Levels of colostral antibodies against neonatal calf diaahoea virus

Ovine rotavirus strain LLR-85-based bovine rotavirus candidate vaccines: construction, characterization and immunogenicity evaluation

Group A bovine rotaviruses (BRVs) are the most important cause of diarrheal diseases in neonatal calves and cause significant morbidity and mortality in the young animals, and epidemiologic surveillance of bovine rotavirus G genotypes conducted in various cattle populations throughout the world has shown that approximately 90% of the bovine rotavirus isolates belong to G6 and G10. Based on the modified Jennerian approach to immunization, we constructed and characterized a reassortant rotavirus stain, which bears a single bovine rotavirus VP7 gene encoding G genotype 6 specificity while the remaining 10 genes are derived from the ovine attenuated rotavirus LLR-85. The reassortant rotavirus strain, named as R191, and its parental virus strain LLR-85 were combined as bivalent vaccine candidates to inoculate the colostrums-deprived neonatal calves for evaluation of the immunogenicity. The calves were orally inoculated with the reassortant R191 (group 1), the parental rotavirus LLR-85 (group 2), or combined the R191 and LLR-85 (group 3), and serum specimens were detected to determine the immune response of IgG and IgA antibodies. Results showed that seroconversion to positivity for IgG and IgA antibodies occurred at postinoculation day (PID) 10 in all of the inoculated calves, and the highest titers of the serum IgG (range 1:800 to 1:6400) and IgA (range 1:800 to 1:3200) antibodies were obtained at PID 21 for all calves. Meanwhile, virus shedding was detected after inoculation, showing that the inoculated virus was positive in 2 of 77 fecal specimens (2.6%) collected from the inoculated calves during the first 7 days of oral inoculation with the rotavirus vaccine candidates. The results suggested that the rotavirus strains R191 and LLR-85 are promising bivalent vaccine candidates for the prevention of bovine G6 and G10 rotavirus infection.

Pathogenesis of rotavirus infection in turkey poults

The pathogenesis of rotavirus infection was examined after experimental infection of conventional and specific-pathogen-free (SPF) turkey poults. In six experiments birds were exposed to turkey rotavirus isolates Tu-1 or TU-2 or the chicken isolate Ch-1 at 7, 10 or 42 days of age. Poults were examined between 1 and 24 days post-infection (dpi) for diarrhoea, gross and histopathologic lesions, virus excretion in the intestinal tract, viral antigen in intestinal epithelial cells, and the development of serum antibodies. Between 2 and 5 dpi watery droppings were observed in conjunction with remarkable paleness of the intestinal tract which was grossly observable. Maximum viral replication occurred between 2 and 5 dpi, during which period viral antigen could be demonstrated in the epithelial cells of the duodenum, jejunum, ileum and colon. Sporadically, virus antigen-positive cells were seen in the cecum. As early as 4 to 5 dpi rotavirus antibodies could be detected by indirect immunofluorescence assays. Remarkable leukocyte infiltration of the lamina propria, vacuolation of the epithelial cells and scalloping of the villous surface at the tips were observed in the intestine of infected birds. Infection with rotavirus caused a significant impairment at 2 and 4 dpi of absorption of D-xylose from the intestinal tract.

Pathogenic rotaviruses isolated from pigs and calves

Rotavirus is commonly isolated from diarrhoeic calves and pigs. Bacterium-free faecal filtrates containing rotavirus from five different outbreaks of disease in calves all caused diarrhoea and clinical illness in gnotobiotic calves and five different isolates from pigs were inoculated into gnotobiotic pigs with similar results. The author was unsuccessful in finding an avirulent strain although one of the calf isolates was from a non-diarrhoeic calf. The laboratory strain of calf virus retained its virulence after being passaged seven times in gnotobiotic calves, which included sucrose density gradient purification on two occasions. The calf tissue culture-adapted virus retained its virulence. Rotavirus isolates from humans, calves, pigs and foals were infectious to pigs. Although sharing a common antigen the viruses were separable according to host infectivity, virulence and neutralizing antigens. In both calves and pigs the main lesion was loss of the epithelial cell of the small intestine and stunting of villi. Passive protection of the calf and pig was poor. Circulating antibody was not protective and although high levels of clolostral antibody in the gut lumen at the time of infection protected calves clinically, the antibody level secreted in milk declined 10-fold 48 hours after parturition. Frequently other viruses are found together with rotavirus in cases of diarrhoea. Their role is being investigated.

Acrylamide concentration affects the relative position of VP7 gene of serotype G2 strains as determined by polyacrylamide gel electrophoresis

BACKGROUND

During the course of development and characterization of various rotavirus reassortants, we found that the relative position of the gene encoding neutralization and protective antigen VP7 of certain rotavirus strains in a PAGE gel was influenced by the concentration of acrylamide.

