Passive immunity to bovine rotavirus in newborn calves fed colostrum supplements from immunized or nonimmunized cows

Effects of maternal antibodies on protection and development of antibody responses to human rotavirus in gnotobiotic pigs

Although maternal antibodies can protect against infectious disease in infancy, they can also suppress active immune responses. The effects of circulating maternal antibodies, with and without colostrum and milk antibodies, on passive protection and active immunity to human rotavirus (HRV) were examined in gnotobiotic pigs. Pigs received intraperitoneal injections of high-titer serum (immune pigs [groups 1 and 2]) from immunized sows, low-titer serum from naturally infected sows (control pigs [groups 3 and 4]), or no serum (group 5). Immune or control colostrum and milk were added to the diet of groups 2 and 4, respectively. After inoculation (3 to 5 days of age) and challenge (postinoculation day [PID] 21) with virulent HRV, the effects of maternal antibodies on protection (from diarrhea and virus shedding), and on active antibody responses (measured by quantitation of antibody-secreting cells [ASC] in intestinal and systemic lymphoid tissues by ELISPOT) were evaluated. Groups 1 and 2 had significantly less diarrhea and virus shedding after inoculation but higher rates of diarrhea and virus shedding after challenge than did groups 3 and 5. Group 1 and 2 pigs had significantly fewer immunoglobulin A (IgA) ASC in intestinal tissues at PID 21 and at postchallenge day (PCD) 7 compared to group 5. Significantly fewer IgG ASC were present in the intestines of group 2 pigs at PID 21 and PCD 7 compared to group 5. There was a trend towards fewer ASC in intestinal tissues of group 2 than group 1, from PID 21 on, with significantly fewer IgA ASC at PCD 7. IgG ASC in the duodenum and mesenteric lymph nodes of group 3 and 4 pigs were significantly fewer than in group 5 at PCD 7. These decreases in ASC emphasize the role of passive antibodies in impairing induction of ASC rather than in merely suppressing the function of differentiated B cells. To be successful, vaccines intended for populations with high titers of maternal antibodies (infants in developing countries) may require higher titers of virus, multiple doses, or improved delivery systems, such as the use of microencapsulation or immune stimulating complexes, to overcome the suppressive effects of maternal antibodies.

Passive immunity to bovine rotavirus in newborn calves fed colostrum supplements from cows immunized with recombinant SA11 rotavirus core-like particle (CLP) or virus-like particle (VLP) vaccines

Heterotypic passive immunity to IND (P/5/G6) bovine rotavirus (BRV) was evaluated. Three groups of calves (n = 5 per group) were fed 1% pooled colostrum supplements (birth to 7 days of age) from BRV seropositive cows vaccinated with recombinant SA11(P/2/G3) rotavirus-like particles (VLPs), recombinant SA11 rotavirus core-like particles (CLPs), or inactivated SA11 rotavirus (SA11). Control calves (n = 5 per group) received either pooled colostrum from unvaccinated (BRV field exposure seropositive) control cows, or no colostrum. IgG1 antibody titers to IND BRV for the pooled colostrum were: 1,048,576 (VLP); 1,048,576 (CLP); 262,144 (SA11); and 16,384 (control colostrum). Elevated titers of BRV neutralizing (VN) antibodies were present in VLP colostrum (98,000), and SA11 colostrum (25,000), but not in CLP colostrum (1400), compared to colostrum from nonvaccinates (2081). Calves were orally inoculated with virulent IND BRV at 2 days of age and challenged at post-inoculation day (PID) 21. Calves were monitored daily for diarrhea and faecal BRV shedding through PID 10 and post-challenge day (PCD) 10. After colostrum feeding, the IgG1 antibody titers were highest in serum and faeces of calves fed VLP and CLP colostrum, but VN and IgA antibodies were highest in calves fed VLP colostrum. After BRV inoculation, calves fed colostrum from vaccinated cows had significantly fewer days of BRV-associated diarrhea and BRV shedding than control calves. All calves fed VLP colostrum were protected from diarrhea after BRV inoculation; two calves shed BRV. In the CLP colostrum group, one calf developed BRV-associated diarrhea and all calves shed virus. In the SA11 colostrum group, three calves developed BRV-associated diarrhea and four calves shed virus. BRV-associated diarrhea and shedding occurred in 9 of 10 control calves. Active IgM antibody responses occurred in faeces and/or serum of most calves after BRV inoculation. However, the highest active antibody responses (IgM and IgG1 in serum, and IgM, IgG1 or IgA in faeces) after BRV inoculation were in calves fed control or no colostrum, in association with clinical diarrhea in most of these calves. After challenge at PID 21, BRV-associated diarrhea and shedding were of short duration or absent, in all groups. These results demonstrate the efficacy of colostrum from VLP vaccinated cows to provide heterologous, passive protection against BRV diarrhea and shedding in calves. In comparison, calves fed CLP or SA11 colostrum were only partially protected against BRV diarrhea or shedding.

Enhancement of passive immunity with maternal vaccine against newborn calf diarrhea

The effects of a maternal vaccine against newborn calf diarrhea associated with group A bovine rotavirus (BRV), bovine coronavirus (BCV), bovine parvovirus and K99 Escherichia coli (E. coli) were examined on a beef cow-calf herd. After vaccination, serum or colostrum antibody titers to BRV, BCV and E. coli K99 in the vaccinated cows were significantly higher than those in unvaccinated control cows. Serum antibody titers to BRV, BCV and E. coli K99 in calves from the vaccinated cows were also significantly higher than those in calves from the control cows for 3-4 weeks after birth. These results suggested that the immunization of cows with the maternal vaccine enhanced the passive immunity levels in calves against BRV, BCV and K99 E. coli.

Further studies on the efficacy of a live vaccine against mastitis caused by Streptococcus uberis

Three groups of dairy cows were immunized by subcutaneous (s.c.) administration of a preparation of live Streptococcus uberis (strain 0140J) and an intramammary infusion of a soluble surface extract derived from same the bacteria. Animals in Groups 1 and 2 received two s.c. vaccinations plus an intramammary inoculation. Animals in Group 3 received two s.c. vaccinations but did not receive the intramammary infusion. In addition to the vaccinated animals, each group also contained two non-vaccinated (control) animals. All animals were challenged experimentally by intramammary infusion (in two quarters per animal) of ca 100 c.f.u. of S. uberis (strain 0140J or C221) and monitored for clinical signs of disease, bacterial numbers in milk, somatic cell count in milk, and daily milk yield for the following 10 days. Animals in Group I were challenged with strain 0140J. Only one out of six challenged quarters of three vaccinated cows developed clinical disease compared to all (four out of four) quarters of non-vaccinated cows. Animals in Group 2 were challenged with strain C221. All challenged quarters of three vaccinated (six out of six) and two non-vaccinated (four out of four) cows developed clinical mastitis. Animals in Group 3 were challenged with strain 0140J. Five out of eight quarters on four vaccinated cows developed clinical mastitis but the onset was delayed in comparison with that in both non-vaccinated cows in which four out of four challenged quarters developed clinical mastitis. These results indicated that vaccination with live S. uberis protects against challenge with the homologous strain but was less effective against a heterologous strain. Reduced protection was also seen when the intramammary booster was omitted.

