Gastro-Intestinal Viral Infections Flashcards
Rotavirus
Epidemiology
Most important cause of gastro-enteritis in
children 6 months to 2 years
Severe infections especially in malnourished
children
High mortality rate in developing countries due to
dehydration
An increased incidence in winter
Nosocomial infections in newborns are
asymptomatic or clinically mild
In adults normally asymptomatic or mild, but can
cause serious epidemics in institutionalized old
people
Spread is mainly faecal/oral
Rotaviruses are shed in the faeces in amounts up
to 10 log10 particles per gram of stool
Infectious with <=10 particles
Resistant to drying out and acid due to nonenveloped(naked) virion
Fomites and hands therefore important in
transmission
Respiratory transmission also possible
Soviet Science
In 1983, Mikhail Balayan visualized
HEV using immune electron microscopy
– examined his own stool which he collected after selfadministration of infectious material • Whilst investigating an outbreak
in central Asia, he made a
smoothie from yoghurt and an
infected patient’s stool – the viral genome was subsequently isolated and
sequenced with the use of bile samples and stool collected from
other monkeys
Rotavirus:
Pathogenesis
Spread is mainly faecal/oral with intestinal infection most prominent
Host factor that affects the clinical outcome of infection is age. Thus, neonates, rarely have symptomatic disease; this
protection is thought to be mediated primarily by
transplacental transfer of maternal antibodies.
Reductions in these antibodies coincide with the age of maximum susceptibility of infants to severe rotavirus-induced disease (range, 3 months to 2 years)
Rotavirus can infect adults, but severe symptomatic disease is relatively uncommon and can result from infections with an unusual virus strain or extremely high doses of virus
Systemic Infection Rotavirus infection is not limited to the intestine its extraintestinal spread was documented more than 45 years ago in mice, when virus was detected in multiple organs
Rotavirus
Clinical Picture
Incubation period is 1-3 days
Characteristically vomiting with fever, followed by
diarrhoea
Sufficient for diagnosis if this picture is seen in
winter in a child 6 months - 2 years
Breast fed children
have fewer
infections
Re-infection with
another serotype can occur
Clinical spectrum ranges from subclinical illness or mild
watery diarrhoea of limited duration to frequent profuse diarrhoea with vomiting and fever:
-dehydration with shock
-electrolyte imbalance
-Death
Rotavirus illness usually begins with acute onset of fever and vomiting, followed one or two days later by frequent watery stools
About 30-40% of children may have a moderate fever
(temperature >39°C)
Vomiting usually lasts for only one or two days and other gastrointestinal symptoms generally resolve in three to seven days
Rotavirus:
Laboratory Diagnosis
Human rotaviruses cannot be isolated in normal cell cultures.
Can be demonstrated in stools by
electronmicroscopy
(EM), ELISA, latex
agglutination
Electron microscopy, polyacrylamide gel
electrophoresis, antigen detection assays, reverse transcription polymerase chain reaction (RT-PCR)
Diagnosis of rotavirus was initially by electron microscopy, with and without agglutination by
immune sera
Large numbers of rotavirus particles (up to 10
log10/g faeces) are excreted during the acute phase of infection
Antigen detection tests, including commercially
available enzyme linked immunosorbent assays
(ELISAs) and immunochromatographic assays, are widely used
RT-PCR is widely used in research laboratories to
detect the viral genome
Rotavirus:
Prevention
Wash hands
Millions of children are infected every year and
many (>2 million/year) die because of
dehydration
Because rotavirus infects nearly all children in both
industrialised and developing countries early in life, good hygiene and sanitation alone are considered inadequate
for prevention
Observational studies have shown that breast feeding
confers protection from rotavirus gastroenteritis, although one case-control study indicated that it may only
postpone
