Chapter 6: Transmission of Infection, the Compromised Host, and Epidemiology

prevent the spread of disease

Understanding the ways in which infectious diseases are transmitted and the tole of a compromised host in the process are vital for developing methods to ________________________________________

- Where pathogens responsible for infection are found

- Mechanisms of transmission from the environment to a host

- Mechanisms of transmission from a host to the wider population

In order to understand the transmission of disease, it is important to look at what?

compromised host

The _______________________ must be viewed as an integral part of the infection process

The greater is the risk of successful infection

The more compromised the host, the what?

Epidemiology

An understanding in the basic principles of ___________________ is critical in preventing the spread of disease

Transmission (spread) of the infection

What is the final requirement for a successful pathogen/infection?

1. Reservoirs of infectious organisms- places where pathogens can grow and accumulate

2. Mechanisms of transmission- the various ways in which pathogens move from place to place

What are the 2 factors that affect the spread of infection?

1. Humans: the obviously sick, prodromal (infectious, but before symptoms), and carriers (no symptoms)

2. Animals: zoonotic diseases

3. Nonliving

What are the 3 Reservoirs where pathogens can accumulate?

Some diseases can be transmitted before symptoms are experienced (prodromal)

Why is it difficult to determine if a human is a resovoir?

No symptoms, can still infect others; shedding the infectious agent, examples are AIDS, diphtheria, typhoid

What are asymptomatic carriers (within the human reservoirs)?

Zoonotic diseases

diseases transferred from animals to humans

Rabies and lyme disease

What are examples of zoonotic diseases within animal reservoirs?

Usually occur after direct contact with an animal; can also occur via indirect contact (litter boxes, fur, feathers, infected meats)

When do zoonotic diseases usually occur, but when can they also occur?

Water, food, and soil

What do nonliving reservoirs of infection include?

Water is essential for drinking, so we are exposed to it daily. It also flows downhill and downstream, so water borne infections move

Which is the most dangerous nonliving reservoir and why?

In countries with poor sanitation and low levels of personal hygiene

Infections from nonliving are often seen where?

High levels of fecal contamination in the water

We cannot live without water, and as a result, regions with poor sanitation practices can have what?

Infection to spread via the fecal-oral route of infection

What do high levels of fecal contamination in the water lead to?

Natural spoilage (fridges just slow this)

What is food contamination a product of?

Surveillance; we may be seeing more and more people get sick from food contamination

What has decreased when it comes to food contamination?

They need to find a way to pass the physical barrier that protects the body from disease

The soil is a normal habitat for many pathogenic organisms, but what?

Through breaks in the skin

How must soil pathogens enter the body?

Tetanus- neurotoxin that can be lethal (muscle contractions)

What is an example of a soil pathogen that enters the body?

1. Contact transmission

2. Vehicle transmission

3. Vector transmission

What are the 3 main mechanisms of transmission?

1. Direct

2. Indirect: Fomites

3. Droplets (

What are the 3 subcategories of contact transmission?

1. Waterborne

2. Foodborne

3. Airborne

What are the 3 subcategories of vehicle transmission?

1. Mechanical

2. Biological

What are the 2 subcategories of vector transmission?

Contact Transmission

healthy person exposed to pathogens by either touching or being close to an infected person or object

intermediary between an infected person and the uninfected person

There is no what in direct contact transmission?

Touching, handshaking, kissing, and sexual interactions; as well as dog or other animal bites

What does direct contact transmission encompass?

1. Hepatitis A

2. Smallpox

3. Staphylococcal infections

4. Mononucleosis

5. STDs

What are 5 diseases that are transmitted through direct contact?

Intermediates that are usually nonliving articles (tissues, handkerchiefs, towels, bedding, contaminated needles)

What does indirect contact transmission take place through?

HIV and hepatitis B

What do contaminated needles easily transfer?

Fomites

nonliving intermediates that act as the agents of transmission via indirect contact

Influenza and whooping cough

Droplet transmission is seen in the transfer of respiratory diseases such as what?

Sneezing, coughing, and even laughing

What can droplet transmission occur through?

