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Lassa virus (LASV) is endemic in West Africa and induces a viral hemorrhagic fever (VHF) with up to 30% lethality among clinical cases. The mechanisms involved in control of Lassa fever or, in contrast, the ensuing catastrophic illness and death are poorly understood. We used the cynomolgus monkey model to reproduce the human disease with asymptomatic to mild or fatal disease. After initial replication at the inoculation site, LASV reached the secondary lymphoid organs. LASV did not spread further in nonfatal disease and was rapidly controlled by balanced innate and T-cell responses. Systemic viral dissemination occurred during severe disease. Massive replication, a cytokine/chemokine storm, defective T-cell responses, and multiorgan failure were observed. Clinical, biological, immunological, and transcriptomic parameters resembled those observed during septic-shock syndrome, suggesting that similar pathogenesis is induced during Lassa fever. The outcome appears to be determined early, as differentially expressed genes in PBMCs were associated with fatal and non-fatal Lassa fever outcome very early after infection. These results provide a full characterization and important insights into Lassa fever pathogenesis and could help to develop early diagnostic tools.

Background: Lassa fever and Ebola are characterized by non-specific initial presentations that can progress to severe multisystem illnesses with high fatality rates. Samples from additional subjects are examined to extend and corroborate biomarkers with prognostic value for these diseases., Methods: Liquid Chromatography Mass Spectrometry metabolomics was used to identify and confirm metabolites disrupted in the blood of Lassa fever and Ebola patients. Authenticated standards are used to confirm the identify of key metabolites., Results: We confirm prior results by other investigators that the amino acid L-threonine is elevated during Ebola virus infection. L-Threonine is also elevated during Lassa virus infection. We also confirmed that platelet-activating factor (PAF) and molecules with PAF moiety are reduced in the blood of patients with fatal Lassa fever. Similar changes in PAF and PAF-like molecules were not observed in the blood of Ebola patients., Conclusions: Metabolomics may provide tools to identify pathways that are differentially affected during viral hemorrhagic fevers and guide development of diagnostics to monitor and predict outcome.

Objective: Healthcare personnel (HCP) were recruited to provide serum samples, which were tested for antibodies against Ebola or Lassa virus to evaluate for asymptomatic seroconversion., Setting: From 2014 to 2016, 4 patients with Ebola virus disease (EVD) and 1 patient with Lassa fever (LF) were treated in the Serious Communicable Diseases Unit (SCDU) at Emory University Hospital. Strict infection control and clinical biosafety practices were implemented to prevent nosocomial transmission of EVD or LF to HCP., Participants: All personnel who entered the SCDU who were required to measure their temperatures and complete a symptom questionnaire twice daily were eligible., Results: No employee developed symptomatic EVD or LF. EVD and LF antibody studies were performed on sera samples from 42 HCP. The 6 participants who had received investigational vaccination with a chimpanzee adenovirus type 3 vectored Ebola glycoprotein vaccine had high antibody titers to Ebola glycoprotein, but none had a response to Ebola nucleoprotein or VP40, or a response to LF antigens., Conclusions: Patients infected with filoviruses and arenaviruses can be managed successfully without causing occupation-related symptomatic or asymptomatic infections. Meticulous attention to infection control and clinical biosafety practices by highly motivated, trained staff is critical to the safe care of patients with an infection from a special pathogen.

Lassa fever is a severe viral hemorrhagic illness caused by Lassa virus. Based on estimates, the number of LASV infections ranges from 300,000 to 500,000 cases in endemic areas with a fatality rate of 1%. Development of fast and sensitive tools for the control and prevention of Lassa virus infection as well as for clinical diagnostics of Lassa fever are crucial. Here we reported development and evaluation of a one-step quantitative RT-qPCR assay for the Lassa virus detection - LASV-Fl. This assay is suitable for the detection of lineages I-IV of Lassa virus. The limit of detection of the assay ranged from 10 3 copies/ml to 10 5 copies/ml and has 96.4% diagnostic sensitivity, whereas analytical and diagnostic specificities both were 100%. Serum, whole blood and tissue are suitable for use with the assay. The assay contains all the necessary components to perform the analysis, including an armored positive control (ARC+) and an armored internal control (IC). The study was done during the mission of specialized anti-epidemic team of the Russian Federation (SAET) in the Republic of Guinea in 2015-2018. Based on sequencing data, LASV-specific assay was developed using synthetic MS2-phage-based armored RNA particles, RNA from Lassa virus strain Josiah, and further, evaluated in field conditions using samples from patients and Mastomys natalensis rodents., (Copyright © 2019 Elsevier B.V. All rights reserved.)

