Microbial Symbiosis, Pathogen Reservoirs, and Disease Transmission in Infectious Diseases

Symbiosis

Means 'to live together'.

Mutualism

A type of symbiosis where both organisms benefit.

Commensalism

A type of symbiosis where one organism benefits and the other is neither helped nor harmed.

Amensalism

A type of symbiosis where one organism is harmed and the other is neither helped nor harmed.

Parasitism

A type of symbiosis where one organism benefits at the expense of the other.

Normal microbiota

Organisms that colonize the body's surfaces without normally causing disease.

Resident Microbiota

Microbiota that are a part of the normal microbiota and remain in the body throughout life.

Transient Microbiota

Microbiota that remain in the body for a short period and cannot persist due to competition, elimination, or changes in the body.

Opportunistic pathogens

Normal microbiota that cause disease under certain circumstances.

Reservoirs of infection

Sites where pathogens are maintained as a source of infection.

Animal reservoir

A type of reservoir where pathogens are maintained through direct contact with animals or their waste.

Human carriers

Asymptomatic infected individuals who can transmit pathogens.

Nonliving reservoir

Reservoirs such as soil, water, and food that can harbor pathogens.

Zoonoses

Diseases that are transmitted from animals to humans.

Tapeworm infestation

Caused by Dipylidium caninum, transmitted through ingestion of larvae in dog saliva.

Fasciola infestation

Caused by Fasciola hepatica, transmitted through ingestion of contaminated vegetation.

Malaria

Caused by Plasmodium spp., transmitted by the bite of Anopheles mosquito.

Toxoplasmosis

Caused by Toxoplasma gondii, transmitted through ingestion of contaminated meat, inhalation of pathogen, or direct contact with infected tissues.

Ringworm

Caused by Trichophyton spp. and Microsporum spp., transmitted through direct contact.

Anthrax

Bacterial disease caused by Bacillus anthracis, transmitted through direct contact with infected animals or inhalation.

Bubonic plague

Bacterial disease caused by Yersinia pestis, transmitted through flea bites from infected rodents.

Lyme disease

Bacterial disease caused by Borrelia burgdorferi, transmitted through tick bites from infected deer.

Salmonellosis

Bacterial disease caused by Salmonella spp., transmitted through ingestion of fecally contaminated water or food.

Rabies

Viral disease caused by Lyssavirus sp., transmitted through the bite of infected animals such as bats, skunks, foxes, and dogs.

Hantavirus pulmonary syndrome

Viral disease caused by Hantavirus sp., transmitted through inhalation of viruses in dried feces and urine from deer mice.

Yellow fever

Viral disease caused by Flavivirus sp., transmitted through the bite of Aedes mosquitoes.

Contamination

The mere presence of microbes in or on the body.

Infection

When organism evades body's external defenses, multiplies, and becomes established in the body.

Portals of Entry

Sites through which pathogens enter the body.

Parenteral route

Entry via the parenteral route circumvents the usual portals; pathogens deposited directly into tissues beneath the skin or mucous membranes.

Adhesion

Process by which microorganisms attach themselves to cells; required to establish colonies successfully within the host.

Virulence Factors

Factors that contribute to the ability of a microorganism to cause disease.

Pathogenicity

Ability of a microorganism to cause disease.

Virulence

Degree of pathogenicity.

Adhesion factors

Specialized structures or attachment molecules that aid in the adhesion of microorganisms.

Biofilms

Complex communities of microorganisms that adhere to surfaces.

Extracellular enzymes

Secreted by the pathogen; dissolve structural chemicals in the body and help maintain infection, invade, and avoid body defenses.

Toxins

Chemicals that harm tissues or trigger host immune responses that cause damage.

Toxemia

Refers to the presence of toxins in the bloodstream.

Exotoxins

Type of toxins that are secreted by bacteria and can cause damage to the host.

Endotoxins

Type of toxins that are part of the bacterial cell wall and can trigger immune responses.

Antiphagocytic factors

Factors that prevent phagocytosis by the host's phagocytic cells.

Bacterial capsule

Composed of chemicals not recognized as foreign; slippery and difficult for phagocytes to engulf.

Antiphagocytic chemicals

Prevent fusion of lysosome and phagocytic vesicles; leukocidins directly destroy phagocytic white blood cells.

Stages of Infectious Disease

The disease process occurs following infection and typically includes five stages: Incubation period, Prodromal period, Illness, Decline, Convalescence.

Incubation period

The time between exposure to the pathogen and the onset of symptoms.