OBJECTIVES

We investigated systematically various factors that affected the relative position of the rotavirus VP7 gene in a PAGE gel.

STUDY DESIGN

We analyzed dsRNAs of selected rotavirus strains bearing G1, G2, G3 or G9 specificity by PAGE at varying concentrations of acrylamide.

RESULTS

We demonstrated that the relative position of the VP7 gene of three G2 strains varied depending upon the concentration of acrylamide in a PAGE gel, which occurred not only in a homologous G2 virus gene background but also in a heterologous G3 virus gene background; and the VP7 gene bearing G1, G3, G4 or G9 specificity did not display this phenomenon when the PAGE running conditions were varied.

CONCLUSIONS

The concentration of acrylamide in a PAGE gel was the major factor that influenced the relative position of the VP7 gene of G2 rotavirus strains (i.e., VP7 gene coding assignment by PAGE).

A rotavirus strain isolated from pig-tailed macaque (Macaca nemestrina) with diarrhea bears a P6[1]:G8 specificity

A distinct rotavirus strain (PTRV) was isolated in cell cultures from a stool sample obtained from a diarrheic 3-year-old female pig-tailed macaque (Macaca nemestrina) that was born at the breeding colony of the University of Washington in Seattle. Unlike other known simian rotavirus strains including vervet monkey rotavirus SA11 which bears P5B[2]:G3 or P6[1]:G3 specificity, rhesus monkey rotavirus MMU18006 with P5B[3]:G3 specificity, pig-tailed macaque rotavirus YK-1 with P[3]:G3 specificity and rhesus monkey rotavirus TUCH with P[24]:G3 specificity, the cell-culture-grown PTRV strain was shown to bear P6[1]:G8 specificity as determined by VP4 (P)- and VP7 (G)-specific neutralization assays as well as gene sequence analyses. The virus in the original diarrhea stool was also shown to bear genotypes P[1] and G8. In addition, the PTRV strain exhibited a "long" electropherotype, subgroup I specificity and NSP4 genotype A specificity. The PTRV probe formed (i) 8-9 hybrid bands with genomic RNAs of various bovine rotavirus strains and (ii) only 2-3 hybrid bands with simian rotavirus RNAs as demonstrated by RNA-RNA hybridization, suggesting a possible bovine origin of the virus. Serologic analysis of serum samples obtained from selected pig-tailed macaques in the colony suggested that a rotavirus bearing P[1]:G8 specificity was endemic among macaques for at least 8 years (1987-1994). This is the first report describing an isolation of a simian rotavirus bearing a non-G3 VP7 and possibly a P6[1] specificities. Because of its unique simian serotype, this virus may prove to be valuable in challenge studies in a non-human primate model in studies of rotavirus immunity.

Porcine rotavirus strain Gottfried-based human rotavirus candidate vaccines: Construction and characterization

Rotavirus gastroenteritis remains the leading cause of severe diarrheal disease in infants and young children worldwide, and thus, a safe and effective rotavirus vaccine is urgently needed in both developing and developed countries. Various candidate rotavirus vaccines that were developed by us and others have been or are being evaluated in different populations in various parts of the world. We have recently confirmed that a porcine rotavirus Gottfried strain bears a P (VP4) serotype (P2B[6]) closely related to human rotavirus P serotype 2A[6] which is of epidemiologic importance in some regions of the world. Based on the modified Jennerian approach to immunization, we have constructed 11 Gottfried-based single VP7 or VP4 gene substitution reassortant vaccine candidates which could provide: (i) an attenuation phenotype of a porcine rotavirus in humans; and (ii) antigenic coverage for G serotypes 1-6 and 8-10 and P serotype 1A[8], 1B[4] and 2A[6]. In addition, following immunization of guinea pigs with Gottfried VP4, we found low but consistent levels of neutralizing antibodies to VP4 with P1A[8] or P1B[4] specificity, both of which are of global epidemiologic importance. Thus, porcine-based VP7 reassortant rotavirus vaccines may provide an advantage over rhesus- or bovine-based VP7 reassortant vaccines since the VP4s of the latter vaccines do not evoke antibodies capable of neutralizing the viruses bearing P1A[8], P1B[4] or P2A[6] VP4.

