By Charlene Porter
Washington File Staff Writer

Washington -- The number of human deaths now tied to a lethal strain of avian influenza known as H5N1 has risen to 25, with 19 in Vietnam and six in Thailand, the only two nations where human cases have been positively identified. The World Health Organization (WHO) announced two additional deaths February 12 along with some of the most detailed data yet presented about the symptoms and course of the disease.

This outbreak of avian influenza, also known as bird flu, has appeared in eight Asian nations. Tens of millions of birds -- 27 million in Vietnam alone -- have been killed as a means to prevent the further spread of this highly contagious viral strain.

International health authorities are on edge about this disease evolving into a viral strain that would be efficiently transmitted human-to-human. If that happens, the potential for a major global epidemic is high because the H5N1 viral strain has only rarely occurred in humans. No immunity would thwart the progression of what is behaving like a very savage virus.

The humans who have been infected so far have had direct contact with diseased birds or their fecal matter. Though a couple of cases might indicate human-to-human transmission, an analysis produced by the U.S. Centers for Disease Control and Prevention (CDC) in collaboration with Thai doctors indicates that no evidence of sustained person-to-person transmission has been identified.

Most of the clinical knowledge of the H5N1 strain comes from a 1997 outbreak in Hong Kong. In a report published in the CDC's Mortality and Morbidity Weekly Report (MMWR), the fatality rate of patients affected in that 1997 outbreak was 33 percent; six of 18 patients. The mortality rate among the pool of human cases identified in this outbreak is much higher -- 76 percent.

A WHO situation update issued February 12 also cites a distinction about H5N1 as compared to more commonly appearing flu strains. "H5N1infection affects more body organs and systems than normal influenza," it says.

That disease trait emerges from the descriptions of the Thai cases in the CDC report. Fever and cough were the first symptoms to appear in the patients -- four boys ages 6 and 7, and one woman age 58. Within days, two of the five patients developed renal failure; cardiac failure occurred in four of the five. "In all five cases, disease was severe, with pneumonia progressing to respiratory failure and death," said the CDC's MMWR. (The CDC findings were compiled before the WHO announcement of a sixth death in Thailand.)

The WHO assessment of the outbreak issued February 12 makes no pretense that health officials know all there is to know about the human cases. It also raises the distinct possibility that more human cases have occurred than have been detected, that perhaps those with less severe symptoms have not been identified in the rural areas where much of the avian form of the disease has occurred.

"(T)he current small number of laboratory-confirmed cases cannot be taken as an accurate indication of the magnitude of the present or potential threat to human health," says the WHO report.

Health officials are also finding that two classes of drugs frequently used in treatment of flu viruses just aren't working against H5N1, although alternative flu drugs that have shown some effectiveness are available. Work on a first-phase vaccine is under way in the United Kingdom and the United States, but development and safety testing would take many months to complete. Whether that work is pursued to completion will depend on what course this outbreak takes.