Murine model of rotavirus infection

The murine model of homologous rotavirus infection has been used to study the determinants of protection. The local IgA immune response appears to be the critical factor in generating protective immunity after natural infection. A series of knockout mice were used to evaluate the contribution of T cells and B cells to immunity and resolution from primary infection. Both arms of immune system played a role in the resolution of primary infection but antibody was much more important for prevention of reinfection.

Isotype-specific antibody responses to rotavirus and virus proteins in cows inoculated with subunit vaccines composed of recombinant SA11 rotavirus core-like particles (CLP) or virus-like particles (VLP)

The isotype antibody responses to bovine IND P5, G6 and simian SA11 P2, G3 rotavirus and SA11 rotavirus proteins (VP4, VP6 and VP7) in serum, colostrum and milk were analysed by ELISA in three groups of vaccinated cows and nonvaccinated controls. Pregnant cows were vaccinated intramuscularly and intramammarily with recombinant baculovirus-expressed SA11 rotavirus VLP (triple-layered virus-like particles containing rotavirus VP2, VP4, VP6 and VP7); CLP (double-layered core-like particles containing rotavirus VP2 and VP6); or inactivated SA11 rotavirus, respectively. Rotavirus antigen titers were highest (30-200-fold) in ELISA in the VLP vaccine compared to the inactivated SA11 vaccine. The IgG1, IgG2 and IgM geometric mean antibody titers (GMT) to rotavirus (titers to bovine rotavirus vs SA11 rotavirus did not differ significantly for any isotype or group) and the IgG2 GMT to VP6 in serum at calving in the vaccinated groups were significantly (P < 0.05) higher than in the control group. In colostrum, IgG1 and IgA rotavirus antibody titers were significantly elevated for VLP (IgG1 GMT 832225; IgA GMT 16384), CLP (IgG1 GMT 660561; IgA GMT 10321) and SA11 (IgG1 GMT 131072; IgA GMT 1448) vaccinated cows compared to control cows (IgG1 GMT 11585; IgA GMT 45). The IgG1 and IgA GMT to rotavirus were significantly elevated (6-100-fold) in milk of VLP and CLP vaccinated cows compared to SA11 vaccinated or control cows. The isotype antibody responses to VP6 in serum, colostrum and milk paralleled the responses to rotavirus, but titers were approximately 2-10-fold lower. Only cows vaccinated with VLP had significantly enhanced serum, colostral and milk antibody titers to rotavirus VP4 and VP7. These results demonstrate that rotavirus antibody titers in serum, colostrum and milk are significantly enhanced by use of non-infectious VLP, CLP and inactivated SA11 rotavirus vaccines, but the VLP or CLP vaccines induced the highest antibody responses, corresponding to their higher rotavirus antigen titers measured by ELISA.

Development of mucosal and systemic lymphoproliferative responses and protective immunity to human group A rotaviruses in a gnotobiotic pig model

Gnotobiotic pigs were orally inoculated with virulent Wa strain (G1P1A[8]) human rotavirus (group 1), attenuated Wa rotavirus (group 2) or diluent (controls) and were challenged with virulent Wa rotavirus 21 days later. On various postinoculation or postchallenge days, virus-specific responses of systemic (blood and spleen) and intestinal (mesenteric lymph node and ileal lamina propria) mononuclear cells (MNC) were assessed by lymphoproliferative assays (LPA). After inoculation, 100% of group 1 pigs and 6% of group 2 pigs shed virus. Diarrhea occurred in 95, 12, and 13% of group 1, group 2, and control pigs, respectively. Only groups 1 and 2 developed virus-specific LPA responses prior to challenge. Group 1 developed significantly greater mean virus-specific LPA responses prior to challenge and showed no significant changes in tissue mean LPA responses postchallenge, and 100% were protected against virulent virus challenge. By comparison, both group 2 and controls had significantly lower LPA responses at challenge and both groups showed significant increases in mean LPA responses postchallenge. Eighty-one percent of group 2 and 100% of control pigs shed challenge virus, and both groups developed diarrhea that was similar in severity postchallenge. The virus-specific LPA responses of blood MNC mirrored those of intestinal MNC, albeit at a reduced level and only at early times postinoculation or postchallenge in all pigs. In a separate study evaluating antibody-secreting-cell responses of these pigs (L. Yuan, L.A. Ward, B.I. Rosen, T.L. To, and L.J. Saif, J. Virol. 70:3075-3083, 1996), we found that the magnitude of a tissue's LPA response positively correlated with the numbers of virus-specific antibody-secreting cells for that tissue, supporting the hypothesis that the LPA assesses T-helper-cell function. The magnitude of LPA responses in systemic and intestinal tissues also strongly correlated with the degree of protective immunity elicited by the inoculum (p = 0.81). We conclude that blood may provide a temporary "window" for monitoring intestinal T cells and that the LPA can be used to assess protective immunity to human rotaviruses.

Identification of group B rotaviruses with short genome electropherotypes from adult cows with diarrhea

Two field strains (BB-RVLV and KD) of group B rotaviruses from adult dairy cows with diarrhea displayed short genome electropherotypes. Gnotobiotic calves inoculated with fecal filtrates of each group B rotavirus developed diarrhea, and only group B rotaviruses or antigens were detected in the feces by immunoelectron microscopy and in intestinal epithelial cells by immunofluorescent staining, respectively. The feces or intestinal contents of the cows and inoculated calves were negative for group A and C rotaviruses by enzyme-linked immunosorbent assay, immunoelectron microscopy, or cell culture immunofluorescence assays. Comparison of the genome electropherotypes of the calf-passaged BB-RVLV and KD strains with the original samples and reference bovine group A, B, and C rotaviruses revealed conservative of their short-genome electropherotypes and double-stranded RNA migration patterns characteristics of group B rotaviruses. To our knowledge, our previous study (L.J. Saif, K.V. Brock, D.R. Redman, and E.M. Kohler, Vet. Rec. 128:447-449, 1991) and this report are the first description of bovine group B rotaviruses (in a mixed infection with bovine coronavirus or singly in fecal contents) in adult cows with diarrhea and this is the first report of short-genome electropherotypes among group B rotaviruses.

