Humanized Mouse Model of Ebola Virus Disease Mimics the Immune Responses in Human Disease

Animal models recapitulating human Ebola virus disease (EVD) are critical for insights into virus pathogenesis. Ebola virus (EBOV) isolates derived directly from human specimens do not, without adaptation, cause disease in immunocompetent adult rodents. Here, we describe EVD in mice engrafted with human immune cells (hu-BLT). hu-BLT mice developed EVD following wild-type EBOV infection. Infection with high-dose EBOV resulted in rapid, lethal EVD with high viral loads, alterations in key human antiviral immune cytokines and chemokines, and severe histopathologic findings similar to those shown in the limited human postmortem data available. A dose- and donor-dependent clinical course was observed in hu-BLT mice infected with lower doses of either Mayinga (1976) or Makona (2014) isolates derived from human EBOV cases. Engraftment of the human cellular immune system appeared to be essential for the observed virulence, as nonengrafted mice did not support productive EBOV replication or develop lethal disease. hu-BLT mice offer a unique model for investigating the human immune response in EVD and an alternative animal model for EVD pathogenesis studies and therapeutic screening.

Development of a reverse genetics system to generate recombinant Marburg virus derived from a bat isolate

Recent investigations have shown the Egyptian fruit bat (Rousettus aegyptiacus) to be a natural reservoir for marburgviruses. To better understand the life cycle of these viruses in the natural host, a new reverse genetics system was developed for the reliable rescue of a Marburg virus (MARV) originally isolated directly from a R. aegyptiacus bat (371Bat). To develop this system, the exact terminal sequences were first determined by 5' and 3' RACE, followed by the cloning of viral proteins NP, VP35, VP30 and L into expression plasmids. Novel conditions were then developed to efficiently replicate virus mini-genomes followed by the construction of full-length genomic clones from which recombinant wild type and GFP-containing MARVs were rescued. Surprisingly, when these recombinant MARVs were propagated in primary human macrophages, a dramatic difference was found in their ability to grow and to elicit anti-viral cytokine responses.

Rift Valley fever, Sudan, 2007 and 2010

Viral sequences analyzed indicate recent virus movement and support the need for surveillance.

To elucidate whether Rift Valley fever virus (RVFV) diversity in Sudan resulted from multiple introductions or from acquired changes over time from 1 introduction event, we generated complete genome sequences from RVFV strains detected during the 2007 and 2010 outbreaks. Phylogenetic analyses of small, medium, and large RNA segment sequences indicated several genetic RVFV variants were circulating in Sudan, which all grouped into Kenya-1 or Kenya-2 sublineages from the 2006–2008 eastern Africa epizootic. Bayesian analysis of sequence differences estimated that diversity among the 2007 and 2010 Sudan RVFV variants shared a most recent common ancestor circa 1996. The data suggest multiple introductions of RVFV into Sudan as part of sweeping epizootics from eastern Africa. The sequences indicate recent movement of RVFV and support the need for surveillance to recognize when and where RVFV circulates between epidemics, which can make data from prediction tools easier to interpret and preventive measures easier to direct toward high-risk areas.

Genomic analysis of filoviruses associated with four viral hemorrhagic fever outbreaks in Uganda and the Democratic Republic of the Congo in 2012

In 2012, an unprecedented number of four distinct, partially overlapping filovirus-associated viral hemorrhagic fever outbreaks were detected in equatorial Africa. Analysis of complete virus genome sequences confirmed the reemergence of Sudan virus and Marburg virus in Uganda, and the first emergence of Bundibugyo virus in the Democratic Republic of the Congo.

Seasonal pulses of Marburg virus circulation in juvenile Rousettus aegyptiacus bats coincide with periods of increased risk of human infection

Marburg virus (family Filoviridae) causes sporadic outbreaks of severe hemorrhagic disease in sub-Saharan Africa. Bats have been implicated as likely natural reservoir hosts based most recently on an investigation of cases among miners infected in 2007 at the Kitaka mine, Uganda, which contained a large population of Marburg virus-infected Rousettus aegyptiacus fruit bats. Described here is an ecologic investigation of Python Cave, Uganda, where an American and a Dutch tourist acquired Marburg virus infection in December 2007 and July 2008. More than 40,000 R. aegyptiacus were found in the cave and were the sole bat species present. Between August 2008 and November 2009, 1,622 bats were captured and tested for Marburg virus. Q-RT-PCR analysis of bat liver/spleen tissues indicated ~2.5% of the bats were actively infected, seven of which yielded Marburg virus isolates. Moreover, Q-RT-PCR-positive lung, kidney, colon and reproductive tissues were found, consistent with potential for oral, urine, fecal or sexual transmission. The combined data for R. aegyptiacus tested from Python Cave and Kitaka mine indicate low level horizontal transmission throughout the year. However, Q-RT-PCR data show distinct pulses of virus infection in older juvenile bats (~six months of age) that temporarily coincide with the peak twice-yearly birthing seasons. Retrospective analysis of historical human infections suspected to have been the result of discrete spillover events directly from nature found 83% (54/65) events occurred during these seasonal pulses in virus circulation, perhaps demonstrating periods of increased risk of human infection. The discovery of two tags at Python Cave from bats marked at Kitaka mine, together with the close genetic linkages evident between viruses detected in geographically distant locations, are consistent with R. aegyptiacus bats existing as a large meta-population with associated virus circulation over broad geographic ranges. These findings provide a basis for developing Marburg hemorrhagic fever risk reduction strategies.

Ancient ancestry of KFDV and AHFV revealed by complete genome analyses of viruses isolated from ticks and mammalian hosts

BACKGROUND

Alkhurma hemorrhagic fever virus (AHFV) and Kyasanur forest disease virus (KFDV) cause significant human disease and mortality in Saudi Arabia and India, respectively. Despite their distinct geographic ranges, AHFV and KFDV share a remarkably high sequence identity. Given its emergence decades after KFDV, AHFV has since been considered a variant of KFDV and thought to have arisen from an introduction of KFDV to Saudi Arabia from India. To gain a better understanding of the evolutionary history of AHFV and KFDV, we analyzed the full length genomes of 16 AHFV and 3 KFDV isolates.

