More than 2,400 years ago, a sickness struck Athens. The disease is said to have killed up to one third of all Athenians, including their leader Pericles. The huge loss of life  helped to change the balance of power between Athens and its enemy, Sparta, in the ancient world. Historians say the sickness began in what is now Ethiopia. They say it passed through Egypt and Libya before it entered Greece. Knowledge of the disease has come mainly from the writings of the ancient Greek historian Thucydides, who survived it. So what caused the fall of Athens? Now, a study based on genetic  testing says it was probably typhoid   fever.  Greek researchers announced the results. Journal of Infectious Diseases published the findings online last week. Researchers from the University of Athens tested human remains from an ancient burial place in the Greek capital. The researchers collected genetic material from teeth. They say tests found genetic evidence similar to that of the modern-day Salmonella  . Manolis Papagrigorakis led the University of Athens team. He says the findings throw light on one of the most debated mysteries in medical history. Typhoid fever is a life-threatening disease that is common today in developing countries. Experts say there are more than 21,000,000 cases each year.  Typhoid can be spread by food or drink that has been handled by a person infected with the bacteria  that causes it. Bacteria in human waste can pollute water supplies. So water used for drinking or to wash food can also spread the infection. Hand washing is important to reducing the spread of typhoid. And there are vaccines   that can help prevent it. Some people recover but continue to carry the bacteria. These carriers can get sick again. And they may continue to infect others. Doctors can do tests to make sure the bacteria has left the body. How many ways of spreading the typhoid bacteria are mentioned in the text?
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