04 April 2006
New Human Avian Influenza Cases Confirmed in Indonesia, Egypt
U.S. computer model visualizes pandemic spread, amid bird flu fears
By Cheryl Pellerin
Washington File Staff Writer
Washington –
The Indonesian Ministry of Health has confirmed another human death caused by infection with the H5N1 avian influenza virus, and the World Health Organization (WHO) has confirmed four new human cases in Egypt.
The most recent confirmations bring the total number of human avian influenza cases to 191, including 108 deaths, according to the WHO.
The Indonesian patient, whose illness was confirmed April 4, was a 20-month-old girl from Kapuk, West Jakarta. She developed symptoms of fever and cough March 17, was hospitalized March 22 and died the next day.
Field investigation found a history of deaths in a chicken flock near her home about a week before her symptoms began. Chicken deaths in the neighborhood have continued, but the cause is not yet known.
The newly confirmed case brings the total in Indonesia to 30, of which 23 were fatal.
AVIAN FLU IN EGYPT
Samples from four patients, previously announced by the Egyptian Ministry of Health as infected with the H5N1 avian influenza virus, were tested and found positive in a WHO collaborating laboratory in the United Kingdom.
Of the four cases, confirmed April 3, two have died and two recovered and were discharged from the hospital. The deaths occurred in two 30-year-old women from the Qaliubiya governorate near Cairo. One died March 17, the other March 27.
Two patients have recovered – a 32-year-old man, who worked on a farm where poultry recently were culled, and a 17-year-old boy, whose father runs a poultry farm in the Gharbiya governorate in the Nile Delta.
A fifth patient still is hospitalized. External diagnostic confirmation of the 18-year-old girl from the Kafr El-Sheikh governorate is pending.
On April 2, Egyptian authorities announced that local laboratory tests showed two more residents of Kafr El-Sheikh – a 6-year-old girl and her 18-month-old sister – had H5N1 infections.
Further confirmation is pending and the girls are hospitalized in stable condition.
Egypt has a large population of poultry, many kept on roof terraces near people. H5N1 outbreaks in poultry have been reported in 19 of the country’s 26 governorates.
Since the first outbreak was confirmed February 17, more than 25 million birds have died or been destroyed. Egypt is the ninth country – along with Azerbaijan, Cambodia, China, Indonesia, Iraq, Thailand, Turkey and Vietnam – to report laboratory-confirmed human cases in the current outbreak, which began in Vietnam in December 2003.
HUMAN PANDEMIC FEARS
No human case so far has been transmitted from person to person – all human illness to date has come from sick birds – but if the bird flu virus mutated enough to become easily transmissible among people, pandemic influenza could sweep the globe.
Around the world, experts say vaccine production capacity is inadequate to protect all those who would be vulnerable to pandemic influenza. (See related article.)
Slow vaccine production methods already have led to U.S. supply problems in the routine preparation and distribution of vaccines for the annual flu viruses.
Pandemic influenza resulting from a highly virulent strain like avian influenza is predicted to produce a staggering level of illness.
An estimate compiled by the U.S. Congressional Budget Office predicts that pandemic influenza could make 90 million people critically ill and kill 2 million in the United States alone, with vastly higher numbers worldwide.
Several potential avian influenza vaccines are being developed – including one funded by the National Institute of Allergy and Infectious Diseases (NIAID), one of the U.S. National Institutes of Health; two by pharmaceutical company GlaxoSmithKline; and others by Sanofi-Aventis and Chiron Corporation – but no one can be sure that a vaccine developed now will be an exact match against a future pandemic flu virus.
At the U.S. Department of Energy Los Alamos National Laboratory in New Mexico, a team of scientists says such an inexact match with the human immune system may not spell disaster for a large population.
COMPUTER MODEL OF AVIAN FLU
By developing a model that represents the U.S. population and tests different properties of a potential pandemic flu virus, the researchers – from Los Alamos, the University of Washington and the Fred Hutchinson Cancer Research Center in Seattle – evaluated the effectiveness of different intervention strategies.
The results are specific to the United States, but the researchers said the general findings can apply to other developed countries and could help those drafting preparedness plans in the United States and abroad.
“The goal for the U.S. modeling project was to determine how to slow spread long enough so that a well-matched vaccine could be developed and distributed,” said team leader Ira Longini.
The results showed that advance preparation of a modestly effective vaccine in large quantities may be better for a population than waiting for a well-matched vaccine that may not become available until a pandemic is under way.
The team also found that, depending on the contagiousness of the virus, a variety of approaches could reduce the number of cases to less than that of an annual flu season.
“The best approach,” said NIH Director Dr. Elias Zerhouni, “is to use all of the tools available to us, including computer modeling. By predicting the impact of intervention strategies, these models can help health officials and policymakers plan for a real pandemic.”
MODELING INFECTIOUS DISEASE
The modeling work is part of a research program called the Models of Infectious Disease Agent Study (MIDAS), supported by NIH’s National Institute of General Medical Sciences (NIGMS).
Researchers in the network develop computer models to understand better the spread of infectious diseases, whether the diseases occur naturally or deliberately.
With growing concerns that the H5N1 strain of the avian flu virus, initially found in birds throughout Southeast Asia, eventually could be transmitted easily between people, the research network has been modeling pandemic flu in different parts of the world.
“The MIDAS researchers previously developed models of a potential pandemic flu outbreak in Thailand and surrounding areas that showed containment at the source is feasible,” said NIGMS Director Jeremy Berg. “But we need to consider the possibility that if the outbreak isn’t contained, it could quickly spread globally.”
Using data from the 2000 U.S. Census and the Department of Transportation, the team developed a model of the demographics and travel patterns of 281 million people in the United States.
They used information about the potential virus based on previous flu pandemics, including different assumptions about its possible contagiousness, and reduced the number of overall cases to or below 10 percent of the population, the average percentage reported during an annual flu season.
The team then introduced a small number of hypothetical travelers, infected but not yet symptomatic, arriving daily at 14 major U.S. international airports, and, using high-performance computers at Los Alamos, simulated a virtual outbreak.
INTERVENTION STRATEGIES
To identify intervention strategies, the researchers tested different interventions – distributing anti-viral treatments to infected people and others near them to reduce symptoms and susceptibility; vaccinating people, possibly children first, with one or two shots of a vaccine not well matched to the strain that may emerge; social distancing, such as restricting travel and quarantining households; and closing schools.
The results showed that with no intervention a pandemic flu with low contagiousness could peak after 117 days and infect about 33 percent of the U.S. population. A highly contagious virus could peak after 64 days and infect about 54 percent of people.
The researchers then compared what might happen in scenarios involving the use of different interventions.
When the virus was less contagious, the three most effective single measures included distributing several million courses of anti-viral treatment to targeted groups seven days after a pandemic alert, school closures and vaccinating 10 million people per week with one dose of a poorly matched vaccine.
Vaccinating school children first was more effective than random vaccination when the vaccine supply was limited. Regardless of contagiousness, social distancing measures alone had little effect. When the virus was highly contagious, all single intervention strategies left nearly half the population infected.
The only measures that reduced the number of cases to below the annual flu rate involved a combination of at least three different interventions, including a minimum of 182 million courses of anti-viral treatment.
For more information on U.S. and international efforts to combat avian influenza, see Bird Flu.
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