The Top 10: Epidemic Hall of Infamy

Historically speaking, these infectious diseases have been the deadliest, followed closely by other childhood diseases like diphtheria, as well as typhus and hepatitis B and C.

1. Influenza or “flu”

Viral respiratory illness
Spread: by tiny droplets from sneeze or cough
Symptoms: fever, headache, fatigue, cough, sore throat, runny/stuffy nose, muscle aches and sometimes intestinal upset
Best prevention: annual vaccination for seasonal flu
Impact: Seasonal flu annually sickens about 5–20 percent of the U.S. population, sending 200,000 people to the hospital and killing 36,000 people.
Note: Scientists fear a more serious influenza, currently found primarily in poultry and wild birds, might change into a more serious form, called pandemic influenza, that could easily pass from person to person as did the Spanish Influenza of 1918.

2. Smallpox

Ancient disease caused by the variola virus
Spread: person-to-person or via contaminated bedding/clothing
Symptoms: high fever and extensive rash; can cause permanent scarring or death
Best prevention: was eliminated worldwide by an aggressive global vaccination program; last naturally occurring case reported in 1977
Impact: brought to the New World by explorers and settlers, devastating native peoples; killed about 300 million people in just the 20th century
Note: Except for laboratory stockpiles, the variola virus has been eliminated, but the U.S. still prepares for a bioterrorist-caused outbreak.

3. Plague (bubonic and pneumonic)

Caused by Yersinia pestis bacterium
Spread: bites from infected fleas/rodents (bubonic) or by inhaling the bacteria through close contact with an infected person (pneumonic)
Symptoms: (bubonic) swollen glands; (pneumonic) fever, chills, headache, extreme exhaustion, lung infection, breathing difficulty
Best prevention: avoid contact with infected animals/fleas; antibiotics if exposure certain
Impact: killed one-third of Europe’s population in 1348–50; today, World Health Organization reports 1,000–3,000 cases annually
Note: Ten to 20 people in the U.S. develop plague annually from fleas or rodents, but the country’s last person-to-person infection was in 1924.

4. Cholera

A toxin-producing bacterial infection of the intestines
Spread: contaminated food or water
Symptoms: diarrhea, vomiting, dehydration, kidney failure
Best prevention: sanitary water supplies and sewage treatment; early treatment with fluid replacement and, in severe cases, antibiotics
Impact: In summer 1832, cholera killed more than 3,000 people in New York, then 4,000 more in New Orleans a few months later. With more than 120 countries reporting indigenous cases since 1991, cholera seems to be on the rise globally. In 2004, the World Health Organization said that 56 countries officially reported 101,383 cholera cases, including 2,345 deaths.
Note: kills half of untreated people with severe cases but less than 1 percent of those who get prompt fluid replacement

5. Tuberculosis (TB)

Caused by the Mycobacterium tuberculosis bacterium; TB usually attacks lungs; can affect kidney, spine and brain
Spread: person-to-person through air
Symptoms: bad cough, chest pain, coughing blood if bacterium settles in lungs
Best prevention: good ventilation; skin tests to identify people carrying TB without obvious symptoms; treatment of those identified with active TB disease. Antibiotics can cure most cases.
Impact: Two billion people—one-third of world’s population—are thought to be infected with TB bacteria. Annually, 8 million people worldwide develop active TB and nearly 2 million die.
Note: TB was once the leading cause of death in the U.S.

6. Malaria

Four kinds of malaria parasites can infect people
Spread: bites from infected mosquitoes
Symptoms: high fever, shaking chills and flu-like illness
Best prevention: avoid mosquito bites; take regionally specific anti-malaria drugs
Impact: Annually 300 million–500 million cases of malaria occur worldwide, killing more than 1 million people. Most of the 1,300 U.S. malaria cases each year are in travelers and immigrants returning from high malaria-risk areas.
Note: Development of a malaria vaccine, not yet available, is a top international public health research priority.

7. AIDS (Acquired Immune Deficiency Syndrome)

Caused by Human Immunodeficiency Virus (HIV)
Spread: sexual contact, sharing needles/syringes with infected person, transfusions or mother-to-infant transmission
Symptoms: damages immune system, progressively destroying ability to fight infections and certain cancers
Best prevention: avoid unprotected sex or needle-sharing; combinations of antiviral drugs can slow spread of HIV in body and delay opportunistic infections
Impact: Worldwide, AIDS is leading cause of death of 15-to-49-year-olds with cases totaling 45 million in 2005.
Note: National Institute for Allergies and Infectious Diseases estimates 950,000 Americans are infected with HIV, one-quarter of whom don’t know it.

8. Yellow Fever

Viral disease
Spread: by mosquitoes
Symptoms: headache, fever, jaundice, kidney failure
Best prevention: vaccination, avoiding mosquito bites
Impact: common in rural sub-Saharan Africa and South America; Africa also experiences urban yellow fever outbreaks. In 2001, the World Health Organization reported there were 200,000 estimated cases of yellow fever, with 30,000 deaths, per year.
Note: The last great U.S. epidemic occurred in 1878 in New Orleans, killing 13,000 people.

9. Polio

Highly infectious viral disease
Spread: person-to-person contact
Symptoms: fever, fatigue, headache, vomiting, neck stiffness, pain in limbs; one in 200 infections leads to irreversible paralysis, killing 5–10 percent of those paralyzed when breathing muscles are affected; mainly strikes children under age 5
Best prevention: vaccination
Impact: Until effective vaccines were developed in 1950s, polio annually crippled thousands of children in industrialized countries. Today only four countries worldwide remain polio-endemic: India, Nigeria, Pakistan and Afghanistan.
Note: The worst U.S. polio epidemic caused more than 27,000 cases and 7,000 deaths in 1916.

10. Measles

Highly communicable viral respiratory disease
Spread: coughing and sneezing
Symptoms: rash, high fever, cough, runny nose and red, watery eyes; complications include ear infections, pneumonia, encephalitis, seizures and death.
Best prevention: measles vaccine
Impact: About 454,000 people, mostly children, died from measles worldwide in 2004.
Note: Before a vaccine became available in 1963, almost everyone got the measles. After the vaccine, U.S. cases dropped by 98 percent.

Information for the Top 10 was drawn primarily from the Centers for Disease Control and Prevention, the World Health Organization and the National Institute of Allergy and Infectious Disease.

— Pat Bailey

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Pat Bailey writes about the agricultural and veterinary sciences for UC Davis.