A case of Lassa fever: experience at St Thomas's Hospital

The knowns and unknowns of cardiac autoimmunity in viral myocarditis

Myocarditis can result from various infectious and non-infectious causes that can lead to dilated cardiomyopathy (DCM) and heart failure. Among the infectious causes, viruses are commonly suspected. But the challenge is our inability to demonstrate infectious viral particles during clinical presentations, partly because by that point, the viruses would have damaged the tissues and be cleared by the immune system. Therefore, viral signatures such as viral nucleic acids and virus-reactive antibodies may be the only readouts pointing to viruses as potential primary triggers of DCM. Thus, it becomes hard to explain persistent inflammatory infiltrates that might occur in individuals affected with chronic myocarditis/DCM manifesting myocardial dysfunctions. In these circumstances, autoimmunity is suspected, and antibodies to various autoantigens have been demonstrated, suggesting that immune therapies to suppress the autoimmune responses may be necessary. From this perspective, we endeavoured to determine whether or not the known viral causes are associated with development of autoimmune responses to cardiac antigens that include both cardiotropic and non-cardiotropic viruses. If so, what their nature and significance are in developing chronic myocarditis resulting from viruses as primary triggers.

Fifty years of imported Lassa fever: a systematic review of primary and secondary cases

RATIONALE FOR SYSTEMATIC REVIEW

Lassa fever is the most common cause of imported haemorrhagic fevers cases in non-endemic countries. As a disease with a high case fatality rate that has regularly caused clusters of nosocomial transmission in endemic areas, prompt diagnosis is vital. We conducted a systematic review of imported cases of the last 50 years with the aim of defining the clinical and epidemiological characteristics that will enhance early diagnosis, prompt initiation of treatment and an appropriate public health response to Lassa fever cases.

METHODS

We performed a retrospective, systematic review of 36 primary and two secondary cases of Lassa fever in non-endemic countries outside West Africa by searching the PubMed database. This yielded 56 relevant publications that were included in our analysis.

RESULTS

The case fatality rate of 35.1% for imported cases was higher than that reported for endemic countries. The majority of patients showed clinical features consistent with Lassa fever and had a typical exposure. There was a considerable delay in diagnosis in imported cases with high associated numbers of contacts. Ribavirin was rarely used for post-exposure prophylaxis. Only two secondary transmissions occurred. Thirty-one percent of patients received Lassa fever-specific treatment and five required intensive care.

CONCLUSIONS

Although importation of Lassa fever to non-endemic countries is a rare event, it has repeatedly happened over five decades. Suspicion of Lassa fever should be based on careful consideration of clinical features and exposure history in order to assist early diagnosis in returning travellers from West Africa.

Lassa Fever in Travelers from West Africa, 1969-2016

Lassa virus is a rodentborne arenavirus responsible for human cases of Lassa fever, a viral hemorrhagic fever, in West Africa and in travelers arriving to non–Lassa-endemic countries from West Africa. We describe a retrospective review performed through literature search of clinical and epidemiologic characteristics of all imported Lassa fever cases worldwide during 1969–2016. Our findings demonstrate that approximately half of imported cases had distinctive clinical features (defined as fever and >1 of the following: pharyngitis, sore throat, tonsillitis, conjunctivitis, oropharyngeal ulcers, or proteinuria). Delays in clinical suspicion of this diagnosis were common. In addition, no secondary transmission of Lassa fever to contacts of patients with low-risk exposures occurred, and infection of high-risk contacts was rare. Future public health investigations of such cases should focus on timely recognition of distinctive clinical features, earlier treatment of patients, and targeted public health responses focused on high-risk contacts.

A rapid research needs appraisal methodology to identify evidence gaps to inform clinical research priorities in response to outbreaks-results from the Lassa fever pilot

BACKGROUND

Infectious disease epidemics are a constant threat, and while we can strengthen preparedness in advance, inevitably, we will sometimes be caught unaware by novel outbreaks. To address the challenge of rapidly identifying clinical research priorities in those circumstances, we developed and piloted a protocol for carrying out a systematic, rapid research needs appraisal (RRNA) of existing evidence within 5 days in response to outbreaks globally, with the aim to inform clinical research prioritization.

