Killers Without Cures

Killers Without Cures – lethal viruses

Nicole Dyer

In the last three decades more than 50 lethal viruses (microscopic particles that cause infection) once found only in animals have infected humans. Viruses like Ebola and Marburg spread like wildfire from one victim to another, often killing the afflicted in days. These viruses are so life-threatening they’re called “hot agents” slang for the deadliest microbes (germs) on Earth. No treatment yet exists for Ebola or Marburg, but scientists have just identified a protein that may cause the Ebola virus’s grisliest symptom–massive bleeding. The find may spur a cure.

Last year, the less deadly but still dangerous West Nile virus–native to West Africa–made its mysterious appearance in the U.S. for the first time. Seven victims died in New York City and 62 others fell ill, putting health officials on emergency alert for the next attack.

What are these viruses and how are they spread? How does a virus travel from a remote African rainforest to a crowded American city? What happens when one breaks loose in a community? To find out, follow virus hunters on a 1995 mission to stop a deadly outbreak.

Day 1 Kikwit, Zaire, Africa

Sister Dinarose Belleri, a 58-year-old nurse, tends to her patients in a small community hospital. Normally energetic, today Sister Belleri feels under the weather. Probably just the flu, she thinks, and heads home to rest. But hours later her body burns with fever, her muscles ache, and she vomits blood.

Day 3 Zaire, Africa

Sister Belleri dies, and dozens of other villagers contract the same illness. It’s a mysterious epidemic (high rate of disease in a single area). Doctors suspect the culprit is one of two types of infectious microbes: a bacteria, a single-celled organism, or a virus, a chemical package of genetic material (either RNA or DNA). Viruses are the smallest life-forms on Earth–10 to 30 times smaller than bacteria–and live and multiply by invading living cells (see diagram).

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Bacteria and viruses lurk everywhere–in the air, water, soil, and in every human. Most bacteria or viruses don’t trigger disease, or are readily combated by the immune system, the body’s natural mechanism to fight infection.

Doctors at the community hospital suspect a virus is loose. If the mystery microbe was a bacteria, Sister Belleri and others might have recovered after taking antibiotics, drugs that destroy bacteria. So victims’ blood samples are flown thousands of miles away to a special laboratory equipped to handle “hot agents.” The lab–located at the Centers for Disease Control and Prevention (CDC) in Atlanta, Ga.–is one of only a dozen in the world.

Day 6 Atlanta, Georgia

Blood samples arrive at the CDC, sealed in a container labeled “biohazard.” Handling a hot agent is especially dangerous since a microbe may be airborne, capable of traveling in tiny water droplets through air. Airtight spacesuits and helmets hooked up to air tanks keep scientists from inhaling the germs.

In the lab, a scientist places a blood droplet in a petri dish filled with healthy human cells, and a nutrient-rich medium (food required for cell growth). After 24 hours the cells develop reddish-blue lumps–clear evidence of a virus.

Under an electron microscope (which uses beams of electrons instead of light rays), scientists magnify the virus 100,000 times. Surprisingly, it looks like a spaghetti string. Of the more than 1,400 known viruses, less than six feature this unusual shape–most typically look like tennis balls.

Based on two clues–the odd shape and a victim’s disease symptoms–scientists suspect the virus belongs to a rare virus family called filoviruses (“filo” means long filament). So far only two viruses on Earth are members–Ebola and Marburg.

Ebola was first identified in Zaire, Africa, nearly 25 years ago when an outbreak killed 245 people. A virus sample was frozen and stored at the CDC lab. Like detectives matching criminal fingerprints, scientists compare the two samples–they’re identical! A killer that hasn’t surfaced in 20 years is at large in Kikwit.

Day 7 Atlanta, Georgia

An emergency medical “SWAT” team, including CDC disease detective and Ebola expert Dr. Ali S. Khan, take on the Kikwit case. As an epidemiologist, Khan travels the world investigating epidemics spawned by microbes. “A big part of my job is trying to figure how and where an outbreak begins,” he says. “We talk to everyone associated with the virus–family, friends, victims–in order to piece the puzzle together.”

