Microscopic Agglutination Test (MAT)  

The MAT which was originally described by Galton et al. (1965) and modified by Cole et al. (1973), is the most widely used serological test for leptospirosis (Thiermann and Garrett, 1983; Ellis, 1986a).  The MAT is best used as a screening test when investigating the possibility of L. hardjo infection in groups or herds of cattle.  At least 30 animals (or 10% of large groups) should be bled and animals of various ages should be included (Hathaway et al., 1986).  The MAT is particularly useful in the diagnosis of disease caused by incidental, non-host-adapted serovars or acute disease caused by host-adapted serovars.  However, because of the frequent low or possibly negative MAT titres in animals recently infected with L. hardjo, making a diagnosis on the basis of a serological result from one animal is extremely difficult (Elder et al., 1985).  Ellis et al. (1982a) reported that there was no value in examining paired serum samples from individual cows after abortion because titres are either falling or static at the time of abortion.

 

For a diagnosis of leptospiral abortion in cattle, a reciprocal titre of 3000 is proposed by Elder et al. (1985) as the threshold for L. pomona but no similar critical figure is available for L. hardjo.  For a herd diagnosis of leptospirosis due to L. hardjo, ten animals from each of the yearling, first calver, second calver and older age groups should be tested (Hathaway et al., 1986).  The main detriment of the MAT is low sensitivity because some cattle exhibit a low response to L. hardjo (Broughton et al., 1984).  Study conducted by  Ellis et al. (1981) on 200 randomly selected cattle at abattoir indicated that 46.4% of renal carriers had antibody titres of less than 1/100 and 9.6% had no detectable MAT titre against L. hardjo. 

 

Cross-reactions caused by exposure to leptospires of the same serogroup can occur, for example, infection by L. balcanica (Mackintosh et al., 1981) and L. medanensis can produce false positive L. hardjo reactions.  The MAT has the disadvantages that it is tedious and time consuming (Cousins et al., 1985), and the use of live culture imposes a risk of human infection.  Another disadvantage is the failure of the MAT to differentiate between titres after vaccination and those after natural infection, since the titres may be of similar magnitude (Adler et al., 1982; Hodges and Day, 1987).