Download Transmissible Gastroenteritis (TGE)

Transmissible Gastroenteritis (TGE)
Transmissible gastroenteritis (TGE) is a gastro-intestinal disease of pigs caused by a coronavirus. TGE
is an acute, rapidly spreading, viral disease of pigs which is spread by the faecal-oral route. TGE is
characterised by diarrhoea, vomiting, dehydration and high mortality in piglets and has similar
presentation to Porcine Epidemic Diarrhoea virus (PED).
TGE affects only pigs and is not zoonotic. There is no risk to other animals or to humans and no risk
to food safety. TGE is a listed disease of the World Organization for Animal Health (OIE) but is not a
notifiable disease in Great Britain. The disease was first described in the US in the 1940s.
In the UK TGE has not been reported in recent years because immunity to a related coronavirus,
porcine respiratory coronavirus (PRCV), which emerged in the mid 1980s, provides cross-protection
against TGE. There is usually no clinical disease with PRCV infection but on occasions there can be
mild respiratory disease. PRCV does not produce clinical enteric disease. PRCV typically forms an
endemic infection in pig herds and infected pigs develop antibodies which also neutralize TGEV.
Clinical signs
In acute outbreaks, the incubation period is very short, 18 hours to three days. The disease spreads
rapidly in piglets to affect all susceptible pigs. Clinical signs include transient vomiting, watery,
yellow diarrhoea which may contain undigested milk, weight loss, dehydration, and high mortality,
especially in pigs less than two weeks of age. The diarrhoea may be foul smelling because of
maldigestion and excess fat in the faeces - foul steatorrhea. The pigs weaken rapidly and usually die
within one to two days. TGE can cause up to 100% neonatal mortality during the initial stages of an
outbreak but the mortality rate is usually 10-20%. Disease tends to persist in the farrowing houses
over a period of 3 to 4 weeks until sows develop sufficient immunity to protect the piglets.
Growing and finishing pigs with epidemic TGE may show inappetance, profuse diarrhoea, vomiting,
rapid dehydration, shivering and marked thirst. Pigs infected after 4 weeks of age usually survive but
may remain stunted. In naïve sows and gilts, especially those that have farrowed recently and are
heavily exposed to virus from piglets with TGE, the disease can be of moderate severity with
anorexia, vomiting, diarrhoea, depression and agalactia. They usually recover within 5-10 days.
Epidemic TGE is seen in the US in herds in which most of the pigs are TGEV and PRCV seronegative
and susceptible and was reported in mid-2013 in a herd in Ontario, Canada.
Piglets suckling immune dams may not show signs of disease if they get sufficient colostrum. TGE
can become endemic in large herds as pigs become infected when maternal immunity fails and
leaves them susceptible. Pigs usually become infected in late lactation or post-weaning when the
lactogenic immunity in the sow's milk is no longer protecting the pigs from infection. Clinical signs
can be mild and usually include diarrhoea, dehydration, unthriftiness and stunting.
In growing and finishing pigs, signs usually are mild except for a few days of profuse watery
diarrhoea and occasional vomiting. Morbidity is high but mortality is low.
Transmission
The virus spreads by direct pig contact or indirect exposure through fomites (i.e. objects or
substances capable of carrying infectious organisms) which are contaminated with faecal material
which contain virus. Pigs that survive TGE develop antibodies against the virus but continue to
excrete virus in faeces or nasal secretions for at least two to eight weeks; some individuals have
been shown to excrete virus intermittently for up to 18 months. Infected sows can transmit virus in
their milk or faeces to their piglets. Although faeces are the major source of infection, there may be
some aerial spread of the virus, at least for short distances. Other animals and insects known to act
as mechanical carriers of virus for various lengths of time and distance include dogs, cats, foxes,
starlings and flies.
When virus is introduced into a herd of naïve pigs, all age groups are affected and the disease
assumes epidemic characteristics. Once premises are infected and there is a constant source of
immunologically naïve pigs because of frequent or continuous farrowing or frequent introduction of
susceptible animals, TGE may persist as a chronic disease in the herd. Infection often persists in
successive groups of pigs entering a contaminated nursery.
Factors other than virulence of the virus and host resistance seem to play little part in susceptibility
to infection. Outbreaks often occur on premises with excellent husbandry, nutrition and hygiene
standards.
Diagnosis
Producers who see unusual signs of diarrhoea in their herds should speak to their veterinary surgeon
without delay. Early diagnosis is critical to address the issue and limit potential for spread.
Veterinary surgeons should contact the AHVLA veterinary diagnostic laboratory to find out what
samples are preferred for diagnostic investigations.
On post-mortem gross lesions in piglets include marked dehydration, distension of the small
intestine with foamy, yellow, foul-smelling fluid and scattered milk curds. The intestinal wall is very
thin and nearly transparent. On histopathology severe villous atrophy can be seen in the small
intestine from 24h after infection.
If TGE is suspected based on clinical signs and lesions, the diagnosis of TGE can be confirmed by
laboratory testing. The laboratory can provide more detailed information on the tests available and
the recommended tissue and timing of sampling. Methods for diagnosis include:





