RNA viruses Flashcards
Why do RNA viruses have a higher mutation rate?
uses their own machinery to transcribe/translate RNA/DNA
less ability to catch mistakes
positive vs negative sense RNA
positive: can go directly into ribosome to begin translation
negative: has RNA dependent RNA polymerase to copy RNA into RNA able to be translated by ribosome
mononegavirales
mono: 1 genome, neg: negative sense
enveloped (easy to destroy)
helical nucleocapsid
buds from plasma membrane at sites containing peplomers
families: paramyxoviridae, rhabdoviridae, filoviridae, bornaviridae
paramyxoviridae
- mononegavirales (enveloped, - sense, helical)
- Replicate in the cytoplasm (Eosinophilic intracytoplasmic inclusions are common)
- Labile in the environment (Disinfection is easy, Transmission is by aerosol or close contact)
- Single stranded RNA viruses
- Replication is in the respiratory tract
- Virions are released by budding
- Produce a fusion protein (Syncytial cell formation is common)
- The viruses have a narrow host range
rinderpest
mononegavirales, paramyxoviridae (enveloped, - sense, helical)
kills cattle
globally eradicated!
factors enabling eradication:
* An efficacious vaccine
* Reliable diagnostic tests
* The absence of carrier animals and wildlife reservoirs
* control of animal movement
canine distemper virus
mononegavirales, paramyxoviridae (enveloped, - sense, helical)
intranuclear and intracytoplasmic inclusions in brain
Highly contagious
Infects many cell types, including epithelial, lymphoid, and oligodendroglial cells, and causes generalized infection
Affects the skin, the respiratory, gastrointestinal, and urinary tract, and the brain
Infection occurs between 3 – 6 months old when maternal antibody declines
Acute disease is followed by recovery and lifelong immunity or neurologic disease and death
Clinical signs:
* Leukopenia
* Diarrhea, vomiting
* Conjunctivitis, nasal discharge
* Coughing (could be mild kennel cough)
* Hardening of the nose and footpads
* can be subclinical
* failure of enamel development of teeth (enamel hypoplasia, odontodystrophy)
Old dog encephalitis occurs years after recovery and results in neurologic deterioration and death
Bovine parainfluenza virus 3 (PI3) and Bovine respiratory syncytial virus (BRSV)
mononegavirales, paramyxoviridae (enveloped, - sense, helical)
Bovine Respiratory Disease complex viruses
short lived immunity
vaccines available
PI3 is less pathogenic than BSRV
Bovine parainfluenza virus 3 (PI3)
mononegavirales, paramyxoviridae (enveloped, - sense, helical)
Often subclinical- does not usually cause serious disease, not very pathogenic
Part of Bovine resp disease (BRD) complex?
Vaccines available
Immunity short-lived
Bovine respiratory syncytial virus (BRSV)
mononegavirales, paramyxoviridae (enveloped, - sense, helical)
* Moderate to severe disease
* Part of bovine resp disease (BRD) complex!
* Vaccines available
* Infection immunosuppressive
* Immunity short-lived
* Adults-Atypical interstitial pneumonia
rhabdoviridae
mononegavirales, enveloped, helical, single stranded negative sense
shaped like a bullet
causes eosinophilic intracytoplasmic inclusions (negri bodies)
ex: rabies
negri bodies
eosinophilic intracytoplasmic inclusions
in rhabdoviridae
RABIES
Rabies virus
mononegavirales, rhabdovirus, enveloped, helical, single stranded negative sense
* Infects the nervous system of all mammals, including humans
* nearly always fatal once symptoms appear.
* Endemic on all continents except Australia and Antarctica
* If rabies is suspected, the suspect animal must be killed and brain tissue collected for testing.
* Usually maintained in and transmitted by a particular host, depending on the geographic region (raccoons, skunks, bats and foxes)
* Enters peripheral nerve endings
* Limited replication locally in myocytes or other tissues.
* Transported to the central nervous system by retrograde axoplasmic flow
* Clinical signs develop due to neuronal damage caused by viral replication.
* Incubation up to 6 months
* Clinical course is short (few days to weeks)
* Virus is released at axon terminals where it infects many non-nervous tissues including the salivary glands.
* negri bodies
rabies vaccination
- Vaccines for dogs and cats contain inactivated virus (genotype 1) and are safe and effective.
- A vaccinia-rabies glycoprotein recombinant vaccine has been developed for oral administration to wildlife.
vesicular stomatitis
rhabdovirus, mononegavirales, enveloped, helical, single stranded negative sense
* only vesicular diseases that effects horses (also effects pigs, sheep, cattle)
* Infects the epithelium of all mammals, including humans
* Infection results in vesicular disease
* Mucosal vesicles and ulcers
* Vesicles on the udder and coronary band
* Because it mimics other vesicular diseases like foot and mouth disease, VS is a reportable disease
* Transmission is by sand flies, midges, black flies, or direct contact
* Vesicular stomatitis is** endemic** in Central America and in regions of South America and the United States.
