Serologic correlates of immunity in a tetravalent reassortant rotavirus vaccine trial. US Rotavirus Vaccine Efficacy Group

The correlation of antibody responses (serum rotavirus IgA and neutralizing antibody to serotype G1-G4 human rotaviruses and rhesus rotavirus [RRV]) in a reassortant rotavirus vaccine trial with protection against rotavirus infection or disease was investigated. Most subjects administered 4 x 10(5) pfu of either the serotype G1 monovalent or serotype G1-G4 tetravalent vaccine seroconverted for at least one of the six antibodies (85% and 91%, respectively). However, fewer than one-third seroconverted to any prototype G1-G4 human rotavirus. Analyses of covariance indicated that higher prevaccination neutralizing antibody titers negatively affected postvaccination titers. Significant relationships were found between several postvaccination rotavirus antibody titers and protection, and serotype-specific correlates of protection were identified between anti-Wa titers and G1 illnesses (P = .03) and between anti-RRV titers and G3 illnesses (P < .001). Overall, however, serotype-specific immunity was no more significant than heterotypic immunity, and no specific titer of any antibody analyzed was a reliable indicator of protection.

Particle bombardment-mediated DNA vaccination with rotavirus VP6 induces high levels of serum rotavirus IgG but fails to protect mice against challenge

The rotavirus inner capsid protein VP6 contains conserved epitopes that are potential targets for eliciting protective immunity against different serotypes within the same group of rotavirus. In order to determine whether VP6 alone can induce protective immunity, an expression vector pcDNA1/EDIM6 containing gene 6 of rotavirus EDIM strain was constructed and used as a vaccine in an adult mouse model. Cloned gene 6 was determined to be 1356 nucleotides long and contained a 5' noncoding region of 23 nucleotides, a 3' noncoding region of 139 nucleotides, and a coding frame of 1194 nucleotides for a polypeptide of 397 amino acid residues. Recombinant VP6 was expressed in rabbit reticulocyte lysate and the heat-denatured recombinant VP6 migrated in SDS-gels with an apparent molecular weight of approximately 43 kDa. Five additional polypeptide bands corresponding to oligomers of recombinant VP6 were observed when the expressed product was not heat denatured. To determine the immunogenicity of recombinant VP6, female BALB/c mice were injected intramuscularly or intradermally with pcDNA1/EDIM6, or were inoculated epidermally with plasmid-coated gold beads using the Geniva Accell particle delivery device. Only intradermal injection and particle delivery elicited measurable serum anti-rotavirus IgG responses, but responses developed following particle delivery were significantly (P < 0.001) greater. However, none of the delivery methods induced serum or stool anti-rotavirus IgA responses and, when challenged with EDIM no protection against infection was observed in the immunized mice. Therefore, parenteral immunization with VP6 alone elicited large anti-rotavirus IgG responses but did not elicit protection against murine rotavirus infection in this model.

Divergence of VP7 genes of G1 rotaviruses isolated from infants vaccinated with reassortant rhesus rotaviruses

