Preventing, Diagnosing, and Treating Viral Infections Flashcards
define passive vaccine
give the product of an immune response (antibodies or immune cells) to a recipient; short term protection, no memory response (example is maternal antibodies passively transferred to baby)
define active vaccine
vaccinate with a modified form of the pathogen or part of a pathogen to induce the recipient to make antibodies; gives long term protection and induce a memory response
define inactivated vaccine (2)
- chemically inactivate the vaccine via formalin, beta-propriolactone, or nonionic detergents
- infectivity of virus is eliminated but antigenicity is not compromised; “looks just like the real thing”
define subunit vaccine (3)
- break virus into components
- clone specific viral proteins and express in bacteria, yeast, insect cells, or cell culture; then purify proteins and use for vaccine
- antigens usually capsids or membrane proteins
define replication competent/attenuated/modified live vaccine (3)
- viral replication occurs and stimulates an immune response
- infection (post vaccine) induces mild or inapparent disease
- made by serial passages: either through a nonhost cell causing a virus to change to grow well in a different type of species and no longer as virulent in og species, or by altering temperature and causing viruses to change to grow well in temps not found at normal site of infection
define antigen
signs of the pathogen inside the host
define antibody
signs of host immune response to the pathogen
explain the goal of vaccination and how they work
- induce a critical level of immunity in individuals that will prevent them from getting sick (or infected if a great vaccine)
- when enough people in a community have the critical level of immunity, the infectious agent will be unable to spread (herd immunity)
- each virus has a different threshold to prevent its spread
goal of vaccination is to prevent symptoms of disease!! really good vaccines also prevent transmission to others and have long lasting immunity; need to educate your immune system about a pathogen so when it encounters the pathogen you get a quick memory response that produces antibodies to the pathogen, preventing disease symptons
explain the pros and cons of using inactivated vaccines versus attenuated vaccines
response depends on how much immune system was tickled; inactivated must be given multiple times in order to stimulate a robust enough response
attenuated is more reactogenic: stimulates a more robust response but can make sicker with vaccine and can cause live shedding
inactivated: less reactogenic; less robust response but safer
explain what it means when an antigen test is positive versus when an antibody test is positive
a positive antigen test allows you to conclude that the animal contains the virus at the time of the test (sensitivity and specificity aisde)
a positive antibody test allows you to conclude that the animal has been exposed to the pathogen sometime in the past and has generated an immune response to the pathogen
what viral product is being detected in PCR?
- specific sequences of DNA
- can use to detect RNA viruses but must first convert the RNA to DNA via reverse transcriptase
- tests will have specific primers to amplify specific viruses, so you MUST have an IDEA of what virus you are testing for first
explain why antivirals are not often used in veterinary medicine (8)
- they are expensive and not cost effective for food animals (slaughter withdrawal issues)
- unsure whether they will really help animals: need to administer early in disease when virus is actively replicating and being shed; can have adverse effects, and few studies have been done to prove efficacy in pet/food animals
- difficult to develop for animal use: even humans don’t have broad spectrum antiviral drugs (like for antibiotics); so would need to know exactly what virus dealing with before try to use a specific drug
- resistance is always a possibility, especially with ssRNA (sloppy) viruses!
- only 50 antiviral drugs have been approved for human use and can be used extra-label in COMPANION animals (NEVER food animals!)
- drugs need to block virus without causing damage or side effects to the host, but since virus replication is so linked to the host cell, finding the right compounds is difficult
- lack of good cell culture models makes testing antivirals really difficult
- compounds need to be very potent and effective to stop a virus that replicates at a logarithmic rate; compound really needs to stop virus replication completely since replication is so rapid
explain how AZT and acyclovir stop viral replication
- AZT is a deoxythymidine analog that is converted to triphosphate form (pppAZT) in host cells by the cellular enzyme thymidine kinase
- pppAZT is incorporated by reverse transcriptase into actively growing viral DNA and blocks the ability of reverse transcriptase to incorporate nucleotides (can’t make full length viral genomes)
- AZT is toxic to the host though because it affects DNA synthesis in uninfected host cells too, but host DNA has a backspace to remove it before stops its own synthesis
- acyclovir only acts in herpesviridae infected cells and works like AZT but has fewer side effects because it is only activated in virally infected cells but still terminates viral DNA replication
explain how neuraminidase (NA) inhibitors decrease influenza spread
NA is required to cleave sialic acid parts from infected cells so that the budding virions can escape and infect additional cells; NA inhibitors block activity and viral particles do not spread well; VERY EASY TO GET RESISTANCE TO THIS DRUG
describe mechanisms to prevent spread of disease in the clinic and the field
hygiene, sanitation, PPE
