Chain of Infection Overview

Questions and Answers

What is the sequence called when an infectious agent leaves its reservoir and infects a susceptible host?

Chain of infection

The reservoir for Clostridium botulinum is primarily humans.

False

Which of the following diseases are transmitted from person to person without intermediaries? (Select all that apply)

Rabies

Streptococcal infection (correct)

Hepatitis A

Measles (correct)

What are asymptomatic carriers?

Individuals who are infected but do not exhibit symptoms. Signup and view all the answers

Zoonoses refer to infectious diseases that are transmissible from which hosts to humans?

Vertebrate animals Signup and view all the answers

What are some portals of entry for organisms into the human body?

Mucous membranes, skin, and the parenteral route. Signup and view all the answers

Which portal of entry is the most common for most pathogens?

Mucous membranes Signup and view all the answers

The portal of entry through breathing is primarily the __________ tract.

respiratory Signup and view all the answers

Hepatitis A virus can enter the body through the gastrointestinal tract.

True Signup and view all the answers

Study Notes

Chain of Infection

Transmission of infectious agents follows a sequence: exit from the reservoir, conveyance via a mode of transmission, entry into a susceptible host.
This sequence is termed the 'chain of infection.'

Reservoirs of Infection

Reservoir: habitat where an infectious agent lives, grows, and multiplies.
Types of reservoirs include humans, animals, and the environment.
Example: Clostridium botulinum has soil as a reservoir, with improperly canned food as a source of botulism infections.

Human Reservoirs

Many infectious diseases have human reservoirs, such as sexually transmitted diseases, measles, and respiratory pathogens.
Carriers can be asymptomatic or symptomatic:
- Asymptomatic carriers: infected but show no symptoms.
- Incubatory carriers: transmit during the incubation period before symptoms appear.
- Convalescent carriers: recovered but still transmit the disease.
- Chronic carriers: harbor the pathogen for extended periods.

Environmental Reservoirs

Environmental sources like plants, soil, and water can host infectious agents.
Fungal agents causing histoplasmosis primarily live in soil.
Legionnaires' disease outbreaks are often linked to water supplies.

Animal Reservoirs

Many diseases are zoonotic, transmitted from animals with humans as incidental hosts.
Recognized zoonoses include brucellosis (cows), anthrax (sheep), and rabies (various mammals).
Newly emergent zoonoses in North America include West Nile encephalitis (birds) and monkeypox (prairie dogs).
Diseases like HIV/AIDS, Ebola, and SARS are believed to have originated from animal hosts.

Zoonoses and Epidemics

Zoonoses: diseases transmissible from vertebrate animals to humans, with over 200 known types.
These diseases constitute a significant percentage of new and existing human diseases.
Control of zoonotic diseases requires attention, as elimination in humans may not reduce public health risks in animals.

Portals of Entry

Pathogens can enter hosts through:
- Mucous membranes (most common)
- Skin
- Parenteral route (injections or other means bypassing the digestive tract)

Mucous Membranes

Most frequent route for pathogen entry; cover tissues contacting the external environment.
Mucous membranes span approximately 400 square meters in the human body.
Key entry points:
- Respiratory tract: main entry for pathogens like colds, smallpox, tuberculosis, and influenza.
- Gastrointestinal tract: pathogens enter through food, water, and contaminated fingers.

Gastrointestinal Tract Challenges

The environment in the gastrointestinal tract can be inhospitable due to hydrochloric acid and digestive enzymes.
Some microorganisms can survive this hostile environment.
Common pathogens entering through this route include Hepatitis A virus, Giardia, Vibrio cholerae, and Salmonella.

Description

This quiz covers the key concepts of the chain of infection, including how transmission occurs from the agent to the susceptible host. It explains the roles of reservoirs and portals of exit and entry in the infection process. Test your understanding of these fundamental concepts in infection control.