A large placebo-controlled efficacy trial of the rhesus tetravalent (RRV-TV) and serotype G1 monovalent (RRV-S1) rotavirus vaccines was conducted in 1991-1992 at 24 sites across the United States. Protection was 49% and 54% against all diarrhea but 80% and 69% against very severe gastroenteritis for the two vaccines, respectively. Post-vaccination neutralizing antibody titers to the G1 Wa strain, whose VP7 protein is nearly identical to that of the D strain of rotavirus contained in both vaccines, did not correlate with protection against subsequent illness with G1 strains. This result raised the possibility that in infants who developed post-vaccination neutralizing antibody to Wa, breakthrough (i.e., vaccine failure-the occurrence of rotavirus diarrhea after immunization) may have been due to infection by G1 strains that were sufficiently antigenically distinct from the vaccine strain to evade the neutralizing antibodies elicited by vaccination. To test this hypothesis, we initially compared post-vaccination neutralizing antibody titers of vaccinees against Wa and G1 breakthrough strains using sera from subjects who experienced breakthrough. Post-immunization neutralizing antibody titers to Wa elicited by vaccination were significantly (P < 0.001) greater than to the breakthrough strains subsequently obtained from these subjects. This difference did not, however, correlate with lack of protection since similar differences in titer to Wa and breakthrough strains were found using post-vaccination sera from vaccinees who either experienced asymptomatic rotavirus infections or no infections. To determine the genetic basis for these differences, we compared the VP7 gene sequences of Wa with vaccine strain D, 12 G1 breakthrough strains, and 3 G1 control strains isolated during the same trial from placebo recipients. All breakthrough strains were distinct from Wa and D in antigenically important regions throughout the VP7 protein, but these differences were conserved between breakthrough and placebo strains. Furthermore, a comparative analysis of the deduced amino sequences form VP7 genes of G1 rotaviruses from 12 countries indicated that four distinct lineages have evolved. All breakthrough and control strains from the U.S. vaccine trial were in a lineage different from strain D, the serotype G1 vaccine strain. Although the overall results do not support our original hypothesis that immune selection of antigenically distinct escape mutants led to vaccine breakthrough in subjects with a neutralization response to Wa, it cannot be excluded that breakthrough could be partially due to antigenic differences in the VP7 proteins of currently circulating G1 strains.

Serum rotavirus neutralizing-antibody titers compared by plaque reduction and enzyme-linked immunosorbent assay-based neutralization assays

Comparisons in rotavirus neutralizing-antibody responses were made with sera collected from vaccinated infants. The methods were a plaque reduction assay and a new enzyme-linked immunosorbent assay-based neutralization assay. Agreement of 94% was found in detecting at least fourfold seroresponses, and correlation coefficients between titers obtained by the two methods showed excellent agreement, indicating that either could be used reliably.

Naturally occurring dual infection with human and bovine rotaviruses as suggested by the recovery of G1P8 and G1P5 rotaviruses from a single patient

Culture adaptation of rotaviruses from an infant with severe diarrhea in Cincinnati, Ohio, yielded not only a virus with the original RNA electropherotype (CJN) but also rotaviruses with other electropherotypes, the most dominant of which was called CJN-M [Ward RL, Knowlton DR, Schiff GM, Hoshino Y, Greenberg HB (1988) in J Virol 62: 1543-1549]. RNA-RNA hybridization and sequencing studies indicated that CJN was a typical G1P8 human rotavirus while CJN-M was a G1P5 strain and contained four gene segments (including segment 4) of a bovine rotavirus. Thus, the infant was apparently dually infected with human and bovine rotaviruses.

Evidence that protection against rotavirus diarrhea after natural infection is not dependent on serotype-specific neutralizing antibody

This case-control study sought to determine whether protection against clinically significant rotavirus diarrhea in children aged 4-35 months correlated with titers of serum neutralizing antibody and, if so, whether this protection was serotype-specific. Titers of acute-phase sera from 156 cases of treated rotavirus diarrhea in rural Bangladesh were contrasted with titers from 312 contemporaneously selected, age-matched controls. Analyses of the culture-adapted rotaviruses from the cases revealed that 24%, 15%, 43%, and 17% belonged to serotypes 1-4, respectively. Titers of both homologous and heterologous neutralizing antibody in acute blood specimens of cases were significantly lower than those of matched controls. However, multivariate logistic regression models demonstrated that only antibody titers to heterotypic rotaviruses were independently associated with protection against rotavirus disease. These data, which indicate that the correlation of protection with neutralizing antibody titers is not serotype-specific, suggest that immunity to rotavirus disease may be mediated by other factors.

Seroepidemiologic evaluation of antibodies to rotavirus as correlates of the risk of clinically significant rotavirus diarrhea in rural Bangladesh

A case-control study was conducted among children and adult women in rural Bangladesh to evaluate whether serologic immunity to rotavirus was associated with a lower risk of rotavirus diarrhea of sufficient severity to cause patients to seek medical care. Acute-phase sera from 219 cases of rotavirus diarrhea, detected among patients treated in three diarrheal treatment centers, were compared with sera from 477 contemporaneously selected community controls. Overall, serum IgG antirotavirus antibody titers were nearly one-fourth as high in cases as in controls (107 vs. 417 units/ml; P less than .001). Among persons aged greater than or equal to 8 months, in whom titers of maternal antirotavirus antibodies should have been negligible, even the lowest range of detectable titers (100-200 units/ml) was associated with a substantial (75%, P less than .05) reduction of the risk of rotavirus diarrhea. We conclude that titers of serum IgG antirotavirus antibodies induced by earlier infection were inversely related to the risk of clinically significant rotavirus diarrhea.

