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Epidemics and Pandemics

• Infected food and water - One way an epidemic can begin is if the food or water gets infected with a disease. If the local water supply of a city gets infected, then a number of people of the city will become sick, starting an epidemic.
• Changes or mutations in the pathogen - Sometimes the pathogen that causes a disease may change and become more contagious. This means that it can more easily infect people and make them sick.
• Introduction of a new disease - Many epidemics begin when a new disease is introduced to a population. This occurred when the Europeans brought smallpox to the Americas killing as much as 90% of the native population.
• Lower resistance to a disease - Sometimes famine and poor nutrition can cause a population to have lower resistance to a disease causing an epidemic.
• Natural disasters and wars - Natural disasters and wars can trigger the start of epidemics by causing infected water, bringing in new diseases, and lowering the resistance to disease of the population.

• Insects - Insects can carry diseases and transmit them from person to person. Examples of insect-borne diseases include the bubonic plague and malaria.
• Airborne transmission - Infection can also travel through the air, usually when a person coughs or sneezes. Examples of airborne diseases include influenza, measles, and tuberculosis.
• Foods and water - Some diseases can be spread through infected food or water. Examples include cholera, dysentery, and typhoid fever.

• Fewer hosts - When an epidemic first starts out it can attack the weakest and most susceptible people. These people may die or survive. If these people survive they may build up immunities to the disease. Over time, the disease finds fewer and fewer hosts it can easily attack. Eventually the epidemic slows down and comes to an end.
• Seasonal - Some diseases are seasonal. The flu, for example, is spread more easily during the winter and tends to die out come spring time.
• Fewer carriers - Sometimes the carriers of the disease may become inactive. An example of this is malaria that is transmitted by mosquitoes. Mosquitoes become inactive during the cold weather or winter.

1. The virus is found in animals, but not in humans.
2. The virus has been found in humans.
3. There are small clusters of the disease found, but it is not spreading rapidly.
4. The virus is being passed from human-to-human and there are community outbreaks of the disease.
5. The virus has spread to at least two countries. A full-fledged pandemic is imminent.
6. The disease is now classified as a full-fledged pandemic.

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