Systematic and intestinal antibody-secreting cell responses and correlates of protective immunity to human rotavirus in a gnotobiotic pig model of disease

Neonatal gnotobiotic pigs orally inoculated with virulent (intestinal-suspension) Wa strain human rotavirus (which mimics human natural infection) developed diarrhea, and most pigs which recovered (87% protection rate) were immune to disease upon homologous virulent virus challenge at postinoculation day (PID) 21. Pigs inoculated with cell culture-attenuated Wa rotavirus (which mimics live oral vaccines) developed subclinical infections and seroconverted but were only partially protected against challenge (33% protection rate). Isotype-specific antibody-secreting cells (ASC were enumerated at selected PID in intestinal (duodenal and ileal lamina propria and mesenteric lymph node [MLN]) and systemic (spleen and blood) lymphoid tissues by using enzyme-linked immunospot assays. At challenge (PID 21), the numbers of virus-specific immunoglobulin A (IgA) ASC, but not IgG ASC, in intestines and blood were significantly greater in virulent-Wa rotavirus-inoculated pigs than in attenuated-Wa rotavirus-inoculated pigs and were correlated (correlation coefficients: for duodenum and ileum, 0.9; for MLN, 0.8; for blood, 0.6) with the degree of protection induced. After challenge, the numbers of IgA and IgG virus-specific ASC and serum-neutralizing antibodies increased significantly in the attenuated-Wa rotavirus-inoculated pigs but not in the virulent-Wa rotavirus-inoculated pigs (except in the spleen and except for IgA ASC in the duodenum). The transient appearance of IgA ASC in the blood mirrored the IgA ASC responses in the gut, albeit at a lower level, suggesting that IgA ASC in the blood of humans could serve as an indicator for IgA ASC responses in the intestine after rotavirus infection. To our knowledge, this is the first report to study and identify intestinal IgA ASC as a correlate of protective active immunity in an animal model of human-rotavirus-induced disease.

Rotavirus subunit vaccines

We evaluated rotavirus subunit vaccines for use in humans and animals. Insect cells were co-infected with combinations of individual baculovirus recombinants expressing human, bovine or simian rotavirus VP2, VP4, VP6 or VP7 to produce virus-like particles (VLPs). To determine whether immunization with VLPs could induce active protective immunity, VLPs were administered parenterally to rabbits, and the immune response and protection from rabbit ALA rotavirus challenge were evaluated. Complete or partial protection was attained, showing that parenteral immunization with VLPs induces active protective immunity. We also examined whether heterotypic immune responses could be induced with a limited number of broadly reactive VP7 proteins or with chimeric particles (multiple VP7 types on individual particles). The feasibility of this approach was determined by immunizing mice with VLPs containing a G3 VP7 or G1 VP7 and chimeric G1/G3 VLPs. Broadly reactive neutralizing antibody was induced by the G1 VLPs. VLPs also have been successfully used to boost lactogenic (colostral and milk) immunity in dairy cows. Taken together, these results show that VLPs can be effective immunogens in rabbits, mice and dairy cattle when administered parenterally, a limited number of VLPs may be sufficient to produce a broadly protective vaccine, and G3 VLPs may serve as an effective subunit vaccine for use in bovines.

Hyperimmune cow colostrum reduces diarrhoea due to rotavirus: a double-blind, controlled clinical trial

The therapeutic efficacy of hyperimmune bovine colostrum (HBC) from cows immunized with four serotypes of human rotavirus was evaluated in a double-blind, randomized trial in 75 boys, aged 6-24 months, infected with rotavirus diarrhoea. The treatment group received 100 ml of HBC three times a day for 3 consecutive days, while the controls received the same amount of bovine colostrum from significantly shorter duration of diarrhoea than the controls (median 56 versus 72 h (p<0.001); confidence interval of median difference (CI) 8-32 h). Total stool output (g/kg) between admission and cessation of diarrhoea was reduced by 29% in the HBC-treated group compared with controls (median 205 versus 290 g (p=0.04); CI = 1-154 g). In 50% of the children in the study group, diarrhoea stopped by 48 h, whereas 100% of the controls were still suffering from diarrhoea. No untoward effects were noted in either group. Colostrum from cows immunized with rotavirus antigen is clinically effective in reducing the duration and severity of childhood diarrhoea due to rotavirus.

Characterization of the bovine group A rotavirus strain neonatal calf diarrhea virus-Cody (NCDV-Cody)

The neonatal calf diarrhea virus-Cody (NCDV-Cody) strain was found to contain a mixture of rotaviruses with G6 and G8 VP7 genes. Challenge exposure of calves with the mixed virus inoculum indicated that both viruses were maintained by passage in vivo. This is the first P1:G8 rotavirus to be characterized in cattle in the United States.

Stimulation of rotavirus IgA, IgG and neutralising antibodies in baboon milk by parenteral vaccination

A rhesus rotavirus vaccine adjuvanted with ISCOMs was injected intramuscularly to 5 pregnant baboons, with repeated doses 1-2 and 14 weeks after delivery. Maternal blood and milk samples and blood samples from their babies were collected at 2-weekly intervals until 26 weeks after parturition. Samples were assayed for rotavirus antibodies by ELISAs and neutralisation tests. Vaccination produced statistically significant increases in maternal serum IgG and neutralising antibodies, and in milk IgA, IgG, and neutralising antibodies. Control baboon mothers sampled from 12 weeks after delivery had lower serum and milk antibody titres, but responded to vaccination at 16 weeks by producing a similar antibody profile in serum and milk to those previously vaccinated. Because of the endemic nature of human rotaviral infections, similar maternal vaccinations have potential as a means of increasing milk antibodies to a level at which they may be protective to infants.

Subgroup determination of group A rotaviruses recovered from piglets in Nigeria

Subgroup analysis using subgroup-specific monoclonal ELISA revealed a preponderance of subgroup 2-specific antigens of group A porcine rotaviruses over subgroup 1. Of 113 polyacrylamide gel electrophoresis-positive test samples, obtained from 4 States of Nigeria, 31 (27.4%) and 45 (39.8%) were determined to have subgroup 1 and 2 specificities, respectively. However, 37 (32.7%) test samples could not be classified into any of the known group A rotavirus subgroups. These "unclassifiable" samples probably had neither subgroup 1 nor 2 specificities in ELISA or could belong to a third subgroup unknown or not investigated in this study. In all age groups investigated, subgroup 1 and 2 specific antigens were prevalent. This was also observed after yearly analysis of subgroup specificity; however, a higher prevalence of subgroup 2 specificity was observed in 1990 and 1991. Subgroup 1 rotaviruses were found in all the 4 States sampled (Plateau, Benue, Oyo, and Cross River), whereas subgroup 2 rotaviruses were detected only in Plateau State. All rotaviruses recovered in this study had long genome electrophoretic migration patterns, irrespective of subgroup. Thus genomic diversity of group A rotaviruses does not necessarily reflect antigenic diversity, as there is no mandatory correlation between genome electropherotype pattern and subgroup specificity.