Culture adaptation and characterization of group A rotaviruses causing diarrheal illnesses in Bangladesh from 1985 to 1986

Group A rotaviruses collected between 1985 and 1986 during comprehensive surveillance of treated diarrheal episodes occurring in a rural Bangladesh population were culture adapted and characterized by electropherotype, serotype, and subgroup. Of 454 episodes of rotavirus-associated diarrhea, rotaviruses were culture adapted from 381 (84%), and 335 contained 11 electrophoretically identical segments in unpassaged and cultured preparations. These 335 comprised 69 different electropherotypes with between 1 (32 isolates) and 79 representatives. The persistence of specific rotavirus strains within the study population, as defined by the detection of viruses with particular electropherotypes, was generally limited to a period of only a few months. All 335 isolates were serotyped by neutralization with hyperimmune antisera to prototype rotavirus strains representative of serotypes 1 to 4, i.e., Wa, DS-1, P, and ST-3. It was found that 80, 48, 119, and 88 isolates belonged to serotypes 1 to 4, respectively. The concentrations of hyperimmune antisera required to neutralize these isolates, however, were at least threefold greater than those needed to neutralize the homologous strains. Therefore, the isolates appeared to have altered neutralization epitopes from their prototype strains. Furthermore, the serotype 4 isolates were consistently shown to be much more closely related to the serotype 4B VA70 strain than the serotype 4A ST-3 strain. All but two isolates identified as serotypes 1, 3, or 4 had long electropherotypes and were subgroup II, and all but one serotype 2 isolate were subgroup I and had short electropherotypes. The three disparate strains appeared to be genetic reassortants. Evidence is presented that dual infections required for reassortant formation were not uncommon. Thus, formation of multiple reassortants may have been a cause for the observed rapid shift in viral strains within the study population.

Prevention of surface-to-human transmission of rotaviruses by treatment with disinfectant spray

A model was developed to examine the effects of disinfectants on the transmission of infectious rotavirus from a dried surface to humans. The initial experiments were designed to find a method of preserving rotavirus infectivity during drying. Culture-adapted human rotavirus (CJN strain) was dried at room temperature in different organic suspensions, including fecal matter, several laboratory media, and nonfat dry milk (NDM). Recoveries of infectious virus were then compared. Fecal matter provided little protection in this study relative to distilled water, but the other suspensions were quite protective, especially NDM, which consistently allowed recoveries of greater than 50%. When 10(3) focus-forming units of unpassaged CJN virus were dried in NDM and administered to subjects who licked the dried material, 100% (8 of 8) became infected. The effect of Lysol brand disinfectant spray (LDS) was next examined. Although NDM provided some protection against inactivation by LDS, spraying under conditions recommended by the manufacturer consistently caused the CJN virus titer to decrease greater than 5 log10. Consumption of CJN virus (10(3) focus-forming units) sprayed with LDS caused no infection in 14 subjects, whereas 13 of 14 subjects who consumed the unsprayed virus became infected (P less than 0.00001). The methods developed in this study could be used to test the effects of other disinfectants on the spread of infectious rotavirus from inanimate surfaces to humans.

Development of an improved method for measuring neutralizing antibody to rotavirus

An improved assay was developed for measuring neutralizing antibody titers against rotaviruses. This procedure used the same initial steps as performed to determine antibody titers by the focus reduction neutralization (FRN) assay. However, instead of counting infected cells after staining with fluorescein, reductions in virus infectivity by neutralizing antibody were determined by quantitation of viral antigen production using an ELISA. A linear relationship was found between ELISA absorbance values and focus forming units for each of four prototype rotaviruses, representative of serotypes 1-4. Thus, the serum dilution that resulted in neutralization of 60% of infectious virus (i.e. the neutralizing antibody titer) could be readily determined from absorbance values. Titers found by this method were similar to and as reproducible as those found by the FRN assay. Because this method is less laborious and the results are obtained by objective rather than subjective methods, it represents an improvement over the FRN assay.

