Leptospirosis in poikilothermic vertebrates. A review

Autochthanous leptospirosis does occur in the poikilothermic vertebrates, as evidenced by positive serological reactions and by the isolation of pathogenic leptospiral serovars. These findings in aquatic members of this group are of special importance in view of the increased worldwide interest in aquaculture farming. Since 1975, 24 of the 101 (23.7%) reported human cases of leptospirosis in Hawaii have been associated with aquaculture industries (taro farms, prawn farms and watercress farms). Antibody synthesis and persistence in these animals is variable, and seems to depend to some extent on environmental temperatures. Some members of the group apparently lack the capacity for immunological memory, experience a considerable delay (lag-phase) in antibody formation, demonstrate the "paradoxical reaction" found in other animals, and can maintain living pathogenic leptospirae in their organs in the absence of detectable antibody utilizing our present serologic methods. For these reasons, serological studies as the sole source of evidence for leptospiral infection cannot be recommended. The immunologic mechanism of lower vertebrates is not known, some studies suggesting that there may be more than one antibody system active in these animals, especially the turtles, and further investigation at the cellular and subcellular levels is indicated. The growth temperatures and nutritional requirements of leptospirae isolated from other than warm-blooded animals is also poorly understood. Some knowledge has been contributed by various investigators in recent years, but much more work needs to be done in studying the nutritional and metabolic requirements of leptospirae isolated from all sources, including the various fauna resident in and around the fresh water streams and ponds.