Infectious diseases are among the leading causes of death worldwide. They are caused by microscopic organisms such as bacteria, viruses, parasites, fungi and protozoa.
The diseases can spread through contact between one person to another, as well as via animals and insect bites. Other infectious diseases are acquired by ingesting contaminated food or water or through exposures in the environment.
To learn more about infectious diseases and why they continue to affect so many people worldwide, read this section. There is also an overview on the different types of infection and the various ways these diseases are transmitted.
To prevent contracting infectious diseases, the single most important thing to do is to stay up to date with recommended vaccinations. For more tips of how to reduce your risk of infecting yourself or others, see Prevention.
Infectious diseases are caused by microscopic organisms such as bacteria, viruses, parasites, fungi and protozoa. These organisms penetrate the body’s natural barriers and multiply to create symptoms that can range from mild to deadly. The diseases can spread, directly or indirectly, from one person to another. They can also be transmitted through animals and insect bites. Others are acquired by ingesting contaminated food or water or other exposures in the environment.
Despite advances in the treatment and control of infectious diseases, humans continue to be vulnerable to a wide array of organisms and infectious diseases remain among the leading causes of death worldwide. The reasons for this include:
While some infections, such as measles, HIV and yellow fever, affect the entire body, others affect only one organ or system of the body. According to the Infectious Diseases Society of America , the most frequent local infections occur in the upper respiratory tract, such as the common cold. Other common sites of infection include the digestive tract, the reproductive and urinary tracts, the lungs, the eyes or ears. Local infections can cause especially serious illnesses if they affect vital organs such as the heart, brain or liver. They also can spread through the blood stream to cause a variety of symptoms.
The outcome of any infection depends on the severity of infectious agents, the number of organisms in the infecting inoculum and the response of the immune system. A compromised immune system, which can result from certain types of cancer treatment or diseases such as AIDS, may allow organisms that are ordinarily harmless to reproduce and cause life-threatening illness.
Transmission can occur in several different ways. Respiratory diseases are typically transmitted through the inhalation of airborne microbes spread by sneezing, coughing, talking and kissing. Sexually transmitted diseases are acquired through contact with bodily fluids, generally as a result of sexual intercourse. Alternatively, gastrointestinal diseases are usually transmitted through the consumption of contaminated food or water.
Other common ways in which infectious agents enter the body are through skin contact, bites from vectors such as ticks or mosquitoes that carry and transmit organisms, and transmission from mothers to their unborn children via the birth canal and placenta.
Follow these tips to decrease your risk of contracting or passing on an infectious disease: