Animal Models of Lassa Fever

Lassa virus in novel hosts: insights into the epidemiology of lassa virus infections in southern Nigeria

Identification of the diverse animal hosts responsible for spill-over events from animals to humans is crucial for comprehending the transmission patterns of emerging infectious diseases, which pose significant public health risks. To better characterize potential animal hosts of Lassa virus (LASV), we assessed domestic and non-domestic animals from 2021-2022 in four locations in southern Nigeria with reported cases of Lassa fever (LF). Birds, lizards, and domestic mammals (dogs, pigs, cattle and goats) were screened using RT-qPCR, and whole genome sequencing was performed for lineage identification on selected LASV positive samples. Animals were also screened for exposure to LASV by enzyme-linked immunosorbent assay (ELISA). Among these animals, lizards had the highest positivity rate by PCR. Genomic sequencing of samples in most infected animals showed sub-lineage 2 g of LASV. Seropositivity was highest among cattle and lowest in pigs. Though the specific impact these additional hosts may have in the broader virus-host context are still unknown - specifically relating to pathogen diversity, evolution, and transmission - the detection of LASV in non-rodent hosts living in proximity to confirmed human LF cases suggests their involvement during transmission as potential reservoirs. Additional epidemiological data comparing viral genomes from humans and animals, as well as those circulating within the environment will be critical in understanding LASV transmission dynamics and will ultimately guide the development of countermeasures for this zoonotic health threat.

Emerging and reemerging infectious diseases: global trends and new strategies for their prevention and control

To adequately prepare for potential hazards caused by emerging and reemerging infectious diseases, the WHO has issued a list of high-priority pathogens that are likely to cause future outbreaks and for which research and development (R&D) efforts are dedicated, known as paramount R&D blueprints. Within R&D efforts, the goal is to obtain effective prophylactic and therapeutic approaches, which depends on a comprehensive knowledge of the etiology, epidemiology, and pathogenesis of these diseases. In this process, the accessibility of animal models is a priority bottleneck because it plays a key role in bridging the gap between in-depth understanding and control efforts for infectious diseases. Here, we reviewed preclinical animal models for high priority disease in terms of their ability to simulate human infections, including both natural susceptibility models, artificially engineered models, and surrogate models. In addition, we have thoroughly reviewed the current landscape of vaccines, antibodies, and small molecule drugs, particularly hopeful candidates in the advanced stages of these infectious diseases. More importantly, focusing on global trends and novel technologies, several aspects of the prevention and control of infectious disease were discussed in detail, including but not limited to gaps in currently available animal models and medical responses, better immune correlates of protection established in animal models and humans, further understanding of disease mechanisms, and the role of artificial intelligence in guiding or supplementing the development of animal models, vaccines, and drugs. Overall, this review described pioneering approaches and sophisticated techniques involved in the study of the epidemiology, pathogenesis, prevention, and clinical theatment of WHO high-priority pathogens and proposed potential directions. Technological advances in these aspects would consolidate the line of defense, thus ensuring a timely response to WHO high priority pathogens.

Treatment of highly virulent mammarenavirus infections-status quo and future directions

INTRODUCTION

Mammarenaviruses are negative-sense bisegmented enveloped RNA viruses that are endemic in Africa, the Americas, and Europe. Several are highly virulent, causing acute human diseases associated with high case fatality rates, and are considered to be significant with respect to public health impact or bioterrorism threat.

AREAS COVERED

This review summarizes the status quo of treatment development, starting with drugs that are in advanced stages of evaluation in early clinical trials, followed by promising candidate medical countermeasures emerging from bench analyses and investigational animal research.

EXPERT OPINION

Specific therapeutic treatments for diseases caused by mammarenaviruses remain limited to the off-label use of ribavirin and transfusion of convalescent sera. Progress in identifying novel candidate medical countermeasures against mammarenavirus infection has been slow in part because of the biosafety and biosecurity requirements. However, novel methodologies and tools have enabled increasingly efficient high-throughput molecular screens of regulatory-agency-approved small-molecule drugs and led to the identification of several compounds that could be repurposed for the treatment of infection with several mammarenaviruses. Unfortunately, most of them have not yet been evaluated in vivo. The most promising treatment under development is a monoclonal antibody cocktail that is protective against multiple lineages of the Lassa virus in nonhuman primate disease models.