A porcine G9 rotavirus strain shares neutralization and VP7 phylogenetic sequence lineage 3 characteristics with contemporary human G9 rotavirus strains

Of five globally important VP7 (G) serotypes (G1-4 and 9) of group A rotaviruses (the single most important etiologic agents of infantile diarrhea worldwide), G9 continues to attract considerable attention because of its unique natural history. Serotype G9 rotavirus was isolated from a child with diarrhea first in the United States in 1983 and subsequently in Japan in 1985. Curiously, soon after their detection, G9 rotaviruses were not detected for about a decade in both countries and then reemerged in both countries in the mid-1990s. Unexpectedly, however, such reemerged G9 strains were distinct genetically and molecularly from those isolated in the 1980s. Thus, the origin of the reemerged G9 viruses remains an enigma. Sequence analysis has demonstrated that the G9 rotavirus VP7 gene belongs to one of at least three phylogenetic lineages: lineage 1 (strains isolated in the 1980s in the United States and Japan), lineage 2 (strains first isolated in 1986 and exclusively in India thus far), and lineage 3 (strains that emerged/reemerged in the mid-1990s). Currently, lineage 3 G9 viruses are the most frequently detected G9 strains globally. We characterized a porcine rotavirus (A2 strain) isolated in the United States that was known to belong to the P[7] genotype but had not been serotyped by neutralization. The A2 strain was found to bear serotype G9 and P9 specificities as well as NSP4 [B] and subgroup I characteristics. By VP7-specific neutralization, the porcine G9 strain was more closely related to lineage 3 viruses than to lineage 1 or 2 viruses. Furthermore, by sequence analysis, the A2 VP7 was shown to belong to lineage 3 G9. These findings raise intriguing questions regarding possible explanations for the emergence of variations among the G9 strains.

Rotavirus serotype G9 strains belonging to VP7 gene phylogenetic sequence lineage 1 may be more suitable for serotype G9 vaccine candidates than those belonging to lineage 2 or 3

A safe and effective group A rotavirus vaccine that could prevent severe diarrhea or ameliorate its symptoms in infants and young children is urgently needed in both developing and developed countries. Rotavirus VP7 serotypes G1, G2, G3, and G4 have been well established to be of epidemiologic importance worldwide. Recently, serotype G9 has emerged as the fifth globally common type of rotavirus of clinical importance. Sequence analysis of the VP7 gene of various G9 isolates has demonstrated the existence of at least three phylogenetic lineages. The goal of our study was to determine the relationship of the phylogenetic lineages to the neutralization specificity of various G9 strains. We generated eight single VP7 gene substitution reassortants, each of which bore a single VP7 gene encoding G9 specificity of one of the eight G9 strains (two lineage 1, one lineage 2 and five lineage 3 strains) and the remaining 10 genes of bovine rotavirus strain UK, and two hyperimmune guinea pig antisera to each reassortant, and we then analyzed VP7 neutralization characteristics of the eight G9 strains as well as an additional G9 strain belonging to lineage 1; the nine strains were isolated in five countries. Antisera to lineage 1 viruses neutralized lineage 2 and 3 strains to at least within eightfold of the homotypic lineage viruses. Antisera to lineage 2 virus neutralized lineage 3 viruses to at least twofold of the homotypic lineage 2 virus; however, neutralization of lineage 1 viruses was fourfold (F45 and AU32) to 16- to 64-fold (WI61) less efficient. Antisera to lineage 3 viruses neutralized the lineage 2 strain 16- to 64-fold less efficiently, the lineage 1 strains F45 and AU32 8- to 128-fold less efficiently, and WI61 (prototype G9 strain) 128- to 1024-fold less efficiently than the homotypic lineage 3 viruses. These findings may have important implications for the development of G9 rotavirus vaccine candidates, as the strain with the broadest reactivity (i.e., a prime strain) would certainly be the ideal strain for inclusion in a vaccine.

Human rotavirus strains bearing VP4 gene P[6] allele recovered from asymptomatic or symptomatic infections share similar, if not identical, VP4 neutralization specificities

A rotavirus VP4 gene P[6] allele has been documented in a number of countries to be characteristically associated with an endemic predominantly asymptomatic infection in neonates in maternity hospital nurseries. The mechanisms underlying the endemicity and asymptomatic nature of such neonatal infections remain unknown. Rotavirus strains sharing this same P genotype, however, have more recently been recovered from an increasing number of symptomatic diarrheal episodes in infants and young children in various parts of the world. Previously, we have shown that an asymptomatic P[6] rotavirus neonatal infection is not associated with a unique VP7 (G) serotype but may occur in conjunction with various G types. Although amino acid sequence comparisons of the VP4 gene between selected "asymptomatic" and "symptomatic" P[6] rotavirus strains have been reported and yielded information concerning their VP4 genotypes, serotypic comparisons of the outer capsid spike protein VP4 of such viruses have not been studied systematically by two-way cross-neutralizations. We determined the VP4 neutralization specificities of four asymptomatic and four symptomatic P[6] strains: two each of asymptomatic and symptomatic strains by two-way tests, and two each of additional asymptomatic and symptomatic strains by one-way tests. Both asymptomatic and symptomatic P[6] strains were shown to bear similar, if not identical, VP4 neutralization specificities. Thus, P[6] rotavirus strains causing asymptomatic or symptomatic infections did not appear to belong to unique P (VP4) serotypes. In addition, a close VP4 serotypic relationship between human P[6] rotavirus strains and the porcine P[6] rotavirus Gottfried strain was confirmed.