Follow-up of birth cohorts indicates that, although children can be infected with rotavirus four to five times in the first two years of life, the incidence of severe rotavirus gastroenteritis is reduced with each repeat infection
Therefore, orally administered, live, attenuated rotavirus vaccines have been developed to mimic the effect of natural infection and prevent severe rotavirus disease
Names for the Rotavirus vaccine
2 vaccines on market and now part of EPI:
- Oral Rotarix ®
- RotaTeq ®
Norovirus:
Epidemiology
Highly infectious, very small inoculum necessary to
cause infection
Resistant to drying out, acid, etc
Involved in small epidemics/outbreaks (common
source outbreaks) e.g. food, water
Faecal-oral transmission
Norovirus is a well-described cause of epidemic
gastroenteritis in both adult and paediatric
populations
The general population is broadly vulnerable to
disease across all age groups, but the majority of
morbidity and mortality occurs at the extremes of
age
The faecal-oral route is the main mode of
transmission
Transmission modalities include transmission via
aerosolized viral particles in vomitus and through
food, water, and environmental contamination
Caliciviruses Adenoviruses 40 & 41
E
Norovirus:
Clinical Picture
Incubation period 12-48 hours, followed by
sudden onset of vomiting; with diarrhoea less
prominent
Sometimes accompanying systemic symptoms,
e.g. fever, myalgia
Norovirus
Diagnosis
The optimal specimen for the diagnosis of norovirus
infection is diarrheal stool
Specimens should be collected in a closed
container within 48 to 72 h of the onset of symptoms,
although norovirus may be detected in stool
samples for 7 to 10 days or longer
Specimens should be refrigerated at 4°C prior to testing and frozen at -20°C or -70°C for long-term
storage
Vomitus is an alternative specimen type that may be
used to supplement stool sample testing during outbreak investigations
Collection and handling are the same as for stool specimens
Other Gatroenteritis Viruses
Astroviruses
Caliciviruses
Adenoviruses 40 & 41
Enteroviruses
Types:
Poliovirus types 1, 2, 3
Coxsackie A and B
Echoviruses
Enteroviruses
-Mainly found in the GIT and are resistant to acid
and bile
-Replicate in the GIT but primarily cause systemic
infections
-Most infections are asymptomatic, but a small
percentage lead to a febrile disease with or
without rash
Poliovirus:
Epidemiology
There are 3 types which are present: 1,2 and 3
Man is only natural host
Currently eliminated in many countries due to
vaccination but cases still occur in some
developing countries such as Pakistan,
Afghanistan, Nigeria.
Virus is transmitted by oral-oral and faecal-oral
routes
Poliovirus is highly infectious
Found in the oropharynx for 1 week before and in
stools for 3-6 weeks after development of
symptoms
Use of the attenuated Sabin vaccine has an
effect on the epidemiology.
Where this vaccine is
used efficiently there is almost no more paralytic
polio, and the wild type virus has been replaced
in nature by the vaccine virus
Acquired immunity is monotypic, but permanent
Poliovirus type 1 is the most important cause of
paralytic polio
Followed by type 3
Type 2 virtually none, due to vaccine
Last wild-type polio seen is SA since 1989
Switch from Trivalent to Bivalent vaccines in April
2016
POLIOVIRUSES CLINICAL PICTURES asymptomatic infection mild disease (flu-like) aseptic meningitis paralytic poliomyelitis
POLIOVIRUSES
CLINICAL PICTURES If clinical disease appears, there are 2 stages: Small disease Corresponds to the viremic phase; non-specific
(“abortive polio”) malaise, fatigue, fever, headache,
nausea, vomiting, constipation, sore throat (flu-like)
POLIOVIRUSES
CLINICAL PICTURES Main disease - may appear directly (without small
disease) phase 1: aseptic meningitis with headache,
malaise, fever, vomiting, pain in limbs. Recovery often occurs within 1 week phase 2: rare - flaccid paralysis due to damage to
lower motor neurons (peak reached within 2-3
days). Recovery follows a short static phase and
muscle function improves over 4-6 weeks (after 6
months usually no further improvement)
