Infections and Infectious Diseases

Infections

• Infection is the invasion of a host organism's bodily tissues by disease-causing organisms, their multiplication, and the reaction of host tissues to these organisms and the toxins they produce.

Definitions

• Disease: Any deviation from a condition of good health and well-being.
• Infectious Disease: A disease condition caused by the presence or growth of infectious microorganisms or parasites.
• Pathogenicity: The ability of a microbe to cause disease.
• Virulence: The degree of pathogenicity in a microorganism.

Types of Infections

• Acute Infection: Sudden onset, rapid progression, and often with severe symptoms.
• Chronic Infection: Delayed onset and slow progression.
• Primary Infection: Develops in an otherwise healthy individual.
• Secondary Infection: Develops in an individual who is already infected with a different pathogen.
• Localized Infection: Restricted to a specific location or region within the body of the host.
• Systemic Infection: Spread to several regions or areas in the body of the host.
• Clinical Infection: An infection with obvious symptoms.
• Subclinical Infection: An infection with few or no obvious symptoms.
• Opportunistic Infection: Caused by microorganisms that are commonly found in the host’s environment.

Causative Agents

• Bacteria
• Viruses
• Fungi
• Protozoa
• Helminths
• Prions

Epidemiology

• The study of the transmission of disease.
• Communicable Disease: A disease that can be transmitted from one individual to another.
• Contagious Disease: A communicable disease that is easily spread from one individual to another.
• Noncommunicable Disease: A disease that is not transmitted from one individual to another.
• Endemic Disease: A disease condition that is normally found in a certain percentage of a population.
• Epidemic Disease: A disease condition present in a greater than usual percentage of a specific population.
• Pandemic Disease: An epidemic affecting a large geographical area; often on a global scale.

Reservoir of Infection

• The source of an infectious agent.
• Carrier: An individual who carries an infectious agent without manifesting 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.

Human Reservoirs

• Persons with acute or subclinical illness.
• Carriers: during incubation, convalescent carriers, chronic carriers, and intermittent carriers.

Nature of Microorganisms

• Microorganisms are small, living organisms that are not visible to the naked eye.
• Pathogens: Microorganisms that can cause disease.
• Non-pathogens: Microorganisms that do not cause disease; can be beneficial.

Chain of Infection

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Signs and Symptoms of Inflammation

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Q&A

• Pathogenicity is the ability of an organism to cause an infection.
• Hypertension is a non-communicable disease.