Day 8 Zaire, Africa

Dr. Khan and his team arrive in Kikwit. Their first priority is to quarantine or separate the sick from the healthy, since Ebola is transmitted from person to person through close contact, body fluids, or by contaminated needles and syringes.

Wearing protective masks and gowns, the team scours the village door to door, inquiring if anyone has Ebola-like symptoms (high fever, headaches, excessive bleeding). Armed soldiers block all entrances to Kikwit to try to thwart the spread of Ebola outside the village.

Day 12 Zaire, Africa

By following a trail of more than 300 people infected with Ebola, the team deduces that Patient Zero–the first infected person–was a charcoal worker whose job sent him into the rainforest. The patient was most likely infected by an Ebola-carrying animal, possibly a bat. Seven of his household’s members later died from the infection. Sister Belleri probably cared for one member at the Kikwit hospital. Then she unknowingly infected dozens of patients and hospital workers.

Day 25 Zaire, Africa

The team sanitizes the Kikwit hospital by scrubbing blood from mattresses and walls, so new patients can be cared for safely. Doctors and nurses now wear protective masks, rubber gloves and gowns. Without a vaccine (drug that triggers the immune system to fight off a virus), the only way to halt this epidemic is to keep uninfected people from coming into contact with Ebola.

Day 50 Zaire, Africa

The quarantine strategy is working. Six weeks pass without a single new reported case of Ebola. Khan and his team have successfully stopped the killer–for now. But several questions remain unanswered: Where did Ebola come from? When did it first infect humans and how? Is the virus active in animals other than primates (monkeys and humans), like bats or mice? And when and where will it show up next? “We still don’t know the answers to these questions,” Khan admits.

What scientists do know, however, is that most “hot viruses” emerge from tropical rainforests. As humans settle in these forests they encounter microbes’ natural hosts (like monkeys or mosquitoes). So it becomes easier for an animal virus to infect humans. And as more people travel into the world’s remote regions–by jet, car, train–a virus once native only to West Africa can suddenly appear in New York City.

The Kikwit outbreak is over, but scientists are on the constant lookout for other potentially lethal microbes. In West Africa, for example, Lassa virus infects 100,000 to 300,000 people per year, killing more than 5,000 annually. It’s transmitted by a rodent called the multimammate rat, found in the savannas and forests of West, Central and East Africa. And in the U.S. as of last May, the Hantavirus–a microbe carried by the deer mouse–has infected a total of 250 people. The virus drowns its victims by causing the lungs to fill up with fluid.

FIGHTING BACK

By now, you may be ready to seal yourself up in a microbe-proof spacesuit. That may not be necessary, thanks to researchers racing to develop microbe-fighting medications. Scientists at the National Institutes of Health have isolated a protein that sticks out of the Ebola virus surface and destroys endothelial cells (lining blood vessel walls). The discovery could spur new treatments for Ebola.

For now, however, when it comes to deadly viruses–like HIV, Ebola, Lassa–prevention is the only cure. “Preventing outbreaks means teaching people, especially health care workers, about new infectious diseases and how to stop their spread,” says Khan. “Taking simple precautions, like wearing rubber gloves and masks when caring for infected patients, can mean the difference between life and death.”

How a Virus Attacks a Cell

A virus consists of only a few genes (RNA or DNA) surrounded by a protein shell. Unlike other microbes, a virus isn’t active until it infects a living cell. Here, proteins that stick out from the viral shell attach to a receptor on the surface of a human cell. The virus injects its genes into the cell’s control center (nucleus). Using the cell’s tools to reproduce, the genes create new virus particles. Most infected cells burst open, releasing millions of viruses that infect other cells in the body.

4 OF THE DEADLIEST VIRUSES ON EARTH

These extremely hazardous viruses cause rare but lethal disease in humans.

