caliciviridae
TRANSCRIPT
CALICIVIRIDAEABY ELIJAH BERNARDINO
The Caliciviridae family include the following genera:
• Genus Vesivirus; type species: Vesicular exanthema of swine virus
• Genus Lagovirus; type species: Rabbit hemorrhagic disease virus
• Genus Norovirus; type species: Norwalk virus• Genus Sapovirus; type species: Sapporo virus
CALICIVIRIDAE
Caliciviridae
Vesivirus (swine, cats)
Lagovirus (rabbits) NorovirusSapovirus (humans, “noro lite”)
GI (humans) GII (humans)GIV (humans) GV (mice)GIII (pigs and cows)
GI.1 to GI.8GII.1 to GII.17 (GII.4 is the most
common outbreak strain)
CALICIVIRIDAE• The Caliciviridae family are a family of viruses, members of
Class IV of the Baltimore scheme. Common name: CALCIVIRUS.• The name calicivirus is derived from the Latin
word calyx meaning cup or goblet. This name is appropriate as many strains have visible cup-shaped depressions.
• The family consists of several viruses of veterinary importance including vesicular exanthema virus of swine, feline calicivirus, rabbit hemorrhagic disease, virus, and European brown hare syndrome.
• Caliciviruses cause systemic diseases and gastroenteritis but some cause vesicular diseases.
• Viruses: Noroviruses and Hepatitis E. (Although Hepatitis E is being reclassified into its own family Hepeviridae)
3-D Structure of Calicivirus Capsid Negative EM stain
Norwalk virus Norwalk virus
CALCIVIRUSESCHARACTERISTICS:• Small size 40 nm in diameter• They are positive-sense, non-enveloped,
the capsid appears hexagonal/spherical and has icosahedral symmetry .
• Single molecule of linear single-stranded positive-sense RNA
• Genome size 7.4 – 7.7 kilobases• Resistant to heat, detergent-based disinfectants, but
rapidly inactivated by acidity (99% inactivation at pH = 3)• Found in a number of organisms such as humans, cattle,
pigs, cats, chickens, reptiles, dolphins and amphibians.
CALCIVIRUSESTRANSMISSION:• Generally by the fecal-oral route, but they can also be transmitted via the
respiratory route.
REPLICATION:• Virus attaches to host receptors and is internalized.• Uncoating, and release of the viral genomic RNA into the cytoplasm.• VPg is removed from the viral RNA, which is then translated into a
processed ORF1 polyprotein to yield the mature non-structural proteins involved in RNA transcription.
• Negative-sense complementary ssRNAs are synthesized using the genomic RNAs as a templates.
• New genomic RNAs are synthesized using the negative-sense RNAs as templates.
• Expression of sgRNA yields the basic protein (and capsid protein).• Assembly and release of new virions.
Human Diseases and Animal Viruses• Calicivirus infections commonly cause
acute gastroenteritis, which is the inflammation of the stomach and intestines.
• Symptoms can include vomiting and diarrhea.• These symptoms emerge after an incubation time
of 2 days and the symptoms only generally last for 3 days.
• Most calicivirus infections do not call for medical attention, but those who are immunocompromised may need to be hospitalized for rehydration therapy.
• Feline calicivirus (FCV) represents an important pathogen of cats.
• Sapovirus, Norovirus and Vesivirus have been detected in pigs, making this animal species of particular interest in the study of calicivirus pathogenesis and host range.
• The first mouse norovirus, murine norovirus 1 (MNV-1), was discovered in 2003. Since then, numerous murine norovirus strains have been identified and they were assigned a new genogroup in the genus Norovirus.
• Rabbit hemorrhagic disease virus (RHDV) is a pathogen of rabbits that causes major problems throughout the world where rabbits are reared for food and clothing, make a significant contribution to ecosystem ecology, and where they support valued wildlife as a food source.
FELINE CALICIVIRUS (FCV)• It is one of the two important viral causes of
respiratory infection in cats, the other being feline Herpesvirus.
• FCV produces an acute or subacute disease characterized by conjunctivitis, rhinitis, tracheitis, pneumonia, and vesicular ulceration of the oral epithelium
• Cheetahs are the other species of the family Felidae known to become infected naturally.
Electron micrograph of FCV
PATHOGENICITY: • Natural transmission is via aerosol and formites -
often transmitted to susceptible cats by human
handlers. • Incubation period is 2 to 6 days. • Lesions are confined to respiratory tract, oral
cavity, and eyes. • The virus is shed in large amounts from infected
cats for months - persistent infection occurs in most animals, resulting in carriers.
• Different strains of FCV vary in virulence.
