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CORONA VIRUSES
COLD AND SARS
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Coronaviruses are the largest RNA viruses
They infect humans and animals in which
they cause respiratory and enteric diseases.
Coronaviruses cause about one third of
"common colds" and the newly recognized
Severe acute respiratory syndrome (SARS).
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Epidemiology
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Most people harbor anti-coronavirus
antibodies but reinfection is common
indicating that there are many
circulating serotypes of the virus in the
human population.
Major outbreaks occur every few years
with a cycle that depends on the type
of virus involved.
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Pathogenesis
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Coronaviruses cause respiratory and
enteric disease in a variety of animals.
In humans, the major site of virus
replication is the epithelial cells of the
respiratory tract
about one-third of colds are caused by
coronaviruses.
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The symptoms are
(runny nose, sore throat, cough,
headache, fever, chills etc.)
incubation period 3 days.
Viral spread is limited by the immune
response of most patients but this
immunity is short-lived.
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Symptoms may last about a week with
considerable variation between patients.
 Often there are no apparent symptoms but
the patient still sheds infectious virus
Transmission is by transfer of nasal secretions
such as in aerosols caused by sneezes.
 Viruses that infect epithelial cells of the
enteric tract cause diarrhea.
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In humans, these viruses have been
implicated in infections of the middle
ear, and some pneumonias in immunosuppressed patients
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Diagnosis
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Most coronavirus infections go undiagnosed
and the disease is self-limiting.
Diagnosis can be carried out using immunoelectron microscopy and serology.
There are no anti-viral for routine coronavirus
infections but over-the-counter remedies to
alleviate symptoms are useful
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Severe acute respiratory syndrome
(SARS )
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In late 2002, a new syndrome was
observed in southern China
(Guangdong Province).
It was named severe acute
respiratory syndrome (SARS).
This disease, has now been reported in
Asia, North America, Africa and Europe.
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The SARS coronavirus causes severe
respiratory disease.
The incubation period averages about 6
days.
Common early symptoms include fever above
380C, malaise, chills, headache, dizziness,
cough, and sore throat, followed a few days
later by shortness of breath.
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Many patients have abnormal chest
radiographs.
Some cases progress rapidly to acute
respiratory distress, requiring ventilatory
support.
Death from progressive respiratory failure
occurs in almost 10% of cases, with the
death rate highest among the elderly.
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It has been shown that SARS
coronavirus can be airborne in a health
care setting, suggesting that airborne
transmission might occur. SARS
contamination of frequently touched
surfaces, such as a bed table (fomites),
has been observed also.
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Laboratory Diagnosis
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Antigen and Nucleic Acid Detection
Coronavirus antigens in cells in
respiratory secretions may be detected
using the ELISA test if a high-quality
antiserum is available.
Enteric coronaviruses can be detected
by examination of stool samples by
electron microscopy.
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Polymerase chain reaction (PCR) assays
are useful to detect coronavirus nucleic
acid in respiratory secretions and in
stool samples.
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SARS virus RNA was detectable in plasma by
PCR, with viremia most readily detectable
between days 4 and 8 of infection.
Isolation of human coronaviruses in cell
culture has been difficult.
However, the SARS virus was recovered from
oropharyngeal specimens using Vero monkey
kidney cells.
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Serology
Because of the difficulty of virus
isolation, serodiagnosis using acute and
convalescent sera is the practical means
of confirming coronavirus infections.
ELISA and hemagglutination tests may
be used.
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Treatment, Prevention, &
Control
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There is no proven treatment for SARS
other than management of symptoms.
Drugs are under development
There is no vaccine against the SARS
virus or any other human corona virus.
A major problem with live virus vaccine
is antigenic shift and unpredictable
outcomes.
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Control measures that were effective in
stopping the spread of SARS included
isolation of patients,
quarantine of those who had been exposed,
and travel restrictions,
as well as the use of gloves, gowns, goggles,
and respirators by health care workers.
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Slow virus & Prions
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Slow virus infections
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The term " Slow virus infections " refers
to the tempo of the DISEASE, not to the
growth rate of the virus.