Marburg

Identified: 1967, Germany

Virus family: Filoviridae

Last seen: Kenya, Zimbabwe, and South Africa

Common Animal Host: green monkeys (Cercopithecus aethiops)

Spread by: contact with infected fluids (e.g. blood, saliva)

Symptoms: fever, vomiting, bleeding from stomach, gums, nose, and bowels

Estimated Deaths: 100

Treatments: none

Lassa

Identified: 1969, Nigeria

Virus family: Arenviridae

Last seen: West Africa

Common Animal Host: rats (Mastomys natelensis)

Spread by: contact with infected fluids or rat droppings

Symptoms: fever, vomiting, fluid in lungs, swelling of the face and neck

Estimated Deaths: 5,000

Treatments: anti-viral drug Ribavirin (only works if given within first six days of illness)

Ebola

Identified: 1976, Zaire

Virus family: Filoviridae

Last seen: Zaire, Gabon, and Liberia

Common Animal Host: chimpanzees and monkeys (Macaca fascicularis)

Spread by: contact with infected fluids (e.g. brood, saliva)

Symptoms: fever, vomiting, bleeding from stomach, gums, nose, and bowels

Estimated Deaths: 1,100

Treatments: none

Hanta

Identified: 1976, Korea

Virus family: Bunyaviridae

Last seen: Vermont, Rhode Island, Colorado, Utah, New Mexico, Arizona

Common Animal Host: Deer mice (Peromyscus maniculatus)

Spread by: contact with infected fluids; exposure to infected rodents and their droppings

Symptoms: breathing difficulty, fluid in lungs, multi-organ failure

Estimated Deaths: 100 (U.S.)

Treatments: none

BUILDING A BETTER BUG

When a mosquito plunges its needle-like beak (proboscis) into your skin, you expect nothing more than an annoying itch. But for 62 people chomped by mosquitoes (Culex tarsalis) in New York City last year, the bite resulted in illness due to encephalitis, a brain-swelling disease caused by the West Nile virus (seven later died). Normally found in Africa, West Nile is transmitted to humans by infected mosquitoes.

West Nile is one of many life-threatening mosquito-borne parasites (species which feed off of other species) that worry public health officials. According to the World Health Organization, every year more than 500 million people develop deadly diseases from mosquito bites–including dengue, yellow fever, and malaria.

To fight back, biologist Bruce Christensen at the University of Wisconsin in Madison is trying to “genetically engineer” a mosquito incapable of carrying disease. Most mosquitoes have a natural ability to kill parasites. They have anti-parasitic genes (hereditary chemicals) that become active when confronted by a parasite, protecting the mosquito from infection, Christensen explains: “But in some species these genes aren’t activated.”

Christensen’s job is to locate anti-parasite genes and figure out how to “turn them on” If successful, the next step is to introduce the genetically-enhanced mosquitoes into the wild and hope they multiply and overpopulate disease-spreading mosquitoes.

“Nobody knows if it will work,” Christensen admits. But if it does, “Frankenbugs” may finally take the disease out of mosquito bites.

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Cross-Curricular Connection

Geography: Have students identify the locations of different tropical forests on a current map of Africa. Compare the current map with a map of African forests from the 1980s.

Did you Know?

* Ebola-Zaire is the most deadly virus to date. It kills about 90 percent of those infected.

* Worldwide last year, HIV killed 2.8 million people. But unlike Ebola, HIV kills slowly. HIV-infected people can live up to 15 years before showing signs of illness.

* The first U.S. Hantavirus outbreak occurred in the Southwest in 1993. Of the 33 people killed, most were healthy young adults.

National Science Education Standards Grades 5-8: natural hazards * diversity and adaptation of organisms * structure and function in living systems * abilities of technological design

Grades 9-12: the cell * behavior of organisms * personal and community health * natural and human-induced hazards * science and technology in local, national, and global challenges

Resources

Outbreak: Disease Detectives at Work, by Mark Friedlander (Lerner Publications Co., 2000)

Level 4: Virus Hunters of the CDC, by Susan Fisher-Hoch, M.D. (Turner Publishing, Inc., 1996)

Special Pathogens Branch of the Centers for Disease Control and Prevention: www.cdc.gov/ncidod/dvrd/spb/

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