Indirect ELISA based on Hendra and Nipah virus proteins for the detection of henipavirus specific antibodies in pigs

A Luciferase Immunosorbent Assay Based on Attachment Glycoprotein for the Rapid and Easy Detection of Nipah Virus IgG Antibodies

Nipah virus (NiV) is a virulent zoonotic disease whose natural host is the fruit bat (Pteropus medius), which can coexist with and transmit the virus. Due to its high pathogenicity, wide host range, and pandemic potential, establishing a sensitive, specific, and rapid diagnostic method for NiV is key to preventing and controlling its spread and any outbreaks. Here, we established a luciferase immunosorbent assay (LISA) based on the NiV attachment glycoprotein (G) to detect NiV-specific immunoglobulin G by expressing a fusion protein of nanoluciferase (NanoLuc) and the target antigen. Sensitivity analysis was performed and compared to an indirect enzyme-linked immunosorbent assay (ELISA), and specificity and cross-reactivity assessments were performed using NiV-positive horse serum and Ebola virus-, Crimean-Congo hemorrhagic fever virus-, and West Nile virus-positive horse sera. The optimal structural domain for NiV detection was located within amino acids 176-602 of the NiV G protein head domain. Moreover, the LISA showed at least fourfold more sensitivity than the indirect ELISA, and the cross-reactivity results suggested that the LISA had good specificity and was capable of detecting NiV-specific immunoglobulin G in both mouse and horse serum. In conclusion, the establishment of a rapid, simple NiV LISA using the G protein head domain provides a resource for NiV monitoring.

Hendra Virus: An Update on Diagnosis, Vaccination, and Biosecurity Protocols for Horses

Hendra virus (HeV) emerged as a zoonotic pathogen in the 1990s, causing low morbidity but high mortality in humans and horses. Pteropid bats are the natural reservoir of HeV and other important zoonotic viruses such as Nipah and Ebola viruses. Equivac HeV, manufactured by Zoetis (Parkville, Victoria, Australia), is the only commercially available vaccine for horses. There is no commercial vaccine for humans. The epidemiology, clinical features, pathology, diagnosis, management, and prevention of HeV will be reviewed.

Structure, function, and evolution of the Orthobunyavirus membrane fusion glycoprotein

La Crosse virus, responsible for pediatric encephalitis in the United States, and Schmallenberg virus, a highly teratogenic veterinary virus in Europe, belong to the large Orthobunyavirus genus of zoonotic arthropod-borne pathogens distributed worldwide. Viruses in this under-studied genus cause CNS infections or fever with debilitating arthralgia/myalgia syndromes, with no effective treatment. The main surface antigen, glycoprotein Gc (∼1,000 residues), has a variable N-terminal half (Gc^S) targeted by the patients' antibody response and a conserved C-terminal moiety (Gc^F) responsible for membrane fusion during cell entry. Here, we report the X-ray structure of post-fusion La Crosse and Schmallenberg virus Gc^F, revealing the molecular determinants for hairpin formation and trimerization required to drive membrane fusion. We further experimentally confirm the role of residues in the fusion loops and in a vestigial endoplasmic reticulum (ER) translocation sequence at the Gc^S-Gc^F junction. The resulting knowledge provides essential molecular underpinnings for future development of potential therapeutic treatments and vaccines.

