Exam 3: Infection and Epidemiology Part 2 Flashcards
How can a contamination lead to an infection, and how can an infection lead to disease?
A person can become contaminated with a pathogen. The pathogen may overcome the body’s external defenses and invade the body establishing an infection. The infection may succumb to the body defenses (most do) however some infections evade the body’s defenses, multiply, and adversely affect the body function. Thus a disease is caused.
What is a disease?
Any harmful deviation from the normal structural or functional state of an organism, generally associated with certain signs and symptoms and differing in nature from physical injury. Normally a result of an infection that evades the body’s defenses.
Do all diseases result from infection? Explain.
No, diseases may be hereditary, congenital, some fall into multiple categories.
Symptoms
are subjective characteristics of a disease that can be felt by the patient alone. E.g pain, headache, disness, fatigue, nausea, etc.
Signs
objective manifestation of disease that can be observed or measured by others. Swelling, vomiting, fever, rash ,redness, etc.
Difference between symptoms and signs?
Symptoms=subjective
Signs=objective
What is a syndrome? Give at least one specific example.
A group of symptoms and signs that collectively characterize a particular disease or condition. AIDS/HIV characterized by low T-cell count, weight loss, increased susceptibility to and prevalence of opportunistic infections, etc.
What is a subclinical infection? Is there another term for such an infection?
Also called “asymptomatic”, infections that lack symptoms and goes unnoticed. Certain signs my still be detected with proper testing.
What is etiology?
The study of the cause of disease.
What is the germ theory of disease? When and by whom was it proposed?
Theory states “Microorganisms are the causes of many diseases”. Proposed during the golden age of microbiology 1800-1900s. Proposed by Louis Pasteur and Robert Koch.
How did Robert Koch propose that we establish that a particular pathogen is the cause of a particular disease?
Koch’s postulate: series of criteria used to establish a specific infectious agent is the cause of a specific disease.
Koch established Bacillus anthracis as the cause of anthrax and Mycobacterium tuberculosis as the cause of tuberculosis.
List Koch’s postulates
- The suspected agent must be present in every case of the disease.
- The suspected agent must be isolated and grown in pure culture.
3.The cultured agent must cause the disease when it is inoculated into a healthy susceptible host.
- The same agent must be recovered from the diseased experimental host.
*All of these criteria must be satisfied to establish the microbe as the causative agent of the disease in question. *
Can Koch’s postulates always be satisfied? Explain, giving at least two specific examples.
No, sometimes it’s not ethically appropriate to inoculate a healthy individual with a disease for example smallpox.
Many microbes cannot be grown in pure culture, for example viruses are obligate intracellular parasites requiring a living host.
Some infected individuals do not exhibit disease, human carriers of avirulent strains.
Some diseases are polymicrobial, caused by a combination of pathogens or the combination of a pathogen and an environmental genetic factor. e.g. Hepatitis B and D virus together cause liver cancer.
Same condition can be caused by multiple pathogens. E.g. Common cold is caused by rhinoviruses or coronaviruses, but can also be caused by respiratory syncytial viruses and many others. E.G Pneumonia can be caused by a variety of bacteria, viruses, and or fungi.
List the molecular Koch’s postulates and compare them to Koch’s initial postulates. How might they be an improvement?
Similar to Koch’s Postulates but relies on molecular techniques to study a microbe. Especially relevant to pathogenic species of E.Coli and Streptococcus pyogens which can cause several diseases depending upon which virulence factors are produced by a given strain.
- The virulence factor gene or its products should be found in pathogenic strains of the organism.
- Mutating the virulence gene to disrupt its function should reduce the virulence of the pathogen.
- Reversion of the mutated virulence gene or replacement with a wild-type version should restore virulence to the strain.
- Still not always possible to apply all these criteria, but at least provides an approach to study. *
What is an adhesion factor?
Specialized structures or attachment proteins that facilitate the adhesion of pathogens to cells.
Ligands
Type of adhesion factor.
Viruses and many bacteria have ligands that bind to complementary receptors on host cells. Ligands are glycoproteins or lipoproteins. Receptors on host cells are generally glycoproteins. Termed “adhesions” in bacteria. Termed “attachment proteins” or “spike proteins” in viruses.
Ligand-receptor binding often determines pathogen-host specificity.
Give at least one example of a bacterial adhesion factor.
Adhesion fimbriae of neisseria gonorrhoeae adhere to cells lining the human urethra and vagina.
Ligands
Give at least one example of a viral adhesion factor.
Ligands, specifically known as “attachment proteins” or “spike proteins”.
Give at least one example of an adhesion factor possessed by a protozoan.
adhesion disks
Give at least one example of an adhesion factor possessed by a helminth.
Suckers and hooks in some parasitic worms
Can adhesins vary within an individual or a population? Could this be beneficial? Explain.
Yes. variations in adhesions can be advantageous to the pathogens. Some bacteria possess multiple types of adhesions each binding to a different type of receptor. Some pathogens change their adhesions over time, helping pathogens evade the immune system and or each binds to a different type of receptor.
Is it possible that a bacterium or virus might lose its ability to make a ligand? What is the result?
Yes, due to mutations, chemical exposure, radiation, etc. These microbes become harmless and “avirulent”. Commonly used in vaccines.
What is a biofilm? Do you currently possess any biofilms? Explain.
Sticky web of bacteria and polysaccharides that adhere to a host surface. Complex synergistic relationships between numerous microorganisms.
Yes, dental plaque on teeth.
Pathogenicity
ability of a microorganism to cause disease. It either can CAN or CANNOT cause disease.
Virulenece
Not the factors.
degree of pathogenicity, relative ability to cause disease. High virulent organisms almost always cause disease while less virulent organisms cause disease only in weakened hosts. Does not describe the severity of the disease.
Can an infectious agent with low virulence cause a serious disease? Can a highly virulent infectious agent routinely cause a mild disease? Explain.
Yes, virulence does not describe the severity of the disease.
What are virulence factors? By what general means to they act?
Traits or molecules of pathogens that facilitate pathogenicity.
Enable the pathogen to enter a host, adhere to host cells, gain access to nutrients, escape detection or removal by the immune system.
Types of virulence factors
Adhesion factors
biofilm formation
extracellular enzymes
toxins
antiphagocytic factors.
