Leptospirosis in Cattle and Swine in South Dakota

Animals infected with Leptospira do not always display the acute signs of the disease but may have a sub-clinical chronic form which may go unnoticed. These infected animals may continue to infect the healthy animals which they contact. The presence of the disease has been demonstrated in almost every state either by the presence of antibodies, identification of the organisms in tissue section, or by culture isolation. The need of information concerning the extent and severity of Leptospira infection of cattle and swine in South Dakota led to this study. Many people are of the opinion that a disease is not present until an organism has been isolated. Leptospira have been isolated at the South Dakota State College Veterinary laboratory from both cattle and swine. Confirmation of the identity of Leptosirapomona was made by calf inoculation. The most reliable test at the present time is the agglutination-lysis test which is carried out with the use of live organisms which have been sub-cultured from seven to ten days. The use of a live culture is a hazard for laboratory workers. This test shows a slight degree of cross agglutination between some species of leptospira. The test is very time consuming because several dilutions are required, therefore, it would make it difficult to test large numbers of samples. By using a killed culture, Stoenner has developed a macroscopic rapid plate agglutination test and a capillary tube test. These tests are very specific for the species. Since a macroscopic plate antigen has been developed for Leptospirapomona, several biological supply houses have started producing it in large quantities, to supply practicing veterinarian and clinical laboratories. This study is a comparison of the rapid plate and agglutination-lysis test in order to determine the degree of titer required by the agglutination-lysis test to give a positive plate test