Formation and selection of intergenogroup reassortants during cell culture adaptation of rotaviruses from dually infected subjects

A previous study showed that intergenogroup reassortants of human rotaviruses can persist in nature (R.L. Ward, O. Nakagomi, D.R. Knowlton, M.M. McNeal, T. Nakagomi, J.D. Clemens, D.A. Sack, and G.M. Schiff, J. Virol. 64:3219-3225, 1990), but the mechanisms involved in their formation and selection had not been determined. In this study it was shown that, during cell culture adaptation of rotaviruses belonging to different genogroups from stools of dually infected subjects, intergenogroup reassortants were formed and selected, presumably mimicking the processes that occur in nature.

Evidence for natural reassortants of human rotaviruses belonging to different genogroups

Of 335 rotavirus isolates associated with diarrheal disease in Bangladesh that were culture adapted and subsequently characterized for electropherotype, subgroup, and serotype, 9 had properties that suggested they may be natural reassortants between human rotaviruses belonging to different "genogroups." Two of these were examined in greater detail by RNA-RNA hybridization with prototype strains representative of each of the three proposed human rotavirus genogroups. One subgroup II isolate, 248, with a "long" electrophoretic pattern was neutralized by hyperimmune antisera to both serotype 2 and 4 strains. Consistent with these results, seven RNA segments of this isolate formed hybrids with human strains belonging to the Wa genogroup and four segments hybridized with strains belonging to the DS-1 genogroup. The second isolate examined, 456, belonged to subgroup II and had a long electrophoretic pattern but was found to be a serotype 2 strain. This isolate also appeared to be an intergenogroup reassortant because three of its segments formed hybrids with strains belonging to the Wa genogroup and eight hybridized with viruses of the DS-1 genogroup. On the basis of the relative migration rates of these RNA-RNA hybrids during gel electrophoresis, a suggested origin for each gene segment was proposed which was consistent with the results expected from electrophoretic, subgroup, and serotypic analyses.

Serum-neutralizing antibody to VP4 and VP7 proteins in infants following vaccination with WC3 bovine rotavirus

Serum specimens from infants 2 to 12 months old vaccinated with the WC3 bovine rotavirus were analyzed to determine the relative concentrations of neutralizing antibody to the VP4 and VP7 proteins of the vaccine virus. To do this, reassortant rotaviruses that contained the WC3 genome segment for only one of these two neutralization proteins were made. The segment for the other neutralization protein in these reassortants was from heterotypic rotaviruses that were serotypically distinct from WC3. Sera were examined from 31 infants who had no evidence of a previous rotavirus infection and the highest postvaccination WC3-neutralizing antibody titers (i.e., 160 to 600) of the 103 subjects administered the vaccine. A reassortant (3/17) that contained both neutralization proteins from the heterotypic rotaviruses, i.e., EDIM (EW strain of mouse rotavirus) VP7 and rhesus rotavirus VP4, was not neutralized by these sera (geometric mean titer [GMT], less than 20). A reassortant (E19) that contained EDIM VP7 and WC3 VP4 was also very poorly neutralized by these antisera (GMT = 20). In contrast, antibody titers to a reassortant (R20) that contained WC3 VP7 and rhesus rotavirus VP4 were higher than those against WC3 (GMTs of 458 and 313, respectively). Thus, VP7 appeared to be the dominant immunogen for production of neutralizing antibody after intestinal infection of previously uninfected infants vaccinated with WC3 bovine rotavirus.

