Use LEFT and RIGHT arrow keys to navigate between flashcards;
Use UP and DOWN arrow keys to flip the card;
H to show hint;
A reads text to speech;
42 Cards in this Set
- Front
- Back
|
2 types of virus transmission |
1) Horizontal - direct or indirect 2) Vertical - in utero - during birth - colostrum - milk (first few weeks) |
|
|
Which viruses can be passed before birth? |
BVDV Blue tongue Feline parvo |
|
|
Which viruses can be passed during birth? |
Canine herpes virus |
|
|
Which viruses can be passed shortly after birth? |
CAE meadi-visna |
|
|
What are the consequences of vertical transmission? |
Embryonic death/abortion - PRRS virus (swine) = late term abortion Congenital disease - BVDV - border disease Congenital defets - Akabana virus - blue tonue - feline parvo (cerebellar hypoplasia) |
|
|
Modes of horizontal transmission |
1) Direct contact 2) Indirect contact (fomites) 3) Common vehicles 4) Airborne 5) Vector-borne 6) Iatrogenic |
|
|
What are some methods of direct contact that spread viruses? |
1) Licking 2) Rubbing 3) Biting - rabies virus (zoonotic) 4) Sexual contact - herpesvirus 5) Skin abrasions - Capri pox virus |
|
|
What is a fomite? |
An inanimate (non-living) object that can carry a pathogen from an animal to an animal or person |
|
|
What are some common vehicles that transmit viruses? |
1) Fecal-oral (enteric viruses) 2) Colostrum/milk - CAE - Maedi-visna - tick borne encephalitis virus) 3) Virus contaminated meat - classic swine - vesicular exanthema of swine 4) Virus contaminated bone products - BSE |
|
|
What is the difference between large droplets and micro droplets in airborne transmission of viruses? |
Large droplets settle down while microdroplets evaporate and travel Microdroplets also form droplet nucleus in aerosols and remain suspended in air for long period of time, then travel on wind and weather |
|
|
3 examples of arthropod borne virus transmission? |
Mosquitoes - equine encephalitis virus Soft ticks - African swine fever virus Culicoides - blue tongue virus |
|
|
What is the blue tongue virus transmission life cycle? |
Virus undergoes extrinsic incubation in vector for 4-20 days Culicoid bites a susceptible host Get viremia within 2-4 days Infected sheep gets bitten by uninfected culicoid vector and extrinsic incubation occurs again |
|
|
What is a nosocomial infection? |
Acquired infection while in clinic or hospital |
|
|
What level of stability in environment do viruses transmitted by respiratory route have? |
Low stability |
|
|
What level of stability in environment do viruses transmitted by fecal-oral route have? |
Higher stability |
|
|
Are enveloped or non-enveloped viruses more stable in the environment? |
Enveloped viruses labile (easily broken down) - detergents can dissolve the envelope - except orf virus, Marek's disease virus Non-enveloped viruses more stable - Adenoviruses, circoviruses |
|
|
What are 2 mechanisms of survival of viruses in nature? |
1) Physical stability of virus in environment 2) Maintenance of serial infections - chain of transmission Basically, survives either in the environment, or in the animal |
|
|
2 types of serial infections: |
1) Clinical infection - more productive source of virus (make a lot of virus) 2) Inapparent infection - more numerous and more important, due to better opportunity for virus dissemination - contribute to contamination in environment |
|
|
Control of a virus should be focused on which serially infected animals? |
Inapparently infected animals |
|
|
What are the 4 major patterns by which viruses maintain serial transmission? |
1) Acute self-limiting - transmission is affected by population size 2) Persistent infections 3) Vertical transmission 4) Arthropod-borne transmission |
|
|
3 examples of acute self-limiting infections |
Influenza Rota viral diarrhea Infectious bursal disease |
|
|
What is important about an acute self-limiting infection? |
There are high yields of virus during disease, and animal will present with clinical signs But, a continuous supply of susceptible hosts is required, and infectious virions disappear with clinical recovery |
|
|
What are the 3 types of persistent infections? |
1) Persistent infection 2) Chronic infection 3) Latent infection |
|
|
What is a persistent infection? |
Animal probably acquired the virus during gestation Clinical disease and death occur after years of shedding the virus with inapparent infection |
|
|
What is a chronic infection? |
Initially, the animal has clinical disease and high yield of infectious virions - resembles an acute infection Then the animal will show clinical recovery, but still shed the virus at low levels for months or years |
|
|
What is one example of a persistent infection? |
BVDV |
|
|
What are 2 examples of chronic infections? |
FMDV Feline calici virus |
|
|
What is a latent infection? |
Intermittent shedding with/without clinical consequences Initially, animal is able to mount an immune response, and the virus that does not get cleared goes and hides in the ganglia/neurons (trigeminal) - it does not produce viral proteins or replicate Stress or decrease in immunity reactivates the latent virus, which establishes a productive infection in the primary (original) replication/infection site (such as oral mucosa) When the immune system mounts a response against this, the virus goes and hides again |
|
|
What is the only example of a classic latent infection? |
Herpes virus |
|
|
3 factors causing viruses to change and leading to emergence of viral diseases? |
1) Virological determinants 2) host determinants 3) Constant changes in environment |
|
|
How do virological determinants lead to emerging viral diseases? |
Viruses exist not as individuals of a single genotype, but as a population of genetically distinct but related viral strains - so there are many mutations that can take place Also, the number of viral species continues to grow |
|
|
How does a novel virus evolve from enzootic viruses? |
Viruses have a short generation time and high mutation rate Viral replication, under selective pressure, leads to genetic and biological variants These biological variants are difference in virulence, tropism etc |
|
|
What is the main difference concerning mutation between DNA and RNA viruses? |
DNA viruses use cell machinery in the nucleus Cellular DNA replication has proof reading mechanisms, so the mutation rate is much lower than RNA viruses RNA viruses do not have proof reading since most replicate in the cytoplasm with their own RNA polymerases |
|
|
What is the rate of mutation in DNA viruses? RNA viruses? |
DNA: 10^-10 or 11 per incorporated nucleotide/per replication cycle = relatively small RNA: 10^-3-4 = relatively large |
|
|
Why is mutation of RNA viruses so rapid? |
One mutation is added to each new genome with each round of replication - this leads to exponential replication! Called QUASISPECIES |
|
|
What are 3 ways viruses can evolve using drastic genetic changes? |
1) Intramolecular recombination 2) gene deletion / acquisition 3) reassortment |
|
|
What is intramolecular recombination? |
double stranded DNA viruses can undergo template switching between closely related viruses |
|
|
What is an example of intramolecular recombination? |
Ancient sinbis like viruses+ easter equine encephalitis virus -> western equine encephalitis virus |
|
|
What is reassortment? |
Exchange of entire gene segments between viruses 1) host cell infected with two strains of a virus - such as influenza and rotavirus 2) RNAs of both viruses are copied in the nucleus/cytoplasm 3) the infected cell produces both parental viruses as well as a reassortant which inherits on RNA segment form either strain |
|
|
What are 2 pre-requirements for reassortment to occur? |
The viruses must be in the same cell and they must have segmented genomes |
|
|
What are 2 environmental factors that influence emergence of viral disease? |
Ecological changes - such as increase in arthropod borne viral infections due to changing weather patterns Human activities - translocation of viruses and their vectors |
|
|
What is a host determinant that affects emergence of viral disease? |
The virus must infect a host and successfully invade it, by passing the complex and sophisticated antiviral defenses - it then has genes that it can pass on to progeny that can also overcome these defenses |
