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that diseases are caused by microorganisms.

Building on this new understanding of disease, scientists and physicians achieved incredible successes, identifying fifty causative agents of diseases ranging from typhoid, tuberculosis, cholera, plague and malaria between 1880 and 1920.

Cholera is an infectious disease that causes severe watery diarrhea, which can lead to dehydration and even death if untreated. It is caused by eating food or drinking water contaminated with a bacterium called Vibrio cholerae.

cholera outbreaks are still a serious problem in other parts of the world, where cholera affects an estimated 3 to 5 million people and causes more than 100,000 deaths each year.

Smallpox is a potentially deadly infectious disease, now eradicated worldwide after successful global immunization programs. Over the centuries before being eliminated, smallpox devastated populations worldwide.

What Causes Smallpox: The Variola Virus Smallpox is caused by the variola virus. There are two forms of this virus. The more dangerous form, variola major, caused smallpox disease that was fatal for about 30% of people infected. A virus called variola minor caused a less deadly form of smallpox, with a fatality rate of about 1%. 

How Smallpox Is Spread Smallpox disease is highly contagious. It spreads from person to person primarily by breathing in the virus, which is transmitted in saliva, during close, face-to-face contact with an infected person.

Caused by the bacterium Yersinia pestis, plague is an infectious disease that occurs mainly in rodents, such as rats and squirrels. It can be transmitted from rodents to humans by the bite of a flea from an infected animal. Plague was the cause of some of the most-devastating epidemics in history, including the Black Death of the 14th century.

Caused

Cholera is most frequently transmitted by water sources contaminated with the causative bacterium Vibrio cholerae, although contaminated foods, especially raw shellfish, may also transmit the cholera-causing bacteria.

The main treatment for cholera is fluid and electrolyte replacement, both oral and IV. Antibiotics usually are used in severe infections in which dehydration has occurred.

Cholera can be prevented with appropriate measures such as safe drinking water and noncontaminated foods; some protection can be obtained from oral vaccines while avoiding areas where cholera commonly occurs or has had a recent outbreak.

What Are the Different Types of Flu?There are three types of flu viruses: A, B, and C. Type A and B cause the annual influenza epidemics that have up to 20% of the population sniffling, aching, coughing, and running high fevers. Type C also causes flu; however, type C flu symptoms are much less severe.The flu is linked to between 3,000 and 49,000 deaths and 200,000 hospitalizations each year in the United States. The seasonal flu vaccine was created to try to avert these epidemics.

Characteristics 1) Start Suddenly 2) Spread Rapidly 3) People of all ages are affected4) Many people become ill5) The attack rate and death rate is high

Painful diarrhea, high fever, nasty red rashes and sleeplessness typically characterize the illness.

Left untreated, typhoid can result in death.

Salmonella typhi, the parasite that causes typhoid fever, spreads through water and food, making the disease highly contagiou

In the fall of 1918 the Great War in Europe was winding down and peace was on the horizon.

The Americans had joined in the fight, bringing the Allies closer to victory against the Germans. Deep within the trenches these men lived through some of the most brutal conditions of life, which it seemed could not be any worse. Then, in pockets across the globe, something erupted that seemed as benign as the common cold. The influenza of that season, however, was far more than a cold. In the two years that this scourge ravaged the earth, a fifth of the world's population was infected. The flu was most deadly for people ages 20 to 40. This pattern of morbidity was unusual for influenza which is usually a killer of the elderly and young children. It infected 28% of all Americans (Tice). An estimated 675,000 Americans died of influenza during the pandemic, ten times as many as in the world war. Of the U.S. soldiers who died in Europe, half of them fell to the influenza virus and not to the enemy (Deseret News). An estimated 43,000 servicemen mobilized for WWI died of influenza (Crosby). 1918 would go down as unforgettable year of suffering and death and yet of peace. As noted in the Journal of the American Medical Association final edition of 1918:

The influenza pandemic circled the globe. Most of humanity felt the effects of this strain of the influenza virus. It spread following the path of its human car

Mary Mallon, now known as Typhoid Mary, seemed a healthy woman when a health inspector knocked on her door in 1907, yet she was the cause of several typhoid outbreaks. Since Mary was the first "healthy carrier" of typhoid fever in the United States, she did not understand how someone not sick could spread disease -- so she tried to fight back.

