What is Infection?

Questions and Answers

What is the term used to describe the process of a pathogen invading an organism and causing illness?

Infectivity

Immunity

Infection (correct)

Pathogenesis

Which of the following is an example of a non-living agent that can cause infection?

Fungi

Bacteria

Viruses (correct)

Parasites

What is the term used to describe the ability of a pathogen to invade and cause illness in an organism?

Immunity

Pathogenicity

Inoculation

Infectivity (correct)

Through which of the following routes can pathogens spread?

Through multiple routes, including blood, air droplets, mucous membranes, and others Signup and view all the answers

What is the term used to describe the spectrum of severity of infections?

Infection spectrum Signup and view all the answers

What is the primary cause of infectious diseases?

Invading pathogens Signup and view all the answers

What is the difference between infection and disease?

Infections are always caused by external agents, while diseases can be caused by internal factors Signup and view all the answers

What is the characteristic of opportunistic infections?

They are caused by normally harmless microorganisms Signup and view all the answers

What is the immune system's response to infectious disease?

It attacks a foreign agent, like a bacteria or virus Signup and view all the answers

What is the result of the immune system's attack on the body in autoimmune disease?

It mistakenly thinks some part of the body is a foreign invader and starts attacking it Signup and view all the answers

What is the main characteristic of prions?

They are infectious particles of misfolded proteins. Signup and view all the answers

What is the cause of rheumatoid arthritis?

An internal error in the immune system. Signup and view all the answers

What is the difference between an infection and a disease?

An infection is a causal factor, while a disease is a resulting imbalance. Signup and view all the answers

What is the common characteristic of all infectious diseases?

They are caused by the presence of harmful pathogens in the body. Signup and view all the answers

What is the result of the battle between the pathogen and the immune system during an infectious disease?

Damage accumulates on both sides of the fence, as pathogens produce toxic chemicals and damage cells and tissues, and immune cells produce toxic substances to kill pathogens but also damage self cells. Signup and view all the answers

Study Notes

Infection

Infection occurs when harmful agents, called pathogens, invade another organism and cause systemic or localized illness.
Pathogens can be living organisms (bacteria, fungi, parasites) or non-living agents (viruses, prions).
Pathogens can spread through various means, including blood, air droplets, mucous membranes, sexual intercourse, insect bites, a break in the skin, fomites, or any orifice.
Infections can be transmissible within the same species (intraspecies) or between different species (interspecies).
Not all infections are from interspecies or intraspecies contact; some infections come from environmental exposure, such as water, soil, or food.

Signs and Symptoms of Infection

Signs of infection depend on the pathogen and may include redness, swelling, fever, abscess formation, myalgias, malaise, diarrhea, vomiting, difficulty breathing, impairment of body systems, and changes in pulse and blood pressure.
Symptoms can be caused by the direct effects of pathogens or by the immune system's response to the pathogen.

Types of Infectious Agents

Parasites: eukaryotes that can be unicellular and microscopic or macroscopic multicellular worms, with complex lifecycles.
Bacteria: simple, single-celled, prokaryotic, microscopic organisms that multiply quickly by binary fission.
Viruses: non-living, nanoscopic, infectious particles of DNA or RNA protected by a protein shell, which commandeers host cells to produce more viral copies.
Fungi: eukaryotic, microscopic, unicellular organisms, such as yeasts, or macroscopic multicellular molds.
Prions: infectious particles of misfolded proteins that biochemically coax normally folded proteins to malfunction, not alive and cannot reproduce.

Disease

Disease occurs when some part of an organism cannot function properly, causing internal biochemical or structural imbalances with signs of illness.
Any perturbation in normal functioning or homeostatic imbalance with signs of illness can be categorized as a disease.
Diseases can be caused by internal processes (e.g., autoimmune reaction) or external factors (e.g., infectious microorganisms).
Examples of diseases include rheumatoid arthritis, Huntington's disease, cancer, type 2 diabetes, and strep throat.

Infectious Disease

Infectious disease occurs when infectious pathogens cause persisting localized or systemic symptoms.
Infectious diseases occur when a harmful agent enters the body and cells from the innate and adaptive immune system are unable to clear the agent quickly.
Signs and symptoms of infectious diseases vary based on the type of infectious agent, but most commonly involve fever, malaise, muscle pain, diarrhea, vomiting, and headache.

Examples of Infectious Diseases

Salmonella, caused by the food-borne bacteria Salmonella enterica.
Toxoplasmosis, caused by the parasite Toxoplasma gondii.
Schistosomiasis, caused by parasites like Schistosoma haematobium.
Scarlet fever, impetigo, or strep throat, caused by the bacteria Streptococcus pyogenes.
Legionnaires disease, caused by the bacteria Legionella pneumophila.
Meningococcal disease (meningitis or pneumonia), caused by the bacteria Neisseria meningitidis.
Human immunodeficiency viruses (HIV), caused by a type of Lentivirus.
Chicken pox, caused by the varicella-zoster virus.
Creutzfeldt-Jakob disease (CJD), caused by a prion.
Chlamydia, caused by the sexually transmitted bacteria Chlamydia trachomatis.

Disease vs. Infection

The difference between infection and disease is rooted in its etiology, or causal factor.
Infections and infectious diseases are always caused by invading pathogens contracted from other organisms or the environment.
Not all diseases are caused by pathogens; diseases can also be caused by internal processes or genetic mutations.
The immune system's response to infectious disease and noninfectious diseases is different.

Types of Disease

Infectious disease
Genetic disease
Metabolic disease
Autoimmune disease
Autoinflammatory disease
Allergic diseases
Neoplastic disease
Primary immune deficiency diseases

Opportunistic Infections

Opportunistic infections are caused by microorganisms that do not normally cause disease in a person with a properly functioning immune system.
Examples of opportunistic infections include Pneumocystis jirovecii pneumonia in someone with AIDS or an atypical Mycobacterium infection in someone with a primary immune deficiency.