3.5 RNA viruses 1 Flashcards
Family PicoRNAviridae structural and genomic characteristics. where do they replicate?
- Pico= micro; rna (RNA virus)
- Size: ~20-30 nm (very small)
- Positive ssRNA
- Replicates in the cytoplasm
- Icosahedral symmetry
- Non-enveloped
reportable diseases in the picornaviridae family
Genus Aphthovirus
- Foot and mouth disease virus – OIE list 2020
Genus Enterovirus
- Swine vesicular disease virus (swine vesicular disease) – OIE list 2020
genuses under the picornaviridae category
Aphthovirus
Enterovirus
Cardiovirus
Avihepatovirus
Teschovirus
Tremovirus
immediately notifiable diseases in the picornaviridae family
Genus Avihepatovirus
- Duck hepatitis A virus (hepatitis) - OIE list 2020
Genus Teschovirus
-Porcine teschovirus – (Teschen disease: encephalomyelitis)
Genus Tremovirus
-(Avian encephalomyelitis virus – encephalomyelitis)
what animals does foot and mouth disease affect?
Affects cloven-hooved mammals
- Mostly: cattle, pigs, buffalo
- African buffalo: one of the main wild reservoirs
- Sheep and goats: mild disease
Humans: flu-like symptoms
is foot and mouth disease contagious? how is it transmitted?
Highly contagious!
* Ingestion or inhalation of virtually any body fluid
* Direct or indirect contact: droplets, contaminated semen
* Vectors (vehicles, equipment, clothes or humans)
* Aerosols/Airborne: infective for miles
what is the morbidity of FMD in susceptible populations? Mortaility? Does it affect the livestock trade?
-FMD places economic constraints on the international livestock trade
-In a susceptible population, morbidity reaches 100% with rare fatalities except in young animals.
what symptoms of FMD do we expect to see in cattle?
- In cattle
– Oral vesicles
– Teat lesions
– Foot lesions - Ulcerations, pain, reduced production, secondary infections with other viruses and bacteria,
what symptoms of FMD do we expect to see in pigs?
Hoof lesions and lameness is very common
* Vesicles on snout
* Oral lesions less common
how many serotypes of FMD are there? how does this affect vaccinations?
-7 distinct serotypes (A, O, C, Asia 1, SAT 1, SAT 2, SAT 3)
-Many are not cross protective which makes vaccination difficult
* Problems: serotype specific
-Vaccines: used in endemic regions
when was the last case of FMD on USA? Canada?
United States
-9 outbreaks prior to 1929
-All ended by eradication
1929: Last case in U.S.
Canada
-5000 animals
-$5 billion USD
1952: Last case reported
=> have been other outbreaks in Taiwan, UK, South Korea, other countries globally
Which of the following is CORRECT about Picornaviruses?
a. Non-enveloped viruses can remain in the environment for a
prolonged period
b. Foot and mouth disease causes severe economic losses in the cattle and swine industry
c. Picornaviruses encode their own RNA dependent RNA polymerase
d. Picornavirus genome can be directly translated by ribosomes
e. All of the above
e. All of the above
what are the structural and genomic characteristics of the Caliciviridae family? where does viral replication take place?
- Positive sense single stranded RNA genome
- Non-enveloped virus- resistant in the environment
- Virus replication takes place in the cytoplasm
what caliciviridae are under Genus Vesivirus?
- Feline calicivirus
- Vesicular exanthema of swine
what caliciviridae are under Genus Lagovirus? Are they reportable?
- Viral haemorrhagic disease of rabbits
= Immediately notifiable disease
what symptoms does feline calicivirus cause? What are the clinical signs? what possible sequelae are there?
- Oral and upper respiratory infection in cats
- Virulent systemic disease as well
- Clinical disease shows conjunctivitis, rhinitis, increased salivation +/- tracheitis, pneumonia
-Ocular discharge
-Characteristic lingual ulcers
-Ulcers are very painful and may cause cats to stop eating – generally the mouth heals very quickly, but these can last 7-10 days
how is feline calicivirus transmitted?
