Seroprevalence of noroviruses in swine

Abstract

Noroviruses (NVs) are important human pathogens that cause acute gastroenteritis. Genetically related animal enteric NVs have also been described, but there is no evidence of interspecies transmission of NVs. In this study we characterized antibody prevalence among domestic pigs by using recombinant capsid antigens of two human NVs (Norwalk and Hawaii) and one swine NV (SW918) that is genetically related to GII human NVs. Recombinant SW918 capsid protein expressed in baculovirus self-assembled into virus-like particles (VLPs) that were detected by antibodies against GII (Hawaii and Mexico), but not GI (Norwalk and VA115), human NVs. NVs recognize human histo-blood group antigens as receptors, but SW918 VLPs did not bind to human saliva samples with major histo-blood group types. Seventy-eight of 110 (71%) pig serum samples from the United States and 95 of 266 (36%) pig serum samples from Japan possessed antibodies against SW918. Serum samples from pigs in the United States were also tested for antibodies against human NVs; 63% were positive for Norwalk virus (GI) and 52% for Hawaii virus (GII). These results indicate that NV infections are common among domestic pigs; the finding of antigenic relationships between SW918 and human NVs and the detection of antibodies against both GI and GII human NVs in domestic animals highlights the importance of further studies on NV gastroenteritis as a possible zoonotic disease.

FIG. 1.

Electrophoresis of recombinant SW918 VLPs. Discontinuous sucrose gradient (10 to 50%) fractions (f1 to f12) of Sf9 cultures infected with recombinant SW918 baculovirus were collected and analyzed for the presence of SW918 capsid proteins. Equal amounts (5 ul) of fractions (f3 to f10) were separated by SDS-10% PAGE and protein bands were visualized by Coomassie blue staining. The arrow indicates the ∼60-kDa full-length capsid protein.

FIG. 2.

Negatively stained SW918 VLPs. Grids were stained with 1% ammonium-molybdate and examined using a Zeiss EM 10 transmission electron microscope. Arrows indicate VLPs with typical morphology.

FIG. 3.

Western blot immunostaining of SW918 capsid protein. SW918 VLPs (300 and 150 ng) were separated by SDS-10% PAGE, blotted onto nitrocellulose membranes, and stained with anti-NV antibodies raised in guinea pigs. A: preimmunization antibody; B: pooled, cross-immunization antibody (GI + GII); C: anti-Norwalk virus antibody (GI); D: anti-VA115 antibody (GI); E: anti-Mexico virus antibody (GII); F: anti-Hawaii virus antibody (GII). Arrows indicate the ∼60-kDa full-length capsid protein.