Marmosets as models of infectious diseases

Animal models of infectious disease often serve a crucial purpose in obtaining licensure of therapeutics and medical countermeasures, particularly in situations where human trials are not feasible, i.e., for those diseases that occur infrequently in the human population. The common marmoset (Callithrix jacchus), a Neotropical new-world (platyrrhines) non-human primate, has gained increasing attention as an animal model for a number of diseases given its small size, availability and evolutionary proximity to humans. This review aims to (i) discuss the pros and cons of the common marmoset as an animal model by providing a brief snapshot of how marmosets are currently utilized in biomedical research, (ii) summarize and evaluate relevant aspects of the marmoset immune system to the study of infectious diseases, (iii) provide a historical backdrop, outlining the significance of infectious diseases and the importance of developing reliable animal models to test novel therapeutics, and (iv) provide a summary of infectious diseases for which a marmoset model exists, followed by an in-depth discussion of the marmoset models of two studied bacterial infectious diseases (tularemia and melioidosis) and one viral infectious disease (viral hepatitis C).

Lassa virus NP DEDDh 3'-5' exoribonuclease activity is required for optimal viral RNA replication and mutation control

Lassa virus (LASV), a mammarenavirus from Arenaviridae, is the causative agent of Lassa fever (LF) endemic in West Africa. Currently, there are no vaccines or antivirals approved for LF. The RNA-dependent RNA polymerases (RdRp) of RNA viruses are error-prone. As a negative-sense RNA virus, how LASV copes with errors in RNA synthesis and ensures optimal RNA replication are not well elucidated. LASV nucleoprotein (NP) contains a DEDDH 3'-to-5' exoribonuclease motif (ExoN), which is known to be essential for LASV evasion of the interferon response via its ability to degrade virus-derived double-stranded RNA. Herein, we present evidence that LASV NP ExoN has an additional function important for viral RNA replication. We rescued an ExoN-deficient LASV mutant (ExoN- rLASV) by using a reverse genetics system. Our data indicated that abrogation of NP ExoN led to impaired LASV growth and RNA replication in interferon-deficient cells as compared with wild-type rLASV. By utilizing PacBio Single Molecule, Real-Time (SMRT) long-read sequencing technology, we found that rLASV lacking ExoN activity was prone to producing aberrant viral genomic RNA with structural variations. In addition, NP ExoN deficiency enhanced LASV sensitivity to mutagenic nucleoside analogues in virus titration assay. Next-generation deep sequencing analysis showed increased single nucleotide substitution in ExoN- LASV RNA following mutagenic 5-flurouracil treatment. In conclusion, our study revealed that LASV NP ExoN is required for efficient viral RNA replication and mutation control. Among negative-sense RNA viruses, LASV NP is the first example that a viral protein, other than the RdRp, contributes to reduce errors in RNA replication and maintain genomic RNA integrity. These new findings promote our understanding of the basics of LASV infection and inform antiviral and vaccine development.

The Arenaviridae Family: Knowledge Gaps, Animal Models, Countermeasures, and Prototype Pathogens

Lassa virus (LASV), Junin virus (JUNV), and several other members of the Arenaviridae family are capable of zoonotic transfer to humans and induction of severe viral hemorrhagic fevers. Despite the importance of arenaviruses as potential pandemic pathogens, numerous gaps exist in scientific knowledge pertaining to this diverse family, including gaps in understanding replication, immunosuppression, receptor usage, and elicitation of neutralizing antibody responses, that in turn complicates development of medical countermeasures. A further challenge to the development of medical countermeasures for arenaviruses is the requirement for use of animal models at high levels of biocontainment, where each model has distinct advantages and limitations depending on, availability of space, animals species-specific reagents, and most importantly the ability of the model to faithfully recapitulate human disease. Designation of LASV and JUNV as prototype pathogens can facilitate progress in addressing the public health challenges posed by members of this important virus family.

