RNA viruses

Question 1

Why do RNA viruses have a higher mutation rate?

Answer 1

uses their own machinery to transcribe/translate RNA/DNA
less ability to catch mistakes

Question 2

positive vs negative sense RNA

Answer 2

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

Question 3

mononegavirales

Answer 3

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

Question 4

paramyxoviridae

Answer 4

• 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

Question 5

rinderpest

Answer 5

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

Question 6

canine distemper virus

Answer 6

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

Question 7

Bovine parainfluenza virus 3 (PI3) and Bovine respiratory syncytial virus (BRSV)

Answer 7

mononegavirales, paramyxoviridae (enveloped, - sense, helical)
Bovine Respiratory Disease complex viruses
short lived immunity
vaccines available
PI3 is less pathogenic than BSRV

Question 8

Bovine parainfluenza virus 3 (PI3)

Answer 8

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

Question 9

Bovine respiratory syncytial virus (BRSV)

Answer 9

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

Question 10

rhabdoviridae

Answer 10

mononegavirales, enveloped, helical, single stranded negative sense
shaped like a bullet
causes eosinophilic intracytoplasmic inclusions (negri bodies)
ex: rabies

Question 11

negri bodies

Answer 11

eosinophilic intracytoplasmic inclusions
in rhabdoviridae
RABIES

Question 12

Rabies virus

Answer 12

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

Question 13

rabies vaccination

Answer 13

• 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.

Question 14

vesicular stomatitis

Answer 14

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.

Question 15

rabies vs vesicular stomatitis

Answer 15

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

Question 16

orthomyxoviruses

Answer 16

enveloped, helical, single stranded negative sense
replicates in nucleus, no inclusion bodies
SEGMENTED GENOME: can shuffle RNA in new combinations– reassortment
influenza

Question 17

reassortment

Answer 17

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.

Question 17

reassortment

Answer 17

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.

Question 18

influenza A cycle of transmission

Answer 18

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

Question 19

avian influenza

Answer 19

• 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

Question 20

highly pathogenic avian influenza

Answer 20

Caused by Influenza A
High morbidity and mortality in domestic poultry
Direct transmission from poultry to humans
Human-to-human transmission (inefficient)

Question 21

equine influenza

Answer 21

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

Question 22

canine influenza

Answer 22

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

Question 23

copy choice (template switching) recombination

Answer 23

• 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.

Question 24

coronavirus

Answer 24

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

Question 25

alphacoronavirus 1

Answer 25

Feline coronavirus (including feline infectious peritonitis virus) Transmissible gastroenteritis virus (TGE) Canine coronavirus

Question 26

feline enteric coronavirus

Answer 26

mutation of coronavirus causes it to infect macrophages

Question 27

feline infectious peritonitis and immune response of cat

Answer 27

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

Question 28

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

Answer 28

A

Question 29

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

Answer 29

D

Question 30

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

Answer 30

Immunohistochemistry of biopsies of affected organs

Question 31

A safe and highly effective vaccine is available for FIP. true/false

Answer 31

false

Question 32

FIP Vaccine

Answer 32

There is only one licensed FIP vaccine available; however, this vaccine has minimal if any effectiveness in preventing FIP

Question 33

canine coronavirus

Answer 33

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.

Question 34

transmissable gastroenteritis

Answer 34

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.

Question 35

porcine epidemic diarrgea virus

Answer 35

similar signs to transmissable gastroenteritis but lower mortality

Question 36

bovine coronavirus

Answer 36

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**

Question 37

equine coronavirus

Answer 37

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**

Question 38

coronaviruses in general key concepts

Answer 38

Coronaviruses infect and replicate in r**espiratory 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)**

Question 39

pestiviruses

Answer 39

**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

Question 40

bovine viral diarrhea virus and time of gestation

Answer 40

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)

Question 41

bovine viral diarrhea virus and persistant infection

Answer 41

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

Question 42

mucosal disease and bovine viral diarrhea

Answer 42

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

Question 43

non cytopathic vs cytopathic virus of bovine viral diarrhea

Answer 43

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

Question 44

hairy shaker lamb disease (border disease)

Answer 44

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)

Question 45

hog cholera

Answer 45

pestivirus Conjunctivitis and ocular discharge Reproductive losses Neurologic tremors in piglets Splenic infarction Necrosis of tonsillar tissue Can survive in meat >feed uncooked garbage