Influenza Flashcards
What viral family does Influenza belong to?
Orthomyxoviridae
What type of genome does Influenza have?
segmented negative RNA genome, 8 segments
How are influenza isolates named?
Species infected; H and N type
H and N are… ? In relation to the influenza virus
the spikes on the surface of the virus
H produces _____?
Why?
hemagglutinin (16 types)
Cell attachment, important for host tropism; has cleavage site that controls tissue tropism and spread, affects disease severity
N produces _____?
Why?
neuramidase (9t types)
aids in release of the virus from the cells
Why is a segmented genome good for a virus like influenza?
allows for rapid genetic evolution (mix n’ match)
Why can influenza rapidly evolve genetically?
segmented genome
What is an antigenic change?
When a viral genome changes enough so as to to prevent immune protection (not quite the same virus as last time)
What is antigenic drift?
why does this happen in influenza?
accumulation of single nucleotide changes, gradual over a long period of time
no prrofreading mechanism, mistakes are passed to progeny
What is antigenic shift?
how does this happen in relation to influenza?
genetic reassortment/change in combination of segments
animal infected with 2 different strains can produce new strains from genomic mix n match
Viral replication?
H involved with adsorption
N involved with Release
It was formerly believed that pigs were the “melting pot” for new flus, however…
we as humans may be!
Is an epidemic more likely to come from an antigenic drift or shift?
antigenic shift; antigenic drift is responsible for allowing people to be infected multiple times by the “same” virus
Anti virals were first discovered in ____ against herpesvirus by ____
1960s; “hit or miss”
____ in 1980s turned attention to antivirals
AIDS
Antivirals are difficult to design because _____.
Typically ____ an enzyme required for _____.
Must be take _____ or _____.
- most also damage host cells
- inactivate
- viral replication
- prophylactically
- early in infection
There are drugs that block various stages of the viral replication cycle, such as…
- entry (amantadine)
- viral component synthesis (AZT)
- release (neuraminidase inhibitors)
H5N1 - High Path Avian Influenza
- Low pathology strain exits in US poultry and wildlife, no clinical signs in most poultry or wild birds
- High pathology strain arose in Asia in 1996, found in Africa, Europe and Asia, has killed thousands of turkeys, chickens, and geese
- First human case 1997, 562 human cases in 15 countries 59% fatality
Swine Flu vs Novel H1N1
- Influenza isolated from swine 1930
- Shifted from seasonal disease to year round endemic
- H1N1 in US swine at least 75 years; not the most predominant now and not the “novel H1N1”
- Zoonotic disease
- Novel H1N1 does not appear more severe for swine, may be for some subgroups of humans
National Animal Health Laboratories Network (NAHLN) diagnostic testing in Emergency responses
- Same PCR protocol for all laboratories
- Positives confirmed by appropriate government agency, only virus isolation positive samples considered “true” positives
Avian
- Avian flu surveillance in migratory wild birds, ended Spring 2011
- State organizations sampling poultry
Swine (H1N1)
- Focus on clinically ill animals and those associated with human cases
- A basis for further study of what influenzas are circulating in swine
- Addition of testing feral swine
A POSITIVE result is defined as the presence of a product and is typically interpreted to indicate that the pathogen in question was present in the sample.
- Reasons for “false positives” include: _____
- “True positive” results can be difficult to interpret:_____
- Contamination (field, lab)
- Recent use of MLV vaccines
- Residual nucleic acid from past infections (e.g. a latent herpesvirus infection)
- Nonspecific amplification that produces a product of the same size, less of a problem in real-time
- The extreme sensitivity of PCR allows detection of very small quantities of genomic material.
- Numerous examples exist where the virus/bacteria may be present yet cause no disease (FIP/FeCV, PCV-2).
A negative result is defined as the absence of a product.
Reasons for “false negatives” include:_____
- Divergence between the sequence of the pathogen and that of the nucleotide primers
- Presence of endogenous inhibitors in the sample
- Fecal samples require additional steps for nucleic acid extraction
- Hemoglobin is a known inhibitor of PCR
- Heparin is a known inhibitor of PCR
- Autolysis/sample degradation (probably more of a concern with RNA viruses)
- Improper sample selection (wrong tissue, wrong time)
Other tests:
- Virus isolation-viable virus
- Serology- rapid testing, subtype testing, confirms exposure
