cis-Acting Element at the 5' Noncoding Region of Tacaribe Virus S RNA Modulates Genome Replication

Tacaribe virus (TCRV) is the prototype of New World mammarenaviruses, a group that includes several members that cause hemorrhagic fevers in humans. The TCRV genome comprises two RNA segments, named S (small) and L (large). Both genomic segments contain noncoding regions (NCRs) at their 5' and 3' ends. While the 5'- and 3'-terminal 19-nucleotide sequences are known to be essential for promoter function, the role of their neighboring internal noncoding region (iNCR) sequences remains poorly understood. To analyze the relevance of the 5' and 3' iNCRs in TCRV S RNA synthesis, mutant S-like minigenomes and miniantigenomes were generated. Using a minireplicon assay, Northern blotting, and reverse transcription-quantitative PCR, we demonstrated that the genomic 5' iNCR is specifically engaged in minigenome replication yet is not directly involved in minigenome transcription, and we showed that the S genome 3' iNCR is barely engaged in this process. Analysis of partial deletions and point mutations, as well as total or partial substitution of the 5' iNCR sequence, led us to conclude that the integrity of the whole genomic 5' iNCR is essential and that a local predicted secondary structure or RNA-RNA interactions between the 5' and 3' iNCRs are not strictly required for viral S RNA synthesis. Furthermore, we employed a TCRV reverse genetic approach to ask whether manipulation of the S genomic 5' iNCR sequence may be suitable for viral attenuation. We found that mutagenesis of the 5' promoter-proximal subregion slightly impacted recombinant TCRV virulence in vivo. IMPORTANCE The Mammarenavirus genus of the Arenaviridae family includes several members that cause severe hemorrhagic fevers associated with high morbidity and mortality rates, for which no FDA-approved vaccines and limited therapeutic resources are available. We provide evidence demonstrating the specific involvement of the TCRV S 5' noncoding sequence adjacent to the viral promoter in replication. In addition, we examined the relevance of this region in the context of an in vivo infection. Our findings provide insight into the mechanism through which this 5' viral RNA noncoding region assists the L polymerase for efficient viral S RNA synthesis. Also, these findings expand our understanding of the effect of genetic manipulation of New World mammarenavirus sequences aimed at the rational design of attenuated recombinant virus vaccine platforms.

Glycoprotein N-linked glycans play a critical role in arenavirus pathogenicity

Several arenaviruses cause hemorrhagic fevers in humans with high case fatality rates. A vaccine named Candid#1 is available only against Junin virus (JUNV) in Argentina. Specific N-linked glycans on the arenavirus surface glycoprotein (GP) mask important epitopes and help the virus evade antibody responses. However the role of GPC glycans in arenavirus pathogenicity is largely unclear. In a lethal animal model of hemorrhagic fever-causing Machupo virus (MACV) infection, we found that a chimeric MACV with the ectodomain of GPC from Candid#1 vaccine was partially attenuated. Interestingly, mutations resulting in acquisition of N-linked glycans at GPC N83 and N166 frequently occurred in late stages of the infection. These glycosylation sites are conserved in the GPC of wild-type MACV, indicating that this is a phenotypic reversion for the chimeric MACV to gain those glycans crucial for infection in vivo. Further studies indicated that the GPC mutant viruses with additional glycans became more resistant to neutralizing antibodies and more virulent in animals. On the other hand, disruption of these glycosylation sites on wild-type MACV GPC rendered the virus substantially attenuated in vivo and also more susceptible to antibody neutralization, while loss of these glycans did not affect virus growth in cultured cells. We also found that MACV lacking specific GPC glycans elicited higher levels of neutralizing antibodies against wild-type MACV. Our findings revealed the critical role of specific glycans on GPC in arenavirus pathogenicity and have important implications for rational design of vaccines against this group of hemorrhagic fever-causing viruses.

Several arenaviruses cause severe hemorrhagic fevers in humans. The only vaccine against arenavirus infections is Candid#1, a live attenuated vaccine against Argentine hemorrhagic fever. So far, we have successfully attenuated additional one of the arenaviruses, Machupo virus, the causative agent of Bolivian hemorrhagic fever. Unraveling this attenuation mechanism might help the development of live-attenuated vaccines for other arenaviruses. In this study, we revealed that the specific glycans of the viral glycoproteins play an important role in pathogenicity in vivo. The glycans facilitate the virus to evade neutralizing antibodies. This study would contribute to the development of arenavirus vaccine candidates.

TRIM2, a novel member of the antiviral family, limits New World arenavirus entry

Tripartite motif (TRIM) proteins belong to a large family with many roles in host biology, including restricting virus infection. Here, we found that TRIM2, which has been implicated in cases of Charcot-Marie-Tooth disease (CMTD) in humans, acts by blocking hemorrhagic fever New World arenavirus (NWA) entry into cells. We show that Trim2-knockout mice, as well as primary fibroblasts from a CMTD patient with mutations in TRIM2, are more highly infected by the NWAs Junín and Tacaribe virus than wild-type mice or cells are. Using mice with different Trim2 gene deletions and TRIM2 mutant constructs, we demonstrate that its antiviral activity is uniquely independent of the RING domain encoding ubiquitin ligase activity. Finally, we show that one member of the TRIM2 interactome, signal regulatory protein α (SIRPA), a known inhibitor of phagocytosis, also restricts NWA infection and conversely that TRIM2 limits phagocytosis of apoptotic cells. In addition to demonstrating a novel antiviral mechanism for TRIM proteins, these studies suggest that the NWA entry and phagocytosis pathways overlap.

Involvement of Pro-Inflammatory Macrophages in Liver Pathology of Pirital Virus-Infected Syrian Hamsters

New World arenaviruses cause fatal hemorrhagic disease in South America. Pirital virus (PIRV), a mammarenavirus hosted by Alston’s cotton rat (Sigmodon alstoni), causes a disease in Syrian golden hamsters (Mesocricetus auratus) (biosafety level-3, BSL-3) that has many pathologic similarities to the South American hemorrhagic fevers (BSL-4) and, thus, is considered among the best small-animal models for human arenavirus disease. Here, we extend in greater detail previously described clinical and pathological findings in Syrian hamsters and provide evidence for a pro-inflammatory macrophage response during PIRV infection. The liver was the principal target organ of the disease, and signs of Kupffer cell involvement were identified in mortally infected hamster histopathology data. Differential expression analysis of liver mRNA revealed signatures of the pro-inflammatory response, hematologic dysregulation, interferon pathway and other host response pathways, including 17 key transcripts that were also reported in two non-human primate (NHP) arenavirus liver-infection models, representing both Old and New World mammarenavirus infections. Although antigen presentation may differ among rodent and NHP species, key hemostatic and innate immune-response components showed expression parallels. Signatures of pro-inflammatory macrophage involvement in PIRV-infected livers included enrichment of Ifng, Nfkb2, Stat1, Irf1, Klf6, Il1b, Cxcl10, and Cxcl11 transcripts. Together, these data indicate that pro-inflammatory macrophage M1 responses likely contribute to the pathogenesis of acute PIRV infection.