Ring around the rosy, A pocket full of posies, Ashes … ashes, We all fall down.

A familiar nursery rhyme that children have recited as a harmless play song for generations

ironically refers to one of Europe's most devastating diseases. The bubonic plague, better known as the “The Black Death,” has existed for thousands of years. The first recorded case of the plague was in China in 224 B.C.E. But the most significant outbreak was in Europe in the mid-fourteenth century. Over a five-year period from 1347 to 1352, 25 million people died. One-third to one-half of the European population was wiped out!

Yellow fever

Yellow fever (YF) is a viral haemorrhagic fever transmitted by infected mosquitoes. Yellow fever can be recognized from historic texts stretching back 400 years. Infection causes a wide spectrum of disease, from mild symptoms to severe illness and death. The "yellow" in the name is explained by the jaundice that affects some patients, causing yellow eyes and yellow skin. There are three types of transmission cycle: sylvatic, intermediate and urban. All three cycles exist in Africa, but in South America, only sylvatic and urban yellow fever occur.

Sylvatic (or jungle) yellow fever occurs in tropical rainforests where monkeys, infected by sylvatic mosquitoes, pass the virus onto other mosquitoes that feed on them; these mosquitoes, in turn bite and infect humans entering the forest. This produces sporadic cases, the majority of which are often young men working in the forest e.g. logging. The intermediate cycle of yellow fever transmission occurs in humid or semi-humid savannahs of Africa, and can produce small-scale epidemics in rural villages. Semi-domestic mosquitoes infect both monkey and human hosts and increased contact between man and infected mosquito leads to disease. This is the most common type of outbreak seen in recent decades in Africa. Urban yellow fever results in large explosive epidemics when travellers from rural areas introduce the virus into areas with high human population density. Domestic mosquitoes, most notably Aedes aegypti, carry the virus from person to person. These outbreaks tend to spread outwards from one source to cover a wide area. Yellow fever can be prevented by vaccination. In order to protect people living in areas at high risk of yellow fever transmission, WHO's dual strategy for prevention of yellow fever epidemics relies on preventive mass immunization campaigns followed by infant routine immunization. Yellow fever causes epidemics that can affect 20% of the population. When epidemics occur in unvaccinated populations, case-fatality rates may exceed 50%. No treatment beyond supportive care exists. For more information

DefinitionTyphoid fever is an infection that causes diarrhea and a rash -- most commonly due to a type of bacteria called Salmonella typhi (S. typhi).

Alternative NamesEnteric fever

Causes, incidence, and risk factorsThe bacteria that cause typhoid fever -- S. typhi -- spread through contaminated food, drink, or water. If you eat or drink something that is contaminated, the bacteria enter your body. They travel into your intestines, and then into your bloodstream, where they can get to your lymph nodes, gallbladder, liver, spleen, and other parts of your body.

Yellow Fever vaccine side-effects What are the risks from Yellow Fever vaccine? A vaccine, like any medicine, could cause a serious reaction. But the risk of a vaccine causing serious harm, or death, is extremely low. Mild Problems Yellow fever vaccine has been associated with fever, and with aches, soreness, redness or swelling where the shot was given. These problems occur in up to 1 person out of 4. They usually begin soon after the shot, and can last up to a week.

The Black Death: Bubonic Plague In the early 1330s an outbreak of deadly bubonic plague occurred in China. The bubonic plague mainly affects rodents, but fleas can transmit the disease to people. Once people are infected, they infect others very rapidly. Plague causes fever and a painful swelling of the lymph glands called buboes, which is how it gets its name. The disease also causes spots on the skin that are red at first and then turn black.