Efficacy of rhesus rotavirus vaccine MMU-18006 against gastroenteritis due to serotype 1 rotavirus

We conducted a clinical trial of rhesus rotavirus vaccine MMU-18006 (RRV, serotype 3) to assess the immunogenicity, transmissibility and booster effect of this vaccine in a welfare nursery in Sapporo, from September 1986 to October 1988. After the trial, in March 1989, an outbreak of gastroenteritis due to a wild strain of serotype 1 rotavirus (RV-1) occurred in the study population. Infants were divided into three groups based on vaccination history: five booster vaccinees, 18 one-dose vaccinees and 18 control infants who did not receive vaccine. There was a significant relationship between asymptomatic infection and higher levels of preoutbreak antibody titres against KU (serotype 1) but not RRV. Significant protection from rotavirus illness was observed both in the booster vaccine group and in the one-dose vaccine group but not in the control group. Rotavirus-specific serum IgA immune response was considered to be one of the indicators of recent rotavirus infection, and did not correlate with resistance to rotavirus illness. Our results revealed that protection from rotavirus illness was serotype-specific and that previous rotavirus infection, including vaccination, was important to induce the heterotypic immune response, and that ageing or booster inoculation of RRV might play a role in the protection against serotype 1 rotavirus infection. From our findings, a booster administration was thought to be important to induce effective heterotypic immunity and should be included in a future rotavirus vaccine trial to obtain sufficient protection against four major serotypes of rotavirus.

Rotaviruses: immunological determinants of protection against infection and disease

Although studies of rotavirus immunity in experimental animals and humans have often yielded conflicting data, a preponderance of evidence supports the following answers to the questions initially posed. 1. What is the importance of virus serotype in formulating an optimal vaccine? Both vp4 and vp7 induce virus-neutralizing antibodies after either natural infection or immunization; the capacity of vp4 to induce rotavirus-specific neutralizing antibodies is probably greater than that of vp7. However, protection against disease after immunization of infants and young children is induced by strains heterotypic to the challenge virus (e.g., immunization with WC3 induces protection against disease induced by serotypically distinct human G1 strains). In addition, oral inoculation of infants with primate or bovine reassortant rotaviruses containing genes that encode human vp7 has not consistently induced a higher level of protection against challenge than that induced by parent animal rotaviruses (see Table I). Therefore, although vp4 or vp7 or both are probably important in inducing protection against challenge, it has not been clearly demonstrated that inclusion of the epidemiologically important human (as distinct from animal) P or G type is important in protection against human disease. 2. Which immunological effector arm most likely protects against rotavirus disease? No immunological effector arm clearly explains protection against heterotypic challenge. Protection against disease is not predicted by rotavirus-specific neutralizing antibodies in serum. Rotavirus-specific, binding sIgA in feces [detected by enzyme-linked immunosorbent assay (ELISA)] induced after natural infection does correlate with protection against disease induced by subsequent infection. However, protection after immunization with WC3 may occur in the absence of a detectable fecal sIgA response. The relationship between rotavirus-binding sIgA and sIgA-mediated neutralizing activity directed against the challenge virus remains to be determined. Binding rotavirus-specific sIgA in feces detected by ELISA may only be a correlate of other events occurring at the intestinal mucosal surface. The presence of broadly cross-reactive, rotavirus-specific CTLs at the intestinal mucosal surface of mice acutely after infection is intriguing. It would be of interest to determine the degree to which the presence of cross-reactive, rotavirus-specific CTLs in the circulation is predictive of the presence of virus-specific CTLs among intestinal lymphocytes and protection against challenge. Unfortunately, studies of virus-specific CTLs are difficult to perform in children. 3. By what means is virus antigen best presented to the host to elicit a protective immune response? Oral inoculation may not be necessary to induce a protective, virus-specific immune response at the intestinal mucosal surface.(ABSTRACT TRUNCATED AT 400 WORDS)

Rotavirus vaccines and vaccination potential

The development of a successful rotavirus vaccine is a complex problem. Our review of rotavirus vaccine development shows that many challenges remain, and priorities for future studies need to be established. For example, the evaluation of administration of a vaccine with OPV or breast milk might receive less emphasis until a vaccine is made that shows clear efficacy against all virus serotypes. Samples remaining from previous trials should be analyzed to determine epitope-specific serum and coproantibody responses to clarify why only some trials were successful. Detailed evaluation of the antigenic properties of the viruses circulating and causing illness in vaccinated children also should be performed for comparisons with the vaccine strains. In future trials, sample collection should include monitoring for asymptomatic infections and cellular immune responses should be analyzed. The diversity of rotavirus serotype distribution must be monitored before, during, and after a trial in the study population and placebo recipients must be matched carefully to vaccine recipients. Epidemiologic and molecular studies should be expanded to document, or disprove, the possibility of animal to human rotavirus transmission, because, if this occurs, vaccine protection may be more difficult in those areas of the world where cohabitation with animals occurs. We also need to have an accurate assessment of the rate of protection that follows natural infections. Is it realistic to try to achieve 90% protective efficacy with a vaccine if natural infections with these enteric pathogens only provide 60% or 70% protection? Subunit vaccines should be considered to be part of vaccine strategies, especially if maternal antibody interferes with the take of live vaccines. The constraints on development of new vaccines are not likely to come from molecular biology. The challenge remains whether the biology and immunology of rotavirus infections can be understood and exploited to permit effective vaccination. Recent advances in developing small animal models for evaluation of vaccine efficacy should facilitate future vaccine development and understanding of the protective immune response(s) (Ward et al. 1990b; Conner et al. 1993).

Passive protection against bovine rotavirus-induced diarrhea in murine model by specific immunoglobulins from chicken egg yolk

Chicken egg yolk immunoglobulins (yIg) specific against bovine rotavirus (BRV) serotypes 6 (strain Shimane) and 10 (strain KK-3) were used for oral passive immunization of suckling mice against experimental BRV challenge. The protective capacity of the antibody preparation was tested using different concentrations of yIg against a challenge dose of 10(7.5) TCID50 for Shimane and 10(7.0) TCID50 for KK-3 strain. There was a significant homotypic (P < 0.05) and heterotypic (P < 0.01) protection using 160 anti-Shimane or 160 anti-KK-3 neutralizing antibody titer (NAT) compared to control mice given yIg derived from eggs of mock-immunized (control) hens. The titer of infectious BRV recovered from intestinal tissue or luminal chyme decreased with increasing homotypic yIg NAT. A decrease in degree and duration of BRV antigen localization in the villus epithelial lining was observed in mice treated with homotypic yIg at optimum dose for prevention of diarrhea. The NAT in sera of challenged mice increased with decreasing NAT in the yIg given before challenge suggesting that protection was dose-dependent. The present findings indicate that a passive protection could be achieved by the use of yIg against BRV-induced diarrhea in this murine model.

