First report of BVDV circulation in sheep in Argentina.

Pestiviruses are capable of infecting a wide range of animals within the order Artyodactila. Currently, the genus Pestivirus includes Bovine Viral Diarrhea Virus 1 (BVDV-1) and 2 (BVDV-2), Border Disease Virus (BDV), and Classical Swine Fever Virus (CSFV). BVDV-1, BVDV-2 and BDV are able to cross species barrier to infect a wide range of hosts, whereas CSFV is restricted to domestic pigs and wild boars. In Argentina, 70% of cattle are seropositive to BVDV. Although there were some serological studies in llamas, alpacas and buffaloes, no reports existed about the circulation of BVDV in sheep in Argentina. Based on these, 54 blood samples of healthy ovines were analysed by serology. The results showed that 46.3% of the analysed sheep were seropositive to BVDV-1, 13% to BVDV-2 and 20.4% for both BVDV-1 and BVDV-2. The molecular analysis confirmed the presence of BVDV-1a in some samples.

Detection of bovine viral diarrhoea virus (BVDV) nucleic acid and antigen in different organs of water buffaloes (Bubalus bubalis).

Bovine viral diarrhoea virus (BVDV) is a pestivirus that infects mainly bovine cattle. Nevertheless, there are several reports about infections in other members of the Artiodactyla order including serological studies, that indicate infection of BVDV in buffaloes. The aim of this article is to study the presence of BVDV in three young water buffaloes, displaying nonspecific clinical signs, compatible with the BVDV infection. Both immunohistochemistry and RT-PCR confirmed the presence of BVDV in the animals. The sequence analysis on RT-PCR amplicons revealed high identity with reference strains of genotypes 1a and 1b. Although BVDV was unequivocally identified in the sick animals, it has not been proved it is responsible for the clinical signs. Further studies are needed to clarify the pathogenic role of BVDV infection in this animal species, and the role of buffaloes in the epidemiology of BVDV infection.

Phylogenetic analysis of bovine pestiviruses: testing the evolution of clinical symptoms.

This study presents a phylogenetic analysis of 115 bovine pestiviruses. A sequence data set from the 5' untranslated genomic region was analyzed with maximum parsimony, bootstrapping and parsimony jackknifing. We tested for the proposed classifications of the group and analyzed the evolution of the symptoms associated with Pestivirus infections in bovines. Based on the historical framework provided by our phylogenetic trees, we also characterized the extent and importance of contamination caused in biologicals by the virus. Our phylogenetic analyses showed that the previously defined genotypes are monophyletic, except for genotype 1a. Based on our cladograms, we propose the existence of more than 12 monophyletic groups within the species BVDV 1. The mapping of clinical symptoms suggests that the emergence of some genotypes could have been driven by a change in the pathogenic process. Enteric Problems appear to be ancestral, while Reproductive and Respiratory Problems arise with the emergence of genotypes 1b, 1d and the herein-proposed genotype Arg 1. The distribution of contaminant strains on the cladograms shows that pestiviral contamination is a common process, and also suggests that a contaminated product might be a vehicle for virus dispersion. Implications for virus evolution, virus taxonomy, veterinary medicine and biotechnology are discussed.

Genetic typing of bovine viral diarrhea virus isolates from Argentina.

Genetic typing of 29 Bovine Viral Diarrhea Virus (BVDV) isolates from Argentina was carried out by sequencing 245 nucleotides of the RT-PCR products of the 5'-UTR region. Sequence analysis shows that these Argentinean BVDV include types 1 and 2. The majority (26/29) of the isolates are type 1, which comprises subtypes 1a and 1b, together with an additional subgroup within subtype 1a. This subgroup is close to the South African subgroup Ic of 1a viruses, and to the deer pestivirus strain "Deer". The three type 2 BVDV were isolated from fetal tissues or serum during the 7-8 years before a clinical outbreak in Argentina had been reported. Only inactivated vaccines are used in bovines of the country, thus the analysed viruses are authentic field strains. The long term circulation of type 2 BVDV (situation similar to that of North America before the epidemic of 1993), and the existence of viral populations which differ from the reference strains commonly used in vaccine elaboration should be considered by manufacturers of diagnostic reagents and vaccines.

Application of single-strand conformation polymorphism to the study of bovine viral diarrhea virus isolates.

