Age-Dependent Resistance to Transmissible Gastroenteritis of Swine: III. Effects of Epithelial Cell Kinetics on Coronavirus Production and on Atrophy of Intestinal Villi

Abstract

Abstract. Coronavirus titers in small intestine, degree of villous atrophy and apparent rates of regeneration of intestinal villi were compared in newborn, 3-week-old and adult pigs for 1 week after they were exposed to the transmissible gastroenteritis virus of swine. The response within the newborn group was homogeneous, resulting in high virus titers, maximal villous atrophy and comparatively slow regeneration. In general, virus titers were lower, villous atrophy was less severe and regeneration more rapid in both older groups than in the newborn pigs. However, the response varied greatly in the older groups. The 3-week-old group was divided into two populations. The major population had low virus titers and developed partial villous atrophy, whereas the minor population had marked villous atrophy and virus titers comparable to those of the newborn pigs. These observations support the hypothesis that the accelerated replacement of villous epithelium in the small intestine of pigs during the first 3 weeks contributes to the innate age-dependent resistance to transmissible gastroenteritis. The accelerated replacement of villous epithelial cells in older pigs contributes to resistance in two ways. The increased proliferative capacity of crypt epithelium results in a more rapid regeneration of atrophic villi; and the comparatively young villous absorptive cells resulting from accelerated replacement produce less virus per cell than the older ones of the newborn pig.Transmissible gastroenteritis of swine is an acute diarrheal disease caused by destruction of absorptive epithelial cells of the intestinal villi by a specific coronavirus. The resultant lesion is called villous atrophy. Crypt epithelium is not affected directly by the virus, and intestinal villi rapidly regenerate in pigs that survive the acute diarrheal phase of the disease [16]. Acute viral diseases of the small intestine in several species follow a similar sequence of selective cell destruction, leading to variable degrees of villous atrophy and diarrhea, followed by rapid regeneration of villi and the return of normal function. Epizootic diarrhea of infant mice [ 11, lethal intestinal virus infec-

Isolation, genomic characterization, and pathogenicity of a Chinese porcine deltacoronavirus strain CHN-HN-2014

“…Our clinical observations show that the 5-day-old pigs were more susceptible to PDCoV infection than the 21-day-old pigs. This age-dependent disease severity in PDCoV infection is consistent with previous reports of PEDV and TGEV infections (Moon et al, 1975;Shibata et al, 2000) and might be attributable to the lower turnover rate of enterocytes in 5-day-old pigs than in 21-day-old pigs during PDCoV infection, as has been described in PEDV infection . A recent report showed that an outbreak of PDCoV infection was observed in gilts and sows in Thailand (Janetanakit et al, 2016), indicating that the pathogenicity of PDCoV is not confined to piglets.…”

Porcine deltacoronavirus induces TLR3, IL-12, IFN-α, IFN-β and PKR mRNA expression in infected Peyer’s patches in vivo

“…Interestingly, unlike in newborn piglets, PDCoV infection did not cause vomiting and death in weaned piglets at a high dose (1 × 10 9 TCID 50 /head) in 7 days, indicating that newborn piglets were more susceptible to PDCoV infection than weaned piglets. This phenomenon demonstrated that PDCoV infection is another age-dependent disease severity like PEDV and TGEV (Moon et al, 1975;Isao et al, 2000). Furthermore, we collected fecal swabs from the PDCoV-challenged piglets and detected the viral fecal shedding by real-time PCR.…”

Serial Studies of Virus Multiplication and Intestinal Damage in Gnotobiotic Piglets Infected with Rotavirus

“…Rings of fixed gut were dehydrated and embedded in paraffin wax, and sections 5 pm thick were cut and stained with haematoxylin and eosin. The severity of the lesions in each of the five gut positions was estimated as the ratio, average villus length : average crypt length, calculated from measurements of the five longest complete villi and their associated crypts at each position, made with a light microscope equipped with a x 10 objective and ocular micrometer (Hooper and Haelterman, 1969;Moon, Norman and Lambert, 1973;Thake, Moon and Lambert, 1973;Moon et al, 1975). No attempts were made to measure crypts associated with Peyer's patches.…”