CORONAVIRIDAE

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CORONAVIRIDAE

• Crown viruses

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General Characteristics- Coronaviruses

• Single-stranded, positive sense RNA viruses
• Enveloped and pleomorphic
• Infect a wide range of mammalian and avian
  species
• Cause respiratory and enteric disease,
  encephalomyelitis, hepatitis, serositis, and
  vasculitis in domestic animals. In humans, common
  cold.
• Pronounced tropism for epithelial cells of the
  respiratory and the intestinal tract.
• In general, mild or inapparent infections in
  adults but severe diseases in newborn or young
  animals.
• Stability of virus cold temperature relatively
  stable labile at room temperature highly
  photosensitive

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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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Classification and General Characteristics

• Coronaviruses have also been associated with
  infections of the respiratory and enteric tracts
  and with central nervous system disease in
  monkeys, rats, rabbits, and other species.
• Unusually large club-shaped peplomers projecting
  from the envelope give the particle the
  appearance of a solar corona pleomorphic 75-160
  nm
• Family Coronaviruses have been divided into four
  antigenic groups (Table 1). Viruses within each
  group show some antigenic cross-reactivity, and
  there may be a number of serotypes within one
  virus species. Animals immune to one serotype are
  susceptible to infection with different serotypes
  of the same coronavirus.

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Table 1. Antigenic Groups and Diseases Caused by
Coronaviruses
Antigenic Group Virus Disease
I (mammalian) Human coronavirus 299E Common
cold Transmissible gastroenteritis Gastroenteriti
s Feline infectious peritonitis Peritonitis,
pneumonia virus, meningoencephalitis, pano
phthalmitis, wasting Canine coronavirus Enteritis
II (mammalian) Human coronavirus OC43 Common
cold Mouse hepatitis virus (many Hepatitis,
encephalomyelitis, serotypes) enteritis Bovine
coronavirus Gastroenteritis Porcine
hemagglutinating Vomiting, wasting,
and encephalomyelitis virus encephalomyelitis
III (avian) Infectious bronchitis virus
of Tracheobronchitis, nephritis chickens (3
eight serotypes) IV (avian) Bluecomb disease
virus of Enteritis turkeys
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Coronavirus Structure

• The envelope carries three glycoproteins
• S - Spike protein receptor binding, cell fusion,
  major antigen
• E - Envelope protein small, envelope-associated
  protein
• M - Membrane protein transmembrane - budding
  envelope formation In a few types, there is a
  third glycoprotein
• HE - Haemagglutinin-esterase
• The genome is associated with a basic
  phosphoprotein, N.

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Coronavirus replication. Numbers of mRNAs and
locations of nonstructural (NS) proteins may vary
for different cornaviruses. Virions bind to the
cell membrane and enter by membrane fusion or
endocytosis. Viral genomic RNA acts as mRNA to
direct the synthesis of viral RNA-dependent RNA
polymerase. This enzyme copies the viral genomic
RNA to form full-length (-) strand templates.
These templates are copied to form new () strand
genomic RNA, an overlapping series of subgenomic
mRNAs, and leader RNA. All mRNAs are capped and
polyadenylated and form a nested set with common
3 ends. Each mRNA codes for a single
polypeptide. The N protein binds to novel viral
RNA to form helical nucleocapsids. E1, E2, and
E3 glycoproteins are produced on membrane-bound
polysomes. Some coronaviruses do not encode E3.
Cornaviruses that encode E3 cause hemadsorption
in infected cells. Virions are formed by budding
at membranes of the Golgi apparatus and the RER,
but not at the plasma membrane. Virions are
released by cell lysis or by fusion of
post-Golgi, virion-containing vesicles with the
plasma membrane.
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Replication
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SARS Severe Acute Respiratory Sydrome

• February 2003 Guangdong, China
• Viral pneumonia, fever cough,
• dyspnea, headache, and hypoxemia
• High case fatality

Lipsitch et al 2003, Science 300 1966
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SARS Coronavirus
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SARS
Where did SARS come from?
palm civet (paguma larvata)
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SARS diagnosis
Serology ELISA, questionable Virology-PCR
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Viruses of Veterinary Importance Coronaviruses

