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Weird Science: Deadly Flu

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In the early 1900’s thousands of people were killed by a deadly strain of influenza, or flu virus (SF Fig. 1.4). Obviously, this virus was different from the flu virus caught by hundreds of people every day. This flu virus had acquired a mutation that made it more deadly. This group of viruses—collectively known as influenza—is infamous for its ability to mutate quickly. In many cases these mutations do not make much difference to public health, as the flu symptoms humans experience from the different mutations of virus are similar. However, some mutations change the impact of the virus on the body, increasing the virulence, or ability to cause disease, of the virus, making it more deadly. Flu viruses do not only affect humans, they are also widespread in bird populations. The strains of influenza in birds are rarely of concern to humans because normally bird flu virus cannot be transmitted from birds to humans. However, sometimes a mutation occurs that allows a virus to be transmitted from an animal host to a human host.


SF Fig. 1.4. (A) A transmission electron microscope image shows the Influenza A H1N1 virus.

Image courtesy of Cynthia Goldsmith, Centers for Disease Control and Prevention (CDC)

SF Fig. 1.4. (BA microbiologist handles a vial of Influenza A H1N1 virus while wearing protective safety equipment inside a self-contained virus laboratory.

Image courtesy of James Gathany, Centers for Disease Control and Prevention (CDC)


The bird flu virus known as H5N1 caused an outbreak in humans in 2005. The bird flu cases reported in most humans were from people who had been in direct contact with infected birds. This indicates that while the virus had mutated to allow it to be transmitted from birds to humans, the virus had not acquired the ability to be spread from human to human. This limited the spread of the virus in the 2005 H5N1 outbreak. However, in 2011, 62 human H5N1 cases and 34 deaths were reported from five countries—Bangladesh, Cambodia, China, Egypt, and Indonesia. Six countries— Bangladesh, China, Egypt, India, Indonesia, and Vietnam—have widespread and ongoing infections in their poultry. Poultry outbreaks have occurred in other countries recently as well. And yet, human infection with H5N1 remains rare. Most infections occurred after direct or close contact with poultry infected with H5N1. The concern with viruses like H5N1 is that a second mutation could allow the virus to spread from human to human and perhaps cause a pandemic, or worldwide, outbreak of flu in human populations. The pandemic flu in the early 1900’s killed over 20 million people worldwide, more than were killed in fighting during World War I.

Exploring Our Fluid Earth, a product of the Curriculum Research & Development Group (CRDG), College of Education. University of Hawaii, 2011. This document may be freely reproduced and distributed for non-profit educational purposes.