METHODS

The protocol was derived from rapid review methodologies and optimized through effective use of pre-defined templates and global time zones. It was piloted using a Lassa fever (LF) outbreak scenario. Databases were searched from 1969 to July 2017. Systematic reviewers based in Canada, the UK, and the Philippines screened and extracted data using a systematic review software. The pilot was evaluated through internal analysis and by comparing the research priorities identified from the data, with those identified by an external LF expert panel.

RESULTS

The RRNA pilot was completed within 5 days. To accommodate the high number of articles identified, data extraction was prioritized by study design and year, and the clinical research prioritization done post-day 5. Of 118 potentially eligible articles, 52 met the data extraction criteria, of which 46 were extracted within the 5-day time frame. The RRNA team identified 19 clinical research priorities; the expert panel independently identified 21, of which 11 priorities overlapped. Each method identified a unique set of priorities, showing that combining both methods for clinical research prioritization is more robust than using either method alone.

CONCLUSIONS

This pilot study shows that it is feasible to carry out a systematic RRNA within 5 days in response to a (re-) emerging outbreak to identify gaps in existing evidence, as long as sufficient resources are identified, and reviewers are experienced and trained in advance. Use of an online systematic review software and global time zones effectively optimized resources. Another 3 to 5 days are recommended for review of the extracted data and to formulate clinical research priorities. The RRNA can be used for a "Disease X" scenario and should optimally be combined with an expert panel to ensure breadth and depth of coverage of clinical research priorities.

Absence of Nosocomial Transmission of Imported Lassa Fever during Use of Standard Barrier Nursing Methods

Nosocomial transmission of Lassa virus (LASV) is reported to be low when care for the index patient includes proper barrier nursing methods. We investigated whether asymptomatic LASV infection occurred in healthcare workers who used standard barrier nursing methods during the first 15 days of caring for a patient with Lassa fever in Sweden. Of 76 persons who were defined as having been potentially exposed to LASV, 53 provided blood samples for detection of LASV IgG. These persons also responded to a detailed questionnaire to evaluate exposure to different body fluids from the index patient. LASV-specific IgG was not detected in any of the 53 persons. Five of 53 persons had not been using proper barrier nursing methods. Our results strengthen the argument for a low risk of secondary transmission of LASV in humans when standard barrier nursing methods are used and the patient has only mild symptoms.

Aeromedical Evacuation of Patients with Contagious Infections

Most patients with infectious diseases, including biologic warfare casualties, can be safely transported by aeromedical evacuation (AE) using standard precautions. However, certain contagious diseases (e.g., tuberculosis, pneumonic plague, viral hemorrhagic fever) require transmission-based precautions to protect the other patients, medical personnel, and aircrew. AE planning for these patients must take into account international public health regulations. Given adequate resources, foresight, and expertise, the AE of infected patients and biologic warfare casualties can be safely accomplished.

This chapter provides a review of the aeromedical evacuation of patients with communicable diseases. Topics include a review of the ecology of aircraft cabins and engineering features of aircraft ventilation systems that minimize the risk of disease transmission; examples of point source outbreaks related to air travel; in-flight preventive measures including the use of patient isolators; and US military and international policy and legal aspects of transporting patients with communicable diseases. Examples include in-flight transmission of tuberculosis, severe acute respiratory syndrome (SARS), smallpox, and measles.The chapter will also discuss experience in transporting patients with contagious diseases including viral hemorrhagic fevers and new patient isolation technologies that were used for the long-distance transport of patients with Ebola virus disease during the 2014–2016 West African epidemic.

Mapping the zoonotic niche of Lassa fever in Africa

Background

Lassa fever is a viral haemorrhagic illness responsible for disease outbreaks across West Africa. It is a zoonosis, with the primary reservoir species identified as the Natal multimammate mouse, Mastomys natalensis. The host is distributed across sub-Saharan Africa while the virus' range appears to be restricted to West Africa. The majority of infections result from interactions between the animal reservoir and human populations, although secondary transmission between humans can occur, particularly in hospital settings.

Methods

Using a species distribution model, the locations of confirmed human and animal infections with Lassa virus (LASV) were used to generate a probabilistic surface of zoonotic transmission potential across sub-Saharan Africa.

Results

Our results predict that 37.7 million people in 14 countries, across much of West Africa, live in areas where conditions are suitable for zoonotic transmission of LASV. Four of these countries, where at-risk populations are predicted, have yet to report any cases of Lassa fever.

