A communicable disease is one that spreads from one person or animal to another or from a surface to a person. They are the result of pathogens, such as viruses and bacteria. Communicable diseases include colds and flu.

Communicable diseases can transmit through contact with bodily fluids, insect bites, contaminated surfaces, water, and foods, or through the air.

This article will discuss communicable diseases, their symptoms, and how to avoid them.

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A communicable disease is any disease that passes between people or animals. People sometimes refer to communicable diseases as “infectious” or “transmissible” diseases.

Pathogens, including bacteria, viruses, fungi, and protozoa, cause communicable diseases.

Learn more about the different types of pathogens here.


Once a pathogen has entered a person’s body, it often will begin replicating. The individual may then begin to experience symptoms.

Symptoms will vary depending on the disease. Some people will not experience any symptoms. However, they can still transmit the pathogen.

Some symptoms are a direct result of the pathogen damaging the body’s cells. Others are due to the body’s immune response to the infection.

Some communicable diseases may be mild, and symptoms pass after a few days. However, some can be serious and potentially life threatening. Symptom severity may vary depending on a person’s overall health and immune function.

Four main types of pathogens cause infection: Viruses, bacteria, fungi, and protozoa.


Viruses are tiny pathogens that contain genetic material. Unlike other pathogens, they lack the complex structure of a cell.

To replicate, they must enter the cells of other living beings. Once inside, they use the cell’s machinery to make copies of themselves.


Bacteria are microscopic, single-celled organisms. They exist in almost every environment on earth, including inside the human body.

Many bacteria are harmless, and some help the body to function. However, bacteria can also cause infections that damage the body.


Fungi are a type of organism that includes yeasts, molds, and mushrooms. There are millions of different fungi. However, only around 300 cause harmful illnesses.

Fungal infections can occur anywhere in the body. However, they commonly affect the skin and mucus membranes.


Protozoa are microscopic organisms that typically consist of a single cell.

Some protozoa are parasitic, meaning they live on or inside another organism and use the organism’s nutrients for their own survival. Parasitic protozoa can cause various diseases.

Learn more about parasitic infections here.

Common viral, bacterial, fungal, and protozoa diseases include:


Rhinoviruses are a group of viruses that are the most common cause of the common cold. Symptoms of a cold may include:

A person can catch a rhinovirus by inhaling contaminated droplets from the cough or sneeze of another person.

Similarly, rhinoviruses are spread by people touching their nose, eyes, or mouth after touching items or surfaces that have come into contact with the virus.


Coronaviruses are a large group of viruses that affect the respiratory system. This family includes the SARS-CoV-2 virus. Some coronaviruses can cause common cold and flu symptoms, while others can cause more severe outcomes.

Coronavirus resources

For more advice on COVID-19 prevention and treatment, visit our coronavirus hub.

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Influenza viruses are infections that attack the respiratory system. Some potential symptoms include:

A person can catch influenza viruses in the same way they may catch rhinoviruses.


HIV attacks the immune system of its host. This makes the person vulnerable to other infections and diseases. A person can contract HIV as a result of contact with blood or other body fluids containing the virus.

The symptoms of HIV may develop gradually and in stages. They can include:

The only way a person can be certain they have HIV is to have an HIV test.

Although there is no cure for HIV, medications can help to keep the virus under control or make it undetectable. Without such treatment, HIV can develop into AIDS.

Learn more about undetectable HIV here.

Other medications can help prevent a person from contracting HIV. People at high risk of HIV and those who believe they may have had exposure to it should speak with their primary healthcare professional about these options.

HIV and AIDS resources

For more in-depth information and resources on HIV and AIDS, visit our dedicated hub.

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Salmonella and Escherichia coli

Nontyphoidal Salmonella and Escherichia coli (E. coli) are two different types of bacteria that can infect the digestive system. Another form of salmonella, Salmonella typhi, can also cause typhoid.

They typically spread through contaminated foods, such as uncooked meats and eggs, unwashed fruits and vegetables, and contaminated water sources.

Salmonella can also spread through contact with live animals, including chickens, and through person-to-person contact.

