Caliciviridae

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• GOALS FOR THE VIROLOGY LECTURES
• Each lecture attempts to answer the following
  questions.
• What are the general characteristics of this
  virus family?
• What are some of the important viruses in this
  family?
• What type of disease do the viruses cause?
• Which animals does the virus infect?
• Is the disease zoonotic?
• What is the method of transmission of the virus?
• What is the worldwide distribution of the
  viruses? When and
• where should you be looking out for these
  diseases?
• How do you diagnose the disease differential
  diagnosis Briefly
• How is the disease controlled Briefly.

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Viruses with ve RNA genomes
foot and mouth disease virus
Picornaviridae

porcine enteroviruses
Caliciviridae
Coronaviridae
feline calicivirus
coronaviruses
Arteriviridae
equine arterivirus, PRRSV
Flaviviridae
flaviviruses (WNV)
pestiviruses (BVD)
Togaviridae
equine encephalitis viruses
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Caliciviridae
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.
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General Characteristics of Caliciviridae

• Small size 40 nm in diameter
• Non-enveloped, nucleocapsid 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)

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Images of Caliciviridae
3-D Structure of Calicivirus Capsid
Negative EM stain
Norwalk virus
Norwalk virus
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Classification
There are 4 genera, Vesivirus, Lagovirus, and 2
unnamed genera. Vesivirus many genotypes.
Vesicular exanthema virus of swine 13
genotypes Sam Miguel virus of sea lions 17
genotypes Feline Calicivirus Cetacean
calicivirus (Tur-1) Primate calicivirus
(Pan-1) Skunk calicivirus Reptile calicivirus
(Cro-1)
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Lagovirus 2 genotypes Rabbit hemorrhagic
disease virus European brown hare syndrome
Unnamed genus - SRSV group 2 viruses Toronto
virus Lordsdale virus Several swine caliciviruses
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Unnamed Second Genus Contains human
caliciviruses, including - Sapporo virus -
Manchester virus Unclassified
caliciviruses There are a number of
unclassified caliciviruses, including bovine
enteric calicivirus, canine calicivirus, mink
calicivirus, porcine enteric calicivirus, walrus
calicivirus, lion calicivirus, chicken
calicivirus.
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VESICULAR EXANTHEMA VIRUS (VEV) -Vesivirus 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.
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VE Pathogenesis

• Virus transmitted by contact and contamination
  of
• formites.
• Incubation period was 18 to 48 hours.
• Morbidity was very high.
• Recovery was rapid with no complications.
• Immunity was solid following infection but there
  were
• many non-cross-protective serotypes resulting
  in
• heterologous re-infections.

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Clinical Disease

• Fever, lameness, rapid weight loss.
• Vesicles in snout, oral cavity, teats, and feet.
  
• Mortality was low.
• Virus causes encephalitis, myocarditis,
  diarrhea,
• and failure to thrive.
• Pregnant sows may abort.

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Vesicular exanthema snout showing ruptured
vesicle
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Vesicular exanthema tongue showing ulcerative
lesions
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Epidemiology and Control
USA Policy that led to eradication Slaughter of
all affected animals because of fear of FMD.
Garbage feed to pigs was cooked. No vaccination
was attempted.
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Diagnosis

• Virus isolation in swine cell cultures
• Serologic tests Diff Diagnosis FMDV, VSV
• VE viruses were very heterogenous - 13 antigenic
  
• serotypes known.
• Electron microscopy

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FELINE CALICIVIRUS (FCV) - Vesivirus Feline
calicivirus disease is one of the two major
respiratory diseases in cats worldwide FCV
produces an acute or subacute disease
characterized by conjunctivitis, rhinitis,
tracheitis, pneumonia, and vesicular ulceration
of the oral epithelium
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FCV Pathogenesis

• 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.
• Morbidity is very high.

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Clinical disease

• 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.
• Mortality can be as high as 30 in young kittens.

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FCV Diagnosis
1. Clinical presentation 2. Virus isolation
feline cell cultures 3. Serology DD Feline
rhinotracheitis and feline herpesvirus-1
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Epidemiology and Control

• Disease is distributed worldwide.
• Even though all Felidae species are susceptible,
  
• natural infections have only been reported
  in domestic
• cats and cheetahs.
• The main control method is by vaccination
  -Attenuated
• and inactivated vaccines are widely used.