An attenuated Machupo virus with a disrupted L-segment intergenic region protects guinea pigs against lethal Guanarito virus infection

Machupo virus (MACV) is a New World (NW) arenavirus and causative agent of Bolivian hemorrhagic fever (HF). Here, we identified a variant of MACV strain Carvallo termed Car91 that was attenuated in guinea pigs. Infection of guinea pigs with an earlier passage of Carvallo, termed Car68, resulted in a lethal disease with a 63% mortality rate. Sequencing analysis revealed that compared to Car68, Car91 had a 35 nucleotide (nt) deletion and a point mutation within the L-segment intergenic region (IGR), and three silent changes in the polymerase gene that did not impact amino acid coding. No changes were found on the S-segment. Because it was apathogenic, we determined if Car91 could protect guinea pigs against Guanarito virus (GTOV), a distantly related NW arenavirus. While naïve animals succumbed to GTOV infection, 88% of the Car91-exposed guinea pigs were protected. These findings indicate that attenuated MACV vaccines can provide heterologous protection against NW arenaviruses. The disruption in the L-segment IGR, including a single point mutant and 35 nt partial deletion, were the only major variance detected between virulent and avirulent isolates, implicating its role in attenuation. Overall, our data support the development of live-attenuated arenaviruses as broadly protective pan-arenavirus vaccines.

[Study of sensitivity of laboratory animals to a causative agent of argentine hemorrhagic fever]

AIM

Study sensitivity of laboratory animals to a causative agent ofArgentine hemorrhagic fever.

MATERIALS AND METHODS

Junin virus strain XJ P37 was obtained from the State Collection of Causative Agents of Viral Hemorrhagic Fevers of the Pathogenicity Group I of Scientific Research Center of the 33rd Central Scientific Research Test Institute (SRC of the 33rd CSRTI). Junin virus strain XJ P37 culture with biological activity of 5.2 1g PFU x ml was used in the experiments. Mice (2 - 4 and 7 - 14 days old), guinea pigs (250 - 300 g), 1.8 - 2.5 kg shinshilla breed rabbits, 2.0 - 3.0 kg javanese macaque monkeys were obtained from vivarium of the SRC of the 33rd CSRTI. Vero (B) and GMK-AH-1 (D) cell cultures were obtained from cell culture collection of the SRC of the 33rd CSRTI. Biological activity calculation of Junin virus was carried out by Kerber in I.P. Amsharin modification.

RESULTS

Lethality in animals was from 12.5 to 50% after intranasal and intraperitoneal infection of guinea pigs, intramuscular, intraperitoneal and subcutaneous infection of rabbits, intracerebral and intranasal infection of mice at the doses from 0.4 to 1.0 x 10(5) PFU. Death of infected monkeys after intramuscular administration of the virus at 1.0 x 10(4) PFU dose was not observed. In 100% of surviving animals formation of virus-neutralizing antibodies was registered.

CONCLUSION

Evaluation of sensitivity of laboratory animals to Junin virus has shown that intracerebrally infected mice may be used to maintain causative agent culture, infected guinea pigs - to prepare virus-containing cultures and modelling infection exacerbation in humans. Intramuscularly infected rabbits may be used to obtain hyper-immune sera.

Epidemiology and pathogenesis of Bolivian hemorrhagic fever

The etiologic agent of Bolivian hemorrhagic fever (BHF), Machupo virus (MACV) is reported to have a mortality rate of 25-35%. First identified in 1959, BHF was the cause of a localized outbreak in San Joaquin until rodent population controls were implemented in 1964. The rodent Calomys collosus was identified as the primary vector and reservoir for the virus. Multiple animal models were considered during the 1970s with the most human-like disease identified in Rhesus macaques but minimal characterization of the pathogenesis has been published since. A reemergence of reported BHF cases has been reported in recent years, which necessitates the further study and development of a vaccine to prevent future outbreaks.

Comparative analysis of disease pathogenesis and molecular mechanisms of New World and Old World arenavirus infections

Arenaviruses can cause fatal human haemorrhagic fever (HF) diseases for which vaccines and therapies are extremely limited. Both the New World (NW) and Old World (OW) groups of arenaviruses contain HF-causing pathogens. Although these two groups share many similarities, important differences with regard to pathogenicity and molecular mechanisms of virus infection exist. These closely related pathogens share many characteristics, including genome structure, viral assembly, natural host selection and the ability to interfere with innate immune signalling. However, members of the NW and OW viruses appear to use different receptors for cellular entry, as well as different mechanisms of virus internalization. General differences in disease signs and symptoms and pathological lesions in patients infected with either NW or OW arenaviruses are also noted and discussed herein. Whilst both the OW Lassa virus (LASV) and the NW Junin virus (JUNV) can cause disruption of the vascular endothelium, which is an important pathological feature of HF, the immune responses to these related pathogens seem to be quite distinct. Whereas LASV infection results in an overall generalized immune suppression, patients infected with JUNV seem to develop a cytokine storm. Additionally, the type of immune response required for recovery and clearance of the virus is different between NW and OW infections. These differences may be important to allow the viruses to evade host immune detection. Understanding these differences will aid the development of new vaccines and treatment strategies against deadly HF viral infections.

Dual host-virus arms races shape an essential housekeeping protein

Relentless selective pressures exerted by viruses trigger arms race dynamics that shape the evolution of even critical host genes like those involved in iron homeostasis.

Transferrin Receptor (TfR1) is the cell-surface receptor that regulates iron uptake into cells, a process that is fundamental to life. However, TfR1 also facilitates the cellular entry of multiple mammalian viruses. We use evolutionary and functional analyses of TfR1 in the rodent clade, where two families of viruses bind this receptor, to mechanistically dissect how essential housekeeping genes like TFR1 successfully balance the opposing selective pressures exerted by host and virus. We find that while the sequence of rodent TfR1 is generally conserved, a small set of TfR1 residue positions has evolved rapidly over the speciation of rodents. Remarkably, all of these residues correspond to the two virus binding surfaces of TfR1. We show that naturally occurring mutations at these positions block virus entry while simultaneously preserving iron-uptake functionalities, both in rodent and human TfR1. Thus, by constantly replacing the amino acids encoded at just a few residue positions, TFR1 divorces adaptation to ever-changing viruses from preservation of key cellular functions. These dynamics have driven genetic divergence at the TFR1 locus that now enforces species-specific barriers to virus transmission, limiting both the cross-species and zoonotic transmission of these viruses.

