Infection: Invasion by and multiplication of pathogenic microorganisms (bacteria, fungi, viruses, parasites,…) in a bodily part or tissue, which may produce subsequent tissue injury and progress to overt disease through a variety of cellular or toxic mechanisms.
Communicable disease: is a disease that can spread from one person to another or from animals to people.
Disease: A change away from a normal state of health to an abnormal state in which health is diminished. This means that an infection (growth and multiplication of pathogens) causes a disease.
Sign: A sign is an objective change in body function that may be observed and measured by an individual in addition to the patient’s feelings.
Health: is defined as a complete state of physical, mental and social well-being and not the mere absence of disease.
Symptom: A symptom is a change in body function felt by the patient.
Syndrome: A collection of signs and symptoms characterizing a disease or an abnormality.
Etiology: The cause of a disease or abnormal condition; or a branch of medical science concerned with the cause of disease.
Pathophysiology: The functional changes associated with or resulting from disease or injury. or The study of such changes. It is also known as physiopathology.
Pathogenesis: The development of morbid conditions; more specifically the cellular events and reactions and other pathologic mechanisms occurring in the development of a disease.
Pathogenicity: The ability of a microbe to cause disease.
Virulence: The degree of pathogenicity in a microorganism.
Acute infection: An infection characterized by sudden onset, rapid progression, and often with severe symptoms.
Chronic infection: An infection characterized by delayed onset and slow progression.
Primary infection: An infection that develops in an otherwise healthy individual.
Secondary infection: An infection that develops in an individual who is already infected with a different pathogen.
Pathophysiology: The functional changes associated with or resulting from disease or injury. or The study of such changes. It is also known as physiopathology.
Pathogenesis: The development of morbid conditions; more specifically the cellular events and reactions and other pathologic mechanisms occurring in the development of a disease.
Pathogenicity: The ability of a microbe to cause disease.
Virulence: The degree of pathogenicity in a microorganism.
Acute infection: An infection characterized by sudden onset, rapid progression, and often with severe symptoms.
Chronic infection: An infection characterized by delayed onset and slow progression.
Primary infection: An infection that develops in an otherwise healthy individual.
Secondary infection: An infection that develops in an individual who is already infected with a different pathogen.
Carrier: An individual who carries an infectious agent without any sign and symptoms, yet who can transmit the agent to another individual.
Fomites: Any inanimate object capable of being an intermediate in the indirect transmission of an infectious agent.
Direct mechanisms of disease transmission: Directly from person to person
Examples: Direct skin contact, Airborne
Indirect mechanisms of disease transmission: By the intermediate agents or objects.
Examples: Food and Waterborne transmission; Fomites; Animal vectors
Parasite: it is an organism that lives in or on a second organism, called a host, usually causing it some harm.
Parasitology: The study of parasitic diseases
Infestation: parasitic attack or subsistence on the skin and/or its appendages, as by insects, mites, or ticks; sometimes used to denote parasitic invasion of the organs and tissues, as by helminths.
Factors Necessary for the existence of communicable disease
The presence of a particular communicable disease in an area at a certain time depends on three main factors:
a) Agent of a disease: a living organism that causes the disease e.g. bacteria, a virus, parasite…
b) The host: a human or animal in which or on which an infectious agent lives and develops.
c) The environment: consisting of the various elements surrounding a person.
Host
Host is defined as an organism, which harbors the parasite and provides nourishment and shelter.
Types of Host
1. Definitive host: The host in which the adult parasites replicate sexually (example, anopheles species), is called as definitive host. Th e definitive hosts may be human or nonhuman living things.
2. Intermediate host: Th e host in which the parasite undergoes asexual multiplication is called as intermediate host. (example, in malaria parasite life cycle, humans are the intermediate hosts).
Subclinical Infection
This is an infection that has not yet shown the clinical symptoms of the disease. The infection can be detected by the laboratory diagnosis and not by the clinical symptoms.
Clinical Infection
This is an infection that shows the clinical symptoms of the disease.