• Bovine coronavirus (BCV)
• Transmissible gastroenteritis (TGE)
• Feline infectious peritonitis (FIP)
• Infectious bronchitis disease virus (IBDV)

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Bovine Coronavirus (BCV)

• Viral diarrhea- Rotaviruses are the major cause
  of diarrhea in the young calf. Coronaviruses are
  also important. The pathogenesis is similar
  between the two viruses
• Disease is most commonly seen in calves at about
  1 week of age, the time when antibody in the
  dam's milk has fallen to a low level. The
  diarrhea usually lasts for 4 or 5 days. The
  destruction of the absorptive cells of the
  intestinal epithelium of the small intestine, and
  to a lesser extent those of the large intestine,
  leads to the rapid loss of water and
  electrolytes.
• Glucose and lactate metabolism is affected
  hypoglycemia, lactic acidosis, and hypervolemia
  can lead to acute shock, heart failure, and
  death, although coronavirus diarrhea is generally
  less severe than that caused by rotaviruses.
  Bovine coronaviruses may cause diarrhea in humans.

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Viral causes of diarrhea in neonates

• Rotavirus
• Coronavirus
• BVD
• Bredavirus
• Calicivirus
• Parvovirus
• Astrovirus

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Susceptability of neonates

• Rotaviruses 4 to 14 days
• Coronavirus 4 to 30

4 days
0
Colostral Antibodies in gut
Susceptible period
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Diagnosis

• FA of fecal samples
• EM

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Prevention

• Vaccination of pregnant animals
• Colostrum for 2 weeks

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vaccines against calf diarrhoea
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Bovine Coronavirus (BCV)

• Winter dysentery is a sporadic acute disease of
  adult cattle that occurs in many countries
  throughout the world, and it is believed to be
  caused by coronaviruses.
• The clinical syndrome is characterized by bloody
  diarrhea accompanied by decreased milk
  production, depression, and anorexia.
• Available vaccines are not effective, because
  they do not appear to contain sufficient
  antigenic mass and cannot be given early enough.
  Alternatives to vaccinating calves are to
  immunize the dam to promote elevated antibody
  levels in the colostrum or to feed antibody
  directly to the calf in colostrum.

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Transmissible Gastroenteritis Virus (TGEV)
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Transmissible Gastroenteritis Virus (TGEV)

• TGEV of swine usually occurs in the winter months
• Characterized by an explosive outbreak of
  vomiting and profuse diarrhea
• Transmissible gastroenteritis is one of the major
  causes of death in young piglets in the a
  midwestern United States. Mortality is high,
  vaccines are of limited efficacy, and it appears
  to be difficult to prevent the introduction of
  the virus into herds.

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Transmissible Gastroenteritis Virus (TGEV)

• Clinical
  Features
• The disease is usually recognized at farrowing
  time.
• The incubation period is usually 1-3 days, and
  all litters within the farrowing house are
  commonly affected at the same time.
• The clinical signs in piglets are vomiting
  followed by a watery diarrhea and rapid loss of
  weight. The diarrhea is profuse, with an
  offensive odor, and often contains curds of
  undigested milk.
• Piglets infected when under 7 days of age
  generally die within 2 to 7 days of the onset of
  signs piglets over 3 weeks of age usually live
  (may be unthrifty for several weeks). In growing,
  finishing, and adult swine the disease is
  commonly associated with inappetence and diarrhea
  of a few days' duration, and may even go
  unnoticed. Sows infected late in pregnancy may
  develop pyrexia, but they are otherwise normal
  and rarely abort.

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TGE IHC Immunocytochemistry Infected
Epithethial Cells
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Transmissible Gastroenteritis Virus (TGEV)

• Diagnosis
• presumptive diagnosis of TGE can be made from
  the sudden appearance of a rapidly spreading and
  often fatal disease of young piglets accompanied
  by vomiting and diarrhea.
• clinical diagnosis can be confirmed by
  demonstration of specific antigen by
  immunofluorescence, isolation of virus, and
  demonstration of rising antibody titers in paired
  sera.

