Oestrosis is a parasitic disease of sheep and goats caused by the nasal bot
fly Oestrus ovis. In the United Kingdom the economic losses as a result of
infestation can be considered negligible, but the differentiation of O ovi
s cases from more serious diseases such as listeriosis, gid and sheep scab
is of considerable importance. Currently diagnosis of oestrosis relies on t
he subjective observation of clinical signs or the demonstration of larvae
postmortem. This paper assesses the effectiveness of a direct enzyme-linked
immunosorbent assay (ELISA) using a crude somatic antigen from first-stage
larvae (L-1) in the serodiagnosis of oestrosis. The system has been valida
ted with sera from both endemic and non-endemic areas and the results corre
lated with the clinical data found postmortem. The sensitivity and specific
ity of the assay were 97.4 per cent and 97.6 per cent, respectively, using
a cut-off point based on 35 per cent binding of a reference positive contro
l serum.