METHODOLOGY/PRINCIPAL FINDINGS

Viral genomes were sequenced and compared to two AHFV sequences available in GenBank. Sequence analyses revealed higher genetic diversity within AHFVs isolated from ticks than human AHFV isolates. A Bayesian coalescent phylogenetic analysis demonstrated an ancient divergence of AHFV and KFDV of approximately 700 years ago.

CONCLUSIONS/SIGNIFICANCE

The high sequence diversity within tick populations and the presence of competent tick vectors in the surrounding regions, coupled with the recent identification of AHFV in Egypt, indicate possible viral range expansion or a larger geographic range than previously thought. The divergence of AHFV from KFDV nearly 700 years ago suggests other AHFV/KFDV-like viruses might exist in the regions between Saudi Arabia and India. Given the human morbidity and mortality associated with these viruses, these results emphasize the importance of more focused study of these significant public health threats.

Multiple Crimean-Congo hemorrhagic fever virus strains are associated with disease outbreaks in Sudan, 2008-2009

Background

Crimean-Congo hemorrhagic fever (CCHF) activity has recently been detected in the Kordufan region of Sudan. Since 2008, several sporadic cases and nosocomial outbreaks associated with high case-fatality have been reported in villages and rural hospitals in the region.

Principal Findings

In the present study, we describe a cluster of cases occurring in June 2009 in Dunkop village, Abyei District, South Kordufan, Sudan. Seven CCHF cases were involved in the outbreak; however, clinical specimens could be collected from only two patients, both of whom were confirmed as acute CCHF cases using CCHF-specific reverse transcriptase polymerase chain reaction (RT-PCR). Phylogenetic analysis of the complete S, M, and L segment sequences places the Abyei strain of CCHF virus in Group III, a virus group containing strains from various countries across Africa, including Sudan, South Africa, Mauritania, and Nigeria. The Abyei strain detected in 2009 is genetically distinct from the recently described 2008 Sudanese CCHF virus strains (Al-fulah 3 and 4), and the Abyei strain S and L segments closely match those of CCHF virus strain ArD39554 from Mauritania.

Conclusions

The present investigation illustrates that multiple CCHF virus lineages are circulating in the Kordufan region of Sudan and are associated with recent outbreaks of the disease occurring during 2008–2009.

The tick-borne virus which causes the disease Crimean-Congo hemorrhagic fever (CCHF) is known to be widely distributed throughout much of Africa, Southern Europe, the Middle East, Central Asia, and Southern Russia. Humans contract the virus from contact with infected people, infected animals (which do not show symptoms), and from the bite of infected ticks. CCHF was recently recognized in the Sudan when several hospital staff and patients died from the disease in a rural hospital. The genetic analysis of viruses associated with the 2008 and 2009 outbreaks shows that several CCHF viral strains currently circulate and cause human outbreaks in the Sudan, highlighting CCHF virus as an emerging pathogen. The Sudanese strains are similar to others circulating in Africa, indicating movement of virus over large distances with introduction and disease outbreaks in rural areas possible. Understanding the epidemiology of zoonotic diseases such as CCHF is especially important in the Sudan given the large numbers of livestock in the country, and their importance to the economy and rural communities. It is imperative that hospital staff consider CCHF as a possible disease agent, since they are at a high risk of contracting the disease, especially in hospitals with limited medical supplies.

High diversity and ancient common ancestry of lymphocytic choriomeningitis virus

Lymphocytic choriomeningitis virus (LCMV) is the prototype of the family Arenaviridae. LCMV can be associated with severe disease in humans, and its global distribution reflects the broad dispersion of the primary rodent reservoir, the house mouse (Mus musculus). Recent interest in the natural history of the virus has been stimulated by increasing recognition of LCMV infections during pregnancy, and in clusters of LCMV-associated fatal illness among tissue transplant recipients. Despite its public health importance, little is known regarding the genetic diversity or distribution of virus variants. Genomic analysis of 29 LCMV strains collected from a variety of geographic and temporal sources showed these viruses to be highly diverse. Several distinct lineages exist, but there is little correlation with time or place of isolation. Bayesian analysis estimates the most recent common ancestor to be 1,000-5,000 years old, and this long history is consistent with complex phylogeographic relationships of the extant virus isolates.

Nosocomial outbreak of Crimean-Congo hemorrhagic fever, Sudan

To confirm the presence of Crimean-Congo hemorrhagic fever in Sudan, we tested serum of 8 patients with hemorrhagic fever in a rural hospital in 2008. Reverse transcription–PCR identified Crimean-Congo hemorrhagic fever virus. Its identification as group III lineage indicated links to virus strains from South Africa, Mauritania, and Nigeria.

The phylogenetics and ecology of the orthopoxviruses endemic to North America

The data presented herein support the North American orthopoxviruses (NA OPXV) in a sister relationship to all other currently described Orthopoxvirus (OPXV) species. This phylogenetic analysis reaffirms the identification of the NA OPXV as close relatives of “Old World” (Eurasian and African) OPXV and presents high support for deeper nodes within the Chordopoxvirinae family. The natural reservoir host(s) for many of the described OPXV species remains unknown although a clear virus-host association exists between the genus OPXV and several mammalian taxa. The hypothesized host associations and the deep divergence of the OPXV/NA OPXV clades depicted in this study may reflect the divergence patterns of the mammalian faunas of the Old and New World and reflect a more ancient presence of OPXV on what are now the American continents. Genes from the central region of the poxvirus genome are generally more conserved than genes from either end of the linear genome due to functional constraints imposed on viral replication abilities. The relatively slower evolution of these genes may more accurately reflect the deeper history among the poxvirus group, allowing for robust placement of the NA OPXV within Chordopoxvirinae. Sequence data for nine genes were compiled from three NA OPXV strains plus an additional 50 genomes collected from Genbank. The current, gene sequence based phylogenetic analysis reaffirms the identification of the NA OPXV as the nearest relatives of “Old World” OPXV and presents high support for deeper nodes within the Chordopoxvirinae family. Additionally, the substantial genetic distances that separate the currently described NA OPXV species indicate that it is likely that many more undescribed OPXV/NA OPXV species may be circulating among wild animals in North America.