- Large droplets will fall to ground quickly (real droplets, won't float in air), but smaller droplets can stay airborne for long periods

- The smaller the droplet, the more dangerous it is as an agent of disease

Although droplet transmission is confined to short distances, why is the size of the droplet important?

Pathogens riding along on supposedly clean components

What does vehicle transmission involve?

Air, food, water, blood, bodily fluids, drugs, intravenous fluids

What are examples of vehicles in vehicle transmission?

Air

What is the most difficult vehicle to control?

- Dust uses air as a vehicle and can contain huge numbers of pathogens

- Microbial spores and fungal spores can also use air to travel from host to host

Why is air the most difficult vehicle to deal with?

Expensive; re-circulated air is cheaper than fresh air: hospitals, prisons, airliners, etc.

What kind of problem is air as a vehicle for infectious diseases?

HEPA filters

What do they use in hospitals and surgical suites to try to help with air vehicle transmission?

There is re-circulated air; we need to increase turnover of air

Why do people get so sick in prisons, airliners?

Bioweapons (pathogens to aerosol form)

What does air vehicle transmission have the potential for?

By a carrier known to be associated with some disease, usually arthropods

In vector transmission, how are pathogens transmitted to a healthy person?

- Fleas

- Ticks

- Flies

- Lice

- Mosquitos

What are examples of vectors for vector transmission?

Mechanical vector transmission

pathogens are on vector's body parts and are passively brush off the vector and onto the host (or they contaminate another object, such as food at a picnic)

Biological transmission

pathogens are within the vector and transmission to the host is through a bite

Plague (flea), malaria (mosquito), yellow fever (mosquito), Rocky Mountain spotted fever (tick), Lyme disease (tick)

What are some examples of biological vector transmission?

Direct contact

Identify the mechanism of transmission: sexual intercourse

Mechanical vector

Identify the mechanism of transmission: fly landing on your picnic lunch after visiting a pile of manure

Droplet contact

Identify the mechanism of transmission: violent, uncovered sneeze of the passenger next to you on an airplane

Indirect contact

Identify the mechanism of transmission: passing a pencil to your classmate (pink eye/conjunctivitis)

Biological vector

Identify the mechanism of transmission: mosquito bite (West Nile, Dengue fever, Malaria)

Vehicle, food

Identify the mechanism of transmission: fecal bacteria in your sandwich due to failure of kitchen staff to wash hands after defecation

Indirect contact

Identify the mechanism of transmission: broken, malfunctioning dishwasher leaves water glasses with bacterial contamination

Indirect contact

Identify the mechanism of transmission: discarded, used Kleenex filled w? cold/flu viruses

Airborne vehicle

Identify the mechanism of transmission: SARS aerosol wafting into hall from patients room

????? Droplet or indirect contact

Identify the mechanism of transmission: TB acquired in the subway

Direct contact

Identify the mechanism of transmission: Handshake (cold, flu)

Direct contact

Identify the mechanism of transmission: rabies from the bite of a rabid raccoon

Biological vector

Identify the mechanism of transmission: tick bite (Lyme disease, Rocky mountain spotted fever)

Indirect contact

Identify the mechanism of transmission: Dirty towels, bedding (MRSA)

Indirect contact

Identify the mechanism of transmission: shower room floor (athlete's foot fungus)

Foodborne vehicle

Identify the mechanism of transmission: Failure to clean cutting board (raw chicken, salmonella)

Indirect contact

Identify the mechanism of transmission: using IV needle after placed on non-sterile surface of bedding

Waterborne vehicle

Identify the mechanism of transmission: Strep A impetigo from re-using water in hydro therapy session for a second patient

host

Initially, the overall health of the ______ has a clear influence on the disease

- Age: disease levels tend to increase as we age

- Gender: some diseases are more prevalent in 1 gender or another

- Lifestyle (a catch-all for a variety of human activities)

- Occupation: more infections are seen in health care workers

- Emotional state: a vulnerable emotional state can decrease immunocompetence in the host

- Climate: appears that there is a greater incidence of respiratory infections in colder climates

For all people, the disease transmission is affected by what and how (6)?

