Chapter 15- Microbial mechanisms of pathogenicity Flashcards
Pathology
scientific study of disease
Etiology
the study of the cause of the disease
Pathogenesis
the manner in which a disease develops
Infection
the multiplication of any parasitic organisms. Can lead to disease sometimes, but not always
Disease
A disturbance in the state of health where the body can’t carry out all of its normal functions. When you have signs and symptoms that deviate from normal structure and function
Pathogens
Any organism that can cause disease
Signs of disease
Objective and measurable, directly observed by a clinician when examining a patient. Includes changes in vital signs, fever. blood cell counts
Symptoms of disease
Subjective, felt or experienced by a patient but can’t be confirmed or measured. Includes pain
Syndrome
A collection of signs or symptoms that occur together and indicate a specific disease or infection (a specific group of signs and symptoms)
Infectious disease
Caused by infectious agents. Bacterial, viral, parasitic. Can be transferred from one host to another and is caused directly by a pathogen
Noninfectious disease
Caused by some other factor, like a poison. Non-communicable disease cannot be spread from host to host- food poisoning, tetanus
Iatrogenic disease
Contracted as the result of a medical procedure. Also acquired in a hospital setting, but occurs in specific circumstances. A procedure like surgery is one example
Nosocomial disease
acquired in hospital settings- by anyone, not just a patient
Zoonotic disease
transmitted from animals to humans. Coronavirus is an example
Subclinical disease
No noticeable signs or symptoms (inapparent infection), like someone who has been infected but is asymptomatic (can occur with COVID). Only considered asymptomatic if you’re not taking any medication
Incubation period
Time between acquiring an infection to the appearance of signs/symptoms. The disease can be transmitted at this point. Depends on many factors- the dose of the infectious pathogen, the host’s status (pre existing disease), the pathogenicity of the microorganism (does it produce a lot of virulence factors)
Prodromal phase
Short period where nonspecific mild symptoms occur- this is when you first start not feeling well. Headache, fatigue, etc
Prodrome
A symptom indicating the onset of disease
Invasive phase
When you start expressing typical signs and symptoms of the disease- fever, swollen lymph nodes, sore throat, headache, nausea. Most infections don’t go past this stage- the host immune response disables the pathogen before it causes symptoms
Fever
Generally seen during the invasive stage of disease. It is a protective mechanism to fight infection. High temperatures help the immune system and certain enzymes to function better and inhibits microbial growth. Organisms that infect humans are normally mesophiles and can’t survive at higher temperatures. Use of antipyretics can actually prolong the infection
Acme
The critical stage or crisis of a disease. When pathogens invade and damage the host tissues. This is the point where the disease can become chronic. This is like when a fever reaches a high point and breaks, and the person recovers
Decline phase
Declining signs and symptoms. The host defenses start to kick in and the treatment you started during the invasive phase starts working. People are still susceptible to secondary infections at this stage- like developing bacterial pneumonia after the flu- the lungs become damaged and create a good environment for bacteria
Convalescence period
When your tissues are repaired and healing takes place. People can still be infectious- they can be infectious in all stages of disease depending on the pathogen. Smallpox is an example- scabs still carry the virus during the convalescence period
Stages in the course of an infectious disease (6)
- Incubation period
- Prodromal phase
- Invasive phase
- Acme
- Decline phase
- Convalescence period
Sequelae
Occurs when you still have lasting effects from the disease, even after the convalescence period is completely over- this doesn’t happen to everyone. It is sometimes caused by the host’s response to the infection, anti inflammatories or immunosuppressants can be used to decrease the immune response and prevent this from happening. Can include scarring, kidney or heart damage
Acute disease
Symptoms develop rapidly, like strep throat
Chronic disease
Disease develops slowly, over weeks or months or even over a lifetime. Slow to resolve. Tuberculosis is an example
Subacute disease
Symptoms between acute and chronic. Symptoms develop more slowly than acute but can last longer, like chronic. Bacterial endocarditis is an example
Latent disease
Disease with a period of no symptoms when the causative agent is inactive. Herpes, varicella zoster, and HIV are examples
What is the purpose of Koch’s postulates?
They are a systematic approach to identify the causative pathogen of a disease
Koch’s postulates (4)
- The suspected pathogen must be found in every case of disease and not be found in healthy individuals
- The suspected pathogens can be isolated and grown in pure culture
- A healthy test subject infected with the suspected pathogen must develop the same signs and symptoms of disease found initially
- The pathogen must be re-isolated from the new host and must be identical to the pathogen used to inoculate the organism
Stanley Falkow
Created a revised form of Koch’s postulates (molecular postulates) in 1988. Their premise is not the ability to isolate a particular pathogen but rather to identify the gene that may cause the organism to be pathogenic
Molecular Koch’s postulates (3)
- The phenotype of the disease should be associated only with pathogenic strains of a species- E. coli has nonpathogenic strains
- Inactivation of the suspected genes associated with pathogenicity should result in a measurable loss of pathogenicity- inactivating a gene of pathogenic E. coli means that the Shiga toxin is not produced
- Reversion of the inactive gene should restore the gene phenotype- the Shiga toxin should be able to cause disease again
Pathogenicity
capacity to produce disease or harm the host. Depends on the number of infectious organisms that enter the body, virulence, and attenuation
Virulence
intensity of the disease produced by the pathogen. How many toxins or proteins that disrupt normal functions can it produce (the ability to produce virulence factors)
Attenuation
Weakening of the disease-producing ability of the pathogen. Some organisms are very virulent at first and become less virulent as they pass to other hosts. Pathogens will not be able to survive if they are so virulent that they kill all their hosts. Attenuation is used as a means of vaccination- an attenuated pathogen can cause an immune response, but is not as virulent
ID50
Infectious dose for 50% of the test population- the dose required for an animal to get sick
LD50
Lethal dose for 50% of the test population- the dose required to kill the animals
Primary pathogen
always causes disease whenever it’s present
Opportunistic pathogen
Can only cause disease when the host’s defenses are compromised- when the immune status or health status changes
Steps of pathogenesis (5)
- Exposure or entry
- Adhesion (tissue attachment and colonization)
- Invasion
- Infection/host damage
- Pathogen exit
Pathogens are characterized by the presence of virulence factors. They must achieve all of these stages to cause disease
Exposure and entry to the host
Not all contact causes infection or disease- a pathogen has to be able to infect the susceptible host tissue. Pathogens enter through portals of entry
Portals of entry
The points where the pathogens are able to enter the body. Placenta, eyes, nose, mouth, broken skin, anus, urethra, vagina
Adhesion molecules
Help the pathogen to stick to a cell