Genotypic selection following coinfection of cultured cells with subgroup 1 and subgroup 2 human rotaviruses

The purpose of this study was to determine why identifiable reassortants between subgroup 1 and subgroup 2 rotaviruses have been so rarely isolated from human specimens. Cultured cells were coinfected with pairs of subgroup 1 and 2 human rotaviruses and passaged multiple times to simulate natural reassortant formation and selection in vivo. After coinfection of MA-104 cells with subgroup 1 (DS-1) and subgroup 2 (either Wa or P) strains, approximately 14% of the plaque-picked progeny were shown to be reassortants. During multiple passages of these coinfected cultures, however, complete (Wa virus coinfection) or nearly complete (P virus coinfection) loss of detectable DS-1 segments from progeny was observed. Thus, when all segments of the subgroup 2 viruses were present in coinfected cultures, these segments dominated in the selected progeny. Coinfection with subgroup 1-subgroup 2 rotavirus reassortants and the DS-1 strain followed by multiple passages, however, resulted in complete loss of some segments from the subgroup 2 strains originally present in the reassortants. Therefore, segments from the parental subgroup 2 viruses appeared to be selected in toto during multiple passages because they were dominant as a group, not because individual segments of these viruses were consistently favoured over their subgroup 1 virus counterparts.

Phenotypic mixing during coinfection of cells with two strains of human rotavirus

Coinfection of MA-104 cells with serotype 1 (Wa strain) and serotype 3 (P strain) human rotaviruses resulted in progeny viruses that were phenotypically mixed in their major outer-shell structural-protein VP7 and in the genome segment that encodes this protein (segment 9). Segments from the Wa virus predominated in these progeny whether they were of parental or reassortant genotype. Neutralization with monoclonal antibodies specific for VP7 proteins of the coinfecting viruses caused an alteration in genomic distribution favoring the strain heterologous to the neutralizing monoclonal antibody. Because the percentage of change in distribution of segment 9 was similar to that of the other combined segments, there appeared to be no greater association between VP7 and segment 9 than with other segments of the homologous virus during encapsulation. From these results, it was calculated that the progeny of coinfection with P segment 9 were 77.4% mosaic structures and 14.8% pseudotypes; progeny of coinfection with Wa segment 9 were 40.2% mosaic structures and 1.3% pseudotypes. Similar determinations were made for the reassortant progeny alone.

Relative concentrations of serum neutralizing antibody to VP3 and VP7 proteins in adults infected with a human rotavirus

Two outer capsid rotavirus proteins, VP3 and VP7, have been found to elicit neutralizing-antibody production, but the immunogenicity of these proteins during human rotavirus infection has not been determined. The relative amounts of serum neutralizing antibody against the VP3 and VP7 proteins of the CJN strain of human rotavirus were, therefore, determined in adult subjects before and after infection with this virus. Reassortant strains of rotavirus that contained the CJN gene segment for only one of these two neutralization proteins were isolated and used for this study. The geometric mean titer of serum neutralizing antibody to a reassortant virus (CJN-M) that contained VP7 of CJN and VP3 of another human rotavirus was 12.7 times less than that of antibody to CJN before infection and 20.3 times less after infection. This indicated that most neutralizing antibody was against the VP3 rather than the VP7 protein of CJN. This result was confirmed with other reassortants between CJN and animal rotavirus strains (EDIM and rhesus rotavirus). These findings suggest that VP3 is the primary immunogen that stimulates neutralizing antibody during at least some rotavirus infections of humans.

Reassortant formation and selection following coinfection of cultured cells with subgroup 2 human rotaviruses

Reassortant formation following coinfection has been suggested as a mechanism of evolution of rotaviruses. This study was designed to examine the selection of reassortants following coinfection of cultured cells with pairs of subgroup 2 human rotaviruses. The three pairs studied (Wa x P, CJN x 31, 62 x 69) were chosen to maximize the number of RNA segments that could be electrophoretically distinguished. After coinfection and multiple passages, reproducible selection of reassortants was observed with each pair. Although more segments were selected from the virus of a pair that grew to higher titre, certain segments were selected independently of the relative growth properties or multiplicities of infection of the coinfecting viruses; selection of other segments was dependent on both. In determining the time and cause of selection it was found that no selection of genomic RNA segments was detectable prior to or during viral particle assembly in coinfected cells. However, selection was evident within the infectious progeny population after a single cycle of replication. Therefore, selection of specific reassortants following coinfection was apparently due to differences in the infectivities of progency viruses and not in their assembly. This implies that these infectivities were a function of the parental origin of specific genomic segments.