Lassa virus (LASV) causes Lassa fever (LF), a viral hemorrhagic fever endemic in West Africa. LASV strains are clustered into six lineages according to their geographic location. To confirm a diagnosis of LF, a laboratory test is required. Here, a reverse transcription loop-mediated isothermal amplification (RT-LAMP) assay using a portable device for the detection of LASV in southeast and south-central Nigeria using three primer sets specific for strains clustered in lineage II was developed. The assay detected in vitro transcribed LASV RNAs within 23 min and was further evaluated for detection in 73 plasma collected from suspected LF patients admitted into two health settings in southern Nigeria. The clinical evaluation using the conventional RT-PCR as the reference test revealed a sensitivity of 50% in general with 100% for samples with a viral titer of 9500 genome equivalent copies (geq)/mL and higher. The detection limit was estimated to be 4214 geq/mL. The assay showed 98% specificity with no cross-reactivity to other viruses which cause similar symptoms. These results suggest that this RT-LAMP assay is a useful molecular diagnostic test for LF during the acute phase, contributing to early patient management, while using a convenient device for field deployment and in resource-poor settings., (Copyright © 2019 Elsevier B.V. All rights reserved.)

Lassa fever is a deadly viral haemorrhagic fever caused by Lassa Virus (LASV). Rodents, especially, Mystomys natalensis , are the known reservoirs of LASV and humans are the defined hosts. Monkeys share many illnesses with humans and experimental LASV infections in monkeys are fatal but natural LASV infection of monkeys has not been reported. Serum samples obtained between August 2015 and December 2017 from 62 monkeys belonging to six species in Southern Nigeria were tested for LASV as part of an ongoing surveillance of monkeys in the region for zoonotic pathogens. Commercially available Recombinant LASV (ReLASV) Pan-Lassa enzyme-linked immunosorbent assay (ELISA) test kits (Zalgen Labs, Germantown, MD, USA) were used to detect antibodies (IgG and IgM) and antigen specific for LASV nucleoprotein in the sera. Lassa-fever-specific IgG and IgM, and antigen specific for LASV nucleoprotein were detected in 5/62, 0/62, and 1/62 samples, respectively. The presence of LASV-specific antibodies in the sera suggests natural exposure to the virus, while the presence of LASV antigen may mean that monkeys are carriers of the virus. There is a need to broaden Lassa fever surveillance to include nonhuman primates (NHPs) for their probable role in the epidemiology of the disease., HIGHLIGHTS ., • Rodents are the natural reservoirs of Lassa fever virus (LASV) and humans are the defined hosts., • Experimental LASV infections in non-human primates (NHP) are fatal but natural infection of NHP with the virus have not been reported., • We detected antigen and antibody specific for LASV in free-living Monkeys from southern Nigeria which implies that monkeys in the region are naturally exposed to LASV and are probable carriers of the virus., Competing Interests: The authors have no conflicts of interest to declare., (© 2019 Atlantis Press International B.V.)