Natural transmission occurs through small droplets in the air (such as from a sneeze) and contaminated objects, which can be carried to a susceptible cat by a handler.
how is feline calicivirus treated?
Treatment is largely directed toward the signs of illness
what are the morbidity and mortality statistics for unvaccinated cats with feline calicivirus?
- High morbidity in unvaccinated cats
- Low mortality, except kittens infected with virulent strain (interstitial pneumonia)
if a cat has recovered from calicivirus, can it still be contagious?
- Recovered cats can shed for a long time
what percentage of cats are subclinical carriers of feline calacivirus?
up to 25%
after infection with feline calicivirus, is a cat immune? does prior infection also protect against related strains?
- Infection-induced immunity is not life-long and does not protect against all strains
how can we prevent feline calicivirus?
vaccines are available
What is NOT CORRECT about caliciviruses?
a. Non-enveloped viruses can persist in the environment for a
prolonged period
b. Vesicular exanthema of swine virus mimics foot-and-mouth disease clinical signs
c. Feline calicivirus causes oral and respiratory infection in cats d. Feline calicivirus can cause high mortality in unvaccinated cats e. None of the above
d. Feline calicivirus can cause high mortality in unvaccinated cats
=>causes high morbidity, not mortality
what are the structural and genomic characteristics of family flaviviridae? where do they replicate?
- Positive sense single stranded RNA
- Replication in the cytoplasm
- Icosahedral symmetry
- Enveloped
what immediatley notifiable diseases are there in the flaviviridae family?
Genus Flavivirus
-West Nile virus – West Nile fever
-Japanese encephalitis virus (swine, horses, humans)
what reportable viruses are there in the flaviviridae family?
Genus Pestivirus
-Classical swine fever (Hog cholera virus) OIE list 2020
what familiy does BVD belong to? what genus?
Family Flaviviridae, Genus Pestivirus
what causes bovine diarrhea virus?
BVD is a complex disease caused by a heterogenous group of related BVDV that differ in antigenicity, cytopathogenicity, and virulence
what species are affected by BVDV? what is the distribution?
- Susceptible species: cattle of all ages, buffalo, camelids
- Distribution: worldwide
how is BVDV transmitted?
- Transmission: horizontal (direct contact via tears, and saliva, contaminated feed, water or litter (urine, feces), milk, semen) vertical (transplacental)
two biotypes of BVDV? what are the main differences and similarities?
Based on effect on cultured cells there are two biotypes: non-cytopathic and cytopathic
-Non-cytopathic (ncp) > Does not cause cytopathic effects in cell culture
-Cytopathic (mutant) (cp) > Causes cytopathic effects in cell culture
-Both biotypes cause disease, however, only the non-cytopathic type causes persistent infections
-Noncytopathic BVDV is the predominant viral biotype in nature, whereas cytopathic BVDV is relatively rare
how many major genotypes of BVDV are there? what are their characteristics? how do these genotypes relate with biotypes?
- There are two major genotypes (distinct genetic groups) of
BVDV - Type 1 – BVDV-1; classic BVD viruses
- Type 2 – BVDV-2; recently described, highly pathogenic
- Each genotype contains isolates of both cytopathic and non- cytopathic
- The extent of antigenic variation among BVDV of different genotypes and sub-genotypes remains unknown
BDV disease pattern vary between and within herds based on:
- herd immunity
- presence/absence of persistently infected animals
BVD Clinical and pathological manifestation vary based on:
- age
- pregnancy status
characteristics of a BVD persistently infected animal
- No immunity to the virus, but sheds high amounts of virus
- Initially appears healthy, but survives less than 2 years
common age group infected by BVD
Cattle of all ages are susceptible but young animals (3-8 months age) are commonly infected
pathogenesis of BVD
Initial replication in nasal mucosa and tonsils > regional lymph nodes > lymphoid tissue and intestine > erosive/ulcerative lesions in the GI tract
clinical signs of BVD
- Clinical signs include explosive diarrhea, nasal and ocular discharge, ulcers in lips, muzzle and oral cavity
- Some strains induce profound thrombocytopenia that leads to extensive haemorrhage in the entire GI tract
BVD: postnatal infections in pregnant cows, outcome depends on?
