Natural History of Aerosol Induced Lassa Fever in Non­Human Primates.

Lassa virus (LASV), an arenavirus causing Lassa fever, is endemic to West Africa with up to 300,000 cases and between 5000 and 10,000 deaths per year. Rarely seen in the United States, Lassa virus is a CDC category A biological agent inasmuch deliberate aerosol exposure can have high mortality rates compared to naturally acquired infection. With the need for an animal model, specific countermeasures remain elusive as there is no FDA-approved vaccine. This natural history of aerosolized Lassa virus exposure in Macaca fascicularis was studied under continuous telemetric surveillance. The macaque response to challenge was largely analogous to severe human disease with fever, tachycardia, hypotension, and tachypnea. During initial observations, an increase trend of activated monocytes positive for viral glycoprotein was accompanied by lymphocytopenia. Disease uniformly progressed to high viremia followed by low anion gap, alkalosis, anemia, and thrombocytopenia. Hypoproteinemia occurred late in infection followed by increased levels of white blood cells, cytokines, chemokines, and biochemical markers of liver injury. Viral nucleic acids were detected in tissues of three non­survivors at endpoint, but not in the lone survivor. This study provides useful details to benchmark a pivotal model of Lassa fever in support of medical countermeasure development for both endemic disease and traditional biodefense purposes.

Lesson learned from the investigation and response of Lassa fever outbreak, Margibi County, Liberia, 2018: case report.

BACKGROUND: Lassa fever (LF) is a viral hemorrhagic disease caused by the Lassa virus (LASV) and endemic in West African countries with an estimation of 300,000 to 500,000 cases and 5,000 deaths annually. The Margibi County Health Team of Liberia received a report of an unidentified febrile illness case from the Kakata district. We conducted the investigation to identify the causative agent and the source of infection to support treatment, control and prevention interventions. CASE PRESENTATION: We identified LASV in the blood specimens' of two patients by Reverse Transcriptase Polymerase Chain Reaction (RT-PCR). Both the confirmed cases have manifested respiratory distress, weakness, and difficulty of swallowing, muscle, joint and back pains, and vomiting with blood. The symptoms started with mild fever and gradually developed. Initially, the primary health facilities have miss-diagnosed the patients as malaria and respiratory tract infections. The primary health facilities have referred the patients to the referral hospital as the patients have failed to respond to antimalarial and antibiotics. The hospital suspected LF and sent blood specimens to the National Reference Laboratory while the patients were on supportive treatment in the isolation room. At the time when the laboratory result returned to the hospital, the patients died of LF illness before ribavirin administered. CONCLUSIONS: Our investigation revealed that the two hospitalized and deceased febrile cases were associated with LASV. The primary health facilities have failed to recognize the cases as suspected LF at the earliest time possible. The clinicians and health facilities, especially primary health facilities, need to consider LF as a differential diagnosis when the patient failed to respond to anti-malaria and broad-spectrum antibiotics.

A cluster of nosocomial Lassa fever cases in a tertiary health facility in Nigeria: Description and lessons learned, 2018.

BACKGROUND: Lassa fever is an acute viral haemorrhagic disease endemic in Nigeria. The 2018 Lassa fever outbreak in Nigeria was unprecedented, with 8% of all cases occurring among healthcare workers (HCWs). A disproportionately high number of these infections occurred in HCWs working in a tertiary health facility in Nigeria. This paper describes the cluster of Lassa fever infections among HCWs in a treatment centre and the lessons learnt. METHODS: We analysed clinical, epidemiological and laboratory data from surveillance and laboratory records kept during the 2018 outbreak. Interviews were conducted with surviving HCWs using a questionnaire developed specifically for the investigation of Lassa fever infections in HCWs. Descriptive analysis of the data was performed in Microsoft excel. RESULTS: The index case was a 15-year-old male who presented at the health facility with fever and uncontrolled nasopharyngeal bleeding, following a recent uvulectomy by a traditional healer. Overall, 16 HCWs were affected (15 confirmed and 1 probable) with five deaths (CFR-31.6%). Of the 15 confirmed cases, five (33.3%) were asymptomatic. Nine HCWs were direct contacts of the index case; the remaining six HCWs had no direct contact with the index case. HCW interviews identified a low index of suspicion for Lassa fever leading to inadequate infection prevention and control (IPC) practices as possible contributing factors to nosocomial transmission. CONCLUSION: Maintaining a high index of suspicion for Lassa fever in all patients, especially in endemic areas, is essential in adhering to adequate IPC practices in health facilities in order to prevent nosocomial transmission of Lassa fever among HCWs. There is a need to continually train and sensitise HCWs on strict adherence to IPC measures while providing care, irrespective of a patient's provisional diagnosis.