Isolation of genetically diverse Marburg viruses from Egyptian fruit bats

In July and September 2007, miners working in Kitaka Cave, Uganda, were diagnosed with Marburg hemorrhagic fever. The likely source of infection in the cave was Egyptian fruit bats (Rousettus aegyptiacus) based on detection of Marburg virus RNA in 31/611 (5.1%) bats, virus-specific antibody in bat sera, and isolation of genetically diverse virus from bat tissues. The virus isolates were collected nine months apart, demonstrating long-term virus circulation. The bat colony was estimated to be over 100,000 animals using mark and re-capture methods, predicting the presence of over 5,000 virus-infected bats. The genetically diverse virus genome sequences from bats and miners closely matched. These data indicate common Egyptian fruit bats can represent a major natural reservoir and source of Marburg virus with potential for spillover into humans.

Efficient reverse genetics generation of infectious junin viruses differing in glycoprotein processing

The New World arenaviruses, Junin, Machupo, Guanarito, Sabia, and Chapare, are associated with rapidly progressing severe hemorrhagic fever with a high rate of case fatality in various regions of South America. The threat of natural or deliberate outbreaks associated with these viruses makes the development of preventive or therapeutic measures important. Here we describe a Junin virus functional minigenome system and a reverse genetics system for production of infectious Junin virus. This robust, highly efficient system involves transfection of cells with only two plasmids which transcribe the virus S and L antigenomic RNAs. The utility of the system is demonstrated by generating Junin viruses which encode a glycoprotein precursor (GPC) containing the following: (i) the wild-type (SKI-1/S1P peptidase) cleavage site, (ii) no cleavage site, or (iii) a cleavage site where the SKI-1/S1P motif (RSLK) is replaced by a furin cleavage site (RRKR). In contrast to the wild-type virus, Junin virus lacking a GPC cleavage site replicated within successfully transfected cells but failed to yield infectious virus particles. This confirms observations with other arenaviruses suggesting that GPC cleavage is essential for arenavirus infectivity. In contrast, infectious Junin virus which encoded GPC cleaved by furin-like proteases was easily generated. The two-plasmid, high efficiency aspects of this Junin virus reverse genetics system show great promise for addressing important questions regarding arenavirus hemorrhagic fever disease and for development of precisely attenuated live arenavirus vaccines.

Genetic detection and characterization of Lujo virus, a new hemorrhagic fever-associated arenavirus from southern Africa

Lujo virus (LUJV), a new member of the family Arenaviridae and the first hemorrhagic fever–associated arenavirus from the Old World discovered in three decades, was isolated in South Africa during an outbreak of human disease characterized by nosocomial transmission and an unprecedented high case fatality rate of 80% (4/5 cases). Unbiased pyrosequencing of RNA extracts from serum and tissues of outbreak victims enabled identification and detailed phylogenetic characterization within 72 hours of sample receipt. Full genome analyses of LUJV showed it to be unique and branching off the ancestral node of the Old World arenaviruses. The virus G1 glycoprotein sequence was highly diverse and almost equidistant from that of other Old World and New World arenaviruses, consistent with a potential distinctive receptor tropism. LUJV is a novel, genetically distinct, highly pathogenic arenavirus.

In September and October 2008, five cases of undiagnosed hemorrhagic fever, four of them fatal, were recognized in South Africa after air transfer of a critically ill index case from Zambia. Serum and tissue samples from victims were subjected to unbiased pyrosequencing, yielding within 72 hours of sample receipt, multiple discrete sequence fragments that represented approximately 50% of a prototypic arenavirus genome. Thereafter, full genome sequence was generated by PCR amplification of intervening fragments using specific primers complementary to sequence obtained by pyrosequencing and a universal primer targeting the conserved arenaviral termini. Phylogenetic analyses confirmed the presence of a new member of the family Arenaviridae, provisionally named Lujo virus (LUJV) in recognition of its geographic origin (Lusaka, Zambia, and Johannesburg, South Africa). Our findings enable the development of specific reagents to further investigate the reservoir, geographic distribution, and unusual pathogenicity of LUJV, and confirm the utility of unbiased high throughput pyrosequencing for pathogen discovery and public health.

Newly discovered ebola virus associated with hemorrhagic fever outbreak in Uganda

Over the past 30 years, Zaire and Sudan ebolaviruses have been responsible for large hemorrhagic fever (HF) outbreaks with case fatalities ranging from 53% to 90%, while a third species, Côte d'Ivoire ebolavirus, caused a single non-fatal HF case. In November 2007, HF cases were reported in Bundibugyo District, Western Uganda. Laboratory investigation of the initial 29 suspect-case blood specimens by classic methods (antigen capture, IgM and IgG ELISA) and a recently developed random-primed pyrosequencing approach quickly identified this to be an Ebola HF outbreak associated with a newly discovered ebolavirus species (Bundibugyo ebolavirus) distantly related to the Côte d'Ivoire ebolavirus found in western Africa. Due to the sequence divergence of this new virus relative to all previously recognized ebolaviruses, these findings have important implications for design of future diagnostic assays to monitor Ebola HF disease in humans and animals, and ongoing efforts to develop effective antivirals and vaccines.

