Transmissible Gastroenteritis
Other names: TGE; one of the many causes of scours [Remember, just like diarrhea in humans or pets, scours is actually a *symptom* of disease, not a disease itself!]
Cause: TGE virus (a coronavirus)
Note: “To understand an overall picture of TGE, it is necessary to describe a deletion mutant of TGEV, porcine respiratory coronavirus (PRCV). PRCV appeared in the 1980s and has become prevalent worldwide, including the United States. PRCV replicates primarily in the respiratory tract and, to a minimal extent, in small intestinal epithelial cells. Usually, no clinical disease is produced or, uncommonly, mild respiratory disease is observed. PRCV does not produce clinical enteric disease. PRCV typically forms an endemic infection in intensely managed swine herds and infected pigs produce neutralizing antibodies which also neutralize TGEV. Therefore, when pigs already affected by PRCV get infected by TGEV, these pigs develop a less severe clinical form of TGE.” (Purdue)
Species: swine
Signs: In herds without immunity due to endemic disease, an epidemic occurs with pigs showing vomiting, profuse watery diarrhea (often containing curds of undigested milk in nursing piglets; severely malodorous due to steatorrhea), shivering, unthrifty appearance, excessive thirst, dehydration, metabolic acidosis, hyperkalemia, cardiac arrhythmias. Mortality varies greatly by age: nearly 100% of piglets less than 1 month old die, but death is rare in older pigs. If nursing piglets survive, diarrhea lasts about 5 days. Duration of diarrhea may be shorter in older pigs. Growth may be permanently stunted. Lactating sows may develop agalactia. Pregnant sows occasionally abort. On necropsy, the small intestine of piglets will be thin-walled, and the entire intestinal tract will contain greenish or yellow watery fluid and clumps of undigested milk. In older pigs, the intestines appear normal, except the large intestine will contain liquid rather than solid feces. Villous atrophy in the small intestines may be seen with use of a hand lens. Epidemics typically occur in winter because the virus survives better in the cold.
In herds with endemic transmissible gastroenteritis and/or PRCV, signs are similar but less severe, depending on level of immunity. Maternal antibodies usually protect piglets until 4-5 days of age, but as the antibody level in milk decreases, disease may occur. Diarrhea may be mild in some litters but severe in others. If passive immunity was protective throughout nursing, disease often develops during the first few days after weaning.
Pigs that survive may continue to shed virus for up to 18 months, though 2-8 weeks is more typical. Asymptomatic carriers are often a source of exposure to new herds.
Transmission: Fecal-oral/nasal route; virus spread by direct contact with infected feces, aerosolization of virus, fomites, and human and animal vectors. Incubation period is between 18 hours and 3 days. The virus survives longer in the environment in colder temperatures (freezing does not kill the virus).
Diagnosis: Usually presumptive based on history and clinical signs in the epidemic form. Laboratory testing required to diagnose endemic form because it is easily confused with other causes of scours. Testing options include detection of viral antigen, detection of viral nucleic acic, microscopic detection of virus at high magnification by electron microscopy, isolation and identification of virus, and/or detection of a significant titer increase for TGE. A combination of different test methods provides the most accurate diagnosis.
Treatment: Supportive care (make sure farrowing/nursery room temperature is at least 89°F; provide a clean, dry, and draft-free environment; provide oral electrolyte solutions to combat dehydration; provide oral nutrient solutions to combat starvation in nursing piglets). Administering swine immunoglobulins may be beneficial. As with all viral illnesses, antibiotics are only beneficial if secondary bacterial infections occur.
Prevention: Vaccination of sows with previous exposure to TGE virus or PRCV boosts immunity enough to protect newborn piglets, but vaccination may not be effective in herds free of TGE because vaccination alone does not raise the immunity enough to pass to the piglets. Vaccines are not available in the UK. Planned infection of pregnant sows at least 2–4 weeks before farrowing in herds known to be infected may also provide adequate immunity (this is done by mixing ground, TGE virus–infected intestine and feces in the feed. Only use infectious material from the same herd. In the UK it is not permissible to feed ground intestines; only feces and gut contents may be used), but this carries risk of transmitting other diseases as well, and should only be done if a later epidemic seems inevitable. Passive protection of piglets is provided by continual nursing of immune sows. Active immunity develops after infection of the intestinal mucosa with TGE virus, and provides protection for 6–18 mo afterwards. Morbidity may be decreased by weaning pigs at an older age via a creep feeding system.
TGE can be eliminated from herds via maximizing immunity in the sow herd and practicing “all-in/all-out” management of farrowing, nursery, and grower rooms.
Another method of eliminating TGEV from a facility is complete depopulation during a hot month, followed by thorough cleaning and disinfection of the entire premises and allowing the facility to remain empty for several weeks, then restocking with serologically negative swine.
To prevent TGE from entering into a sero-negative herd, maintain a closed herd. Any new animals should be from a TGE-free herd, test sero-negative for TGEV, be quarantined for 2-4 weeks, and then re-tested again before they are introduced into the herd. Because the virus is easily spread via people, animals (including dogs, cats, birds, rodents, flies), and fomites, strict sanitation and biosecurity is required to prevent the disease from spreading to uninfected herds. TGE virus is vulnerable to heat and various disinfectants, such as sodium hypochrolite, iodines, quaternary ammonium compounds, and phenol.
Note: This virus is common in the USA, but rare in Europe.
Sources: Linkedin (drawing of sick piglets), Merck Veterinary Manual, Purdue University, Iowa State University, NADIS
