Download hepatitis virus

5 medically important hepatitis viruses:
 1. Hepatitis A: infectious heptitis
 2. Hepatitis B: Serum hepatitis
 3. Non-A, Non-B: HCV
 4. Hepatitis D (delta agent)
 5. Hepatitis E : Enteric Hepatitis
 6. Post transfusion: HGV
Other viral causes: EB virus, CMV, Yellow
fever, Enterovirus, Herpes virus
HEPATITIS A VIRUS
 Causes Hepatitis A
 It is a enterovirus, family picornaviridae
 Recently classified under Hepatoviruses
 ss RNA, non-enveloped.
 Icosahedral nucleocapsid
 Replicates in the cytoplasm
of the cell
 Also known as enterovirus 72
 It has 1 serotype
 It has no antigenic relationship b/w hepatitis B or
other hepatitis viruses
Replication- similar to enteroviruses. Eg-polio
virus.
Transmission and Epidemiology
 Faeco-oral route
 Reservoir :- humans
 Children adolescents more commonly infected
(an-icteric subclinical infection)
 Adults: icteric manifestations
 Virus is shed 2 weeks before & after appearance
of symptoms.
 Institutional outbreaks recorded. Eg- day
care centres, hostels, ICU
 Outbreaks directly related to sanitation. Eg-
fecal contamination of drinking water, food
grown in polluted water, street food.
 Rarely transmitted by blood. Eg- seen rarely
with haemophiliacs transfused with blood
products
 There is no chronic infection unlike in HBV or
HCV because generally level of viremia is low.
 Many people maybe infected and recovered
(IgA seen in 50-70% of population)
 Secondary attack rate in house hold contacts
common
Pathogenesis and immunity
 Virus replicates in GI tract and spread to liver
hematogenously
 Hepatocytes are infected but mechanism of
cell damage is unclear.
 Cytotoxic T-cells may damage the
hepatocytes infected with virus.
 If infection is cleared damage will be repaired
and there is no chronic infection
 Hepatitis from other virus usually indistinguishable
pathologically (all look the same histo-pathologically)
Immune response
 IgM is detected at the appearance of jaundice
 Peaks 2-3 weeks, disappears in 3-4 months
 So IgM Ab to HAV is important in diagnosis of
HAV.
 1-3 weeks after the IgM appears IgG is seen.
 IgG : provides life long immunity
Clinical features
 Incubation period (2-4 weeks)
 Pre-Icteric phase: fever, nausea ,vomiting
 Icteric Phase: jaundice, dark urine, pale
stools, eleavted transaminases.
 Spontaneous recovery is the rule in 2-3 weeks
time
 Most of the cases maybe asymptomatic (maybe
solely detected on basis of IgG Ab)
 No chronic hepatitis or chronic carrier state
 So no predisposition to hepatocellular carcinoma
Laboratory diagnosis
1. Biochemical investigations- LFT
2. Detection of anti HAV IgM, IgG: persists for
decades
3. Detection of HAV particles: IEM of faeces,
liver, bile
4. HAV antigen detection: by ELISA
5. Isolation in cell culture possible but not
routinely done
6. PCR: viral RNA
Serological tests for Hepatitis A virus
Stage of infection
IgM
IgG
Acute HAV
infection
+
----
Previous HAV
infection
__
+
Treatment and prevention
 No antiviral therapy
 Formaldehyde inactivated vaccine: vaccine:
(virus grown in cell culture) given to
children above 12 months & adults- initial
dose and booster dose 6-12 months later
 Live attenuated vaccine: single dose , S/c
 Detection of HAV antibody prior to vaccination is
cost-effective
 Passive immunization with immunoglobulin (HAV
Ig) for post exposure prophylaxis can prevent
disease in close household contacts & travellers
 Proper hygiene and superior sewage disposal, hand
washing after bowel movements etc
 Good sanitation help prevent (like for any
food/water borne diseases)
 Chlorination of water also helps.
