4. ETIOLOGY &
Astroviruses, as the name implies, are small star-
shaped viruses with five to six pointed surface
projections. However, this morphology is only
observed in a small percentage of particles by immune
Astroviruses are non-enveloped RNA viruses found in
many parts of the world, mainly in young birds less
than five weeks old.
They are commonly associated with the runting-
stunting syndrome of broilers (although a recent study
indicates that a parvovirus may also be linked to this
syndrome), and enteritis in guinea fowl.
5. ETIOLOGY &
Astroviruses have also been associated with stunting and
pre-hatching mortality in duck and goose embryos.
To date, six different avian astroviruses have been
confirmed: two of turkey-origin (TAstV-1 TAstV2);
two of chicken-origin [Avian Nephritis Virus (ANV)
and Chicken Astrovirus (CAstV)]; and two of duck-
origin (DAstV-1 and -2).
The molecular characterization of these viruses
shows wide genetic variability among each type,
and this variability influences the ability to detect
them by molecular and serological techniques (see
the phylogenetic tree of fig.29.1).
7. ETIOLOGY &
Astroviruses are transmitted horizontally via the fecal-oral
route. Vertical transmission is suggested based on field
observations for the astrovirus associated with avian
nephritis. Morbidity can be elevated, while mortality is
normally low unless other pathogens are present.
In a study conducted in three different American states,
diagnostic investigations compared PEMS positive turkey flocks to
PEMS-free flocks raised at the same time and in the same
regions. Although not significant at p-value < 0.05, there seems to
be an association between PEMS and astrovirus status (see
Tabl.29.1). Figure 29.7 also shows that flocks found to be infected
with astrovirus had, on average, about double the mortality rate.
9. CLINICAL SIGNS
Astroviruses in chickens have been mainly associated
with mild stunting. An exception would be avian
nephritis, a rare acute condition. Normally, chickens
infected with the avian nephritis virus (ANV) remain
subclinical (detected by RT-PCR mainly in Japan, China,
Africa, Europe, and the United States). Under field
conditions, the clinical expression will vary from a
runting syndrome to death caused by nephropathy and
Chickens affected with the ANV show lesions largely
limited to the kidney. Epithelial cells of the proximal
convoluted tubules are necrotic. Granulocytes are
present, as well as a lymphocytic infiltration in the
interstitium with some fibrosis. Visceral urate deposits
are generalized in chicks dying from this condition.
10. Fig 1. Pathologic changes of RSS chicken. 1-A, intestinal
bleeding; 1-B, yolk malabsorption; 1-C, perihepatitis; 1-D,
Gross and histopathological lesions from a gout-affected
commercial broiler chick. 1a: Prominent ureter and urate
deposition in the kidney. 1b: Urate deposition on the heart.
1c: Interstitial nephritis and urate deposits in the kidney (arrows).
1d: Infiltration of inflammatory cells in the myocardium (arrow).
1c and 1d: bar =100 µm, haematoxylin and eosin staining
12. CLINICAL SIGNS
In turkeys, clinical signs are normally noted before six weeks
of age (mainly 1 to 3 weeks) and may last up to 12-14 days.
They include diarrhea, listlessness and nervousness. In
turkeys, growth depression often follows the initial clinical
signs. It is, at least in part, a consequence of decreased
intestinal absorption in infected poults.
In turkeys at necropsy, typical observations are dilated ceca
with yellowish frothy content and gaseous fluid. The overall
intestinal track shows a loss of tone (intestinal wall is
thinner than normal). Diarrhea is partly attributed to the
osmotic effect of undigested and unabsorbed nutrients
drawing water to the lumen of the intestine.
Microscopically, a crypt hyperplasia is noted in the small
intestine, but no villous atrophy; although a mild shortening
of the villi has been noted in some experiments. Changes
occur as early as one day post-infection.
14. CLINICAL SIGNS
In ducks, astroviruses have been associated with hepatitis, which can be
fatal. They have been confirmed in what is called Duck Hepatitis Virus
(DHV) type II [to differentiate this condition from Type I caused by
DHV type II is an astrovirus also known as duck astrovirus-1, (DAstV-1). It
occurs in ducklings from 10 days to 6 weeks of age (mature ducks are
not affected), and causes lesions similar to those of DHV type I .
Recent studies have shown that another astrovirus, reported to date
only in the United States, and different from . DHV type II astrovirus, can
also cause hepatitis. It is named Duck Astrovirus type 2 (DAstV-2)
lesions are mainly observed in the liver and kidneys.
The liver is pale with small hemorrhages that may form bands.
The spleen is enlarged with pale foci. Kidneys are often swollen with a
Small hemorrhages may be noticed in the intestinal wall and on the heart
Death may occur in an hour to four days after the onset of clinical signs,
including loose droppings, polydypsia, excessive urate excretion and
nervous signs (convulsions, opisthotonos).
Diagnosis can be made by observing aggregates of
typical astrovirus particles by immune electron
microscopy. Other diagnostic tools include antigen
capture enzyme-linked immunosorbent assays (AC-
ELISA) and reverse transcriptase polymerase chain
reaction (RT-PCR) or real-time RT-PCR.
Confirmation of diagnosis in cases of avian nephritis
requires demonstrating the presence of ANV antigens
by immunohistochemistry or viral RNA by in situ
For duck hepatitis, an indirect ELISA has been
developed. Electron microscopy is also used.
19. TREATMENT &
No vaccine or treatment exists for chicken broilers or poults.
Some recent reports suggest that vaccinating chicken
breeders may offer some protection from the runting
syndrome for progeny.
Like for any other enteric conditions, good
management practices (good ambient temperature,
litter management, etc.) may reduce the impact of
the infection on flock performances
It seems that DHV type II and III infections could be
controlled by the use of live attenuated vaccines
given to breeder ducks to confer passive immunity
20. TREATMENT &
Astroviruses are extremely environmentally stable and resistant to most
disinfectants. They are not inactivated by phenolics, acidic pH, detergents,
ambient temperature, quaternary ammonia, and most alcohols.
Only a few disinfectants such as 0.3 % formaldehyde, 0.1 % β-propriolactone
, 90% methanol, and potassium peroxymonosulfate ( 1.5 % Virkon S) can
destroy this virus.
Emphasis should be placed on thorough cleaning and disinfection with a
downtime of at least two weeks between flocks.
Manual of poultry diseases
Koci MD & Schultz-Cherry SL. Avian astroviruses.
Review article. Av Pathol, 2002;31:213-227.
Pantin-Jackwood MJ et al. Enteric viruses detected by molecular mathods in
commercial chicken and turkey flocks in the Unites States between 2005 and 2006.
Av Diseases, 2008,52:235-244.
Nighot P.K et al. Astrovirus infection induces sodium malabsorption and redistributes
sodium hydrogen exchanger expression. Virology (2010) 401; 146-154.
Schultz-Cherry S.L. Astrovirus Infections.
In Diseases of Poultry, 13th Ed., Ed. DE. Swayne, Wiley-Blackwell, 2013, pp 391-395.
Pantin-Jackwood MJ et al. Avian Astroviruses. In Astrovirus Research. Essential Ideas,
Everyday Impacts, Future Directions. Ed. S Schultz-Cherry .
Springer; ISBN: 978-1-4614-4734-4 (Print) 978-14614-4735-1 (Online); pp151-180.
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