U.S. troops from foreign soils offers a unique opportunity for the introduction or reintroduction of infectious diseases into the United States.
The following examples describe infectious diseases that have emerged in association with military operations, some of which involved U.S. Troops.
Epidemic typhus, caused by Rickettsia prowazekii, has been a frequent accompaniment of warfare in Europe, dating back to the siege of Naples by the French in 1528 (Zinsser, 1935). The disease, which is acquired by contact with the feces of infected body lice, was a major problem in World War II.
Trench fever, caused by Rochalimaea quintana (Rickettsia quintana) , which are transmitted by body lice, made its first appearance in troops during World War I (Fuller, 1964).
Epidemic hemorrhagic fever, now known to be due to a zoonotic infection caused by Hantaan virus, was reported in Japanese and Soviet troops in Manchuria before the onset of World War II and was later (1951) recognized in United Nations troops in Korea (Benenson, 1990).
Scrub typhus, caused by a rickettsia transmitted by the bite of an infected larval mite of the genus Leptotrombidium, was a major medical problem (surpassed only by malaria in some areas) in the Pacific Theater in both World War II (Philip, 1948) and the Vietnam conflict (Berman et al., 1973).
A massive outbreak (involving 30,000 to 50,000 cases) of acute schistosomiasis, caused by Schistosoma japonicum, is reputed to have occurred in Chinese troops in 1950. The troops were being taught to swim in infected canals in southern China in preparation for what, because of the outbreak, became an aborted invasion of Taiwan in 1950 (Kiernan, 1959).
Leptospirosis, caused by Leptospira interrogans, was first identified as an important military disease in British troops during jungle operations against Communist terrorists in what was then Malaya in the late 1950s (U.S. Army Medical Research Unit, Malaya, 1962).
Leishmaniasis, due to Leishmania tropica, was known to be endemic in the Persian Gulf region before U.S. troops were committed in Operation Desert Shield. Known to cause cutaneous lesions, the capacity of L. tropica to ''visceralize" (i.e., invade bone marrow, liver, and spleen) was not well documented before its discovery in returning U.S. troops. The apparently atypical visceral expression of the disease may not be unusual at all but merely a natural consequence of the exposure of more than 500,000 susceptible troops to infected sand fly vectors in an endemic area. A total of 26 cases of leishmaniasis in U.S. troops—17 cutaneous and 9 visceral—had been diagnosed as of April 1992 (M. Grogl, Chief, Leishmania Section, Division of Experimental Therapeutics, Walter Reed Army Institute of Research, Washington, D.C., personal communication, 1992).