The slaughter of naturally-infected heifers and oxen at regular intervals after the first P. bovicola ovipositional blood spots appeared revealed that no female worms with embryonated eggs could be found after 259 days, no live worms after 372 days, and no carcass lesions after 519 days. In one bull, however, blood spots and carcass lesions persisted throughout 2 seasons. With the possible exception of bulls, therefore, annual reinfection of cattle appears to be necessary for the continuation of the transmission cycle of P. bovicola.
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