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Transcript
Gastrointestinal infectious
virus
Gastrointestinal infectious virus
• a group of viruses that parasitize the
enteric tract and cause diseases.
• fecal-oral route
Gastrointestinal infectious virus
• belong to picornaviridae: 6 genera
– Enterovirus
– Rhinovirus
– Hepatovirus
– Par-echovirus
– Aphthovirus: foot-and-mouth disease viruses
– Cardiovirus: encephalomyocarditis
Enteroviruses
Virus family
Serotypes
Polio
1-3
Coxsackie A
1-22, 24
Coxsackie B
1-6
Echovirus
Enteric, cytopathic, human, orphan
1-9, 11-27, 29-34
Hepatitis A
Enterovirus 72
Other Enteroviruses
68-71
Common biological properties
•
•
•
•
•
•
24-30nm
spherical
naked, icosahedral
+ssRNA
multiply in the cytoplasm
Resistance
– resistant -- ether, acid (tolerate pH3-5)
– sensitive -- drying, heat and UV
– survive for a long period in water and sewage
Pathogenicity
– Portal of entry
– Viremia
– Target tissue
– Different enteroviruses bind to different target
cells
Pathogenicity-clinical
• Neurologic infection
– aseptic meningitis, paralysis, encephalitis
• Cardiac and muscular infection
– myocarditis, pericarditis
• Infection of skin and mucosa
– hand- foot-and- mouth disease
• Resoiratory infection: common colds
• Alimentary infection: diarrhea in children.
POLIOVIRUS
paralytic poliomyelitis
Biological properties
•
•
•
•
30nm
Naked
icosahedral capsid
+ssRNA
Synthesis of +ssRNA containing viruses
Pathogenesis
• Poliovirus infections
• 3 types (type 1, 2, 3)
– type 1 causes most epidemics
• Progression of poliovirus infection
– Types of illness
•
•
•
•
Asymptomatic illness
Abortive poliomyelitis
Nonparalytic poliomyelitis
Paralytic poliomyelitis
Poliovirus→throat→regional lymphatic nodes → blood
Peyer’s patches
the small intestine
1-2% ↓
90%↓
CNS (motor neurons)
unapparent infection
mild↙
↘serious 0.1-0.2%
no
Flaccid paralysis
↙
↓special syndrome
a few days↓
headache
progressive
post-poliomyelitis muscle atrophy
complete recovery
←
stiff and pain
↓rare
medulla paralysis
↓eventually
death ← respiratory and heart failure
Prevention
• Poliovirus vaccines 1960
• Sabin (live attenuated virus) vaccine OPV
Albert Sabin
• Salk (killed virus) vaccine
IPV
Jonas Salk
Property
Safety
Efficiency
Sabin vaccine
Satisfactory
3 doses at 6-8 weeks interval,
Salk vaccine
Satisfactory
Primary vaccination: 2-3 doses at
4-6 weeks intervals, boosters doses
oral
every 3-5 years; injection
Cost
More
Less
Nature of immunity Induce both local and systemic immunity Systemic Ab,
no local immunity
Duration of immunity
lifelong
May need to be maintained by
booster doses periodically
Spread of vaccine Spread naturally to unvaccinated individuals
No spread
by fecal-oral spread
Stability
Less stable and more difficult for
Stable; preservation and
transportation are convenient
Preservation and transport in tropic area
Coxsackie viruses
• Name of the town of Coxsakie, NY
• Classification based on pathogenicity in mice
• Group A
– widespread myositis. flaccid paralysis
– fatal
• Group B
– generalized. heart - CNS- focal myositis
– myocarditis, hepatitis,and encephalitis
Diseases
• Herpangina
– coxsackie A virus
• Hand-foot-and-mouth disease
– coxsackievirus A16 and enterovirus 71
• Pleurodynia
– coxsackie B virus
• Myocardial and pericardial infections
– coxsackie B virus. (B3)
• Viral meningitis
– coxsackievirus or echovirus
Hand, foot and mouth disease
• This is an exanthem (a rash) caused by Coxsackie A16.
• Symptoms include fever and blisters on the hands,
palate and feet.
Human diseases caused by enteroviruses
Coxsackie
A virus
Coxsackie
B virus
Echovirus
Enterovirus
(other)
Asymptomatic
infection
yes
yes
yes
yes
Meningitis
Paralysis
yes
yes
yes
yes
yes
yes
yes
no
Febrile
exanthems
yes
yes
yes
yes
Acute
respiratory
disease
yes
yes
yes
yes
Myocarditis
Orchitis
yes
no
yes
yes
yes
yes
no
no
睾丸炎
Chapter 28
Acute Gastroenteritis Viruses
Acute gastroenteritis viruses
• Rotavirus
• Norwalk virus/small round structured virus
(SRSV)
• “Classic” calicivirus
• Enteric adenovirus
• Astrovirus
• These viruses cause acute gastroenteritis with
the similar symptoms, such as diarrhea and
vomiting.
Human Rotavirus (HRV)
• reoviridae
• the name reovirus
• respiratory enteric
orphan virus
• in 1959
• Albert Sabin
• the Latin word “rota”,
meaning “wheel”
Electron micrograph of rotavirus
Biologicalproperties
• 60-80nm
• icosahedral
• naked
– Capsid: Possess two
concentric capsid
shells, icosahedral
– Core: Possess a
double-stranded
segmented RNA
genome
Classification
– HRV 7 groups (A~G)
– Groups A~C: human and animal diarrhea
• Group A: infantile acute gastroenteritis
• Group B: outbreaks in adults
• Group C: only sporadic diarrhea
– Group D-G: animal diarrhea
Pathogenesis
• Rotavirus
• one of the most common causes of
infantile diarrhea worldwide.
– High risk people:
• children 6 months - 2 years old
– Route of transmission: fecal-oral route
Pathogenesis
• Virus infects columnar epithelial cells
covering the villi of the small intestine
• multiply in the cytoplasm
• causes cell lysis and abnormal function
• damage their transport mechanisms to
interrupt sodium and water absorption
Pathogenesis
• infection prevents the absorption of water
• causing a net secretion of water and loss of ions,
which together results in a watery diarrhea and
vomiting→ dehydration, acidosis, shock and
death
• Diarrhea
– watery (no blood or leukocytes),
– lasting 3-9 days
Pathogenesis
• Many cases and outbreaks are nosocomial
• Incubation period 1-4 days
• Contagious Period - Before onset of diarrhea to
a few days after end of diarrhea
• Spread via fecal - oral route through fomites
Diagnosis
• Rapid diagnosis
– antigen detection in
stool by ELISA
• Electron microscopy
Treatment
• Supportive - rehydration (oral / intravenous)
– Antiviral agents not known to be effective
• Prevention of spread
– Handwashing with good technique
– Disinfection of surfaces, toilets, toys
• Vaccine
– Rotashield was first licensed for use in infants in 1998.
Acute gastroenteritis virus
Virus
Shape and Size
NA
Routes of Transmission
Season of Disease
Clinical feature
Rotavirus Spherical, 60-80 dsRNA
Fecal-oral
Late autumn, winter
Enteric Spherical, 70-90
Adenovirus
Fecal-oral
Whole year,
summer
SRSV
dsDNA
Spherical, 27nm +ssRNA
Fecal-oral,
respiratory tract
Winter
Classic
Spherical, 31-38 +ssRNA
calicivirus
Fecal-oral
Whole year
Astrovirus Spherical, 28-30 +ssRNA
Fecal-oral
Winter
Infant(<2Y),
Watery diarrhea
Infantile diarrhea
Any age
Infantile watery diarrhea
Infant(<5Y) diarrhea