August 31, 2009

UNIT 6: Classification and DiversityPandemics — Is the Next One on the Way?

Imagine that a new virus emerges and people have no immunity. There is no vaccine. If this were to happen, there could be mandatory travel restrictions, quarantines, and social distancing—including staying out of all crowded places. In the United States alone, such an outbreak could kill up to 2 million people. But how can such a virus emerge, and how can we prepare for it?

Pandemics

When a new virus emerges, the species that it infects has had little or no opportunity to evolve immunity. If the virus infects people, there is often little time to produce vaccines. For these reasons, a new virus may be able to spread easily from person to person.

A new virus can cause a pandemic, which is a disease outbreak that affects large areas of the world and has a high fatality rate. The 1918 flu pandemic was the most devastating pandemic recorded in world history. This virus infected nearly one-fifth of the world’s population, killing about 50 million people worldwide. It spread mainly along global trade routes and with the movement of soldiers during World War I.

If a new and deadly disease emerges today, a carrier could travel around the world in 24 hours. More than a million people travel internationally by plane every year, easily reaching their destinations before symptoms of any diseases they may be harboring appear.

The "Perfect" Virus

Not every virus is well-suited to cause massive human casualties. For many viruses, humans represent a dead-end infection because they cannot be passed from human to human. For other viruses, victims die too quickly for the virus to reproduce. Quarantines can contain this type of virus relatively easily.

What characteristics would make an emerging virus likely to cause a pandemic? The virus would need to be adapted to humans as hosts and easily spread through casual contact. Victims would also have to survive infection long enough without symptoms to go about their daily business and infect other people. Finally, the most deadly virus would mutate rapidly, foiling the attempts of scientists to develop a vaccine or a drug that targets it.

Diseases that Jump to New Species

Some diseases, called zoonoses, can jump between species. If a virus evolves the ability to jump from a nonhuman animal species to humans, our immune systems will have had little opportunity to evolve defenses. And if this virus exchanges genetic material with another human virus, a new virus that is capable of spreading from person to person may form.

Perhaps the most familiar zoonosis is the avian flu virus. Sometimes called the bird flu, this virus normally infects wild birds such as ducks and geese as well as domestic birds such as chickens. The spread of avian flu does not rely on any human form of transportation, since migrating birds can carry it to other continents.

Avian Flu H5N1

Is avian flu the perfect killer virus? Researchers are currently tracking a form of avian flu called H5N1. Like other flu viruses, H5N1 mutates rapidly. However, mutations are random and may or may not help the virus adapt to new host species.

Unfortunately, a faster, less random way for viruses to mutate exists. Some animals can be infected with viruses from two different species at the same time. For example, if a pig becomes infected by both avian and human flu viruses at the same time, the viruses can exchange genetic information. If this happens, the avian flu can jump the species barrier, becoming a flu virus that can be transmitted from one human to another.

Unanswered Questions

Despite the danger that a new virus represents, no one knows how the virus may mutate or whether it will cause a pandemic. Some of the most important questions include the following:

• How can vaccines be developed quickly enough to stop a disease that can spread in hours or days?
• Can a broad-spectrum antiviral drug be developed that could target more than one flu virus?
• What specific molecular factors allow a virus to jump from one species to another?

UPDATES: Straight from the Headlines

• Will There Be Another Flu Pandemic Soon?
• Avian Flu: The Current Situation
• Cold Symptoms Linked to Immune Response, Not Cold Virus
• B Memory Cells Still Remember 1918 Flu Virus
• WHO Declares H1N1 Flu Virus Outbreak a Pandemic
• Researchers Find H1N1 Flu Virus Able To Infect Lung Cells

Last updated August 31, 2009 | Comments (6) | Permalink | UNIT 6: Classification and Diversity