Genetic differences between mammalian species dictate the patterns of viral infection observed in nature. They also define how viruses must evolve in order to infect new mammalian hosts, giving rise to new and sometimes pandemic diseases. Because viruses must enter cells before they can replicate, new diseases often emerge when existing viruses evolve the ability to bind to the cell-surface receptor of a new species. At the same time, host cell receptors also evolve to counteract virus attacks. This back-and-forth evolution between virus and host can lead to an arms race that shapes the sequences of the proteins involved. In wild rodent populations, the retrovirus MMTV and New World arenaviruses both exploit Transferrin Receptor 1 (TfR1) to enter the cells of their hosts. Here we show that the physical interactions between these viruses and TfR1 have triggered evolutionary arms race dynamics that have directly modified the sequence of TfR1 and at least one of the viruses involved. Computational evolutionary analysis allowed us to identify specific residues in TfR1 that define patterns of viral infection in nature. The approach presented here can theoretically be applied to the study of any virus, through analysis of host genes known to be key to controlling viral infection. As such, this approach can expand our understanding of how viruses emerge from wildlife reservoirs, and how they drive the evolution of host genes.

[Bolivian hemorrhagic fever]

Analysis of data of the available literature on epidemiology of Bolivian hemorrhagic fever, manifestations of human disease, biological properties of the causative agent and development carried out abroad of means and methods of diagnostics, prophylaxis and therapy of this infection that presents a potential threat for the population and economy of the Russian Federation in case of introduction of the causative agent is presented.

Z proteins of New World arenaviruses bind RIG-I and interfere with type I interferon induction

The retinoic acid-inducible gene I product (RIG-I) is a cellular sensor of RNA virus infection that regulates the cellular beta interferon (IFN-beta) response. The nucleoproteins (NP) of arenaviruses are reported to antagonize the IFN response by inhibiting interferon regulatory factor 3 (IRF-3). Here, we demonstrate that the Z proteins of four New World (NW) arenaviruses, Guanarito virus (GTOV), Junin virus (JUNV), Machupo virus (MAVC), and Sabia virus (SABV), bind to RIG-I, resulting in downregulation of the IFN-beta response. We show that expression of the four NW arenavirus Z proteins inhibits IFN-beta mRNA induction in A549 cells in response to RNA bearing 5' phosphates (5'pppRNA). NW arenavirus Z proteins interact with RIG-I in coimmunoprecipitation studies and colocalize with RIG-I. Furthermore, expression of Z proteins interferes with the interaction between RIG-I and MAVS. Z expression also impedes the nuclear factor kappa light chain enhancer of activated B cells (NF-kappaB) and IRF-3 activation. Our results indicate that NW arenavirus Z proteins, but not Z protein of the Old World (OW) arenavirus lymphocytic choriomeningitis virus (LCMV) or Lassa virus, bind to RIG-I and inhibit downstream activation of the RIG-I signaling pathway, preventing the transcriptional induction of IFN-beta.

Host-species transferrin receptor 1 orthologs are cellular receptors for nonpathogenic new world clade B arenaviruses

The ability of a New World (NW) clade B arenavirus to enter cells using human transferrin receptor 1 (TfR1) strictly correlates with its ability to cause hemorrhagic fever. Amapari (AMAV) and Tacaribe (TCRV), two nonpathogenic NW clade B arenaviruses that do not use human TfR1, are closely related to the NW arenaviruses that cause hemorrhagic fevers. Here we show that pseudotyped viruses bearing the surface glycoprotein (GP) of AMAV or TCRV can infect cells using the TfR1 orthologs of several mammalian species, including those of their respective natural hosts, the small rodent Neacomys spinosus and the fruit bat Artibeus jamaicensis. Mutation of one residue in human TfR1 makes it a functional receptor for TCRV, and mutation of four residues makes it a functional receptor for AMAV. Our data support an in vivo role for TfR1 in the replication of most, if not all, NW clade B arenaviruses, and suggest that with modest changes in their GPs the nonpathogenic arenaviruses could use human TfR1 and emerge as human pathogens.

Differences in tropism and pH dependence for glycoproteins from the Clade B1 arenaviruses: implications for receptor usage and pathogenicity

The Clade B lineage of the New World arenaviruses contains four viruses capable of causing severe hemorrhagic fevers in humans. Within this group, the B1 sub-lineage contains the pathogenic viruses Junin (JUNV) and Machupo (MACV), as well as the non-pathogenic Tacaribe virus (TCRV). In order to elucidate differences that may determine pathogenicity, we studied the entry pathways directed by the glycoproteins (GPs) from these related B1 viruses, using pseudotyped retroviral vectors and GP1 immunoadhesin constructs. Our data revealed variations in the efficiency with which different cell types could be transduced by B1 vectors, and this correlated with the ability of the immunoadhesins to bind to those cells. Interestingly, the tropism directed by the TCRV GP proved to be distinct from that of JUNV and MACV, in particular on lymphocyte cell lines. In addition, the GPs showed variations in their sensitivity to an inhibitor of endosome acidification, with the TCRV GP again being the outlier. Together these data suggest that more than one entry pathway can be used by these closely related viruses and that the ability to cause human disease may be highly dependent on receptor usage.

[Hemorrhagic (Marburg, Ebola, Lassa, and Bolivian) fevers: epidemiology, clinical pictures, and treatment]

The evaluation of the biological and epidemiological properties of Ebola, Marburg, Lassa, and Machupo viruses suggests that they are of social importance for health care authorities. The studies have created prerequisites to the development of reliable biosafety means against these pathogens. Particular emphasis is laid on the methods for infection diagnosis and on the studies to design specific protective agents--immunoglobulins and inactivated vaccines.

Clinical laboratory, virologic, and pathologic changes in hamsters experimentally infected with Pirital virus (Arenaviridae): a rodent model of Lassa fever

The clinical laboratory, virologic, and pathologic changes occurring in hamsters after infection with Pirital virus (Arenaviridae) are described. Pirital virus infection in the hamsters was characterized by high titered viremia, leukocytosis, coagulopathy, pulmonary hemorrhage and edema, hepatocellular and splenic necrosis, and marked elevation of serum transaminase levels. All of the animals died within 9 days. The clinical and histopathological findings in the Pirital virus-infected hamsters were very similar to those reported in severe human cases of Lassa fever, suggesting that this new animal model could serve as a low-cost and relatively safe alternative for studying the pathogenesis and therapy of Lassa fever.