Conclusions

These maps act as a spatial guide for future surveillance activities to better characterise the geographical distribution of the disease and understand the anthropological, virological and zoological interactions necessary for viral transmission. Combining this zoonotic niche map with detailed patient travel histories can aid differential diagnoses of febrile illnesses, enabling a more rapid response in providing care and reducing the risk of onward transmission.

Using modelling to disentangle the relative contributions of zoonotic and anthroponotic transmission: the case of lassa fever

Background

Zoonotic infections, which transmit from animals to humans, form the majority of new human pathogens. Following zoonotic transmission, the pathogen may already have, or may acquire, the ability to transmit from human to human. With infections such as Lassa fever (LF), an often fatal, rodent-borne, hemorrhagic fever common in areas of West Africa, rodent-to-rodent, rodent-to-human, human-to-human and even human-to-rodent transmission patterns are possible. Indeed, large hospital-related outbreaks have been reported. Estimating the proportion of transmission due to human-to-human routes and related patterns (e.g. existence of super-spreaders), in these scenarios is challenging, but essential for planned interventions.

Methodology/Principal Findings

Here, we make use of an innovative modeling approach to analyze data from published outbreaks and the number of LF hospitalized patients to Kenema Government Hospital in Sierra Leone to estimate the likely contribution of human-to-human transmission. The analyses show that almost of the cases at KGH are secondary cases arising from human-to-human transmission. However, we found much of this transmission is associated with a disproportionally large impact of a few individuals (‘super-spreaders’), as we found only of human cases result in an effective reproduction number (i.e. the average number of secondary cases per infectious case) , with a maximum value up to .

Conclusions/Significance

This work explains the discrepancy between the sizes of reported LF outbreaks and a clinical perception that human-to-human transmission is low. Future assessment of risks of LF and infection control guidelines should take into account the potentially large impact of super-spreaders in human-to-human transmission. Our work highlights several neglected topics in LF research, the occurrence and nature of super-spreading events and aspects of social behavior in transmission and detection.

Many pathogens have the ability to infect different species. Lassa fever virus is an important example; this virus infects a species of rodent in West Africa, and can cause a severe disease in people. Lassa fever virus is transmitted from rodent-to-rodent, rodent-to-human, human-to-human and perhaps human-to-rodent. So far, the relative importance of these routes has not been assessed. Here we focus on the risk for humans; undoubtedly, most human infections are acquired by contact with rodents or their urine, but the relative risk of rodent-to-human and human-to-human transmission is unknown. We use mathematical modeling to address this. First, we identified Lassa fever outbreaks known to be due to human-to-human chains of transmission. Then, we looked at people hospitalized with the disease in Kenema Government Hospital, Sierra Leone (KGH), who could have been infected either by rodents or humans. We asked, what should the proportion of patients be who get infected by humans, assuming the statistical patterns observed in the human-to-human chains are the same in both instances? We found that around of patients with Lassa fever in KGH probably acquired the disease from another person. In addition, the patterns of disease in people suggest that these of cases are probably initiated by only a small number of infected people (who could be thought of as super-spreaders).

Viral haemorrhagic fevers in healthcare settings

Viral haemorrhagic fevers (VHFs) typically manifest as rapidly progressing acute febrile syndromes with profound haemorrhagic manifestations and very high fatality rates. VHFs that have the potential for human-to-human transmission and onset of large nosocomial outbreaks include Crimean-Congo haemorrhagic fever, Ebola haemorrhagic fever, Marburg haemorrhagic fever and Lassa fever. Nosocomial outbreaks of VHFs are increasingly reported nowadays, which likely reflects the dynamics of emergence of VHFs. Such outbreaks are associated with an enormous impact in terms of human lives and costs for the management of cases, contact tracing and containment. Surveillance, diagnostic capacity, infection control and the overall preparedness level for management of a hospital-based VHF event are very limited in most endemic countries. Diagnostic capacities for VHFs should increase in the field and become affordable. Availability of appropriate protective equipment and education of healthcare workers about safe clinical practices and infection control is the mainstay for the prevention of nosocomial spread of VHFs.

Travellers and viral haemorrhagic fevers: what are the risks?