HEPATITIS B VIRUS
 Causes Hepatitis B (HBV)
PROPERTIES DNA virus, Hepadnaviridae Family
 Icosahedral nucleocapsid containing partially
ds circular DNA genome.(all other Hepatitis
group are RNA viruses).
 Envelope contains protein surface antigen(HBsAg)
 HBsAg was first discovered in serum of Australian
aborigine. So it is called Australia Antigen.
MORPHOLOGY:
 EM of serum from infected patients reveals 3 morphologic
forms:
Spherical forms:
Most numerous
22nm diamter, made of
HBsAg
Tubular/ filamentous 200nm long
forms:
Made of HBsAg
Complete form/
DANE particle:
42nm spherical virions
Made of HBsAg, HBcAg,
HBeAg & partially ds
DNA
 4 genes –S, C , P, X
 S- region S- codes for major S
S+pre S2- codes for M
- HBsAg
S+ pre S1 and S2- codes for L
 C- region C
P-
-
- HBcAg
C+pre C -
- HBeAg
- DNA polymerase
 X - enhance HBxAg - maybe to exist as coinfection in AIDS, In chronic hepatitis, in
hepato-cellular carcinoma
VIRAL ANTIGENS
Hepatitis B
surface Ag
(HBsAg)
•Australia Ag
•Detected in serum
Hepatitis B core •Intracellular core protein
Ag (HBcAg)
•Not secreted into serum
•Found in hepatocytes
Coded by
S gene
Coded by
C gene
Hepatitis B pre- •Non particulate soluble Ag Coded by
core Ag
•Present in circulation
Pre C gene
(HBeAg)
 Epidemiologically: 4 serotypes of HBV (HBsAg)
 ‘a’ – group specific antigen
 ‘d’ or ‘y’
2 sets of neutrally exclusive epitopes
 ‘w’ or ‘r’
 adw, adr, ayw and ayr are the serotypes
 ayw- West Asia, Mid-east to West & North India
 adw- Europe, Australia, Americas
 adr- South and East India, Far East.
 ayr- very rare.
Transmission and epidemiology3 main modes- Blood, blood products, IV drug abuse
- Sexual contact
- Peri-natally from mother to new born
- Very small amount of blood necessary for
transmission. Eg. Needle stick injury
Distribution
 Worldwide, particularly prevalent in the oriental
countries- including India.
 These areas have high incidence of hepatocellular carcinoma- hepatoma.
 HBV is a tumor associated virus
 Immunization against HBV in Taiwan has
decreased the incidence of hepatoma.
 HBV vaccine: first vaccine against human cancer
 Mutants- Few cases of Hepatitis B will be with
mutant virus
 Called as pre core mutants – so unable to
synthesize HBcAg
 Escape mutants – found in those with combined
immunization- also called as ‘a’ antigen
mutation. They may pose problem in
prophylactic immunization.
PATHOGENESIS OF HEPATITIS B:
 Why is Hep B virus specific for liver cells?
1. Because virus specific receptor on cell
membrane facilitates entry.
2. Transcription factors facilitating viral
mRNA synthesis.
Summary of the Replicative cycle
1. Viral entry- uncoating
2. Viral DNA polymerase synthesize missing portion
of DNA
3. Closed dsDNA formed in nucleus of host cell
4. This DNA will act as template for mRNA synthesis
with help of cellular mRNA polymerase
5. The mRNA formed functions for protein synthesis
and also template for positive strand of DNA
 Next RNA dependant DNA synthesis occurs within
the newly assembled virion core in the cytoplasm
 Hepadna virus are the only virus that produces the
genome DNA by reverse transcription with mRNA
as template. (the process is similar but different
from process in Retrovirus)
 Some of the viral DNA interacts to the host cell genomeso a likely explanation is, that this integrated DNA
maintains the carrier state.