Construction and characterization of rhesus monkey rotavirus (MMU18006)- or bovine rotavirus (UK)-based serotype G5, G8, G9 or G10 single VP7 gene substitution reassortant candidate vaccines

Group A rotaviruses are the single most important etiologic agents of severe diarrhea of infants and young children worldwide and have been estimated to be responsible for approximately 650,000-800,000 deaths annually in children <5-year-old in the developing countries. Thus, the development of a safe and effective rotavirus vaccine has been a global public health goal. Epidemiologic surveillance of rotavirus VP7 (G) serotypes-genotypes conducted in various populations throughout the world has repeatedly shown that approximately 90% of the typeable rotavirus isolates belong to G1-G4. For these reasons, we have developed a rhesus rotavirus (RRV)-based or bovine rotavirus (UK)-based quadrivalent vaccine which is designed to provide antigenic coverage for G1-G4. More recently, G serotypes-genotypes other than G1-G4, including G5, G8-G10, have been detected in various parts of the world. Although the occurrence of such uncommon G types, except for G9, has been focal, still, in order to "be ready and prepared", we have constructed and characterized eight additional reassortant rotavirus vaccines, each of which bears a single human or bovine VP7 gene encoding G serotype 5, 8, 9 or 10 specificity and the remaining 10 genes of RRV strain MMU18006 or bovine rotavirus strain UK. These candidate vaccines could be evaluated singly in special populations or in combination with a RRV- or an UK-based quadrivalent vaccine to broaden its G serotype specificity.

Identification of parental origin of cognate dsRNA genome segment(s) of rotavirus reassortants by constant denaturant gel electrophoresis

Rotaviruses are the single most important etiologic agents of severe diarrhea in infants and young children worldwide. They possess a triple capsid morphology and a genome of 11 segments of double-stranded (ds) RNA. During the course of the development of various live, attenuated reassortant rotavirus vaccines, we often experienced difficulty in identifying the parental origin of certain genome segment(s) of a reassortant vaccine candidate. Various assays have been utilized for determination of the parental origin of reassortant virus genes, including polyacrylamide gel electrophoresis (PAGE), DNA and/or RNA hybridization assays and gene sequence analysis. The traditional PAGE is simple and easy to perform, however, it is common to find that certain cognate dsRNA segment(s) cannot be differentiated by this assay due to a high degree of sequence homology among different rotavirus strains. Constant denaturant gel electrophoresis (CDGE) is one of several methods that have been used to screen DNA fragments for small sequence changes or point mutations. By using the CDGE, we were successful in partially denaturing rotavirus dsRNA thereby changing the physical properties of the genome segment(s) in the gel and thus differentiating the cognate genome segment(s) of rotavirus reassortants. The CDGE provides a simple and reliable assay system for identification of parental gene origins of a rotavirus reassortant.

Generation and characterization of six single VP4 gene substitution reassortant rotavirus vaccine candidates: each bears a single human rotavirus VP4 gene encoding P serotype 1A[8] or 1B[4] and the remaining 10 genes of rhesus monkey rotavirus MMU18006 or bovine rotavirus UK

The global disease burden of rotavirus diarrhea in infants and young children has stimulated interest in the biological and clinical characteristics of these agents, leading to intensive efforts to develop a vaccine. A rhesus rotavirus (RRV)-based quadrivalent vaccine ("RotaShield") was licensed and administered to about 1 million infants and found to be highly effective. However, it was withdrawn because of a link with intussusception. This vaccine was developed according to a modified "Jennerian" approach in which one of the two major outer capsid proteins (VP7) shares neutralization specificity with one of the four epidemiologically important human rotavirus serotypes. The other outer capsid protein (VP4) is derived solely from RRV and is distinct from the VP4 of the four human rotavirus serotypes of epidemiologic importance. In an effort to further increase the immunogenicity of the existing VP7-based RRV quadrivalent vaccine, we generated three single VP4 gene substitution reassortant rotavirus candidate vaccines, each of which bears a single human rotavirus VP4 gene encoding P serotype 1A[8] or 1B[4] specificity while the remaining 10 genes are derived from the rhesus rotavirus. By incorporating one or two of these strains into the quadrivalent vaccine, a pentavalent or hexavalent RRV-based vaccine could be formulated thus providing antigenic coverage not only for VP7 serotype 1, 2, 3 and 4 but also for VP4 serotype 1A[8] or 1B[4], thus possibly augmenting its immunogenicity. Similarly, three single VP4 gene (P1A[8] or P1B[4]) substitution reassortants have also been generated in a background of 10 bovine (UK) rotavirus genes for addition to a second generation UK-based quadrivalent vaccine.