In this report we describe a newly discovered ebolavirus species which caused a large hemorrhagic fever outbreak in western Uganda. The virus is genetically distinct, differing by more than 30% at the genome level from all other known ebolavirus species. The unique nature of this virus created challenges for traditional filovirus molecular based diagnostic assays and genome sequencing approaches. Instead, we quickly determined over 70% of the virus genome using a recently developed random-primed pyrosequencing approach that allowed the rapid development of a molecular detection assay that was deployed in the disease outbreak response. This draft sequence allowed easy completion of the whole genome sequence using a traditional primer walking approach and prompt confirmation that this virus represented a new ebolavirus species. Current efforts to design effective diagnostics, antivirals and vaccines will need to take into account the distinct nature of this important new member of the filovirus family.

The complete genome sequence of a Crimean-Congo hemorrhagic fever virus isolated from an endemic region in Kosovo

The Balkan region and Kosovo in particular, is a well-known Crimean-Congo hemorrhagic fever (CCHF) endemic region, with frequent epidemic outbreaks and sporadic cases occurring with a hospitalized case fatality of approximately 30%. Recent analysis of complete genome sequences of diverse CCHF virus strains showed that the genome plasticity of the virus is surprisingly high for an arthropod-borne virus. High levels of nucleotide and amino acid differences, frequent RNA segment reassortment and even RNA recombination have been recently described. This diversity illustrates the need to determine the complete genome sequence of CCHF virus representatives of all geographically distinct endemic areas, particularly in light of the high pathogenicity of the virus and its listing as a potential bioterrorism threat. Here we describe the first complete CCHF virus genome sequence of a virus (strain Kosova Hoti) isolated from a hemorrhagic fever case in the Balkans. This virus strain was isolated from a fatal CCHF case, and passaged only twice on Vero E6 cells prior to sequence analysis. The virus total genome was found to be 19.2 kb in length, consisting of a 1672 nucleotide (nt) S segment, a 5364 nt M segment and a 12150 nt L segment. Phylogenetic analysis of CCHF virus complete genomes placed the Kosova Hoti strain in the Europe/Turkey group, with highest similarity seen with Russian isolates. The virus M segments are the most diverse with up to 31 and 27% differences seen at the nt and amino acid levels, and even 1.9% amino acid difference found between the Kosova Hoti and another strain from Kosovo (9553-01). This suggests that distinct virus strains can coexist in highly endemic areas.

Complete genome analysis of 33 ecologically and biologically diverse Rift Valley fever virus strains reveals widespread virus movement and low genetic diversity due to recent common ancestry

Rift Valley fever (RVF) virus is a mosquito-borne RNA virus responsible for large explosive outbreaks of acute febrile disease in humans and livestock in Africa with significant mortality and economic impact. The successful high-throughput generation of the complete genome sequence was achieved for 33 diverse RVF virus strains collected from throughout Africa and Saudi Arabia from 1944 to 2000, including strains differing in pathogenicity in disease models. While several distinct virus genetic lineages were determined, which approximately correlate with geographic origin, multiple exceptions indicative of long-distance virus movement have been found. Virus strains isolated within an epidemic (e.g., Mauritania, 1987, or Egypt, 1977 to 1978) exhibit little diversity, while those in enzootic settings (e.g., 1970s Zimbabwe) can be highly diverse. In addition, the large Saudi Arabian RVF outbreak in 2000 appears to have involved virus introduction from East Africa, based on the close ancestral relationship of a 1998 East African virus. Virus genetic diversity was low (approximately 5%) and primarily involved accumulation of mutations at an average of 2.9 x 10(-4) substitutions/site/year, although some evidence of RNA segment reassortment was found. Bayesian analysis of current RVF virus genetic diversity places the most recent common ancestor of these viruses in the late 1800s, the colonial period in Africa, a time of dramatic changes in agricultural practices and introduction of nonindigenous livestock breeds. In addition to insights into the evolution and ecology of RVF virus, these genomic data also provide a foundation for the design of molecular detection assays and prototype vaccines useful in combating this important disease.

Crimean-Congo hemorrhagic fever virus genomics and global diversity

Crimean-Congo hemorrhagic fever (CCHF) is a severe illness with high case fatality that occurs in Africa, Europe, the Middle East, and Asia. The complete genomes of 13 geographically and temporally diverse virus strains were determined, and CCHF viruses were found to be highly variable with 20 and 8%, 31 and 27%, and 22 and 10% nucleotide and deduced amino acid differences detected among virus S (nucleocapsid), M (glycoprotein), and L (polymerase) genome segments, respectively. Distinct geographic lineages exist, but with multiple exceptions indicative of long-distance virus movement. Discrepancies among the virus S, M, and L phylogenetic tree topologies document multiple RNA segment reassortment events. An analysis of individual segment datasets suggests genetic recombination also occurs. For an arthropod-borne virus, the genomic plasticity of CCHF virus is surprisingly high.

Marburgvirus genomics and association with a large hemorrhagic fever outbreak in Angola