* Subclinical infection is common: around 10 to 15% of animals in infected herds exhibit clinical signs.
* Vesicular stomatitis is a zoonotic disease with human clinical signs that resemble influenza.
rabies vs vesicular stomatitis
both: mononegavirales, rhabdovirus, enveloped, helical, single stranded negative sense
* Both viruses have wide host range
* Both viruses are endemic in North America
* Both viruses are zoonotic
* Rabies virus infects neurons, vesicular stomatitis virus infects epithelial cells
* Rabies is transmitted by saliva and bites, VS is transmitted by arthropods
* Rabies is reportable to the health department.
* VS is reportable to state and federal veterinarians
orthomyxoviruses
enveloped, helical, single stranded negative sense
replicates in nucleus, no inclusion bodies
SEGMENTED GENOME: can shuffle RNA in new combinations– reassortment
influenza
reassortment
can occur randomly in RNA viruses with segmented genomes, such as orthomyxoviruses, reoviruses and bunyaviruses.
mixing of the various segments of a segmented genome when a cell is infected with multiple viruses results in rapid antigenic shift in the epidemiology of influenza virus.
reassortment
can occur randomly in RNA viruses with segmented genomes, such as orthomyxoviruses, reoviruses and bunyaviruses.
mixing of the various segments of a segmented genome when a cell is infected with multiple viruses results in rapid antigenic shift in the epidemiology of influenza virus.
influenza A cycle of transmission
direct: non human virus directly affects humans
reassortment host: pigs (most suseptible to the most strains) act as a reassortment host where multiple types of influenza reassort and create new viruses
* new reassorted virus affects other hosts
avian influenza
- Aquatic birds (especially ducks) are the reservoirs of Influenza A
- Provide a genetic pool for the generation of new subtypes
- Migratory water fowl and poultry trade are the cause of international border spread
- Most viruses are species specific but transfer between species does occur
- Viruses replicate in the gastrointestinal tract of birds and transmission of low pathogenic subtypes is fecal-oral
- Human infection with AI is attributed to poor hygiene and close contact with poultry and pigs
- Genetic reassortment in pigs and poultry can lead to new subtypes that can infect humans and result in pandemics
- Avian viruses replicate poorly in humans, but human and avian viruses replicate well in pigs leading to reassortment and emergence of new viruses (H1N1 2009)
- Some viruses can infect other species without reassorting (H5N1 1997) but no human-to-human transmission has been documented
highly pathogenic avian influenza
Caused by Influenza A
High morbidity and mortality in domestic poultry
Direct transmission from poultry to humans
Human-to-human transmission (inefficient)
equine influenza
Horses 1 to 5 years old tend to be most susceptible
Clinical signs include cough, high fever (up to 106°F), and nasal discharge
Transmission is by aerosol or contact with contaminated equipment
Virus replicates in epithelial cells in the upper respiratory tract > rhinitis and tracheitis
narrow range
canine influenza
narrow range
Transmission is through aerosol and contaminated equipment
Dogs are most infectious during the 2-4 day incubation period, before the onset of clinical signs
Mutations avian viruses allowed for dog-to-dog spread
The virus replicates in the epithelium of the respiratory tract, including nasal mucosa and bronchioles in the lungs
Infection results in rhinitis, tracheitis, bronchitis, and bronchiolitis
Necrosis of the epithelium can predispose to secondary bacterial infections
Clinical signs include cough, high fever, and nasal discharge
copy choice (template switching) recombination
- Commonly occurs between positive-sense single-stranded RNA viruses.
- The RNA polymerase switches between template strands during synthesis of the complimentary negative-sense strand.
- An exceptionally high frequency of genetic recombination has been observed in mixed infections of coronaviruses.
coronavirus
enveloped, helical, positive sense single strand
Host cell tropism is typically respiratory and intestinal epithelium
Infection is usually mild in older animals but can be severe in young animals
ex: FIP
alphacoronavirus 1
Feline coronavirus (including feline infectious peritonitis virus)
Transmissible gastroenteritis virus (TGE)
Canine coronavirus
feline enteric coronavirus
mutation of coronavirus causes it to infect macrophages
feline infectious peritonitis and immune response of cat
effective cell mediated immunity
* virus elimination, clinically normal cat
ineffective cell mediated immunity
* continuous replication of FIP
* progressive fatal disease (sever vasculitis =wet, moderate vasculitis =dry)
inadequate cell mediated immunity
* intermediate replication of FIP
* clincially normal cat with periodic shedding
The key initiating pathogenic event in FIP is the productive infection of _______ and _______ by genetic variants of the original enteric coronavirus.