Single-strand conformation polymorphism (SSCP) analysis of polymerase chain reaction (PCR) products is a genetic screening technique for rapid detection of nucleotide substitutions in PCR-amplified genomic DNA or cDNA. It is based on the observation that partially formamide-denatured double-stranded DNA migrates as 2 single-stranded DNA molecules when electrophoresed in nondenaturing polyacrylamide gels. The mobility depends on the 3-dimensional conformation of the strand under the conditions used. It is possible to discriminate between DNA strands differing in only 1 nucleotide. The method was applied to the analysis of Bovine Viral Diarrhea Virus (BVDV) isolates. Reference and Argentinian strains were assessed for variations in their 5' untranslated region (5'-UTR). The PCR products of the 5'-UTR ends were formamide denatured and compared by SSCP analysis in nondenaturing 15% polyacrylamide and 15% polyacrilamide-5% glycerol gels. The reference strains SD-1, Singer, and Oregon C24V had differences in electrophoretic patterns. Despite the high conservation among the 5'-UTR of pestiviruses, the method allowed discrimination among all 9 Argentinian isolates. The 5'-UTR of a fetal kidney-derived isolate (1R93) was PCR amplified and cloned in a plasmid vector; the SSCP analysis of 30 PCR products obtained by direct amplification over randomly selected clones produced 5 different banding patterns, indicating the existence of viral quasispecies. The results show that SSCP may be used to identify and differentiate among BVDV isolates.

[Contamination of bovine fetal serum with bovine viral diarrhea virus]. / Contaminación del suero fetal bovino con virus de la diarrea viral bovina.

Fetal bovine serum (FBS) used in cell culture may be contaminated with viruses, among them bovine viral diarrhea virus (BVDV) affecting the production of biological reagents and the results of diagnosis. The filtration process used in the preparation of commercial FBS abrogates most viral agents that may be present in raw FBS, but BVDV may pass through the filters because of its small size and its pleomorphism. While detection of bovine herpes virus-1 and parainfluenza-3 (PI-3) is determined by observation of the cytopathic effect, and also by hemadsorption in the case of PI-3, the most frequently isolated BVDV is non cytopathic, and infects cells without morphological alterations, inducing problems that arise after several cell generations. Batches of raw and processed FBS were analyzed. Frequencies of BVDV detection in raw serum in Argentina were similar to those published for USA. By conventional methods for BVDV detection, only 2 of 20 commercial batches of FBS had BVDV. Using cell cultures maintained with high concentrations of the serum under study for at least 2 weeks, with detection of viral antigen by indirect immunofluorescence, the percentage of BVDV detection was 80%. This method shows that most lots of commercial FBS contain BVDV. RT-PCR allows faster detection of the viral genome, but it must be validated, as it does not show viral replication. To eliminate the problem of BVDV contamination in FBS, only gamma irradiated FBS is used in our laboratory.

Contaminación del suero fetal bovino con virus de la diarrea viral bovina / Contamination of bovine fetal serum with bovine viral diarrhea virus

Fetal bovine serum (FBS) used in cell culture may be contaminated with viruses, among them bovine viral diarrhea virus (BVDV) affecting the production of biological reagents and the results of diagnosis. The filtration process used in the preparation of commercial FBS abrogates most viral agents that may be present in raw FBS, but BVDV may pass through the filters because of its small size and its pleomorphism. While detection of bovine herpes virus-1 and parainfluenza-3 (PI-3) is determined by observation of the cytopathic effect, and also by hemadsorption in the case of PI-3, the most frequently isolated BVDV is non cytopathic, and infects cells without morphological alterations, inducing problems that arise after several cell generations. Batches of raw and processed FBS were analyzed. Frequencies of BVDV detection in raw serum in Argentina were similar to those published for USA. By conventional methods for BVDV detection, only 2 of 20 commercial batches of FBS had BVDV. Using cell cultures maintained with high concentrations of the serum under study for at least 2 weeks, with detection of viral antigen by indirect immunofluorescence, the percentage of BVDV detection was 80. This method shows that most lots of commercial FBS contain BVDV. RT-PCR allows faster detection of the viral genome, but it must be validated, as it does not show viral replication. To eliminate the problem of BVDV contamination in FBS, only gamma irradiated FBS is used in our laboratory.

