Outbred albino mice infected on the nose and in one foot pad were used as a model for the study of a newly isolated strain of Leishmania tropica from West Africa. The development of local lesions following the inoculation of 107, 105, and 103 amastigotes, respectively, was recorded at weekly intervals through four subsequent animal passages. In addition, the course of infection was followed in four different inbred strains of mice. The specificity and possible spread of infection were checked microscopically by smear preparations and by inoculation of tissue material into NNN medium. Samples for histopathological examination were obtained at different time intervals after the day of infection. The incubation period varied from 2–7 weeks depending upon the size of inoculum. Generally, the mice developed local swelling and, frequently, ulceration at the sites of inoculation. After a few weeks of progress, the lesions assumed a more chronic state, lasting for months without obvious impact on the general health of the mouse. However, the individual response to the infection varied considerably within each group. Histopathologically, parasitized macrophages and polymorphonuclear leucocytes dominated during the first weeks, whereas at later stages of the lesions lymphocytes and plasma cells prevailed. The BALB/c mice differed from the other mouse strains under study by developing a progressive, ultimately fatal infection. Splenomegaly was prominent in the BALB/c mice, whereas clinical signs of generalized infection were missing in the other mouse strains. However, the latter strains also harbored leishmanial parasites in internal organs, as demonstrable by NNN-culture. The study underlines the value of mice for experimental investigations on L. tropica.
At the time of this study, Dr. Bjorvatn from Roslagstull Hospital, Stockholm, was a Guest Worker at the NIH and was supported by a grant from the Swedish Medical Research Council.