CpG oligodeoxynucleotides protect newborn mice from a lethal challenge with the neurotropic Tacaribe arenavirus

The innate immune system is key to limiting the early spread of most pathogens and directing the development of Ag-specific immunity. Recently, a number of synthetic molecules that activate the innate immune system by stimulating TLRs have been identified. Among them, synthetic oligodeoxynucleotides (ODNs) containing unmethylated CpG motifs (CpG ODNs) were shown to activate TLR9-bearing B cells, macrophages, and dendritic cells to induce a strong proinflammatory milieu and a type 1-biased immune response that protects mice from a variety of parasitic, bacterial, and viral infections. Although the protective effect of CpG ODN in adult mice was well established, its effectiveness in neonates, which have lower numbers of dendritic, B, and T cells and tend to favor Th2 responses, was unclear. This study uses the New World arenavirus Tacaribe, a neurotropic pathogen that is lethal in newborn mice, to explore the effectiveness of TLR-mediated innate immune responses. Neonatal BALB/c mice treated with CpG ODN at the time of infection had reduced viral load (p < 0.01) and increased survival (52%, p < 0.001 i.p.; 36%, p < 0.05 intranasally). Protection was achieved in mice treated no later than 3 days postchallenge and appears to be mediated by an increase in Ag-specific Abs (IgG and IgM) and to require inducible NO synthase expression and NO production. To our knowledge, this is the first study assessing the mechanisms by which CpG ODN can protect mice from a neurotropic viral infection.

Preventive and therapeutic approaches to viral agents of bioterrorism

Certain viruses, such as those that cause smallpox and hemorrhagic fevers, have been identified as possible bioterrorism agents by the Centers for Disease Control and Prevention. They have been designated as potential threats because large quantities can be propagated in cell culture, they are transmissible as aerosols and, for the most part, there are only limited vaccine and pharmaceutical strategies for either prevention or treatment of established infection. An additional concern is the potential to genetically modify these agents to enhance virulence or promote resistance to vaccines or identified antivirals. Although the major impact of these agents is human illness, the release of zoonotic agents, such as the Nipah virus, would have consequences for both humans and animals because infected and noninfected animals might need to be sacrificed to control the spread of infection. Continued research is necessary to develop effective strategies to limit the impact of these biological threats.

Role of the endothelium in viral hemorrhagic fevers

OBJECTIVE

To describe endothelial participation in the pathogenesis of viral hemorrhagic fevers and certain other acute infectious diseases.

DATA EXTRACTION AND SYNTHESIS

Survey of published literature on viral hemorrhagic fevers interpreted in light of observations in patients and research on those diseases.

CONCLUSIONS

Endothelial involvement is an extremely important factor in the clinical syndrome termed viral hemorrhagic fever. Endothelial dysfunction is important in the genesis of bleeding, which is not universal and is commonly seen only in the presence of thrombocytopenia or severe platelet dysfunction. The pathogenesis of endothelial dysfunction varies in the different diseases. In some situations, direct endothelial infection is important in increased vascular permeability, changes in the procoagulant vs. anticoagulant balance, or cytokine production. In all the viral hemorrhagic fevers studied to date, cytokine induction is an important factor and also acts on the endothelium. Poor myocardial contractility is a very important issue in viral hemorrhagic fever and is not caused by direct viral infection of the heart; it is increasingly being recognized that these patients present with low cardiac output and high peripheral resistance and that they respond poorly to fluid infusion. The clinical findings in viral hemorrhagic fever differ from those in the sepsis syndrome and should be studied and interpreted separately; this approach will sharpen therapeutic approaches and could shed light on the problems of sepsis in general.

Pirital virus (Arenaviridae) infection in the syrian golden hamster, Mesocricetus auratus: a new animal model for arenaviral hemorrhagic fever

Adult Syrian golden hamsters inoculated intraperitoneally with Pirital virus, a recently discovered member of the Tacaribe complex of New World arenaviruses, developed a progressively severe, fatal illness with many of the pathologic features observed in fatal human cases of Lassa fever and other arenaviral hemorrhagic fevers. Most of the animals became moribund by Day 5 and were dead by Day 7 after inoculation. The most consistent histopathologic changes included interstitial pneumonitis, splenic lymphoid depletion and necrosis, and multifocal hepatic necrosis without significant inflammatory cell infiltration. The liver changes ranged from single cell death by apoptosis to coagulative necrosis of clusters of hepatocytes. Immunohistochemical studies of the liver demonstrated the presence and accumulation ot Pirital virus antigen within hepatocytes as well as Kupffer cells. An in situ terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL) assay showed progressively increasing apoptotic activity in the liver of infected hamsters. A human hepatoblastoma cell line (Hep G2/C3A) inoculated with Pirital virus also developed progressive cell destruction and accumulation of viral antigen, as demonstrated by immunofluorescence. Results of this pilot study suggest that the Pirital virus-hamster model is a very promising new small animal model for studying the pathogenesis of arenavirus infections, particularly, the mechanism of direct virus-induced hepatic injury. It may also be useful for testingantiviral agents for treatment of arenaviral hemorrhagic fevers.

Experimental infection of the cane mouse Zygodontomys brevicauda (family Muridae) with guanarito virus (Arenaviridae), the etiologic agent of Venezuelan hemorrhagic fever

Chronic infections in specific rodents appear to be crucial to the long-term persistence of arenaviruses in nature. The cane mouse, Zygodontomys brevicauda, is a natural host of Guanarito virus (family Arenaviridae), the etiologic agent of Venezuelan hemorrhagic fever. The purpose of this study was to elucidate the natural history of Guanarito virus infection in Z. brevicauda. Thirty-nine laboratory-reared cane mice each were inoculated subcutaneously with 3.0 log10 plaque-forming units of the Guanarito virus prototype strain INH-95551. No lethality was associated with infection in any animal, regardless of age at inoculation. The 13 newborn, 14 weanling, and 8 of the 12 adult animals developed chronic viremic infections characterized by persistent shedding of infectious virus in oropharyngeal secretions and urine. These findings indicate that Guanarito virus infection in Z. brevicauda can be chronic and thus support the concept that this rodent species is the natural reservoir of Guanarito virus.

Viral hemorrhagic fevers and hantavirus infections in the Americas

Several arenaviruses and hantaviruses have been isolated in the Americas during the last 4 decades. These are rodent-borne viruses responsible for the South American hemorrhagic fevers (SAHF) and hantavirus pulmonary syndrome (HPS). Although rare, SAHF and HPS are serious illnesses with high mortality rates. Most viral isolates found in the Americas represent New World lineages of their respective viral families. Their presence in the Western hemisphere is likely ancient, their relationship with their rodent hosts is likely coevolutionary, and their recent detection forebodes the likelihood of detecting additional arena- and hantaviral species in the Americas.