Viral haemorrhagic fevers (VHF) are caused by zoonotic viral infections transmitted to humans directly or by ticks or mosquitoes. The overall risk to travellers is conservatively estimated at <1 in 1 million travel episodes to African countries where infection is present, and febrile patients returning from these countries are at least 1000 times more likely to have malaria than Lassa fever or another VHF. No cases have been reported in fellow travellers exposed to a travelling case and only one asymptomatic seroconversion (to Lassa) has been reported in over 2000 contacts following care of VHF cases in modern Western hospital settings. However, healthcare-associated transmission of infection has been a major problem in some endemic settings. The potential for healthcare-associated infection and the threats posed by unrecognised or new agents necessitate a high index of suspicion and a standardised risk assessment approach to febrile travellers. Travel-related hantavirus infections are increasingly being reported from Europe and the Americas. This article summarises the epidemiology and reports of travel-related VHF cases in the past 40 years, together with strategies for their recognition, management and prevention.

Viral haemorrhagic fevers imported into non-endemic countries: risk assessment and management

BACKGROUND

Viral haemorrhagic fevers (VHFs) are severe infections capable of causing haemorrhagic disease and fatal multi-organ failure. Crimean-Congo, Marburg, Ebola and Lassa viruses cause both sporadic cases and large epidemics over wide endemic areas.

SOURCES OF DATA

Original articles and reviews identified by PubMed search and personal reading; European and United States national guidance and legislation. World Health Organization information, documents and reports. VHFs cause significant morbidity and mortality in their endemic areas; they can cause healthcare-related infections, and their broad diversity and range are increasingly recognized.

AREAS OF CONTROVERSY

There is uncertainty about the risks presented by VHFs in non-endemic countries, particularly in healthcare environments. Consensus on the best modes of care and infection control are only slowly emerging.

GROWING POINTS

With increasing commerce in rural and low-income areas, VHF outbreaks increasingly expand, causing social and economic damage.

AREAS TIMELY FOR DEVELOPING RESEARCH

New ecologies, viral strains and clinical syndromes are being discovered. There is a great need for rapid diagnostic tests and effective antiviral treatments. Vaccine development programmes are challenged by multiple viral strains and the need for trials in rural communities.

Historical Lassa fever reports and 30-year clinical update

Five cases of Lassa fever have been imported from West Africa to the United States since 1969. We report symptoms of the patient with the second imported case and the symptoms and long-term follow-up on the patient with the third case. Vertigo in this patient has persisted for 30 years.

Early risk assessment for viral haemorrhagic fever: experience at the Hospital for Tropical Diseases, London, UK

OBJECTIVES

To implement a policy of systematic screening for viral haemorrhagic fever (VHF) among travellers returning from African countries with fever, commencing at initial clinical contact.

METHODS

A protocol based on UK Advisory Committee on Dangerous Pathogens guidance was developed collaboratively by medical, nursing and laboratory staff. Audit was carried out to quantify resource demands and effects on time to diagnose malaria, the main differential diagnosis.

RESULTS

A protocol is now implemented for all patients presenting to HTD with fever, with clear guidelines for interaction with clinical and laboratory staff at each stage. The protocol required moderate amounts of clinical and laboratory staff time and resulted in some additional hospital admissions. The time to a diagnosis of malaria increased from a median of 90 (range 50-125) min in patients without VHF risk to a median of 140 (range 101-225) min (p=0.0025) in those assessed as at risk.

CONCLUSIONS

Although all acute medical services need to have robust procedures for early detection of patients with serious transmissible conditions, few implement such a policy. Our protocol requires increased human and other resources but has no important impact on the rapidity of diagnosis of malaria, and is now embedded in local practice.

Evaluating the immunogenicity and protective efficacy of a DNA vaccine encoding Lassa virus nucleoprotein

Several viruses in the Arenavirus genus of the family Arenaviridae cause severe, often fatal, hemorrhagic fever. One such virus, Lassa virus (LV), is a frequent cause of disease in Africa, and survivors often are left with substantial neurological impairment. The feasibility of protective immunization against LV infection, and the associated disease, has been demonstrated in animal models, using recombinant vaccinia viruses to deliver Lassa proteins. Circumstantial evidence implicates cellular immunity in this Lassa-induced protection, but this has not been confirmed. Here, we describe DNA vaccines that encode LV proteins. A single inoculation of a plasmid encoding full-length Lassa nucleoprotein (LNP) can induce CD8(+) T cell responses in mice and can protect against challenge with two arenaviruses, lymphocytic choriomeningitis virus (LCMV) and Pichinde virus (PV). A DNA minigene vaccine encoding a 9 amino acid sequence from LNP also induces CD8(+) T cells and protects against arenavirus challenge, thus confirming prior speculation that protective cellular immunity is induced by LV proteins.

