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How infectious diseases spread
Krishna: Infectious diseases spread from humans to humans, animals to humans (zoonotic diseases) , animals to animals in several ways.
Person to person spread
Image source: Harvard University
This is the most common way that we get an infectious disease. Germs can spread from person to person through: the air as droplets or aerosol particles, faecal-oral spread, blood or other body fluids, skin or mucous membrane contact, sexual contact.
Some infections can be spread in more than one way both in human beings and other animals.
Indirect contact: Coming into contact with areas where human beings and animals live and roam, or objects or surfaces that have been contaminated with germs. Examples include dining tables, being in the same place, aquarium tank water, pet habitats, chicken coops, barns, plants, and soil, as well as pet food and water dishes.
Vector-borne: Being bitten by a tick, or an insect like a mosquito or a flea.
Foodborne: Each year, several people get sick from eating contaminated food. Eating or drinking something unsafe, such as unpasteurized (raw) milk, undercooked meat or eggs, or raw fruits and vegetables that are contaminated with feces from an infected animal. Contaminated food can cause illness in people and animals, including pets.
Waterborne: Drinking or coming in contact with water that has been contaminated with feces from infected humans and animals.
Through contact with contaminated food or water : These diseases come from eating or drinking food or water contaminated with germs or their toxins. Often these infections are spread by the faecal-oral route. Examples of food- or water-borne diseases: listeria, typhoid,botulism.
Through faecal-oral spread: Some infections are spread when tiny amounts of faeces from an infected person are taken in by another person by their mouth. The germs may be passed directly from infected hands to the mouth or indirectly through objects, surfaces, food or water contaminated with poo. Examples of diseases spread this way: campylobacter,giardia,hepatitis A.
Airborne: With the recent COVID-19 pandemic, you may have become more conscious about the air you breathe and the surfaces you touch. Disease transmission can happen in different ways, but the most unpredictable method is via airborne transmission.
There are very few diseases that can be transmitted through the air. Airborne diseases linger in dust particles and respiratory droplets, which are eventually inhaled by other people. In fact, you don’t need to be in the same room as a sick person to contract an airborne disease.
Infections are spread when an infected person talks, coughs or sneezes and the small droplets they produce contain germs. The droplets travel a short distance before falling. The droplets may be breathed in by people who are near, or may fall and contaminate an object or surface. Spread can also occur by touching the nose or mouth with hands contaminated by the droplets. Examples of diseases spread by droplet:common cold,influenza (the flu),COVID-19.
Other infections are spread when an infected person talks, breathes, coughs or sneezes tiny particles that contain germs into the air. These are called small particle aerosols. Since these aerosol particles are tiny, they can stay suspended in the air for hours and be breathed in by other people. Examples of aerosol spread: chickenpox,measles,TB.
Through blood or other body fluids: Some infections are spread when body fluids such as blood, saliva, urine, faeces or semen come into direct contact with an uninfected person through kissing, sexual contact or through a needle stick injury. Examples of diseases spread through body fluids: hepatitis B, hepatitis C,HIV.
Through contact with skin or mucous membrane: Some infections are spread directly when skin or mucous membrane (the thin lining of parts of the body such as nose, mouth, genitals) comes into contact with the skin or mucous membrane of an infected person. Infections may be spread indirectly when the skin comes in contact with a contaminated object. Examples of diseases spread this way: head lice, conjunctivitis, ringworm.
Through sexual contact: Sexually transmitted infections (STIs) are most commonly transmitted by sexual contact. This means through vaginal, anal or oral sex. Examples of sexually transmitted infections are:chlamydia,gonorrhoea, syphilis.
Childbirth: Someone who is pregnant can pass a disease onto their child. This is called congenital transmission. Congenital disease transmission can happen even if the parent doesn’t know they have the disease.
Germs can spread to a baby through food that the parent eats at the time of childbirth, or from breastfeeding.
Disease Spread From Animals
Diseases often live and spread in animals and bugs. Some animal infections can also infect humans. Sicknesses that animals pass to humans are called zoonotic diseases.
Bites from infected animals. Some diseases are spread directly from animals to humans through bites or scratches. Others can be spread to humans by vectors, such as insects, that carry the infection from an animal to a human. These vectors include: Ticks, Mosquitoes, Fleas, Flies.
Contact with animals. Animals can spread diseases in other ways besides bites. Germs can spread through animals’ body fluids such as: Feces, Saliva, Blood, Urine, Vomit. Touching or petting animals can also spread disease. Fleas and germs may live in the fur they shed.
Contaminated environment: Some infectious diseases are not spread by contact with an infected person but by contact with an environmental source such as animals, insects or soil. Examples of diseases spread this way are: hydatids (animals), malaria (insect), dengue (insect), tetanus (soil), legionellosis (compost/soil).
Disease Spread From Objects: Many germs can survive on or inside non-living objects. Touching these objects and then touching your mouth, nose or eyes can make you sick. Some common items that spread disease include: Fruits and vegetables, Water, Kitchen utensils, Medical tools, High-touch surfaces like doorknobs, Body fluids from people or animals, Clothing, Bedsheets.
When we know how these infections spread we can also take care to stop these infectious diseases.
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