Delousing plant at U.S. Army Camp Hospital no. 11, St. Nazaire, France during World War I. Lice infestation was the norm in the trenches, it is estimated that up to 97% of officers and men who worked and lived in the trenches were afflicted with lice. Lice often spread disease, the unique so-called Trench Fever. Lice who had sucked the blood of one infected person quickly succeeded in spreading the infection to each successive host. Trench Fever, although not usually life-threatening, was often highly debilitating and resulted in a trench casualty rate of up to 15%. Delousing became routine during World War I, as a result of the recent discovery that lice spread typhus.