reinfection with A. suum nine to 12 months after varying levels of exposure to this nematode, six calves were inoculated with 200,000 to 9,000,000 eggs. Neither death nor, in general, severe clinical signs resulted from reinfection. All calves were examined 15 days after reinfection with pathological changes noted only in the lungs and consisting of emphysema, alveolar wall thickening as well as accumulations of fibrin, eosinophils and hemorrhage in the lumina of alveoli. The findings suggested that exposure to A. suum early in life is not a factor in the development of disease in calves infected at one year of age. It was also found that the eosinophilia that develops following a primary infection with A. suum evidently persists for at least one year.