Role of adult sheep in transmission of infection by Cryptosporidium parvumto lambs: confirmation of periparturient rise

In sheep farms, oocyst shedding by asymptomatic adult carriers is one of th e mechanisms which may explain maintenance of infections by Cryptosporidium parvum between lambing periods. The objective of this work was to investig ate this hypothesis and the existence of a periparturient rise in oocyst sh edding. Fourteen pregnant sheep were randomly selected from two farms with a history of neonatal diarrhoea caused by C. parvum and samples were collec ted from the 6th week before birth until 2 weeks after birth. Faecal sample s were filtered, concentrated and examined for oocysts using an indirect im munofluorescence assay. The kinetics of anti-C. parvum antibodies (IgG and IgA) were studied using an indirect enzyme-linked immunosorbent assay. All except one animal excreted C. parvum oocysts at some time during the experi mental period. The percentage of animals passing oocysts increased in the f irst week post-partum (farm 1) and in the first week before birth (farm 2), The numbers of oocysts excreted ranged from 20-440 oocysts g(-1) of faeces , In contrast, no significant changes in the anti-C. parvum immunoglobulin levels were observed over the sampling period. Finally, a high percentage: of lambs (71%) born to these ewes acquired infection in the first 2 weeks o f life. (C) 1999 Australian Society for Parasitology Inc. Published by Else vier Science Ltd. All rights reserved.