Characterization of nontypeable rotavirus strains from the United States: identification of a new rotavirus reassortant (P2A[6],G12) and rare P3[9] strains related to bovine rotaviruses

Among 1316 rotavirus specimens collected during strain surveillance in the United States from 1996 to 1999, most strains (95%) belonged to the common types (G1 to G4 and G9), while 5% were mixed infections of common serotypes, rare strains, or not completely typeable. In this report, 2 rare (P[9],G3) and 2 partially typeable (P[6],G?; P[9],G?) strains from that study were further characterized. The P[6] strain was virtually indistinguishable by hybridization analysis in 10 of its 11 gene segments with recently isolated P2A[6],G9 strains (e.g., U.S.1205) from the United States, but had a distinct VP7 gene homologous (94.7% a.a. and 90.2% nt) to the cognate gene from P1B[4],G12 reference strain L26. Thus, this serotype P2A[6],G12 strain represents a previously unrecognized reassortant. Three P3[9] strains were homologous (97.8-98.2% aa) in the VP8 region of VP4 to the P3[9],G3 feline-like reference strain AU-1, but had a high level of genome homology to Italian bovine-like, P3[9],G3 and P3[9],G6 rotavirus strains. Two of the U.S. P3[9] strains were confirmed to be type G3 (97.2-98.2% VP7 aa homology with reference G3 strain AU-1), while the other was most similar to Italian bovine-like strain PA151 (P3[9],G6), sharing 99.0% a.a. homology in VP7. Cross-neutralization studies confirmed all serotype assignments and represented the first detection of these rotavirus serotypes in the United States. The NSP4 genes of all U.S. P3[9] strains and rotavirus PA151 were most closely related to the bovine and equine branch within the DS-1 lineage, consistent with an animal origin. These results demonstrate that rare strains with P and G serotypes distinct from those of experimental rotavirus vaccines circulate in the United States, making it important to understand whether current vaccine candidates protect against these strains.

Correlation between maternal serum antibodies and protection against bovine rotavirus diarrhea in calves

The correlation between maternal serum antibodies in beef calves at 2 days old and protection against diarrhea induced by natural bovine rotavirus (BRV) infection was examined. Virus neutralizing (VN) antibody titers against BRV in sera from calves that developed diarrhea by BRV infection within 14 days of age (BRV-diarrheal calves) were significantly lower than those from calves that had no diarrhea. In the BRV-diarrheal calves, a positive correlation was found between the VN antibody titers and age of the onset of diarrhea. There were negative correlations between the VN antibody titers and duration of the diarrhea, VN antibody titers and cumulative diarrhea scores, and the VN antibody titers and duration of virus shedding. These results suggest that the VN antibody titers against BRV in newborn calf serum could be an indicator of protection against BRV-induced diarrhea.

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.

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)

Homotypic and heterotypic immune responses to group A rotaviruses in parenterally immunized sheep

Immune responses to human rotaviruses were investigated in sheep with a view to obtaining antibodies for passive immunotherapy of humans. Eighteen adult sheep with previous natural exposure to rotavirus serotypes G3 and G6 were immunized parenterally with purified preparations of either individual rotavirus serotypes G1, G2, G3, G4 and G8, or a mixture thereof. Two additional sheep were kept as control animals with the flock. The antibody responses were measured on serial serum samples by neutralization tests. The homotypic antibody response ranged from 100-fold (rarely) up to 100,000-fold increases in titre. Heterotypic responses against serotypes G3 and G6 were demonstrated in 7/12 and 15/18 sheep, respectively, but the increases in titre were lower than the homotypic responses, ranging from 10- to 100-fold in most cases and were 1000-fold in two sheep. Interestingly, no heterotypic response against the human rotavirus serotypes was raised after 3 months; moderate titres of cross-neutralizing antibodies for the human serotypes were only observed after a third inoculation.

Active protection against rotavirus infection of mice following intraperitoneal immunization

Active immunity to rotavirus has been demonstrated following oral inoculation with live virus but little is known about the effects of parenteral immunization. In this study, adult mice were immunized by intraperitoneal (ip) inoculation with live rotaviruses and later orally challenged with murine rotavirus (EDIM) to measure active immunity against infection. Three doses of EDIM (8 micrograms/dose) given intraperitoneally (ip) provided full protection against EDIM infection, whether administered with or without Freund's adjuvant. Only partial protection was found when the quantity of immunogen was reduced to < 2 micrograms/dose. Reduction of the number of doses from three to one (8 micrograms/dose), however, still resulted in protection of all mice. Significant protection was also observed after inoculation with one or three doses (2 micrograms/dose) of heterologous rotaviruses. Protection provided by the heterologous strains did not correlate with neutralizing antibody to EDIM, which indicated that neutralizing antibody to the challenge virus was not required for protection. uv-Inactivated EDIM also provided significant protection against EDIM, thus demonstrating that viral replication was not required for protection. These results suggest that parenteral immunization may be an effective method to vaccinate against rotavirus disease.