Critical role for cholesterol in Lassa fever virus entry identified by a novel small molecule inhibitor targeting the viral receptor LAMP1.

Lassa fever virus (LASV) is endemic in West Africa and causes severe hemorrhagic fever and sensorineural hearing loss. We identified a small molecule inhibitor of LASV and used it to analyze the mechanism of entry. Using a photo-reactive analog that retains antiviral activity as a probe, we identified the inhibitor target as lysosome-associated membrane protein 1 (LAMP1), a host factor that binds to the LASV glycoprotein (GP) during infection. We found that LAMP1 binding to LASV GP is cholesterol-dependent, and that the inhibitor blocks infection by competing with cholesterol in LAMP1. Mutational analysis of a docking-based model identified a putative inhibitor binding site in the cholesterol-binding pocket within the LAMP1 domain that binds GP. These findings identify a critical role for cholesterol in LASV entry and a potential target for therapeutic intervention.

[An update on Lassa virus]. / Le virus lassa, état des lieux.

Lassa virus, the etiologic agent of Lassa hemorrhagic fever, infects 100,000 to 300,000 people every year in West Africa with an overall mortality rate ranging from 1 to 2%. It was discovered in 1969 and remains a significant public health risk in endemic areas. Because airborne transmission is possible and mortality can be high under certain conditions, Lassa virus has been classified as a category A bioterrorism agent. Early diagnosis is difficult due to insidious non-specific onset and to the great genetic divergence of the virus that makes RT-PCR assays unreliable. The lack of proper diagnostic tools promotes nosocomial infection and diminishes the efficacy of treatment. Recently, numerous advances have been made in the development of both diagnostic and vaccination techniques. The purpose of this review is to present an update on that research as well as the current epidemiology of Lassa virus.

The role of the vascular endothelium in arenavirus haemorrhagic fevers.

Viral haemorrhagic fevers (VHF) caused by arenaviruses are among the most devastating emerging human diseases. The most important pathogen among the arenaviruses is Lassa virus (LASV), the causative agent of Lassa fever that is endemic to West Africa. On the South American continent, the New World arenavirus Junin virus (JUNV), Machupo (MACV), Guanarito (GTOV), and Sabia virus (SABV) have emerged as causative agents of severe VHFs. Clinical and experimental studies on arenavirus VHF have revealed a crucial role of the endothelium in their pathogenesis. However, in contrast to other VHFs, haemorrhages are not a salient feature of Lassa fever and fatal cases do not show overt destruction of vascular tissue. The functional alteration of the vascular endothelium that precede shock and death in fatal Lassa fever may be due to more subtle direct or indirect effects of the virus on endothelial cells. Haemorrhagic disease manifestations and vascular involvement are more pronounced in the VHF caused by the South American haemorrhagic fever viruses. Recent studies on JUNV revealed perturbation of specific endothelial cell function, including expression of cell adhesion molecules, coagulation factors, and vasoactive mediators as a consequence of productive viral infection. These studies provided first possible links to some of the vascular abnormalities observed in patients, however, their relevance in vivo remains to be investigated.

Fibroblastic reticular cells and their role in viral hemorrhagic fevers.

