A Pathological Study of Rainbow Trout Organs Naturally Infected with Enteric Redmouth Disease
Enteric redmouth disease is a serious infectious disease in salmonids that causes important economic losses in many countries. Since last few years there were reports on the occurrence of the disease in Iran based on the clinical signs. The disease caused great losses in rainbow trout farms in Fars Province, Iran. Biochemical test of the isolated Yersinia ruckeri resembled high degree of similarity between the isolate and the Yersinia ruckeri cited in the literature as serotype O1. Diseased fish showed typical hemorrhages, blackening of skin, exophthalmia and wide hemorrhages on internal organs. By histopathological examination, diseased fish showed generalized bacterimia with inflammation, glomerulonephritis and necrotic foci in kidney, necrosis and mild telangiectasis in liver, telangiectasis in spleen, hemorrhages and hyperemia in the intestinal mucosa, myocardial degeneration, atrophy and edema in heart, atrophy of pancrease tissues and mucus cell and melanophores hyperplasia in skin of the infected fish.
November 05, 2011; Accepted: March 21, 2012;
Published: May 17, 2012
Enteric red mouth disease caused by Yersinia ruckeri was reported initially
among hatchery reared rainbow trout in Idaho, USA. The subsequent dissemination
of this disease throughout the United States was attributed in part to the transport
of infected fish which may have become asymptomatic carriers shed bacteria from
their intestines and established reservoirs for recurrent infections (Cipriano
et al., 1986).
Recently, the production of rainbow trout in Fars province is between the third
main export items after wheat and corn. Fars province, one of the 28 provinces
in Iran situated nearly in South with numerous springs provided aquaculture
industry to flourish. Also production of rainbow trout has been developed during
last few years in different areas in Iran. Recirculation systems for intensive
fish culture are increasing now days. Infectious diseases are being emerging
due to imposed stress factors. Enteric Redmouth Disease (ERM) has been one of
the most significant diseases in salmonid aquaculture with cumulative losses
of more than 50% of fish population in many countries (Arias
et al., 2007; Austin et al., 2003;
Tobback et al., 2010). ERM has been diagnosed
for more than 30 years ago and commercially vaccines are available in European
countries (Fernandez et al., 2007). Since 2002
there were unpublished reports on the occurrence of the disease in Chahar-Mahal
Bakhtiary province in the center of Iran and then in Fars. The number of mortalities
was significantly greater in water recirculation than flow-through system farms.
The occurrence of the disease in 2002 and 2003 in cold and warm seasons are
estimated to be the same, however, adverse environmental conditions have intensified
the severity of the disease. Since last few years, Soltani
et al. (1999) reported a yersiniosis-like infection in farmed rainbow
trout. Also Soltani and Tarahomi (2002) reported on
the isolation of highly virulent Yersinia ruckeri-like bacterium from
diseased rainbow trout cultured in Tehran province with clinical signs of the
disease. Roozbahanim et al. (2009) has designed
a diagnostic kit for yersiniosis in the trout fish in Iran.
The aim of this study was to look at some of histopathological changes in rainbow trout organs during the course of enteric redmouth disease. Such study in the literature is scare and could elucidate the pathogenicity of the disease.
MATERIALS AND METHODS
Diseased fish from a north-western fish farm of Fars province with typical sign of ERM resembling heavy hemorrhages on lips, mouth and pharynx as well as the skin darkening of body and a septicemic hemorrhages on internal organs (Fig. 1, 2) were transported in large plastic bags to the fish disease laboratory.
||Diseased rainbow trout with heavy hemorrhages on lips, mouth
and pharynx as well as in eyes
||Diseased rainbow trout with typical ERM signs on viscera,
petechial hemorrhages affecting stomach, pyloric caeca and intestine
After a blow on the head, fish were sampled. Small pieces of the liver, spleen, intestine, kidney, heart and skin were first immersed in physiological saline then inside 10% buffered formalin for 2 days.
Five micron paraffin embedded slides were prepared and stained by hemotoxyline and eosin. Tissue sections were studied microscopically. Sterile kidney and spleen samples were taken and plated on sheep blood agar to isolate the bacteria.
Gross pathology of rainbow trout affected by ERM showed darkening of the skin, reddening of the tongue, throat and mouth due to subcutaneous hemorrhages. Hemorrhages on body surfaces such as around the mouth, on the operculum, on the base of fins and in eyes were seen in all of the fishes. Internally, congestion of the blood-vessels throughout the peritoneum and petechial hemorrhages affecting visceral organs were also noted.
Histopathological survey of liver revealed focal necrosis, telangiectasis and congestion with presence of bacterial colonies and infiltration of inflammatory cells in the liver tissue. In spleen telangiectasis was prominent (Fig. 3).