Hemorrhagic fever outbreaks such as Ebola are difficult to detect and control because of the lack of low-cost, easily deployable diagnostics and because initial clinical symptoms mimic other endemic diseases such as malaria. Current molecular diagnostic methods such as polymerase chain reaction require trained personnel and laboratory infrastructure, hindering diagnostics at the point of need. Although rapid tests such as lateral flow can be broadly deployed, they are typically not well-suited for differentiating among multiple diseases presenting with similar symptoms. Early detection and control of Ebola outbreaks require simple, easy-to-use assays that can detect and differentiate infection with Ebola virus from other more common febrile diseases. Here, we developed and tested an immunoassay technology that uses surface-enhanced Raman scattering (SERS) tags to simultaneously detect antigens from Ebola, Lassa, and malaria within a single blood sample. Results are provided in <30 min for individual or batched samples. Using 190 clinical samples collected from the 2014 West African Ebola outbreak, along with 163 malaria positives and 233 negative controls, we demonstrated Ebola detection with 90.0% sensitivity and 97.9% specificity and malaria detection with 100.0% sensitivity and 99.6% specificity. These results, along with corresponding live virus and nonhuman primate testing of an Ebola, Lassa, and malaria 3-plex assay, indicate the potential of the SERS technology as an important tool for outbreak detection and clinical triage in low-resource settings., (Copyright © 2018 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works.)

Many emerging viruses such as Ebola and Lassa occur in resource-limited areas of the world. The advent of multiplex immunoassays has facilitated the study of biomarkers of disease since only small amounts of clinical material are required; however, such assays are designed and validated for only plasma or serum. This is a significant impediment when studying infectious diseases in the context of an outbreak in a developing nation. Plasma or serum can be difficult to obtain in the field due to the need for additional processing of infectious materials. Evaluation of multiplex immunoassays using frozen and thawed human whole blood (WB) would permit additional analysis using a more readily available human clinical sample. In this study, frozen and thawed human WB was directly compared with frozen and thawed plasma from normal healthy donors in a series of multiplexed immunoassays for 59 different biomarkers. We demonstrate that most important biomarkers can be evaluated using thawed WB, which will facilitate the study of human cytokine and other biomarker responses to viruses emerging in resource-limited regions.

A nurse who acquired Lassa virus infection in Togo in the spring of 2016 was repatriated to the United States for care at Emory University Hospital. Serial sampling from this patient permitted the characterization of several aspects of the innate and cellular immune responses to Lassa virus. Although most of the immune responses correlated with the kinetics of viremia resolution, the CD8 T-cell response was of surprisingly high magnitude and prolonged duration, implying prolonged presentation of viral antigens. Indeed, long after viremia resolution, there was persistent viral RNA detected in the semen of the patient, accompanied by epididymitis, suggesting the male reproductive tract as 1 site of antigen persistence. Consistent with the magnitude of acute T-cell responses, the patient ultimately developed long-term, polyfunctional memory T-cell responses to Lassa virus., (Published by Oxford University Press for the Infectious Diseases Society of America 2017. This work is written by (a) US Government employee(s) and is in the public domain in the US.)

Background: Rift Valley fever (RVF) is endemic to the tropical regions of eastern and southern Africa. The seroprevalence of RVF was investigated among the human population in Borno State, Nigeria to determine the occurrence of the disease in the study area in comparison with that of Lassa fever and Crimean-Congo Hemorrhagic fever., Methods: Recombinant nucleoprotein (rNP)-based IgG-ELISAs for the detection of serum antibodies against RVF virus (RVFV), Lassa fever virus (LASV), and Crimean-Congo hemorrhagic fever virus (CCHFV) were used to test human sera in Borno State, Nigeria. The presence of neutralizing antibody against the RVFV-glycoprotein-bearing vesicular stomatitis virus pseudotype (RVFVpv) was also determined in the human sera., Results: Of the 297 serum samples tested, 42 (14.1%) were positive for the presence of RVFV-IgG and 22 (7.4%) and 7 (2.4%) of the serum samples were positive for antibodies against LASV and CCHFV, respectively. There was a positive correlation between the titers of neutralizing antibodies obtained using RVFVpv and those obtained using the conventional neutralization assay with the attenuated RVFV-MP12 strain., Conclusions: The seroprevalence of RVF was significantly higher than that of LASV and CCHF in Borno State, Nigeria. The RVFVpv-based neutralization assay developed in this study has the potential to replace the traditional assays based on live viruses for the diagnosis and seroepidemiological studies of RVF., (© The Author 2014. Published by Oxford University Press on behalf of Royal Society of Tropical Medicine and Hygiene. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)