Concentrations of passively acquired IgG1 antibodies in the intestinal lumen of the neonatal calf

Passively acquired specific antibodies in the intestinal lumen are thought to provide protective immunity against infections with rotaviruses and other enteropathogens. In this study, concentrations of functional antibody in the intestinal lumen derived from diet and circulation were measured using 2,4-dinitrophenol (DNP) specific antibody of the IgG1 isotype, radiolabelled with 125I. The labelled IgG1 antibody was administered to neonatal calves either orally in the daily milk diet for three consecutive days (Group 1), or by a single intravenous injection (Group 2). After equilibration, the concentrations of protein-bound 125I and the specific DNP binding activities of the labelled protein in the intestinal lumen were measured, and intestinal concentrations of functional IgG1 were estimated. In Group 1 calves, protein bound 125I concentrations in the pooled small intestinal contents at 2 and 12 h after a milk meal were 50.8 +/- 20.5% and 7.9 +/- 3.4%, respectively, of the milk concentration. Protein bound 125I concentrations in the small intestinal contents were 0.7 +/- 0.4% (mean +/- SD) of serum concentrations of Group 2 calves, and were similar at 2 and 12 h after a milk meal. For a calf with average serum passive IgG1 concentrations drinking milk with normal IgG1 content, these results predict IgG1 concentrations in the small intestinal contents of milk fed calves at 2 h after a milk meal to be 0.6 mg ml-1, half of which originates from the milk and half from the circulation. At 12 h after a milk meal, intestinal IgG1 concentrations fall to approximately 0.3 mg ml-1, most of which originates from the circulation. Antibody in the intestinal lumen originating from serum retained more antigen (DNP) binding affinity than that ingested in the milk diet. Therefore, both dietary and circulating IgG1 contribute significantly to passive IgG1 antibody concentrations in the small intestinal lumen of neonatal calves, but milk derived IgG1 antibody concentrations in the small intestinal lumen were not maintained between twice daily feedings.

Characterization of field strains of group A bovine rotaviruses by using polymerase chain reaction-generated G and P type-specific cDNA probes

Dot and Northern blot hybridization assays were used to analyze field strains of group A bovine rotaviruses (BRVs) by using nucleic acid probes representing P and G type specificities. The probes were prepared by polymerase chain reaction amplification of hyperdivergent regions of the cloned VP4 (nucleotides 211 to 686) and VP7 (nucleotides 51 to 392) genes from four serotypically distinct (in P or G types) strains of rotaviruses: NCDV (G6, P1), IND (G6, P5), 69M (G8, P10), and Cr (G10, P11). The P and G type cDNA probes were radiolabeled with [32P]dCTP and hybridized with RNA extracted from reference cell culture-passaged rotavirus strains or the field samples. The field samples were obtained from young diarrheic calves from Ohio, Nebraska, Washington State, and Canada. The cDNA probes were specific for their respective G or P types on the basis of analysis of known P and G type reference strains. The G typing analysis of 102 field samples revealed that 36.3% (37 of 102) were G6, 2.9% (3 of 102) were G8, 12.7% (13 of 102) were G10, and 23.5% (24 of 102) were untypeable. The P typing results for 93 samples indicated that 2.2% (2 of 93) were P1 (NCDV-like), 20.4% (19 of 93) were P5 (UK-like), 9.3% (10 of 93) were P11 (B223-like), and 40.8% (38 of 93) were untypeable. This is the first report of the identification among BRV strains in North America of a G type other than G6 or G10. Our report further confirms that G6, P5 rotaviruses are predominant among the BRV field strains that we examined, and the P types of these strains differ from that of the BRV vaccine strain used in the United States (G6, P1). The large number of untypeable G (23.5%) and P (40.8%) types suggests that other or new P and G types exist among BRV field strains.

Development of cDNA probes for typing group A bovine rotaviruses on the basis of VP4 specificity

Dot and Northern (RNA) blot hybridization assays were developed for the P typing of group A bovine rotaviruses (BRV) by using cDNA probes prepared from gene segment 4. The probes were prepared by polymerase chain reaction amplification of hyperdivergent regions (nucleotides 211 to 686) of BRV strain UK, IND, NCDV, and Cr VP4 cDNA by using specific oligonucleotide primers. The probes were P type specific (VP4) and exhibited little or no cross-reactivity with double-stranded RNA from heterologous rotavirus P types. Our studies indicate that at least three P types, as defined by polymerase chain reaction-derived VP4 gene probes from the UK, NCDV, and Cr strains, exist among the seven BRV isolates tested.

Monoclonal anti-idiotype induces antibodies against bovine Q17 rotavirus

This study describes, for the first time, the production and use of an "internal-image" anti-idiotypic monoclonal antibody (MAb) to elicit a rotavirus-specific antibody response. An immunoglobulin G2a MAb, designated RQ31 (MAb1), specific for the outer capsid protein VP4 of bovine Q17 rotavirus and capable of neutralizing viral infection in vitro was used to generate an anti-idiotypic MAb (MAb2). This MAb2, designated RQA2, was selected by enzyme-linked immunosorbent assay (ELISA) using F(ab')2 fragments of RQ31. RQA2 (MAb2) inhibited the binding of RQ31 (MAb1) to the virus but had no effect on the binding of other rotavirus-specific MAbs. The MAb2 also inhibited virus neutralization mediated by MAb1 in a dose-dependent fashion. Naive guinea pigs immunized with the MAb2 produced anti-anti-idiotypic antibodies (Ab3) that reacted with bovine Q17 rotavirus in an ELISA and neutralized rotavirus infection in vitro. The Ab3 response was characterized as MAb1-like because the Ab3 recognizes only the Q17 and neonatal calf diarrhea virus rotavirus strains in ELISA, as did RQ31 (MAb1). The Ab3 response also possessed two other characteristics of RQ31: the abilities to bind the 1.36 (double-capsid) but not the 1.38 (single-capsid) purified rotavirus fraction in ELISA and to immunoprecipitate the VP4 rotavirus protein.

