ISRAEL JOURNAL OF
VETERINARY MEDICINE
INVESTIGATION OF THE FIRST TRANSMISSIBLE
GASTRO-ENTERITIS (TGE) EPIDEMIC IN PIGS IN
ISRAEL
Brenner, J.1, Yadin, H.1, Lavi, J.4, Perl, S.2, Edery, N.2, Elad, D.3,
4
4
5
5
Vol. 59 (3) 2004 Bargut, A. , Pozzi, S. , Lavazza A. , and Cordioli P.
1. Division of Virology and Preventive Neonatal Diseases Unit,
2. Pathology and 3. Bacteriology, Kimron Veterinary Institute, 50250, Bet Dagan,
4 . Freelancer Veterinary Surgeon, Israel and 5. Istituto Zooprofilatico
Sperimentale della Lombardia e dell’Emilia-Romagna “Bruno Ubertini” Via
Bianchi 9, Brescia (BS), Italia.
Abstract
Transmissible gastro-enteritis (TGE) is a contagious disease of pigs that occurs as
explosive epizootics. This communication reports on the evidence that we gathered
in order to confirm the first epidemic of TGE in Israel and external validation
corroborated our clinical suspicion and laboratory findings.
Introduction
Transmissible gastro-enteritis (TGE) is contagious disease of pigs that occurs as explosive
epizootics. TGE is caused by the TGE virus (TGEV), a member of the coronaviridae. A
distinct respiratory variant the Porcine Respiratory Corona Virus ( PRCV) has been
recognized since the 1980’s, a deletion mutant of the TGEV (1). Two other coronaviruses
antigenically distinct are the Porcine Epidemic Diarrhea Virus (PEDV) and the
Hemagglutinating Encephalitis Virus (HEV) (2).
TGEV is a common cause of diarrhea in pigs, affecting all ages but significant deaths only
occur in suckling pigs, with the severity related to the age of the animals infected. Almost all
susceptible piglets under 10 days of age die within few days of exposure, but the mortality
decreases the older they become. Only mild signs such as vomiting, regurgitation and
agalactia are present in the lactating dams. In an endemic situation, namely, in vaccinated
animals and/or where the acute wave has faded, sporadic diarrhea in older animals and postweaning animals in contaminated nurseries are the spare clinical evidences of TGEV
infection. As a member of the coronavirus group, TGEV is primarily an enteric virus,
destroying enterocytes of the small intestine (Fig. 1), causing villous atrophy. Extra-intestinal
sites of virus multiplication include the respiratory tract and mammary tissues (3,4,5), but the
virus is most readily isolated from the intestinal tract and feces.
The first report of clinical disease in pigs caused by coronaviruses dates to 1946 (6) and
TGE occurs throughout the world. The emergence of PRCV coincided with the disappearance
of TGEV in Europe (7). In mid 1980’s, a previously unrecognized porcine coronavirus
spreading through Europe was identified (8). The name porcine epidemic diarrhea virus
(PEDV) was adopted (9). At present, PEDV has been identified in most swine-producing
countries, except in the Americas (9).
When the TGEV spreads within a fully susceptible herd with no previous history of TGEV
infection, up to 100% mortality is expected among newborn pigs, showing marked diarrhea
and dehydration in weaned pigs, while inappetence, vomiting and diarrhea are typical signs in adult
animals. Partial or total agalactia of sows is common (5,9).
The Israeli pig industry benefits from a particular epidemiological situation. Due to religious
customs in the middle east, where the Jewish and Muslim religions prevails, the pig industry is largely
isolated, and far away from any zone with intensive pig industry. Consequently, very few epidemics
have been recorded among the Israeli pig herds. This communication reports on the first epidemic of
TGE in Israel. The investigation was carried out pursuing diagnostic methodology of emerging
diseases.
Materials
and
Methods
Case
description
The first cases of diarrhea followed by dehydration and death of newborn piglets, 1 to 7 days old were
noted in one pigsty in northern Israel on May 7th 2004 and the episode gained epidemic proportions,
with mortality as high as 70 to 80% during the first week of life and proportionally less in convalescent
groups of piglets. The area where this outbreak occurred is nicknamed the “swine hill” which is located
near Evlin. This hill is about 1.5 by 1.5 kilometers. Thirteen pig herds are concentrated in this restricted
zone. One to two days later after the first outbreak, other herds reported the same clinical signs.
Additional clinical signs that accompanied this outbreak were vomiting and regurgitation and a partial
agalactia in lactating sows. Two piglets of 2 days old were brought to the Kimron Veterinary Institute
(KVI) for post mortem examination. The histological examination of the small intestine revealed
typical (4,9) villous atrophy, suggesting an enteric virus infection.
On May 24th a group of investigators from the Kimron Veterinary Institute paid a visit to one of the
affected farms. Upon the visit, the clinical manifestations appeared as reported by the local practitioner.
The followed materials were collected on the farm: 5 individual diarrheic feces samples, 5 moribund
piglets, 6 blood samples with an anti-coagulant (3 of diseased and 3 of convalescent animals,
respectively) and 10 blood samples without anti-coagulant (5 from diseased animals and 5 from
convalescent ones, respectively). Four of the 5 moribund animals arrived alive and one died during
transport. They were sacrificed immediately upon arrival and the feces and intestinal segments as well
as biopsies of all the internal parenchyma and brain, were prepared for histopathological examination.
