Infectious Disease Introduction Pt. 1 Flashcards
What is the main role of the immune system?
Protects the body from pathogens
What are the characteristics of the immune system?
- Can be specific
- Has memory
- Is mobile and fast acting
- Is flexible (can attack things it has never seen before)
- Hopefully does all this without damage to ourselves
What are the non-specific defenses of the human body? What immune system do they belong to?
Physical barriers (such as the skin)
Chemical barriers (such as stomach acid)
Mucus and cilia protect our respiratory tract
Urine flushes out bacteria from our urinary tract
Enzymes are present in our tears (along with high salt content) and our saliva
Other bacteria is present on our skin and within our digestive tract
Innate Immunity
What are the types of cells of the innate immune system? What do they do?
macrophages, neutrophils (PMNs), monocytes, natural killer cells and eosinophils
These cells act as phagocytes which eat anything that doesn’t belong
Usually rely on receptors on the pathogen or things that coat the pathogen (like antibodies and complements)
What additional function in innate immunity do mast cells and basophils have?
- Phagocytize
- Release inflammatory mediators
Define complement. What are the role of complements?
a complex protein network of plasma, and an integral part of the innate immune system
Can lyse pathogens, coat pathogens, and call for back-up
What is the role of chemokines?
- Act as traffic controllers for WBC’s
What is the role of macrophages and monocytes?
- Antigen presenting cells and surveillance
What are the role of neutrophils?
- Defence against bacteria and fungus
What are the role of eosinophils?
- Defence against parasites and respond to allergies
What are the role of basophils?
- Respond to allergies
In the innate immune system, do all cells respond together?
The innate immune system is non-specific
All cells take part to some degree or another
Do both the innate and adaptive work separately?
No they do not
They work together to fight invading pathogens
What are the two major cells of the adaptive immune system? What makes the adaptive system different than the innate?
- T and B Lymphocytes
- Specific and bale to remember
What are the sub-divisions of the innate immune system?
- Humoral mediated - within the serum
- Cellular mediated - within the cells
Describe the activation of T-lymphocytes
- activated by antigen presenting cell
- activated T cells secrete IL-2 which can stimulate production of more activated T cells
Activated T cells can become….
a) Helper Cells (CD4+)
b) Cytotoxic Cells (CD8+)
c) Regulating Cell
What is the role of Helper cells (CD4+)?
- secrete IL’s and interferon
- stimulates CD8+ cells
- stimulates production of antibodies
What is the role of cytotoxic (CD8+) cells?
- Kill cells recognized as foreign
What is the role of a regulating cell?
- Regulates the T cell response
How are B-lymphocytes activated?
- activated after they recognize antigens (usually through the help of T-lymphocytes)
What can activated B-cells become?
a) Plasma Cells
b) Memory cells
What is the role of plasma cells?
- Secrete antibodies
What is the role of memory cells?
- Important in future attacks
Antibodies bind to…. and
Antibodies bind to antigens
- May trap the antigens or clump them together
- Increase the attack of immune cells
What are cytokines? Examples?
- Soluble factors secreted by cells
- Can activate cells, call for backup, etc.
- Interleukins (IL”s)
- TNF
- IFN
What are inflammatory mediators? Examples?
- Any soluble factor that causes inflammation
- Usually secreted by various cells
Examples: Histamine, Prostaglandins (PG’s)
Define Infection
- get a response of host immune systems and person gets ill
- e.g. pneumonia
Define sub-clinical infection
- specific response in the body is evoked (ie. Ab production), but person not ill
- e.g. influenza, EBV, SARS-Cov-2
Define colonization
- presence of organism at a body site without production of disease
- e.g. Skin wounds colonized with staph
Describe the process of disease production?
Invasion of microorganism
–> Breach of host defences
Elaboration of toxins
–> Some bacteria produce toxins which can damage cells
–> May be damage even at distant sites
What are some examples of bacteria that produce toxins?
- Botulism –> Botulism toxin
- Cholera –> Toxins that cause tissue damage
- Tetanus –> Tetanus anti-toxin more important than antibiotics
- Staph Aureus –> Food poisoning of toxins that remain
Normal Microbiota of the Skin
Diphtheroids (e.g. Corynebacterium sp.)
Propionibacteria –> acne
Staphylococci (esp coagulase negative strains)
Streptococci
Normal Microbiota of the Gastrointestinal Tract
Bacteroides sp.
Clostridium sp.
