The Relationship of Human Leprosy and Rat Leprosy

Rat leprosy exhibits certain pathological, bacteriological and clinical features in common with leprosy of man. The delicate rodlike morphology of the bacilli of Stefansky (26) and of Hansen (9), their strongly acid-fast and alcohol-fast staining reactions, and their resistance to cultivation on artificial mediums indicate a close relationship of these two generally accepted etiological agents. In consequence, a firm belief in their identity has been expressed frequently in the literature. From the viewpoint of epidemiological considerations the unity of the two germs is rendered improbable, since a comparison of the known regional distribution of rat leprosy does not necessarily coincide with that of human leprosy. The original observations of pean (6) indicated this fact. He diagnosed rat leprosy in a district outside of London which had been free from the human malady for centuries. The same situation exists in California today, where rats infected with Stcfansky's bacillus are repeatedly encountered in the systematic campaign which is relentlessly waged against bubonic plague. This area would hardly be considered a focus of the human disease, although transients with the disease contracted elsewhere are not rare. Perhaps the most definite example of a lack of coexistence is to be found in the reports of studies from the Hawaiian Islands (4, 5, 17, 18) which is an endemic center of the human infection. In a careful examination of over 16,000 wild rats, the majority of which were trapped in Honoluluwhere possibly due to congestion the in-