Background: Lassa fever is a viral hemorrhagic fever endemic in West Africa. The reservoir host of the virus is a multimammate rat, Mastomys natalensis. Prevalence estimates of Lassa virus antibodies in humans vary greatly between studies, and the main modes of transmission of the virus from rodents to humans remain unclear. We aimed to (i) estimate the prevalence of Lassa virus-specific IgG antibodies (LV IgG) in the human population of a rural area of Guinea, and (ii) identify risk factors for positive LV IgG., Methods and Findings: A population-based cross-sectional study design was used. In April 2000, all individuals one year of age and older living in three prefectures located in the tropical secondary forest area of Guinea (Gueckedou, Lola and Yomou) were sampled using two-stage cluster sampling. For each individual identified by the sampling procedure and who agreed to participate, a standardized questionnaire was completed to collect data on personal exposure to potential risk factors for Lassa fever (mainly contact with rodents), and a blood sample was tested for LV IgG. A multiple logistic regression model was used to determine risk factors for positive LV IgG. A total of 1424 subjects were interviewed and 977 sera were tested. Prevalence of positive LV Ig was of 12.9% [10.8%-15.0%] and 10.0% [8.1%-11.9%] in rural and urban areas, respectively. Two risk factors of positive LV IgG were identified: to have, in the past twelve months, undergone an injection (odds ratio [OR] = 1.8 [1.1-3.1]), or lived with someone displaying a haemorrhage (OR = 1.7 [1.1-2.9]). No factors related to contacts with rats and/or mice remained statistically significant in the multivariate analysis., Conclusions: Our study underlines the potential importance of person-to-person transmission of Lassa fever, via close contact in the same household or nosocomial exposure.

Acute arenavirus disease in primates, like Lassa hemorrhagic fever in humans, begins with flu-like symptoms and leads to death approximately 2 weeks after infection. Our goal was to identify molecular changes in blood that are related to disease progression. Rhesus macaques (Macaca mulatta) infected intravenously with a lethal dose of lymphocytic choriomeningitis virus (LCMV) provide a model for Lassa virus infection of humans. Blood samples taken before and during the course of infection were used to monitor gene expression changes that paralleled disease onset. Changes in blood showed major disruptions in eicosanoid, immune response, and hormone response pathways. Approximately 12% of host genes alter their expression after LCMV infection, and a subset of these genes can discriminate between virulent and non-virulent LCMV infection. Major transcription changes have been given preliminary confirmation by quantitative PCR and protein studies and will be valuable candidates for future validation as biomarkers for arenavirus disease.

The clinical laboratory, virologic, and pathologic changes occurring in hamsters after infection with Pirital virus (Arenaviridae) are described. Pirital virus infection in the hamsters was characterized by high titered viremia, leukocytosis, coagulopathy, pulmonary hemorrhage and edema, hepatocellular and splenic necrosis, and marked elevation of serum transaminase levels. All of the animals died within 9 days. The clinical and histopathological findings in the Pirital virus-infected hamsters were very similar to those reported in severe human cases of Lassa fever, suggesting that this new animal model could serve as a low-cost and relatively safe alternative for studying the pathogenesis and therapy of Lassa fever.

Of the 876 rodents caught in different parts of Ekpoma, Nigeria, and environs, 218 were Mastomys natalensis, while 658 were other rodents. Of the 218 M. natalensis caught, 102 (46.79%) were positive for complement fixing antibody to Lassa virus.

The pathogenesis of neurologic complications of Lassa fever is poorly understood. A Nigerian patient had fever, disorientation, seizures, and blood-brain barrier dysfunction, and Lassa virus was found in cerebrospinal fluid (CSF) but not in serum. The concentration of Lassa virus RNA in CSF corresponded to 1 x 10(3) pfu/mL, as determined by a quantitative real-time polymerase chain reaction assay. To characterize the Lassa virus in CSF, the 3.5-kb S RNA was sequenced. In the S RNA coding sequences, the CSF strain differed between 20% and 24.6% from all known prototype strains. These data suggest that Lassa virus or specific Lassa virus strains can persist in the central nervous system and thus contribute to neuropathogenesis. Lassa virus infection should be considered in West African patients or in travelers returning from this area who present only with fever and neurologic signs.

