Which disease carried by the body louse was responsible for the death of 150,000 soldiers during World War I?

Epidemic typhus is the correct answer because it is a disease transmitted by the body louse, causing significant mortality during World War I. This disease is caused by the bacterium Rickettsia prowazekii, which infects the lice. The conditions in trench warfare, including overcrowding and poor hygiene, led to the rapid spread of lice and, consequently, epidemic typhus among soldiers. The illness can lead to severe complications and has historically been associated with high fatality rates, especially in conditions like those seen during the war.

The other diseases listed are not transmitted by the body louse. Malaria is transmitted by mosquitoes, Rocky Mountain spotted fever is carried by ticks, and yellow fever is also spread through mosquito bites. Each of these diseases has different vectors and historical contexts, making them unrelated to the epidemic typhus outbreak among soldiers in war conditions.