The Korean War's silent killer strikes again.

• Author: Hoffman, George J.

Almost half a century has passed since the start of the Korean War on June 25, 1950. More than three years of fighting between United Nations and communist forces culminated indecisively with the July 27, 1953, signing of what has become an uneasy truce.

Although the belligerents finally stopped killing each other, a different type of assailant -- oblivious to the armistice -- continued its relentless assault. It waged war not only on the ravaged Korean peninsula, but throughout the world. Today, the battle against this adversary isn't being fought by armies, but by soldiers of science whose basic weapon is research. They have yet to achieve victory, as their elusive target adopts divergent forms.

Not differentiating friend from foe, this enemy of both enemies first attracted international attention after it struck U.S. troops during the Korean War. No stranger in a part of the world where it had been active for centuries, it blindly attacked opposing sides and civilians with equal intensity and was irrefutably responsible for the demise of untold numbers on and off the battlefields. Unarmed and unnoticed as it moved among its prey-striking indiscriminately -- this insidious killer was a disease: Korean hemorrhagic fever (KHF). Allied and communist troops alike, as well as civilians, endured its wrath.

KHF is a widespread and often fatal illness caused by a rodent-borne species of Hantavirus known clinically as Hantaan virus. The same or closely related Hantavirus maladies (called epidemic hemorrhagic fever in China and by several different names in at least 20 countries) are pervasively rampant throughout the Far East.

Hantaan virus is the pathogenic namesake of the Hant'an River and Valley. It was there, in the area near the confluence of the Hant'an and lmjin rivers, that the earliest significant concentration of hemorrhagic fever cases among UN troops was reported during the Korea War.

Thirty-three years after the fighting had ended, the basically identical ailment, precipitated by the same viral pathogen, launched another brutal assault. Of a contingent of U.S. Marines engaging in peacetime maneuvers with their South Korean counterparts in 1986, 14 became ill and two died. The culprit was identified as Hantaan Hantavirus. The Marines in the mid 1980s and the combatants in the early 1950s were in rodent-infested areas where there was vulnerability to KHF, the primary vector of which is rats. The Marines, during preparedness exercises, were in the field. Allied forces (mostly American) moving up and down the battle-torn peninsula so many years earlier not only lived and fought in desolated fields, they occupied cities and villages destroyed by war. Sometimes, they took refuge in abandoned, filth-permeated houses and buildings where rats and other vermin proliferated.

Flamethrowers, often used to clear brush and debris, were unsuccessful in substantially eliminating the breeding and nesting places of disease carriers. Thus, there was no shortage of hosts favored by Hantaan Hantavirus.

There never has been conclusive evidence of person-to-person transmission of the agent causing KHF. Four known species of rats, several of mice, and common voles have been identified as Hantavirus hosts. The virus is airborne, arising from dusty ground saturated by feces, urine, and saliva deposited by its rodent vectors. Victims are infected through inhalation. Ingestion of contaminated foodstuffs has not been blamed for infection, though viral penetration of skin abrasions has been mentioned as a possibility. The incubation period is approximately a month, sometimes even more, as viral invasion of blood cells accelerates and replication of the pathogen occurs.

How many stricken Americans actually succumbed to the ravages of KHF? Mortality figures from official sources fail to show the full extent of illness and death caused by the disease. Moreover, imprecise or even missing medical records have made it impossible to compile an accurate death count. Conflicting estimates emanate from different sources and range from five to 15%...