Retrospective serosurveillance of bovine norovirus (GIII.2) and nebovirus in cattle from selected feedlots and a veal calf farm in 1999 to 2001 in the United States

Abstract

There is a dearth of information on the seroprevalence of bovine norovirus (BoNoV) and nebovirus in cattle of the US. In this retrospective study, serum IgG antibodies to two bovine enteric caliciviruses, GIII.2 BoNoV (Bo/CV186-OH/00/US) and genetically and antigenically distinct nebovirus (Bo/NB/80/US), were evaluated in feedlot and veal calves from different regions of the US during 1999-2001. Three groups of 6- to 7-month-old feedlot calves from New Mexico (NM) (n=103), Arkansas (AR) (n=100) and Ohio (OH) (n=140) and a group of 7- to 10-day-old Ohio veal calves (n=47) were studied. Serum samples were collected pre-arrival or at arrival to the farms for the NM, AR and OH calves and 35 days after arrival for all groups for monitoring seroconversion rates during the period. Virus-like particles of Bo/CV186-OH/00/US and Bo/NB/80/US were expressed using the baculovirus expression system and were used in ELISA to measure antibodies. A high seroprevalence of 94-100 % and 78-100 % was observed for antibodies to GIII.2 BoNoV and nebovirus, respectively, in the feedlot calves tested. In the Ohio veal farm, an antibody seroprevalence of 94-100 % and 40-66 % was found for GIII.2 BoNoV and nebovirus, respectively. Increased seropositive rates of 38-85 % for GIII.2 BoNoV and 26-83 % for nebovirus were observed at 35 days after arrival and commingling on farms for all groups. Infection of calves with either GIII.2 BoNoV or nebovirus, or both viruses, appeared to be common in the regions studied in the US during 1999-2001. These two viruses likely remain endemic because no commercial vaccines are available.

Fig. 1

Electron micrograph of VLPs of nebovirus Bo/NB/80/US strain. Nebovirus VLPs were purified by CsCl-gradient ultracentrifugation from the cell culture supernatants of recombinant baculovirus-infected Sf9 cells. For visualization of VLPs, EM was performed without incubation with antiserum. Bar, 200 nm

Fig. 2

Geometric mean antibody titers for GIII.2 BoNoV and nebovirus in the feedlot and veal calves from different regions of the US during 1999-2001. Three groups of 6- to 7-month-old feedlot calves from New Mexico (NM) (A), Arkansas (AR) (B), and Ohio (OH) (C) and a group of 7- to 10-day-old Ohio veal calves (D), comprising animals commingled from different regions of the US, were studied. Serum samples were collected pre-arrival or on arrival at the farms for the NM, AR and OH calves, and 35 days after arrival for all groups to monitor seroprevalence and seropositive increase rates during the period. The VLPs of Bo/CV186-OH/00/US and Bo/NB/80/US strains were expressed using the baculovirus expression system and were used in ELISA to measure IgG antibodies