Enterically Transmitted NonA NonB Hepatitis Etnanbh

Etiology

ET-NANBH is a virus structurally similar to but immunologically distinct from hepatitis A. It has recently been associated with a number of previously inexplicable hepatitis epidemics. As yet the virus has not been grown in culture, but it can be serially passed through monkeys and has been identified by electron microscopy. Biochemical characterization remains to be done.

Geography and Epidemiology

Most epidemics attributed to ET-NANBH have occurred in less developed countries at times when even the normally limited sanitation procedures have broken down. Most of these have been in South Asia, but there have also been epidemics in the southern former Soviet Union, in refugee camps in Somaliland, and in Mexican villages, where water supplies became grossly contaminated. All ages are commonly affected, but there may actually be a preponderance of adult cases. These circumstances suggest that ET-NANBH virus is less infectious than hepatitis A and that, even in conditions of generally poor sanitation, most people remain only minimally susceptible.

Clinical Manifestations

ET-NANBH usually causes a hepatitis that is indistinguishable from that caused by hepatitis A or B. However, infected pregnant women have an unusually high mortality rate, which may reach 20 percent.

History

A major epidemic of ET-NANBH occurred in New Delhi in 1955. The New Delhi sewage emptied into the Ganges River a little below the point of a water supply intake. In that year there was a drought, the river became low, and the sewage began to flow upstream. Alert water technicians recognized the problem and raised chlorination levels, so that there was no unusual outbreak of bacterial disease. However, a month or so later, 68 percent of the exposed population developed jaundice, and more than 10 percent of the affected pregnant women died. Careful investigations were made at the time, but the cause of the epidemic remained undetermined until recently, when Daniel Bradley and his associates developed a test based on reactions (observed in the electron microscope) of immune sera and virus from feces of patients in a more recent Burmese epidemic.

Francis L. Black

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