Such diseases have a prolonged
incubation period (which can be months
or years), and a protracted, progressive
clinical course.
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Slow virus diseases may be caused by
conventional or unconventional viruses.
The symptoms associated with slow
viral/prion diseases of the central
nervous system tend to have multiple
neurological symptoms and different
patients may present with different
symptoms
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CONVENTIONAL VIRUSES
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Progressive multifocal
leukoencephalopathy (PML)
This is a rare, fatal, demyelinating disease of
the CNS which kills oligodendrocytes
It results in memory loss, loss of coordination, mental problems, and vision
problems.
Patients who develop PML frequently have
some abnormality of the immune system.
PML develops in up to 5% of patients with
AIDS.
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Subacute sclerosing panencephalitis
(SSPE)
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This disease is a rare complication of measles virus
infection and develops approximately 1 to 10 years
after the initial infection.
It is progressive and fatal and is characterized by
mental and motor deterioration.
Risk factors include acquiring primary measles at
early age.
SSPE is associated with defective forms of the virus
in the brain and so it is difficult to isolate infectious
virus from patients.
Incidence has decreased since the introduction of
anti-measles vaccination.
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Progressive rubella panencephalitis (PRP)
PRP is a very rare consequence of rubella
virus infection
results in mental and motor deterioration.
the onset of PRP occurs at 8 to 19 years
of age.
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UNCONVENTIONAL VIRUSES :PRIONS
These are very small, filterable agents that
require host cells to grow.
They have no capacity for energy generation or
protein synthesis.
 In some ways, however, they are rather
different from viruses for we cannot see any
evidence of virus particles in infected tissues
or purified preparations of infectious material.
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These unconventional viruses or agents are
often called 'prions' - since protein is
present in purified preparations of infectious
material
No-one has been able to prove that these
agents contain nucleic acid.
These agents are resistance to treatments
commonly used to inactivate viruses
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These agents cause diseases which are
confined to the CNS
have a prolonged incubation period
show a slow, progressive, fatal course
of disease
show a spongiform encephalopathy
characteristically result in vacuolation of
neurons
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These diseases (transmissible spongiform
encephalopathies) are relatively rare in man.
They may be acquired, inherited, or occur
sporadically.
but there is speculation that they may be
more common than previously thought and
they may have implications in the study of
other CNS degenerative diseases
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Kuru
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Kuru is a disease of man. It causes
tremors and ataxia (failure of muscle
coordination) and, in later stages,
dementia.
It is transmitted by rites for the dead
which included autopsy and cannibalism
in Fore people in Papua/New Guinea.
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No one born since these practices ceased has
acquired Kuru. There is no evidence for
transmission to fetus, transmission via
milk or intimate social contact.
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Creutzfeldt-Jakob disease (CJD)
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CJD is a disease of man resulting in
dementia and also tremors and lack of
motor co-ordination.
The disease can be transmitted to
animals in the laboratory.
disease have been observed to develop
at ages 16 to 80+ years
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CJD can be transmitted by medical
manipulations:
eg. cornea transplants, dura mater
transplants, use of improper sterilized
equipment in neurosurgery.
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New variant CJD disease
(human BSE)
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This is a form of CJD
has been reported in the United Kingdom in
patients who are usually younger (frequently
under 40; average age at death: 28 years)
than is the case for most CJD patients
(average age of death: 68 years)
This disease is also different from the usual
CJD in that patients tend to present with
psychiatric problems and in that the course of
the disease tends to be more protracted.
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Sufferers may eventually show any or all of
the symptoms described above for other
human prion diseases.
The disease was first seen in 1996 and there
is strong evidence to suggest that it is
associated with exposure to BSEcontaminated beef.
Strong BSE control measures have now been
implemented. Autopsy reveals a distinctive
neuropathological appearance and more PrP
(prion protein)
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This raises questions about sterilization of
surgical instruments etc. and the possibility of
iatrogenic spread.
There is a possibility that vCJD agents may
have been transmitted by blood transfusion
it is thought leuko-depletion might decrease
the chances of transmission by blood
transfusion.
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