After intracerebral challenge with 100 PFU of Lassa virus (strain Josiah), all infected mice (CBA/calac) died (control group). Production of pro-inflammatory cytokines (IL-1beta, TNF-alpha) significantly increased in the blood of these mice during the infection. For neutralization of increasing concentrations of these cytokines recombinant IL-1RA was used intraperitonealy at a dose 100 microg kg(-1), everyday, within 5 days from the third day after the challenge. Injections of IL-1RA decreased the concentration of IL-1beta and TNF-alpha and resulted in survival of all infected mice (treatment group). Marburg fever (strain Popp) caused in guinea pigs by 5 LD(50) of virus lead to the significant increase of TNF-alpha in the animal's blood and caused a lethal outcome (control group). Treatment of infected guinea pigs by IL-1RA or anti-TNF serum decreased the concentration of TNF-alpha and resulted in survival of half of the animals (treatment group). For the treatment recombinant IL-1RA was used at a dose 100 microg kg(-1), intramuscularly, everyday, within 6 days from the third day after the challenge or anti-TNF serum, intramuscularly 0.5 ml (2000 U ml(-1); 1 U of the antiserum neutralises 0.03 ng of TNF-alpha), everyday, within 6 days from the third day after the challenge.

T cells must play the major role in controlling acute human Lassa virus infection, because patients recover from acute Lassa fever in the absence of a measurable neutralizing antibody response. T cells alone seem to protect animals from a lethal Lassa virus challenge, because after experimental vaccination no neutralizing antibodies are detectable. In order to study human T-cell reactivity to single Lassa virus proteins, the nucleoprotein (NP) of Lassa virus, strain Josiah, was cloned, expressed in Escherichia coli, and affinity purified. Peripheral blood mononuclear cells (PBMC) obtained from 8 of 13 healthy, Lassa virus antibody-positive individuals living in the Republic of Guinea, western Africa, were found to proliferate in response to the recombinant protein (proliferation index >/=10). PBMC obtained from one individual with a particularly high proliferative response were used to generate 50 NP-specific T-cell clones (TCC). For six of these the epitopes were mapped with overlapping synthetic peptides derived from the sequence of the NP. These CD4(+) TCC displayed high specific proliferation and produced mainly gamma interferon upon stimulation with NP. Because variation of up to 15% in the amino acid sequences of the structural proteins of naturally occurring Lassa virus variants has been observed, the reactivity of the TCC with peptides derived from the homologous epitopes of the Nigeria strain of Lassa virus and of the eastern Africa arenavirus Mopeia was tested. With the Nigeria strain of Lassa virus the levels of homology were 100% for two of these epitopes and 85% for three of them, whereas homology with the respective Mopeia epitopes ranged from 92 to 69%. Reactivity of the TCC with peptides derived from the variable epitopes of the Nigeria strain and of Mopeia was reduced or completely abolished. This report shows for the first time that seropositive individuals from areas of endemicity have very strong memory CD4(+) T-cell responses against the NP of Lassa virus, which are partly strain specific and partly cross-reactive with other Lassa virus strains. Our findings may have important implications for the strategy of designing recombinant vaccines against this mainly T-cell-controlled human arenavirus infection.

We attempted to protect three rhesus monkeys from Lassa fever by vaccination with a preparation of purified whole Lassa virus which had been inactivated by gamma irradiation. The vaccinated monkeys developed antibodies against the three major viral proteins of Lassa virus demonstrated by radioimmunoprecipitation. When the three vaccinated monkeys and two unvaccinated control monkeys were challenged all five became severely ill and died. Prior to death a secondary, high-titer antibody response to Lassa virus was observed in the three vaccinated monkeys, whereas the two unvaccinated monkeys developed a primary, low-titer antibody response. Though titers of Lassa virus in serum reached peak levels earlier following challenge in the non vaccinated, at the time of death serum and organ virus titers did not differ significantly. Changes in platelet aggregation, leukocyte counts, and liver enzymes, abnormalities of which have been associated with severity of Lassa fever, were found to be comparable in the two groups. The humoral antibody response measured in these animals following vaccination, although of the same magnitude as found in humans recovered from Lassa fever, was insufficient to protect the animals from this fatal disease. Evidence is now accumulating that the cell-mediated immune response must be activated in order to protect against challenge with arenaviruses.