Epidemiology and Transmission Dynamics of Viral Encephalitides in West Africa

Encephalitis is an inflammation of the brain, often caused by an autoimmune reaction, or in most cases because of a direct viral, bacterial, or parasitic infection. Viral encephalitides (VE) presents a significant public health concern globally, especially in West Africa. There are more than five hundred known arthropod-borne viruses (arboviruses), with over a hundred of them identified to cause encephalitic diseases in humans and animals, giving rise to a tremendous burden of the diseases and socioeconomic strains in tropical and subtropical regions worldwide. Despite their importance, few effective preventive and control measures in the form of vaccines and therapies are available, and when they are, their use is limited. These limitations are largely hinged on the paucity of information about the molecular epidemiology and transmission patterns of VE in West Africa. Here, we reviewed the transmission dynamics, molecular epidemiology, and the ecological drivers of VE in West Africa. Collectively, timely and accurate interventions are essential for encephalitic viral disease control. Moreover, the integrated health system approach, combining surveillance, vaccination, vector control, and community engagement, could be effective in preventing viral encephalitis globally.

Deep-Learning-Based Whole-Lung and Lung-Lesion Quantification Despite Inconsistent Ground Truth: Application to Computerized Tomography in SARS-CoV-2 Nonhuman Primate Models

RATIONALE AND OBJECTIVES

Animal modeling of infectious diseases such as coronavirus disease 2019 (COVID-19) is important for exploration of natural history, understanding of pathogenesis, and evaluation of countermeasures. Preclinical studies enable rigorous control of experimental conditions as well as pre-exposure baseline and longitudinal measurements, including medical imaging, that are often unavailable in the clinical research setting. Computerized tomography (CT) imaging provides important diagnostic, prognostic, and disease characterization to clinicians and clinical researchers. In that context, automated deep-learning systems for the analysis of CT imaging have been broadly proposed, but their practical utility has been limited. Manual outlining of the ground truth (i.e., lung-lesions) requires accurate distinctions between abnormal and normal tissues that often have vague boundaries and is subject to reader heterogeneity in interpretation. Indeed, this subjectivity is demonstrated as wide inconsistency in manual outlines among experts and from the same expert. The application of deep-learning data-science tools has been less well-evaluated in the preclinical setting, including in nonhuman primate (NHP) models of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection/COVID-19, in which the translation of human-derived deep-learning tools is challenging. The automated segmentation of the whole lung and lung lesions provides a potentially standardized and automated method to detect and quantify disease.

MATERIALS AND METHODS

We used deep-learning-based quantification of the whole lung and lung lesions on CT scans of NHPs exposed to SARS-CoV-2. We proposed a novel multi-model ensemble technique to address the inconsistency in the ground truths for deep-learning-based automated segmentation of the whole lung and lung lesions. Multiple models were obtained by training the convolutional neural network (CNN) on different subsets of the training data instead of having a single model using the entire training dataset. Moreover, we employed a feature pyramid network (FPN), a CNN that provides predictions at different resolution levels, enabling the network to predict objects with wide size variations.

RESULTS

We achieved an average of 99.4 and 60.2% Dice coefficients for whole-lung and lung-lesion segmentation, respectively. The proposed multi-model FPN outperformed well-accepted methods U-Net (50.5%), V-Net (54.5%), and Inception (53.4%) for the challenging lesion-segmentation task. We show the application of segmentation outputs for longitudinal quantification of lung disease in SARS-CoV-2-exposed and mock-exposed NHPs.

CONCLUSION

Deep-learning methods should be optimally characterized for and targeted specifically to preclinical research needs in terms of impact, automation, and dynamic quantification independently from purely clinical applications.

Zebrafish-based platform for emerging bio-contaminants and virus inactivation research

Emerging bio-contaminants such as viruses have affected health and environment settings of every country. Viruses are the minuscule entities resulting in severe contagious diseases like SARS, MERS, Ebola, and avian influenza. Recent epidemic like the SARS-CoV-2, the virus has undergone mutations strengthen them and allowing to escape from the remedies. Comprehensive knowledge of viruses is essential for the development of targeted therapeutic and vaccination treatments. Animal models mimicking human biology like non-human primates, rats, mice, and rabbits offer competitive advantage to assess risk of viral infections, chemical toxins, nanoparticles, and microbes. However, their economic maintenance has always been an issue. Furthermore, the redundancy of experimental results due to aforementioned aspects is also in examine. Hence, exploration for the alternative animal models is crucial for risk assessments. The current review examines zebrafish traits and explores the possibilities to monitor emerging bio-contaminants. Additionally, a comprehensive picture of the bio contaminant and virus particle invasion and abatement mechanisms in zebrafish and human cells is presented. Moreover, a zebrafish model to investigate the emerging viruses such as coronaviridae and poxviridae has been suggested.

