Porcine Transmissible Gastroenteritis Virus

Transmissible gastroenteritis of pigs (TGE) is an acute gastrointestinal infectious disease in pigs caused by the transmissible gastroenteritis virus. Clinically, it is characterized by fever, vomiting, severe diarrhea, dehydration, and high mortality rates among piglets under 2 weeks of age. TGE is classified as a Category B disease under OIE regulations, making it a mandatory quarantine pig infection. While the disease can affect pigs of all ages, it poses the most significant threat to piglets. Today, TGE remains widespread across many pig-raising countries and regions, resulting in substantial economic losses. Let’s now explore this pathogen in more detail.

The transmissible gastroenteritis virus (TGEV) is a member of the coronavirus genus within the Coronaviridae family; it has a single-stranded RNA genome, an enveloped structure, and exhibits pleomorphic morphology. The viral particles measure 60–160 nm in diameter and are characterized by radially arranged, rod-shaped spike proteins on their surface, which extend 12–25 nm in length.

TGEV remains stable when frozen and can survive for extended periods in cold environments. However, it readily degrades under room temperature or higher conditions. The virus can be stored at -20°C for 6 to 18 months without a significant drop in viral titer, even at 21°C.

It is relatively unstable—when stored at 37°C for 4 days, the virus completely loses its infectivity. TGEV is photosensitive and becomes inactivated after just 6 hours of exposure to sunlight. It is also highly susceptible to quaternary ammonium compounds and peroxide-based disinfectants.

TGEV is present in various organs, body fluids, and excretions of affected piglets, but the highest viral loads are found in the jejunum, duodenum, and mesenteric lymph nodes.

The transmissible gastroenteritis virus (TGEV) spreads both through the respiratory and digestive tracts, with infection in pigs primarily occurring via the pig’s mouth, nose, and mucous membranes. When viral particles are present in the external environment, the virus enters the respiratory system through the nasal cavity, where it rapidly multiplies. From there, TGEV travels via the bloodstream to infect and replicate in the intestinal epithelial cells of the pig’s small intestine. This leads to severe villus atrophy and impaired absorption, resulting in diarrhea. In vulnerable piglets, the mortality rate after infection can approach 100%. As pigs grow older, clinical symptoms typically become milder, and most recover naturally—though they may remain long-term carriers of the virus. If co-infected with porcine respiratory coronavirus (PRCV), however, the disease course tends to worsen significantly. The disease usually manifests either as an acute outbreak or a localized epidemic. Sows that have previously been exposed to TGEV on a farm generally develop immunity and are unlikely to be reinfected. Importantly, the disease exhibits a distinct seasonal pattern, with outbreaks peaking during the colder winter and spring months.

Sick and virus-carrying pigs are the primary sources of infection, particularly in closed pig houses with high humidity and densely populated farms, where transmission is more likely to occur. Clinically affected or infected pigs shed viral particles through feces, vomit, and respiratory secretions.

The disease was first reported in the United States in 1946 and subsequently erupted in numerous countries across the Americas, Asia, and Europe. Today, TGE has become a globally widespread infectious disease affecting pigs. Although the prevalence of TGEV among diarrheic pigs in China has remained low in recent years, certain viral strains continue to circulate in both southern and northern regions of the country.

From January 2008 to November 2016, a total of 29,397 cases of porcine enteric disease were reported across 41 states in the United States and Mexico, with a PCR positivity rate of 2.3%. In 2008, the TGEV positivity rate was 4%, rising to 6.8% in 2010 before dropping sharply to 0.4% by 2014. Following the introduction of Porcine Epidemic Diarrhea in the U.S., the prevalence of TGEV further declined to below 0.1%. According to our company’s testing statistics from July 2020 to July 2023, no positive cases of TGEV were detected.

Since the virus primarily targets the gastrointestinal tract, research related to this area has also been impacted. During TGEV outbreaks, not only do pigs suffer from severe diarrhea, but piglets can experience nearly 100% mortality. Additionally, the disease can lead to miscarriages in some late-pregnant sows, while simultaneously stalling growth and development in nursery pigs and growing-finishing pigs. Although many farms that have experienced this disease have managed to bring it under control, the virus continues to persist within the growing pig population. As a result, weaned piglets become infected once maternal antibodies wane, shedding the virus into the environment and further spreading the infection. This has allowed TGE to evolve into a localized, endemic form of the disease—characterized by high incidence rates among pig herds, relatively low mortality, yet persistent transmission that makes eradication nearly impossible, leading to an ongoing cycle of infection.