A liquid-hybridization method for typing the Vp4 and Vp7 genes of bovine rotaviruses

A simple liquid-hybridization assay was developed which allows assessment of the degree of hybridization between the two serotype-determining genes of the bovine rotavirus strain UK and the homologous genes of the isolate under test. 32P-labelled transcription probes were produced from cloned complementary DNA (cDNA) copies of UK gene segments 4 and 8 and hybridized to double stranded RNA (dsRNA) extracted from rotavirus-positive field samples. Subsequent treatment with ribonuclease A (RNase A), separation of the RNase A-resistant hybrid fragments by polyacrylamide gel electrophoresis (PAGE) and autoradiography yielded a specific, reproducible banding pattern for each isolate. A total of 74 field samples was tested by both the hybridization assay and by an enzyme-linked immunosorbent assay (ELISA) using serotype-specific monoclonal antibodies (Mabs). The results obtained were in excellent agreement and confirmed that serotype G6 rotaviruses predominated. Hybridization of these G6 viruses with the gene 4 probe suggested that viruses with Vp4s related to that of UK rotavirus are also common. The hybridization assay was more sensitive than the ELISA.

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.

Some infectious causes of diarrhea in young farm animals

Escherichia coli, rotaviruses, and Cryptosporidium parvum are discussed in this review as they relate to enteric disease in calves, lambs, and pigs. These microorganisms are frequently incriminated as causative agents in diarrheas among neonatal food animals, and in some cases different strains or serotypes of the same organism cause diarrhea in humans. E. coli causes diarrhea by mechanisms that include production of heat-labile or heat-stable enterotoxins and synthesis of potent cytotoxins, and some strains cause diarrhea by yet undetermined mechanisms. Rotaviruses and C. parvum induce various degrees of villous atrophy. Rotaviruses infect and replicate within the cytoplasm of enterocytes, whereas C. parvum resides in an intracellular, extracytoplasmic location. E. coli, rotavirus, and C. parvum infections are of concern to producers, veterinarians, and public health officials. These agents are a major cause of economic loss to the producer because of costs associated with therapy, reduced performance, and high morbidity and mortality rates. Moreover, diarrheic animals may harbor, incubate, and act as a source to healthy animals and humans of some of these agents.

Immunity to rotaviruses

A potent, multivalent, serotype-specific RV vaccine and improved tests for measuring vaccine potency would help eliminate the necessity to pretest for vaccine efficacy in every country selected for its deployment. Until then, the need will continue for vaccine trials in various countries because the pathogenesis and epidemiology of RV and RV serotypes differ between and within countries. Although RV vaccinology is complex, it has forged ahead of our knowledge of RV immunopathogenesis and epidemiology.

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.

Comparison of the amino acid sequences of the major neutralization protein of four human rotavirus serotypes

We sequenced the gene coding for the major neutralizing protein (VP7) from eight human rotavirus strains representing serotype 1, 2, 3, or 4. In addition, the corresponding gene of the rhesus rotavirus vaccine strain MMU 18006 (serotype 3) was sequenced. Comparative analyses of their deduced amino acid sequences revealed an overall 15-29% divergence in the VP7 proteins that define four different rotavirus serotypes and confirmed the presence of six discrete regions of clustered sequence divergence (amino acids 39-50, 87-101, 120-130, 143-152, 208-221, and 233-242). When the same regions were compared among rotaviruses belonging to the same serotype, a high degree of homology (91-99%) was detected. These observations indicate that differences in the serotype specificity among rotaviruses are the result of a high degree of sequence divergence in several discrete regions of the VP7 gene and that these regions are highly conserved within a given serotype.

Bovine milk immunoglobulins for passive immunity to infantile rotavirus gastroenteritis

Pregnant cows were successfully hyperimmunized with all four human rotavirus serotypes, resulting in a 100-fold increase in neutralizing milk antibody titers over those of controls. Milk antibodies were isolated batchwise from 1,000 kg of pooled milk for the first 10 lactation days, yielding 10 kg of freeze-dried milk immunoglobulin concentrate consisting of 50% bovine milk immunoglobulins. Milk immunoglobulin concentrate showed neutralizing activities against all four human rotavirus serotypes that were 100 times higher than those in pooled human milk samples and 10 times higher than those in a commercial pooled immunoglobulin preparation from pooled human blood serum. In vitro neutralization tests showed that milk immunoglobulin concentrate had powerful antiviral activity, even against very high doses of infectious rotaviruses. Because the technology of the milk immunoglobulin concentrate ensures that it is innocuous and can be used for oral application, it is proposed that milk immunoglobulin concentrate be used to induce passive immunity to infantile rotavirus gastroenteritis.