In March 2005, the Centers for Disease Control and Prevention (CDC) investigated a large hemorrhagic fever (HF) outbreak in Uige Province in northern Angola, West Africa. In total, 15 initial specimens were sent to CDC, Atlanta, Ga., for testing for viruses associated with viral HFs known to be present in West Africa, including ebolavirus. Marburgvirus was also included despite the fact that the origins of all earlier outbreaks were linked directly to East Africa. Surprisingly, marburgvirus was confirmed (12 of 15 specimens) as the cause of the outbreak. The outbreak likely began in October 2004 and ended in July 2005, and it included 252 cases and 227 (90%) fatalities (report from the Ministry of Health, Republic of Angola, 2005), making it the largest Marburg HF outbreak on record. A real-time quantitative reverse transcription-PCR assay utilized and adapted during the outbreak proved to be highly sensitive and sufficiently robust for field use. Partial marburgvirus RNA sequence analysis revealed up to 21% nucleotide divergence among the previously characterized East African strains, with the most distinct being Ravn from Kenya (1987). The Angolan strain was less different ( approximately 7%) from the main group of East African marburgviruses than one might expect given the large geographic separation. To more precisely analyze the virus genetic differences between outbreaks and among viruses within the Angola outbreak itself, a total of 16 complete virus genomes were determined, including those of the virus isolates Ravn (Kenya, 1987) and 05DRC, 07DRC, and 09DRC (Democratic Republic of Congo, 1998) and the reference Angolan virus isolate (Ang1379v). In addition, complete genome sequences were obtained from RNAs extracted from 10 clinical specimens reflecting various stages of the disease and locations within the Angolan outbreak. While the marburgviruses exhibit high overall genetic diversity (up to 22%), only 6.8% nucleotide difference was found between the West African Angolan viruses and the majority of East African viruses, suggesting that the virus reservoir species in these regions are not substantially distinct. Remarkably few nucleotide differences were found among the Angolan clinical specimens (0 to 0.07%), consistent with an outbreak scenario in which a single (or rare) introduction of virus from the reservoir species into the human population was followed by person-to-person transmission with little accumulation of mutations. This is in contrast to the 1998 to 2000 marburgvirus outbreak, where evidence of several virus genetic lineages (with up to 21% divergence) and multiple virus introductions into the human population was found.

A tale of two clades: monkeypox viruses

Human monkeypox was first recognized outside Africa in 2003 during an outbreak in the USA that was traced to imported monkeypox virus (MPXV)-infected West African rodents. Unlike the smallpox-like disease described in the Democratic Republic of the Congo (DRC; a Congo Basin country), disease in the USA appeared milder. Here, analyses compared clinical, laboratory and epidemiological features of confirmed human monkeypox case-patients, using data from outbreaks in the USA and the Congo Basin, and the results suggested that human disease pathogenicity was associated with the viral strain. Genomic sequencing of USA, Western and Central African MPXV isolates confirmed the existence of two MPXV clades. A comparison of open reading frames between MPXV clades permitted prediction of viral proteins that could cause the observed differences in human pathogenicity between these two clades. Understanding the molecular pathogenesis and clinical and epidemiological properties of MPXV can improve monkeypox prevention and control.

Persistence of antibody to hepatitis B and protection from disease among Alaska natives immunized at birth

BACKGROUND

Alaska Native (AN) children were at high risk of acquiring hepatitis B virus (HBV) infection before vaccination began in 1983. We evaluated the long-term protection from hepatitis B (HB) vaccination among AN children immunized when infants.

METHODS

During 1984-1995, we recruited a convenience sample of AN children who had received a three dose series of HB vaccine starting at birth and had serum antibody to hepatitis B (anti-HBs) concentrations of >/= 10 mIU/mL at 7-26 months of age. We evaluated anti-HBs concentrations and the presence of anti-HBc in participants' sera every other year up to age 16 years. Anti-HB core antigen (anti-HBc)-positive specimens were tested for hepatitis B surface antigen and for HBV DNA.

RESULTS

We followed 334 children for 3151 person-years (median, 10 years per child) with 1610 specimens collected. Anti-HBs concentrations dropped rapidly among all participants. Among children 2, 5 and 10 years of age, 37 of 79 (47%), 33 of 176 (19%) and 8 of 95 (8%), respectively, had anti-HBs concentrations of >/= 10 mIU/mL. Receipt of recombinant vaccine was significantly associated with a more rapid antibody decline (P < 0.001). Six (1.8%) children acquired anti-HBc, 3 of whom had definite breakthrough infections (at least 2 consecutive anti-HBc-positive specimens or at least 1 anti-HBc-positive specimen and HBV DNA detection by PCR). None of these children had detectable hepatitis B surface antigen, and none had symptoms of hepatitis.

CONCLUSIONS

Anti-HBs concentrations declined over time among AN infants successfully immunized with HB vaccine starting at birth. Transient anti-HBc appeared in a small percentage of children; however, none developed clinical signs of hepatitis or chronic HBV infection.

Genetic variation of hepatitis B surface antigen coding region among infants with chronic hepatitis B virus infection

Variants in the amino acid composition of the primary antibody-binding site of hepatitis B surface antigen (HBsAg) have been identified in a number of populations with chronic hepatitis B virus (HBV) infection. Direct sequencing of amplified or cloned PCR products, solid phase detection of sequence-specific PCR products (SP-PCR), and limiting dilution cloning PCR (LDC-PCR) were compared to determine their sensitivity in detecting differing concentrations of HBsAg variants. LDC-PCR had the greatest sensitivity and could detect HBsAg variants at a concentration of 0.1% of the total viral population. HBsAg variants were detected in 51% of infants with chronic HBV infection acquired after postexposure prophylaxis, and more than half of the variants were detected only by the most sensitive methods.

[Study of the effect of antiviral drugs on the reproduction of the respiratory syncytial virus by enzyme immunoassay]

A test system based on EIA was developed for evaluating the efficiency of drugs active towards the respiratory syncytial virus (RSV) in cell culture. Virasole and its structural analog ribamedii active towards RSV infection and arbidol whose activity in RSV infection is unknown were tested. Like virasole and ribamedil, arbidol inhibited the expression of RSV antigens, the inhibitory effect increasing with the drug concentration and decreased with increase of the multiplicity of virus infection. MIC50 for arbidol, virasole, and ribamedil were 10, 5, and 6 micrograms/ml, respectively. These data prompt clinical trials of arbidol in RSV infection.

Alteration in the antigenic structure of M1 protein of influenza A virus mutant resistant to a new antiviral compound mopyridone

Using 14 monoclonal antibodies (MoAbs) in solid-phase ELISA it was found that influenza virus A/Hong Kong/1/68 (H3N2) mutants resistant to the antiviral compound mopyridone as compared to the mopyridone-sensitive mutant manifested significant changes in the antigenic structure (sites 1A, 2 and 3) of M1 protein. No differences in M1 were found between rimantadine-resistant and rimantadine-sensitive mutants of influenza virus A(H3N2).