An Outbred Guinea Pig Disease Model for Lassa Fever Using a Host-Adapted Clade III Nigerian Lassa Virus

Nigeria experiences annual outbreaks of Lassa fever (LF) with high case numbers. At least three clades of Lassa virus (LASV) have been documented in Nigeria, though recent outbreaks are most often associated with clade II or clade III viruses. Using a recently isolated clade III LASV from a case of LF in Nigeria in 2018, we developed and characterized a guinea pig adapted virus capable of causing lethal disease in commercially available Hartley guinea pigs. Uniform lethality was observed after four passages of the virus and was associated with only two dominant genomic changes. The adapted virus was highly virulent with a median lethal dose of 10 median tissue culture infectious doses. Disease was characterized by several hallmarks of LF in similar models including high fever, thrombocytopenia, coagulation disorders, and increased inflammatory immune mediators. High viral loads were noted in all solid organ specimens analyzed. Histological abnormalities were most striking in the lungs and livers of terminal animals and included interstitial inflammation, edema, and steatosis. Overall, this model represents a convenient small animal model for a clade III Nigeria LASV with which evaluation of specific prophylactic vaccines and medical countermeasures can be conducted.

Vaccine Candidates against Arenavirus Infections

The viral family Arenaviridae contains several members that cause severe, and often lethal, diseases in humans. Several highly pathogenic arenaviruses are classified as Risk Group 4 agents and must be handled in the highest biological containment facility, biosafety level-4 (BSL-4). Vaccines and treatments are very limited for these pathogens. The development of vaccines is crucial for the establishment of countermeasures against highly pathogenic arenavirus infections. While several vaccine candidates have been investigated, there are currently no approved vaccines for arenavirus infection except for Candid#1, a live-attenuated Junin virus vaccine only licensed in Argentina. Current platforms under investigation for use include live-attenuated vaccines, recombinant virus-based vaccines, and recombinant proteins. We summarize here the recent updates of vaccine candidates against arenavirus infections.

Hearing loss in outbred Hartley guinea pigs experimentally infected with Pichinde virus as a surrogate model of human mammarenaviral hemorrhagic fevers

Lassa fever (LF) is a neglected tropical disease that is caused by Lassa virus (LASV), a human hemorrhagic fever-causing mammarenavirus. A notable sequela of LF is sensorineural hearing loss (SNHL) that can develop in about 33% of the patients. Animal models of LF-associated SNHL have been limited in size and scope because LASV is a biosafety level 4 (BSL4) pathogen that requires its handling in a high biocontainment laboratory. In this report, we describe the development of an alternative arenavirus hearing loss model by infecting outbred Hartley guinea pigs with a virulent strain (rP18) of the Pichinde virus (PICV), which is a guinea pig-adapted mammarenavirus that has been used as a surrogate model of mammarenaviral hemorrhagic fevers in a conventional (BSL2) laboratory. By measuring auditory brainstem response (ABR) throughout the course of the virulent rP18 PICV infection, we noticed that some of the animals experienced an acute but transient level of hearing loss. Cochleae of hearing-impaired animals, but not of controls, had demonstrable viral RNA by quantitative RT-PCR, indicating the presence of virus in the affected inner ear with no overt histopathological changes. In contrast, neither the outbred Hartley guinea pigs infected with a known avirulent strain (rP2) of PICV nor those that were mock-infected showed any evidence of hearing loss or viral infection of the inner ear. This is the first report of an immunocompetent small animal model of mammarenavirus-induced hearing loss that can be used to evaluate potential therapeutics against virus-induced hearing impairment under a conventional laboratory setting.

Comparative Animal Models of Human Viral Infections

Comparative animal modeling has long served as a cornerstone for understanding the biological effects of infection by many DNA and RNA viruses [...].