Contaminación del suero fetal bovino con virus de la diarrea viral bovina / Contamination of bovine fetal serum with bovine viral diarrhea virus

Fetal bovine serum (FBS) used in cell culture may be contaminated with viruses, among them bovine viral diarrhea virus (BVDV) affecting the production of biological reagents and the results of diagnosis. The filtration process used in the preparation of commercial FBS abrogates most viral agents that may be present in raw FBS, but BVDV may pass through the filters because of its small size and its pleomorphism. While detection of bovine herpes virus-1 and parainfluenza-3 (PI-3) is determined by observation of the cytopathic effect, and also by hemadsorption in the case of PI-3, the most frequently isolated BVDV is non cytopathic, and infects cells without morphological alterations, inducing problems that arise after several cell generations. Batches of raw and processed FBS were analyzed. Frequencies of BVDV detection in raw serum in Argentina were similar to those published for USA. By conventional methods for BVDV detection, only 2 of 20 commercial batches of FBS had BVDV. Using cell cultures maintained with high concentrations of the serum under study for at least 2 weeks, with detection of viral antigen by indirect immunofluorescence, the percentage of BVDV detection was 80. This method shows that most lots of commercial FBS contain BVDV. RT-PCR allows faster detection of the viral genome, but it must be validated, as it does not show viral replication. To eliminate the problem of BVDV contamination in FBS, only gamma irradiated FBS is used in our laboratory.(AU)

Contaminación del suero fetal bovino con virus de la diarrea viral bovina. / [Contamination of bovine fetal serum with bovine viral diarrhea virus]

Fetal bovine serum (FBS) used in cell culture may be contaminated with viruses, among them bovine viral diarrhea virus (BVDV) affecting the production of biological reagents and the results of diagnosis. The filtration process used in the preparation of commercial FBS abrogates most viral agents that may be present in raw FBS, but BVDV may pass through the filters because of its small size and its pleomorphism. While detection of bovine herpes virus-1 and parainfluenza-3 (PI-3) is determined by observation of the cytopathic effect, and also by hemadsorption in the case of PI-3, the most frequently isolated BVDV is non cytopathic, and infects cells without morphological alterations, inducing problems that arise after several cell generations. Batches of raw and processed FBS were analyzed. Frequencies of BVDV detection in raw serum in Argentina were similar to those published for USA. By conventional methods for BVDV detection, only 2 of 20 commercial batches of FBS had BVDV. Using cell cultures maintained with high concentrations of the serum under study for at least 2 weeks, with detection of viral antigen by indirect immunofluorescence, the percentage of BVDV detection was 80

. This method shows that most lots of commercial FBS contain BVDV. RT-PCR allows faster detection of the viral genome, but it must be validated, as it does not show viral replication. To eliminate the problem of BVDV contamination in FBS, only gamma irradiated FBS is used in our laboratory.

Biología de los priones: actualización / Prion biology: update

The word "prion" was created in 1982 to name the etiological agent of the transmissible spongiform encephalopathies (TSE), a group of degenerative diseases affecting central nervous system of man and animals, including bovine spongiform encephalopathy (BSE) and variant Creutzfeldt-Jakob disease (vCJD). Prions present two isoforms: PrPC, cellular or normal, which exists in all vertebrates and is sensitive to detergents and proteases, and PrPSc, disease associated, partially resistant. The molecular weight of both PrPC and PrPSc is 30-35 kD; after treatment with detergents and proteases PrPSc originates PrP27-30 (27-30 kD). PrPC is also denominated PrPsens, and PrPSc is PrPres. PrPSc and PrP27-30 cause disease. PrPC presents polymorphisms specifically associated with some TSE. The "prion hypothesis" says that PrPSc transmits its characteristic resistance to PrPC through conformational changes, and accumulation of the protein, without involvement of nucleic acids, causes disease. Most of the hypothesis has been demonstrated with transgenic mice, computer models and recombinant proteins, but the existence of strains of the TSE agents has not been explained. The description of similar mechanisms of propagation of protein conformational properties in Saccharomyces cereviseae has extended the meaning of the prion definition. Although the transmission of conformational changes between PrPC and PrPSc was experimentally shown, the pathogenesis of the TSE remains unknown. The relationship between BSE and vCJD is mentioned.