Viral hemorrhagic fevers (VHFs) caused by Ebola, Marburg and Lassa viruses often manifest as multiple organ dysfunction and hemorrhagic shock with high mortality. These viruses target numerous cell types, including monocytes and dendritic cells, which are primary early targets that mediate critical pathogenetic processes. This review focuses on fibroblastic reticular cells (FRCs), another prevalent infected cell type that is known as a key regulator of circulatory and immune functions. Viral infection of FRCs could have debilitating effects in secondary lymphoid organs and various other tissues. FRCs may also contribute to the spread of these deadly viruses throughout the body. Here, we review the salient features of these VHFs and the biology of FRCs, emphasizing the potential role of these cells in VHFs and the rapid deterioration of immune and hemovascular sytems that are characteristic of such acute infections.

Poor housing quality increases risk of rodent infestation and Lassa fever in refugee camps of Sierra Leone.

Lassa fever, a viral hemorrhagic fever endemic in parts of West Africa, is a severe febrile illness transmitted to humans by the rodent Mastomys natalensis. To determine risk of Lassa fever in households in Sierra Leonean refugee camps, we analyzed the spatial relationships between households with a Lassa case and focal locations of potential rodent habitats. Quality and hygiene factors of households were assessed to determine possible risk factors for household rodent infestation and occurrence of Lassa fever. The odds to have a rat burrow were higher in case houses than in control houses (OR 24, 95% CI 6.0-93). Case houses scored significantly worse in the quality of housing and external hygiene. These findings suggest that risk of Lassa fever in refugee camps depends on individual housing quality and the hygiene of the immediate surrounding environment.

Lassa virus.

Lassa virus is a RNA virus belonging to the family of Arenaviridae. It was discovered as the causative agent of a hemorrhagic fever--Lassa fever--about 30 years ago. Lassa fever is endemic in West Africa and is estimated to affect some 100,000 people annually. Great progress in the understanding of the life cycle of arenaviruses, including Lassa virus, has been made in recent years. New insights have been gained in the pathogenesis and molecular epidemiology of Lassa fever, and state-of the-art technologies for diagnosing this life-threatening disease have been developed. The intention of this review is to summarize in particular the recent literature on Lassa virus and Lassa fever. Several aspects ranging from basic research up to clinical practice and laboratory diagnosis are discussed and linked together.

Fiebres hemorrágicas / Hemorrhagic fevers

Las fiebres hemorrágicas constituyen síndromes de alta prevalencia actualmente en nuestro medio, razón por la cual es importante revisar su etiología, patogénesis y posibilidades terapáuticas. La reciente descripción de un virus hemorrágico en Venezuela hace este tópico de mayor interés

[Experimental Lassa fever in hamadryas baboons]. / Eksperimental'naia likhoradka Lassa u pavianov gamadrilov.

Intramuscular or aerogenic inoculation of baboons with Lassa virus reproduced a severe form of the disease which clinically, pathoanatomically and virologically resembles the severe form of human Lassa fever reported in the literature. The severity of monkey infection is demonstrated by rapid development of symptoms of general toxicity in the presence of fever, manifestations of hemorrhagic diathesis, high level of viremia and isolation of the causative agent from nasopharyngeal washings.

Lassa fever.

Lassa fever is an acute viral illness which causes considerable morbidity and mortality in West Africa. The risk of importing the disease into the UK is small but real, and it continues to be a worldwide concern among public health officials. This article summarizes its epidemiology and clinical presentation, and discusses current theories of its pathogenesis.

Pathogenesis of viral hemorrhagic fevers: Rift Valley fever and Lassa fever contrasted.