POLIOVIRUSES
CLINICAL PICTURES If the CNS is involved there is invariably
involvement of the brain, but few patients show
any signs Most serious syndrome is bulbar poliomyelitis due
to paralysis of the cranial nerves, especially the
pharynx with inability to swallow. If the respiratory
centre of the medulla is involved, respiratory
failure takes place
2020/10/09
6
POLIOVIRUSES
CLINICAL PICTURES Spinal poliomyelitis is seen when the cervical and
dorsal segments of the spinal cord are affected,
with paralysis of the intercostal muscles and the
diaphragm with resultant respiratory failure
POLIOVIRUSES
LABORATORY DIAGNOSIS Virus isolation or PCR: Early on in disease from the
throat and stools After paralysis virus can be found in the stool 2 stool samples taken 24 hours apart, on ice with
completed AFP surveillance form
POLIOVIRUSES
PREVENTION Chlorinate water for domestic use Control sewage systems for sufficient virus
inactivation Vaccines:
i) Salk vaccine (inactivated, given by injection)
POLIOVIRUSES
PREVENTION
ii) Sabin vaccine (live, attenuated - given by mouth
(OPV)) Disadvantages: mutation back to virulence interference between the 3 serotypes interference between vaccine strains and other enteroviruses Advantages: prevents paralysis as well as spread of wild type virus
OPV
2020/10/09
7
POLIOVIRUSES
PREVENTION Immunization schedule: bivalent OPV at birth and
6 weeks. Then 6, 10 and 14 weeks, IPV. Then last
dose IPV at 18 months Withhold breast milk for breast-fed babies a few
hours before and after; specific IgA in breast milk
can destroy the vaccine virus No contra-indication in RSA; vaccine-associated
polio 1/million vaccinations
POLIOVIRUSES NOTE: Polio is a notifiable disease
O
Poliovirus:
Clinical Picture
- Asymptomatic infection
- Mild disease (flu-like)
- Aseptic meningitis
- Paralytic poliomyelitis
If clinical disease appears, there are 2 stages:
1. Small disease: Corresponds to the viremic phase; non-specific (“abortive polio”) malaise, fatigue, fever, headache,
nausea, vomiting, constipation, sore throat (flu-like)
- Main disease-may appear directly (without small
disease) :
*Phase 1: aseptic meningitis with headache,
malaise, fever, vomiting, pain in limbs. Recovery often occurs within 1 week
*Phase 2: rare - flaccid paralysis due to damage to
lower motor neurons (peak reached within 2-3
days). Recovery follows a short static phase and
muscle function improves over 4-6 weeks (after 6
months usually no further improvement)
If the CNS is involved there is invariably
involvement of the brain, but few patients show
any signs
Most serious syndrome is bulbar poliomyelitis due
to paralysis of the cranial nerves, especially the
pharynx with inability to swallow. If the respiratory
centre of the medulla is involved, respiratory
failure takes place
Spinal poliomyelitis is seen when the cervical and
dorsal segments of the spinal cord are affected,
with paralysis of the intercostal muscles and the
diaphragm with resultant respiratory failure
Poliovirus:
Laboratory Diagnosis
Virus isolation or PCR: Early on in disease from the
throat and stools
After paralysis virus can be found in the stool-2 stool samples taken 24 hours apart, on ice with
completed AFP surveillance form
Chlorinate water for domestic use Control sewage systems for sufficient virus
inactivation Vaccines:
i) Salk vaccine (inactivated, given by injection)
POLIOVIRUSES
PREVENTION
ii) Sabin vaccine (live, attenuated - given by mouth
(OPV)) Disadvantages: mutation back to virulence interference between the 3 serotypes interference between vaccine strains and other enteroviruses Advantages: prevents paralysis as well as spread of wild type virus
OPV
2020/10/09
7
POLIOVIRUSES
PREVENTION Immunization schedule: bivalent OPV at birth and
6 weeks. Then 6, 10 and 14 weeks, IPV. Then last
dose IPV at 18 months Withhold breast milk for breast-fed babies a few
hours before and after; specific IgA in breast milk
can destroy the vaccine virus No contra-indication in RSA; vaccine-associated
polio 1/million vaccinations
POLIOVIRUSES NOTE: Polio is a notifiable disease
O
