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- 1Typically less than 100 lives a year. UPDATE: A severe Ebola outbreak was detected in West Africa in March 2014. The number of deaths in this latest outbreak has outnumbered all other known cases from previous outbreaks combined. The World Health Organization is reporting nearly 2,000 deaths in this latest outbreak.
Once a person is infected with the virus, the disease has an incubation period of 2-21 days; however, some infected persons are asymptomatic. Initial symptoms are sudden malaise, headache, and muscle pain, progressing to high fever, vomiting, severe hemorrhaging (internally and out of the eyes and mouth) and in 50%-90% of patients, death, usually within days. The likelihood of death is governed by the virulence of the particular Ebola strain involved. Ebola virus is transmitted in body fluids and secretions; there is no evidence of transmission by casual contact.
There is no vaccine and no cure.
- 23.1 Million Lives a Year
Human Immunodeficiency Virus has claimed the lives of more than 25 million people since 1981. HIV gets to the immune system by infecting important cells, including helper cells called CD4+ T cells, plus macrophanges and dendritic cells. Once the virus has taken hold, it systematically kills these cells, damaging the infected person’s immunity and leaving them more at risk from infections. The majority of people infected with HIV go on to develop AIDS. Once a patient has AIDS common infections and tumours normally controlled by the CD4+ T cells start to affect the person.
In the latter stages of the disease, pneumonia and various types of herpes can infect the patient and cause death.
- 361,000 Lives a Year
According to the WHO, this merciless virus causes the deaths of more than half a million children every year. In fact, by the age of five, virtually every child on the planet has been infected with the virus at least once. Immunity builds up with each infection, so subsequent infections are milder. However, in areas where adequate healthcare is limited the disease is often fatal. Rotavirus infection usually occurs through ingestion of contaminated stool. Because the virus is able to live a long time outside of the host, transmission can occur through ingestion of contaminated food or water, or by coming into direct contact with contaminated surfaces, then putting hands in the mouth.
Once it’s made its way in, the rotavirus infects the cells that line the small intestine and multiplies. It emits an enterotoxin, which gives rise to gastroenteritis.
- 4Officially eradicated - Due to it's long history, it impossible to estimate the carnage over the millennia
Smallpox localizes in small blood vessels of the skin and in the mouth and throat. In the skin, this results in a characteristic maculopapular rash, and later, raised fluid-filled blisters. It has an overall mortality rate of 30–35%. Smallpox is believed to have emerged in human populations about 10,000 BC. The disease killed an estimated 400,000 Europeans per year during the closing years of the 18th century (including five reigning monarchs), and was responsible for a third of all blindness. Of all those infected, 20–60%—and over 80% of infected children—died from the disease.
Smallpox was responsible for an estimated 300–500 million deaths during the 20th century alone. In the early 1950s an estimated 50 million cases of smallpox occurred in the world each year. As recently as 1967, the World Health Organization (WHO) estimated that 15 million people contracted the disease and that two million died in that year. After successful vaccination campaigns throughout the 19th and 20th centuries, the WHO certified the eradication of smallpox in December 1979.
Smallpox is one of only two infectious diseases to have been eradicated by humans, the other being Rinderpest, which was unofficially declared eradicated in October 2010.
- 5521,000 Deaths a Year
A third of the World’s population (over 2 billion people) has come in contact with this virus, including 350 million chronic carriers. In China and other parts of Asia, up to 10% of the adult population is chronically infected. The symptoms of acute hepatitis B include yellowing of the skin of eyes, dark urine, vomiting, nausea, extreme fatigue, and abdominal pain. Luckily, more than 95% of people who contract the virus as adults or older children will make a full recovery and develop immunity to the disease. In other people, however, hepatitis B can bring on chronic liver failure due to cirrhosis or cancer.
- 6500,000 Deaths a Year
Influenza has been a prolific killer for centuries. The symptoms of influenza were first described more than 2,400 years ago by Hippocrates. Pandemics generally occur three times a century, and can cause millions of deaths. The most fatal pandemic on record was the Spanish flu outbreak in 1918, which caused between 20 million and 100 million deaths. In order to invade a host, the virus shell includes proteins that bind themselves to receptors on the outside of cells in the lungs and air passages of the victim. Once the virus has latched itself onto the cell it takes over so much of its machinery that the cell dies. Dead cells in the airways cause a runny nose and sore throat. Too many dead cells in the lungs causes death.
Vaccinations against the flu are common in developed countries. However, a vaccination that is effective one year may not necessarily work the next year, due to the way the rate at which a flu virus evolves and the fact that new strains will soon replace older ones.
- 756,000 Deaths a Year
An estimated 200-300 million people worldwide are infected with hepatitis C. Most people infected with hepatitis C don’t have any symptoms and feel fine for years. However, liver damage invariably rears its ugly head over time, often decades after first infection. In fact, 70% of those infected develop chronic liver disease, 15% are struck with cirrhosis and 5% can die from liver cancer or cirrhosis. In the USA, hepatitis C is the primary reason for liver transplants.
There is no cure, no vaccine.
- 8197,000 Deaths a Year
Measles, also known as Rubeola, has done a pretty good job of killing people throughout the ages. Over the last 150 years, the virus has been responsible for the deaths of around 200 million people. The fatality rate from measles for otherwise healthy people in developed countries is 3 deaths per thousand cases, or 0.3%. In underdeveloped nations with high rates of malnutrition and poor healthcare, fatality rates have been as high as 28%. In immunocompromised patients (e.g. people with AIDS) the fatality rate is approximately 30%.
During the 1850s, measles killed a fifth of Hawaii's people. In 1875, measles killed over 40,000 Fijians, approximately one-third of the population. In the 19th century, the disease decimated the Andamanese population. In 1954, the virus causing the disease was isolated from an 11-year old boy from the United States, David Edmonston, and adapted and propagated on chick embryo tissue culture.
To date, 21 strains of the measles virus have been identified.