Detection of group C rotavirus antigens and antibodies in animals and humans by enzyme-linked immunosorbent assays

Enzyme-linked immunosorbent assays (ELISAs) were developed to detect group (gp) C rotavirus antigens and antibodies. Both assays were confirmed to be specific for gp C rotavirus by using serogroup A, B, and C rotaviruses; hyperimmune antisera to these serogroups of rotaviruses; and paired serum specimens from animals infected with gp C rotaviruses. The ELISA for antigen detection reacted not only with porcine gp C rotaviruses but also with human and bovine gp C rotaviruses. Following experimental challenge of gnotobiotic pigs with porcine gp C rotavirus, the virus was found by ELISA in all diarrheic feces. A high prevalence of antibodies to gp C rotaviruses was detected in sera from adult pigs (93 to 97%) and cattle (47 to 56%) in the United States and Japan. However, no antibody to gp C rotavirus was detected in the sera (n = 20) of adult horses in the United States. In human sera from Hokkaido, Japan, 3% of children and 13% of adults possessed antibody to gp C rotaviruses. These results suggest that the ELISA that we developed may be useful for surveying gp C rotavirus infections in animals and humans. On the basis of serology, gp C rotavirus infections are common in pigs and cattle in the United States and Japan, but they occur at lower levels in humans from the Hokkaido area of Japan.

Detection and differentiation of bovine group A rotavirus serotypes using polymerase chain reaction-generated probes to the VP7 gene

Dot and Northern blot hybridization assays were developed to detect and differentiate group A bovine rotavirus serotypes using radiolabeled serotype 6 (Nebraska calf diarrhea virus [NCDV] and United Kingdom [UK] strains) or serotype 10 (Crocker [Cr] strain) VP7 gene probes. Partial length VP7-specific cDNA encompassing areas of major sequence diversity were generated by the polymerase chain reaction (PCR) using either cloned VP7 genes (NCDV and UK strains) or reverse transcribed mRNA (Cr strain) as templates. Radiolabeled probes prepared from the PCR-generated cDNA were tested at various stringency conditions to optimize the hybridization assays. At high stringency conditions (52 C, 50% formamide, 5 x standard saline citrate), the NCDV, UK, and Cr probes serotypically differentiated bovine rotavirus isolates in RNA samples prepared from cell culture propagated viruses or in fecal specimens from infected gnotobiotic calves. The sensitivity and specificity of NCDV and Cr VP7 probes were characterized in dot blot hybridization assays, and the probes were estimated to detect at least 1 ng of viral RNA. The serotyping results obtained using VP7 probes were similar to those obtained using serologic assays. Further development of these assays may provide a useful means for the rapid detection and differentiation of bovine rotavirus serotypes in fecal samples from calves in the field.

Reduction in morbidity due to diarrhea in nursing beef calves by use of an inactivated oil-adjuvanted rotavirus-Escherichia coli vaccine in the dam

An outbreak of neonatal diarrhea occurred among beef calves (2000 animals) from one large Argentinian farm in 1985. Rotavirus was detected in 78% (106/136) and enterotoxigenic Escherichia coli in 1.5% of the samples (2/136) obtained from sick calves. In comparison rotavirus was identified in only 1.6% (1/63) of the samples from clinically healthy calves. The rotavirus strain responsible for the outbreak was characterized as serotype 6 belonging to group A. In the following three years the protective capacity of a combined rotavirus-E. coli inactivated vaccine administered to the dams during the last third of the gestation period was evaluated on this farm by comparison of morbidity due to diarrhea in calves from vaccinated vs. placebo cows within the same year. The morbidity due to diarrhea among calves from dams in the vaccinated and placebo groups was 34% and 77%, respectively in 1986; 23% and 47% in 1987, and 15% and 34%, in 1988. In 1987 morbidity of diarrhea in calves born from vaccinated heifers was 54% and 74% in calves from placebo heifers. In 1988 morbidity from diarrhea was 41% and 54%, respectively among calves in these two groups. In all experiments, calves from heifers showed significantly greater morbidity than calves from cows. Differences in diarrhea morbidity between the vaccinated and placebo groups were statistically significant (P less than 0.05). Additional studies showed that the diarrhea had a significant influence (P less than 0.05) on the average live weight of the calves at weaning (5 to 7 months) with an average weight loss of 7.8 kg per calf among the calves affected with diarrhea.

Murine intestinal antibody response to heterologous rotavirus infection

Rotavirus is the most important worldwide cause of severe gastroenteritis. Extensive efforts have been devoted to the design of a vaccine that will prevent disease, but development of a more effective vaccine strategy may require progress in the understanding of the mucosal immune response to replicating viral antigens. In this article, we report the characterization of the intestinal antibody response of a murine model to heterologous infection with the rhesus rotavirus vaccine strain. We have adapted the enzyme-linked immunospot assay to measure this response without the difficulties associated with measurement of antibodies in intestinal contents or the artifacts associated with culturing of lymphocytes. The predominant response in terms of antibody-secreting cells (ASC) is seen in the small intestine lamina propria, which can be measured within 4 days of infection, peaks 3 weeks after infection, and remains near that level for longer than 8 weeks. The magnitude of the immunoglobulin A (IgA) cell response is approximately 10 times greater than the intestinal IgG cell response, and IgM cells are rare. Virus-specific ASC constitute approximately 50% of all ASC in the gut at the peak of the virus-specific response. This response is considerably greater than responses to nonreplicating mucosal antigens measured by similar techniques. Enteral infection engenders minimal virus-specific ASC response in the spleen. Rhesus rotavirus-specific enzyme-linked immunosorbent assay and neutralization assays of serum and intestinal contents did not correlate with virus-specific ASC response.

Effect of immune bovine milk on Streptococcus mutans in human dental plaque

The use of a mouthrinse of bovine milk containing antibodies to Streptococcus mutans resulted in an initial reduction in the numbers of recoverable Strep. mutans in a group of 9 individuals. Ten volunteers who used control bovine milk that contained no antibody activity to Strep. mutans had variable levels of plaque Strep. mutans. In addition, after culture on Mitis Salivarius and Gold's agar, the plaque Strep. mutans from subjects who used the immune bovine milk rinse formed smaller colonies than those from pre-treatment plaque and from all plaque samples of subjects who used the control rinse.

Cell culture propagation of a coronavirus isolated from cows with winter dysentery

Fecal filtrates from cows with winter dysentery were inoculated into gnotobiotic and conventional calves, and a coronavirus was isolated from calf feces. Cytopathic effects were observed on human rectal tumor cells but not bovine cell cultures. The winter dysentery isolates morphologically and antigenically resembled the Mebus strain of bovine coronavirus.

Risk factors for mortality from diarrhea in beef calves in Alberta

A case-study involving 56 randomly selected beef herds in Alberta was conducted to assess the association of a number of suspected risk factors upon the odds of a high mortality from diarrhea among calves less than 30 days of age. Using stepwise logistic regression it was found that an increased percentage of heifers calving in the herd, poor drainage in the nursing area, providing limited shelter in the nursing area, a large calving area, and wintering cows and heifers on the same ground were conditionally associated with an increase in the odds of high mortality from neonatal diarrhea.