Evaluation of three rapid low-resource molecular tests for Nipah virus

Accurate and timely diagnosis of Nipah virus (NiV) requires rapid, inexpensive, and robust diagnostic tests to control spread of disease. Current state of the art technologies are slow and require laboratory infrastructure that may not be available in all endemic settings. Here we report the development and comparison of three rapid NiV molecular diagnostic tests based on reverse transcription recombinase-based isothermal amplification coupled with lateral flow detection. These tests include a simple and fast one-step sample processing step that inactivates the BSL-4 pathogen, enabling safe testing without the need for multi-step RNA purification. The rapid NiV tests targeted the Nucleocapsid protein (N) gene with analytical sensitivity down to 1,000 copies/μL for synthetic NiV RNA and did not cross-react with RNA of other flaviviruses or Chikungunya virus, which can clinically present with similar febrile symptoms. Two tests detected 50,000-100,000 TCID₅₀/mL (100-200 RNA copies/reaction) of the two distinct strains of NiV, Bangladesh (NiV_B) and Malaysia (NiV_M), and took 30 min from sample to result, suggesting these tests are well suited for rapid diagnosis under resource-limited conditions due to rapidity, simplicity, and low equipment requirements. These Nipah tests represent a first step toward development of near-patient NiV diagnostics that are appropriately sensitive for first-line screening, sufficiently robust for a range of peripheral settings, with potential to be safely performed outside of biohazard containment facilities.

Mystery of fatal 'staggering disease' unravelled: novel rustrela virus causes severe meningoencephalomyelitis in domestic cats

'Staggering disease' is a neurological disease entity considered a threat to European domestic cats (Felis catus) for almost five decades. However, its aetiology has remained obscure. Rustrela virus (RusV), a relative of rubella virus, has recently been shown to be associated with encephalitis in a broad range of mammalian hosts. Here, we report the detection of RusV RNA and antigen by metagenomic sequencing, RT-qPCR, in-situ hybridization and immunohistochemistry in brain tissues of 27 out of 29 cats with non-suppurative meningoencephalomyelitis and clinical signs compatible with'staggering disease' from Sweden, Austria, and Germany, but not in non-affected control cats. Screening of possible reservoir hosts in Sweden revealed RusV infection in wood mice (Apodemus sylvaticus). Our work indicates that RusV is the long-sought cause of feline 'staggering disease'. Given its reported broad host spectrum and considerable geographic range, RusV may be the aetiological agent of neuropathologies in further mammals, possibly even including humans.

Development and laboratory evaluation of a competitive ELISA for serodiagnosis of Nipah and Hendra virus infection using recombinant Nipah glycoproteins and a monoclonal antibody

Introduction

Nipah virus (NiV) and Hendra virus (HeV), of the genus Henipavirus, family Paramyxoviridae, are classified as Risk Group 4 (RG4) pathogens that cause respiratory disease in pigs and acute/febrile encephalitis in humans with high mortality.

Methods

A competitive enzyme-linked immunosorbent assay (cELISA) using a monoclonal antibody (mAb) and recombinant NiV glycoprotein (G) was developed and laboratory evaluated using sera from experimental pigs, mini pigs and nonhuman primates. The test depends on competition between specific antibodies in positive sera and a virus-specific mAb for binding to NiV-G.

Results

Based on 1,199 negative and 71 NiV positive serum test results, the cutoff value was determined as 35% inhibition. The diagnostic sensitivity and specificity of the NiV cELISA was 98.58 and 99.92%, respectively. When testing sera from animals experimentally infected with NiV Malaysia, the cELISA detected antibodies from 14 days post-infection (dpi) and remained positive until the end of the experiment (28 dpi). Comparisons using the Kappa coefficient showed strong agreement (100%) between the cELISA and a plaque reduction neutralization test (PRNT).

Discussion

Because our cELISA is simpler, faster, and gives comparable or better results than PRNT, it would be an adequate screening test for suspect NiV and HeV cases, and it would also be useful for epidemiological surveillance of Henipavirus infections in different animal species without changing reagents.

