3.6 RNA viruses 2 Flashcards
what are the general structural and genomic characteristics of family arteriviridae? where does it replicate and in what type of cells?
- Single stranded positive sense RNA genome
- Enveloped virus
- Virus replication in the cytoplasm of macrophages and endothelial cells
what are two important viruses in the family arteriviridae?
Genus Arterivirus
- Porcine reproductive and respiratory syndrome virus
> OIE list 2020 - Equine arteritis virus
what is the most economically significant swine disease? what types are there and where are they found? which type is more severe?
Porcine respiratory and reproductive syndrome (PRRS)
- PRRSV type 1: Europe
- PRRSV type 2: North America (more severe disease)
does PRRS often have very obvious clinical signs? when do we see the greatest losses?
- Frequently subclinical: greatest losses in herds that have concurrent infections
what temperatures are conducive of PRRS survivial? how is it transmitted?
- Virus survives well at low temperatures: infections in winter months
- Horizontal transmission via aerosol, semen, and direct contact
what respiratory related symptoms does PRRS show in breeding age gilts, sows, and boars?
anorexia, fever, lethargy, depression, respiratory distress, mild hypoxic: cyanosis (“blue ears”)
what type of lung issues are associated with PRRS and why?
The virus destroys pulmonary alveolar macrophages, which could lead to secondary bacterial pneumonia
-Interstitial pneumonia
what type of reproductive symptoms do we see with PRRS?
- SMEDI: Stillbirth, Mummification, Embryonic Death, and Infertility
- Abortions are common!
- If piglets are born alive, they will be weak and often die from interstitial pneumonia
2 important coronaviridae for veterinarians
- Enteric coronaviruses (pigs)
- Feline coronavirus
2 important reoviridae for veterinarians
- Rotavirus
- Bluetongue virus
what are the structural and genomic characteristics of family coronaviridae?
- Single stranded positive sense RNA genome
- Enveloped virus with helical nucleocapsid
- High genetic variability: RNA
3 important viruses in Genus Alphacoronavirus
- Feline enteric coronavirus/Feline infectious peritonitis virus
- Transmissible gastroenteritis virus (TGEV)
- Porcine epidemic diarrhea virus (PEDV) OIE list 2020
3 important viruses in Genus Betacoronavirus
- Severe acute respiratory syndrome (SARS) coronavirus
- Middle East respiratory syndrome (MERS) coronavirus
- Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)
important virus in Genus Gammacoronavirus
- Avian infectious bronchitis virus (IBV) OIE list 2020
Presenting syndromes of coronaviruses
- Diarrhea, enteritis – TGEV/PEDV/PDCOV, bovine coronavirus, canine enteric coronavirus, feline enteric coronavirus, bluecomb disease virus (enteritis in turkeys)
- Respiratory infections – IBV, bovine and canine respiratory coronavirus, porcine respiratory coronavirus
- Immune mediated disease – FIP
what are some common and relevant enteric coronaviruses? what are their clinical signs and how can we distinguish the diseases from one another? is there cross-protection between these viruses? what ages are susceptible and what is the mortality?
- Transmissible Gastroenteritis Virus (TGEV)
- Porcine Epidemic Diarrhea Virus (PEDV)
- Porcine Deltacoronavirus (PDCoV)
- Clinically indistinguishable
- Clinical signs: vomiting, profuse watery diarrhea, rapid dehydration
- All 3 viruses are antigenically distinct and cross- protection does not occur
- All ages are susceptible
- High mortality in piglets under 2 weeks of age (up to 100%)
how are enteric coronaviruses transmitted?
- Transmission: oral-fecal, aerosol, direct contact, fomites
Pathogenesis of enteric coronaviruses TGEV – PEDV – PDCOV. where does the virus replicate? what is a consequence of this?
- Viral replication takes place in the villus epithelium of the jejunum and ileum
- Intestinal columnar cells are destroyed by the virus resulting in villus atrophy or blunting
what might we see due to an enteric coronavirus infection upon post mortem?