The outcome depends on age (immunologic maturity) of the fetus, the strain of the virus
BVD: postnatal infections in pregnant cows, what sort of outcomes do we expect depending on the stage of pregnancy?
Early pregnancy (before 40 days)- Embryonic death and resorption
Mid-pregnancy (100-125 days) - Immunotolerance Infected with NCP > cow becomes immune, and fetus becomes tolerant (fetal death or low birth weight or CNS defects) BUT will not make antibody to BVDV- persistent and immunotolerant infection state
Later in pregnancy (> 125 days)
Calves usually survive, +/- damage (e.g. cerebellar hypoplasia)
-Develop neutralizing antibodies and eliminate the virus
how does mucosal disease arise? What are the clinical signs?
- When a persistently infected animal (PI) becomes infected with a CYTOPATHIC strain of BVDV
- The cytopathic strain often originates from mutations arising from the non- cytopathic virus of the same host or rarely from another animal or a vaccine
- Mucosal disease has the same clinical signs as severe, acute BVDV
what is seroconversion?
Seroconversion: The transition from infection with virus to the detectable presence of virus-specific antibodies in the blood. When seroconversion occurs, the result of a virus-specific antibody test changes from negative to positive.
identification and culling of what animals is critical for BVD control? why?
Identifying and culling of persistently infected (PI) animal is critical for BVD control
-PI calf is constantly shedding virus to herdmates
Which of the following disease resembles to oral lesions caused by Foot and Mouth disease in cattle?
a) Bovine virus diarrhea (BVD)
b) Malignant catarrhal fever
c) Vesicular exanthema
d) Swine vesicular disease
e) A and B
e) A and B
Which of the following disease statements is NOT CORRECT about BVD?
a. BVD is caused by closely related but heterogenous viruses showing different cytopathogenicity
b. Persistently infected animals are a major source of BVDV circulation in enzootically infected herds
c. Young animals are highly susceptible to infected due to lack of immunologic maturity
d. Mucosal disease of BVDV is caused by the cytopathic strain
e. None of the above
e. None of the above
=> all are true
What are the structural and genomic characteristics of togaviridae? where does it replicate?
- Enveloped
- ssRNA, positive sense
- Replicate cytoplasm
what is an arbovirus?
transmitted by arthropods
what are 3 immediately notifiable diseases in the family togaviridae? what other qualities do they share?
Genus Alphavirus
- Eastern equine encephalitis virus (EEEV) (uncommon)
- Western equine encephalitis virus (WEEV) (uncommon)
- Venezuelan equine encephalitis virus (VEEV)
All 3 are arboviruses - transmitted by arthropods
All 3 are zoonotic infections
what is the transmission cycle of eastern equine encephalitis?
Mosquito bite
↓
Replication in regional lymph nodes and vessels
↓
Viremia
↓
Replication in lymph nodes and muscle
↓
Secondary viremia
↓
Invasion into brain (cortex)
↓
Neuronal necrosis, clinical signs:
Fever, recumbency, somnolence, paralysis, death
Humans and horses are dead-end-hosts (no subsequent transmission)!
is eastern equine encephalitis found in canada?
yes, reported in Ontario and Quebec
Which of the following viruses are arboviruses (arthropod-borne)?
a. Eastern equine encephalitis virus
b. Venezuelan equine encephalitis virus
c. African swine fever virus
d. All of the above
d. All of the above