Detection of Serum Antibody Responses in Nipah Virus-Infected Pigs

Nipah virus (NiV) is an emerging, zoonotic paramyxovirus that is among the most pathogenic of viruses in humans. During the first reported outbreak of NiV in Malaysia and Singapore in the late 1990s, pigs served as an intermediate host, which enabled the transmission to humans. Although subsequent outbreaks in Asia only reported direct bat-to-human and human-to-human transmission, pigs are still considered a potential source for viral dissemination in the epidemiology of the disease. Thus, serological assays such as Enzyme-linked immunosorbent assay (ELISA) or virus neutralization test (VNT) represent powerful tools to characterize the serum antibody responses in NiV-infected pigs as well as to perform seroepidemiological surveillance studies on the potential circulation of NiV or NiV-related viruses among pig populations worldwide. This chapter describes both methods in detail. Furthermore, we discuss some of the major pitfalls and indicate how to avoid them.

Detection of Nipah and Hendra Viruses Using Recombinant Human Ephrin B2 Capture Virus in Immunoassays

Nipah virus (NiV) and Hendra virus (HeV) are classified as high-consequence zoonotic viruses characterized by high pathogenicity and high mortality in animals and humans. Rapid diagnosis is essential to containing the outbreak. In this study, the henipavirus receptor ephrin B2 was examined to determine whether it could be used as a universal ligand for henipavirus detection in immunoassays. Enzyme-linked immunosorbent assays (ELISAs) were developed using recombinant ephrin B2 as the capture ligand and two monoclonal antibodies (mAbs) as detection reagents. Using mAb F27NiV-34, which cross-reacts with NiV and HeV, we were able to detect NiV and HeV, while mAb F20NiV-65 was used to detect NiV. Therefore, using these two ELISAs, we were able to differentiate between NiV and HeV. Furthermore, we developed a rapid lateral flow strip test for NiV detection using ephrin B2 as the capture ligand combined with mAb F20NiV-65 as the detector. Taken together, our results show that the combination of ephrin B2 and a specific mAb provides an excellent pairing for NiV and HeV detection.

Serological Hendra Virus Diagnostics Using an Indirect ELISA-Based DIVA Approach with Recombinant Hendra G and N Proteins

Since the identification of Hendra virus (HeV) infections in horses in Australia in 1994, more than 80 outbreaks in horses have been reported, and four out of seven spillover infections in humans had a fatal outcome. With the availability of a subunit vaccine based on the HeV-Glycoprotein (HeV-G), there is a need to serologically Differentiate the Infected from the Vaccinated Animals (DIVA). We developed an indirect ELISA using HeV-G expressed in Leishmania tarentolae and HeV-Nucleoprotein (HeV-N) expressed in recombinant baculovirus-infected insect cells as antigens. During evaluation, we tested panels of sera from naïve, vaccinated and infected horses that either originated from a Hendra-virus free region, or had been pre-tested in validated diagnostic tests. Our data confirm the reliability of this approach, as HeV-N-specific antibodies were only detected in sera from infected horses, while HeV-G-specific antibodies were detected in infected and vaccinated horses with a high level of specificity and sensitivity. Given the excellent correlation of data obtained for German and Australian HeV-negative horses, we assume that this test can be applied for the testing of horse serum samples from a variety of geographical regions.

Design and Analysis of a Single System of Impedimetric Biosensors for the Detection of Mosquito-Borne Viruses

The treatment for mosquito-borne viral diseases such as dengue virus (DENV), zika virus (ZIKV), and chikungunya virus (CHIKV) has become difficult due to delayed diagnosis processes. In addition, sharing the same transmission media and similar symptoms at the early stage of infection of these diseases has become more critical for early diagnosis. To overcome this, a common platform that can identify the virus with high sensitivity and selectivity, even for the different serotypes, is in high demand. In this study, we have attempted an electrochemical impedimetric method to detect the ZIKV, DENV, and CHIKV using their corresponding antibody-conjugated sensor electrodes. The significance of this method is emphasized on the fabrication of a common matrix of gold-polyaniline and sulfur, nitrogen-doped graphene quantum dot nanocomposites (Au-PAni-N,S-GQDs), which have a strong impedimetric response based only on the conjugated antibody, resulting in minimum cross-reactivity for the detection of various mosquito-borne viruses, separately. As a result, four serotypes of DENV and ZIKV, and CHIKV have been detected successfully with an LOD of femtogram mL-1.

