Simian hemorrhagic fever virus infection of rhesus macaques as a model of viral hemorrhagic fever: clinical characterization and risk factors for severe disease

Isolation of Diverse Simian Arteriviruses Causing Hemorrhagic Disease

Genetically diverse simian arteriviruses (simarteriviruses) naturally infect geographically and phylogenetically diverse monkeys, and cross-species transmission and emergence are of considerable concern. Characterization of most simarteriviruses beyond sequence analysis has not been possible because the viruses fail to propagate in the laboratory. We attempted to isolate 4 simarteriviruses, Kibale red colobus virus 1, Pebjah virus, simian hemorrhagic fever virus, and Southwest baboon virus 1, by inoculating an immortalized grivet cell line (known to replicate simian hemorrhagic fever virus), primary macaque cells, macrophages derived from macaque induced pluripotent stem cells, and mice engrafted with macaque CD34+-enriched hematopoietic stem cells. The combined effort resulted in successful virus isolation; however, no single approach was successful for all 4 simarteriviruses. We describe several approaches that might be used to isolate additional simarteriviruses for phenotypic characterization. Our results will expedite laboratory studies of simarteriviruses to elucidate virus-host interactions, assess zoonotic risk, and develop medical countermeasures.

Primate hemorrhagic fever-causing arteriviruses are poised for spillover to humans

Simian arteriviruses are endemic in some African primates and can cause fatal hemorrhagic fevers when they cross into primate hosts of new species. We find that CD163 acts as an intracellular receptor for simian hemorrhagic fever virus (SHFV; a simian arterivirus), a rare mode of virus entry that is shared with other hemorrhagic fever-causing viruses (e.g., Ebola and Lassa viruses). Further, SHFV enters and replicates in human monocytes, indicating full functionality of all of the human cellular proteins required for viral replication. Thus, simian arteriviruses in nature may not require major adaptations to the human host. Given that at least three distinct simian arteriviruses have caused fatal infections in captive macaques after host-switching, and that humans are immunologically naive to this family of viruses, development of serology tests for human surveillance should be a priority.

Prevalence and Factors Associated with Acute Kidney Injury in Sub-Saharan African Adults: A Review of the Current Literature

Acute kidney injury (AKI) is a complex condition that can occur in both community and hospital settings and has many aetiologies. These aetiologies may be infectious, toxic, surgical, or related to the different management methods. Although it is a major public health problem worldwide, it must be emphasised that both its incidence and mortality rate appear to be very high in sub-Saharan African (SSA) countries compared to developed countries. The profile of AKI is very different from that of more developed countries. There are no reliable statistics on the incidence of AKI in SSA. Infections (malaria, HIV, diarrhoeal, and other diseases), nephrotoxins, and obstetric and surgical complications are the main aetiologies in Africa. The management of AKI is costly and associated with high rates of prolonged hospitalisation and in-hospital mortality.

Development and Characterization of a cDNA-Launch Recombinant Simian Hemorrhagic Fever Virus Expressing Enhanced Green Fluorescent Protein: ORF 2b' Is Not Required for In Vitro Virus Replication

Simian hemorrhagic fever virus (SHFV) causes acute, lethal disease in macaques. We developed a single-plasmid cDNA-launch infectious clone of SHFV (rSHFV) and modified the clone to rescue an enhanced green fluorescent protein-expressing rSHFV-eGFP that can be used for rapid and quantitative detection of infection. SHFV has a narrow cell tropism in vitro, with only the grivet MA-104 cell line and a few other grivet cell lines being susceptible to virion entry and permissive to infection. Using rSHFV-eGFP, we demonstrate that one cricetid rodent cell line and three ape cell lines also fully support SHFV replication, whereas 55 human cell lines, 11 bat cell lines, and three rodent cells do not. Interestingly, some human and other mammalian cell lines apparently resistant to SHFV infection are permissive after transfection with the rSHFV-eGFP cDNA-launch plasmid. To further demonstrate the investigative potential of the infectious clone system, we introduced stop codons into eight viral open reading frames (ORFs). This approach suggested that at least one ORF, ORF 2b’, is dispensable for SHFV in vitro replication. Our proof-of-principle experiments indicated that rSHFV-eGFP is a useful tool for illuminating the understudied molecular biology of SHFV.

Complete genome sequence and analysis of a new lethal arterivirus, Trionyx sinensis hemorrhagic syndrome virus (TSHSV), amplified from an infected Chinese softshell turtle

Trionyx sinensis hemorrhagic syndrome virus (TSHSV) is a newly discovered lethal arterivirus that causes serious disease in Trionyx sinensis in China. In this study, the complete genome sequence of TSHSV was determined by RACE cloning, and the functions of the predicted proteins were predicted. The complete genome of TSHSV was found to be 17,875 bp in length, and a 3'-end poly(A) tail was detected. Eight TSHSV hypothetical proteins (TSHSV-HPs) were predicted by gene model identification. TSHSV-HP2, 3 and 4 were associated with replicase activity, since papain-like protease (PLPs), serine-type endopeptidase, P-loop-containing nucleoside triphosphate hydrolase, and EndoU-like endoribonuclease motifs were detected. Phylogenetic analysis showed that TSHSV clusters with an arterivirus from a Chinese broad-headed pond turtle.

Clinical Characterization of Host Response to Simian Hemorrhagic Fever Virus Infection in Permissive and Refractory Hosts: A Model for Determining Mechanisms of VHF Pathogenesis

Simian hemorrhagic fever virus (SHFV) causes a fulminant and typically lethal viral hemorrhagic fever (VHF) in macaques (Cercopithecinae: Macaca spp.) but causes subclinical infections in patas monkeys (Cercopithecinae: Erythrocebus patas). This difference in disease course offers a unique opportunity to compare host responses to infection by a VHF-causing virus in biologically similar susceptible and refractory animals. Patas and rhesus monkeys were inoculated side-by-side with SHFV. Unlike the severe disease observed in rhesus monkeys, patas monkeys developed a limited clinical disease characterized by changes in complete blood counts, serum chemistries, and development of lymphadenopathy. Viral RNA was measurable in circulating blood 2 days after exposure, and its duration varied by species. Infectious virus was detected in terminal tissues of both patas and rhesus monkeys. Varying degrees of overlap in changes in serum concentrations of interferon (IFN)-γ, monocyte chemoattractant protein (MCP)-1, and interleukin (IL)-6 were observed between patas and rhesus monkeys, suggesting the presence of common and species-specific cytokine responses to infection. Similarly, quantitative immunohistochemistry of livers from terminal monkeys and whole blood flow cytometry revealed varying degrees of overlap in changes in macrophages, natural killer cells, and T-cells. The unexpected degree of overlap in host response suggests that relatively small subsets of a host's response to infection may be responsible for driving hemorrhagic fever pathogenesis. Furthermore, comparative SHFV infection in patas and rhesus monkeys offers an experimental model to characterize host⁻response mechanisms associated with viral hemorrhagic fever and evaluate pan-viral hemorrhagic fever countermeasures.

Subclinical Infection of Macaques and Baboons with A Baboon Simarterivirus

Simarteriviruses (Arteriviridae: Simarterivirinae) are commonly found at high titers in the blood of African monkeys but do not cause overt disease in these hosts. In contrast, simarteriviruses cause severe disease in Asian macaques upon accidental or experimental transmission. Here, we sought to better understand the host-dependent drivers of simarterivirus pathogenesis by infecting olive baboons (n = 4) and rhesus monkeys (n = 4) with the simarterivirus Southwest baboon virus 1 (SWBV-1). Surprisingly, none of the animals in our study showed signs of disease following SWBV-1 inoculation. Three animals (two rhesus monkeys and one olive baboon) became infected and sustained high levels of SWBV-1 viremia for the duration of the study. The course of SWBV-1 infection was highly predictable: plasma viremia peaked between 1 × 10⁷ and 1 × 10⁸ vRNA copies/mL at 3–10 days post-inoculation, which was followed by a relative nadir and then establishment of a stable set-point between 1 × 10⁶ and 1 × 10⁷ vRNA copies/mL for the remainder of the study (56 days). We characterized cellular and antibody responses to SWBV-1 infection in these animals, demonstrating that macaques and baboons mount similar responses to SWBV-1 infection, yet these responses are ineffective at clearing SWBV-1 infection. SWBV-1 sequencing revealed the accumulation of non-synonymous mutations in a region of the genome that corresponds to an immunodominant epitope in the simarterivirus major envelope glycoprotein GP5, which likely contribute to viral persistence by enabling escape from host antibodies.

Insertion position as well as the inserted TRS and gene sequences differentially affect the retention of foreign gene expression by simian hemorrhagic fever virus (SHFV)

Recombinant SHFV infectious cDNA clones expressing a foreign gene from an additional sg mRNA were constructed. Two 3' genomic region sites, between ORF4' and ORF2b and between ORF4 and ORF5, were utilized for insertion of the myxoma M013 gene with a C-terminal V5 tag followed by one of the three inserted transcription regulatory sequences (TRS), TRS2', TRS4' or TRS7. M013 insertion at the ORF4'/ORF2b site but not the ORF4/ORF5 site generated progeny virus but only the recombinant virus with an inserted TRS2' retained the entire M013 gene through passage four. Insertion of an auto-fluorescent protein gene, iLOV, with an inserted TRS2' at the ORF4'/ORF2b site, generated viable progeny virus. iLOV expression was maintained through passage eight. Although regulation of SHFV subgenomic RNA synthesis is complex, the ORF4'/ORF2b site, which is located between the two sets of minor structural proteins, is able to tolerate foreign gene insertion.

Monkey viral pathology in the Sukhum colony and modeling human viral infections

The data characterizing spontaneous infections of Old World monkeys: measles, poliomyelitis, hepatitis A (HPA), encephalomyocarditis, coronavirus infection, simian hemorrhagic fever (SHF), are presented. The experimental infections were reproduced with the isolated pathogens. On these models, pathogenesis and epidemiology of these diseases were studied. The efficiency of poliomyelitis, measles and HPA vaccines is shown. The priority of data on the discovery of earlier unknown disease-SHF and "Sukhumi" virus-are emphasized. Several important pathogenic mechanisms common for various hemorrhagic fevers were studied on experimental SHF of macaques. This model is uniquely safe and adequate for the assessment of therapy of hemorrhagic fevers dangerous for humans.

Within-Host Evolution of Simian Arteriviruses in Crab-Eating Macaques

Simian arteriviruses are a diverse clade of viruses infecting captive and wild nonhuman primates. We recently reported that Kibale red colobus virus 1 (KRCV-1) causes a mild and self-limiting disease in experimentally infected crab-eating macaques, while simian hemorrhagic fever virus (SHFV) causes lethal viral hemorrhagic fever. Here we characterize how these viruses evolved during replication in cell culture and in experimentally infected macaques. During passage in cell culture, 68 substitutions that were localized in open reading frames (ORFs) likely associated with host cell entry and exit became fixed in the KRCV-1 genome. However, we did not detect any strong signatures of selection during replication in macaques. We uncovered patterns of evolution that were distinct from those observed in surveys of wild red colobus monkeys, suggesting that these species may exert different adaptive challenges for KRCV-1. During SHFV infection, we detected signatures of selection on ORF 5a and on a small subset of sites in the genome. Overall, our data suggest that patterns of evolution differ markedly among simian arteriviruses and among host species.

IMPORTANCE

Certain RNA viruses can cross species barriers and cause disease in new hosts. Simian arteriviruses are a diverse group of related viruses that infect captive and wild nonhuman primates, with associated disease severity ranging from apparently asymptomatic infections to severe, viral hemorrhagic fevers. We infected nonhuman primate cell cultures and then crab-eating macaques with either simian hemorrhagic fever virus (SHFV) or Kibale red colobus virus 1 (KRCV-1) and assessed within-host viral evolution. We found that KRCV-1 quickly acquired a large number of substitutions in its genome during replication in cell culture but that evolution in macaques was limited. In contrast, we detected selection focused on SHFV ORFs 5a and 5, which encode putative membrane proteins. These patterns suggest that in addition to diverse pathogenic phenotypes, these viruses may also exhibit distinct patterns of within-host evolution both in vitro and in vivo.

Arteriviruses, Pegiviruses, and Lentiviruses Are Common among Wild African Monkeys

Nonhuman primates (NHPs) are a historically important source of zoonotic viruses and are a gold-standard model for research on many human pathogens. However, with the exception of simian immunodeficiency virus (SIV) (family Retroviridae), the blood-borne viruses harbored by these animals in the wild remain incompletely characterized. Here, we report the discovery and characterization of two novel simian pegiviruses (family Flaviviridae) and two novel simian arteriviruses (family Arteriviridae) in wild African green monkeys from Zambia (malbroucks [Chlorocebus cynosuros]) and South Africa (vervet monkeys [Chlorocebus pygerythrus]). We examine several aspects of infection, including viral load, genetic diversity, evolution, and geographic distribution, as well as host factors such as age, sex, and plasma cytokines. In combination with previous efforts to characterize blood-borne RNA viruses in wild primates across sub-Saharan Africa, these discoveries demonstrate that in addition to SIV, simian pegiviruses and simian arteriviruses are widespread and prevalent among many African cercopithecoid (i.e., Old World) monkeys.

IMPORTANCE

Primates are an important source of viruses that infect humans and serve as an important laboratory model of human virus infection. Here, we discover two new viruses in African green monkeys from Zambia and South Africa. In combination with previous virus discovery efforts, this finding suggests that these virus types are widespread among African monkeys. Our analysis suggests that one of these virus types, the simian arteriviruses, may have the potential to jump between different primate species and cause disease. In contrast, the other virus type, the pegiviruses, are thought to reduce the disease caused by human immunodeficiency virus (HIV) in humans. However, we did not observe a similar protective effect in SIV-infected African monkeys coinfected with pegiviruses, possibly because SIV causes little to no disease in these hosts.

Specific Detection of Two Divergent Simian Arteriviruses Using RNAscope In Situ Hybridization

Simian hemorrhagic fever (SHF) is an often lethal disease of Asian macaques. Simian hemorrhagic fever virus (SHFV) is one of at least three distinct simian arteriviruses that can cause SHF, but pathogenesis studies using modern methods have been scarce. Even seemingly straightforward studies, such as examining viral tissue and cell tropism in vivo, have been difficult to conduct due to the absence of standardized SHFV-specific reagents. Here we report the establishment of an in situ hybridization assay for the detection of SHFV and distantly related Kibale red colobus virus 1 (KRCV-1) RNA in cell culture. In addition, we detected SHFV RNA in formalin-fixed, paraffin-embedded tissues from an infected rhesus monkey (Macaca mulatta). The assay is easily performed and can clearly distinguish between SHFV and KRCV-1. Thus, if further developed, this assay may be useful during future studies evaluating the mechanisms by which a simian arterivirus with a restricted cell tropism can cause a lethal nonhuman primate disease similar in clinical presentation to human viral hemorrhagic fevers.

Divergent Simian Arteriviruses Cause Simian Hemorrhagic Fever of Differing Severities in Macaques

Simian hemorrhagic fever (SHF) is a highly lethal disease in captive macaques. Three distinct arteriviruses are known etiological agents of past SHF epizootics, but only one, simian hemorrhagic fever virus (SHFV), has been isolated in cell culture. The natural reservoir(s) of the three viruses have yet to be identified, but African nonhuman primates are suspected. Eleven additional divergent simian arteriviruses have been detected recently in diverse and apparently healthy African cercopithecid monkeys. Here, we report the successful isolation in MARC-145 cell culture of one of these viruses, Kibale red colobus virus 1 (KRCV-1), from serum of a naturally infected red colobus (Procolobus [Piliocolobus] rufomitratus tephrosceles) sampled in Kibale National Park, Uganda. Intramuscular (i.m.) injection of KRCV-1 into four cynomolgus macaques (Macaca fascicularis) resulted in a self-limiting nonlethal disease characterized by depressive behavioral changes, disturbance in coagulation parameters, and liver enzyme elevations. In contrast, i.m. injection of SHFV resulted in typical lethal SHF characterized by mild fever, lethargy, lymphoid depletion, lymphoid and hepatocellular necrosis, low platelet counts, increased liver enzyme concentrations, coagulation abnormalities, and increasing viral loads. As hypothesized based on the genetic and presumed antigenic distance between KRCV-1 and SHFV, all four macaques that had survived KRCV-1 injection died of SHF after subsequent SHFV injection, indicating a lack of protective heterotypic immunity. Our data indicate that SHF is a disease of macaques that in all likelihood can be caused by a number of distinct simian arteriviruses, although with different severity depending on the specific arterivirus involved. Consequently, we recommend that current screening procedures for SHFV in primate-holding facilities be modified to detect all known simian arteriviruses.

IMPORTANCE

Outbreaks of simian hemorrhagic fever (SHF) have devastated captive Asian macaque colonies in the past. SHF is caused by at least three viruses of the family Arteriviridae: simian hemorrhagic fever virus (SHFV), simian hemorrhagic encephalitis virus (SHEV), and Pebjah virus (PBJV). Nine additional distant relatives of these three viruses were recently discovered in apparently healthy African nonhuman primates. We hypothesized that all simian arteriviruses are potential causes of SHF. To test this hypothesis, we inoculated cynomolgus macaques with a highly divergent simian arterivirus (Kibale red colobus virus 1 [KRCV-1]) from a wild Ugandan red colobus. Despite being only distantly related to red colobuses, all of the macaques developed disease. In contrast to SHFV-infected animals, KRCV-1-infected animals survived after a mild disease presentation. Our study advances the understanding of an important primate disease. Furthermore, our data indicate a need to include the full diversity of simian arteriviruses in nonhuman primate SHF screening assays.

Rhabdomyolysis in Ebola Virus Disease. Results of an Observational Study in a Treatment Center in Guinea

BACKGROUND

The pathogenesis of Ebola virus disease (EVD) remains unclear. The sporadic nature of Ebola outbreaks and their occurrence in resource-limited settings have precluded the acquisition of extensive clinical and laboratory data. Rhabdomyolysis during EVD has been suggested to occur in previous studies showing increased aspartate aminotransferase-alanine aminotransferase ratios, but, to date, has not been confirmed with creatine kinase (CK) assays.

METHODS

We performed an observational study of 38 patients admitted to an Ebola treatment center from January to April 2015. CK values from patients with confirmed EVD were compared with those in patients without confirmed EVD. A panel of other analyses were also performed. In patients with EVD, characteristics were compared between survivors and nonsurvivors.

RESULTS

High levels of CK were more frequent in patients with EVD than in those without (P = .002), and rhabdomyolysis was more frequent (59% vs 19%, respectively; P = .03). CK levels >5000 U/L were observed in 36% of patients with EVD. Also in patients with EVD, fatal outcome was significantly associated with higher creatinine and bilirubin levels, international normalized ratio, and viral load.

CONCLUSIONS

Rhabdomyolysis is a frequent disorder in EVD and seems to be more common than in other viral infections. It may contribute to the renal failure observed in nonsurviving patients. More studies are needed to determine the impact of rhabdomyolysis on EVD outcome.

Cytokines and viral hemorrhagic fever: potential for therapeutic intervention

ABSTRACT 

The recent Ebola outbreak in West Africa highlights the need to improve our understanding of why viral hemorrhagic fevers (VHFs) are so devastating. There is a requirement to generate effective prophylactics, such as vaccines, and therapies, especially those that are effective postsymptomatically. For a range of pathogens, it appears that overstimulation of pro-inflammatory cytokines, the ‘cytokine storm’, causes serious immunopathology in patients. In this review, we will focus on the cytokine response following infection by representatives of the viruses which can cause VHF: Ebola virus and Marburg virus, Crimean–Congo hemorrhagic fever virus, Dengue virus, Junin and Lassa virus. Specifically, the role of the cytokine storm in causing VHF and the use of therapeutic immunomodulatory compounds to help treat these fatal and debilitating diseases will be explored.

Simian hemorrhagic fever virus: Recent advances

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SHFV induces hemorrhagic fever in macaques but not in African nonhuman primates.

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SHFV infection of macaque but not baboon cells induces proinflammatory cytokines.

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Unique N- and C-terminal genes encoded by SHFV were functionally analyzed.

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PLP1γ can cleave at upstream sites as well as at the expected downstream site.

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Eight minor structural proteins are required for infectious virus production.

The simian hemorrhagic fever virus (SHFV) genome differs from those of other members of the family Arteriviridae in encoding three papain-like one proteases (PLP1α, PLP1β and PLP1γ) at the 5′ end and two adjacent sets of four minor structural proteins at the 3′ end. The catalytic Cys and His residues and cleavage sites for each of the SHFV PLP1s were predicted and their functionality was tested in in vitro transcription/translation reactions done with wildtype or mutant polyprotein constructs. Mass spectrometry analyses of selected autoproteolytic products confirmed cleavage site locations. The catalytic Cys of PLP1α is unusual in being adjacent to an Ala instead of a Typ. PLP1γ cleaves at both downstream and upstream sites. Intermediate precursor and alternative cleavage products were detected in the in vitro transcription/translation reactions but only the three mature nsp1 proteins were detected in SHFV-infected MA104 cell lysates with SHFV nsp1 protein-specific antibodies. The duplicated sets of SHFV minor structural proteins were predicted to be functionally redundant. A stable, full-length, infectious SHFV-LVR cDNA clone was constructed and a set of mutant infectious clones was generated each with the start codon of one of the minor structural proteins mutated. All eight of the minor structural proteins were found to be required for production of infectious extracellular virus. SHFV causes a fatal hemorrhagic fever in macaques but asymptomatic, persistent infections in natural hosts such as baboons. SHFV infections were compared in macrophages and myeloid dendritic cells from baboons and macaques. Virus yields were higher from macaque cells than from baboon cells. Macrophage cultures from the two types of animals differed dramatically in the percentage of cells infected. In contrast, similar percentages of myeloid dendritic cells were infected but virus replication was efficient in the macaque cells but inefficient in the baboon cells. SHFV infection induced the production of pro-inflammatory cytokines, including IL-1β, IL-6, IL-12/23(p40), TNF-α and MIP-1α, in macaque cells but not baboon cells.

A simian hemorrhagic fever virus isolate from persistently infected baboons efficiently induces hemorrhagic fever disease in Japanese macaques

Simian hemorrhagic fever virus is an arterivirus that naturally infects species of African nonhuman primates causing acute or persistent asymptomatic infections. Although it was previously estimated that 1% of baboons are SHFV-positive, more than 10% of wild-caught and captive-bred baboons tested were SHFV positive and the infections persisted for more than 10 years with detectable virus in the blood (100–1000 genomes/ml). The sequences of two baboon SHFV isolates that were amplified by a single passage in primary macaque macrophages had a high degree of identity to each other as well as to the genome of SHFV-LVR, a laboratory strain isolated in the 1960s. Infection of Japanese macaques with 100 PFU of a baboon isolate consistently produced high level viremia, pro-inflammatory cytokines, elevated tissue factor levels and clinical signs indicating coagulation defects. The baboon virus isolate provides a reliable BSL2 model of viral hemorrhagic fever disease in macaques.

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More than 10% of wild-caught and captive-bred baboons tested are SHFV positive.

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Baboons remain persistently infected for longer than 10 years.

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The sequences of baboon SHFV isolates were similar to each other and to SHFV LVR.

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A baboon SHFV (100 PFU) consistently induced hemorrhagic fever disease in macaques.

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A reliable BSL2 macaque model of viral hemorrhagic fever disease was developed.

Genome Sequences of Simian Hemorrhagic Fever Virus Variant NIH LVR42-0/M6941 Isolates (Arteriviridae: Arterivirus)

Simian hemorrhagic fever virus (SHFV) variant NIH LVR42-0/M6941 is the only remaining SHFV in culture, and only a single genome sequence record exists in GenBank/RefSeq. We compared the genomic sequence of NIH LVR42-0/M6941 acquired from the ATCC in 2011 to NIH LVR42-0/M6941 genomes sequenced directly from nonhuman primates experimentally infected in 1989.

Two novel simian arteriviruses in captive and wild baboons (Papio spp.)

Since the 1960s, simian hemorrhagic fever virus (SHFV; Nidovirales, Arteriviridae) has caused highly fatal outbreaks of viral hemorrhagic fever in captive Asian macaque colonies. However, the source(s) of these outbreaks and the natural reservoir(s) of this virus remain obscure. Here we report the identification of two novel, highly divergent simian arteriviruses related to SHFV, Mikumi yellow baboon virus 1 (MYBV-1) and Southwest baboon virus 1 (SWBV-1), in wild and captive baboons, respectively, and demonstrate the recent transmission of SWBV-1 among captive baboons. These findings extend our knowledge of the genetic and geographic diversity of the simian arteriviruses, identify baboons as a natural host of these viruses, and provide further evidence that baboons may have played a role in previous outbreaks of simian hemorrhagic fever in macaques, as has long been suspected. This knowledge should aid in the prevention of disease outbreaks in captive macaques and supports the growing body of evidence that suggests that simian arterivirus infections are common in Old World monkeys of many different species throughout Africa.

