Infectious Diseases

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:

• New, potentially dangerous bacteria, viruses, fungi and parasites such as severe acute respiratory syndrome (SARS) or Ebola emerge more often.
• In addition to the continual discovery of new human pathogens, old infectious diseases are re-emerging. Natural genetic variations and adaptations allow new strains of previously recognised pathogens to evolve and become resistant to available antibiotics and other treatments. Influenza is an example of this.
• Population crowding and easy travel have changed the dynamics of disease transmission by bringing people into closer and more frequent contact with pathogens. This also makes us more vulnerable to the spread of infectious agents.
• According to the National Institute of Allergy and Infectious Diseases , human behavior plays an important role in the re-emergence of infectious diseases. Decreased compliance with vaccination policy has led to the re-emergence of diseases which were previously under control, such as measles. Furthermore, increased use of antimicrobial drugs and pesticides has led to the development of resistant pathogens, allowing many diseases that were formerly treatable with drugs to make a comeback.
• New attention has been placed on eradicated or rare infectious diseases such as smallpox and anthrax, due to bioterrorism. Bioterrorism is a form of warfare that uses specific microorganisms, such as harmful bacteria and viruses, to cause illness or death deliberately in people or animals. 

Types of Infection

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 of Infectious Diseases

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:

• Get vaccinated: Modern vaccines are among the most effective strategies to prevent disease and can drastically reduce your chances of contracting many diseases. Make sure to keep your recommended vaccinations up to date.
• Wash your hands: This is especially important before and after preparing food, before eating and after using the toilet.
• Stay home when you’re feeling ill: If you have a fever, the common cold, diarrhea, or are vomiting, don’t go to work where you can spread the infection.
• Don’t travel when you’re ill: Similarly, don't fly when you're ill. With so many people confined to a small area, you may infect other passengers on the plane.
• Get vaccinated before traveling overseas: If you're traveling out of the country, talk to your doctor about any special vaccinations you may need.
• Practice safe sex: Use protection, such as condoms, if you or your partner have a history of high-risk behavior or sexually transmitted infections.
• Prepare food safely: When preparing food, make sure you use clean utensils and keep counters and other kitchen surfaces clean. In addition, refrigerate any leftover food promptly.
• Don't share personal items: It is particularly important not to share your toothbrush, comb and razor.