The world is filled with microbes that infect and sicken humans. Some cause illnesses that are easy to transmit, but prove more annoying than serious. Others are life threatening, but hard to contract. A few are unfortunately both deadly and easily transmitted. The common link shared by all communicable diseases is that they are caused by microorganisms called pathogens. There are three major groups of pathogens that cause communicable disease: bacteria, viruses, and fungi.

 

 

 

Causes of Diseases

Bacteria

An infected tick can bite a person and transmit Lyme disease

Bacteria are very simple pathogens. Diseases caused by bacteria can be treated with antibiotics. There are three major types of bacteria, classified by their shape: cocci, bacilli, and spirilla. Although there are several thousand known species of bacteria, just more than one hundred cause disease in humans. In many cases, it is not the bacteria that directly cause disease but the toxins produced by the bacteria.

The following are the most common bacterial infections:

• Strep throat
• Pink eye (conjunctivitis)
• Gonorrhea
• Meningitis
• Pneumonia
• Tuberculosis
• Staph infections
• Lyme disease

Viruses

Viruses are the smallest known pathogens, approximately 1/500th the size of bacteria. More than 150 viruses are known to cause disease in humans. Viruses can invade the body and then use the host's cells as genetic material to replicate. The duplicate cells are then released to infect other host cells.

Viral infections can be difficult to treat because many viruses can withstand heat and powerful drugs. Antibiotics cannot kill viruses. In the United States, vaccinations are given to help people produce the antibodies needed to fight specific viruses.

Some common viral infections include:

• Common cold
• Influenza
• Chicken pox
• Measles
• Rabies
• Mononucleosis
• Herpes
• Hepatitis
• AIDS

 

Fungi

Fungi are pathogens capable of a wide range of infections. The most common disease-causing fungi invade mainly deep tissues of the hair, nails, and skin, and cause infections of the scalp and feet. Many fungi are useful to humans, such as edible mushrooms, penicillin, and yeast used to make bread. Most fungal diseases are treated by keeping the affected area clean and dry. Appropriate medications will generally provide prompt relief.

Some types of fungal infections include:

• Athlete's foot
• Ringworm
• Jock itch
• Yeast infections (caused by Candida)

 

Defending Against Invaders

Each day your body is exposed to countless germs. To protect itself against these germs, your body takes action to repel, trap, or destroy them. In fact, it has natural barriers that keep germs out, or destroy them before they can do any damage.

The Body's Major Barriers Against Germs
Skin	Covers your body and acts as a protective barrier
Mucous membranes	Tissues that line your mouth, nose, throat, eyes, and other body parts; coughing and sneezing gets rid of germs trapped by these membranes
Saliva	Located in your mouth; destroys many harmful organisms
Tears	Wash away germs; contain chemicals that kill some harmful organisms
Stomach acid	Located in your stomach; kills many germs

Protecting Against Disease

Although it is possible to contract communicable diseases, there are several steps you can take to lessen the chances. In this interactivity, you will explore various tips about protection against diseases. Click the player button to begin.

View a printable version of this interactivity.

 

 

 

Sexually Transmitted Diseases

Sexually transmitted diseases affect people of all backgrounds and socioeconomic levels. There are more than twenty different types of sexually transmitted diseases (STDs) known today. Some STDs can be cured with appropriate medications. Other STDs, however, are incurable. Therefore, protecting yourself is imperative to your health.

Sexually transmitted diseases affect men and women of all backgrounds and socioeconomic levels.

According to the Centers for Disease Control (2016), approximately 20 million new cases of STDs are reported in the United States each year. Young adults between 15 and 24 years old account for half of these cases.

Take a moment to read the chart below to learn how sexually transmitted diseases differ from most other communicable diseases.

Ways STDs Differ From Most Other Communicable Diseases
1	Most STDs can spread only through sexual contact, especially sexual intercourse.
2	A person infected with an STD may not have visible symptoms, or may have symptoms that disappear and then reappear.
3	Having an STD once does not make you immune in the future.
4	STDs can cause infertility.
5	STDs can be prevented by avoiding sexual activity; protective measures during sexual activity can lessen the chance of contracting an STD.

Many people who think they may have an STD delay seeking medical attention. Some feel embarrassed, and others hope that the symptoms will somehow go away. Postponing medical treatment, however, is dangerous. Prompt diagnosis and treatment is the first step toward curing or controlling a contracted STD and preventing its spread to others.

Common STDs include:

• Chlamydia
• Gonorrhea
• Genital herpes
• Syphilis
• Genital warts
• Human Papillomavirus (HPV)
• Pubic lice
• Pelvic inflammatory disease (PID)
• Human immunodeficiency virus (HIV)
• Acquired immunodeficiency syndrome (AIDS)

 

The Spread of Communicable Diseases

Communicable diseases are defined not only by the pathogen responsible for the disease, but also by the process through which the pathogen can infect people. In this interactivity, you will see how infectious pathogens are spread. Click the player button to begin.

View a printable version of this interactivity.

 

Communicable Diseases Review

Now that you have learned a bit about communicable diseases, review your knowledge in this non-graded activity. Click the player button to get started.