Transmissible Gastro Enteritis, TGE

TGE is a very important and highly infectious disease caused by a coronavirus.

Coronaviruses take their name from the halo-like array of envelope proteins that surround the capsid; they're visible in a TEM negative stain as spiky processes forming a "crown" around the RNA core.

The virus is killed by sunlight within a few hours but will survive for long periods outside the pig in cold conditions. It is very susceptible to disinfectants particularly iodine based ones, quaternary ammonia and peroxygen compounds. 

Disease will persist in the farrowing houses over a period of 3 to 4 weeks until sows have developed sufficient immunity to protect the piglets. 

In herds of less than 300 sows the virus is usually self eliminating provided there are good all-in, all-out procedures in farrowing houses and grower accommodation. In larger herds however the virus will persist in the growing herd because piglets at weaning, still under the influence of the maternal antibody, move into houses where the virus still persists. Once the lactogenic immunity in the sow's milk is no longer being taken in the pigs become infected allowing the virus to multiply. The pigs then shed the virus, contaminating the weaner rooms and infecting pigs being weaned after them. TGE can become endemic in herds in a mild form with high morbidity but low mortality. 

This disease in the weaning and the growing pig is clinically indistinguishable from porcine epidemic diarrhoea. In small grower-finisher units the virus is likely to disappear from the population. In large finishing units in which susceptible pigs are being brought in frequently, the virus is maintained indefinitely in the population by repeated infection of the newcomers.

Symptoms

Weaners & Growers

• When the virus is introduced into a finishing herd for the first time there is rapidly spreading, vomiting and a watery diarrhoea, eventually affecting almost all the animals.
• Disease disappears spontaneously over a 3 to 5 week period.
• Mortality is usually low.
• The main effect on the individual growing pig is dehydration which is resolved in about a week.
• Nevertheless the disease may increase the slaughter age by 5-10 days.

Piglets

• In the sucking piglet the disease is very severe.
• Acute watery diarrhoea.
• Almost 100% mortality within 2 to 3 days in piglets under 7 days of age due to severe dehydration and electrolyte imbalance.
• There is no response to antibiotic therapy.
• The most striking feature is the wet and dirty hairy appearance of all the litter due to the profuse diarrhoea.

Sows

• In acute outbreaks the most striking feature is the rapidity of spread.
• Vomiting.
• Diarrhoea.
• Adult animals show varying degrees of inappetence and usually recover over a 5 to 7 day period.

Causes / Contributing factors

• The virus is shed in large numbers in the faeces.
• Pig faeces therefore are the major source of transmission either directly through the purchased carrier pig or indirectly through mechanical transmission.
• Poor pen floors.
• Poor pen hygiene associated with bad drainage
• Poor hygiene procedures, between pens
• Environmental contamination from one pen to another i.e. boots, brushes, shovels clothing etc.
• Feeder pipes and feed bins. This is a high risk source for the spread of enteric diseases.
• Dogs may shed the virus in their faeces for 2 to 3 weeks.
• Birds and in particular starlings may transmit the disease.
• Contaminated feed.
• Continual use of buildings without all-in, all-out may perpetuate disease.
• Continual purchase of naive weaners.

Diagnosis

The clinical picture in acute disease is almost diagnostic. There are no other enteric diseases that spread so rapidly across all pigs. The ultimate diagnosis of TGE must be made in the laboratory from the intestine of a fresh dead pig using fluorescent antibody tests (FAT's). Isolation of the virus is also carried out. 

The best test, which will give an answer in a matter of hours, is to freeze the ileum (last part of the small intestine), section it for histology and carry out fluorescent antibody tests (FATs) on the sections. ELISAs may also be available in some more sophisticated laboratories. Polymerase chain reaction (PCR) tests would be possible but are probably not available. The blood samples can be subjected to serum neutralisation tests to detect rising antibody titres. Unfortunately these results take at least 2 weeks.

Similar diseases

Porcine epidemic diarrhoea (PED) could give a similar picture but it would be less acute and with less mortality in sucking pigs. 

In the acute form epidemic diarrhoea could give a similar picture but it would be less acute and with less mortality in sucking pigs. Where TGE has become chronic then differentiation from the other causes of diarrhoea must be carried out in a laboratory. If the herd has been infected previously with TGE and there are scour problems persisting it is necessary to determine whether the virus is still present or not. 

Treatment

• There is no specific treatment for TGE.
• Antibiotic treatment by mouth in individual piglets may reduce secondary infections.
• Provide easy access to water containing electrolyte and an antibiotic such as neomycin. Make this available to the litters twice daily.
• Improve the nursing and environment of the litter by providing extra heat and deep bedding to reduce the weights of infection from the diarrhoea.

Management control and prevention

• As soon as disease is suspected isolate those farrowing houses not infected, by using separate personnel boots and coveralls. This is particularly important in piglets under 14 days of age. The longer the disease can be kept away the more pigs will be reared and mortality reduced.
• If it is possible move sows that are within 3 weeks of farrowing from the farm before they become infected so that they could farrow down in an isolated building or outside in arks and escape disease.
• It is essential to develop immunity in the dry sows as soon as possible.
• There are two methods, either squeeze the piglets abdomen and collect the diarrhoea into a bowl or use sawdust or shavings in the areas where the piglets are scouring. Paper towels can also be used to soak up piglet faeces. This material is then mixed with a bucket of water and fed to the pregnant sows, (feed back).
• A further method is to collect the small intestines from a number of pigs that have died and macerate them in a food blending machine. The liquid provides a rich source of virus and this can if required be preserved by deep freezing.
• The disease should be spread as soon as possible across the whole farm. The object is to get a good immunity developed in the shortest possible period of time. It will take approximately 3 to 4 weeks to achieve this.
• Once the infected period is over ensure an all-in and all-out management system of the farrowing houses, weaner and finisher accommodation.
• Disinfection of pens between batches should be carried out using an iodine based disinfectant or one highly active against viruses
• This cleaning process is an important one to ensure the virus does not linger on the farm and become endemic.
• If your herd as become infected with TGE ask the question why and how? Look at all your prevention procedures and biosecurity as discussed in chapter 2. (Do this before you get TGE).
• Always provide boots and protective clothing for any one entering your farm.
• Provide disinfectant foot dips at all entrances.
• Keep starlings and migrating birds away from the farm by not exposing them to feed.
• Do not borrow equipment from another pig farm.
• Site all bins to the exterior of the unit and always have your own feeder pipes to your own feed bins. This is a high risk source for the spread of enteric diseases.
• Vaccination - live modified and killed vaccines are available in some countries. The results in the field are very variable. The objective is to maintain immunity in the colostrum. This can only be carried out by stimulating the gut of the sow to produce antibodies in the milk. Intra-muscular vaccines give a very poor response.

Source:

http://www.thepigsite.com/pighealth/article/301/transmissible-gastroenteritis-tge/

http://www.doctorc.net/HISTO%20CASEBOOK/TGE%20IN%20SWINE/TGEDISCUSS.htm