The level and the time course of accumulation of endogenous interferon were studied in the blood sera of mice experimentally infected with Lassa virus by the intracerebral route. The level of interferon correlated with case-fatality rate of the animals which may be important for the understanding of the pathogenesis of arenavirus infections.

Lassa fever is widespread in West Africa, where the case fatality is about 16% in hospitalized adult patients. The clinical course is highly variable, with a few patients developing severe disease with bleeding, adult respiratory distress syndrome, encephalopathy and hypovolemic shock. We studied 70 patients admitted with suspected Lassa fever to a hospital in Sierra Leone, West Africa. Fourteen patients classified as having severe Lassa fever on the basis of serum aspartate amino transferase (AST) greater than 150 IU/L or viremia of greater than 10(3.6) tissue culture infective dose (TCID) 50/ml were found to have statistically significantly depressed lymphocyte counts when compared with patients with mild Lassa fever (AST less than 150 IU/L or viremia, less than 10(3.6)TCID50/ml), (P less than 0.0001) and with febrile control patients, in whom Lassa infection had been excluded by laboratory criteria (P less than 0.0008). Maximum depression occurred a mean of 10.9 days post onset. Patients with severe Lassa fever also had moderate thrombocytopenia, which was statistically significant when compared with febrile control patients (P less than 0.0003) and this occurred a mean of 10.8 days postonset. The most significant changes were in platelet function, which was markedly depressed in patients with severe Lassa fever (P less than 0.0035 in response to ADP and P = 0.0081 for collagen) when compared with patients with mild Lassa fever, and when compared with febrile controls, (P = 0.0013 for ADP and P less than 0.00001 for collagen). This abnormality was usually maximal on admission to hospital, and probably is an early event, preceding hospitalization in these patients.(ABSTRACT TRUNCATED AT 250 WORDS)

A recurrent theme in studies of the pathology of fatal Lassa fever in man is the lack of histological lesions to explain disordered cell function and death. Recently, we demonstrated the existence of a factor in the plasma of patients with Lassa fever which markedly inhibits the aggregation responses of normal platelets in vitro. To assess whether this factor could mediate more global cellular dysfunction, we studied the effects of Lassa plasma on the respiratory burst of neutrophils. Thirteen of 15 samples from patients in the acute phase of Lassa fever profoundly inhibited the amount of superoxide generated by normal neutrophils in response to the chemotactic peptide, f-met-leu-phe (FMLP) (mean superoxide generated = 54.7 +/- 6.1% of control). In contrast, eight of nine samples from patients who had infections other than Lassa fever enhanced the neutrophil response to the peptide. All Lassa samples which inhibited the ADP-induced aggregation responses of normal platelets inhibited the neutrophil response to FMLP. Unlike the effect on platelets, however, the inhibition of neutrophils was only apparent when the cells were stimulated within 5 min of exposure to the plasma. The inhibition of neutrophils is not due to either interference with FMLP-neutrophil binding or an effect on the NADPH-oxidase, suggesting a suppression of signal transduction. Our data suggest the inhibitory factor in Lassa plasma has global effects on cellular function, and may play a central role in the pathogenesis of this often fatal illness.