Comparison of seven kits for detection of rotavirus in fecal specimens with a sensitive, specific enzyme immunoassay

A sensitive, specific enzyme immunoassay (SSEIA) was compared to four commercial, enzyme-linked immunosorbent assay (ELISA) kits and three latex agglutination assay (LAA) kits: (1) Rotavirus EIA, International Diagnostic Laboratories (IDL), (2) Pathfinder, Kallestadt (KAL), (3) Rotavirus Bio-EnzaBead, Litton (LIT), (4) Rotazyme II, Abbott (RTZII), (5) Slidex Rota-Kit, bioMerieux (SRK), (6) Meritec-Rotavirus, Meridian (MER), and (7) Rotalex, Medical Technology Corporation (RLX). The SSEIA was chosen as the reference method due to its greater sensitivity in comparison to immunoelectron microscopy and polyacrylamide gel electrophoreses of viral RNA segments. Upon evaluation of 136 specimens (of which 44 were positive by SSEIA), the ELISA kits (LIT, KAL, IDL, and RTZII) had sensitivities of 80%, 98%, 91% and 84%; specificities of 95%, 78%, 100%, and 88%; positive predictive values (PPV) of 88%, 68%, 100%, and 77%; and negative predictive values (NPV) of 91%, 99%, 96%, and 92%. When compared with SSEIA, the three LAA tests (SRK, MER, and RLX) had sensitivities of 73%, 75%, and 62%; specificities of 99%, 93%, and 95%; PPVs of 97%, 85%, and 84%; and NPVs of 88%, 89%, and 84%. LAA test results appeared to be reliable, if positive, but the sensitivities of these tests were less than those of the ELISA tests. The ELISA tests that employed specimen specific negative controls were superior in minimizing false positive reactions.

Characterization of virucidal agents in activated sludge

A comprehensive study was carried out to determine the properties of agents responsible for loss of virus infectivity in mixed-liquor suspended solids (MLSS) of activated sludge. Initial experiments revealed that model enteric viruses (poliovirus-1 and rotavirus SA-11) were irreversibly inactivated in MLSS and released their RNA genomes. Enteric viruses belonging to other genera (echovirus-12, coxsackievirus A13, reovirus-3) were also shown to lose infectivity in MLSS. Although the virucidal activity decreased at reduced temperatures, MLSS still retained significant activity at 4 degrees C. The virucidal agents in MLSS were stable for months at 4 degrees C, but their activity decreased approximately 50% during 4 days of aeration at 26 degrees C. Primary effluent, the nutrient source for activated sludge, also contained virucidal activity. After centrifugation of MLSS, almost all virucidal activity was found in the particulate fraction because of inhibitory substances retained in the supernatant fraction. Decreasing or increasing the solids concentration of the particulate fraction did not increase the virucidal activity of the fraction. The effects of heat and antibiotics on the virucidal activity of MLSS, coupled with the finding that the activity can be produced in autoclaved primary effluent seeded with MLSS, strongly support the conclusion that microorganisms are responsible for this activity. Attempts to characterize the virucidal microbial components of MLSS indicated that treatments that resulted in the inactivation or removal of microorganisms also caused a loss of virucidal activity. Thus, it appears that the virucidal components of microorganisms are either short-lived or active only while bound to the organisms themselves.

Human rotavirus studies in volunteers: determination of infectious dose and serological response to infection

An unpassaged, safety-tested strain (CJN) of human rotavirus from a stool specimen of a hospitalized child was administered orally to 62 adult volunteers for determination of the dose required to produce infection with or without illness. Subjects ingested doses ranging from 9 X 10(-3) to 9 X 10(4) focus-forming units in buffered salt solution after consumption of 50 ml of 4% NaHCO3. The amount of virus in the inoculum required to cause infection (shedding of virus, seroconversion, or both) in study subjects was comparable to the minimum detectable in cultures of primary monkey kidney cells. Seventeen of 30 infected subjects became ill with doses equivalent to that required for infection. Although the preinoculation titers of serum neutralizing antibody to the challenge virus in study subjects ranged from less than 1:2 to 1:1,600, the concentration of serum antibody could not be correlated with protection from infection or illness in subjects given an infectious dose of virus.