Sequential isolation of rotavirus from individual calves

An outbreak of neonatal calf diarrhea was studied on a breeding farm of Japanese indigenous beef cattle. During the breeding season of 1982, 43 calves were born over the period 27 February-28 April. All but one of the calves suffered from neonatal diarrhea and 5 died. Bovine rotavirus was isolated in cell cultures from fecal specimens of 39 (90.7%) of the 43 calves during the outbreak, strongly suggesting that this was the causative agent; the virus was readily isolated from 81 (83.5%) of 97 specimens of diarrhea. Rotavirus was subsequently isolated from the feces of 7 of the calves in early May, more than one month after the initial virus isolation in early March. Two of these calves were again rotavirus-positive in early June, 41 days after the second virus isolation. Diarrhea had ceased in all 7 calves in March. Some antigenic differences were shown by the neutralization test between the early and later isolates from one of these calves, suggesting either re-infection with a serologically different virus, or persistent infection with the original virus following antigenic modulation.

Septicemic colibacillosis and failure of passive transfer of colostral immunoglobulin in calves

Septicemic colibacillosis is a highly fatal disease that occurs in calves less than 2 weeks of age. The disease occurs when a calf that fails to absorb protective levels of immunoglobulin from colostrum is exposed to an invasive serotype of E. coli. Management to ensure good passive transfer of colostral immunoglobulin will prevent this disease and reduce calf mortality caused by other infectious diseases as well.

Vaccination against enteric rota and coronaviruses in cattle and pigs: enhancement of lactogenic immunity

Passive immunity against enteric viral infections is dependent upon the continual presence in the gut lumen of a protective level of specific antibodies. This article examines methods currently used to enhance the titre and duration of specific antibody in the mammary secretions of cows and pigs, with particular reference to rotavirus and coronavirus infections. In addition, some of the potential problems to be found in attempting to produce vaccines against these viral infections are outlined.

Antibody to human rotavirus in cow's milk

Rotavirus infection is an important cause of gastroenteritis in infants and young children. Since the virus replicates in the intestinal lumen, we investigated the presence and effectiveness of rotavirus antibody in three forms of milk: raw milk, pasteurized milk, and commercially available infant formulas. Both raw and pasteurized milk contained detectable levels of IgG1 antibody directed at rotavirus. On the other hand, little or no anti-rotavirus antibody was detected in commercially available infant formulas or other sterile milk preparations. The milk samples with rotavirus antibody were capable of inhibiting the replication of simian, bovine, and human rotaviruses in tissue culture. In addition, they were capable of protecting mice from infection and disease in a murine model of rotavirus infection. On the other hand, the formula preparations were incapable of modifying the in vitro replication of rotavirus strains in tissue culture and did not prevent symptomatic gastroenteritis in the mouse model. We conclude that the alteration of milk-processing procedures or the addition of effective antibodies to milk preparations commonly used in the nutrition of young children may alter the clinical course of rotavirus infection or decrease the transmission of rotavirus throughout susceptible populations.

Enteric viral infections of calves and passive immunity

At least eight viruses have been identified, four within the last 5 yr, that produce diarrhea and pathological intestinal lesions in experimentally inoculated calves. Coronavirus and rotavirus frequently are associated with the neonatal calf diarrhea syndrome, but the etiologic role of the newly identified viruses is undefined. All diarrheal viruses replicate within small intestinal epithelial cells, resulting in variable degrees of villous atrophy. Immunity against these viral infections, therefore, must be directed toward protection of the susceptible intestinal epithelial cells. Because most of these viral infections occur in calves less than 3 wk of age, passive lactogenic immunity within the gut lumen plays an important role in protection. This report reviews methods of boosting rotavirus antibody responses in bovine mammary secretions and analyses of passive and active immunity in calves supplemented with colostrum and challenged by rotavirus. Results indicate rotavirus immunoglobulin G1 antibodies in colostrum and milk were elevated after intramuscular and intramammary vaccination of pregnant cows with an Ohio Agricultural Research and Development Center rotavirus vaccine but not after intramuscular immunization with a commercial rota-coronavirus vaccine. Feeding colostrum from intramuscular plus intramammary immunized cows to newborn calves challenged by rotavirus prevented diarrhea and shedding of rotavirus.