Tacaribe virus gene expression in cytopathic and non-cytopathic infections

Tacaribe virus (TV) replication was compared in Vero cells infected under conditions leading either to cell death (c.p.e.(+) infection) or to the establishment of persistence (c.p.e.(-) infection). To this end, two virus preparations were employed: one containing a ratio of standard (plaque-forming) viruses to interfering particles (IP) that would induce a distinct lytic response in Vero cells infected at multiplicities giving synchronous infection and another virus stock enriched in IP that would block the cell-killing potential of the cytolytic virus stock. The following results were obtained: (1) No qualitative differences were observed in the species of intracellular viral RNAs in the lytic infection in comparison with infections leading to persistence or during the early stages of persistence. (2) Levels of viral RNAs were severely reduced when the cells were infected with IP in addition to standard viruses, the RNA accumulation being inversely proportional to the ratio of IP to standard viruses used in the infections. (3) Accumulation of the three measurable mRNAs (those corresponding to the glycoprotein precursor [GPC], to the nucleoprotein [N], and to the p11Z protein) ended earlier in the c.p.e.(-) infections (around 18 hr p.i.) than in the c.p.e.(+) infection (45-68 hr p.i.). (4) The rates of synthesis of the GPC, N, and p11Z proteins were largely determined in both the c.p.e.(+) and c.p.e.(-) infections by the amounts of their corresponding mRNAs. (5) The kinetics of accumulation of the S genomes and also the ratios of the S genome to S antigenome were similar in the different infections (accumulation ending at 45-68 hr p.i.). (6) L genome accumulation proceeded for longer time (until 92 hr p.i.) in the c.p.e.(+) infection than in the c.p.e.(-) infections. In the latter accumulation ended at around 45 hr p.i. Until this time ratios of L genome to L antigenome were similar in the different infections. It is concluded that IP affect virus mRNA synthesis early after infection reducing in this way the rate of viral protein synthesis. Low levels of viral proteins might then limit virus replication. In addition, the results support the idea that in TV infections transcription and replication are independently regulated. The implications of these results with regards to the nature and mode of action of TV IP are discussed.

Description of Guanarito virus (Arenaviridae: Arenavirus), the etiologic agent of Venezuelan hemorrhagic fever

This paper characterizes Guanarito virus, the etiologic agent of Venezuelan hemorrhagic fever. Based on its morphology and antigenic properties, Guanarito virus appears to be a new member of the Tacaribe complex of the genus Arenavirus, family Arenaviridae. Complement fixation and indirect fluorescent antibody tests showed that Guanarito virus and its antiserum are broadly cross-reactive with other members of the Tacaribe complex, but it can be differentiated from other members of the complex by neutralization test. Guanarito virus causes mortality in suckling mice and adult guinea pigs, but not in adult mice. Inoculated rhesus monkeys developed viremia and became ill; however, they subsequently recovered and responded with production of antibody. To date, all isolates of Guanarito virus have come from sick persons or wild rodents living within a single geographic focus in the central plains of Venezuela.

Safety and immunogenicity of a live-attenuated Junin (Argentine hemorrhagic fever) vaccine in rhesus macaques

The safety and immunogenicity of Candid #1, a live-attenuated Junin virus vaccine, were evaluated in rhesus macaques. Candid #1 was inoculated subcutaneously in graded doses ranging from 16 to 127,200 plaque-forming units (PFU) into four groups of five animals each; four controls received saline. There was no significant effect of the immunization on any physical, hematologic, or biochemical parameter measured. Junin virus was recovered by cocultivation from peripheral blood mononuclear cells (PBMC) of 14 (70%) of 20 animals from 1 to 21 days after immunization; 27 (12%) of 223 PBMC samples that represented animals in all four dose groups were positive. In contrast, virus was recovered from the plasma of only two of 20 macaques (two of 225 samples [0.9%]), and only once (by amplification) from throat swabs. No evidence of reversion was detected in any blood isolate. All animals developed a detectable neutralizing antibody response following vaccination. These results indicate that Candid #1 is safe and immunogenic in nonhuman primates.

Experimental neuroinvasiveness of wild and laboratory Junin virus strains

The neuroinvasiveness of Candid 1 and XJCL3 laboratory strains and CbalV4454 and CbaFHA5069 wild strains of Junin virus was studied in albino mice, guinea pigs, and a South American wild rodent, Calomys musculinus (Cm), of different ages inoculated by a non-neural route. Infectivity in brain, blood and organs, as well as lethality, were determined. The results with the 3 hosts indicate that Junin virus neuroinvasiveness is virus-strain-dependent, host species- and age-dependent, with the Candid 1 strain proving to be the least neuroinvasive of the strains studied. The lethal efficiency index (log PFU/LD50) in 2-day old albino mice and the neuroinvasiveness index (Log PFU/ND50) in 6 +/- 1 day-old Cm of the various strains using the intraperitoneal (ip) route could therefore be useful markers of Junin virus neuroinvasiveness. Moreover, different patterns of infection were established using the results of the presence of infectious virus in brain and viraemia in the 3 hosts. In nearly all cases, virus neuroinvasion was present without detectable viraemia (virus in plasma). Current evidence leads to the assumption that virus might reach the brain associated with the white cells in blood (undetectable by conventional isolation methods) or by another possible mechanism of neuroinvasion which is not haematogenous.

Candid No. 1 Argentine hemorrhagic fever vaccine protects against lethal Junin virus challenge in rhesus macaques

The protective efficacy of Candid No. 1, a live-attenuated vaccine against Argentine hemorrhagic fever (AHF), was evaluated in non-human primates. Twenty rhesus macaques immunized 3 months previously with graded doses of Candid No. 1 (16-127, 000 PFU), as well as 4 placebo-inoculated controls, were challenged with 4.41 log10 PFU of virulent P3790 strain Junin virus. All controls developed severe clinical disease; 3 of 4 died. In contrast, all vaccinated animals were fully protected; none developed any signs of AHF during a 105-day follow-up period. Viremia and virus shedding were readily detected in all placebo-vaccinated controls, while virus could be recovered only once (by amplification) from throat swabs of 2 Candid No. 1 vaccinees on day 21. Vigorous secondary-type neutralizing and immunofluorescent antibody responses were seen in most vaccinees that had received 3 log10 PFU Candid No. 1 or fewer; all others, including those receiving 127,200 PFU, maintained relatively stable titers during follow-up. Candid No. 1 was highly immunogenic and fully protective against lethal Junin virus challenge in rhesus macaques, even at extremely low (16 PFU) vaccine doses.

Experimental infection of suckling mice with a host range mutant of Junin virus

Experimental infection of three mouse strains with a non-pathogenic mutant of Junin virus named Cl67 was compared with respect to the parental XJCl3 strain. After intracerebral (ic) or intraperitoneal inoculation, XJCl3 was highly virulent for 2 day-old C3H/HeJ, OF1, and BALB/cJ mouse strains, whereas its derivative Cl67 was attenuated. Survival of the Cl67-infected mouse was associated with a restricted replication at the site of inoculation which would impair spread of virus. Thus, the reduced virulence of Cl67 for suckling mice is independent of the mouse strain and the route of viral entry. When Cl67 was preinoculated ic 10 days before the challenge inoculation with XJCl3 by the same route, mice were partially protected from lethal infection. Since neutralizing antibodies were first detected at 30 days post-infection, an interference mechanism is postulated as a mechanism of protection of the mice.

