Antibodies to Rickettsia conorii in dogs: seasonal differences.

Eight dogs, having showed positivity to Rickettsia conorii in serum samples obtained during the spring and summer, were studied again by means of a second determination during the next winter, 4-10 months later. Serum titer became negative in six dogs, persisted high in one, and fell from 1:640 to 1:40 in another dog. This seasonal difference suggests a short persistence of antibodies in dogs after contact with R. conorii in the Mediterranean area.