Genus-specific leptospiral antigen and its possible use in laboratory diagnosis

SYNOPSIS Sheep red cells, sensitized with a genus-specific leptospiral substance extracted from a water leptospira, were preserved by freeze drying. The serological reactivity of the preparation was tested against a total of 41 sera from proven cases of human leptospirosis and 27 from proven cases of animal leptospirosis. The sensitized, freeze-dried red cells appeared to be a sensitive reagent for the detection of leptospiral antibodies by haemagglutination. The use of this reagent as a screening test for leptospiral diagnosis is discussed. In the reported haemagglutination test on human and rabbit antisera the findings suggested that only IgM (19S) antibodies took part in the reaction. The diagnosis of leptospiral infections in man and animals may be established either by isolating the organisms or by detection of specific antibodies. Generally speaking, isolation of leptospires from infected man and animals is time-consuming and beyond the scope of most diagnostic laboratories. Undoubtedly, the isolation of the infecting strain is the most desirable method to diagnose the infection but this depends on the stage of illness, type of material collected, availability of suitable medium (Ellinghausen and McCullough, 1965), and labora-tory facilities for handling animals. On the other hand, detection of specific leptospiral antibodies is a relatively easy and more convenient procedure. Among the serological tests the microscopic agglutination test using live (or killed) leptospires as antigens is the standard reference test for leptospiral diagnosis (World Health Organization, 1967). However, as a screening test the microscopic agglutination test suffers from certain disadvantages (World Health Organization, 1967), eg, cultures ofa large number of serotypes have to be maintained, it involves the handling of live organisms, and it is also time-consuming, particularly when large num-bers of sera need to be tested. This investigation was initiated to develop a suitable stable reagent for the routine screening of suspected serum samples by diagnostic laboratories. It is an extension of th