- UTIs are seen more in women

- Pneumonia is seen more in men

What are 2 diseases that are more prevalent in one gender over the other?

- warmer climates allow longer periods when vectors are present

- climate can effect changes in the variety of infectious organisms that may be present in a given location

What are 2 other facts about how the climate affects disease transmission?

Lifestyle, occupation, trauma, travel, aging

What are other situations that can weaken the immune defenses of the host?

Exit in the same way they enter, are identical to portals of entry

What are portals of exit for disease transmission?

Nasal secretions, saliva, sputum, respiratory droplets; blood vaginal secretions, semen, urine, feces

What are specific portals of exit for disease transmission?

The infected host

What is a very important part of the disease process?

Spread of disease and pathogens

What can be dependent on the host?

Immunocompetence

The host's ability to mount a defense is referred to as its what?

The potential for damaging infectious disease increases

What happens if host defenses are in some way compromised?

In acquired immunodeficiency syndrome (AIDS)

How is the point that "if the host defenses are in some way compromised, the potential for damaging infectious disease increases" dramatically illustrated?

1. People w/ AIDS and people with genetic immunodeficiency diseases

2. People undergoing chemotherapy and patients taking broad-spectrum antibiotics

3. Surgical, transplant, and burn patients

4. Premature and newborn infants

5. Healthcare workers

6. The elderly

7. Patients on artificial ventilators

Several groups of people are considered to be vulnerable to infection and therefore immunocompromised to varying degree. What are they?

- AIDS patients

- Genetic Immunodeficiency

- Chemotherapy for cancer

- Transplantation patients

- Burn and Post-Op Patients

- Patients on respirators

- Catheterized patients (IV and urinary)

- Preemies, newborns, and the elderly

- Patients taking broad-spectrum antibiotics

- Stress of hospitalization, disease, trauma, etc.

Compromised hosts have become much more common:

Defensive competence of the host

What has a major role in the extent and severity of many infectious diseases?

Neutropenia

lower than normal numbers of neutrophils in the blood

A form of primary phagocytic defense and an important component of a host's innate immune response

What are neutrophils?

The administration of cytotoxic chemotherapy for the treatment of malignant tumors seen in cancer

What is the most common cause of profound neutropenia?

1. Cancer or other diseases that damage the bone marrow

2. Congenital disorders characterized by poor bone marrow function

3. Viral infections that disrupt bone marrow function

4. Autoimmune disorders that destroy neutrophils and bone marrow cells

5. Overwhelming infections that use up neutrophils faster than they can be produced

What are other causes of neutropenia?

Bacterial or fungal

What are primarily the types of infections seen with neutropenia?

1. Gram negative bacteria from either the patients colon on the environment can cause life-threatening septicemias

2. gram positive staph can cause infections originating in the bloodstream

3. mucocutaneous candidiasis can be caused by candida albicans

4. fungal pneumonia caused by Aspergillus fumigatus

What are general increased risk of diseases in those with neutropenia?

As soon as the neutrophil level decreases

When can bacterial neutropenia infections begin?

Neutrophil levels have been low for a prolonged period of time

When are fungal neutropenia infections usually only seen after?

Surgical procedures and catheterization

What are fungal neutropenia infections associated with?

It recognizes the differences b/w host organs and transplanted organs

What happens in organ transplantation with the immune system?

Depending on how closely the donor and recipient match, differences in body parts; only exception is identical twins

What does organ transplantation rejection depend on?

A reaction in which the body sets out to destroy the transplanted organ or rejection

What can organ transplantation result in?

Through the administration of drugs

How is rejection of the transplanted organs suppressed?

Reduce rejection but cause increased susceptibility to infectioni

What do the drugs given to organ transplant patients do?

Treatment with broad spectrum antibiotics

What do infections in organ-transplant patients require?

Superinfections and antibiotics resistance

What can the overuse of broad spectrum antibiotics lead to?

Bc of the loss of large areas of the primary physical barrier to infection- the skin

Why are burn patients at risk?