General pathology of human and canine histoplasmosis.

Abstract

The experience of the last fifteen years with histoplasmosis in man and in animals (especially dogs) has resulted in a coherent picture of the pathogenesis of the disease. The causative organism, Histoplasma capsulatum, exists in the soil, and its inhalation initiates the infection. A small area of pneumonia develops; in this focus, central caseation occurs regularly. The regional lymph nodes become similarly involved and, with the pulmonary focus, form the complex. In man, early hematogenous spread is common, especially to the spleen. Healing of the caseated complex and the hematogenous foci by encapsulation and calcification is the rule. In a small number of cases, bronchogenic, lymphogenic, and hematogenic dissemination may occur, resulting in progressive or even fatal acute or chronic disease. Baum and Schwarz (1) have given a comprehensive diagrammatic representation of the pathogenic relationships between the various types of histoplasmosis in human beings. The epidemic type of the disease did not fit well into the diagram. It was set apart as the possible result of multiple simultaneous primary foci following overwhelming exposure. Rubin and associates (2) also described it as the consequence of the increased severity of exposure. Baum and Schwarz (1) have drawn attention to patients who are immigrants to the endemic area. This is an anamnestic detail of importance because the shorter the time of residence in the endemic area, the lesser the probable age of infection. It is likely that the age of the patient at the time of infection is of considerable importance to the subsequent course of the infection.