A macrophages & monocytes
B hepatocytes & Kupffer cells
C platelets & erythrocytes
D neutrophils & plasma cells
A
What is considered the most important differentiating factor that is associated with one cat exhibiting the “wet” form of FIP and another cat exhibiting the “dry” form of FIP?
A viral serotypes
B specific spike proteins affected by viral mutations
C age of the cat
D severity of immune-mediated vasculitis
D
The most appropriate ante-mortem test for FIP is ________.
ELISA test for FCoV
ELISA test for FCoV antibodies
AGID test for FCoV antibodies
Serum neutralization test for FCoV antibodies
Immunohistochemistry of biopsies of affected organs
Immunohistochemistry of biopsies of affected organs
A safe and highly effective vaccine is available for FIP.
true/false
false
FIP Vaccine
There is only one licensed FIP vaccine available; however, this vaccine has minimal if any effectiveness in preventing FIP
canine coronavirus
The ability of canine coronavirus (CCoV) to cause disease is variable and the agent can be isolated from normal dogs and those with **diarrhea. **
A genetically and antigenically distinct virus, canine respiratory coronavirus (CRCoV), has been described and is associated with mild respiratory disease, particularly in kenneled dogs.
transmissable gastroenteritis
coronavirus
**highly contagious, coronaviral disease of young pigs **
closely related antigenically to feline coronavirus and canine coronavirus and all three viruses are now considered a single species and referred to as alphacoronavirus 1
Digestion and cellular transport of nutrients and electrolytes are severely disrupted resulting in the** accumulation of fluid in the intestinal lumen and diarrhea**
The sudden onset and rapid spread of diarrhea among newborn pigs along with almost 100% mortality is highly suggestive of TGE.
porcine epidemic diarrgea virus
similar signs to transmissable gastroenteritis but lower mortality
bovine coronavirus
one of the causes of calf diarrhea and is also associated with winter dysentery in adult housed cattle.
Average age of diarrhea onset is 7-10 days.
There is evidence of its involvement in the bovine respiratory disease complex.
Virus is transmitted by the fecal-oral route
equine coronavirus
Betacoronavirus 1
Usually subclinical or self-limiting
Typically associated with enteric disease in foals
Like bovine coronavirus, disease is seen more in winter months, in stressed animals, or under poor environmental conditions
Equine coronavirus has not yet been associated with respiratory disease
coronaviruses in general key concepts
Coronaviruses infect and replicate in respiratory or intestinal epithelium
Most disease are mild in adults and can be severe in young animals
Important cause of diarrhea in young pigs and calves
A mutation in the feline enteric coronavirus results in immune-complex disease (FIP)
pestiviruses
single stranded RNA
replicate in cytoplasm
labile in environemnt
Transmission is vertical or horizontal by nose-to-nose contact
The main source of virus is persistently-infected animals
bovine viral diarrhea virus and time of gestation
outcome is very strain dependent
can cause:
* infertility if affected near conception
* abortion if cow is infected in first 150 days gestation
* if calf is infected before 150 days gestation = noncytopathic BVDV (spreads forever, persistant infection)
* if calf is infected ~150 days gestation = congenital defects (cerebellar hypoplasia most common)
* after 150 days = normal acute infection (will have precolostral antibodies to BVDV)
bovine viral diarrhea virus and persistant infection
calf must be infected before 150 days gestation
cow usually has acute infection during pregnancy
all persistantly infected cows produce persistantly infected calfs
can cause mucosal disease
non cytopathic strain
mucosal disease and bovine viral diarrhea
persistant infected animal with non cytopathic strain causes mucosal disease
cannot tell difference between acute infection with a virulent noncytopathic strain from mucosal disease resulting from superinfection of a PI with a cytopathic strain
non cytopathic vs cytopathic virus of bovine viral diarrhea
non cytopathic
* causes PI
* causes prolonged testicular infections
* disseminates more widely throughout the body
* vast majority of field strains
* stronger humoral immune response
* less robust cell-mediated immune response
cytopathic
* does not cause PI
* does not cause prolonged testicular infections
* stimulates rapid immune response which limits dissemination
* vast minority of field strains
* less robust humoral immune response
* stronger cell-mediated immune response
hairy shaker lamb disease (border disease)
pestivirus
Named for Welsh/English border
Reproductive losses (resorption, abortion, or mummification)
Neurologic tremors & fleece abnormalities
Hypomelinogenesis
Persistently infected animals (before ~60 to 85 d of 150 gest)
hog cholera
pestivirus
Conjunctivitis and ocular discharge
Reproductive losses
Neurologic tremors in piglets
Splenic infarction
Necrosis of tonsillar tissue
Can survive in meat >feed uncooked garbage