Analysis of internal proteins of influenza A (H2N2) viruses isolated from birds in East Germany in 1983

Proteins and RNAs of influenza A (H2N2) viruses isolated from birds in 1983 in East Germany were compared antigenically with those of H2N2 human strains. The electrophoretic mobility of the viral proteins and of the S1-treated double-stranded RNAs from two human and six avian strains, as well as the results of EIA-tests using monoclonal antibodies to their matrix protein and nucleoproteins indicate an antigenic relationship between the avian isolates and human strains of H2N2 subtype. One of the avian strains had a reduced amount of matrix protein.

[The detection of antibodies to HIV protein p24 in human blood sera by the method of lanthanide immunofluorescent analysis]

A competitive time-resolved fluoroimmunoassay (TR-FIA) system for the detection of antibodies to protein p24 of HIV was developed on the basis of monoclonal antibodies. The advantages of this test system over analogous enzyme immunoassay system and commercial test system "Antigen" (USSR) were demonstrated. The newly developed test system of TR-FIA was used for examination of sera from HIV-infected persons.

[The strain-specific diagnosis of influenza by using lanthanide immunofluorescence analysis based on monoclonal antibodies to the hemagglutinin of the influenza A virus]

Nine monoclonal antibodies (MCA) to hemagglutinin of influenza A/Taiwan/1/86 (H1N1) virus and 5 MCA to influenza A/Mississippi/1/85 (H3N2) virus were generated and characterized. The MCA were used for the development of diagnostic test systems on the basis of time-resolved fluoroimmunoassay. The same MCA were used as primary and detecting antibodies in the test system specific for HA of the H1 serosubtype, whereas in the test system specific for influenza A serosubtype H3 virus MCA of different epitope appurtenance were used as primary and secondary antibodies. The sensitivity of the test system for HA of serosubtype H1 was found to be 10 ng/ml and that for serosubtype H3 5 nh/ml. The developed test systems were tried on the clinical material collected during the epidemic periods of 1983-1989.

[Standardization of conditions for detecting the internal proteins of the influenza virus in studying their antigenic properties in solid-phase immunoenzyme analysis]

The influence of the conditions of adsorption and virion destruction by freezing-thawing and detergents on the detection of M1 and NP proteins of different influenza virus strains by solid-phase enzyme immunoassay with direct virion adsorption on polystyrene was studied. It was found that for the detection of M1 protein the optimal conditions included virion disruption with detergent and adsorption to polystyrene at 4 degrees C, and for NP protein disruption by freezing-thawing at adsorption to polystyrene at 37 degrees C. In the study of the antigenic properties of protein M1 of different influenza virus strains using monoclonal antibodies it was shown to be necessary, first, to achieve maximum detection of proteins and, second, to standardize the amount of the adsorbed antigen with polyclonal antibodies.

[Indication of the influenza virus in clinical samples using immunoenzyme and lanthanide immunofluorescence analyses]

A comparative study of the potentials of enzyme-immunoassay (EIA) and lanthanide immunofluorescent assay (LIFA) for influenza virus detection in nasopharyngeal aspirates and nasopharyngeal washings was carried out. Monospecific and polyclonal antisera to hemagglutinin polyclonal antisera to matrix protein as well as polyclonal and monoclonal antisera to nucleoprotein were used. The nasopharyngeal aspirates were shown to contain virus-specific antigens in the amounts sufficient for influenza virus detection with polyclonal and monoclonal antibodies. There was a good correlation between chromophore results by EIA and fluorescence level in LIFA. The sensitivity of the test systems used (EIA and LIFA) was shown to be insufficient for the detection of virus-specific material in the nasopharyngeal washings. Besides, there was no correlation between the results obtained by different test systems. It was concluded that nasopharyngeal aspirates should be collected for rapid influenza diagnosis by EIA and LIFA.

[Stat-diagnosis of influenza using lanthanide immunofluorescence analysis]

A test system for influenza diagnosis has been developed on the basis of monoclonal antibodies to influenza A and B virus proteins using the principles of lanthanide immunofluorescence analysis. The diagnostic test system was shown to be highly specific in detecting influenza A and B virions in model systems. For the one-step variant of a double sandwich used in the study, the total time of diagnostic experiment using clinical materials was shown to be reduced to 15-20 min.

[Heterogeneous distribution of influenza A matrix protein in polyacrylamide gel, detected using an immunoblotting method with monoclonal antibodies]

The immune blotting method using monoclonal antibodies to Ml protein showed protein Ml to migrate in several bands in polyacrylamide gel electrophoresis (PGE) of influenza A virus polypeptides. The heterogeneous distribution of Ml protein in PGE is due to the formation of aggregates: dimers, trimers, and polymers of a higher order. The capacity of Ml protein for aggregation is typical not of all influenza virus strains and most likely is not associated with gel overloading. Since dimers and trimers of Ml protein comigrate in the gel with virus-specific proteins such as NP and proteins of a polymerase complex, this circumstance should be take into consideration in using PGE for isolation of pure influenza virus proteins.

Antigenic reactivity of matrix protein and nucleoprotein of influenza virus as detected by EIA after dissociation with different detergents

Solid phase enzyme-immunoassay (EIA) was employed to assess the antigenic reactivity of matrix protein (M) and nucleoprotein (NP) of influenza A virus adsorbed to polystyrene in the presence of different detergents such as beta-octaglucoside (OG), Triton X-100, Tween-20, sodium dodecylsulphate (SDS), sodium deoxycholate (Doch-Na), Nonidet P-40 (NP-40), and sarcosyl at concentrations ranging from 0 to 2%. The antigenic reactivity of NP was the highest in the absence of detergents. For M protein, Doch-Na, SDS, NP-40 and sarcosyl of 0.05-0.1% enhanced the chromatophoric response in EIA 1.5-2 times. In contrast, the antigenic reactivity of M protein remained unchanged after OG or Triton X-100 treatments, and it decreased in the presence of Tween-20.

