Hepatitis E virus infections in chickens cause Hepatitis-splenomegaly (HS) syndrome, characterized by increased mortality and decreased egg production. The causative agent is avian hepatitis E virus (HEV), which is similar in morphology and genome to human HEV. Clinical signs include enlarged livers and spleens, and regressed or ruptured ovaries in laying hens over 24 weeks old. The virus spreads horizontally through the fecal-oral route and possibly vertically from infected breeding flocks. There is currently no vaccine or treatment available, so control relies on biosecurity measures to limit spread between flocks.

1. Ahmad Hassan
2020-AG-443

2. Hepatitis E virus infections in chicken
Contents :
Introduction
Etiology
Morphology
Chemical composition
Transmission

3. Hepatitis E virus infections in chicken
Contents :
Susceptibility to Chemical
and Physical Agents
Clinical Signs
Gross Lesions
Pathogenesis
Control
Diagnosis

4. Introduction and history
Hepatitis‐splenomegaly (HS) syndrome is a disease of
layer and broiler‐breeder chickens. First described in Australia in
the 1980s and subsequently in the UK and USA .
Although first described as HS syndrome, the disease is also referred
to as big liver and spleen (BLS) disease,.

5. Characterized by
increased mortality and decreased egg production and is
caused by avian hepatitis E virus (avian HEV)
Dead birds have red fluid or clotted blood in their abdomens,
and enlarged livers and spleens,
regressed or ruptured ovaries

6. Etiology
The primary causative agent of HS syndrome or BLS is
avian HEV.
All HEV are classified in the family of Hepeviridae.
The virus genome was sequenced and found to have over 60%
similarity to human Hepatitis E virus. Further studies are
required in order to fully characterize
and determine the classification of the virus

7. Morphology
Human HEV is a spherical, non‐enveloped, symmetrical
virus particle of approximately 32–34 nm in diameter.
bile samples from chickens with HS
syndrome are almost similar in size and morphology to human
HEV.

8. Chemical composition
The genome of avian HEV is a single stranded,
positive sense RNA molecule of 6,654 bp in
length excluding the poly (A) tail, which is
approximately 600 bp shorter than that of
mammalian HEVs

9. Virus spead and transmission
Horizontal transmission occurs between flocks on farms by the
faecal–oral route, although
spread within a flock may be relatively slow.
BLS antigen was detected in 1-day-old culled broiler chicks and
in the livers of broiler chickens that were the progeny of a BLS
affected flock. Thus, suggesting that vertical transmission
probably occurs following field infection. Chickens of all ages
are susceptible to infection but clinical disease is only seen in
birds over 24 weeks of age.

10. Susceptibility to Chemical
and Physical Agents
Liver suspensions containing avian HEV remained infectious
after treatment with chloroform and ether but
lost infectivity after incubating at 56°C for 1 hour or 37°C
for 6 hours.

11. Pathogenesis
The gastrointestinal tissues appear to be the first site of
avian HEV replication following oral inoculation,
Avian HEV is thought to enter the host through the fecal–oral
route. After replication in the liver, avian HEV is released to the
gallbladder from hepatocytes and then is excreted in feces.

12. Clinical Signs
The morbidity and mortality due to the disease in the
field are low, and the majority of avian HEV infections
are subclinical, In some outbreaks, there has been a drop in
egg production of up to 20%, but in other outbreaks egg
production
has not been affected. Hepatitis‐splenomegaly syndrome is
characterized by above‐normal mortality in broiler
breeder hens and laying hens of 30–72 weeks of age.

13. Gross lesions
At postmortem examination,birds are generally in good bodily condition
but there are gross changes to the liver, spleen and ovaries.
Liver : The liver is often enlarged and small subcapsular haemorrhages
are seen.
Red fluid in the abdomen may be present with clotted blood.
Spleen: The spleen is two or three times larger than normal with a mottled
appearance ,
blood can be seen in the abdominal cavity
Ovaries : Regression and rupture of the ovaries may occur, causing egg
peritonitis. Other lesions include pulmonary congestion with oedema and
enteritis, particularly in the duodenum.

14. .
Enlarged and haemorrhagic liver
from a chicken with
hepatitis‐splenomegaly syndrome
(HSS)

15. .
Two enlarged and
mottled white spleens
from 56‐week‐old
chickens with
hepatitis‐splenomegaly
syndrome

16. Diagnosis
A presumptive diagnosis of HS syndrome can be made on
the basis of clinical signs and pathological lesions.
However, ELISA and (R-T) PCR are useful in the identification.

17. Control
A vaccine against avian HEV is not yet available.
Currently there is no treatment for avian HEV infection.
Implementation of strict biosecurity in chicken farms
may limit the spread of virus.

18. Thank you
.REF : DISEASES OF POULTRY / EDITOR-IN-CHIEF, DAVID E. SWAYNE ;
ASSOCIATE
EDITORS, MARTINE BOULIANNE
POULTRY DISEASES SIXTH EDITION BY MARK EDDISON, PUAL F
MCMULLIN