 The progeny HBV with its HBsAg envelope is released
from the cell by budding through cell membrane
 It can also infect adjacent cells by intracellular bridges
Pathogenesis and immunity
 Virus enters blood--------- infects hepatocytes
 Viral antigens are displayed on the surface of
cells- cytotoxic T cell mount an immune attack
against infected hepatocytes- inflammation and
necrosis
 Immune attack mediated by cytotoxic T cell
 So pathogenesis maybe due to cell mediated
immune injury
 Direct injury is not seen as we know that HBV
show no CPE in lab cell line.
 Ag-Ab complexes also cause some early
symptoms, eg. Arthralgia
 Complication of chronic hepatitis e.g. Immune
complex glomerulonephritis and vasculitis(type
III)
CARRIER STATE
 5% of Hep B infection lead to chronic carrier state
 Chronic carrier is defined as HBsAg positivity in
the blood for at least 6 months- meaning
prolonged presence of HBV and HBsAg in blood
 Reasons- persistent infection of hepatocytes
leading to prolonged presence of HBV and HBsAg
in blood
 Adequacy of cytotoxic T cell response i.e. whether
a person can clear the infection or become a chronic
carrier
 HBV DNA exists as an episome in the cytoplasm
of persistently infected cells. A small no. of copies
of HBV DNA is integrated to the host cell DNA.
 High rate of hepato cellular carcinoma occurs in
chronic carriers
 HBV genome has no oncogene
 Carcinoma maybe due to persistent cellular
regeneration that attempts to replace the dead
hepatocytes or due to insertional mutagenesis .
 Chronic carriage is more likely if infection is in
newborn than adults , as immune system is less
competent than in adults
 90% of those infected as neonates become chronic
carrier
 If recovery- life long immunity after natural
infection because humoral Ab against HBsAg.
 Antibody to HBcAg is not protective.
Clinical findings
 Mean incubation 10-12 weeks, much longer than
HAV. (3-4weeks)
1. Pre-icteric phase: GI symptoms
2. Icteric phase
 Surrogate markers- Transaminase levels increase, so
LFT needs to be performed.
 Clinical outcome: carrier state or complete recovery
 Hepatic complications: fulminant hepatitis or
cirrhosis or Hepato-cellular carcinoma
 Extra-hepatic complications: during prodromal
phase: serum sickness like syndrome ( arthritis,
rash, angioedema, proteinuria) in 5-10% patients
due to Immune complex deposition.
LAB DIAGNOSIS
HBsAg:
 First marker to be elevated (8-12wks post
infection)
 HBsAg- it appears during the incubation period
(2-6 wks before clinical & biochemical evidence
of hepatitis)
 HBsAg +ve: indicates active infection
 Becomes negative in 1-2 months after jaundice
 Persisting > 6mths: carrier state/ chronic
hepatitis
 HBsAg: epidemiological marker
HBsAb or Anti HBs
 Corresponding Antibody of HBsAg
 Remains elevated indefinitely
 Indicates recovery, immunity & non
infectivity
 Only marker of Hep B vaccination
HBeAg & HBV DNA
 Appear shortly after appearance of HBsAg in
serum
 Markers of
Active viral replication
2. High viral infectivity
3. Present in acute & chronic active hepatitis or
super carriers
1.
HBcAg:
 Hidden antigen due to surrounding HBsAg
 Non secretory, hence not detected in blood
 Detected in hepatocytes by immunoflourescence
test
HBcAb IgM (Anti HBc)
 First Ab to be elevated following infection
 Appears within 1-2 wks following HBsAg &
persists for 3-6 mths
 Indicates acute infection
 Only marker during WINDOW PERIOD
HBcAb IgG:
 Appears during late acute stage & remains
+ve during chronic & carrier state & recovery
 Epidemiological marker
Anti HBeAb
 Appear after clearance of HBeAg
 Presence signifies low viral replication & low
infectivity
Others –
 Transaminase levels (LFT)
 Imaging of liver for evidence of hepatoma
etc.
Treatment and prevention
1. Pegylated interferon
2. Nucleoside/ nucleotide analogues-
Lamivudine (thiocytadine), tenofovir
- inhibit reverse transcriptase of HIV and also
effective against HBV.
