In the glandular type the glands are enlarged and the lymph sinuses packed with the causative bacilli.
In rat leprosy it has been found that infection of other rats takes places as readily through slight abrasions of the skin as when material is injected subcutaneously.
The idea is that natural infection occurs by way of the skin and through the lymphatics. There is no evidence that insects play a part in transmission.
Rat leprosy prevails extensively in Europe, Asia and America. Although similar etiologically and pathologically there does not seem to be any connection between the disease in rat and in man, as is the case with human and rat plague.
The prevalence of rat leprosy in the various parts of the world varies greatly; thus in Odessa 4 to 5% of the rats are infected while in San Francisco only ⅕ of 1%.
Pathology and Morbid Anatomy
In whatever way introduced the leprosy bacilli tend to invade and multiply in the lymphatics of the corium and subcutaneous tissues. In response to irritation, cells of disputed type, possibly plasma cells, appear and phagocytize the bacilli in large numbers, so that eventually the outline of the cell, as brought out in acid-fast staining, is that of a mass of red bacilli.
These red-staining bodies are called lepra cells. In addition, endothelial cells phagocytize the bacilli and these with their bacilli, together with the free lying masses of bacilli in the lymphatic sinuses, make the so-called “globi” when seen in transverse section. The toxicity of the lepra bacillus is only slight so that we may have very large giant cells of the Langhans type and this probably explains the absence of caseation in leprosy. The arteries of the leproma, as the granulomatous mass is termed, undergo an arteritis with thickening of their walls.