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RABBIT HEMORRHAGIC DISEASE VIRUS Genus -
Lagovirus Is a highly infectious disease of
European rabbits first identified in China in
1984 It killed 470, 000 rabbits in the first 6
months in 1985 and rapidly spread throughout
China
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RHDV Pathogenesis

• Infection is via fecal-oral route. Incubation
  period is
• short.
• Lungs most severely affected with congestion and
  
• hemorrhage.
• Splenomegaly and massive liver necrosis. Large
  blood
• clots in blood vessels indicative of
  disseminated
• intravascular coagulation.

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Clinical disease

• Disease occurs in rabbits over 2 months old.
• Younger rabbits do not develop disease after
  infection.
• Peracute disease - Fever, depression, sudden
  death
• within 6 to 24 hours.
• Acute and subacute diseases serosanguinous
  nasal
• discharges nervous signs.
• Morbidity is 100
• Mortality rate is 90 in rabbits over 2 months
  old.

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RHDV Diagnosis
NOTE Virus has not been isolated in culture. 1.
Hemagglutination test RHDV agglutinates
human erythrocytes 2. Immunofluorescence
Epidemiology and Control Inactivated homogenate
vaccine available with adjuvant Recent DNA
vaccine developed but not available
commercially.
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RHDV as Biological Control NOTE In Australia and
New Zealand rabbits number as many as 100
million - cause an estimated 600 million annual
damage (loss of animal species, habitat and crop
destruction). RHDV virus accidentally founds
its way to the Australian rabbits and served as
an excellent biocontrol agent. Virus also
accidentally introduced in New Zealand and
rabbit numbers dropped by up to 60 in some
areas.
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19 August 2002 MINISTER KEMP'S ANSWERS ON
RABBIT DISEASE FAIL TO SETTLE FRIGHTENING
QUESTIONS Federal Minister for the Environment
and Heritage, Dr David Kemp, has side-stepped
several Questions on Notice posed by Senator Bob
Brown about proposals to further spread the
deadly haemorrhagic Rabbit Calicivirus Disease
(RCD) in Australia. Animals Australia received
copies of Dr Kemp's answers to 3 of the 4
questions, but the Minister has failed to give
any assurance that a new bait delivery system for
the disease is safe. After its mysterious first
appearance in China in 1984, and its unexplained
escape from Wardang Island (South Australia) in
1995, RCD was deliberately released by
Governments across Australia in 1996 in the hope
of reducing the wild rabbit population. The
National Registration Authority is now
considering a proposal to further spread the
disease in Australia by placing the live virus on
food baits. The Minister was asked if he is
aware of a recent study that showed that pigs
inoculated with the virus became sick. Senator
Brown also asked the Minister to give a cast iron
assurance that the disease will never spread to
Australian pigs, or to any other species,
including humans. Dr Kemp side-stepped this
question - merely saying all decisions are based
on a risk analysis. Executive Director of
Animals Australia, Glenys Oogjes, said, "We are
not surprised that the Minister is unable to give
that assurance. The only scientists who have ever
claimed that this virus - RCD - is safe for other
species are those with a vested interest in
covering up the risks - and even they have never
said it will not cross species, only that
cross-species infection is 'unlikely'. The new
proposal for the disease to be put in baits
(rather than injected into rabbits) will make it
even more available to a broader range of
animals. It is madness!" In 1996 Environment
Australia (EA) gave the original proposal to
release RCD infected rabbits into wild rabbit
populations the thumbs up. A recent assessment
report by EA of the current proposal to use virus
baits has (again) concluded that the chances of
cross-species infection are minimal.
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Caliciviruses 1 minute quiz

• Please write responses to the questions on a
  piece of paper,add your name, date, and hand it
  in.
• Caliciviruses only cause GIT infections. True or
  false
• (2) Why has RHDV worked so well as biological
  control?
• The calicivirus genome is almost the same size as
  that
• of picornaviruses. True or False