Prodromal period

The stage of an infectious disease characterized by early symptoms.

Illness

The stage of an infectious disease where symptoms are most severe.

Decline

The stage of an infectious disease where symptoms begin to subside.

Convalescence

The stage of recovery following an illness.

Incubation Periods of Selected Infectious Diseases

Staphylococcus foodborne infection: <1 day; Influenza: About 1 day; Cholera: 2 to 3 days; Genital herpes: About 5 days; Tetanus: 5 to 15 days; Syphilis: 10 to 21 days; Hepatitis B: 70 to 100 days; AIDS: 1 to >8 years; Leprosy: 10 to >30 years.

Symptoms

Subjective characteristics of disease felt only by the patient.

Signs

Objective manifestations of disease observed or measured by others.

Syndrome

Symptoms and signs that characterize a disease or an abnormal condition.

Asymptomatic/subclinical

Infections lack symptoms but may still have signs of infection.

Pain

A symptom sensed by the patient, often associated with discomfort.

Nausea

A symptom sensed by the patient, characterized by a feeling of unease in the stomach.

Headache

A symptom sensed by the patient, often described as pain in the head.

Chills

A symptom sensed by the patient, often associated with fever.

Sore throat

A symptom sensed by the patient, characterized by pain in the throat.

Fatigue

A symptom sensed by the patient, described as tiredness or lethargy.

Malaise

A symptom sensed by the patient, characterized by a general feeling of discomfort.

Itching

A symptom sensed by the patient, often causing a desire to scratch.

Abdominal cramps

A symptom sensed by the patient, characterized by pain in the stomach area.

Swelling

A sign detected or measured by an observer, characterized by an increase in size of a body part.

Rash or redness

A sign detected or measured by an observer, often indicating irritation or infection.

Vomiting

A sign detected or measured by an observer, characterized by expulsion of stomach contents.

Diarrhea

A sign detected or measured by an observer, characterized by frequent loose or liquid bowel movements.

Fever

A sign detected or measured by an observer, characterized by an elevated body temperature.

Pus formation

A sign detected or measured by an observer, indicating infection or inflammation.

Anemia

A sign detected or measured by an observer, characterized by a decrease in red blood cells.

Leukocytosis/leukopenia

A sign detected or measured by an observer, indicating an increase/decrease in the number of circulating white blood cells.

Bubo

A sign detected or measured by an observer, characterized by a swollen lymph node.

Tachycardia/bradycardia

Signs detected or measured by an observer, indicating an increase/decrease in heart rate.

Etiology

Study of the cause of disease.

Hereditary diseases

Caused by errors in the genetic code received from parents.

Congenital diseases

Anatomical and physiological defects present at birth caused by various factors.

Degenerative diseases

Result from aging.

Nutritional diseases

Result from lack of some essential nutrients in diet.

Endocrine diseases

Due to excesses or deficiencies of hormones.

Mental diseases

Emotional or psychosomatic disorders.

Immunological diseases

Characterized by hyperactive or hypoactive immunity.

Neoplastic diseases

Characterized by abnormal cell growth.

Infectious diseases

Caused by an infectious agent.

Iatrogenic diseases

Caused by medical treatment or procedures.

Idiopathic diseases

Diseases with an unknown cause.

Healthcare-Associated diseases

Diseases acquired in a health care setting.

Germ theory of disease

Infections by pathogenic microorganisms cause disease

Koch's Postulates

A set of postulates one must satisfy to prove that a particular pathogen causes a particular disease

Exceptions to Koch's postulates

Some pathogens can't be cultured in the laboratory, diseases caused by a combination of pathogens and other cofactors, ethical considerations prevent applying Koch's postulates to pathogens that require a human host

Difficulties in satisfying Koch's postulates

Diseases can be caused by more than one pathogen, pathogens that are ignored as potential causes of disease

Transmission

Transmission is from a reservoir or a portal of exit to another host's portal of entry

Contact transmission

Transmission involving body contact between hosts

Direct contact transmission

Usually involves body contact between hosts; transmission within a single individual can also occur

Indirect contact transmission

Pathogens are spread from host to host by fomites

Droplet transmission

Spread of pathogens in droplets of mucus by exhaling, coughing, and sneezing

Vehicle Transmission

Transmission of pathogens through a medium such as air, water, or food

Airborne transmission

When pathogens travel more than 1 m via an aerosol

Waterborne transmission

Important in the spread of many gastrointestinal diseases; fecal-oral infection

Foodborne transmission

Spread of pathogens in and on foods; inadequately processed, cooked, or refrigerated foods