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above normal levels, counter immunological impairments caused by operational stressors?''

Background

The infectious disease threats facing soldiers vary with geography, but disease has usually accounted for more noneffective days than has combat or even nonbattle injury. In World War II, Rommel and his troops were seriously hampered by diarrheal disease (shigella) in North Africa, and the elite Merrill's Marauders and other units in the China-Burma theater were rendered ineffective by malaria (Reister, 1975). Malaria and diarrheal diseases remain high-priority research targets because of the consequences to the military mission and their widespread occurrence. Emerging infectious diseases and unexpected disease threats have occurred in recent conflicts (Heppner et al., 1993), presenting new challenges for which there may be no specific protection. This may also be true in the defense against some biological threat agents (Liu et al., 1996), for which physiological enhancements of immune protection may present one of the few options for protection. Enhancements of physiological defenses and the responsiveness to vaccines may center on nutritional strategies.

Even in military training, infectious diseases are a threat. For example, in 1990, half of the high attrition from Ranger school was attributed to medical problems, with one class decimated by pneumonia (Riedo et al,. 1991), and cellulitis continues to be a problem of Ranger students (Martinez-Lopez et al., 1993). The infectious disease problem in Ranger students appears largely to have been corrected through a nutritional intervention. Immune function deficits were attenuated with increased feeding, and dramatic reductions in infection (25% prevalence reduced to 2%) paralleled the changes in immune function tests (Kramer et al., 1997).

The interaction of nutrition and infection has been investigated extensively by military researchers in previous work. Most of this research centered on the consequences of infection to nutrition. COL William Beisel defined an entire field of research in the 1970s at the U.S. Army Medical Research Institute of Infectious Diseases with his work on cytokine-induced malnutrition (Beisel, 1995). His early work also described the physiological effects of lymphocytic endogenous mediator, properties of the cytokine now identified as interleukin-1 (IL-1). Beisel demonstrated that a variety of diseases produced hypermetabolism, loss of protein and vitamins, and wasting of the muscle mass. These effects were mediated through cytokines. More recently, cytokines have been implicated in responses to inflammation as well as immunological responses to a wide variety of stressors (Roubenoff, 1993). These responses are largely responsible for modified immune function and, in some settings, suboptimal resistance to disease, which is a consequence of the accumulated stressors. With this common cytokine pathway, the effect on immune status may represent a generalized stress response to a diversity of stressors. These



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