zoonoses and communicable diseases common to ... - PAHO/WHO

164 BACTERIOSESThe same diagnostic procedures are employed for animals as for man. Blood orurine may be used for the bacteriologic examination, depending on the stage of theillness. If a necropsy is performed on a sacrificed or dead animal, kidney culturesshould be made. Examination of several tissue samples from the same individual isnot always easily done in veterinary practice, but individual diagnosis of domesticanimals is not as important as herd diagnosis. Discovery of high antibody titers inseveral members of a herd and a clinical picture compatible with leptospirosis indicatea recent infection.Low titers may indicate residual antibodies from a past infection or recentlyformed antibodies that have not yet had time to reach a high level.The serologic reference test that is used most for man as well as for animals ismicroscopic agglutination (MAT). This test should be carried out using representativeserovars from different serogroups, especially those occurring in the region. Itis necessary to bear in mind that cross-reactions are produced not only betweendifferent serovars of the same serogroup but, at the beginning of the infection(two to three weeks), also between serovars of different serogroups, and a heterologousserovar titer may predominate. Reaction to the homologous serovarbecomes more pronounced with time. Cross-reactions are much more frequent inman than in animals.The macroscopic plate test with inactivated antigens can be used as a preliminaryor screening test for man and animals. It is fast and easy, and particularly useful fordiagnosing disease in a herd.Plate agglutination is a genus-specific test, which uses as an antigen the patocstrain of saprophytic leptospira (L. biflexa) to determine if the patient is sufferingfrom leptospirosis (Mazzonelli et al., 1974). Reaction to this test is marked duringthe acute phase of leptospirosis and then quickly becomes negative (Faine, 1982).Among more recent tests, those of interest are indirect immunofluorescenceand enzyme-linked immunosorbent assay (ELISA). With both, the types ofimmunoglobulins (IgM or IgG) can be determined by using the correspondingantigens. IgM appears after the first week of the disease and IgG appears afterseveral weeks. In some human cases, IgG antibodies cannot be detected for reasonsas yet unknown.The utility of ELISA for diagnosing infection due to hardjo was compared withMAT. It was found that a positive reaction can be obtained with MAT 10 days afterthe animal has been experimentally infected; ELISA does not give a positive reactionuntil 25 days after infection. In addition, there was a 90% concordance betweenboth tests. Cross-reactions with sera from animals inoculated with other serotypesoccurred in fewer than 1% (Bercovich et al., 1990).The serovar hardjo is subdivided into subserovars or genotypes: hardjo genotypehardjo-bovis and hardjo genotype prajitno. A DNA probe for genotype hardjo-boviswas developed by LeFebvre (1987). Three methods for detecting hardjo type hardjoboviswere compared: with DNA hybridization, 60 of the 75 urine samples fromcows experimentally exposed were positive; with immunofluorescence, 24 sampleswere positive; and with culturing, only 13 were positive. The DNA probe was shownto be much more sensitive than the other techniques in detecting the genotypehardjo-bovis (Bolin et al., 1989a).A very sensitive generic test is polymerase chain reaction (PCR), which can detectas few as 10 leptospires (Mérien et al., 1992).