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

Colostrum was collected and pooled from each of five cows in three experimental groups: group I cows received intramuscular and intramammary inoculations of adjuvanted modified live Ohio Agricultural Research and Development Center rotavirus vaccine; group II cows were injected intramuscularly with a commercial modified-live rota-coronavirus vaccine; and group III cows were uninoculated controls. Pooled colostrum from group I cows had higher (P less than 0.05) enzyme-linked immunosorbent assay (ELISA) immunoglobulin G (IgG1) and virus neutralization (VN) rotavirus antibody titers (ELISA IgG1 = 2,413,682; VN = 360,205) than did colostrum from group II (ELISA IgG1 = 8,192; VN = 4,395) or group III cows (ELISA IgG1 = 5,916; VN = 2,865). The antibody titers of these last two colostrum pools did not differ (P greater than 0.05). Samples of these colostrum pools were fed as daily supplements (percent [vol/vol] in cow's milk infant formula) to 28 newborn, unsuckled, antibody-seronegative, male Holstein calves. Eight calves received no supplemental colostrum. The calves were orally challenged with virulent bovine rotavirus and monitored daily for diarrhea and fecal rotavirus shedding. Diarrhea and rotavirus shedding occurred in the eight calves fed no supplemental colostrum and persisted longest in this group. The pooled colostrum from group I cows protected eight of eight calves from both rotavirus diarrhea and shedding when fed as a 1% supplement. The pooled colostrum from neither group II nor group III cows protected 12 other calves against rotavirus diarrhea or shedding when fed at the same concentration (1%). Six rotavirus-challenged calves fed 0.1% supplemental colostrum from group I cows and two calves fed 10 and 50% supplemental colostrum from control cows displayed partial passive immunity, exemplified by delayed onset and shortened duration of rotavirus-associated diarrhea and virus shedding.

Comparison of different antigen preparations as substrates for use in passive hemagglutination and enzyme-linked immunosorbent assays for detection of antibody against bovine enteric coronavirus

Purified coronavirus, detergent extracts of purified coronavirus, and virus-infected Madin-Darby bovine kidney cells were evaluated as antigen substrates in enzyme-linked immunosorbent assay (ELISA) and passive hemagglutination systems. Only detergent-extracted and -unextracted, purified viruses were reactive as antigen substrates in ELISA, whereas all three antigen preparations could be used for sensitization of erythrocytes in the passive hemagglutination assay. The passive hemagglutination system with infected cell extracts exhibited a similar level of sensitivity and specificity to the ELISA system employing purified coronavirus but enabled 300 times more tests to be performed per volume of virus-infected cell culture.

Protection against cholera in breast-fed children by antibodies in breast milk

We performed a prospective study to examine whether the IgA antibodies against cholera that are present in breast milk protect breast-fed infants and children against colonization with Vibrio cholerae 01 and disease. Among families of patients with cholera, we collected breast milk from mothers who had not had diarrhea in the previous week and monitored them and their breast-fed children for cholera colonization and diarrhea for 10 days. Breast milk was assayed for IgA antibodies to cholera toxin and lipopolysaccharide. Ninety-three mother--child pairs were studied; 30 infants became colonized with V. cholerae 01 and disease developed in 19. There were no differences between the antibody levels in milk fed to children who became colonized and in milk fed to children who did not. However, among the children who became colonized, those who had diarrhea drank breast milk containing significantly lower levels of both kinds of cholera antibodies than were present in the milk consumed by children who had no symptoms. We conclude that breast-milk antibodies against cholera do not appear to protect children from colonization with V. cholerae 01 but do protect against disease in those who are colonized.

Pathogenesis of rotavirus infection in mice

Three parameters of rotavirus infection, i.e., clinical disease, viral antigen in infected intestines, and infectious virus in feces, were assessed in infant mice nursed by mothers with or without preexisting rotavirus antibody. Diarrhea was the only consistent sign of clinical disease, and its course followed that of infection by about 1 day. Infected intestinal epithelial cells, except crypt cells, were observed by immunofluorescence microscopy in the duodenum, jejunum, ileum, and colon. Infection progressed in a proximal-to-distal direction with time. Viral antigen appeared in intestinal tissue later, was present in lower amounts, and disappeared sooner from infants nursed by mothers with preexisting rotavirus antibody, indicating that protection was passively transferred to these infants although the course of clinical disease was not changed.

Immunity to rotavirus in conventional neonatal calves

The local and systemic humoral immune responses to rotavirus were studied in six conventional neonatal calves. Attenuated bovine rotavirus was administered either orally or directly into an isolated intestinal loop. The parameters monitored were neutralizing rotavirus antibody in serum, immunofluorescent and neutralizing rotavirus antibody in intestinal loop washings, and rotavirus antibody-producing cells in intestinal mucosa. An antibody response was observed in the serum and intestinal secretions from one calf only. Viral replication was not detected in the isolated intestinal loop. Rotavirus antibody-producing cells were found in the intestinal mucosa of five calves. Double staining revealed that most of these cells produced antibody of the immunoglobulin A class. The conclusions were: (i) a previously described system to detect rotavirus antibody-producing cells can be used to study immune responses in neonatal calves, (ii) the class or subclass of antibody in rotavirus antibody-producing cells can be determined by double immunofluorescent staining, (iii) neonatal calves respond to rotavirus inoculation with a local immunoglobulin A response, and (iv) most of the rotavirus antibody-producing cells are located in the mucosa of the proximal small intestine.