Rapid vascular clearance of two strains of Junin virus in Calomys musculinus: selective macrophage clearance

Clearance of Junin (JUN) virus strains with different virulence for Calomys musculinus (Cm) was followed using the Candid #1 virulent and CbaFHA 5069 attenuated strains. In addition, virulent virus albino mice (AM) were included as control host and Venezuelan equine encephalitis (VEE-VI) virus as control virus. The virus inoculum (Vo) and the blood samples (Vt) obtained at different times post-inoculation (p.i.) were titrated on Vero cells and the cleared plaque forming-units (PFU) were calculated as the log Vt/Vo. In Cm both JUN virus strains were cleared rapidly (within 5 min the Candid #1 strain and within 10 min the CbaFHA 5069 strain); meanwhile, VEE-VI virus could be recovered from blood until 30 min p. i. Furthermore, JUN and VEE-VI viruses showed the same behaviour in Am as in Cm. We conclude that the JUN virus strains of different virulence for Cm did not show differences in their clearance from the blood of these animals. Moreover, the rapid clearance observed was independent of the animal host and viral dose.

Neurovirulence of wild and laboratory Junin virus strains in animal hosts

The neurovirulence of Candid #1 and XJCL3 laboratory strains and CbalV4454 and CbaFHA5069 wild strains of Junin virus was studied in albino mice, guinea pigs, and a South American wild rodent, Calomys musculinus, of different ages inoculated by the intracerebral route. Infectivity in brain and organs, lethality, and neuropathological lesions were determined. The laboratory and wild strains showed similar neurovirulence only in 2-day-old mice. The neurovirulence of laboratory strains decreased with the age of the animal, and the Candid #1 strain affected only 2-day-old mice. In guinea pigs, the 2 wild strains and XJCL3 laboratory strain were neurovirulent for 11-day-old and adult animals giving moderate lymphocytic infiltration in the brain and mild lesions in the spinal cord. Virus titres from the brain and the spinal cord were lower with the XJCL3 and CbalV4454 strains than with the CbaFHA5069 strain; with the latter, virus was recovered only from the lymph nodes, the lung, kidney, liver, and spleen. The Candid #1 strain was not neurovirulent even for 11-day-old animals. In contrast, the laboratory strains were neurovirulent for Calomys musculinus, depending on the age of the animal. Virus was recovered from the brains showing lymphocyte infiltration but not from other organs. The CbaFHA5069 strain was not neurovirulent, although virus was recovered from the brain, spleen, liver, lymph nodes, and salivary glands. These results with the 3 hosts indicate that Junin virus neurovirulence is virus strain-dependent, and host species and age-dependent, with the Candid #1 strain proving the least neurovirulent of the strains studied.

[Immunopathology induced in the rat by Junin virus]

Intra-cerebral infection of the 10-day-old rat with the XJ prototype strain of Junin virus induces an immunopathological encephalitis with 100% mortality. In contrast with previous observations, our present work with antithymocyte serum (ATS) demonstrates a pathological role for the cellular immune response in this experimental model. As regards ATS treatment, 3 schedules were employed, the most efficient being daily 0.01 ml/g weight doses from day -1 to day +9, then +12, +14 and +16, taking day 0 as the time of virus infection. Survival reached 54% and the average day of death was delayed 12 days (Table 1). No differences were recorded in brain viral titres in treated vs untreated infected controls (Table 2). Lastly, splenocyte transfer from infected 10-day-old rats, to infected 2-day-old animals, which are known to develop persistence without death, led to 40% mortality in recipients vs 0% in 2-day-old non-transferred infected controls. Therefore, it may be concluded that: a) encephalitis in the 10-day-old rat is immunological in nature and b) transfer of lymphocytes to infected 2-day-old rats, induces disease and death.

[Intracerebral infection of athymic mice with an attenuated strain of Junín virus]

Infection of newborn immunocompetent (nu/+) mice with the XJ prototype strain of Junin virus, etiological agent of Argentine Hemorrhagic Fever, produces a lethal meningo-encephalitis due to cellular immune response. The same strain inoculated into athymic (nu/nu) mice produces an asymptomatic persistent infection. The purpose of this work was to determine the nu/nu mice response when infected with XJCl3, an attenuated Junin virus strain, since this strain behaves differently to the pathogenic prototype in various experimental hosts and humans. Fifty five suckling nu/nu mice and 45 nu/+ were inoculated intracerebrally with 10(3) PFU of the XJCl3 strain. Twenty nu/nu and 20 nu/+ were kept as uninoculated controls. Similar percentages of mortality were recorded for nu/nu and nu/+ infected animals (86 and 87%). In contrast, no morbi-mortality was detected in control animals which were kept in the same animal room. High virus titers were detected in brains and lungs of infected nu/nu at 7, 14, 21 and 70 days post-infection(pi). Virus titers in blood were 1 log lower than those found in organs. Immunohistochemical studies of brains showed viral antigen in the cytoplasm of cortical neurons at 21 and 70 days pi. An interstitial pneumonitis was detected in lungs of infected nu/nu at 7 and 21 days pi, while no lesions were observed in brains and spleens. Results show that the XJl3 strain behaves in a very different way in newborn nu/nu mice as the XJ prototype strain. Further studies are necessary to determine the pathogenic mechanisms involved.

Reduced virulence of a Junin virus mutant is associated with restricted multiplication in murine cells

C167, a mutant derived from the XJC13 strain of Junin virus, is highly attenuated in its pathogenic properties for newborn mice. Whereas 10(2).PFU of XJC13 injected intracerebrally killed 100% of two-day-old mice, the mutant showed no detectable lethality. Survival of mice infected with C167 was associated with a reduced and delayed virus replication in brain and a defective spread of virus from the site of inoculation to the other tissues, including spleen, kidney, thymus, liver, peritoneal cells and serum. As an apparent consequence of the restricted replication of C167 in mice, no detectable interferon induction and low levels of neutralizing antibodies were observed. Analysis of multiplication kinetics of C167 and XJC13 in different cell cultures in vitro has confirmed that the attenuated phenotype of C167 was related to a specific inefficient replication in murine cells. This host-range restriction was due to a combination of adsorption and penetration blockage.

Actions of complement on Junin virus

Fresh sera from normal rhesus monkeys, guinea pigs, and rabbits inactivated 90%-99% of the infectivity of Vero cell-passaged, attenuated strains of Junin virus (JV) within 60 minutes. Selective depletion studies showed that inactivation occurred by the classical complement pathway. Complement had little effect on virulent JV strains. Adsorption of the fresh sera with JV-infected Vero cells showed that inactivation was not mediated by low levels of antibodies in normal sera. The cells used for propagation of the virus affected inactivation: virus passaged in Vero cells (a continuous African green monkey kidney line) was more susceptible than virus passaged in FRhL-2 cells (a diploid strain derived from fetal rhesus monkey lung). Complement was important for in vitro neutralization of virulent JV strains by immune sera but was unnecessary for neutralization of attenuated strains. Thus, complement may be important in host resistance to Argentine hemorrhagic fever in two ways: first, complement activation may contribute to the attenuated phenotype of some strains; and second, complement may be necessary for efficient neutralization of virulent strains.