Biología de los priones: actualización / Prion biology: update

The word "prion" was created in 1982 to name the etiological agent of the transmissible spongiform encephalopathies (TSE), a group of degenerative diseases affecting central nervous system of man and animals, including bovine spongiform encephalopathy (BSE) and variant Creutzfeldt-Jakob disease (vCJD). Prions present two isoforms: PrPC, cellular or normal, which exists in all vertebrates and is sensitive to detergents and proteases, and PrPSc, disease associated, partially resistant. The molecular weight of both PrPC and PrPSc is 30-35 kD; after treatment with detergents and proteases PrPSc originates PrP27-30 (27-30 kD). PrPC is also denominated PrPsens, and PrPSc is PrPres. PrPSc and PrP27-30 cause disease. PrPC presents polymorphisms specifically associated with some TSE. The "prion hypothesis" says that PrPSc transmits its characteristic resistance to PrPC through conformational changes, and accumulation of the protein, without involvement of nucleic acids, causes disease. Most of the hypothesis has been demonstrated with transgenic mice, computer models and recombinant proteins, but the existence of strains of the TSE agents has not been explained. The description of similar mechanisms of propagation of protein conformational properties in Saccharomyces cereviseae has extended the meaning of the prion definition. Although the transmission of conformational changes between PrPC and PrPSc was experimentally shown, the pathogenesis of the TSE remains unknown. The relationship between BSE and vCJD is mentioned.(AU)

[Prion biology: update]. / Biología de los priones: actualización.

The word "prion" was created in 1982 to name the etiological agent of the transmissible spongiform encephalopathies (TSE), a group of degenerative diseases affecting central nervous system of man and animals, including bovine spongiform encephalopathy (BSE) and variant Creutzfeldt-Jakob disease (vCJD). Prions present two isoforms: PrPC, cellular or normal, which exists in all vertebrates and is sensitive to detergents and proteases, and PrPSc, disease associated, partially resistant. The molecular weight of both PrPC and PrPSc is 30-35 kD; after treatment with detergents and proteases PrPSc originates PrP27-30 (27-30 kD). PrPC is also denominated PrPsens, and PrPSc is PrPres. PrPSc and PrP27-30 cause disease. PrPC presents polymorphisms specifically associated with some TSE. The "prion hypothesis" says that PrPSc transmits its characteristic resistance to PrPC through conformational changes, and accumulation of the protein, without involvement of nucleic acids, causes disease. Most of the hypothesis has been demonstrated with transgenic mice, computer models and recombinant proteins, but the existence of strains of the TSE agents has not been explained. The description of similar mechanisms of propagation of protein conformational properties in Saccharomyces cereviseae has extended the meaning of the prion definition. Although the transmission of conformational changes between PrPC and PrPSc was experimentally shown, the pathogenesis of the TSE remains unknown. The relationship between BSE and vCJD is mentioned.

[Bovine diarrhea virus: an update]. / Virus de la diarrea viral bovina: una actualización.

Bovine Viral Diarrhea Virus (BVDV) is a pathogen of cattle, member of the family Flaviviridae, genus pestivirus, which also includes Classical Swine Fever Virus (CSFV, or hog cholera virus), and Border Disease Virus of sheep (BDV). It causes important economical losses associated mainly with reproductive failure. Pestiviruses are small enveloped viruses, with a diameter of about 40 nm. The nucleocapsid is probably icosahedral . The genome consists of a single stranded positive RNA, encoding approximately 430 kD of proteic product. Genetic expression consists of the synthesis of a polyprotein which is co- and post-translationally processed. According to its behavior "in vitro" two biotypes can be distinguished: non cytopathic (ncp) and cytopathic (cp), most probably derived from the ncp through mutations and/or recombination. BVDV is able to cross the placenta and infect the fetus, causing a variety of problems, from fetal death to the birth of a persistently infected (P) calf, according to the fetal age at the time of infection. PI animals are immunotolerant to the virus and shed it in all secretions. Only the ncp biotype has been isolated from PI animals. The superinfection of a PI animal with a cp strain causes mucosal disease, always fatal. Outbreaks of a severe, sometimes hemorrhagic disease, caused by ncp BVDV, have occurred in Canada and USA since 1993. Genomic and serological differences between the "traditional" strains and the viruses isolated from these outbreaks led to the division of BVDV in subtypes I and II, both including cp and ncp strains. Analyses of the non coding 5'-UTR zone of the genome of pestiviruses from different species (bovine, ovine, porcine) suggest that there are at least 3 genotypes within the genus. A new classification of these viruses, based on genomic sequence instead of species of origin, has been proposed. Genomic heterogeneity exists in the BVDV genome, which presents 3 hypervariable zones, 2 of them in the major neutralizing protein. In Argentina prevalence of BVDV antibodies in cattle population is 70%, and the prevalence of persistent infections is around 1%.