Monoclonal antibodies specific for the hemagglutinin-neuraminidase protein define neutralizing epitopes specific for Newcastle disease virus genotype 2.VII from Egypt

Background

Newcastle disease is a devastating disease in poultry caused by virulent Newcastle disease virus (NDV), a paramyxovirus endemic in many regions of the world despite intensive vaccination. Phylogenetic analyses reveal ongoing evolution of the predominant circulating genotype 2.VII, and the relevance of potential antigenic drift is under discussion. To investigate variation within neutralization-sensitive epitopes within the protein responsible for receptor binding, i.e. the Hemagglutinin-Neuraminidase (HN) spike protein, we were interested in establishing genotype-specific monoclonal antibodies (MAbs).

Methods

An HN-enriched fraction of a gradient-purified NDV genotype 2.VII was prepared and successfully employed to induce antibodies in BalbC mice that recognize conformationally intact sites reactive by haemagglutination inhibition (HI). For subsequent screening of mouse hybridoma cultures, an NDV-ELISA was established that utilizes Concanavalin A (ConA-ELISA) coupled glycoproteins proven to present conformation-dependent epitopes.

Results

Six out of nine selected MAbs were able to block receptor binding as demonstrated by HI activity. One MAb recognized an epitope only present in the homologue virus, while four other MAbs showed weak reactivity to selected other genotypes. On the other hand, one broadly cross-reacting MAb reacted with all genotypes tested and resembled the reactivity profile of genotype-specific polyclonal antibody preparations that point to minor antigenic differences between tested NDV genotpyes.

Conclusions

These results point to the concurrent presence of variable and conserved epitopes within the HN molecule of NDV. The described protocol should help to generate MAbs against a variety of NDV strains and to enable in depth analysis of the antigenic profiles of different genotypes.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12985-021-01540-0.

Generation and characterization of monoclonal antibodies specific for the Pseudorabies Virus nuclear egress complex

During herpesvirus replication, newly synthesized nucleocapsids exit the nucleus by a vesicle-mediated transport, which requires the nuclear egress complex (NEC), composed of the conserved viral proteins designated as pUL31 and pUL34 in the alphaherpesviruses pseudorabies virus (PrV) and herpes simplex viruses. Oligomerization of the heterodimeric NEC at the inner nuclear membrane (INM) results in membrane bending and budding of virus particles into the perinuclear space. The INM-derived primary envelope then fuses with the outer nuclear membrane to release nucleocapsids into the cytoplasm. The two NEC components are necessary and sufficient for induction of vesicle budding and scission as shown after co-expression in eukaryotic cells or in synthetic membranes. However, where and when the NEC is formed, how membrane curvature is mediated and how it is regulated, remains unclear. While monospecific antisera raised against the different components of the PrV NEC aided in the characterization and intracellular localization of the individual proteins, no NEC specific tools have been described yet for any herpesvirus. To gain more insight into vesicle budding and scission, we aimed at generating NEC specific monoclonal antibodies (mAbs). To this end, mice were immunized with bacterially expressed soluble PrV NEC, which was previously used for structure determination. Besides pUL31- and pUL34-specific mAbs, we also identified mAbs, which reacted only in the presence of both proteins indicating specificity for the complex. Confocal microscopy with those NEC-specific mAbs revealed small puncta (approx. 0.064 μm²) along the nuclear rim in PrV wild type infected cells. In contrast, ca. 5-fold larger speckles (approx. 0.35 μm²) were detectable in cells infected with a PrV mutant lacking the viral protein kinase pUS3, which is known to accumulate primary enveloped virions in the PNS within large invaginations of the INM, or in cells co-expressing pUL31 and pUL34. Kinetic experiments showed that while the individual proteins were detectable already between 2-4 hours after infection, the NEC-specific mAbs produced significant staining only after 4-6 hours in accordance with timing of nuclear egress. Taken together, the data indicate that these mAbs specifically label the PrV NEC.

