Use of pooled serum samples to determine flock-level prevalence of Anaplasma phagocytophilum antibodies in Irish sheep

Anaplasma phagocytophilum is a tick-borne intracellular pathogen which mainly affects ruminants. We aimed to determine the seroprevalence of Anaplasma phagocytophilum in Irish sheep flocks using a commercially available ELISA test. Samples were collected from 376 sheep flocks with a geographical spread throughout Ireland. Twenty serum samples from each flock were analysed pooled and individually, and analysis was carried out on an equal number of flocks showing positive and negative pooled results. Receiver Operator Characteristics were analysed to determine sensitivity and specificity of performing pooled serum analysis and to determine an optimal test % inhibition cut-off.Based on pooled sample analysis using this optimal test % inhibition cut-off, 28% of the flocks were seropositive. Within flock prevalence ranged from 0 to 90%, with the mean in positive flocks being 52.3%. This study demonstrated the usefulness of pooled serum analysis as a means of screening sheep flocks for Anaplasma phagocytophilum antibodies and is the first survey of the disease in the Irish national sheep flock.