Histopathology of the intestine showed haemorrhages in the tunica muscularies and serosal surface, hyperemia and hemorrhages in tunica mucosa , presence of sloughed epithelial cells and RBC in the intestinal lumen, bacteria in lumen of congested vessels, congestion of tunica serosa and tunica muscularis and hemorrhage in fat around the intestine (Fig. 4).
Kidney tissues in histopathology showed severe haemorrhage, hyperplasia of interstitial hematopoietic tissue, tubular necrosis and glomerulonephritis (Fig. 5).
Study of histopathological slides of the heart of rainbow trout's infected with ERM revealed a myocardial degeneration, hemorrhage, infiltration of leukocytes, edema and atrophy (Fig. 6).
The heart of rainbow trout naturally infected with ERM showing infiltration of leukocytes, edema, atrophy and myocardial degeneration (Fig. 6).
Histopathological study of pancrease showed hemorrhages in peripancreatic lipid tissues and atrophy of pancrease tissues (Fig. 7).
|| Telangiectasis in the spleen of rainbow trout naturally affected
by ERM (X 400)
||The intestine of rainbow trout naturally infected by ERM with
severe congestion of tunica serosa and tunica muscularis
||The kidney of rainbow trout infected by ERM showing interstitial
hemorrhage hyperplasia of interstitial hematopoietic tissue and tubular
||The heart of rainbow trout naturally infected with ERM showing
infiltration of leukocytes, edema, atrophy and myocardial degeneration
Pathological examination of the skin of the rainbow trout naturally infected by ERM showed an apparent increase in mucus cells and melanophores (Fig. 8).
||The pancreas of diseased rainbow trout with ERM showing hemorrhages
in peripancreatic lipid tissues and atrophy of pancreas tissues
||The skin of rainbow trout naturally infected with ERM showing
mucus cells and melanophores hyperplasia
Yersiniosis has a worldwide distribution and is considered endemic in most
trout producing countries and in natural hosts in marine habitats (Khalil
et al., 2006; Surendraraj et al., 2009;
Akinjogunla et al., 2011). Enteric redmouth disease
is an acute or chronic fish disease which has caused significant losses in aquaculture
associated with intensive culture and poor water quality. It seems that younger
rainbow trout are more susceptible due to their undeveloped immune response.
Diagnosis for a preventive strategy is important. Not much case reports have
been published on the pathology of this bacterium for rainbow trout. However,
a consistent feature of enteric redmouth disease mentioned by Roberts
(2001) is generalized hemorrhagic petechia over abdominal organs with swelling
and reddening of the kidney and spleen that is similar to our findings. Present
results showed necrotic foci and infiltration of leukocytes with associated
hemorrhage which is similar to the finding of Tobback et
al. (2007) and Roberts (2001).
The disease happens in temperature more than 10°C and in a stressed condition
(Surendraraj et al., 2009). In different species
of fish such as common carp, a chronic disease characterized by prominent peritonitis
and enteritis, exhaustion of the erythroid, granuloid and lymphoid components
in haematopoietic kidney tissue as well as focal degeneration and necrosis in
organs that indicated a high sensitivity of carp to intraperitoneal infection
with a relatively low dose of Y. ruckeri has been documented (Berc
et al., 1999).
Yersiniosis is clinically characterized by bleeding in the base of fins, inside
and around the mouth, bilateral exophthalmia with or without hemorrhage, peri
ocular and peri oral hemorrhage. Internally, small hemorrhages are noted in
liver, pancreas, large intestine, swim bladder and lateral muscles. In diseased
fish, the spleen becomes enlarged and dark and the intestine is inflamed and
filled with purulent material. Hemorrhagic inflammation in hindgut, accumulation
of fluid in stomach and intestines, enlargement of hematopoietic organs, kidneys
and splenomegaly are among the pathologic landmarks (Avci
and Birincioglu, 2005; Roozbahanim et al., 2009).
Noga (1996) noted that bacterial colonization of vascularized
tissues caused telangiectasis of gill, kidney, liver, spleen and heart that
can lead to necrosis of the hematopoietic tissue causing anemia. Necrosis and
sloughing of the gastrointestinal tract were also noted that is in coordination
with our findings. Severe necrosis of hematopoietic tissue of kidney is also
reported by other workers (Furhman et al., 1983;
Horne and Barnes, 1999).
Infected fish with Y. ruckeri (O1 serotype) usually estimated up to
70% mortality. Diseased fish showed typical hemorrhages, blackening of skin,
exophthalmia and wide hemorrhages on internal organs with typical histopathological
changes demonstrated in this study. Serotype O1 has a worldwide distribution
while serotype O2b is restricted to North America and Baltic Countries (Welch
et al., 2011).
In the expansion of aquaculture industry in different provinces of Iran with moderate geographical climates, it seems more work is required to estimate the infected farms. There is also a need to develop a vaccine against enteric redmouth disease for the prevention of the disease.
Staff in the Aquatic Animal Health Unit and the Department of Pathology, School of Veterinary Medicine, Shiraz University Helped much for this study.
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