Chapter 12: Lesson 12.1 Communicable Diseases

The term communicable means “able to be .” If a disease is communicable, that means it can be transmitted to you. In other words, a (also called an infectious disease) is a condition you can develop after coming into contact with living things or objects infected with the disease.

Twelve-year-old Dakota knows that such as the flu are different from diseases such as heart disease that he might inherit from his parents or grandparents. A communicable disease is one that he can “catch.” When his friend Tavon came to school with the flu last month, for example, Dakota ended up sick, too. Dakota cannot, however, catch heart disease.

In this lesson, you will learn about the causes of communicable diseases. You will also learn about common communicable diseases that you may encounter in your life. Finally, you will learn possible treatment methods for communicable diseases.

Understanding Communicable Disease

Common living things that you can see are called . You, your teacher, your , and the trees outside are all examples of organisms. Many living things, however, are too small to see with the naked eye. These are so small that you cannot even see them without the use of a microscope. Certain , known as , can cause communicable diseases (Figure 12.1). The term pathogen is a more scientific way of describing germs.

Pathogens are everywhere. They are so , however, that you cannot see them. Pathogens are only with a , which magnifies them, or creates a bigger image of them. These microscopic organisms influence human lives in many ways. Pathogens include .

Bacteria

are single-celled organisms that live in almost every place where life can thrive. Bacteria even the . In fact, so many bacteria live in the body that, of the several trillions of cells that make up your body, are bacterial cells.

You may find it scary that bacteria are nearly everywhere. The good news is that most bacteria are helpful. For example, the bacteria found in your body help the function efficiently. These bacteria also prevent harmful bacteria from thriving in your body. The bad news is that certain varieties of bacteria can cause different kinds of . Some of these illnesses may be minor, while others can be quite serious and even deadly.

One type of bacteria that can cause disease is . E. coli bacteria in healthy people’s and animals’ . There are different varieties of E. coli bacteria, however. Some varieties are harmless, while others can cause . Exposure to harmful E. coli bacteria can occur from eating contaminated food, such as , or drinking (Figure 12.2). If you get sick from food poisoning, you may develop symptoms such as diarrhea, nausea, fever, and vomiting.

Another common type of bacteria, , is present in about of people’s . The bacteria S. aureus often does not cause any harm. It can, however, spread to others through contact with contaminated hands. Sometimes, S. aureus causes (skin and soft tissue infections). Anyone can get a staph infection, especially if you have a cut or scratch. People with chronic diseases and are at greater risk of developing a more serious staph infection.

Viruses

are very different from in your body. Viruses are much smaller than bacteria, and they are completely incapable of doing anything cells can do on their own. Viruses on other cells for . In fact, every virus must live inside a cell and use that cell’s resources and energy to grow and reproduce.

Viruses must be inside another living organism to thrive. Though viruses can stay on surfaces for a short time, they will die quickly if they do not find an organism in which to live. Once inside the body, a virus invades a person’s cells and multiplies quickly.

(singular—fungus) are , plant-like microorganisms that thrive in damp, warm places. These are much more complex than and . Examples of fungi include . A fungus cannot produce its own food, so it receives nourishment from plants, foods, and animals.

Like bacteria, few fungi , and many are beneficial. For example, the mold known as Penicillium notatum makes the life-saving drug , an antibiotic that controls bacterial infections. Other fungi, however, damage crops and stored foods. A few fungi cause infections, or mycoses, in humans. , athlete’s foot, and jock itch are common fungal infections. People with weakened immune systems may be more likely to contract a fungal infection.

Protozoa

are organisms that live nearly everywhere, and only a few cause diseases. Many kinds of protozoa form the basis of , providing nutrients for other organisms. Certain protozoa, however, cause some of the world’s most feared diseases. These include , a dangerous flu-like illness, and , a severe intestinal infection. Protozoa thrive in , and typically spread through contaminated water.