Calomys callidus as a potential Junin virus reservoir

The present study investigated whether C. callidus, a species belonging to the Calomys genus, is capable of developing experimentally a persistent Junin virus (JV) infection. Newborn and adult cricetids were inoculated with the attenuated XJ-Clone 3 strain of JV by intracerebral or mucosal route. The present results indicate that the species is susceptible to JV infection, capable of shedding virus chronically through saliva and developing a persistent infection as shown by the detection of virus in brain tissue at 60 days post infection. These findings, and the fact that this cricetid shares its distribution areas with Calomys musculinus and Akodon azarae, support C. callidus as a potential JV reservoir.

Antigenic relationships between attenuated and pathogenic strains of Junin virus

Antigenic relationships between attenuated and pathogenic strains of Junin virus (JV) were investigated. Five strains of either human or rodent origin were tested by cross-neutralization assay with hyperimmune antisera, raised in rabbits, against each strain. Polyclonal antisera could be used to distinguish among these JV strains, as the titer values differed significantly with ratios of homologous to heterologous titers, which ranged from 1.3 to 22.3. This demonstrates, independent of their virulence, a heterogeneity among the JV strains tested. The relatedness among JV strains was expressed quantitatively through a dendrogram based on taxonomic distance coefficients. The field strains of JV were grouped into two clusters, according to their geographic origin.

Susceptible adult murine model for Junin virus

The adult mouse model had been considered resistant to Junin virus (JV) infection. However, we found that C3H/HeJ murine strain proved highly susceptible up to 5 months of age to intracerebral inoculation with the prototype XJ JV strain, showing neurological signs and 80-90% mortality within 13 days. Neutralizing antibodies (Nt Ab) were absent, but low immunofluorescent Ab levels (1:5) were detected as from day +7. The virus could only be rescued by coculture of brain samples with Vero cells. Histopathological findings were consistent with the suckling mouse model and with a delayed-type hypersensitivity reaction. XJ inoculation by extraneural routes failed to cause disease, however, it induced Nt Abs. Ic infection with XJCL3 strain of JV attenuated for man and guinea pig, but not for mouse, induced high Nt Ab levels but not mortality. In either case, mice resisted ic XJ challenge. Thus, C3H/HeJ is the first adult mouse model susceptible to JV.

Viral strain dependent differences in experimental Argentine hemorrhagic fever (Junin virus) infection of guinea pigs

Guinea pigs infected with low-passage Junin virus of human origin showed viral strain dependent differences in mortality, LD50, time to death, and in viral spread and distribution. Different Junin strains appeared to cause at least two broad patterns of Argentine hemorrhagic fever in guinea pigs. A number of strains of Junin virus caused a viscerotropic type of illness in which virus replicated predominantly in lymph nodes, spleen, and bone marrow. With the most severe visceral forms of Argentine hemorrhagic fever, the guinea pigs became viremic, developed necrosis of spleen, lymph nodes, and bone marrow, showed gastric hemorrhages, and all animals died within 13-15 days. Other Junin strains induced a neurological type of illness with transient viral replication in and lymphocyte depletion of spleen and lymph nodes, with no detectable viremia or viral replication in bone marrow. Subsequently, virus was found in the brain with varying severities of polioencephalitis, and the guinea pigs frequently showed rear leg paralysis before death occurred 28-34 days after inoculation. Not all animals infected with a neurotropic strain developed all these signs. One viral strain induced some signs characteristic of both patterns of illness. Although the disease forms in the guinea pig model did not strictly correlate with those observed in the humans from which these strains were obtained, the different strains of Junin virus consistently caused very different patterns of illness in infected guinea pigs.

Interferon response in the guinea pig infected with Junín virus

The "in vivo" interferon (IFN) induction capacity of two Junín virus strains--the attenuated XJCl3 and the intermediate virulent MC2--was studied in the guinea pig experimental model. Three different doses of XJCl3 strain--2,000, 10,000, and 50,000 TCID50--and a single dose of 10,000 TCID50 of MC2 were assayed. Animals were bled from day 0 to day 14 postinjection (pi) XJCl3 groups showed a constant serum IFN response. MC2 infection showed that 16% of the animals failed to develop interferonemia. The IFN activity was alpha type in most cases. The IFN serum levels induced by the MC2 strain were always lower than those attained after XJCl3 infection. The response to the positive control assayed, Newcastle disease virus, was higher and earlier than that obtained for Junín virus strains. The highest IFN individual value, which induced 160 guinea pig IFN U/ml, was detected at day 2 following XJCl3 infection, and corresponded to the highest XJCl3 dose assayed. Average values ranged from 23 to 65 guinea pig IFN U/ml, for XJCl3 groups and 15 guinea pig IFN U/ml for the MC2 group, measured at the day of maximal response. IFN presence was studied in homogenates from brain, spleen, and lymph nodes; it was detected in organs from guinea pigs infected with XJCl3 but not in organs from MC2 infected animals. IFN levels in sera or in organs failed to correlate with the histological findings. Demonstration of viral antigens in organs of infected animals, and seroconversion of Junín virus (JV) confirmed the evolution of the disease. A significant weight loss was observed just after serum IFN disappearance.(ABSTRACT TRUNCATED AT 250 WORDS)

[Identification of the mRNA of the nucleocapsid proteins of pathogenic arenaviruses]

Total RNA from cells infected with Machupo and Lassa viruses as well as individual sedimentation classes of these RNAs were translated in the cell-free protein-synthesizing system from rabbit reticulocytes. The translation products were precipitated either with anti-Machupo immune gamma-globulin or monoclonal antibodies to nucleocapsid protein (NP) of Lassa virus. Both total RNA and RNA fraction with the sedimentation coefficient 15-16S promoted the synthesis of protein which comigrated in gel with NP protein of purified virions. It is concluded that monocistron mRNA for NP protein of arenaviruses has the sedimentation coefficient 15-16 S.