Although many viral infections have on occasion been associated with hemorrhagic complications, infection with any of several RNA viruses regularly results in vascular involvement and the syndrome called viral hemorrhagic fever (VHF). In spite of clinically useful similarities among various VHFs, there are significant differences in their pathogenesis and clinical evolution; these are often related to characteristics of their viral taxon. Infection with Rift Valley fever (RVF) virus, a phlebovirus, appears to be regulated by interferon and terminated by neutralizing antibody. In contrast, Lassa fever (LF) virus, an arenavirus, is resistant to interferon, and LF is terminated by cellular immune effector mechanisms. The lytic virus-cell interaction typical of RVF virus suggests its major effects occur by direct, virus-induced cellular necrosis, particularly in the liver. In the primate RVF model, disseminated intravascular coagulation (DIC) may be important. LF virus--characteristically noncytopathic--may exert its effects through induction of mediator secretion from infected macrophages. DIC does not appear to be a central pathogenetic mechanism in LF. Pichinde virus, which is not pathogenic for humans, provides an alternate model for study of LF. Infected guinea pigs do not show histologic lesions that could explain their body wasting, cardiovascular deterioration, and pulmonary edema. In the heart, for example, loss of tissue mass, protein, and contractile function proceed without direct viral involvement or myocarditis. Sulfidopeptide leukotrienes have been implicated as one relevant soluble mediator participating in the disease state.

[Effect of immunosuppression on the development and outcome of an acute infection in mice caused by administration of the Lassa virus]. / Vliianie immunosupressii na razvitie i iskhod ostroi infektsii, vyzyvaemoi u myshei vvedeniem virusa Lassa.

In experimental infection of mice with Lassa virus, the infectious virus could be detected in all the organs and brain tissues tested. Histopathological lesions were demonstrated in cerebral and spinal cord tissues only. Roentgen irradiation in a dose of 500 R and cyclophosphamide protected mice against a lethal Lassa virus dose. Cyclosporin A in various doses exerted no effect on the outcome of the acute infection. The adoptive transfer of splenocytes from mouse donors inoculated intraperitoneally prevented the development of lethal disease symptoms and death of mice-recipients. It is suggested that immunocompetent cells are involved in the development and outcome of experimental infection of mice with Lassa virus.

Clustering of disease in population units: an exact test and its asymptotic version.

An exact probability test and its asymptotic version are described for testing the hypothesis that clustering of disease observed among population units is likely to have been due to chance alone. The test is based on a scheme for ranking possible arrangements of ill and well persons by degree of clustering, as measured by the sum, over all population units, of the ratio of the number of case pairs in a unit to the size of the unit. The proposed measure of clustering is attractive because increasing segregation of ill and well persons consistently results in a higher index of clustering. The power of the test seems at least as good as that of methods with less attractive clustering measures. The exact version allows analysis of clustering in a small number of population units, while the asymptotic version permits calculations based on larger samples.

Pathogenesis of Lassa virus infection in guinea pigs.

A rodent model for human Lassa fever was developed which uses inbred (strain 13) and outbred (Hartley) guinea pigs. Strain 13 guinea pigs were uniformly susceptible to lethal infection by 2 or more PFU of Lassa virus strain Josiah. In contrast, no more than 30% of the Hartley guinea pigs died regardless of the virus dose. In lethally infected strain 13 guinea pigs, peak titers of virus (10(7) to 10(8) PFU) occurred in the spleen and lymph nodes at 8 to 9 days, in the salivary glands at 11 days, and in the lung at 14 to 16 days. Virus reached low titers (10(4) PFU) in the plasma and brain and intermediate titers in the liver, adrenal glands, kidney, pancreas, and heart. In moribund animals, the most consistent and severe histological lesion as an interstitial pneumonia. In contrast, the brain was only minimally involved. The immune response of lethally infected strain 13 guinea pigs, as measured by the indirect fluorescent antibody test, was detectable within 10 days of infection and was similar in timing and intensity to the fluorescent antibody test response of both lethally infected and surviving outbred animals. In contrast to the fluorescent antibody response, neutralizing antibody developed late in convalescence and was thus detected only in surviving outbred guinea pigs. The availability of a rodent model for human Lassa fever in uniformly susceptible strain 13 guinea pigs should facilitate detailed pathophysiological studies and efficacy testing of antiviral drugs, candidate vaccines, and immunotherapy regimens to develop control methods for this life-threatening disease in humans.