Infectious Disease Module 1 Flashcards
What is MIC?
Minimal inhibitor concentration - lowest concentration of antimicrobial that inhibits macroscopic bacterial growth in the lab
- bacterial cultures are grown to a specific
density then inoculated with anti-microbial at
increasing concentration until the
concentration is reached that prevent further
growth - this level is equated to expected
serum levels of dry to predict success
What is the most reliable method for isolating viruses?
PCR
What is gram staining used for?
Differentiating gram postive and negative bacteria
What is the Ziehl-Neelson used for?
Used for acid fast bacteria such as mycobacteria
What is immunohistochemistry/immunocytochemistry used for?
uses labelled monoclonal antibodies to detect microorganism antigen
What is an antigen?
Molecule or molecular structure on virus/bacteria that can interact with Ab or T-cell receptor
What are tests used to detect antigen?
- ELISA - Enzyme linked immunosorbent assay
- IFA - Direct immunofluorescent assay
- Indirect immunofluorescent assay
- Microscopic aggregate assay
- Nucleic-acid detection: development of assays
that can detect DNA and RNA of all classes of
micro-organisms (FISH assays) - PCR - small amounts of DNA can be detected
by amplification- Real time or quantitative PCR
- Takes into account the number of times the
DNA has been copied to get a set amount of
DNA - this helps with antigen load (FIV
infection) - Can be used for RNA detection as well
What are antibody tests used for?
They use serology: evidence of infection, assessment of immune response to infectious organism
Allows detection of antibodies or immunoglobulins that are formed against all classes of infections
When are IgM and IgG antibodies produced?
IgM - produced during early stages of diseases - within 7 days
IgG - follows IgM and takes weeks to increase - there can be a lag before antibodies are found in the blood (seroconversion)
Paired titers may be used to discriminate vaccination against infection
How can antigen based immunoassays be interpreted?
Positive:
- Pathogen present
- Antigen present but no viable organism in sample
- Vaccine antigen present
- Cross reacting antigen present
- Technical error
- Poor specificity test - false positive
Negative
- Pathogen absent
- Antigen present but below level of detection
- Antigen present but in immune complexes
- Technical error
How can antibody based immunoassays be interpreted?
Positive:
- Response to the pathogen (active infection)
- Previous exposure to pathogen
- Previous vaccination
- Technical error
- Poor specificity - false positives
Negative:
- Exposure to the pathogen has no occured
- Too early in disease course - before seroconversion
- Marked immunosuppression
- Techinical error
- Poor sensitivity - false negatives
What is sensitivity?
Proportion or number of animals with the disease that test positive = yields true positive
- Negative results rules out disease
- false negatives: animals that are positive that test negative
What is specificity?
Proportion or number without the disease that test negative
- Positive result rules in
- High specificity - fewer false positives (animals that don’t have disease that test positive)
What is positive predictive value?
probability that given a positive result the patient has the disease
- Don’t by dividing TP by all the animals tested
What is the negative predictive value?
Probability that given a negative result the patient does not have the disease
How is parvo transmitted?
Trans-placental - if infected before 8 weeks or in-utero likely to have myocarditis
Fecal - oral - Replication occurs within the lymphoid tissue, spreading quickly through rapidly dividing cells (GIT)
- They replicate in intestinal crypt cells resulting in villous collapse, intestinal bleeding and subsequent bacterial infection
- Intesitnal protein loss due to inflammation - hypoalbuminaemia
- Damage to bone marrow and progenitors can lead to neutropenia
How is parvo diagnosed?
- History C/S
- Bloods: leucopenia/neutropenia
- Parvo ELISA snap test - 80% specific (vaccs may cause a weak positive 5-15 days)
- PCR based to confirm - high sensitivity
- Fecal electron microscope, Viral isolation
- PM
Treatment of Parvo
- Correct hypovolaemia
- Dehydration correction +/- transfusion (colloids, plasma, whole blood)
- Electrolytes - glucose, K+
- Antimicrobial therapy
- Anti-emetics
- Enteral therapy
- Analgesia
- Interferons/cytokines: exert inhibitory effects on viral and cell proliferation
Feline Panleukopenia transmission
- Fecal oral (litter tray, fomites, environment)
- In utero
Pathophysiology of panleukopenia virus?
- Incubation period 2-10 days - variable shedding
- Tropism for rapidly dividing cells within the bone marrow, GIT, lymphoid cells and foetus
- If late in fetal/neonatal development will go to lymphoid tissue, BM and CNS leading cerebellar hypoplasia, retinopathy
How to diagnose FPV infection?
Canine parvo antigen test
PCR on blood or feces
How to diagnose Leptospirosis?
Difficult with acute disease
- Dark field microscopy with urine samples to see spirochete
- PCR for leptospira antigen in blood and urine (At any point in infection)
- MAT Paired titres: type of serological test that is gold standard (3-7 days then over 10 days test again)
- ELISA snap - 3-10 days
What causes Tetanus
Tetanus caused by anaerobic bacterium clostridoa tetani
- Produces two toxins
1. Tetanospasm - binds to peripheral n. and travels up axon traveling to spinal cord there it binds within the inihibitor interneurons preventing release of glycine
2. Tetanolysin - no c/s
How is tetanus transmitted?
Transmitted through necrotic wounds
- introduces spores which germinate to allow infection to grow in anaerobic environment
- clinical signs 2-3 weeks after infection
Treatment of tetanus?
- Debridement and abs to primary wound site (metro)
- Tetanus antitoxin - doesnt reverse already bound toxin (need to wait for terminals to regrow)
- Takes three weeks to start recovery and 2-3 months for full recovery
- Darkened room with sedative and muscle relaxants - intense nursing