Isolation and characterization of new Puumala orthohantavirus strains from Germany

Orthohantaviruses are re-emerging rodent-borne pathogens distributed all over the world. Here, we report the isolation of a Puumala orthohantavirus (PUUV) strain from bank voles caught in a highly endemic region around the city Osnabrück, north-west Germany. Coding and non-coding sequences of all three segments (S, M, and L) were determined from original lung tissue, after isolation and after additional passaging in VeroE6 cells and a bank vole-derived kidney cell line. Different single amino acid substitutions were observed in the RNA-dependent RNA polymerase (RdRP) of the two stable PUUV isolates. The PUUV strain from VeroE6 cells showed a lower titer when propagated on bank vole cells compared to VeroE6 cells. Additionally, glycoprotein precursor (GPC)-derived virus-like particles of a German PUUV sequence allowed the generation of monoclonal antibodies that allowed the reliable detection of the isolated PUUV strain in the immunofluorescence assay. In conclusion, this is the first isolation of a PUUV strain from Central Europe and the generation of glycoprotein-specific monoclonal antibodies for this PUUV isolate. The obtained virus isolate and GPC-specific antibodies are instrumental tools for future reservoir host studies.

Advanced Immunotechnological Methods for Detection and Diagnosis of Viral Infections: Current Applications and Future Challenges

Diagnosis and identification of viruses is an important component of diagnostic virology laboratory. Although various modes of diagnostic methods are now available at disposal, a vast majority of the diseases across the globe remain undiagnosed. This is largely due to the overlapping undifferentiated set of symptoms across myriad set of RNA and DNA viral diseases. As such, it becomes critical to take into consideration several factors for viral diagnosis ranging from the type and quality of specimen collected, time of specimen collection, mode of transport, accuracy, specificity, sensitivity, and the type of diagnostic method used. This chapter broadly emphasizes various methods on diagnostic virology ranging from the classical methods of diagnosis to the most recently developed molecular methods of detection of virus.

Nipah virus: epidemiology, pathology, immunobiology and advances in diagnosis, vaccine designing and control strategies - a comprehensive review

Nipah (Nee-pa) viral disease is a zoonotic infection caused by Nipah virus (NiV), a paramyxovirus belonging to the genus Henipavirus of the family Paramyxoviridae. It is a biosafety level-4 pathogen, which is transmitted by specific types of fruit bats, mainly Pteropus spp. which are natural reservoir host. The disease was reported for the first time from the Kampung Sungai Nipah village of Malaysia in 1998. Human-to-human transmission also occurs. Outbreaks have been reported also from other countries in South and Southeast Asia. Phylogenetic analysis affirmed the circulation of two major clades of NiV as based on currently available complete N and G gene sequences. NiV isolates from Malaysia and Cambodia clustered together in NiV-MY clade, whereas isolates from Bangladesh and India clusterered within NiV-BD clade. NiV isolates from Thailand harboured mixed population of sequences. In humans, the virus is responsible for causing rapidly progressing severe illness which might be characterized by severe respiratory illness and/or deadly encephalitis. In pigs below six months of age, respiratory illness along with nervous symptoms may develop. Different types of enzyme-linked immunosorbent assays along with molecular methods based on polymerase chain reaction have been developed for diagnostic purposes. Due to the expensive nature of the antibody drugs, identification of broad-spectrum antivirals is essential along with focusing on small interfering RNAs (siRNAs). High pathogenicity of NiV in humans, and lack of vaccines or therapeutics to counter this disease have attracted attention of researchers worldwide for developing effective NiV vaccine and treatment regimens.

