Cedars Sinai Marina del Rey Hospital Alert: COVID-19 (CORONAVIRUS) information for patients and visitors LEARN MORE >>

What causes infectious diseases? Do these spread from one person to another?

These diseases range from common infections such as cold, flu, sore throat, bronchitis, laryngitis to more lethal illnesses such as AIDS.

Viral infections are more contagious when compared to bacterial infections. Based on the disease-causing microorganism, infectious diseases spread through air, blood, insect food, water, and direct skin contact transmission.

Infectious diseases can be caused by microorganisms such as bacteria, viruses, parasites, or fungi. In our body live many microorganisms, most of them harmless or even necessary for the good functioning of our organism.

Causing agents of infectious diseases

  • Bacteria - one-cell organisms that can cause diseases of the respiratory system and urinary tract.
  • Viruses - smaller than bacteria and cause various diseases, from simple colds to severe ones like meningitis or AIDS.
  • Fungi - can cause infections of the skin, the eyes, the nervous, digestive, and respiratory systems.
  • Parasites - can be transmitted to humans from animals, mostly from animal feces or by insect bites. Parasites can also be transmitted from humans to humans.

How do infectious diseases spread?

Some microorganisms may cause various infectious diseases that can be passed from person to person. Other infectious diseases are transmitted by insects and other animals. The easiest way to get infected is by having direct contact with an infected human or animal.

The transmission can happen through direct contacts:

  • Human to human transmission can happen when an infected person coughs or sneezes on another person, or kisses another person. Infectious diseases can also spread with sexual contacts through the exchange of body fluids. The infected person who passes the germs may have no signs and symptoms of the disease, however, it can be a carrier and it can infect others.
  • Animal to human transmission can happen by being bitten or scratched by an infected animal, or by handling animal waste. Some of these infections can be severe or in extreme circumstances, even fatal. There are germs that rely on insect carriers - fleas, lice, ticks, mosquitoes — to move from host to host and cause severe diseases such as Lyme disease or malaria.
  • Mother to the unborn child - pregnant women may pass infectious diseases causing germs to their unborn babies. Some of these microorganisms can be transmitted through the placenta, breast milk, while the germs in the vagina can be passed to the baby during birth.

Infectious diseases can spread by indirect contact

Many of these microorganisms - bacteria, viruses, fungi, and parasites - can linger on objects including doorknobs, faucet handles, tabletops. Infectious diseases can also spread through contaminated water or food. This transmission allows germs to be passed to a number of people through a single source which can be a not properly cooked meat, not properly washed raw fruits or vegetables, not pasteurized juice fruits or milk, water, or ice cubes from an infected source.

Disclaimer: We do not assume responsibility for the use of the provided information or its interpretation. Our efforts are towards providing current and reliable information; however these should not be considered, or used as a substitute for diagnosis or treatment.

Source: https://www.cedars-sinai.edu/Education/Medical-Library/