The application of the film inhibition test (FIT) in the diagnosis of contagious agalactia -A comparison to complement fixation test.

The Film Inhibition Test (FIT) is a serological method, specific for Mycoplasma species, such as M. agalactiae, that have the biochemical property to produce films. The detection of specific anti-M. agalactiae antibodies in serum and milk of small ruminants, with FIT, after experimental and field infection, was studied. The test was compared with Complement Fixation Test (CFT) and the serological results were correlated with the isolation of M. agalactiae. Ten ewes challenged with M. agalactiae and eighty three animals (77 ewes and 6 goats) from several flocks were attended during the different phases of contagious agalactia (CA). The FIT performed in selective Brain Heart agar. The petries were flooded with liquid M. agalactiae culture containing 10(exp 6)-10(exp 7) CFU and paper disks saturated with serum samples were added. For the examination of milk samples wells were opened on the agar. The samples that provoked zones of film inhibition wider than 1 mm were considered as positive. Sonicated M. agalactiae cells were used as an antigen for the CFT. According to the results, specific antibodies were present, from the incubation period of the CA, in serum (77% positive results by FIT and 70% by CFT) and in milk (65% positive results). During the disease, the animals were 100% positive with FIT from the 2nd to 8th month and with CFT from the 2nd to 6th month. Milk samples gave less positive results all the time (maximum 95% at the 2nd month, while 81% at the 6th month). Antibodies were detected from serum for a long time after recovery (in 13th month, 88% positive results with FIT and 63% with CFT) while, at the same time 50% of the milk samples were positive. The M. agalactiae was isolated in milk from the incubation period to the tenth month after the CA manifestation. The detection of antibodies was possible in the case of asymptomatic M. agalactiae-carriers. The specificity of FIT was 0.96 for the serum samples examination and 0.99 for the milk samples to be sensitive and specific, and therefore suitable for the diagnosis of contagious agalactia.