Understanding Immune Responses to Lassa Virus Infection and to Its Candidate Vaccines

Lassa fever (LF) is a deadly viral hemorrhagic fever disease that is endemic in several countries in West Africa. It is caused by Lassa virus (LASV), which has been estimated to be responsible for approximately 300,000 infections and 5000 deaths annually. LASV is a highly pathogenic human pathogen without effective therapeutics or FDA-approved vaccines. Here, we aim to provide a literature review of the current understanding of the basic mechanism of immune responses to LASV infection in animal models and patients, as well as to several of its candidate vaccines.

RIG-I and MDA5 Protect Mice From Pichinde Virus Infection by Controlling Viral Replication and Regulating Immune Responses to the Infection

RIG-I and MDA5 are major cytoplasmic innate-immune sensor proteins that recognize aberrant double-stranded RNAs generated during virus infection to activate type 1 interferon (IFN-I) and IFN-stimulated gene (ISG) expressions to control virus infection. The roles of RIG-I and MDA5 in controlling replication of Pichinde virus (PICV), a mammarenavirus, in mice have not been examined. Here, we showed that MDA5 single knockout (SKO) and RIG-I/MDA5 double knockout (DKO) mice are highly susceptible to PICV infection as evidenced by their significant reduction in body weights during the course of the infection, validating the important roles of these innate-immune sensor proteins in controlling PICV infection. Compared to the wildtype mice, SKO and DKO mice infected with PICV had significantly higher virus titers and lower IFN-I expressions early in the infection but appeared to exhibit a late and heightened level of adaptive immune responses to clear the infection. When a recombinant rPICV mutant virus (rPICV-NPmut) that lacks the ability to suppress IFN-I was used to infect mice, as expected, there were heightened levels of IFN-I and ISG expressions in the wild-type mice, whereas infected SKO and DKO mice showed delayed mouse growth kinetics and relatively low, delayed, and transient levels of innate and adaptive immune responses to this viral infection. Taken together, our data suggest that PICV infection triggers activation of immune sensors that include but might not be necessarily limited to RIG-I and MDA5 to stimulate effective innate and adaptive immune responses to control virus infection in mice.

Inoculation route-dependent Lassa virus dissemination and shedding dynamics in the natural reservoir - Mastomys natalensis

Lassa virus (LASV), a Risk Group-4 zoonotic haemorrhagic fever virus, affects sub-Saharan African countries. Lassa fever, caused by LASV, results in thousands of annual deaths. Although decades have elapsed since the identification of the Natal multimammate mouse (Mastomys natalensis) as a natural reservoir of LASV, little effort has been made to characterize LASV infection in its reservoir. The natural route of infection and transmission of LASV within M. natalensis remains unknown, and the clinical impact of LASV in M. natalensis is mostly undescribed. Herein, using an outbred colony of M. natalensis, we investigate the replication and dissemination dynamics of LASV in this reservoir following various inoculation routes. Inoculation with LASV, regardless of route, resulted in a systemic infection and accumulation of abundant LASV-RNA in many tissues. LASV infection in the Natal multimammate mice was subclinical, however, clinical chemistry values were transiently altered and immune infiltrates were observed histologically in lungs, spleens and livers, indicating a minor disease with coordinated immune responses are elicited, controlling infection. Intranasal infection resulted in unique virus tissue dissemination dynamics and heightened LASV shedding, compared to subcutaneous inoculation. Our study provides important insights into LASV infection in its natural reservoir using a contemporary infection system, demonstrating that specific inoculation routes result in disparate dissemination outcomes, suggesting intranasal inoculation is important in the maintenance of LASV in the natural reservoir, and emphasizes that selection of the appropriate inoculation route is necessary to examine aspects of viral replication, transmission and responses to zoonotic viruses in their natural reservoirs.