Previous studies have shown that haemorrhage in Lassa fever is associated with abnormal in vitro platelet aggregation and a high mortality. In Sierra Leone we studied platelet aggregation in healthy local subjects, patients with laboratory-confirmed Lassa fever and febrile patients in whom Lassa virus infection was excluded. There were no significant differences in the mean platelet counts of these groups. Patients with fulminant Lassa virus infection showed a gross depression of in-vitro platelet responsiveness to 1 and 5 microM ADP and 4 micrograms/ml collagen compared to other groups (P = 0.0004-0.0008 when compared to healthy controls, P = 0.002-0.0008 when compared to mild Lassa fever patients). When plasma samples from five of these patients were mixed 1:1 with control platelet-rich plasma, a marked inhibition of ADP-induced aggregation was observed. No inhibitory activity was detected in plasma obtained from healthy subjects or febrile control patients. The presence of inhibitor was strongly associated with the occurrence of haemorrhage (P = 0.03), depression of platelet aggregation (P = 0.004) and severity of Lassa fever (P = 0.007).

Two hundred thirteen cases of Lassa fever (LF) were diagnosed by virus isolation and seroconversion at Curran Lutheran Hospital in Zorzor, Liberia, between July 1980 and April 1986. An additional 40 cases of probable and presumptive LF were diagnosed on the basis of single serum samples. Of the 246 assessable patients, 23 (9%) died; no data were available for seven patients. Five (16%) of 32 pregnant women and three (43%) of seven immediately postpartum women died. Four (26%) of 15 children less than 12 years died. Case-fatality rates among 125 nonpregnant women and 67 men were approximately 6%. Among 150 patients studied in detail, the case-fatality rate was also 9%. Seventeen (11%) of these patients had abnormal bleeding; of these, six (35%) died. Most platelet counts were at low normal to mildly depressed levels. However, serial counts in seven patients suggested a decrease on about days 10-12 of illness. The symptoms of LF in Liberia are those of a viral syndrome. Edema, sometimes marked, is noted in seriously ill patients. A great variation in mortality and incidence of abnormal bleeding is recorded in reported series of LF; it appears that hemorrhage is a marker for cases with a high mortality. The incidence and severity of hearing defects in LF outbreaks vary. Elucidation of a number of clinical problems in LF requires more information on how strain differences affect the pattern of illness.

The rhesus monkey, an established model of Lassa fever, was used to study hematologic and hemostatic aspects of Lassa fever and whether Mopeia (also known as Mozambique) virus induces any cellular damage in this model. Six days after subcutaneous injection of 10(3.48) plaque forming units (PFU) of Lassa virus (Josiah strain) one group of monkeys received an intravenous injection of 111In-labeled allogeneic platelets and another group received 125I-labeled alogeneic fibrinogen. Lassa virus-infected monkeys developed a severe clinical illness with high viremia and typical pathology. Lassa antigen was found in most tissues using a Lassa nucleocapsid-specific monoclonal antibody. Platelet counts remained within normal limits. Platelet and fibrinogen kinetics were similar in infected and control animals. Hematologic and hemostatic changes indicate that disseminated intravascular coagulation plays no role in this model of Lassa fever. Levels of plasma fibronectin were reduced in Lassa-infected monkeys. Mopeia virus-infected monkeys were normothemic, aviremic, and there was no detection of Mopeia antigen in any tissues using polyclonal or monoclonal antibodies. Mopeia virus was recovered from the spleen of one monkey. Mopeia virus was associated with hepatocellular and renal tubular damage.

The degree of cell and organ damage in clinical and histological studies of patients dying of Lassa fever has been insufficient to explain the catastrophic shock characteristic of the fatal illness. To explore this issue further, we conducted a study of the evolution of shock in three Lassa virus-infected rhesus monkeys. By the sixth day after infection, a marked, progressive reduction of in vitro platelet aggregation occurred despite normal numbers of circulating platelets and a normal platelet survival time and was accompanied by loss of prostacyclin production by postmortem endothelium. Both of these functions recovered rapidly in a surviving animal. There was no evidence of disseminated intravascular coagulation, nor were clotting factors significantly abnormal. We observed association of viral antigen with neutrophils and progressive neutrophilia. Viremia was not reduced by a brisk antibody response in our animals, and there was a general depression of response to mitogens in mixed lymphocyte stimulation assays. Our findings suggest that shock in Lassa fever is due to biochemical dysfunctions of platelets and endothelial cells and results from loss of intravascular plasma volume, effusions, and hemorrhage.