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Transmissible Gastroenteritis Virus (TGEV)

• Epidemiology and Control
• Transmissible gastroenteritis occurs most
  commonly in the winter months (in North America
  between November and April), but its source is
  unknown. Its presence becomes apparent only when
  large numbers of piglets are born at a time when
  weather conditions favor transmission.
• Control is difficult, although good management of
  the farrowing house can reduce the risk. The most
  widely used vaccination regimen involves
  vaccinating the sow with an attenuated vaccine 3
  weeks before farrowing, thus providing piglets
  with high levels of protective antibody in the
  colostrum during the critical first few days of
  life.

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feline infectious peritonitis
Horzinek and H. Lutz An update on FIP Veterinary
Sience Tomorrow Jan, 2001 www.vetscite.org
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FIP

• fatal disease of young cats (3-18 mo) in
  multi-cat houses or catteries
• not seen before 1950
• new virus?
• old virus, new disease
• systemic antibodies not protective, may even be
  harmful (antibody dependent enhancement, early
  death)

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feline enteric coronavirus

• closely related to dog, pig (TGE), human
  coronaviruses
• species specific but K9CV can infect cats
• two serotypes
• serotype I
• more common, 70-95 of isolates, does not cross
  react with K9CV
• difficult to isolate

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FeCV, serotype 2
Both serotypes can lead to FIP causing strains
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FeCV

• very prone to making mistakes during replication
• 1/10,000 nucleotides
• quasispecies
• invariant portion of genome
• primers for RT-PCR
• mild enteric or respiratory disease
• grows mainly in epithelial cells
• persistent infections
• in balance with immune system
• low levels of antibody

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FIPvirus

• derived by mutation from FeCV
• nature of mutation not defined
• few obvious common mutations in FIP causing
  strains
• No reliable technique for differentiating between
  non-virulent and virulent strains
• not usually spread from cat to cat

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epidemiology

• Exposure to FeCV
• 25 of cats from 1-2 cat households are
  seropositive
• 75-100 of cats from catteries seropositive
• susceptible cats become infected immediately
  following exposure
• kittens can become infected in utero or soon
  after maternal antibodies drop below protective
  levels

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epidemiology (FIP)

• 15,000 in 1-2 cat households
• 120 in catteries
• sporadic
• clustered9 (2-3 cats)
• rarely epidemic - 40 mortality
• no gender or breed predisposition

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persistent infections

• cats can shed virus (RT-PCR of blood and feces)
  for long time
• persistence not reinfection
• virus replicates in a few epithelial and lymphoid
  cells
• immunohistochemistry
• each cat has own collection of viruses
• protected from infection by other strains
• premunition
• reason for rare horizontal transmission of FIP

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FIP pathogenesis
FEC
Mild diarrhoea or respiratory illness
virus
immune system
persistent infection
low level of replication in epithelial and
lymphoid cells

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stress
pregnancy in young queens
elective surgery
concurrent infections (FeLV, FIV ?)
weaning, sale, shipment, adaptation
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Virus
immune system
increased virus replication -gt virulent mutants
increased ability to grow in macrophages
immune-mediated lysis of infected cells
cytokines draw in more susceptible cells
vascular permeability
immune complex related damage
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clinical signs

• common signs
• chronic antibiotic unresponsive fever
• progressive anorexia, weight loss
• stunting of growth
• progressive increase in serum proteins
• increase in globulins
• anemia
• serum, urine brown due to bilirubin

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clinical signs

• wet form
• peritonitis
• pleuritis
• dry form
• surface oriented granulomas
• mesenteric lymph nodes, liver, kidneys, cecum
  (palpable)
• cloudiness in eye
• neurological signs
• can change from dry to wet

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diagnosis

• serology
• prognosis?
• no titer - no FIP but may still be infected
• lt100 - less chance of developing FIP
• gt100 - greater chance of getting FIP
• increased globulins and protein (gt35g/L)
• cytology
• degenerate and non-degenerate PMN, macrophages,
  some lymphocytes, protein background
• FeCV positive cells (FAT)

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diagnostic alogrithm (Horzinek and Lutz)
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diagnostic algorithm
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diagnostic algorithm
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control

• vaccine
• Primucell FIP
• Intranasal ts virus
• management
• early weaning and separation

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Viruses of Veterinary ImportanceAvian Infectious
Bronchitis Virus (IBV)

• Avian infectious bronchitis (gasping disease) is
  one of the most important viral diseases of
  chickens. IBV is responsible for an acute
  respiratory disease which can produce very high
  mortality rates in young chicks.