Pathogenicity and virulence mechanisms of Lassa virus and its animal modeling, diagnostic, prophylactic, and therapeutic developments

Lassa fever (LF) is a deadly viral hemorrhagic disease that is endemic to West Africa. The causative agent of LF is Lassa virus (LASV), which causes approximately 300,000 infections and 5,000 deaths annually. There are currently no approved therapeutics or FDA-approved vaccines against LASV. The high genetic variability between LASV strains and immune evasion mediated by the virus complicate the development of effective therapeutics and vaccines. Here, we aim to provide a comprehensive review of the basic biology of LASV and its mechanisms of disease pathogenesis and virulence in various animal models, as well as an update on prospective vaccines, therapeutics, and diagnostics for LF. Until effective vaccines and/or therapeutics are available for use to prevent or treat LF, a better level of understanding of the basic biology of LASV, its natural genetic variations and immune evasion mechanisms as potential pathogenicity factors, and of the rodent reservoir-vector populations and their geographical distributions, is necessary for the development of accurate diagnostics and effective therapeutics and vaccines against this deadly human viral pathogen.

Differential pathogenesis of closely related 2018 Nigerian outbreak clade III Lassa virus isolates

Nigeria continues to experience ever increasing annual outbreaks of Lassa fever (LF). The World Health Organization has recently declared Lassa virus (LASV) as a priority pathogen for accelerated research leading to a renewed international effort to develop relevant animal models of disease and effective countermeasures to reduce LF morbidity and mortality in endemic West African countries. A limiting factor in evaluating medical countermeasures against LF is a lack of well characterized animal models outside of those based on infection with LASV strain Josiah originating form Sierra Leone, circa 1976. Here we genetically characterize five recent LASV isolates collected from the 2018 outbreak in Nigeria. Three isolates were further evaluated in vivo and despite being closely related and from the same spatial / geographic region of Nigeria, only one of the three isolates proved lethal in strain 13 guinea pigs and non-human primates (NHP). Additionally, this isolate exhibited atypical pathogenesis characteristics in the NHP model, most notably respiratory failure, not commonly described in hemorrhagic cases of LF. These results suggest that there is considerable phenotypic heterogeneity in LASV infections in Nigeria, which leads to a multitude of pathogenesis characteristics that could account for differences between subclinical and lethal LF infections. Most importantly, the development of disease models using currently circulating LASV strains in West Africa are critical for the evaluation of potential vaccines and medical countermeasures.

Lassa fever is a severe viral hemorrhagic fever of humans caused by infection with Lassa virus, which is endemic in many countries in West Africa. Annually, an estimated 300,000–500,000 people are infected with Lassa virus, making it one of the most prominent agents responsible for hemorrhagic disease in humans. Despite this significant burden of disease, to date, no approved therapeutic or prophylactic vaccine exists for Lassa fever, due in part to a lack of characterized animal models for studying the disease. Here, we describe guinea pig and non-human primate models for Lassa fever using recently isolated viruses from a 2018 outbreak of Lassa fever in Nigeria. Despite similar collection locations and dates, the isolates obtained from human infections demonstrated a high degree of genotypic heterogeneity and phenotypic characteristics in animal models resulting in both lethal and non-lethal infections. Of interest, one isolate resulted in significant respiratory manifestations, an under-reported disease manifestation in humans. These models will provide comparative models to those already characterized and aid in elucidating disease characteristics of Lassa fever. In addition, they will serve the immediate purpose of evaluating known and novel medical countermeasures to treat and prevent disease in West Africa.

Virulent infection of outbred Hartley guinea pigs with recombinant Pichinde virus as a surrogate small animal model for human Lassa fever

Arenaviruses, such as Lassa virus (LASV), can cause severe and fatal hemorrhagic fevers (e.g., Lassa fever, LF) in humans with no vaccines or therapeutics. Research on arenavirus-induced hemorrhagic fevers (AHFs) has been hampered by the highly virulent nature of these viral pathogens, which require high biocontainment laboratory, and the lack of an immune-competent small animal model that can recapitulate AHF disease and pathological features. Guinea pig infected with Pichinde virus (PICV), an arenavirus that does not cause disease in humans, has been established as a convenient surrogate animal model for AHFs as it can be handled in a conventional laboratory. The PICV strain P18, derived from sequential passaging of the virus 18 times in strain 13 inbred guinea pigs, causes severe febrile illness in guinea pigs that is reminiscent of lethal LF in humans. As inbred guinea pigs are not readily available and are difficult to maintain, outbred Hartley guinea pigs have been used but they show a high degree of disease heterogeneity upon virulent P18 PICV infection. Here, we describe an improved outbred guinea-pig infection model using recombinant rP18 PICV generated by reverse genetics technique followed by plaque purification, which consistently shows >90% mortality and virulent infection. Comprehensive virological, histopathological, and immunohistochemical analyses of the rP18-virus infected animals show similar features of human LASV infection. Our data demonstrate that this improved animal model can serve as a safe, affordable, and convenient surrogate small animal model for studying human LF pathogenesis and for evaluating efficacy of preventative or therapeutic approaches.

