Why is porcine epidemic diarrhea (PED) so difficult to prevent?

Release Date:

2020-04-24

author：

Porcine epidemic diarrhea (PED) is an acute, highly contagious intestinal disease caused by the infectious pathogen—porcine epidemic diarrhea virus. It poses a significant threat to pig producers. So why is PED so difficult to control? The virus’s virulence: Infected pigs, virus‑carrying but clinically asymptomatic pigs, and convalescent pigs can all serve as sources of infection, with fecal–oral transmission being the primary route. Spring and winter are the peak seasons for this disease. PED is particularly devastating in nursing piglets, with mortality rates that can reach as high as 100%. Strain complexity:

Porcine epidemic diarrhea (PED) is an acute, highly contagious intestinal disease caused by the porcine epidemic diarrhea virus, a transmissible pathogen. It poses a significant threat to pig producers. So why is PED so difficult to control?

Pathogenicity of the virus: Infected pigs, seropositive carrier pigs, and clinically recovered pigs can all serve as sources of infection, spreading the virus. Fecal–oral transmission is the primary route of spread, and the disease is most prevalent in spring and winter. The disease poses a particularly severe threat to nursing piglets, with mortality rates that may reach 100%.

Strain complexity: Despite the virus’s high infection rate, isolating and culturing it in vitro is extremely challenging, with a very low success rate. Even when successful isolation is achieved, attaining a high viral titer is often difficult, and the virus may readily lose its infectivity during serial passage in cell cultures.

Limitations of diagnosis: At present, etiological diagnosis is primarily performed using methods such as immunoelectron microscopy, RT‑PCR, immunofluorescence, and immunohistochemistry, while serological testing mainly relies on enzyme‑linked immunosorbent assay (ELISA) and serum neutralization assays. Among these, immunofluorescence, serum neutralization assays, and immunohistochemistry are time‑consuming and labor‑intensive, making them unsuitable for large‑scale clinical screening. Immunoelectron microscopy, in turn, requires specialized electron microscopy equipment, further limiting its practical application.

Diarrhea, a persistent challenge in the swine industry, remains difficult to control, primarily because PEDV is constantly mutating, with its virulence steadily increasing and its pathogenicity growing ever more severe. Currently in China, variant strains belonging to the G2 sublineage dominate, accounting for over 90% of circulating viruses. Moreover, since vaccines based on classical strains exhibit low antigenic similarity to prevalent variants, they fail to provide complete protection. Therefore, pig producers are advised to select diarrhea vaccines that target the current circulating variant strains. “A good strain yields a better vaccine; a higher‑titer strain delivers even better protection!” In addition to strain matching, higher viral titers in the vaccine translate into stronger protective efficacy for the herd. Beyond administering appropriate doses of the diarrhea vaccine, it is essential to enhance management practices and implement stringent biosecurity measures. Regarding environmental conditions, farmers should maintain optimal temperature and humidity levels in the pig houses and ensure that the animals have access to high‑quality, hygienic feed and water. As for biosecurity, in addition to routine environmental disinfection and manure removal, strict disinfection protocols must be followed during farrowing, along with proper colostrum management—steps designed to interrupt transmission via milk and oral‑to‑oral routes.

The Importance of Preventing Postpartum Anorexia and Providing Postpartum Care in Sows

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