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Viruses of Veterinary Importance Avian
Infectious Bronchitis Virus (IBV)

• Clinical Features
• Outbreaks of infectious bronchitis are explosive.
  IBV spreads rapidly to involve the entire flock
  within a few days.
• Chicks between 1 and 4 weeks of age show the most
  severe disease, which is recognized initially by
  coughing, sneezing, nasal discharge, and
  respiratory distress. Mortality in young chicks
  is usually 25-30 but in some outbreaks can be as
  high as 75.
• In older birds the disease often goes unnoticed,
  but in laying hens there is a marked drop in egg
  production, with many soft-shelled and malformed
  eggs being laid.

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Viruses of Veterinary Importance Avian
Infectious Bronchitis Virus (IBV)

• Pathology and Pathogenesis
• The course of the disease in young chicks is from
  7 to 21 days depending on the severity of the
  disease. Necropsy of young chicks dying from
  infectious bronchitis shows sinuosities,
  catarrhal tracheotis, bronchitis, and congestion
  and edema of the lungs. Caseous plugs may be
  present in the bronchi.
• The primary target for viral replication is the
  trachea, but the virus also replicates in the
  lungs, ovaries, and lymphoid tissue.
• IBV can establish persistent infection in some
  chickens, which results in shedding of virus in
  the feces for several months after initial
  exposure to the virus. When virus persists in the
  presence of high levels of antibody, severe
  nephritis can occur, which possibly reflects an
  immune complex-mediated disease.

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Viruses of Veterinary Importance Avian
Infectious Bronchitis Virus (IBV)

• Laboratory Diagnosis
• In contrast to several of the coronaviruses, IBV
  can be easily isolated by the allantoic
  inoculation of 9- to 12-day-old embryonated eggs
  obtained from seronegative hens. Infected embryos
  are to a variable degree stunted or curled
  tightly. A range of cell and organ cultures can
  also be used for virus isolation.
• At least eight genotypes of IBV exist and fall
  into two major groups virus isolates of widely
  differing pathogenicity occur within each
  antigenic group.

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Avian Infectious Bronchitis Virus (IBV)

• Epidemiology and Control
• IBV spreads between birds by aerosol and by
  ingestion of food contaminated with feces.
  Control of infectious bronchitis is difficult
  because of the presence of persistently infected
  chickens in many flocks.
• Outbreaks of infectious bronchitis have declined
  in recent years through use of vaccines however,
  it may occur even in vaccinated flocks following
  the introduction of infected replacement chicks
  from another farm. To minimize this risk, most
  poultry farms purchase only 1-day-old chicks and
  rear them in isolation.
• Attenuated vaccines, administered in the drinking
  water or as aerosols, are widely used to protect
  chicks and are usually given between 7 and 10
  days, and again at 4 weeks. Vaccination earlier
  than 7 days may be unsuccessful because most
  chicks have passive immunity up to this age.
• Local immunity in the respiratory system is
  critical for protection and can be generated by
  heterotypic vaccine strains.

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Avian infectious bronchitis. (A) One synonym for
the disease is gasping disease. (B) Thick
mucopurulent exudate in the trachea. (C)
Nephrosis. The kidney is pale and enlarged to
about five times normal size. (D) Embryos from
embryonated hens eggs inoculated via the
allantoic cavity with serial dilutions of virus
when 9 days old, and examined 11 days later.
Amounts of virus diminish in pairs from right to
left in the top row, and from left to right in
the bottom row.
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Other coronaviruses of importance in veterinary
medicine

• Porcine respiratory coronavirus (PRCV)
• Porcine Hemagglutinating Encephalomyelitis virus
• Porcine epidemic diarrhea virus (PEDV)
• Canine coronavirus (CCV)
• Turkey coronavirus (Bluecomb disease of turkeys)
• Mouse Hepatitis Virus