There is no effective treatment for this disease. During the illness, providing large amounts of glucose-sodium chloride solution, along with plenty of clean drinking water and easily digestible feed, can help larger affected pigs recover more quickly. Administering oral medications such as sulfonamides, furacilin, berberine, or potassium permanganate can help prevent secondary infections and alleviate clinical symptoms. When raising pigs, it’s essential to use clean feed and ensure access to dry, uncontaminated drinking water to minimize the risk of viral infections through water sources. All animals, feed, and water supplies entering or leaving the farm should undergo rigorous testing and quarantine procedures to promptly identify infected pigs and potential pathogens, enabling swift action to halt disease spread. Additionally, pig pens, equipment, feed, and water sources must be regularly sanitized and disinfected to reduce the survival and transmission of harmful pathogens.

Vaccination can enhance pigs' immunity, boosting their ability to fight off viruses and reducing the spread and prevalence of viral infections—making it one of the key strategies for preventing and controlling transmissible gastroenteritis in pigs. Several attenuated vaccines are already in use internationally, with varying administration methods. Oral administration of live attenuated vaccine to pregnant sows often leads to significantly higher antibody levels, providing robust protection not only for the sows themselves but also passing maternal antibodies on to nursing piglets, offering strong immune protection. Additionally, when pregnant sows previously infected with TGEV receive non-intestinal immunization with an attenuated TGEV vaccine followed by intranasal application of a locally produced inactivated TGEV vaccine, their antibody levels can be dramatically improved.

Infected animals can be used to clear the herd through "TGE non-cleaning eradication": In a pig population that has never been vaccinated against TGEV, when an outbreak occurs, no immunization or isolation is implemented. Instead, the entire herd is simultaneously and thoroughly exposed to a highly virulent strain of the virus, ensuring all pigs come into full contact with the pathogen. This approach eliminates susceptible individuals, followed by tightly controlling access—no new breeding pigs are introduced. As a result, the virus circulation within the herd is effectively halted. Once clinical symptoms have completely subsided, strict all-in/all-out management practices are enforced in farrowing and nursery facilities, with thorough cleaning and disinfection carried out between each batch of pigs. Over time, the herd will test negative, and the virus will also be eradicated from the environment.

References

1. Cheng S, Wu H, Chen Z. Evolution of Transmissible Gastroenteritis Virus (TGEV): A Codon Usage Perspective. Int J Mol Sci. 2020 Oct 24;21(21):7898. doi: 10.3390/ijms21217898. PMID: 33114322; PMCID: PMC7660598.

2. Xia L, Yang Y, Wang J, Jing Y, Yang Q. Impact of TGEV Infection on the Pig Small Intestine. Virol J. 2018 Jun 19;15(1):102. doi: 10.1186/s12985-018-1012-9. PMID: 29914507; PMCID: PMC6006930.

3. Liu Q, Wang HY. Porcine enteric coronaviruses: An updated overview of pathogenesis, prevalence, and diagnosis. Vet Res Commun. 2021 Sep;45(2-3):75-86. doi: 10.1007/s11259-021-09808-0. Epub 2021 Jul 12. PMID: 34251560; PMCID: PMC8273569.

4. Yan Q, Liu X, Sun Y, Zeng W, Li Y, Zhao F, Wu K, Fan S, Zhao M, Chen J, Yi L. Swine Enteric Coronavirus: Diverse Pathogen-Host Interactions. *Int J Mol Sci*. 2022 Apr 2;23(7):3953. doi: 10.3390/ijms23073953. PMID: 35409315; PMCID: PMC8999375.

5. Fenner's Veterinary Virology (Fifth Edition), 2017

6. Li Lingling. Clinical Symptoms and Control Measures for Porcine Transmissible Gastroenteritis [J]. Today's Animal Husbandry and Veterinary Medicine, 2023, 39(04):114-116.

7. Yang Yuanrong. A Study on Comprehensive Management Techniques for Eradication of Transmissible Gastroenteritis in Non-Purebred Pigs [D]. Nanjing Agricultural University, 2007.

8. Liu Jiangmei. Advances in Research on Porcine Transmissible Gastroenteritis Virus [J]. China Animal Husbandry & Veterinary Abstracts, 2018, 34(01):74.

9. Chen F, Knutson TP, Rossow S, Saif LJ, Marthaler DG. Decline of transmissible gastroenteritis virus and its complex evolutionary relationship with porcine respiratory coronavirus in the United States. Sci Rep. 2019 Mar 8;9(1):3953. doi: 10.1038/s41598-019-40564-z. PMID: 30850666; PMCID: PMC6408454.