Distended intestines, thinned walls
Atrophy of the villi
do we see enteric coronaviruses of pigs in canada and the US?
have been previously reported in canada and usa
how do we diagnose enteric coronaviruses (TGEV – PEDV – PDCOV)
- Clinical signs + atrophic enteritis (presumptive diagnosis)
- Serology
- PCR, sequencing to differentiate TGEV, PEDV, PDCOV
- Histopathology, IHC, FAT: small intestine sections
how can we control or prevent enteric coronaviruses (TGEV – PEDV – PDCOV)?
- Management: replacement of fluid; warm, dry, clean
environment; antibiotics to prevent complications - Vaccination
what animals does Feline infectious peritonitis effect? what is its distribution?
- Domestic cats and wild Felidae (lions, leopards)
- Distribution: worldwide
- In young cats (<2 years), usually immunocompromised
what cells does are infected in cases of feline infectious peritonitis? what agents are implicated and how so?
Cell Tropism:
* Feline coronavirus (FeCV): intestinal epithelial cells
* Feline infectious peritonitis virus: macrophages
- Only a small percentage of cats that are exposed to the FeCV develop FIP, and this can occur weeks, months, or even years after initial exposure to FeCV
what symptoms does feline coronavirus cause in otherwise healthy cats?
In healthy cats feline coronaviruses cause mild diarrhea and cellular immunity keeps the virus in control
what symptoms does feline coronavirus cause in tressed or immunocompromised cats?
Stressed or immunocompromised cats > viral mutants with mutation of the spike protein (cleavage activation and fusion domains of the spike protein) > profuse replication in macrophages > vascular injury and leakage > FIP
Clinical manifestations/ pathogenesis of FIP. Main feautre, and forms of the disease?
Main feature is vasculitis : microscopically the primary lesion is an acute, immune mediated, perivascular cuff with inflammatory cells and necrosis of the vessel wall
WET form - thick, viscous and clear peritoneal exudate with extensive fibrinous plaques with grey-white nodules (aggregates of macrophages other inflammatory cells)
Dry Form: non-effusive form but characteristic foci of pyogranuloma
What determines wet versus dry form remains unknown
sings of the wet form of FIP
Wet form signs
* Abdominal distension
* Pleural effusion
* Dispnea
* Pericardial effusion
how can we diagnose FIP?
Diagnosis of FIP isn’t straightforward!
* Serology not conclusive,
* PCR amplifying the mutations in the viral genome that allows its replication in macrophages can be helpful
* Definitive diagnosis is done by IHC demonstrating
coronavirus in macrophages
how can we prevent and control FIP?
- FIP is not easy to control- hygiene, quarantine
- There are no effective vaccines
- Broad spectrum coronavirus protease specific antiviral drug has shown promise
Which of the following statements is CORRECT about coronaviruses?
a. Coronaviruses cause enteric or respiratory disease in animals
b. Mutations in the fusion peptide of feline coronavirus allows its replication in macrophages to induce infectious peritonitis
c. Antiviral drugs are promising hopes for the treatment of feline infectious peritonitis
d. All of the above
d. All of the above
what are the structural and genomic characteristics of family reoviridae? where does replication take place?
- Double stranded RNA genome organized into 9-12 segments
- Non-enveloped virus
- Numerous serotypes and strains of each virus species
- Genetic reassortment: cells co-infected with viruses of the same species (genetic shift)
- High rate of mutation (genetic drift)
- Replication takes place in the cytoplasm
what are some important reoviridae in the veterinary world? which are reportable?
Genus Rotavirus
* Rotaviruses (causes gastroenteritis essentially in all animal species)
Genus Orbivirus
* Bluetongue virus (bluetongue) OIE list 2020
* Epizootic hemorrhagic disease of deer viruses (haemorrhagic disease) OIE list 2020
* African horse sickness virus (respiratory, fever, edema) OIE list 2020
what symptoms do rotaviruses typically cause? how are they transmitted?