CLINICAL DISEASES:• Fever, anorexia, lethargy, stiff gait, nasal and ocular discharges. • Conjunctivitis. • Ulcerative lesions are commonly observed in oral
epithelium. • In severe disease, pulmonary edema and interstitial
pneumonia. LAB EXAMINTION:• Virus isolation –feline cell cultures
• Serology – DD – Feline rhinotracheitis and feline
herpesvirus-1
TREATMENT:
• There is no specific treatment for
FCV. Antibiotics are used for secondary
bacterial infections and immune modulators,
such as Lymphocyte T-Cell Immune
Modulator has been used for immune
support.
VESICULAR EXANTHEMA VIRUS (VEV)• VE disease of swine is extinct but the virus is
still present in marine mammals. • VE was an acute febrile disease of swine
characterized by formation of vesicles on the snout, teats, tongue, oral cavity, and feet.
• Disease important because it is indistinguishable clinically with FMD, and VS.
PATHOGENECITY:• Virus transmitted by contact and
contamination of formites. • Incubation period was 18 to 48 hours. • Recovery was rapid with no complications. • Immunity was solid following infection but
there were many non-cross-protective serotypes resulting in heterologous re-infections.
CLINICAL DISEASE:• Fever, lameness, rapid weight loss.• Vesicles in snout, oral cavity, teats, and feet. • Virus causes encephalitis, myocarditis,
diarrhea, and failure to thrive. • Pregnant sows may abort.
Vesicular exanthema snout showing ruptured vesicle
Vesicular exanthema tongue showing ulcerative lesions
LAB EXAMINATION/DIAGNOSIS:
•Virus isolation –in swine cell cultures• Serologic tests –Diff Diagnosis: FMDV, VSV• VE viruses were very heterogenous - 13 antigenic serotypes known.• Electron microscopy
SAPOVIRUSES • Sapoviruses are caliciviruses that together
with the noroviruses, are the most common cause of acute viral gastroenteritis in adults.
• Unlike norovirus, this virus generally only causes mild gastroenteritis in young children.
NOROVIRUS • Also known as “stomach or abdominal influenza”, winter
vomiting disease, vomiting bug, cruise ship virus.• Formerly Norwalk agent, is an RNA virus that causes
approximately 90% of epidemic non-bacterial outbreaks of gastroenteritis around the world, and may be responsible for 50% of all food borne outbreaks of gastroenteritis.
• The viruses are transmitted by faecally contaminated food or water, by person-to-person contact, and via aerosolization of the virus and subsequent contamination of surfaces.
• After infection, immunity to norovirus is usually incomplete and temporary. There is an inherited predisposition to infection, and individuals with blood type O are more often infected, while blood types B and AB can confer partial protection against symptomatic infection
Feature Observation ConsequencesLow infectious dose <102 virus particles Permits droplet/person-to-person,
foodhandler spread, secondary spread
Prolonged asymptomatic shedding
Up to 2 weeks Increases risk of secondary spread, problems with control of food handlers
Environmental stability Survives 10 ppm chlorine, freezing, 67°C
Hard to eliminate from contaminated water; survives in ice, partially cooked oysters
Great strain diversity Many genetic and antigenic types
Requires composite diagnostics; repeated infections with many different antigenic types, underestimate prevalence
Lack of longtime immunity Disease with reinfection Childhood exposure does not protect in adulthood; difficulty in developing vaccine with lifelong protection
Reservoir Humans Occurs only in human host—recent identification of related animal strains
CHARACTERISTICS:
MODES OF TRANSMISSION BY FOOD:• Food sources (i.e., food arrives contaminated)• Preparation• Food handlers• Customers• Most at risk: ready-to-eat foods that require handling
but no subsequent cooking (e.g., salads)PATHOPHYSIOLOGY:• Enteritis of the proximal small intestine and mucosal
lesions of the villous epithelium• Colon and stomach are spared (histopathology)• Delayed gastric emptying during the acute illness• Produces transient (up to 2 weeks duration) D-xylose
malabsorption
LAB EXAMINATION/DIAGNOSIS:• Specific diagnosis of norovirus is routinely made
by polymerase chain reaction (PCR) assays or real-time PCR assays, which give results within a few hours. These assays are very sensitive and can detect concentrations as low as 10 virus particles.
• Tests such as ELISA that use antibodies against a mixture of norovirus strains are available commercially but lack specificity and sensitivity.
PREVENTION:• Hand washing is an effective method to reduce the
spread of norovirus pathogens. • Sanitizing of surfaces where the norovirus may be
present is recommended. Alcohol rubs are not very effective at dealing with Norovirus.
Norovirus