The drugs help to reduce hepatic inflammation
and lower levels of HBV in chronic carriers.
PreventionImmunization- Active – vaccine
Passive – Immunoglobulins
Combined- both
Hepatitis B Vaccine – recombinant subunit
vaccine
HBsAg (vaccine candidate) made in bakers yeast
by DNA recombinant technology
Indication- those frequently exposed to blood or
blood products. E.g – HCW, Patients who require
multiple transfusions, dialysis, frequent STDs,
drug abuses
-Recommended for all new born and adolescents
Dose: 10-20ug/dose , 3 doses (0, 1, 6 mths)
IM injection
 Marker of protection: Anti HBsAg Ab titre of >
10 IU/ml
 Booster doses if Ab titre falls
Hepatitis B immune serum (HBIg)High titer of HBsAb prepared from sera of
patients recovered from Hep B.
Provides immediate, passive protection to
individuals exposed to HBsAg positive blood- e.g.
needle stick injury
For needle stick injury both vaccine and HBIg given at
separate sites.
- for new born whose mother is HBsAg positive
- immediate HBIg followed by vaccination after
delivery.
There is immediate and long term protection.
Inactivation
-autoclaving (1210C for 20mins, 5lb)
-Boiling water 5 mins
-dry heat 1800C for 1 hour.
-UV light for 1 minute at 1.1 watts
-formalin 1:40000 for 3 days at 370C.
Chlorine 10-15 ppm for 30mins.
-heating food for more than 850C for 1 min.
-surfaces – 1:100 chlorine bleach.
Non A, Non B Hepatitis
 Previously described as to those cases of hepatitis in
which existing serological tests had ruled out all
known causes of hepatitis by viral agents.
 Nowadays main cause is determined as Hepatitis C
virus or HCV.
 In addition Hepatitis E, Hepatitis D have been
described.
 Cross protection experiments using chimpanzees
indicates additional Hepatitis virus exist
HEPATITIS C
 Hepatitis C virus causes Hepatitis C.
Properties Flavivirus, enveloped,
genome with ss positive
polarity RNA.
No RNA polymerase.
 Multiple serotypes exists.
 Gene encoding envelope
glycoprotein has hypervariable
regions similar to HIV.
 REPLICATION Unclear because not grown in cell culture but
Flavivirus usually replicate in cytoplasm and translate
their genome RNA into large polyprotein.
 From this functional proteins are cleaved. So Hep C
likely may have similar program of replication
Transmission and epidemiology
 Humans are reservoirs
 Modes- blood, sexually, mother to child.
 Uncertainty exists whether maternal transmission is
through placenta or during birth.
 No evidence of insect vector unlike other Flavi virus
e.g. yellow fever is transmitted by mosquito. (also
infects liver)
 1% donors in USA have antibodies against HCV. In
India unknown.
 People with addiction to IV drugs infected commonly.
 Commonly preparation of Immunoglobulin is
generally safe.
 But instances of transmission of HCV recorded
 This is one example of infection transmitted by
immunoglobulin
Pathogenesis and immunity
 Primarily HCV infects hepatocytes
 No evidence of CPE of liver cells
 Death of hepatocytes caused by immune attack
mediated by cyto T cell
 No evidence of oncogene in viral genome or their
insertion into cancer cell DNA. Still it strongly
predispose to hepatocellular carcinoma.
 Antibody to HCV is made
 75% of patients are chronically infected. They also
produce virus for years.
 Chronic carriage of HCV is higher than HBV.
 10% cases go in for chronic active hepatitis and
cirrhosis
 Those who clear the infection in them there is no
evidence whether there is re-infection or life long
immunity.
Clinical findings
 Appears milder than HBV
 Fever, nausea, anorexia, vomiting, jaundice- common
 Dark urine, pale faeces, increase transaminases levels
seen
 It resembles HBV in predisposing hepatocellular
carcinoma or chronic liver disease
 Chronic carrier state occurs like in HBV
 Many infections are asymptomatic detected by
presence of antibody
 Mean incubation period in 8 weeks.
