Scientists resurrect 1918 flu virus

Scientists have resurrected the influenza virus that killed an estimated 20 million people in 1918, the worst pandemic in history.

They used a process known as "reverse genetics" to reconstruct a living flu virus from dead fragments retrieved from stored hospital tissue samples and a corpse that had been buried in the frozen tundra of Alaska for 80 years.

Tests on animals and human lung cells showed that the reconstructed virus retained the highly lethal properties that made the 1918 strain of influenza such a killer.

Scientists working for the US Centres for Disease Control and Prevention (CDC) in Atlanta, Georgia, said the virus was being kept in one of its high-security laboratories.

The reconstructed virus quickly killed laboratory mice and chick embryos when they were infected with the agent. It also grew rapidly in cultured human lung cells.

In contrast, most flu viruses that infect humans today show none of these lethal characteristics, said Terrence Tumpey, whose study is published today in the journal Science.

The influenza outbreak of 1918 was the largest of the three flu pandemics of the 20th century. A separate study in the journal Nature reveals that the 1918 virus was in effect an avian flu virus that had jumped the species barrier into humans.

* THE THREE FLU PANDEMICS OF THE 20th CENTURY 

1918: Spanish Flu
The Spanish Influenza pandemic is the catastrophe against which all modern pandemics are measured. It is estimated that approximately 20 to 40 percent of the worldwide population became ill and that over 20 million people died. Between September 1918 and April 1919, approximately 500,000 deaths from the flu occurred in the US alone. Many people died from this very quickly. Some people who felt well in the morning became sick by noon, and were dead by nightfall. Those who did not succumb to the disease within the first few days often died of complications from the flu (such as pneumonia) caused by bacteria.

One of the most unusual aspects of the Spanish flu was its ability to kill young adults. The reasons for this remain uncertain. With the Spanish flu, mortality rates were high among healthy adults as well as the usual high-risk groups. The attack rate and mortality was highest among adults 20 to 50 years old. The severity of that virus has not been seen again. 

1957: Asian Flu
In February 1957, the Asian influenza pandemic was first identified in the Far East. Immunity to this strain was rare in people less than 65 years of age, and a pandemic was predicted. In preparation, vaccine production began in late May 1957, and health officials increased surveillance for flu outbreaks.

Unlike the virus that caused the 1918 pandemic, the 1957 pandemic virus was quickly identified, due to advances in scientific technology. Vaccine was available in limited supply by August 1957. Infection rates were highest among school children, young adults, and pregnant women in October 1957. Most influenza-and pneumonia-related deaths occurred between September 1957 and March 1958. The elderly had the highest rates of death.

By December 1957, the worst seemed to be over. However, during January and February 1958, there was another wave of illness among the elderly. This is an example of the potential "second wave" of infections that can develop during a pandemic. The disease infects one group of people first, infections appear to decrease and then infections increase in a different part of the population. Although the Asian flu pandemic was not as devastating as the Spanish flu, about 69,800 people in the US died. 

1968: Hong Kong Flu
In early 1968, the Hong Kong influenza pandemic was first detected in Hong Kong. Deaths from this virus peaked in December 1968 and January 1969. Those over the age of 65 were most likely to die. The same virus returned in 1970 and 1972. The number of deaths between September 1968 and March 1969 for this pandemic was 33,800, making it the mildest pandemic in the 20th century. Why?

The Hong Kong flu virus was similar in some ways to the Asian flu virus that circulated between 1957 and 1968. Earlier infections by the Asian flu virus might have provided some immunity against the Hong Kong flu virus that may have helped to reduce the severity of illness during the Hong Kong pandemic. Instead of peaking in September or October, like pandemic influenza had in the previous two pandemics, this pandemic did not gain momentum until near the school holidays in December. Since children were at home and did not infect one another at school, the rate of influenza illness among schoolchildren and their families declined. Third, improved medical care and antibiotics that are more effective for secondary bacterial infections were available for those who became ill.
SOURCE: US DEPT OF HEALTH AND HUMAN SERVICES

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