Lassa Virus Treatment Options

Lassa fever causes an approximate 5000 to 10,000 deaths annually in West Africa and cases have been imported into Europe and the Americas, challenging public health. Although Lassa virus was first described over 5 decades ago in 1969, no treatments or vaccines have been approved to treat or prevent infection. In this review, we discuss current therapeutics in the development pipeline for the treatment of Lassa fever, focusing on those that have been evaluated in humans or animal models. Several treatments, including the antiviral favipiravir and a human monoclonal antibody cocktail, have shown efficacy in preclinical rodent and non-human primate animal models and have potential for use in clinical settings. Movement of the promising preclinical treatment options for Lassa fever into clinical trials is critical to continue addressing this neglected tropical disease.

Space-Time Trends in Lassa Fever in Sierra Leone by ELISA Serostatus, 2012-2019

Lassa fever (LF) is a viral hemorrhagic disease found in Sub-Saharan Africa and is responsible for up to 300,000 cases and 5000 deaths annually. LF is highly endemic in Sierra Leone, particularly in its Eastern Province. Kenema Government Hospital (KGH) maintains one of only a few LF isolation facilities in the world with year-round diagnostic testing. Here we focus on space-time trends for LF occurring in Sierra Leone between 2012 and 2019 to provide a current account of LF in the wake of the 2014–2016 Ebola epidemic. Data were analyzed for 3277 suspected LF cases and classified as acute, recent, and non-LF or prior LF exposure using enzyme-linked immunosorbent assays (ELISAs). Presentation rates for acute, recent, and non-LF or prior LF exposure were 6.0% (195/3277), 25.6% (838/3277), and 68.4% (2244/3277), respectively. Among 2051 non-LF or prior LF exposures, 33.2% (682/2051) tested positive for convalescent LF exposure. The overall LF case-fatality rate (CFR) was 78.5% (106/135). Both clinical presentations and confirmed LF cases declined following the Ebola epidemic. These declines coincided with an increased duration between illness onset and clinical presentation, perhaps suggesting more severe disease or presentation at later stages of illness. Acute LF cases and their corresponding CFRs peaked during the dry season (November to April). Subjects with recent (but not acute) LF exposure were more likely to present during the rainy season (May to October) than the dry season (p < 0.001). The findings here suggest that LF remains endemic in Sierra Leone and that caseloads are likely to resume at levels observed prior to the Ebola epidemic. The results provide insight on the current epidemiological profile of LF in Sierra Leone to facilitate LF vaccine studies and accentuate the need for LF cohort studies and continued advancements in LF diagnostics.

Lassa hemorrhagic shock syndrome-on-a-chip

Lack of experimental human models hinders research on Lassa hemorrhagic fever and the development of treatment strategies. Here, we report the first chip-based model for Lassa hemorrhagic syndrome. The chip features a microvessel interfacing collagen network as a simple mimic for extracellular matrix, allowing for quantitative and real-time vascular integrity assessment. Luminal infusion of Lassa virus-like particles led to a dramatic increase in vascular permeability in a viral load-dependent manner. Using this platform, we showed that Fibrin-derived peptide FX06 can be used to suppress the vascular integrity loss. This simple chip-based model proved promising in the assessment of disease severity and provides an easy-to-use platform for future investigation of Lassa pathogenesis and drug development in a human-like setting.