Lab diagnosis
 Detection of Ab HCV by ELISA
 Ag used is a recombinant protein formed from 3
immunological stable HCV protein
 Envelope is highly variable antigen so not included.
 This ELISA test
does not distinguish
IgM or IgG
 Many cases of false
 positive occur.
 So confirm by RIBA (Recombinant Immuno Blot
Assay)
 If RIBA is positive further confirmation by PCR based
test to detect viral RNA in serum.
 It also detects active disease exists or not
 Isolation of virus is usually not done.
ProphylaxisGeneral, blood screening
No vaccine
Treatment- α interferon
doubtful
Ribovarin
Hepatitis D
 Causes Hepatitis D or Delta Hepatitis.
 Rizetto and colleagues isolated it first
Properties Unusual virus because it is a defective virus
 It cannot replicate by itself as it has no genes for
envelope
 HDV replicates in cells which is infected by Hep B
virus.
 It uses the HBsAg as its envelope protein
 HBV is helper virus for HDV
 HDV is enveloped virus with RNA genome. (ss
negative polarity, covalently closed circle)
 RNA genome is small encodes one protein only.
 This protein is the internal core protein called delta
antigen.
 HDV genome has no sequence homology to HBV
genome DNA. HDV has no virion polymerase.
 Genome RNA is replicated and transcribed by host cell
RNA polymerase.
 HDV genome RNA is a Ribozyme i.e. it has ability to
self cleave and self ligate which is useful in replication
of the genome.
 HDV replicates in the nucleus.
 But specific replication is complex
 HDV has one serotype as HBsAg is one serotype
 There is no existence of animal reservoir.
Transmission and Epidemiology Same as HBV.
 IV drug abusers mostly infected
 distribution similar to HBV and is worldwide.
 But in a chronic carrier with HBV super-infected with
HDV has a significantly higher case of severe,
fulminant, life threatening liver failure.
 Lab Diagnosis-detecting delta antigen or IgM antibody to delta
antigen in patient’s serum by PCR and ELISA
respectively.
Pathogenesis and immunity
 Likely that pathogenesis is same as HBV.
 Damage due to cytotoxic T cell
 Some evidence suggesting delta agent is
cytopathogenic to hepatocytes is there.
 IgG Ab to delta antigen is not detected for long periods
after infection. So it is uncertain whether long term
immunity to HDV exists.
Clinical features
 Hepatitis delta can occur only in persons infected with
HBV. Since it replicates only in hepatocytes also
infected with HBV.
 The person can be infected with both HDV and HBV –
co-infected.
 Or infected previously with HBV then with HDV –
super-infected.
 Co-infection is more severe than with HBV alone.
 Incidence of chronic hepatitis is the same.
Treatment
 α- interferon can mitigate some of the chronic
hepatitis by HDV, but does not eradicate the chronic
carrier state.
 No specific anti-viral therapy, no vaccine.
 But people immunised against Hepatitis B are
protected.
HEPATITIS E
 Major cause of enterically transmitted Hepatitis.
 Common cause of water-borne epidemics in Asia,
Africa, India and Mexico.
 There was an outbreak in New Delhi in 1955
 HEV is non-enveloped,
ssRNA tentatively classified as Calcivirus.
 Clinically resembles Hep A
 Exception is, it has a high mortality rate in pregnant
women.
 Chronic liver disease does not occur. There is no
prolonged carrier state.
 Tests for HEV not readily available. So diagnosis
typically made by excluding HAV and other causes
 There is no antiviral treatment.
 IEM of faeces, bile can be done.
 ELISA IgM, IgG can also be done.
HEPATITIS G
 It was first isolated in
patients with post-transfusion hepatitis in 1996.
 HGV is member of Flavivirus family like HCV.
 But unlike HCV, HGV is not known to cause acute
hepatitis and chronic active hepatitis and predisposes
to hepatocellular carcinoma.
 HGV role in causation of liver disease is not yet
established.