Detection of viral antigen: fluorescent antibody assay (FA), immunohistochemistry (IHC),
Detection of nucleic acid: reverse-transcriptase polymerase chain reaction (RT-PCR)
Microscopic detection of virus: electron microscopy (EM)
Isolation and identification of virus: cell culture
Detection of a significant antibody response: serology ( may be complicated due to antigenic
similarity between TGEV and PRCV).
Diseases that must be differentiated include colibacillosis, rotavirus, coccidiosis and porcine
epidemic diarrhea.
Prevention and control
Preventive measures for negative herds include maintaining a closed herd and implementing strict
biosecurity practices. The virus is killed by sunlight within a few hours but will survive for long
periods outside the pig in cold conditions. Many disinfectants are effective against TGE virus
including iodides, peroxygen, quaternary ammonium compounds, phenol and sodium hypochlorite.
All in/all out system of production with cleaning and disinfection between farrowings can help break
the cycle of infection.
In the US attenuated and killed virus vaccines are available. Usually sows are vaccinated usually
although some also can be given to neonatal piglets. The vaccines are generally unable to protect a
naïve population in the face of an acute exposure.
Treatment
Like other viral enteric diseases, treatment for TGE is supportive and aims to prevent dehydration in
young pigs.
- A clean, dry, warm and draught free environment.
- Free access to high quality drinking water is critical.
- Supplementing the water with electrolytes and energy supplements may be beneficial.
- If other bacterial diseases (E. coli, salmonella) start causing problems during the outbreak,
appropriate antimicrobials may be needed but will not be effective against the underlying virus
infection.
Older swine usually recover spontaneously. Piglets at least one month old before onset usually
recover if provided with a nutritious starter feed, warm housing and good care.
Good biosecurity protocols such as adequate quarantine, isolation of cases and disinfection help
prevent entry or spread of the disease in the herd.
Biosecurity
Biosecurity is key to both preventing reintroduction of TGE to the UK and limiting spread around the
industry should it be introduced.
National biosecurity



If importing pigs organise a quarantine period before and after arrival in the UK, Request specific
information on clinical incidence of disease, treatments, vaccines, antimicrobial use and
mortality rates from source farms for at least the 6 months before the pigs entered quarantine.
Advice is available from the NPA on recommendations for disease testing before and after
arrival.
Check with suppliers of any imported products coming onto your farm that a chain of assurance
exists to minimise risk that contamination with pig products and pig faeces could have occurred
or that there is an inactivation step within the production process. This is particularly important
for products like porcine plasma which are very high risk.
Anyone visiting farms or abattoirs or coming in contact directly or indirectly with pigs overseas
should take strict precautions to minimise the risk of bringing back not just TGE virus but also
PRRS virus and potentially other strains of infectious agents not currently present in the UK.
- ideally use clothing and footwear provided by farms visited overseas
- shower and thoroughly clean hands and fingernails as soon as possible after contact
with pigs overseas.
- as cross contamination could occur in luggage wash all clothing and thoroughly clean
and disinfect all footwear on return from overseas trips
- try to ensure there is no direct contact with pigs in the UK for up to 72 hours after the
contact with pigs overseas.
Farm biosecurity


Review farm biosecurity as a matter of urgency. Members of the Pig Health Improvement
Project should use the Biosecurity tool on the Pig Health Improvement Project website to
help identify where biosecurity can be strengthened.
If you are not a member of PHIP join for access to biosecurity tool and disease alerts







Isolate and quarantine pigs on arrival on farm and continue vet to vet discussions about animal
health at the herd of origin before mixing with the rest of the herd.
Control risks of introduction by limiting traffic (people and equipment) onto the farm.
- all lorries that have transported pigs should be thoroughly cleaned and disinfected as
soon as possible after unloading pigs
- lorries should thoroughly cleaned and disinfected before leaving abattoirs
- if you are not happy with the cleanliness of a lorry arriving on your farm send it away,
it’s just not worth the risk
- do not allow deadstock collection vehicles on your farm. Arrange an offsite collection
point without delay if you have not already done this.
- allow only essential vehicles on site and make arrangements for all other vehicles to
make deliveries to the perimeter of your unit
Thoroughly clean and disinfect anything coming onto the farm. Seek advice from your veterinary
surgeon on the best disinfectants to use. The PHIP team can provide advice on improving the
effectiveness of your cleaning and disinfection.
Temperatures above 65° C for more than 10 minutes will inactivate the virus.
Complete drying after C&D is also an effective inactivation method.
Enforce downtime requirements of at least 12 hours and maintain a log of visitors
Provide all essential visitors with clean boots and overalls to change into before entering the
unit.
Links
OIE Health Standards
http://www.oie.int/fileadmin/Home/eng/Health_standards/tahm/2.08.11_TRANSMISSIBLE_GASTRO.pdf
Iowa State University vetmed.iastate.edu/vdpam/new-vdpam-employees/food-supply-veterinary-medicine/swine/swinediseases/tge
Indiana Animal Disease Diagnostic Laboratory - Purdue University www.addl.purdue.edu/newsletters/2008/fall/TGE.htm
thepigsite www.thepigsite.com/diseaseinfo/123/transmissible-gastro-enteritis-tge