An additional two sets of the same tissues were store at -20oC, for further analysis. One set of intestinal
segments from the 5 piglets were shipped to the Istituto Zooprofilatico, (IZS) Brescia, Italy.
One week later another batch of diarrheic feces arrived to KVI from newly infected herds. This batch
comprised
nine
pooled
feces;
each
sample
represented
one
infected
litter.
Antigenic
identification
Assuming that if porcine and bovine coronaviruses share common antigenic epitopes, we used the
bovine assays for the diagnosis of rotavirus and coronavirus (Bio-X Combined Digestive ELISA Kit,
for antigenic diagnosis in bovine faeces of rotavirus, coronavirus, E coli K99, B-6900 Marche-enFamenne,
Belgium)
according
to
the
manufacturer’s
instructions.
Another set of antigen diagnosis was carried out at the IZS, using the immuno-fluorescence (IFA) on
intestinal sections, electron-microscopy (EM) and immuno-EM (IEM) with specific anti-TGEV and
polymerase
chain
reaction
(PCR)
(Kim
et
al.,
12),
and
virus
isolation.
For the IFA and for the IEM assays performed on the intestinal sections, hyperimmune serum
specific for porcine coronavirus was used.
Serology
This assay was performed at the IZS in Brescia, using a commercial kit ELISA (INGENASA) for the
presence of anti-TGEV antibodies in infected and convalescent animals.
Necropsy
All the parenchyma samples were processed regularly and were prepared for staining with H&E on
samples embedded in paraffin.
Hematology
Biochemical and hematological profile was done on all the blood samples.
Bacteriology
The routine
laboratory
diagnostic
procedures
were
used
as
described
elsewhere
(10).
Results
Antigenic discovery
In total 63% of the fecal samples were positive for bovine
corona virus antigen(s) (6/10 and 6/9 for the first and second sets
of samples, respectively).
All the assays combined together, namely, EM and IEM, PCR
and IFA (Fig. 2) performed at the IZS in Brescia, showed that in
all the 5 samples TGEV was present although none of the assays
alone could identify the TGEV in all the samples (Table 1).
Virus isolation succeeded in two out of three diseased piglets.
This isolation attempt was performed on piglets originating from
a farm on day 45 of the ongoing TGE epidemic (Lavazza and
Cordioli, personal communication).
Serology
The sera derived from diseased animals had a very weak
ELISA anti-TGEV reaction while the convalescent sera showed
a very strong anti-TGEV reaction.
Necropsy
Villous atrophy was noted, suggesting an acute enterovirus
infection (Fig. 1). Massive infiltration of inflammatory cellular
components, vacuolization of enterocytes and destructive process
were all sequelae of the ongoing infection.
Figure 1. Villous atrophy and vacuolization of ente
massive infiltration of inflammatory cellular compo
Hematology
The WBC, lymphocyte and neutrophil counts are presented in
Table 1.
As seen in Table 2, the hematological profile of the diseased
animals shows a remarkable lymphopenia and a moderate
neutrophilia. The L/N ratio range is a characteristic haematologic
picture of acute viral attack.
Bacteriology
All the bacteriological assays resulted negative for the
presence of enteropathogenic bacteria including Clostridium
perfringens type C, the causative agent of porcine enterotoxemia
in piglets.
Figure 2. Immunofluorescence staining of the sm
monoclonal anti-porcine corona virus antibody.
Table 1 - A Summary of the PCR, ME, IEM and IFA results from the IZS laboratories .
Animal
TGEV-PCR
ME
IEM
IFA pools
Number
1
+
-
-
2
-
+
+
3
-
+/-
+
4
-
+
+
5
+
+
+
+
+
Table 2. Range of White blood cells, lymphocyte and neutrophil counts and ratio N/L of diseased and
convalescent
animals
Diseased
Convalescent
WBC
Lymphocytes
Neutrophiles
L/N* ratio range
9-14.2x103
11-17.8x103
3.1-4.5x103
9.7-11.5x103
3.8-7.6x103
0.8-4.6x103
0.3-0.5/1
3 to 10/1
*lymphocyte/neutrophil ratio.
Discussion
The Israeli intensive pig industry is isolated from other areas of farming. Moreover, it was
maintained in quasi-closed premises, 13 pig herds in one region, with no other industrial
pigsties within approximately 100 km. Due to this particular situation, Israeli Veterinary
Services and KVI lacked species-specific diagnostic tools for the diagnosis of specific swine
diseases. Nevertheless, we have diagnosed TGEV antigens in relatively short time by using
non-species specific diagnostic kit. A specialized laboratory (IZS) that deals regularly with
swine diseases has found the TGEV in the same samples, reconfirming our primary results.
The differential diagnosis (11) of enteric neonatal diseases deals with many possible
causative agents.
The typical findings of villous atrophy (Figure 1) and lymphopenia (Table 2), pointed toward
a probable viral (acute) attack. The clinical manifestations especially the age distribution of
the diseased animals at risk, the rapid spread of the disease among the pigsties, its high
mortality rate, the antigenic ELISA positive reaction in 63% of the fecal samples submitted to
KVI and the confirmations tests from the IZS, lead us to the conclusion that TGEV is
responsible for this episode.
Whether the virus originated from bringing or smuggling of infectious material from abroad,
or from the wild boar population is a matter of speculation.
LINKS TO OTHER ARTICLES IN THIS ISSUE
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