Mechanism of inactivation of enteric viruses in fresh water

Fresh water obtained from nine sources was shown to cause inactivation of poliovirus. Further testing with four of these water samples showed that enteric viruses from different genera were consistently inactivated in these freshwater samples. Studies on the cause of inactivation were conducted with echovirus type 12 as the model virus. The results revealed that the virucidal agents in the waters tested could not be separated from microorganisms. Any treatment that removed or inactivated microorganisms caused loss of virucidal activity. Microbial growth in a sterilized creek water seeded with a small amount of stream water resulted in concomitant production of virucidal activity. When individual bacterial isolates obtained from a stream were grown in this sterilized creek water, most (22 of 27) produced a large amount of virucidal activity, although the amount varied from one isolate to the next. Active and inactive isolates were represented by both gram-positive and gram-negative organisms. Examination of echoviruses inactivated in stream water revealed that loss of infectivity first correlated with a slight decrease in the sedimentation coefficient of virus particles. The cause appeared to be cleavage of viral proteins, most notably, VP-4 and, to a lesser extent, VP-1. Viral RNA associated with particles was also cleaved but the rate was slower than loss of infectivity. These results suggest that proteolytic bacterial enzymes inactivate echovirus particles in fresh water by cleavage of viral proteins, thus exposing the viral RNA to nuclease digestion.

Effect of mutation in immunodominant neutralization epitopes on the antigenicity of rotavirus SA-11

Exposure of rotavirus SA-11 to polyclonal neutralizing antibody from hyperimmunized guinea-pigs permitted selection of variants which were poorly neutralized by antisera against the parental virus. In one-way cross-neutralization experiments, at least 22 of 24 plaque-purified variants could be classified as belonging to a serotype different from that of the parent. Most antisera generated against the variants, however, readily neutralized the parental virus. This indicates that immunodominant neutralization epitopes in the parent differed from those in the variants. Changes in immunodominant epitopes caused the serotypic relationships between the variants and other strains of rotavirus to differ from those of the parental SA-11. The serotypic relatedness of human strain P (human serotype 3) was reduced while, in contrast to results found with the parental SA-11, several of the antisera against the variants recognized the bovine rotavirus NCDV as the same serotype. Causes for these changes are discussed.

Challenge with rubella virus after loss of detectable vaccine-induced antibody

Studies were conducted of experimental challenge with rubella virus in vaccinees whose possession of vaccine-induced antibody after vaccination had been documented and whose antibody level had become undetectable or very low over time. The challenge virus was the Howell strain, which had been shown to produce typical clinical and laboratory features of rubella in susceptible persons. The challenge of the vaccinees resulted in local viral replication in all but one; in viremia, a primary immunologic response, and a secondary antibody response in some; and usually in illness without a rash or in subclinical infection. The results emphasize the importance of continuing careful clinical and laboratory surveillance of vaccinees for determining the persistence of vaccine-induced immunity and of considering methods for identifying and revaccinating the minority of vaccinees who lose such immunity.

Efficiency of human rotavirus propagation in cell culture

This study was designed to find methods to reproducibly propagate human rotaviruses from fecal specimens and to determine the relationship between particle numbers and infectivity. Growth of virus was initially compared in primary and continuous lines of monkey kidney cells. Primary cells (African green and cynomolgus monkey kidney) supported virus growth directly from fecal specimens much more efficiently than did continuous lines of African green (CV-1) or rhesus (MA104) monkey kidney cells. Rotaviruses were grown in primary cells from 14 of 14 fecal specimens of different individuals collected over a 3-year period. Although rotaviruses in fecal samples could not always be grown in the continuous cell lines, two passages in primary cells appeared to fully adapt the viruses for propagation in the continuous cell line tested (MA104). The efficiency of rotavirus growth was quantified with five of the fecal isolates. It was calculated that, on the average, 1 out of every 46,000 particles in fecal specimens infected monkey kidney cells. After three passages in primary cells, an average of 1 out of every 6,600 progeny virus particles appeared to be infectious. Thus, rotaviruses in fecal specimens were consistently grown in primary cells, and passage in these cells both increased virus infectivity and adapted the viruses for growth in continuous cell lines.