Some symptoms of these infections include:


Tuberculosis (TB) is a bacterial infection that primarily attacks the lungs. It may cause the following symptoms:

A person can catch TB by inhaling tiny droplets or “aerosols” from the cough or sneeze of a person who has the infection.


Ringworm is a common fungal infection of the skin. The characteristic symptom of ringworm is a ring-shaped rash. It may be dry, scaly, or itchy.

People may contract ringworm through:

  • close contact with a person who has ringworm
  • sharing towels, bedding, or other personal items with a person who has ringworm
  • close contact with animals with ringworm, typically cats

Without treatment, ringworm may spread to other parts of the body.

Athlete’s foot

Athlete’s foot is a common fungal infection that affects the skin on the feet. It typically causes sore or itchy white patches between the toes.

People can contract athlete’s foot through direct contact with someone who has the fungus or surfaces that have been in contact with the fungus. For example, an individual might contract athlete’s foot after walking barefoot in locker rooms, showers, or swimming pools.


The protozoa Plasmodium genus causes the tropical disease malaria. The parasite primarily transmits through mosquito bites.

Malaria causes symptoms such as:

  • fever and chills
  • headaches
  • vomiting
  • diarrhea
  • muscle pains

Without proper treatment, malaria can be life threatening. Vaccination programs are also effectively protecting people from malaria fatalities.

Lyme disease

Lyme disease is a potentially serious infection that black-legged ticks can pass to humans. It is the most common carrier-spread disease in the United States.

The bacteria Borrelia burgdorferi causes the majority of Lyme disease cases. However, the bacteria Borrelia mayonii may also cause the disease.

Symptoms of Lym disease include:

  • headache
  • fatigue
  • fever
  • skin rash

Lyme disease can spread to the joints, heart, and nervous system if a person does not treat it.

Learn more about Lyme disease here.

A person may develop a communicable disease after becoming infected by the pathogen. This may happen through:

  • direct contact with a person carrying the pathogen
  • contact with bodily fluids containing pathogens
  • inhaling pathogen-containing droplets from another person’s cough or sneeze
  • receiving a bite from an animal or insect carrying the pathogen
  • consuming contaminated water or foods

People can reduce their risk of contracting or transmitting disease-causing pathogens by following the steps below:

  • washing their hands thoroughly and regularly
  • disinfecting surfaces at home often, especially doorknobs and food areas
  • disinfecting personal items such as phones
  • cooking meats, eggs, and other foods thoroughly
  • practicing good hygiene when preparing and handling food
  • avoiding eating spoiled food
  • avoiding touching wild animals
  • receiving available vaccinations
  • taking antimalarial medications when traveling where there is a malaria risk
  • check for ticks and other parasites

Some communicable diseases cause only mild symptoms that disappear without treatment. Others may cause severe symptoms or potentially life threatening complications.

Patients require different treatment depending on disease process and clinical presentation.

Viral infections

Vaccines are a highly effective method for preventing specific viral infections. There are several different types of vaccines.

When a person receives a vaccine, they are receiving a form of the virus. The immune system responds by producing antibodies capable of killing an active form of the virus in the future.

If a person already has a virus, they may require antiviral medications to keep the virus under control.

Bacterial infections

Bacterial infections can range from mild to life threatening. A person who has a bacterial infection may require a course of antibiotics to help control the infection. These medications can help to kill bacteria or slow them down so the immune system can counteract them.

However, many bacteria are developing a resistance to antibiotics, which poses a major health risk. More than 2.8 million antibiotic-resistant infections occur in the U.S. every year.

A person should only ever take antibiotics on a medical recommendation.

Fungal infections

A severe or chronic fungal infection may require prescription antifungal medications and, in rare cases, intravenous medication.

However, people can treat many mild infections, such as ringworm and athlete’s foot, with over-the-counter topical ointments.

Communicable diseases are diseases that can pass from person to person. The pathogens that cause these diseases can spread in various ways, such as through the air, contact with contaminated substances or surfaces, or from animal and insect bites.

Many communicable diseases cause mild symptoms that go away without treatment. Others require treatment to prevent them from becoming more serious.

There are steps a person can take to reduce their risk of contracting and transmitting disease-causing pathogens. These include receiving available vaccinations, practicing regular handwashing, and maintaining good hygiene at home.