Viral antigen nanoparticles for discriminated and quantitative detection of different subtypes of anti-virus immunoglobulins

The aim of this study is to develop a novel method for the accurate diagnosis of the infection status of viral diseases, which requires discriminated and quantitative detection of different anti-virus immunoglubulin subtypes. Considering hepatitis A as a representative model disease, viral antigen nanoparticles (vAgNPs) were designed and synthesized by genetically presenting hepatitis A virus (HAV) antigens on the surface of human heavy chain ferritin (hFTH) nanoparticles to detect anti-HAV antibodies with discriminating immunoglobulin subtypes M and G (IgM and IgG, respectively). The vAgNPs also display multi-copies of hexa-histidine peptide (H6) on their surface to chemisorb gold ions (Au3+), which is vital for the autonomous generation of quantitatively meaningful detection signals. The quantitative level of anti-HAV IgM or IgG in 30 patient sera was successfully analyzed using the vAgNPs of HAV, which was performed through label-free one-step-immunoassay based on the self-enhancement of optical signals from gold nanoparticles clustered on the viral antigen nanoparticles. The diagnostic performance was compared with that of enzyme-linked immunosorbent assay (ELISA), which did not enable accurate quantitative assay due to the poor linearity between the antibody concentration and detection signal. Furthermore, these vAgNP-based immunoassays did not produce any false negative/positive signals, indicating 100% sensitivity and 100% specificity.

Henipavirus-like particles induce a CD8 T cell response in C57BL/6 mice

Nipah virus (NiV), a BSL-4 pathogen, belongs to the genus Henipavirus within the family Paramyxoviridae. To date, no effective vaccine is available. Although most of the current vaccine studies aim to induce a neutralizing antibody response, it has become evident that a promising vaccine should target both, humoral and cell-mediated immune response. Virus-like particles (VLPs) have been shown to activate both arms of the adaptive immune response. In our study, VLPs composed of the NiV surface glycoproteins G and F and the matrix protein of the closely related Hendra virus (HeV M) induced both, a neutralizing antibody response and an antigen-specific CD8 T cell response with proliferation, IFN-γ expression and Th1 cytokine secretion in C57BL/6 mice. In contrast, in BALB/c mice only a neutralizing antibody response was observed. All three viral proteins included in the VLPs were shown to harbor CD8 T cell epitopes; however, the combination of all three proteins enhanced the magnitude of the CD8 T cell response. To conclude, VLPs represent a promising vaccine candidate, as they induce humoral as well as CD8 T cell-mediated immune responses.

Advances in diagnostics, vaccines and therapeutics for Nipah virus

Nipah virus is an emerging zoonotic paramyxovirus that causes severe and often fatal respiratory and neurological disease in humans. The virus was first discovered after an outbreak of encephalitis in pig farmers in Malaysia and Singapore with subsequent outbreaks in Bangladesh or India occurring almost annually. Due to the highly pathogenic nature of NiV, its pandemic potential, and the lack of licensed vaccines or therapeutics, there is a requirement for research and development into highly sensitive and specific diagnostic tools as well as antivirals and vaccines to help prevent and control future outbreak situations.

Nipah virus: epidemiology, pathology, immunobiology and advances in diagnosis, vaccine designing and control strategies - a comprehensive review

Nipah (Nee-pa) viral disease is a zoonotic infection caused by Nipah virus (NiV), a paramyxovirus belonging to the genus Henipavirus of the family Paramyxoviridae. It is a biosafety level-4 pathogen, which is transmitted by specific types of fruit bats, mainly Pteropus spp. which are natural reservoir host. The disease was reported for the first time from the Kampung Sungai Nipah village of Malaysia in 1998. Human-to-human transmission also occurs. Outbreaks have been reported also from other countries in South and Southeast Asia. Phylogenetic analysis affirmed the circulation of two major clades of NiV as based on currently available complete N and G gene sequences. NiV isolates from Malaysia and Cambodia clustered together in NiV-MY clade, whereas isolates from Bangladesh and India clusterered within NiV-BD clade. NiV isolates from Thailand harboured mixed population of sequences. In humans, the virus is responsible for causing rapidly progressing severe illness which might be characterized by severe respiratory illness and/or deadly encephalitis. In pigs below six months of age, respiratory illness along with nervous symptoms may develop. Different types of enzyme-linked immunosorbent assays along with molecular methods based on polymerase chain reaction have been developed for diagnostic purposes. Due to the expensive nature of the antibody drugs, identification of broad-spectrum antivirals is essential along with focusing on small interfering RNAs (siRNAs). High pathogenicity of NiV in humans, and lack of vaccines or therapeutics to counter this disease have attracted attention of researchers worldwide for developing effective NiV vaccine and treatment regimens.

