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How Are Diseases Transmitted?

Overview

Infectious diseases are transmitted from person to person by direct or indirect contact. Certain types of viruses, bacteria, parasites, and fungi can all cause infectious disease. Malaria, measles, and respiratory illnesses are examples of infectious diseases.

Simple preventative measures, such as frequent hand washing, can cut down on disease transmission.

Direct contact

Infectious diseases are often spread through direct contact. Types of direct contact include:

1. Person-to-person contact

Infectious diseases are commonly transmitted through direct person-to-person contact. Transmission occurs when an infected person touches or exchanges body fluids with someone else. This can happen before an infected person is aware of the illness. Sexually transmitted diseases (STDs) can be transmitted this way.

Pregnant women can also transmit infectious diseases to their unborn children via the placenta. Some STDs, including gonorrhea, can be passed from mother to baby during childbirth.

2. Droplet spread

The spray of droplets during coughing and sneezing can spread an infectious disease. You can even infect another person through droplets created when you speak. Since droplets fall to the ground within a few feet, this type of transmission requires close proximity.

Indirect contact

Infectious diseases can also be spread indirectly through the air and other mechanisms. For example:

1. Airborne transmission

Some infectious agents can travel long distances and remain suspended in the air for an extended period of time. You can catch a disease like measles by entering a room after someone with measles has departed.

2. Contaminated objects

Some organisms can live on objects for a short time. If you touch an object, such as a doorknob, soon after an infected person, you might be exposed to infection. Transmission occurs when you touch your mouth, nose, or eyes before thoroughly washing your hands.

Germs can also be spread through contaminated blood products and medical supplies.

3. Food and drinking water

Infectious diseases can be transmitted via contaminated food and water. E. coli is often transmitted through improperly handled produce or undercooked meat. Improperly canned foods can create an environment ripe for Clostridium botulinum, which can lead to botulism. 

4. Animal-to-person contact

Some infectious diseases can be transmitted from an animal to a person. This can happen when an infected animal bites or scratches you or when you handle animal waste. The Toxoplasma gondii parasite can be found in cat feces. Pregnant women and people with compromised immune systems should take extra care (disposable gloves and good hand washing) when changing cat litter, or avoid it altogether.

5. Animal reservoirs

Animal-to-animal disease transmission can sometimes transfer to humans. Zoonosis occurs when diseases are transferred from animals to people. Zoonotic diseases include:

6. Insect bites (vector-borne disease)

Some zoonotic infectious agents are transmitted by insects, especially those that suck blood. These include mosquitos, fleas, and ticks. The insects become infected when they feed on infected hosts, such as birds, animals, and humans. The disease is then transmitted when the insect bites a new host. Malaria, West Nile virus, and Lyme disease are all spread this way.

7. Environmental reservoirs

Soil, water, and vegetation containing infectious organisms can also be transferred to people. Hookworm, for example, is transmitted through contaminated soil. Legionnaires’ disease is an example of a disease that can be spread by water that supplies cooling towers and evaporative condensers.

How to prevent disease transmission

Because infectious diseases can spread through direct or indirect contact, everyone is at risk of illness. You have a higher risk of becoming ill when you’re around sick people or in areas susceptible to germs. If you work in or visit a care center, a day-care center, a hospital, or a doctor’s office, take extra precautions to protect yourself.

1. Illness

Something as simple as touching a doorknob, elevator button, light switch, or another person’s hand increases the likelihood of coming in contact with germs that can make you sick. The good news is that a few simple precautions can prevent some disease transmission. For example, make sure you wash your hands frequently and thoroughly. Use soap and warm water and vigorously rub your hands together for at least 20 seconds. If you can’t wash your hands, use an alcohol-based hand sanitizer. Washing your hands is the gold standard though!

Other tips to prevent the spread of disease in areas with germs include:

  • wash your hands or use hand sanitizer before handling food and after shaking hands
  • always wash with soap and water if your hands are visibly soiled
  • try to minimize touching your mouth or nose with your hands
  • avoid sick people, if possible
  • wear disposable gloves to avoid contact with blood and feces
  • use disposable gloves when caring for an ill person
  • cover your mouth when you sneeze and cough and wash your hands afterward
  • teach children not to put their hands or objects in their mouths
  • sanitize toys and changing tables

2. Foodborne illness

Dangerous organisms can thrive in improperly prepared food. Avoid cross-contamination by keeping raw meats and produce separate. Use different preparation surfaces for raw meats and wash surfaces and utensils thoroughly. 

Freeze or refrigerate perishable foods and leftovers promptly. According to the United States Department of Agriculture, you should set your refrigerator to 40°F (4°C) or below and your freezer to 0°F (-18°C) or below. Cook meats to a minimum internal temperature of 145°F (63°C). Cook ground meats to 160°F (71°C) and poultry to 165°F (73°C).

Be careful about sources of food when visiting foreign countries.

3. Insects and animals

When camping or enjoying wooded areas, wear long pants and long sleeves. Use insect repellent and mosquito netting. Don’t touch animals in the wild. Don’t touch sick or dead animals.

4. Vaccinations

Stay up to date on vaccinations, especially when traveling. Don’t forget to keep your pet’s vaccinations current, too.

Vaccinations can drastically reduce your risk of becoming ill with some infectious diseases. If you can avoid a particular disease, you can also prevent the spread of the disease. There are different types of vaccinations, such as those to prevent:

  • measles
  • mumps
  • influenza
  • human papillomavirus

Speak with your doctor to discuss the benefits and risks of these and other vaccinations.

The takeaway

Infectious diseases are caused by types of bacteria, viruses, parasites, and fungi around us. It’s important to understand how these diseases are transmitted. If you understand the transmission process, you can use this knowledge to protect yourself and help prevent the spread of illnesses. 

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