Battle of the Somme
Lice caused severe itching and also carried a disease called trench fever (pyrrexhia). The first symptoms were shooting pains in the legs. This was followed by a very high fever.  This disease did not kill the soldiers, but it did stop them from fighting.  It was very common. From 1915 to 1918, between one-fifth and one-third of all British troops who got sick had trench fever; about one-fifth of ill German and Austrian troops had the disease.