Rabies-based vaccine induces potent immune responses against Nipah virus

Nipah Virus (NiV) is a re-emerging zoonotic pathogen in the genus Henipavirus of the Paramyxoviridae family of viruses. NiV is endemic to Bangladesh and Malaysia and is highly fatal to both livestock and humans (human case fatality rate = 74.5%). Currently, there is no approved vaccine against NiV on the market. The goal of this study was to use a recombinant RABV vector expressing NiV glycoprotein (NiV G) to develop a bivalent candidate vaccine against NiV disease and rabies virus (RABV) disease, which is also a significant health burden in the regions where NiV is endemic. The rabies vector is a well-established vaccine strain that lacks neurovirulence and can stably expresses foreign antigens that are immunogenic in various animal models. Mice inoculated intranasally with the live recombinant RABV/NiV vaccine (NIPARAB) showed no signs of disease. To test the immunogenicity of the vaccine candidate, groups of C57BL/6 mice were immunized intramuscularly with a single dose of live vaccine particles or two doses of chemically inactivated viral particles. Both vaccination groups showed NiV G-specific seroconversion, and the inactivated (INAC) vaccine group yielded higher titers of NiV G-specific antibodies. Furthermore, cross-reactivity of NiV G-specific immune sera against Hendra virus (HeV), was confirmed by immunofluorescence (IF) and indirect ELISA against soluble recombinant HeV glycoprotein (HeV G). Both live and killed vaccines induced neutralizing antibodies. These results indicate that NIPARAB may be used as a killed virus vaccine to protect humans against NiV and RABV, and possibly as a preventative measure against HeV as well.

Henipaviruses at the Interface Between Bats, Livestock and Human Population in Africa

Nipah virus (NiV) and Hendra virus (HeV) are closely related members within the genus Henipavirus, family Paramyxoviridae, for which fruit bats serve as the reservoir. The initial emergence of NiV infections in pigs and humans in Malaysia, and HeV infections in horses and humans in Australia, posed severe impacts on human and animal health, and continues threatening lives of humans and livestock within Southeast Asia and Australia. Recently, henipavirus-specific antibodies have also been detected in fruit bats in a number of sub-Saharan African countries and in Brazil, thereby considerably increasing the known geographic distribution of henipaviruses. Africa is progressively being recognized as a new high prevalence zone for henipaviruses, as deduced from serological and molecular evidence of past infections in Madagascar, Ghana, Republic of Congo, Gulf of Guinea, Zambia, Tanzania, Cameroon, and Nigeria lately. Serological data suggest henipavirus spillover from bats to livestock and human populations in Africa without reported clinical disease in any of these species. All virus isolation attempts have been abortive, highlighting the need for further investigations. The genome of the Ghanaian bat henipavirus designated Ghana virus (GhV), which was detected in a pteropid Eidolon helvum bat, is the only African henipavirus that has been completely sequenced limiting our current knowledge on the genetic diversity and pathogenesis of African henipaviruses. In this review, we summarize the available data on the circulation of henipaviruses in Africa, discuss potential sources for virus spillover, and highlight existing research gaps.