[Isolation and characteristics of monoclonal antibodies to influenza virus types A and B]

Monoclonal antibodies (MCA) to influenza type A (10F) and B (5H and 6H) viruses have been prepared. By immunoblotting method, MCA 10F were found to be specific for NP-protein of influenza A virus, and MCA 5H and 6H to be specific for hemagglutinin of influenza B virus. It was established that the 10F clone interacted with all the investigated influenza A virus strains with different antigenic formulae (H1N1, H2N2, H3N2) and could be used for typing of this virus type. Clones 5H and 6H react specifically with hemagglutinins of influenza B viruses isolated in 1940, 1979, and 1983 which makes them useful for diagnosis of influenza B.

Simultaneous determination of the level of antibodies to influenza virus surface and internal proteins by enzyme-linked immunosorbent assay

Enzyme-linked immunosorbent assay (ELISA) has been adopted for simultaneous determination of the levels of antibodies to different influenza virus proteins in human sera with known haemagglutination-inhibition (HI) titre. Whole virus of serotypes H1N1 and H3N2, haemagglutinin (HA), matrix (M) and nucleoprotein (NP) proteins have been used as antigens. For detection of antibodies bound to the antigen, peroxidase labelled Staphylococcus protein A conjugate has been used. Correlation of the ELISA and HI titres of anti-HA antibody has been demonstrated. The use of isolated HA as antigen increased the specificity of ELISA. The analysis of human reconvalescent sera has shown that increase in the titre of antibodies to internal proteins does not always coincide with the increase of antibody level to HA. Out of 8 sera with significant increase of the HI titre to the H3 subtype 5 specimens showed 4-fold increase of antibody titre to NP protein. The antibody titre to M protein was elevated in 2 sera only, while 1 serum showed no rise of antibody response to the tested viral proteins.

The influence of the isolation technique of influenza virus nucleoprotein on its antigenic properties

ELISA has been used to study the antigenic properties 1. of influenza virus nucleoprotein (NP-1) isolated from virions with the help of preparative polyacrylamide gel electrophoresis (PAGE); 2. of virion ribonucleoprotein (NP-2), and 3. of NP structures prepared by dissociation of ribonucleoprotein into RNA and protein in sucrose gradient containing NaCl (NP-3). The investigation of immunologic cross-reactivity has shown complete identity of NP-2 and NP-3 and their striking difference from NP-1. In contrast to NP-2, NP-3 was not contaminated by other virus antigens, it was a good immunogen and could be used for preparation of monospecific antisera of high titre. NP-1 did not induce a high antibody response,however, like NP-2 and NP-3, it retained its capacity to react with antisera to native virus. Owing to its simple production and high yield, this protein can be used in serodiagnosis for testing the antibody level against NP-protein in convalescent sera.

[Immunoenzyme demonstration of viruses and virus-specific antibodies by using conjugates based on gene engineering-produced beta-lactamase]

Enzyme immunoassays for the detection of viral antigens and virus-specific antibodies in biological samples have been described. Molecular complexes of antibodies and beta-lactamase (penicillinase) have been used as anti-specific conjugates. To synthesize the conjugate, the enzyme obtained with the aid of genetic engineering has been used. Enzyme immunoassays have been tested for the indication of the influenza virus and virus-induced specific antibodies. Enzyme immunoassays were shown to possess certain advantages (e.g., the use of simple and nontoxic substrate) along with the sensitivity identical to that of other methods, employing peroxidase-based conjugates.

[Use of immunoenzyme analysis employing a staphylococcal protein A conjugate with peroxidase in the serodiagnosis of influenza]

A test-system was developed on the basis of solid-phase enzyme-immunoassay using protein A/peroxidase conjugate for the determination of antibody levels to influenza virus in sera of humans who had experienced a natural infection or received a live influenza vaccine. The accurate observation of the test conditions was demonstrated to give the results well correlating with those of the HI test. The use of isolated hemagglutinin as the antigen considerably increased the specificity of the enzyme-immunoassay and in a number of cases detected a 4-fold or higher rise of antibody titres to hemagglutinin in paired sera of the vaccinees where the HI test showed no rise in antibody titres.

[Possibility of detecting the matrix protein of the influenza virus in intact and disrupted virions by immunoenzyme analysis and immune electron microscopy]

ELISA and immune electron microscopy were used to study possible causes of the detection of antigenic reactivity of influenza virus matrix protein in purified virus suspension directly adsorbed on polystyrene. No interaction of antibody to M protein with the surface of virus and subvirus particles was observed. The process of virus sorption on polystyrene for a long period was shown not to lead to disruption of intact virus particles, and the detection of the internal matrix protein in preparations of purified influenza virus was due only to the presence of partially or completely destroyed virions in the viral suspension.

[The use of immunoenzyme methods in virology]

Data on the development of theoretical basis of immunoenzyme (IE)method s (EMIT analysis and ELISA) and on using these methods in virology are presented. The problems arising in the use of most popular version of IE analysis. ELISA, are elucidated: the schemes for different variants of ELISA; the demands to adsorbent, enzyme and substrate for achieving the maximum of sensitivity of the technique; comparison of the advantages of different ELISA variants in identification of various antigens and antibodies. The data on using ELISA for indication and identification of viral antigens and virus specific antibodies are analyzed. The respiratory viruses have been used to demonstrate the possibilities of IE technique for rapid diagnostic of viral diseases and for studies in viral reproduction and structure.

[Reversible dissociation of influenza virus ribonucleoprotein]

Dissociation of influenza virus RNP under the effect of salt was studied. Separation of RNA and protein components of influenza virus RNP was shown to occur in a linear 15-30% sucrose concentration gradient containing 1.1 M NaCl. Upon RNP dissociation, protein-protein interactions between individual molecules of the structural protein were retained. The sedimentation coefficient of the protein component was 52S. The possibility of reassociation of the RNA-protein complex was studied. More complete reassociation was observed to occur in the presence of 0.1 M NaCl. The resulting RNA-protein complex morphologically is similar to the native RNP of influenza virus.