Diphtheroids
Enterobacteriaceae ( e.g. E. coli, Klebsiella sp.)
Fusobacterium sp.
Streptococci (anaerobic)
Normal microbiota of the upper respiratory tract
Bacteroides sp.
Haemophilus sp.
Neisseria sp.
Streptococci
Normal microbiota of the genital tract
Corynebacterium sp.
Enterobacteriaceae sp.
Lactobacillus sp.
Mycoplasma sp.
Staphylococci
Streptococci
What is the host defence system? What is its role?
Includes both innate and adaptive parts of the immune system
Already learned that host defence is extremely important in preventing infection
But, it is also the most important aspect of curing infection
Do antibiotics always cure an infection?
No
Besides antibiotics, curing an infection may need….
Drainage of abscess
Removal of dead tissue –> does not have blood supply e.g. diabetic foot infection
Removal of foreign bodies or prosthetic device
Decrease in immune suppression
Why are infections on prosthetic devices harder to tx?
- They do not have blood supply, therefore, antibiotics cannot reach the site of infection
- Prosthetic devices can also produce biofilm that prevents the anti-biotics from reaching the target
What are some factors which affect host defences?
Malnutrition
Extremes of age
Immune globulin deficiencies
Deficiencies in cellular immunity
Alcoholism
Diabetes
Immunosuppressive therapy
Invasive procedures
What are some non-specific symptoms of infection?
Malaise
Listlessness –> fatigue
Loss of appetite
Headache
Myalgias –> muscle aches
Arthralgias –> joint aches
What is the most prevalent symptom of infection (usually)? Is it the most important?
FEVER
- due to infection unless proven otherwise
- autoimmune diseases and malignancy can cause fever
- Temperature cycles throughout the day - normally highest in the late afternoon and lowest 12 hours later
- Over focus on actual temp, but what is important is the pattern of an infection
fever temperatures:
a) 6 am
b) 4 pm
c) rectally
d) armpit
37.2 C at 6 am
37.7 C at 4 pm
38.2 C rectally
37.2 C armpit
In an infection, WBC is (increased/decreased). WBC normal range is…..
Increased
Normal range is 5-10 x 109/L
So anything over 10 x 109/L – may be an infection
Can be elevated in patients with leukemia and RA and in patients taking lithium or corticosteroids
Elevations may be mild in less severe infection or in the elderly
In a WBC count, the percentage of WBC subpopulations are…. (3 main ones)
- Total Neutrophils –> 50-70%
- Segmented Neutrophils –> 50-70%
- Bands - 3-5%
- Lymphocytes - 20-40%
What is the difference/relationship between segmented neutrophils and Bands? What is the response to infection?
- Neutrophils are infection fighting
- Segmented neutrophils are mature neutrophils that are circulating within the blood (nucleus is segmented)
- Bands are immature neutrophils found in the bone marrow (nucleus is smooth and parallel). The bone marrow will put out immature cells to fight the infection
- if band levels are increased in the blood (e.g. 10% increase) the body is fighting hard to get rid of the infection
Define left shift. What is the most common cause of a left shift?
The presence of non-segmented neutrophils (Bands)
- Inflammation is the most common cause of a left shift; however, some other conditions such as hemolytic anemia and primary diseases of bone marrow can also cause the release of immatutre neutrophils from the marrow
Anemia and Infection Manifestation
- May be present especially with chronic infection
Erthyrocyte Sedimentation Rate (ESR) and C-Reactive Protein Infection Manifestation
- Both are markers of inflammation. Increased levels with infection.
ESR and CRP are non-specific
Do not necessarily mean infection but can be used to guide tx of infection - e.g. do not stop anti-biotics until ESR is in a normal range
- CAN be used as a monitoring tool in certain infections like endocarditis or osteomylitis
Procalcitonin and Infection Manifestation
- In response to infection, PC is released (increased procalitonin)
- More specific than ESR and CRP
- Indicator of prognosis and when you can stop antibiotics n
What are some non-conventional clinical manifestation (symptoms) of infectious disease?
Increased heart rate –> can be linked to increase in temp or not
Anxiety
Confusion –> Elderly and the young
What are the symptoms of septic shock? What does it eventually lead to?
Decreased BP, then decreased CO
Decrease in renal function
Hepatic dysfunction (increase in bilirubin)
Decreased oxygenation
Disseminated intravascular coagulation (DIC)
EVENTUALLY –> MULTIPLE ORGAN FAILURE
