INFECTIOUS DISEASES

Infectious diseases are caused by microscopic organisms, including bacteria, viruses, fungi and animal parasites. These organisms penetrate the body’s natural barriers and multiply to create symptoms that can range from mild to deadly. Although progress has been made in eradication or control of many infectious diseases, humankind remains vulnerable to a wide array of new and resurgent diseases.

Types of Infection

Some infections, such as measles, malaria, typhus and yellow fever, affect the entire body. Other infections, however, affect only one organ or system of the body. The most frequent local infections, including the common cold, influenza-flu occur in the upper respiratory tract. Other common sites of infection include the digestive tract, the lungs, the reproductive and urinary tracts, and the eyes and ears. Local infections can cause serious illnesses if they affect vital organs such as the heart, brain or liver. They also can spread through the blood stream to cause widespread symptoms. The outcome of any infection depends on the number and virulence of infectious agents, and the response of the immune system. A compromised immune system, which can result from diseases such as AIDS or treatment of diseases such as cancer, may allow organisms that are ordinarily harmless to proliferate and cause life-threatening illness.

Modes of Infection

Common ways in which infectious agents enter the body are through skin-to-skin contact, inhalation of airborne microbes, ingestion of contaminated food or water, entry through broken skin, insect bites, sexual contact, and transmission from mothers to their unborn children via the birth canal and placenta.

Treatment

The development of antibiotics and other disease-fighting drugs has played an important role in the fight against infectious diseases, but some microorganisms develop resistance to the drugs used against them. Modern physicians should prescribe antibiotics carefully. The more widely these drugs are used, the more likely it is that antibiotic-resistant strains of microorganisms will emerge.

The problem is complicated by the rapid biological processes that result in the emergence of new, potentially dangerous bacteria, viruses, fungi and parasites, many of which may be resistant to available antibiotics and other treatments. Factors such as population crowding and easy travel also make us more vulnerable to the spread of infectious agents.

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