[Proteolytic cleavage of influenza virus matrix protein and nucleoprotein in an in vitro system]

Proteolytic modification of NP-protein which is a part of influenza virus ribonucleoprotein (RNP) was studied in vitro. NP-protein of influenza virus (mol. weight 56 000) was shown upon RNP treatment with bromeline to undergo proteolytic cleavage revealing 2 more polypeptides with molecular weights of 53 000 and 45 000 daltons. The same classes of NP-proteins were present in RNPs recovered from subviral units obtained by virus treatment with bromeline at buffer pH below 7. Electrophoresis in 12% polyacrylamide gel under reducing conditions of subvirus units obtained by treatment of virions with bromeline at the buffer pH below 7 also demonstrated proteolytic cleavage of M-protein present in them into fragments with molecular weights of 8 500-12 000 daltons. Similar results were obtained upon direct treatment with bromeline of M-protein isolated from virions.

[Circular dichroism study of the ribonucleoprotein structure of Sendai virus isolated from infected chick embryo cells]

Thermostability and secondary structure of RNA, a component of ribonucleoprotein (RNP) of Sendai virus isolated from infected chick embryo cells (cRNP) and from virions (vRNP) were studied by the method of circular dichroism. The secondary structure of RNA in cRNP was shown to be practically no different from that of free RNA whereas incorporation of RNA into vRNP was accompanied by a significant decrease in the number of paired bases in it. Comparison of thermodenaturation parameters of cRNP and vRNP also revealed significant differences in their structural organization. Thus, melting of cRNP as well as of free RNA is of markedly non-cooperative nature indicating poor RNA-protein interactions in the complex. In contrast, the process of vRNP thermodenaturation occurs in a step-wise manner in a narrow temperature range indicating a significant role in the maintenance of this RNP structure of both RNA-protein and, apparently, protein-protein interactions.

[Effect of formaldehyde on the ribonucleoprotein structure of Sendai virus]

The effect of formaldehyde on the conformation of Sendai virus ribonucleoprotein (RNP) was studied by electron microscopy and a spectrophotometric method. The effect of formaldehyde on RNP conformation was found to depend strongly on the ionic strength of the solution. Under conditions of a low ionic strength in the presence of 1.5% formaldehyde the tightly coiled rods of RNP stained with uranyl acetate become loosely coiled or almost completely extended. At the same time, formaldehyde reaction with RNP results in a decrease in extinction of the RNP suspension in the 250 to 290 spectral region. However, RNP incubation with formaldehyde in the presence of 0.5M NaCl caused no changes in the morphology and spectral properties of the RNP under study. The results indicate that formaldehyde cannot be used for fixation of Sendai virus nucleocapsids before negative staining for electron microscopy examinations.

[Circular dichroism spectra study on the ribonucleoprotein structure of influenza virus]

The CD spectra of Influenza virus RNA and RNP were examined in the ultraviolet region (220--320 nm) at different temperatures, NaCl and urea concentrations. The magnitude of the positive band for RNP decreases gradually upon increasing the temperature, indicating that rather weak interaction between RNA and protein occurs. However the temperature drastically affects the intensity of the negative band about 222 nm. In the temperature range where the protein melts the positive band at longer wavelengths shows a temperature dependence that is similar for RNP and free RNA. Addition of NaCl results in an increase in intensity and blue shift of the positive CD band of RNP. In the presence of 1 M NaCl the CD spectrum of RNP is very close to that of protein-free RNA. Urea concentrations up to 10 M has little effect on the CD spectrum of RNP. These results suggest that only ionic but not hydrophobic and hydrogen bondings are involved in the RNA-protein interaction in Influenza virus RNP.

[Morphological and structural studies of Sendai virus ribonucleoprotein]

The structure and morphology of Sendai virus ribonucleoprotein (RNP) with native and split protein subunits were studied by the method of circular dichroism and electron microscopy. Cleavage of the polypeptide fragment from RNP protein subunits was shown to cause changes in the secondary structure of RNP in situ but not to affect the RNP morphology; when stained with uranyl acetate both RNP types had an appearance of spiral strands.

[Effect of the isolation method and staining procedure on the morphology of the virion ribonucleoprotein of Sendai virus]

Electron microscopic examinations of morphology of Sendai virus ribonucleoprotein (RNP) isolated from purified virions by two methods and simultaneous staining of the preparations with uranyl acetate and phosphotungstate acid (PTA) were carried out. The staining method was shown not to influence the kind of nucleoproteins which had been isolated from disrupted virions by sucrose density gradient centrifugation. With both strains RNP appeared as strongly helixed filaments. The staining method, however, strongly influenced morphology of RNP isolated from disrupted virions by equilibrium centrifugation in cesium chloride density gradient. After uranyl acetate staining RNP had an appearance of hard filaments whereas in the same preparation stained with PTA partially and completely unwound spirals of nucleocapsid were found alongside with strongly spiralized structures.

[Sedimentation and electron microscopic characteristics of RNA isolated from a highly concentrated suspension of Sendai virus]

Sedimentation analysis in a lineal (5%--30%) sucrose concentration gradient of an RNA preparation isolated from a highly concentrated Sendai virus suspension revealed an additional peak with sedimentation coefficient 69S apart from previously known peaks of 46S (genome RNA), 30S and 18S (incomplete virus RNA). Electron microscopy methods showed the single-stranded molecules of 46S RNA to have a marked hairpin structure. Molecules of double-stranded 69S RNA have a specific structure: lineal parts alternate with areas in the form of rosettes. It is suggested that molecules of of 69S RNA are a product of incomplete hybridization between "plus" and "minus" complementary chains of virion RNA.