First Cases of Avian Flu Are Reported

Date December 16, 1997

The avian influenza A (H5N1) strain was isolated from birds in South Africa in 1961, but in May, 1997, it directly passed from birds to humans for the first time when a three-year-old boy died of respiratory failure in Hong Kong. The strain has the potential to mutate into a form more readily passed among humans, which could lead to a devastating human pandemic.

Also known as Avian influenza; bird flu

Locale Hong Kong, China

Key Figures

• Yi Guan (b. 1962), director of the State Key Laboratory of Emerging Infectious Diseases at the University of Hong Kong
• Keiji Fukuda (b. 1955), medical epidemiologist for the World Health Organization’s Global Influenza Program
• Kennedy F. Shortridge (b. 1942), microbiologist and professor emeritus at the University of Hong Kong
• Robert G. Webster (b. 1932), microbiologist at St. Jude Children’s Research Hospital

Summary of Event

Influenza pandemics occur when a new strain quickly appears, sickening and killing large numbers of people worldwide over several years. There have likely been ten to twenty human influenza pandemics that have traveled the globe in the last couple of centuries, but the 1918 pandemic was the most devastating, killing as many as fifty million people worldwide, most of whom were young adults (unlike seasonal influenza, which typically kills only the very young and elderly). The 1997 influenza outbreak in Hong Kong resulted in the hospitalization of eighteen people and the deaths of six individuals. Kennedy Shortridge, a microbiologist at the University of Hong Kong, advocated the prompt culling of all of Hong Kong’s poultry in an effort to stop the virus from spreading, and no new cases were identified for six years.

Most new influenza strains originate in Asia, where millions live in close quarters with domestic animals. Wild birds harbor the virus and migrate to other places, and can spread the virus. Efforts to identify and study the new H5N1 strain were coordinated between Shortridge’s team at the University of Hong Kong and Robert G. Webster and colleagues at St. Jude Children’s Research Hospital.

In 2003, the strain appeared again when two family members visiting Hong Kong became ill, and one of them died. H5N1 was later identified in two tigers and leopards in a Thai zoo, where the animals had eaten infected chickens. Between December, 2003, and February, 2004, there were outbreaks of H5N1 in Vietnam, Thailand, Korea, Japan, Cambodia, Laos, Indonesia, and China. More than 100 million chickens either died or were destroyed. The World Health Organization (WHO) called these incidents the first stage of the outbreak.

The second stage was preceded in April, 2005, by the deaths of 6,345 wild fowl at Qinghai Lake in northwest China. Unlike domestic fowl, wild birds are not usually made ill by influenza strains. Concerns increased because migrating wild fowl can spread the disease by fecal-oral transmission through the watersupply. By May, H5N1 was discovered in Indonesian pigs, and later, Chinese pigs—animals that facilitate gene exchange between avian and human influenza strains—raising concerns that there was an increased possibility of a mutant strain rapidly spreading to humans. By August, three people in Vietnam were infected and died, and birds in Siberia, Tibet, and Kazakhstan were infected. More humans died in Indonesia and Cambodia in September, in addition to outbreaks in birds and poultry in Mongolia, Romania, Turkey, Croatia, and the Greek island of Chios in October.

The WHO issued a stage 3 pandemic alert, applied when there are human infections with a new subtype but no human-to-human transmission (stages 4-6). Local governments and the WHO took measures to lower the risk of a pandemic by implementing active surveillance, immunizing healthy domestic birds, killing infected and exposed birds, and developing vaccinations and antiviral medications for people—difficult tasks, considering that influenza strains are constantly changing, as exemplified by the new strain identified in 1997.

Viruses consist of genetic material that is packaged into a protein shell called the capsid, or coat. Proteins also project from the virus and usually target the host’s immune system. These proteins help the virus to enter the host cell and change more often than other viral components. Once inside the cell, the virus replicates itself with the host’s machinery. Subtypes A, B, and C characterize the capsid types, and only influenza A and B can kill humans. Viral subtypes are also identified on the basis of the two proteins on the surface of the virus: hemagglutinin (HA) and neuraminidase (NA). There are sixteen known HA subtypes and nine known NA subtypes, and many combinations are possible. The H5N1 virus has an HA 5 protein and an NA 1 protein. All known subtypes of A infect birds, but not all subtypes infect birds and people.

Influenza is a challenging disease to anticipate because the virus is constantly changing. An accumulation of small mutations, known as antigenic drift, occurs in the influenza virus and is not likely to cause problems. By contrast, antigenic shift creates new strains to which individuals may not be resistant. The director of the State Key Laboratory of Emerging Infectious Diseases at the University of Hong Kong, Yi Guan, and colleagues noted that from July, 2005, to June, 2006, the proportion of infected ducks, geese, and chickens increased from 0.9 to 2.4 percent, indicating that influenza would be hard to eradicate in domestic birds. They also discovered a new dominant strain called the Fujian strain, responsible for 95 percent of samples examined from April to June, 2006. The hemagglutinin strain from some human cases in China also belonged to this strain, and similar strains were found in Hong Kong, Laos, and Malaysia. Chicken vaccines were ineffective against the Fujian strain.

Significance

Constant surveillance and, following outbreaks, quarantine of farms and destruction of exposed birds are the primary means of stopping the spread of the virus in birds. However, complete elimination of the virus is unlikely, given the crowded and unsanitary conditions of commercially raised, genetically identical chickens. In the United States, many species of live birds are slaughtered in metropolitan areas, but the U.S. Department of Agriculture (USDA) does not regulate these activities. Wild birds are monitored by the U.S. Geological Survey, the U.S. Fish and Wildlife Service, and the National Park Service, but many illegally imported wild birds still make it into the country. Domestic birds are tested by the Animal and Plant Health Inspection Service division of the USDA. The department made efforts to educate large poultry producers and urged farmers to report sick birds.

The best protection against an avian influenza pandemic is vaccination. However, given the high mutation rate of the virus, vaccines stockpiled today are unlikely to protect against future pandemic strains. In addition, it may take many months to manufacture a new vaccine and to distribute it to billions of people worldwide. The United States established the National Strategy for Pandemic Influenza, and the government continued to work closely with the WHO—efforts coordinated by Keiji Fukuda, formerly of the Centers for Disease Control in Atlanta, Georgia. The WHO advocated countries to draft national pandemic preparedness plans and to hold drills.

By 2006, nine years after its discovery, the H5N1 strain of avian influenza had been identified in birds in almost fifty countries, with twenty-eight countries reporting since 2006. The WHO confirmed about two hundred human cases, with more than half of those leading to death. The general consensus in the scientific community is that the world is due for another pandemic. The H5N1 virus looks very similar to the 1918 virus, but the outbreaks of the H5N1 avian influenza that originated in Southeast Asia in mid-2003 and spread to other parts of the world were the largest and most virulent cases of influenza disease on record. The expense and global threat led to coordinated efforts worldwide, including the formation of the International Partnership on Avian and Pandemic Influenza during the U.N. General Assembly in September, 2005. The U.S. Department of State hosted the first meeting in October of that year; included were representatives from eighty-eight countries and organizations such as the WHO, the Food and Agricultural Organization, and the World Organization for Animal Health.

Bibliography

Davis, Mike. The Monster at Our Door: The Global Threat of Avian Flu. New York: Henry Holt, 2006. Gives the political context for why avian influenza may lead to a pandemic.

Greene, Jeffrey, with Karen Moline. The Bird Flu Pandemic: Can It Happen? Will It Happen? How to Protect Yourself and Your Family If It Does. New York: Thomas Dunne Books, 2006. Basic information on the virus and related pandemics, how the virus may spread to the United States, and practical tips for reducing one’s risk before and during a pandemic. Excellent list of Web resources.

Normile, Dennis. “New H5N1 Strain Emerges in Southern China.” Science 314 (November, 2006): 742. The latest information on avian flu is consistently reported in this journal and in Nature.

Sfakianos, Jeffrey N. Avian Flu. New York: Chelsea House, 2006. The biology of avian flu is explained clearly with an excellent glossary.

Siegel, Marc. Bird Flu: Everything You Need to Know About the Next Pandemic. Hoboken, N.J.: John Wiley & Sons, 2006. Argues that there is a lot of alarmist rhetoric about the virus that can be confronted with commonsense precautions. Good bibliography.