Lineage specific antigenic differences in porcine torovirus hemagglutinin-esterase (PToV-HE) protein.

Hemagglutinin-esterases (HE) are viral envelope proteins present in some members from the toro-, corona- and orthomyxovirus families, all related with enteric and/or respiratory tract infections. HE proteins mediate reversible binding to sialic acid receptor determinants, very abundant glycan residues in the enteric and respiratory tracts. The role of the HE protein during the torovirus infection cycle remains unknown, although it is believed to be important in the natural infection process. The phylogenetic analysis of HE coding sequences from porcine torovirus (PToV) field strains revealed the existence of two distinct HE lineages. In a previous study, PToV virus strains with HE proteins from the two lineages were found coexisting in a pig herd, and they were even obtained from the same animal at two consecutive sampling time points. In this work, we report antigenic differences between the two HE lineages, and discuss the possible implications that the coexistence of viruses belonging to both lineages might have on the spread and sustainment of PToV infection in the farms.

Seroprevalence of porcine torovirus (PToV) in Spanish farms.

BACKGROUND: Torovirus infections have been associated with gastroenteritis and diarrhea in horses, cows, pigs and humans, especially in young animals and in children. Although asymptomatic in a large percentage of cases, however toroviruses may pose a potential threat to worsen disease outcome in concurrent infections with other enteric pathogens. Previous studies based on the analysis of limited numbers of samples indicated high seroprevalences against porcine torovirus (PToV) in various European countries. The aim of this work was to perform a seroepidemiological survey of PToV in Spanish farms in order to define the seroprevalence against this virus. RESULTS: Serum samples (n = 2664) from pigs of different ages were collected from 100 Spanish farms coming from 10 regions that concentrate 96.1% of the 3392 farms with 80 or more sows censused in Spain. Samples were screened by means of an indirect enzyme-linked immune-sorbent assay (ELISA) based on a recombinant PToV nucleocapsid protein as antigen. The analysis of the whole serum collection yielded a total of 95.7% (2550/2664) seropositive samples. The highest prevalence (99.6%, 1382/1388) and ELISA values (average O.D. ± standard deviation) were observed in the sows (1.03±0.36) and the lowest prevalence (59.4%, 98/165) and anti-PToV IgG levels (0.45±0.16) were found amongst 3-week-old piglets. Both ELISA reactivity values and seroprevalence percentages rose quickly with piglet's age from 3 to 11 weeks of age; the seroprevalence was 99.3% (2254/2270) when only the samples from sows and pigs over 11-weeks of age were considered. Antibodies against PToV were detected in all analyzed farms. CONCLUSIONS: This report describes the results of the largest torovirus seroepidemiological survey in farmed swine performed so far. Overall, the seroprevalence against PToV in animals older than 11 weeks of age was >99%, indicating that this virus is endemic in pig herds from Spain.

Longitudinal serological and virological study on porcine torovirus (PToV) in piglets from Spanish farms.

A study was performed to evaluate porcine torovirus (PToV) seroprevalence and infection in three multi-site farms from the North-eastern region of Spain. Serum samples from 120 piglets and faecal samples from 36 piglets were longitudinally collected at 1, 3, 7, 11 and 15 weeks of age. Serum samples from their dams (n=30) were also taken 1-week post-farrowing. PToV antibodies in serum were monitored by ELISA, while viral infection was assessed by real-time RT-PCR in faeces. A high seroprevalence (about 100%) was observed in animals older than 11 weeks and in adult sows. Moreover, all 1-week-old animals were seropositive, indicating maternal antibody transference through colostrum. The antibody titers declined to close to or below the ELISA cut-off value by the age of weaning (3 weeks of age). Development of a significant antibody response to PToV occurred before 7 weeks of age in about 50% of piglets, and the remaining animals developed the response by weeks 11 or 15. These results indicate that PToV infection occurred soon after weaning. Although the prevalence of infection in suckling piglets varied among the studied farms, PToV prevalences in 7 and 11-week-old pigs were between 50-67% and 58-75%, respectively, in all farms. Sequencing results indicated that more than one PToV strains were circulating in the studied farms. Present data suggest that PToV was endemic on the studied farms, and provide new insights on the epidemiology of PToV.

Molecular characterization of a new PToV strain. Evolutionary implications.

Toroviruses are emergent viruses, belonging to the Nidovirales order, that remain mostly ignored, despite they are able to infect different species of domestic animals and humans, causing enteric diseases and diarrhea. Thus far, only five variants of porcine torovirus (PToV) have been identified. In this report we describe the identification and partial characterization of a new strain of porcine torovirus (PToV-BRES) that was detected by RT-PCR in a swine faecal specimen from a farm in Brescia (Italy). The complete genes coding for the nucleocapsid (N), hemagglutinin-esterase (HE) and membrane (M) proteins were amplified, and sequence analysis showed that PToV-BRES is a new PToV strain that, based on the HE gene sequence, is phylogenetically related to P4 strain, that was up to now the only member of a distinct PToV lineage. The nucleocapsid protein from PToV-BRES was expressed in insect cells as a his-tagged protein, purified by affinity chromatography and used to develop an ELISA method to detect antibodies against PToV. This assay was evaluated using a serum collection including 45 samples from three commercial farms from Spain. High antibody prevalence against PToV was observed in the three farms, both in adult animals and in piglets, which could suggest that PToV might be endemic in Spanish porcine population. The ELISA method developed in this work could be useful in future epidemiological surveys about toroviruses.