A longitudinal study of bovine coronavirus enteric and respiratory infections in dairy calves in two herds in Ohio

This prospective longitudinal study examined the epidemiology and disease syndrome associated with bovine coronavirus (BCV) infections in a cohort of 8 conventional calves from 0 to 120 days of age, in two dairy herds in Ohio. The periods of respiratory shedding of BCV were determined by direct immunofluorescent (DIF) staining of nasal epithelial cells and ELISA of nasal swab supernatant fluids. The periods of fecal shedding of BCV were determined by ELISA and immunoelectron microscopy (IEM). The isotype-specific antibody titers to BCV in serum (at selected intervals between 0 and 120 days of age) and the post-suckling (24 to 48 h after birth) total immunoglobulin levels were examined by ELISA and zinc sulfate turbidity tests, respectively. Of the 8 calves studied, 4 had evidence of BCV respiratory (by DIF or ELISA) or enteric infections (by IEM or ELISA) in association with diarrhea or rhinitis, even though 7 of 8 calves showed increases in one or more serum antibody isotypes to BCV and 6 of 8 calves showed BCV respiratory or enteric antigen shedding by ELISA. Serological antibody titer increases occurred in 3 calves before 30 days of age and in 4 calves after 30 days of age; two of the latter calves had a second rise in serum antibody titers to BCV after the initial rise. A serological antibody titer increase was not observed in one calf. This suggests that BCV infections may be very common in a closed herd and may occur in older calves, although many may be subclinical and some may be recurrent. There were no statistically significant correlations between total serum immunoglobulin levels or BCV antibody isotype titers in serum (24-48 h after birth) and clinical disease or infection by BCV; however, calves with low levels of IgA BCV antibodies in serum (24-48 h after birth) had a significantly greater average number of days with diarrhea than those calves having high levels of IgA BCV-specific antibodies in serum.

Study of virus excretion in feces of diarrheic and asymptomatic calves infected with rotavirus

Infection of calves by rotavirus could lead to diarrhea or subclinical disease. Therein, kinetic of viral excretion from a group of asymptomatic calves, previously exposed to a virulent strain of rotavirus, is compared to that of a group the calves of which had diarrhea associated with rotavirus infection. As determined by an enzyme-linked immunosorbent assay (ELISA), duration of rotavirus shedding in feces and maximum yield of virus antigen were similar within the two groups of calves. Rotaviruses isolated from the two above groups of animals were antigenically related as shown by neutralization tests, and showed a similar RNA electrophoretic profile. In conclusion, it is likely that both asymptomatic and diarrheic calves infected by rotavirus are equally a major source of contamination to contact healthy calves.

Induction and persistence of local rotavirus antibodies in relation to serum antibodies

The induction and persistence of local rotavirus antibodies, including stool IgA, jejunal IgA, and jejunal neutralizing antibody, were evaluated in 14 adult volunteers infected with the CJN strain of human rotavirus. In addition, the relationships between local rotavirus IgA and serum rotavirus IgA, IgG, and neutralizing antibody were determined. Both stool and serum rotavirus IgA appeared to have similar kinetics. Both antibodies peaked by days 14-17 after inoculation in all subjects, then decreased rapidly. By days 26-28, titers had fallen to 13% and 30% of their respective peaks. Serum rotavirus IgG peaked somewhat later, occurring in five subjects on days 26-28. Serum neutralizing antibody peaked on days 26-28 in all but three subjects. Both serum IgG and neutralizing antibodies also declined more slowly than rotavirus IgA. Although all antibody concentrations had decreased to only a fraction of their peak responses by days 270-365 after rotavirus inoculation they remained higher than baseline levels. For example, stool rotavirus IgA concentrations were 13.5-fold higher than baseline, while jejunal rotavirus IgA and neutralizing antibody were 8.9- and 4.3-fold above baseline, respectively. Similarly, serum antibodies remained 3.7- to 11.2-fold higher than baseline at 270-365 days after rotavirus inoculation. These studies imply that serum rotavirus IgA is a good indicator of local antibody responses. Furthermore, although both serum and local antibody titers peaked within 2-4 weeks after infection, these antibodies persisted at above baseline concentrations for at least 9-12 months after infection.

Efficacy of an inactivated oil-adjuvanted rotavirus vaccine in the control of calf diarrhoea in beef herds in Argentina

We have assessed the potency of an inactivated oil-adjuvanted rotavirus vaccine in beef herds in Argentina. Two different vaccine trials were conducted. In a small-scale experimental trial, involving 21 pregnant cows (13 vaccinated and eight unvaccinated controls), a significant increase in neutralizing antibody titres against different serotypes of bovine rotaviruses was found in both the colostrum and serum of vaccinated cows compared with that of unvaccinated controls. Seven days after birth, half of the calves born to vaccinated dams or to control cows were challenged with live virulent virus whereas the other half of both groups were left in contact with the infected calves in order to mimic a natural field challenge. Although no statistically significant differences in the rate of protection were observed among the different groups of animals, a larger number of vaccinated calves were protected in comparison with their controls, particularly where animals in contact with infected calves were concerned. Secondly, a large-scale field trial was carried out in 17 beef herds involving a total of 4066 vaccinated pregnant cows. In 11 farms morbidity and mortality in calves from vaccinated cows were compared with historical data from the previous 3 years at the same locations. In the other six herds, control groups were used to compare data of the same year: 1540 cows were vaccinated and 2700 were left as controls. Taking into account the previous and current incidence of diarrhoea, morbidity and mortality were significantly reduced in 16 of the 17 beef herds tested. Vaccine effectiveness was also evident in farms where other enteropathogens such as cryptosporidium and coronaviruses were present, together with rotavirus.

Development of protein A-gold immunoelectron microscopy for detection of bovine coronavirus in calves: comparison with ELISA and direct immunofluorescence of nasal epithelial cells

A protein A-colloidal gold immunoelectron microscopy (PAG-IEM) technique was developed for the detection of bovine coronavirus (BCV) in the feces and nasal secretions of infected calves. Feces or nasal swab fluids were incubated sequentially with hyperimmune bovine anti-bovine coronavirus serum and protein A-gold, negatively stained, applied to formvar-coated copper grids and viewed using an electron microscope. The PAG-IEM method specifically identified BCV particles and possible subviral particles in feces and nasal-swab fluids from infected calves. The PAG-IEM method did not label other enveloped enteric viruses or morphologically similar fringed particles commonly found in feces. Detection of BCV using PAG-IEM was compared with ELISA and direct immunofluorescence (IF) of nasal epithelial cells by monitoring fecal and respiratory tract shedding of BCV from two experimentally infected and two naturally infected calves from birth to 3 weeks of age. PAG-IEM and ELISA detected shedding of BCV in fecal (4/4 animals) and nasal (3/4 animals) samples for an average of 5.25 days each. The observed agreement of BCV detection by PAG-IEM and ELISA was 85%. PAG-IEM may be a more sensitive immunoassay for the detection of BCV in diagnostic specimens from infected neonatal calves than ELISA. BCV infection of nasal epithelial cells was detected by immunofluorescence in 4/4 calves, persisted for the duration of the study in 2/4 calves and was sporadic in the other two animals. The observed agreement of BCV detection by PAG-IEM and IF was 57%.