Experimental Argentine hemorrhagic fever in rhesus macaques: virus-specific variations in pathology

Two isolates of Junin virus (Espindola and Ledesma) inoculated into rhesus macaques produced distinct lesions which were strain-constant and similar to reported human cases of Argentine hemorrhagic fever. The Espindola isolate was associated with hemorrhagia, necrosis of bone marrow, and mild hepatocellular necrosis. Ledesma isolate was associated with pronounced polioencephalomyelitis and autonomic ganglioneuritis, but very mild or absent hepatocellular necrosis, bone marrow necrosis, and hemorrhagia. Deaths of Espindola-infected macaques were usually attributed to hemorrhagia with severe secondary bacterial infections, while in Ledesma-infected macaques, death was associated either with early severe secondary bacterial infections or slowly progressive polioencephalomyelitis. These two Junin virus isolates demonstrated hemorrhagic viscerotropism or neurotropism in macaques, suggesting that the variety of Argentine hemorrhagic fever syndromes in man may be virus-isolate determined.

Intracerebral infection of Cebus apella with the XJ-Clone 3 strain of Junín virus

To assess the usefulness of the South American primate Cebus apella as a model for neurovirulence of Junín virus, eight monkeys were inoculated with 10(5) LD50 of the attenuated XJ-Clone 3 Junín virus strain by the intrathalamic route. After the second week, weight loss and polyadenopathies were observed in most animals, one-half of which had a transient leukothrombocytopenia. Moderate clinical central nervous system (CNS) involvement was present in four of eight monkeys, while the rest had only mild neurologic signs. All recovered except one, which developed a deep coma and was killed in a pre-mortem stage at 18 days post-infection (pi). Junín virus was isolated from the throat from five, from the blood from three, and from the brain from two monkeys. In the most severely ill animal, virus titers higher than viremia were detected in both inoculated and contralateral brain hemispheres, as well as in lung, lymph node, and small intestine. Junín antigens and "in vivo" bound immunoglobulins were detected by immunofluorescence (IF) in the brain of four animals at 18, 21, 40, and 155 days pi. Moderate lymphocytic parenchymal and meningeal infiltration were observed in the brain of four animals, and gliosis was also present in the most affected monkey. Although the clinical response to infection was not uniform, all infected monkeys developed high IF antibodies. Cebus apella cannot be used as a highly sensitive model for Argentine hemorrhagic fever (AHF). However, the results obtained show that the XJ-Clone 3 strain can replicate in the primate CNS and to induce lesions and immunoglobulin deposition. In addition, viral persistence is suggested by the late detection of viral antigens in brain at 40 and 155 days pi.

[Attenuation in the virulence of a mutant of Junin virus in suckling mice]

The virulence in neonatal mice of a temperature-sensitive mutant of Junin virus, named C167, was studied. The thermosensitive properties of this mutant were tested by titration on Vero cells at 37 and 40 degrees C. The ratio of infectivity 40/37 was approximately 100-fold lower for C167 with respect to XJC13 (Table 1). The attenuation of C167 was determined by measurement of mean survival time and 50% lethal dose after intracerebral injection of 2 and 11 day old mice. For C167 the lethality index (expressed ad the ratio TCID50/LD50) was greater than 580, while for XJC13 the index was 4.4 (Table 2). The lack of virulence of C167 was correlated with a restricted ability to replicate in suckling mouse brains. By contrast, the mutant and the parental virus grew to a similar titre in Vero cells (Figure 2). Both viruses were indistinguishable in cross-neutralization tests using hyperimmune antisera.

Cytolysis of Junin infected target cells by immune guinea pig spleen cells

Spleen cells from guinea pigs infected with an attenuated strain of Junin virus (the causative agent of Argentine hemorrhagic fever) specifically lysed virus-infected syngeneic target cells in vitro. This activity was detected as early as 6 days after infection, reached a maximum on days 10-13, and persisted at lower levels, at least through day 30. Monoclonal antibody to guinea pig T cells had no effect on the activity. After B or T cell enrichment techniques, the cytolysis was found with the B cell fraction. Aggregated IgG blocked the cytolysis. These characteristics suggested lytic activity was mediated at least in part by an antibody-dependent cell-mediated cytotoxicity (ADCC) mechanism. Although some cytolysis could be detected by using exogenously added antiserum and normal spleen effector cells, such reconstruction showed less efficient killing than when spleen cells from Junin-infected guinea pigs were used. This apparent discrepancy was resolved when spleen cells from these infected animals exhibited enhanced activity in non-viral ADCC systems as well. The cytotoxic activity by spleen cells against Junin-infected targets was detected only with non-fatal Junin infections. Cytolysis could not be measured in spleen cell suspensions from guinea pigs lethally infected with Junin virus; i.e. adults infected with a virulent strain of Junin and baby guinea pigs or immunosuppressed adult animals infected with an attenuated strain. However, spleen cells from both the immunosuppressed, infected adults and the adult guinea pigs infected with a virulent strain of Junin were able to mediate cytotoxicity in a nonviral system (antibody-sensitized Vero cells). The development of spleen cell cytotoxicity by Junin-infected guinea pigs against Junin-infected target cells correlated with whether the infection was resolved or was lethal.

Partial characterization of two temperature-sensitive mutants of junin virus

Two temperature sensitive (ts) mutants of Junin virus, a member of Arenaviridae, have been partially characterized. Both mutants, named ts-32 and ts-40, had a relative plating efficiency 40 degrees C/34 degrees C lower than 10(-3) an exhibited a leak yield below 10(-4). Standard growth curves showed that at 34 degrees C the viral mutants multiplied slower than wt virus and at high multiplicity did not display autointerference. No differences in thermolability were observed between wt and ts mutants. By contrast, when the pathogenic properties of the mutants were investigated they were significantly attenuated for mice. At the restrictive temperature both mutants were unable to synthesize viral-specific polypeptides, while at the permissive temperature the pattern was similar to wt virus. Shift-up and down experiments suggested that ts defect is expressed between 2 and 4 hours post-infection. It is concluded that ts-32 and ts-40 are early function mutants. The possible nature of their defect is discussed.

Junin virus access to CNS by extraneural rat inoculation

This study was carried out to determine the pathways along which two strains of Junin virus (JV), the pathogenic XJV and the attenuated XJC13V, reach the CNS following IP inoculation of 2-day-old rats. A sequential study of infectivity and antigen distribution in peritoneal macrophages, spleen, and brain was performed. Mortality was 85% with the former strain, but only 15% with the latter. At 4-7 days PI, XJV-infected animals had viral antigen in 10% of peritoneal macrophages. Viremia and spleen virus lasted for 10-15 days. Low brain titers were detected at day 7, with a peak at day 15. Brain antigen correlated with virus titers. In contrast, XJC13V-infected rats, macrophage antigen appeared later and to a lesser degree (1% of cells). Viremia and spleen virus were transient, while both the titer of brain virus and the viral antigen proved lower. Antibody titers were over twofold higher for XJ-infected animals. It is suggested that the different replication rate at the inoculation site could account for the greater ability of the XJV strain to reach the CNS. A greater antigen mass and/or more numerous antigenic determinants presented by the macrophage could explain the higher antibody titers found in XJ-injected rats, which were unable, however, to prevent viral spread.