Foetal infections with bovine viral diarrhoea virus in Argentina.

The frequency of isolation of bovine viral diarrhoea virus (BVDV) from primary tissue cultures and organs from bovine foetuses was studied between 1992 and 1994. Around 25% of primary tissue cultures were BVDV positive. Primary testis cultures were inoculated with homogenates of spleen, kidney, lung and liver from 52 foetuses. Cells were passaged twice and BVDV antigen investigated by indirect immunofluorescence. Non-cytopathic BVDV was detected in at least one organ in 11/52 foetuses (21.2%): 6/10 spleens, 4/7 kidneys, 7/9 lungs and 3/5 livers. Cytopathic BVDV was detected in lung and kidney from two foetuses. Since only gamma-irradiated sera are used in the laboratory and only inactivated BVDV vaccines are applied in Argentina, it was concluded that these isolations represented field infections. In addition to the 11 virus positive foetuses, two foetuses were positive for BVDV antibodies, which suggested a 25% prevalence of infection. These results stress the need for disease control on a herd basis and the requirement for biological reagents of bovine origin for the detection of BVDV.

Bovine spongiform encephalopathy surveillance in Argentina.

Bovine spongiform encephalopathy (BSE) is a new disease of cattle first described in the United Kingdom in November 1986. BSE belongs to the scrapie-related group of diseases. The epidemiological studies performed in the United Kingdom demonstrate that the BSE epidemic was caused by feeding cattle with ruminant-derived protein contaminated by a scrapie-like agent. Until June 1994, the disease had been detected in indigenous cattle in Ireland, Switzerland and France. Three cases reported in Germany, two in the Sultanate of Oman, and single cases in the Falkland Islands (Islas Malvinas), Denmark, Portugal and Canada occurred in animals imported from the United Kingdom. Several countries have implemented surveillance programmes analysing the risk factors involved in the epidemic. An analysis of risk factors conducted in Argentina shows that it is highly unlikely that BSE or scrapie exist in the country, or will arise via feed in the future. As a continuation of the analysis of risk factors, a surveillance programme was implemented in the field and in abattoirs. Specialised personnel were trained in the clinical, histopathological and biochemical detection of the disease through a network of laboratories which covered 85% of the total cattle population and 100% of the high-risk group (dairy cows over five years of age). By using a statistical procedure with reference to the bovine population in nine provinces, 1,019 brains from animals belonging to the high-risk group were selected and studied by histopathological and biochemical analyses for BSE detection. The results were negative in all cases. It can be concluded from this analysis (with a sensitivity of detection of 2.95 per 1,000, and 95% statistical confidence) that Argentina may be regarded as BSE-free, and that the importation of infected animals or by-products may represent the sole potential source of introduction of BSE infection into the country in the future.

Viral antibodies in bovine fetuses in Argentina.

In order to establish the prevalence of viral infections of the bovine fetus in Argentina, a serological survey for antibodies against viral agents currently affecting cattle in this country was conducted. Antibodies against foot-and-mouth disease virus (FMDV), bovine herpesvirus-1 (BHV-1), bovine leukaemia virus (BLV), bovine rotavirus (BRV), bovine coronavirus (BCV), bovine viral diarrhoea virus (BVDV) and parainfluenza-3 (PI-3) were investigated in a total of 315 fetal serum samples. Conventional techniques were used: indirect immunofluorescence (FMDV, BHV-1, BVDV and BCV), radial immunodiffusion (BLV), ELISA (BRV) and haemagglutination inhibition (PI-3). Antibodies against BHV-1, BVDV and PI-3 were detected in samples from fetuses in the second and third trimester of gestation, with a prevalence of 1.21 per cent (two of 165), 2.03 per cent (four of 197) and 5.08 per cent (nine of 177), respectively. Either antibodies or non-antibody factors able to bind to BRV and BCV antigens were detected with a prevalence of 2.44 per cent (five of 205) and 4.54 per cent (five of 110), respectively. In addition, 14.68 per cent of non-specific inhibitors of PI-3 mediated haemagglutination were found. No seropositives against FMDV and BLV were detected.

Fine mapping of a peptide sequence containing an antigenic site conserved among arenaviruses.