Pathogenicity of Nipah henipavirus Bangladesh in a swine host

In 1998 an outbreak of fatal encephalitis among pig farm workers in Malaysia and Singapore led to the discovery of Nipah henipavirus (NiV), a novel paramyxovirus closely related to Hendra henipavirus with case fatality rates of nearly 40%. Following its initial emergence nearly annual outbreaks of NiV have occurred in Bangladesh with a different, NiV Bangladesh, genotype, where the role of pigs in its transmission remains unknown. The present study provides the first report on susceptibility of domestic pigs to NiV Bangladesh following experimental infection, characterizing acute and long-term phases of disease and pathogenesis. All pigs were successfully infected with NiV Bangladesh following oronasal inoculation, with viral shedding confirmed by a novel genotype-specific qRT-PCR in oral, nasal and rectal excretions and dissemination from the upper respiratory tract to the brain, lungs, and associated lymphatic tissues. Unlike previous NiV Malaysia findings in pigs, clinical signs were absent, viremia was undetectable throughout the study, and only low level neutralizing antibody titers were measured by 28/29 days post-NiV-B infection. Results obtained highlight the need for continued and enhanced NiV surveillance in pigs in endemic and at-risk regions, and raise questions regarding applicability of current serological assays to detect animals with previous NiV-B exposure.

Evidence of exposure to henipaviruses in domestic pigs in Uganda

Hendra virus (HeV) and Nipah virus (NiV), belonging to the genus Henipavirus, are among the most pathogenic of viruses in humans. Old World fruit bats (family Pteropodidae) are the natural reservoir hosts. Molecular and serological studies found evidence of henipavirus infection in fruit bats from several African countries. However, little is known about the potential for spillover into domestic animals in East Africa, particularly pigs, which served as amplifying hosts during the first outbreak of NiV in Malaysia and Singapore. We collected sera from 661 pigs presented for slaughter in Uganda between December 2015 and October 2016. Using HeV G and NiV G indirect ELISAs, 14 pigs (2%) were seroreactive in at least one ELISA. Seroprevalence increased to 5.4% in October 2016, when pigs were 9.5 times more likely to be seroreactive than pigs sampled in December 2015 (p = 0.04). Eight of the 14 ELISA‐positive samples reacted with HeV N antigen in Western blot. None of the sera neutralized HeV or NiV in plaque reduction neutralization tests. Although we did not detect neutralizing antibodies, our results suggest that pigs in Uganda are exposed to henipaviruses or henipa‐like viruses. Pigs in this study were sourced from many farms throughout Uganda, suggesting multiple (albeit rare) introductions of henipaviruses into the pig population. We postulate that given the widespread distribution of Old World fruit bats in Africa, spillover of henipaviruses from fruit bats to pigs in Uganda could result in exposure of pigs at multiple locations. A higher risk of a spillover event at the end of the dry season might be explained by higher densities of bats and contact with pigs at this time of the year, exacerbated by nutritional stress in bat populations and their reproductive cycle. Future studies should prioritize determining the risk of spillover of henipaviruses from pigs to people, so that potential risks can be mitigated.

Nipah virus infection: A review

Nipah virus (NiV) is an emerging bat-borne pathogen. It was first identified 20 years ago in Malaysia and has since caused outbreaks in other parts of South and Southeast Asia. It causes severe neurological and respiratory disease which is highly lethal. It is highly infectious and spreads in the community through infected animals or other infected people. Different strains of the virus show differing clinical and epidemiological features. Rapid diagnosis and implementation of infection control measures are essential to contain outbreaks. A number of serological and molecular diagnostic techniques have been developed for diagnosis and surveillance. Difficulties in diagnosis and management arise when a new area is affected. The high mortality associated with infection and the possibility of spread to new areas has underscored the need for effective management and control. However, no effective treatment or prophylaxis is readily available, though several approaches show promise. Given the common chains of transmission from bats to humans, a One Health approach is necessary for the prevention and control of NiV infection.