Effect of Strain Variations on Lassa Virus Z Protein-Mediated Human RIG-I Inhibition

Mammarenaviruses include several known human pathogens, such as the prototypic lymphocytic choriomeningitis virus (LCMV) that can cause neurological diseases and Lassa virus (LASV) that causes endemic hemorrhagic fever infection. LASV-infected patients show diverse clinical manifestations ranging from asymptomatic infection to hemorrhage, multi-organ failures and death, the mechanisms of which have not been well characterized. We have previously shown that the matrix protein Z of pathogenic arenaviruses, including LASV and LCMV, can strongly inhibit the ability of the innate immune protein RIG-I to suppress type I interferon (IFN-I) expression, which serves as a mechanism of viral immune evasion and virulence. Here, we show that Z proteins of diverse LASV isolates derived from rodents and humans have a high degree of sequence variations at their N- and C-terminal regions and produce variable degrees of inhibition of human RIG-I (hRIG-I) function in an established IFN-β promoter-driven luciferase (LUC) reporter assay. Additionally, we show that Z proteins of four known LCMV strains can also inhibit hRIG-I at variable degrees of efficiency. Collectively, our results confirm that Z proteins of pathogenic LASV and LCMV can inhibit hRIG-I and suggest that strain variations of the Z proteins can influence their efficiency to suppress host innate immunity that might contribute to viral virulence and disease heterogeneity.

Pichinde Virus Infection of Outbred Hartley Guinea Pigs as a Surrogate Animal Model for Human Lassa Fever: Histopathological and Immunohistochemical Analyses

Lassa virus (LASV) is a mammarenavirus (arenavirus) that causes zoonotic infection in humans that can lead to fatal hemorrhagic Lassa fever (LF) disease. Currently, there are no FDA-approved vaccines or therapeutics against LASV. Development of treatments against LF and other related arenavirus-induced hemorrhagic fevers (AHFs) requires relevant animal models that can recapitulate clinical and pathological features of AHF diseases in humans. Laboratory mice are generally resistant to LASV infection, and non-human primates, while being a good animal model for LF, are limited by their high cost. Here, we describe a small, affordable, and convenient animal model that is based on outbred Hartley guinea pigs infected with Pichinde virus (PICV), a mammarenavirus that is non-pathogenic in humans, for use as a surrogate model of human LF. We conducted a detailed analysis of tissue histopathology and immunohistochemical analysis of different organs of outbred Hartley guinea pigs infected with different PICV strains that show differential disease phenotypes and pathologies. Comparing to infection with the avirulent PICV strain (P2 or rP2), animals infected with the virulent strain (P18 or rP18) show extensive pathological changes in different organs that sustain high levels of virus replication. The similarity of tissue pathology and viral antigen distribution between the virulent PICV–guinea pig model and lethal human LASV infection supports a role of this small animal model as a surrogate model of studying human LF in order to understand its pathogenesis and for evaluating potential preventative and therapeutic options against AHFs.

Need for preventive and control measures for Lassa fever through the One Health strategic approach

Lassa virus (LASV) has increasingly been recognised as a significant public-health pathogen transmitted by rodents. LASV infection leads to life-threatening Lassa fever, which has high potential for severe morbidity and mortality. There have been several scientific efforts to understand the genomics and ecological epidemiology of Lassa. However, very limited studies have focused on the short- and long-term impacts of environmental factors, human behaviours and rodent activities on LASV transmission dynamics and control. Recently, a very plausible and ideal way to address the Lassa epidemic has been considered through the One Health approach. The One Health system of intervention is capable of providing better and comprehensive information necessary to address the complex interplay between human, ecological, and environmental determinants of LASV transmission, persistence and re-emergence. Thus, the aim of this article was to review critically the impacts of various environmental factors on rodent infestations, LASV transmission and how human activities contribute to the persistence of Lassa with regard to exploring how they could be harnessed for better understanding of Lassa prevention and control through a concerted One Health approach.

Lassa Fever: Viral Replication, Disease Pathogenesis, and Host Immune Modulations

Despite major discoveries made in the last few decades about Lassa fever, there are still many unresolved key issues that hamper the development of effective vaccines and therapies against this deadly disease that is endemic in several West African countries. Some of these issues include the lack of a detailed understanding of the viral and participating host factors in completing the virus life cycle, in mediating disease pathogenesis or protection from disease, and in activating or suppressing host innate and cellular immunity against virus infection, as well as of the animal models required for testing vaccines and therapeutics. This Special Issue is devoted to understanding some of these important issues and to exploring the current status of the research and development in combating Lassa fever.