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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?

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slide1
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.
slide2
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

slide3
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.

slide4
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)

slide5
Images of Caliciviridae

3-D Structure of Calicivirus Capsid

Negative EM stain

Norwalk virus

Norwalk virus

slide6
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)
slide7
Lagovirus – 2 genotypes

Rabbit hemorrhagic disease virus

European brown hare syndrome

Unnamed genus - SRSV group 2 viruses

Toronto virus

Lordsdale virus

Several swine caliciviruses

slide8
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.
slide9
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.
slide10
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.

slide11
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.
slide12
Vesicular exanthema

snout showing ruptured

vesicle

slide13
Vesicular exanthema

tongue showing ulcerative

lesions

slide14
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.

slide15
Diagnosis
  • Virus isolation –in swine cell cultures
  • Serologic tests –Diff Diagnosis: FMDV, VSV
  • VE viruses were very heterogenous - 13 antigenic

serotypes known.

  • Electron microscopy
slide16
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
slide17
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.
slide18
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.
slide19
FCV Diagnosis
      • 1. Clinical presentation
      • 2. Virus isolation –feline cell cultures
  • 3. Serology – DD – Feline rhinotracheitis and feline herpesvirus-1
slide20
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.

slide21
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

slide22
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.

slide23
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.
slide24
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.

slide25
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.
slide26
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.

slide27
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
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