Health At The End Of The Millennium
Another Wired Curriculum from The United Nations CyberSchoolBus
Transmission of Infectious Diseases
We are told to cover our mouths when sneezing or coughing. We are told not to share a glass with someone who's sick. We are told to wash our hands before coming to the table and not to eat food that has been dropped on the floor. Why?
The reason is simple: by following these rules we are preventing disease-
At the same time, there is no need for exaggerated alarm. Not all diseases are as easily transmitted as, say, influenza. And not all diseases are transmitted in the same way.
Here are some of the ways in which major infectious diseases get transmitted to people.
If not careful, people can transmit certain types of infections to each other.
People can pass on infectious diseases to others through droplets of moisture produced when coughing or sneezing. These droplets can carry certain microbes. Influenza is a virus transmitted by droplets. A more dangerous one is tuberculosis, one of the re-emerging diseases.
Direct contact and bodily fluids
There other infectious diseases that can be passed on from one person to another but not simply through droplets. Polio and leprosy are passed on through direct contact. Some diseases, such as HIV/AIDS, can be transmitted sexually. Others, such as hepatitis, are passed on through blood.
Both food and water, if contaminated, can transmit infectious diseases to humans.
Waterborne diseases are a serious problem in poorer areas of the world where lack of safe water contributes to spreading infectious diseases such as cholera, dysentery and typhoid. The biggest danger comes from diarrhoeal diseases which are caused by contaminated water and food and kill up to 3 million people, mostly children, every year.
Like water, contaminated food can carry bacteria that cause diarrhoeal diseases. A number of other bacteria are transmitted by food only. Most significant among these are salmonellae, campylobacter and Escherichia coli. These are present all over the world. Estimates for food borne diseases in the United States range from 6.5 million to 80 million cases a year.
Many insects carry viruses and protozoans which they transmit to humans (these insects are called 'vectors'). Of these, the mosquito is the greatest menace.
Mosquitos can spread an astonishing range of diseases: malaria, dengue and yellow fever are three examples. These three together are responsible for several million deaths a year.
Other insects carry diseases too: household bugs cause Chagas disease, fleas carry the plague, and tse-tse flies spread sleeping sickness.
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