Common Communicable Diseases

For a disease to be , it must be able to from one source to another. causing communicable diseases may travel by various methods of transmission (Figure 12.4). A method of is simply the way a disease gets from one organism or object to another. Methods of transmission are either , depending on how the transmission occurs.

is the movement of a pathogen from a person with a communicable disease to a susceptible person. A person who is susceptible to a disease is likely to be easily affected or harmed by it. A person who has a may be more to a disease than someone with a healthy immune system.

is the movement of a pathogen to a susceptible person through a source that acts only as a disease carrier. In this case, the carrier is simply moving a pathogen from one source to another. diseases are a type of indirect transmission passed by mosquitoes, ticks, fleas, lice, and flies.

There are many examples of communicable diseases. You will likely encounter one or more communicable disease during your life. Some common communicable diseases include Lyme disease, West Nile virus disease, influenza, mononucleosis, tonsillitis, and conjunctivitis.

Lyme Disease

is a bacterial infection transmitted by infected ticks. Early signs and symptoms include a “bulls-eye” circular rash, , headache, and . Lyme disease can be treated with . Untreated, the infection can cause inflammation of joints, heart, nerves, brain, and spinal cord; paralysis of face muscles; fluttering heartbeat; and shortness of breath. To prevent Lyme disease, use and remove ticks promptly.

West Nile Virus (WNV) Disease

disease (WNV) is a viral infection transmitted by . Most people with WNV show no symptoms. Some people develop a , body aches, joint pains, vomiting, diarrhea, or rash. Rarely, people develop severe WNV, which can cause convulsions, paralysis, , and . No vaccine or specific treatments for WNV are available. Medications can reduce fever and relieve some discomfort. People with severe WNV are often hospitalized. To prevent WNV, wear long sleeves and pants, use insect repellant, stay indoors when mosquitoes are most active, and eliminate sources of standing water.

Tonsillitis

A virus or bacterium may cause , which is an infection that affects the (Figure 12.5). The tonsils usually the body from . Sometimes, however, the tonsils become infected.

Symptoms of include , fever, , and voice changes. If you think you have tonsillitis, you should contact a doctor. Often, the best treatment for tonsillitis is getting lots of rest and drinking plenty of fluids.

Conjunctivitis

, also known as , is a viral or bacterial infection that causes inflammation of the conjunctiva in the eye. The conjunctiva is the tissue that and inner surface of the eyelid. of the conjunctiva results in itchiness and a red or pink appearance, which gives this condition its name (Figure 12.6).

If pinkeye is the result of a , treatment typically involves the application of to the affected eye. If the infection is viral, however, antibiotics will not work. A viral infection will run its course and go away as the body fights it.

COVID-19

is a serious and contagious that first occurred in China during December 2019. The disease quickly spread to other countries and became a pandemic. Scientists soon discovered the disease was caused by a new virus they named , also called or novel coronavirus.

Signs and symptoms of COVID-19 include fever, cough, fatigue, muscle aches, nausea, and vomiting. These signs and symptoms may develop up to . Severe illness is characterized by difficulty breathing, wheezing, and pneumonia. primarily through contact with produced by coughing, sneezing, breathing, and talking. A person may contract the virus by inhaling these droplets or touching them and then touching the nose, eyes, or mouth. People can transmit the virus before or without developing symptoms at all.

In response to the pandemic, scientists worked to develop a COVID-19 vaccine, as well as other effective treatments. The FDA authorized the first COVID-19 vaccine for use in December 2020.

Treating Communicable Diseases

Treatment methods for infections vary depending on the type of infection. To , many doctors such as penicillin or amoxicillin. Antibiotics are substances that target and kill pathogenic, or harmful, bacteria.

While antibiotics are generally very effective, some pathogenic bacteria have developed antibiotic resistance. This means certain antibiotics are ineffective against them. Antibiotic resistance is a growing issue. The best way to avoid contributing to it is to take antibiotics exactly as instructed by a doctor.

While antibiotics generally work well to treat bacterial infections, they do not work against viruses, fungi, and protozoa. cure a , but some medications can help treat the symptoms, such as a fever and body aches. The best treatment methods for viral infections include rest, good nutrition, and fluids to strengthen the body so it can fight the virus.

To treat , doctors often prescribe or creams that are applied directly to the infected area. Doctors may also prescribe medications to treat infections caused by protozoa. These medications are determined on a case-by-case basis, depending on the type of illness and the person’s symptoms and overall health.