IMPORTANCE

Historically, the emergence of primate viruses both in humans and in other primate species has caused devastating outbreaks of disease. One strategy for preventing the emergence of novel primate pathogens is to identify microbes with the potential for cross-species transmission in their natural state within reservoir species from which they might emerge. Here, we detail the discovery and characterization of two related simian members of the Arteriviridae family that have a history of disease emergence and host switching. Our results expand the phylogenetic and geographic range of the simian arteriviruses and define baboons as a natural host for these viruses. Our findings also identify a potential threat to captive macaque colonies by showing that simian arteriviruses are actively circulating in captive baboons.

High genetic diversity and adaptive potential of two simian hemorrhagic fever viruses in a wild primate population

Key biological properties such as high genetic diversity and high evolutionary rate enhance the potential of certain RNA viruses to adapt and emerge. Identifying viruses with these properties in their natural hosts could dramatically improve disease forecasting and surveillance. Recently, we discovered two novel members of the viral family Arteriviridae: simian hemorrhagic fever virus (SHFV)-krc1 and SHFV-krc2, infecting a single wild red colobus (Procolobus rufomitratus tephrosceles) in Kibale National Park, Uganda. Nearly nothing is known about the biological properties of SHFVs in nature, although the SHFV type strain, SHFV-LVR, has caused devastating outbreaks of viral hemorrhagic fever in captive macaques. Here we detected SHFV-krc1 and SHFV-krc2 in 40% and 47% of 60 wild red colobus tested, respectively. We found viral loads in excess of 10⁶–10⁷ RNA copies per milliliter of blood plasma for each of these viruses. SHFV-krc1 and SHFV-krc2 also showed high genetic diversity at both the inter- and intra-host levels. Analyses of synonymous and non-synonymous nucleotide diversity across viral genomes revealed patterns suggestive of positive selection in SHFV open reading frames (ORF) 5 (SHFV-krc2 only) and 7 (SHFV-krc1 and SHFV-krc2). Thus, these viruses share several important properties with some of the most rapidly evolving, emergent RNA viruses.

Differential responses of disease-resistant and disease-susceptible primate macrophages and myeloid dendritic cells to simian hemorrhagic fever virus infection

Simian hemorrhagic fever virus (SHFV) causes a fatal hemorrhagic fever in macaques but an asymptomatic, persistent infection in baboons. To investigate factors contributing to this differential infection outcome, the targets of SHFV infection, macrophages (MΦs) and myeloid dendritic cells (mDCs), were differentiated from macaque and baboon peripheral blood monocytes and used to compare viral replication and cell responses. SHFV replicated in >90% of macaque MΦs but in only ∼10% of baboon MΦs. Although SHFV infected ∼50% of macaque and baboon mDCs, virus replication was efficient in macaque but not in baboon mDCs. Both types of macaque cultures produced higher virus yields than baboon cultures. A more efficient type I interferon response and the production of proinflammatory cytokines, including interleukin-1β (IL-1β), IL-6, IL-12/23(p40), tumor necrosis factor alpha (TNF-α), and macrophage inflammatory protein 1α (MIP-1α), in response to SHFV infection were observed in macaque but not baboon cultures, suggesting less efficient counteraction of these responses by viral proteins in macaque cells. Baboon cultures produced higher levels of IL-10 than macaque cultures both prior to and after SHFV infection. In baboon but not macaque cell cultures, SHFV infection upregulated IL-10R1, a subunit of the IL-10 receptor (IL-10R), and also SOCS3, a negative regulator of proinflammatory cytokine production. Incubation of macaque cultures with human IL-10 before and/or after SHFV infection decreased production of IL-6, IL-1β, and MIP-1α but not TNF-α, suggesting a role for IL-10 in suppressing SHFV-induced proinflammatory cytokine production in macaques.

The search for animal models for Lassa fever vaccine development

Lassa virus (LASV) is the most prevalent arenavirus in West Africa and is responsible for several hundred thousand infections and thousands of deaths annually. The sizeable disease burden, numerous imported cases of Lassa fever (LF) and the possibility that LASV can be used as an agent of biological warfare make a strong case for vaccine development. Currently there is no licensed LF vaccine and research and devlopment is hampered by the high cost of nonhuman primate animal models and by biocontainment requirements (BSL-4). In addition, a successful LF vaccine has to induce a strong cell-mediated cross-protective immunity against different LASV lineages. All of these challenges will be addressed in this review in the context of available and novel animal models recently described for evaluation of LF vaccine candidates.