Chapter 8: Infectious Processes

infectious diseases

represents a pathologic situation in which microorganism, normally external to the body, gain entry to the internal structures and cause dysfunction

pathogen

disease causing microorganism

infectious process

pathogen - enters body, multiples, spreads = tissue damage

“how pathogens cause diseases, the steps that occur when pathogens enters body”

host microbe relationship

how they live in or on the body and how the body responds

• transient microorganisms

• commensal microorganisms

• human microbiome

• nutritional status

• age

• chronic illness

• immunization stats

transient microorganisms

microbes that have little consequence as they pass through the host without causing harm and without establishing residence in host

commensal microorganisms

bacteria and fungi comprising normal flora have established long term residency with the host but do not cause harm and usually benefit host

• can cause opportunistic infections when gaining access to parts of the body where they don’t belong

human microbiome

can be affected by diet, metabolism, hormones, meds, allowing each individual to likely have a different microbiome

• is affected by probiotic and antibiotic use (antibodies can kill good and bad bacteria so use probiotic to be specific)

antibiotic use

can disrupt gut microflora and provide a niche for enteric pathogens to take root in their absence, can induce epithelial injury and inflammatory resposne

nutritional status

protein malnutrition is associated with defects in cell mediated immunity

age

younger you are = more immunity

older you are = at risk for immune system becoming dysregulated

chronic illness

(ie. diabetes, cancer, heart disease etc)

associated with an increased risk of infection, malnutrition and the medications play a role

immunization status

most effective means to reduce morbidity and mortality from vaccine preventable diseases

two goals:

1. give immunity to host by direct exposure to the altered pathogen without causing disease

2. decrease the # of susceptible hosts in population = limiting the possibility of transmission of the disease (herd immunity)

pathogen characteristics

pathogens posses certain characteristics that assist in their penetration and survived in the host despite the presence of intact defense system

routes of transmission

direct and indirect routes

direct transmission

1. droplets - exchange of body fluids

2. bite of an animal, contact with contaiminanted soil

3. through the placenta (vertical transmission)

droplets

exchange of body fluids

indirect transmission

1. vehicle borne

2. vector borne

3. airborne transfers

vehicle borne

infectious agent is transported to host ie. vehicle could be food, water, clothing, plasma, tissue

vector borne

mechanical (insect carries infectious agent on feet or proboscis)

biological (agent grows in insect before insect can transfer the agent)

airborne transfers

aerosols including suspension of particles

What is an infection?

An infection occurs when a pathogen (such as bacteria, viruses, fungi, orparasites) enters the body and triggers a host response.

• can be subclinical (no symptoms) or clinical (symptomatic)

• may remain localized (wound infection) or become systemic (sepsis)

• requires presence of pathogen + host response

• not all infections are infectious diseases

types of pathogens

• bacteria

• viruses

• fungi

subclinical

no symptoms

clinicals

symptomatic

systemic

Infection spreads or causes a body-wide response, potentially leading to sepsis (pathogen invade, multiple, and overwhelm system)

infectious disease

An infectious disease is a disease caused by a pathogen that produces clinical signs or symptoms.

• infection always symptomatic and clinically apparent (obvious signs and symptoms)

• communicable diseases can spread person to person

• ex. TB, covid, flu

• sexually transmitted diseases

• all infectious diseases are infections

host characteristic

• physical and mechanical barriers (epithelial cells of the skin; acts as a protective physical barrier to invasion)

• impaired immune function

pathogen characteristics

• adherence and invasion

• bacterial endotoxin

• bacterial exotoxins and enzymes

• evasion of immune cells

• endospore formation

• antimicrobial resistance

adherence and invasion

ability to adhere to the contact surface; to live on hard surface

bacterial endotoxin

LPS in the membrane of gram negative bacteria that is highly immune genetic and attracts immune cells to area of infection

bacterial exotoxins and enzymes

secreted by bacteria and cause havoc even when the bacteria is gone, can also case shock by activating and attracting immune system

evasion of immune cells

develop an outside coating on surface to hide from phagocytosis

endospore formation

bacteria forms internal spore so when conditions are more favorable, gain the nutrients they were lacking, bacteria survives in new endospore form

antimicrobial resistance

pathogen gains resistance to body’s defenses

• pathogen are active to overcome body’s defenses

transmission of infection

how one disease transfers from one source to another or one person to another

emerging infectious diseases

• Pathogens can spread faster and in greater numbers because of global transport networks.

  • Examples: coronavirus, Ebola, Zika

weapons of bioterrorism

• bioterrorism fortification

• Reducing risk of exposure (good)

• Improving public health surveillance (good)

breaking chain of transmission

ex. sterile technique, body substance isolation, handwashing, through cooking of food blocks the mode of transmission

ex. masking, gloving, condom use blocks the portal of entry and portal of exit

healthcare associated infections (HAI)

infections that occur in healthcare facilities (ie. hospitals, doctors offices, and dental offices)

• Direct result of contact with healthcare personnel

• Bacterial, viral, or fungal pathogens

• Viewed as a patient safety issue by The Joint Commission

• Rising costs and public awareness increase importance of prevention

ex. cauti, clabsi

HAI vulnerability factors

patients are at risk

• Lower resistance to pathogens (compromised immune systems)

• Increased exposure to pathogens (some antibiotic-resistant)

• Invasiveprocedures

  • (break natural defense barriers)

bacteria

• Single-celled, rigid-wall organisms without internal organelles

• live inside or outside body (can be normal flora)

• Characterized according to

  • Shape (cocci, rods, spirals)

  • Reaction to stains (gram negative, gram positive, acid fast)

• Oxygen requirements (aerobic, anaerobic)

• antibiotics used to treat bacteria but can disrupt normal flors

characterization of bacteria

• Characterized according to

  • Shape (cocci, rods, spirals)

  • Reaction to stains (gram negative, gram positive, acid fast)

viruses

• smallest pieces of genetic material (DNA, RNA) associated with proteins and lipids

• antibodies dont work, use vaccines (antiviral medications) to help prevent symptoms, isolation tactic (self isolation)

• has to enter host to reproduce

• not living

virus characteristics

• Small pieces of genetic material (DNA, RNA) associated with proteins and lipids

• Intracellular pathogens that use the host’s energy sources and enzymes to replicate

• Viral replication may or may not destroy thehost cell.

• DNA viruses may be incorporated directly into the host genome.

• RNA viruses serve as templates for the production of viral RNA and proteins

fungi

• Eukaryotic microorganisms with the ability to form complex structures with thick cell walls

• Can be superficial, subcutaneous or systemic

• ex. yeast, caused by opportunistic infections, treated with an anti fungal medication

antibodies

causes thrush because they destroy normal flora so then you prescribe anti fungal to cure it

parasites

• Establish themselves with, and benefit from, another organism

• Examples: Parasites include protozoa, helminths (roundworms, flatworms), and arthropods

• live on / inside host and can be transmitted through food, water, insects, contact

• treated with anti parasitic medication