The lymphocytic choriomeningitis virus (LCMV) structural glycoproteins GP-1 (Mr 44K) and GP-2 (Mr 35K) are encoded on a single intracellular proteolytic cleavage precursor glycoprotein, GP-C (Mr 76K). We have used a series of synthetic peptides derived from the deduced amino acid sequence of LCMV GP-C to define an antigenic site containing two topographically overlapping epitopes. Three mouse monoclonal antibodies directed against two epitopes on GP-2 were assayed for binding in solution phase blocking and solid-phase enzyme-linked immunoadsorbant assays to a series of peptides representing the sequence of the intracellular precursor glycopeptide GP-C. Both epitopes were initially localized to a single peptide GP-C 370-382 (Cys-Asn-Tyr-Ser-Lys-Phe-Trp-Tyr-Leu-Glu-His-Ala-Lys) in the GP-2 segment of GP-C. Further analysis demonstrated that both epitopes were contained within a nine amino acid segment, GP-C 370-378, which contains five residues conserved among LCMV, Lassa, Pichinde, and Tacaribe viruses. Assays with N-terminal deletions from this sequence suggested that the minimal epitope recognized by the broadly cross-reactive monoclonal 33.6 (epitope GP-2a) consisted of five amino acids, GP-C 374-378 (Lys-Phe-Trp-Tyr-Leu). Reactivity of a second monoclonal, 9-7.9 (epitope GP-2B) but not 33.6, was abolished when substitution of tyrosine for phenylalanine was made at position 375 in the antigenic sequence corresponding to a naturally occurring sequence difference between LCM and Lassa viruses. Polyclonal sera from human cases and from animals experimentally infected with Junin, LCM, and Lassa viruses, respectively, bound to the antigenic peptide GP-C 370-382 but not to control peptides. As was the case with the monoclonals, this binding activity was abrogated by blocking with the antigenic peptide but not with control peptides in solution.

MRC-5 cells, a model for Junín virus persistent infection.

Persistent infection of MRC-5 cells was established following inoculation with attenuated Junín virus (JV). In the acute phase of the infection both the pathogenic XJ and the attenuated XJ0 and XJC13 strains showed severe c.p.e. and free viral titres reached 10(5) p.f.u./ml. Recovery and establishment of persistently infected MRC-5 sublines (MRC-5PI) proved a very common event and seemed to be independent of viral strain, m.o.i. employed or virus passage history. These MRC-5PI sublines released virus throughout their life span and infectious centre assays performed at different passage levels with two sublines showed that 5 to 9% of the cells were producing virus. Heterotypic but not heterologous resistance to superinfection developed, as observed in persistent JV-heteroploid cell systems. Analysis of released JV showed that attenuation had not been markedly altered, but alteration in plaque morphology under methyl cellulose, appearance of temperature-sensitive mutants and alterations in mouse pathology imply that some properties of JV have been altered. Results presented here stress once again the ability of JV to establish persistent infections. The source and diploid characteristics of MRC-5 cells make them a satisfactory model for JV persistence studies.

Attenuated Junin virus infection in Callithrix jacchus.

Twenty marmosets, male Callithrix jacchus, were used during this study. Fifteen of the marmosets were inoculated with 5,000 TCID50 of the attenuated XJC13 strain of Junin virus by intramuscular route and five were left as uninoculated controls. Animals were observed for a 420-day period. In order to carry out virologic, hematologic, serologic, and histologic studies the animals were bled and/or killed at different days post infection(pi). Results obtained showed that the attenuated strain produced an infection with no mortality or signs of illness. There was only a slight loss of weight at 18-40 days pi, which was soon recovered. Viremia was present from day 6 to 22, titers peaking at 4.0 log. Viral spread was limited to the lungs, spleen, lymph nodes, and bone marrow in the animal killed on day 14. No virus was found in the organs of the animal killed on day 23, and neither hematologic alterations nor pathologic lesions were seen in these monkeys except for ganglionar hypertrophy with immunoblast proliferation. Antigen was detected by immunofluorescence (IF) in lymph nodes, spleen, adrenals, lungs and brain. Neutralizing antibodies were detected from the third week onward. Protection conferred by the XJC13 strain proved effective when XJC13-inoculated monkeys were challenged with 1,000 TCID50 of the pathogenic XJ strain at days 60 or 380 pi, while normal controls died. When viral persistence was searched for on days 370, 390, and 420 pi, no infectious virus was detected, but viral antigen was seen in certain organs, which, however, lacked tissue damage.(ABSTRACT TRUNCATED AT 250 WORDS)