- Diarrhea in intensively reared young farm animals worldwide -significant economic losses
- Transmission is horizontal with ingestion of contaminated feed; air, water – extremely stable in the environment
what occurs that increases the infectivity of rotaviruses?
- Proteolytic enzymes can cleave outer capsid proteins to increase infectivity
how do clinical signs and diagnosis of rotaviruses differ between species?
- Clinical signs and diagnosis of rotaviruses are very similar in all species
how many types of rotaviruses are there, and what are these types based on?
There are 8 groups of rotaviruses based on genotypic and serologic analysis
* Group A – cattle, swine, other animals, (humans)
* Group B – humans, swine, (occasionally calves)
* Groups C - only pathogens of human, swine, and cattle
* Group E- only viruses from swine
* Groups D, F and G - only pathogens of birds
incubation period of rotavirus?
- Short incubation period: 16-24 hours
what do we frequently see in calves affected with rotavirus?
- Calf (1-3 days of age) diarrhea is frequent
-Yellow/green feces in early infection
when are pigs most susceptible to rotavirus?
Pigs are very susceptible
(~1-3 weeks, and 2-7 days postweaning)
what is the pathogenesis of rotaviruses?
Pathology = intestinal maldigestion and malabsorption due to to destruction of the terminally differentiated enterocytes lining the tips of the intestinal villi
infection of villous enterocytes > villous atrophy > malabsorptive diarrhea
-NSP4 enterotoxin triggers a signal transduction pathway in enterocytes to induce secretory diarrhea
how are rotaviruses diagnosed? what does virus isolation require?
- ELISA for viral protein detection
- PCR viral nucleic acid
- Viral protein (antigen) detection in intestinal tissue sections
- Histopathology: villus atrophy, cuboidal cells covering the villi, crypt hyperplasia
- Virus isolation requires trypsin to facilitate cleavage of a capsid protein
how do we treat rotaviruses?
- electrolytes, and antibiotics (young animals have permeable guts, and they are super prone to secondary bacterial infections)
how do we control rotaviruses?
- Hygiene is very important
- Proper cleaning and disinfection of rotavirus exposed herds
- Vaccines are available
Which of the following statements is NOT CORRECT about rotaviruses?
a. Diarrhea is a common and conserved sign across species
b. Higher rates of genetic shift and drift due to the segmented nature of their genome
c. Hygiene is important to control rotavirus since the non-enveloped virus is not stable in the environment
e. All of the above
c. Hygiene is important to control rotavirus since the non-enveloped virus is not stable in the environment
=> hygiene is important, because the non-enveloped virus IS stable in the environment
what is bluetongue virus? what species does it effect and how many serotypes are there? How is it transmitted and where is it generally found?
- Reoviridae, genus Orbivirus
- Affects: sheep, cattle, goats, deer
- 24 serotypes of bluetongue virus
- Transmitted through insect vector (arthropod-borne)
- Mostly a tropical and temperate disease -
Canada is currently free of the disease
what are the characteristics of most bluetongue virus infections? when do epidemics occur?
- Most infections are subclinical
- Epidemics occur when:
- New virus strain or new animal introduced to a stable ecosystem
- Environmental alterations that promote vector proliferation
what is the pathogenesis of bluetongue virus? where does it replicate and what symptoms do we see as a result?
- Virus replicates within endothelial cells and macrophages
Effects of vascular injury:
* Thrombosis and infarction of tissues
* Tissue ulceration
* Cyanosis of lips and tongue (hypoxic)
* Cyanosis and necrosis of coronary band
what is the general clinical presentation of bluetongue virus?
> Most common in sheep
- Fever
- Reluctant to move
-Edema: lips, nose, ears, tongue
-Ulcers in nose and mouth
- Abortion
