Infectious Disease: Types, Causes & Treatments

Disorders produced by organisms, such as bacteria, viruses, fungus, or parasites, are known as infectious diseases. Our bodies are home to a variety of creatures. In most cases, they are beneficial or even safe. But certain microbes have the potential to cause disease in specific situations.

It is possible for some infectious diseases to spread from person to person. Others are spread by animals or insects. And you could contract others if you consume tainted food or water or come into contact with environmental organisms.

Infectious diseases: what are they?

Infectious diseases are illnesses brought on by pathogens—dangerous organisms—that enter your body from the outside. Infectious disease-causing pathogens include viruses, bacteria, fungus, parasites, and, in rare cases, prions. Infectious diseases can be contracted from other people, insect bites, contaminated food, drink, or soil.

Microorganisms like bacteria, viruses, fungus, parasites, and foot infections cause infectious diseases.

Based on the patient’s symptoms, the findings of the physical examination, and risk factors, doctors may suspect an infection. First, medical professionals ascertain if the patient is infected rather than suffering from another condition. For instance, contagious foot infections can be passed on by touch with surfaces like floors, towels, or clothing. Although it frequently starts between the toes, it can also affect your toenails and other body areas. Itching is the most typical symptom, although it can also result in a reddish, scaly rash, flaking or blistering between the toes, and other conditions and for instance, pneumonia could be present in a person with a cough and breathing issues (a lung infection). Instead of an illness, the person may instead be suffering from asthma or heart failure. A chest x-ray in this patient can assist medical professionals recognise pneumonia from the other potential illnesses.

Classifications of organisms

Depending on their size, metabolic makeup, or how they interact with the human host, the agents of infection can be categorised into many classes. Bacteria, viruses, fungus, and parasites are the types of organisms that cause infectious diseases.


A number of factors include:

  • Bacteria –  Infections with the urinary system, TB, and strep throat are all brought on by these one-celled organisms.
  • Viruses – The common cold and AIDS are among the many diseases caused by viruses, which are even smaller than bacteria.
  • Fungi – Fungi are the root cause of numerous skin conditions, including athlete’s foot and ringworm. Your brain system or lungs may contract an infection from different fungi.
  • Parasites – A mosquito bite releases a small parasite that causes malaria. Through animal excrement, humans may contract other parasites.

A direct exchange

Contact with a person or an infected animal is one of the most straightforward ways to contract most infectious diseases. Direct contact with an infected person can spread infectious diseases such as:

From one person to another. Direct transmission of bacteria, viruses, or other germs from one person to another is the most common way that infectious diseases are conveyed. This can happen if a person who isn’t affected touches, kisses, coughs, sneezes, or has the virus or bacteria on them.

Additionally, these pathogens can disperse through sexual contact and the exchange of bodily fluids. The person who spreads the infection may only be a carrier and not exhibit any signs of the illness.

From animal to human. Even a pet’s bite or scratch can make you ill and, in dire cases, even kill you if it’s an infected animal. Managing animal excrement can sometimes be dangerous. For instance, cleaning your cat’s litter box puts you at risk of contracting toxoplasmosis.

mother to a child in utero. An unborn child may contract infectious illnesses from a pregnant woman. Some pathogens can cross the placenta or enter breast milk. During delivery, a newborn may also receive vaginal germs.

Infection-related immune reaction

The clinical (visible) response to the initial invasion of a pathogenic (disease-causing) bacterium in the body might range from none at all to various degrees of nonspecific reactions to a specific infectious disease. Nevertheless, an immune response that serves as defense constantly occurs. When a person’s immune system is fully effective, there is no evident physical reaction; when it is only half effective, the person experiences symptoms but recovers from an infectious disease; and when it is ineffective, the person may become fatally ill and perish from the infectious process.

The two types of immunity

Every animal species has some level of built-in disease resistance. For instance, foot-and-mouth disease is very resistant to humans, yet it kills thousands of cattle and sheep with whom they may come into contact. Rats have a high level of resistance to diphtheria, whereas unimmunized children are very susceptible to the illness.

1. Immunization

In reaction to an organism infection or vaccination that involves administering a live or inactivated organism or its toxin orally or intravenously, antibodies are generated in the body. When administered alive, the organisms are somehow lab-attenuated so that they still trigger antibodies but don’t cause their typical sickness. Regardless of stimulation, the body’s antibody-making cells are still sensitive to the infectious agent and can react to it again by producing further antibodies. Therefore, a person is frequently rendered immune to a second attack of the disease after only one, providing the theoretical justification for active immunization by vaccines.

2. Diphtheria toxoid

The occurrence of the disease was drastically reduced in many regions of the world once diphtheria toxoid was developed in the early 20th century. The morbidity and mortality previously linked to diphtheria have been almost reduced thanks to primary prevention efforts that involve routine baby and child immunization across the community. Local outbreaks continue to happen despite the fact that the reported annual incidence of diphtheria has been largely stable since the 1960s.

Virus-based infectious illnesses that are common:

  1. Typical cold
  2.  a flu (influenza)
  3. COVID-19
  4. Abdominal flu (gastroenteritis)
  5. Hepatitis
  6. Syncytial respiratory virus (RSV)

Typical bacterial infections that cause these disease:

  1. Throat infection
  2. Salmonella
  3. Tuberculosis
  4. Coughing fit (pertussis)
  5. Sexually transmitted diseases such as chlamydia, gonorrhoea, dyskaryosis and others (STIs)
  6. Infections of the urinary tract (UTIs)
  7. E. coli
  8. Clostridial Difficulties (C. diff)

Common fungi-based infectious illnesses

  1. (Like athlete’s foot) Ringworm
  2. Nail fungus infections
  3. Candida vaginitis (vaginal yeast infection)
  4. Thrush
  5. Parasitic infections that are frequently spread by:
    1. Giardiasis
    2. Toxoplasmosis
    3. Hookworms
    4. Pinworms


An infectious disease’s cause determines how it should be treated. Bacterial illnesses: Antibiotics are typically used to treat bacterial infections. These drugs either eliminate bacteria or prevent them from procreating. Antibiotics can be administered intravenously (IV), orally (pill, capsule, or liquid), orally, topically (cream, drop, or IV line).

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