Effect of nutritional deprivation on mucosal viral infections

Suckling BALB-c mice, subjected to nutritional deprivation in artificially expanded litters (18 to 20 pups), were compared to normally nourished pups (7-9 per litter) in a series of experiments designed to provide data on morphologic and functional alterations of the small intestine during malnutrition and infection. The effects of protein calorie malnutrition (PCM) on the viral replication pattern and severity of clinical disease were examined in suckling mice infected with murine rotavirus (MRV). The infection in nutritionally deprived animals was characterized by a significant decrease in the minimal infectious dose and in the incubation period for the onset of diarrhea as well as increased severity of disease when compared to well nourished controls. Rotavirus-specific antibody, administered orally prior to virus inoculation, significantly reduced MRV replication in both groups but most strikingly in malnourished animals. Additional studies of the uptake of a macromolecule [ovalbumin (OVA)] following oral administration to experimental and control groups showed more rapid and complete absorption in the malnourished animals. Infection further enhanced the uptake of OVA, suggesting that both PCM and rotavirus infection alter the permeability of the small intestine. An unexpected observation of rotavirus-associated hepatitis in CB-17scid mice was also made in nearly 40% of malnourished mice inoculated with 10(6) PFU of Rhesus rotavirus (RRV). Mice with PCM exhibited a susceptibility to hepatitis between SCID mice (80%) and immunologically normal mice (18%). While these data are not sufficient to confirm a nutritionally-mediated immunoincompetence, they do suggest that either loss of immune competence and/or increased gut permeability in malnourished animals may allow a more severe homologous rotavirus infection as well as extraintestinal spread of heterologous rotavirus.

Protection against neonatal rotavirus infection by breast milk antibodies and trypsin inhibitors

The role of breast milk antirotavirus immunoglobulin A (IgA) and trypsin inhibitors in limiting the acquisition of rotavirus infection during the initial 5 days of life was evaluated among 42 exclusively breast-fed hospital-born infants, 22 of whom experienced rotavirus infection. The mean concentrations of antirotavirus IgA (ELISA Units) in the breast milk of mothers of the 22 rotavirus-infected neonates was 130.4 +/- 46.4; the corresponding value in 20 noninfected neonates was 384.3 +/- 328.3 (P less than 0.001). Similarly, the trypsin inhibitory capacity (mumols/mt/ml) of breast milk in the rotavirus-infected group was significantly lower (0.109 +/- 0.095) than that in the noninfected group (0.376 +/- 0.191; P less than 0.001). The trypsin inhibitory capacity of milk showed an inverse correlation with infant stool tryptic activity (P less than 0.01). Our results indicate that the acquisition of rotavirus infection during the early neonatal period depends on the concentrations of antirotavirus IgA and trypsin inhibitors in human milk and that protection is mediated by high levels of these antiviral factors.

Influence of immunomodulatory agents on bovine humoral and cellular immune responses to parenteral inoculation with bovine rotavirus vaccines

Sodium diethyldithiocarbamate (DTC), mycobacterium cell wall extract (MCWE, Regressin), killed Corynebacterium parvum (C. parvum, Immunoregulin) and muramyldipeptide (MDP) were each combined with purified, live bovine rotavirus and inoculated into 3 month-old Holstein-Friesian calves in order to examine their ability to potentiate specific humoral and cellular immune responses. The vaccinated calves were boosted twice at 3 and 6 weeks after initial vaccine inoculation. The rotavirus was administered intramuscularly either in an aqueous suspension or in a water-in-oil (WIO) emulsion, prepared with incomplete Freund's adjuvant (IFA). DTC and C. parvum were given by the intravenous route, while MCWE and MDP were incorporated directly in the rotavirus suspension. Two groups of calves were also vaccinated either with rotavirus and IFA or with rotavirus emulsified in mineral oil and a mannide oleate compound (MOC, Montanide 888). A control group of calves was given phosphate-buffered saline (PBS) solution emulsified with IFA. The different vaccine preparations were then compared by studying the kinetics of serum rotavirus-neutralizing antibody production and of proliferative response by blood lymphocytes following in vitro stimulation with bovine rotavirus. The results showed that: (1) the bovine rotavirus should be incorporated in a WIO emulsion in order to induce a cell-mediated immune response as detected by the rotavirus-specific in vitro stimulation test with blood lymphocytes, and to produce higher neutralizing antibody titers in the serum; (2) the vaccines prepared with the mineral oil-MOC complex or IFA both induced comparable levels of humoral and cellular immune responses. The use of mineral oil and MOC as adjuvant may be preferred to IFA, because of the facility of preparing the vaccine and of the low viscosity of the resulting WIO emulsion: (3) the addition of MDP to the WIO emulsion prepared with IFA resulted in a higher cell-mediated immune response as determined by the in vitro blood lymphocyte transformation index specific for bovine rotavirus.

Passive immunity to bovine rotavirus infection associated with transfer of serum antibody into the intestinal lumen

The effect of circulating passive antibody on immunity to bovine rotavirus infections in neonatal calves was investigated. In the first experiment, rotavirus antibody titers in the small intestinal lumina of 5- and 10-day-old calves with a wide range of serum rotavirus antibody titers were determined. Neutralizing antibody was present in the small intestinal lumina in titers that correlated with the calves' serum titers (r = +0.84, P less than 0.01). Immunoglobulin G1 was the predominant isotype of intestinal luminal rotavirus antibody. Calves not fed colostrum during the absorptive period lacked rotavirus antibody in circulation and in the intestinal lumen at 7 days of age, even when they were fed large volumes of colostrum with a high rotavirus antibody titer at 48 h after birth. Therefore, rotavirus antibody is not retained in the intestinal lumen for 5 days following a colostrum meal, and the luminal antibody in the 5- and 10-day-old seropositive calves were probably derived from circulating antibody. In a second experiment, calves were passively immunized by subcutaneous injection of colostral whey with a high immunoglobulin G1 rotavirus antibody titer and challenged with virulent bovine rotavirus 48 h later. The passively immunized calves were protected from rotavirus infection and diarrhea compared with calves with comparable serum immunoglobulin concentrations but with lower serum rotavirus with lower serum rotavirus antibody titers. The results of these experiments indicate that circulating immunoglobulin G1 antibody appears in the gastrointestinal tract of neonatal calves and that circulating rotavirus antibody can prevent infection and diarrhea after rotavirus challenge.