Leptospirosis research by Sanarelli, 19th century. Illustration of human tissue showing colouration (yellow) due to the disease leptospirosis. This page is part of research carried out by Italian microbiologist Giuseppe Sanarelli (1864-1940). This is Plate VI from Sanarelli's 'Etiologia y patogenia de la fiebre amarilla' (1897). This work, published in Montevideo, Uruguay, where Sanarelli worked from 1895 to 1898, is about the etiology (cause) of diseases then known as yellow fever, some of which are now known to be caused by other pathogens. Leptospira bacteria can cause severe icterohaemorrhagic leptospirosis (Weil disease), which is difficult to differentiate from yellow fever.