Key Concepts:
Vocabulary: communicable disease, infection, virus, bacteria, toxins, vector
Understanding Communicable Diseases
Understanding the Causes of Communicable Diseases
Main Idea: Communicable diseases are caused by several kinds of microorganisms.
You’ve probably “caught” an illness from someone before. The illness you contracted was a communicable disease, adisease that is spread from one living organism to another or through the environment. Such illnesses are also known ascontagious and infectious diseases.
Communicable diseases can occur when pathogens, micro-organisms that cause disease, enter your body. If your body does not fight off the invaders quickly and successfully, you develop an infection, a condition that occurs when pathogens i~ the body multiply and damage body cells. Figure 23.1 lists diseases caused by common pathogens, which include viruses, bacteria, fungi, protozoa, and rickettsias.
Viruses
Two of the most common communicable diseases-the cold and the flu are caused by viruses. A virus is a piece ofgenetic matenal surrounded by a protein coat. In order to reproduce, viruses invade the cells of living organisms.
Once a virus has penetrated a cell, it begins to multiply. The new viruses burst out of the cell and start taking over 0ther cells. As the virus multiplies and spreads disease sets in, and the body’s immune system jumps into action. Usually, the virus runs its course and is killed by the immune system. Antibiotics do not work against viruses, but can sometimes treat the symptoms of a virus.
Bacteria
Bacteria are single-celled microorganisms that live almost everywhere on earth. Most bacteria are harmless. Some are even helpful, like the ones that help you digest food. Unfortunately, some bacteria do cause diseases.
Disease-causing bacteria can produce toxins, substances that kill cells or interfere with their functions. Unlike diseases caused by viruses, a bacterial disease can often be treated with antibiotics. However, because of the overuse of these drugs, some bacteria have become resistant to antibiotics as they have evolved.
Other Pathogens
Other types of organisms that can cause communicabIe diseases include the following:
How Diseases Spread
Main Idea: Diseases can be transmitted in a variety of ways.
Pathogens infect humans and other living things in a variety of ways. Knowing how diseases are transmitted is your first line of defense against them.
Direct Contact
Many pathogens are transmitted through direct contact with an infected person. This includes touching, biting, kissing, and sexual contact. Other transmission methods include
Indirect Contact
You dori’t have to be in direct contact with a person to become infected. Indirect contact can be just as dangerous.
Contaminated Objects If you touch a contaminated object (for example, a doorknob), you could pick up pathogens. The pathogens can enter your body if you then rub your eyes. To protect yourself, keep your hands away from your mouth, nose, and eyes, and wash your hands regularly.
Vectors Pathogens are often spread by a vector, an organism that carries and transmits pathogens to humans or other animals. Common vectors include flies, mosquitoes, and ticks. Diseases that spread this way, such as malaria, West Nile virus, and Lyme disease, are called vector-borne diseases.
Contamintated Food and Water
When food is improperly handled or stored, harmful bacteria can develop. This is true not only for meat and fish but for fruits and vegetables as well. Water supplies that become contaminated with human or animal feces can also cause illnesses such as hepatitis A.
Airborne Transmission
When an infected person sneezes or coughs, pathogens are released into the air as tiny droplets that can travel as far as lO feet. Even w~en the droplets evaporate, the pathogens may float on dust particles until they are inhaled. Other pathogens such as fungal spores are also small enough to spread this way. Diseases spread by airborne transmission include chicken pox, tuberculosis, influenza, and inhalation anthrax.
Taking Precautions
Main Idea: You can take steps to prevent infection.
There is no guaranteed way to avoid communicable diseases completely, but a few simple practices can dramatically reduce your risk. As you learn about these practices, think about how you can include them in your daily life.
Wash Your Hands
Washing your hands regularly with soap and warm water is the single most effective way to protect yourself from catching or spreading disease. Always wash your hands
before you eat.
after you use the bathroom.
after handling pets.
before and after inserting contact lenses or applying makeup.
after touching an object handled by an infected person.
Protect Yourself from Vectors
Some vector-borne diseases, such as West Nile virus and bird flu, are on the rise. To protect yourself, follow these steps
Wear pants and long-sleeved shirts to avoid insect bites.
Other Prevention Strategies
These additional strategies will also help reduce your risk of getting or spreading communicable diseases:
• Avoid sharing personal items, such as eating utensils.
• Handle food properly.
• Eat well and exercise. Getting the nutrients your body needs and staying fit will help you fight against infection.
• Avoid tobacco, alcohol, and other drugs.
• Abstain from sexual contact.
• Cover your mouth when you cough or sneeze, and wash your hands after using a tissue.
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