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.

Imported Lassa fever in Germany: surveillance and management of contact persons

This study sought to assess the risk of secondary transmission after import of Lassa fever into Europe. A total of 232 persons exposed to a case of Lassa fever imported into Germany were identified. The level of exposure was determined for 157 persons (68%), and 149 (64%) were tested serologically. High-risk or close contact was reported by 30 (19%) of 157 persons. No symptomatic secondary infections were observed. However, Lassa virus-specific immunoglobulin G antibodies were detected in a serum sample obtained from a physician who examined the index patient on day 9 of illness. The physician received ribavirin prophylaxis and did not develop symptoms of Lassa fever. On the basis of these data, the contact was classified as having a probable secondary infection. The study indicates a low risk of transmission during the initial phase of symptomatic Lassa fever, even with high-risk exposures. The risk may increase with progression of disease and increasing virus load.

Molecular diagnostics of viral hemorrhagic fevers

This review addresses the diagnostics of viral hemorrhagic fevers (VHFs). In the first part, an overview is given on classical methods of VHF diagnostics as well as novel molecular diagnostic tools. Currently available polymerase chain reaction (PCR) assays for diagnosis of VHF are summarized and discussed. In the second part, VHF diagnostics are described in particular for Lassa fever, yellow fever, and Crimean-Congo hemorrhagic fever, based on cases that were imported into or occurred within Europe. The third part is focussed on important differential diagnoses of VHF.

Nosocomial spread of viral disease

Viruses are important causes of nosocomial infection, but the fact that hospital outbreaks often result from introduction(s) from community-based epidemics, together with the need to initiate specific laboratory testing, means that there are usually insufficient data to allow the monitoring of trends in incidences. The most important defenses against nosocomial transmission of viruses are detailed and continuing education of staff and strict adherence to infection control policies. Protocols must be available to assist in the management of patients with suspected or confirmed viral infection in the health care setting. In this review, we present details on general measures to prevent the spread of viral infection in hospitals and other health care environments. These include principles of accommodation of infected patients and approaches to good hygiene and patient management. They provide detail on individual viral diseases accompanied in each case with specific information on control of the infection and, where appropriate, details of preventive and therapeutic measures. The important areas of nosocomial infection due to blood-borne viruses have been extensively reviewed previously and are summarized here briefly, with citation of selected review articles. Human prion diseases, which present management problems very different from those of viral infection, are not included.

Imported vector- and rodent-borne virus infections--an introduction

Travel is a potent force in the emergence of virus infections. Migration of humans and animals has been the pathway for disseminating virus diseases throughout history. In recent years, dengue virus has been identified as the most important travel-related, vector-borne virus disease. Other vector-borne virus infections, such as sandfly fever, Rift Valley fever, chikungunya fever and Japanese encephalitis, have been diagnosed in travelers returning from endemic areas. Crimean-Congo haemorrhagic fever may not only be imported by infected live stock, but also by travelers. Of rodent-borne virus infections, Lassa fever has been diagnosed occasionally in travelers returning from endemic areas. The potential impact of imported filoviruses is currently discussed.

Effects of Ill Health on the Service of Scottish Presbyterian Missionaries 1867-1929

The experience of Scottish Presbyterian missionaries serving overseas between 1867 and 1929 was analyzed. Data were compiled during a 4-year postgraduate research program from such sources as the General Assembly Reports of the Foreign Mission Committees of the Church of Scotland, numerous missionary magazines, school records, medical directories, and newspaper and medical journal obituaries. Data show that the year of appointment, the mission station and continent location, and medical knowledge were all influencing factors on the length of missionary service, early retirement on account of ill health, death in service, and age at death. This method of comparative, historical study may have further useful applications in looking at the health experience of other groups who lived and worked abroad at the turn of the century, such as civil servants, the military, or other comparable missionary groups.

A cumulative review of studies on travellers, their experience of illness and the implications of these findings

A cumulative review of illness experienced by 13,816 travellers returning to Scotland since 1977, shows an overall attack rate of 36%. Alimentary complaints predominated; 18% of travellers had these alone and a further 10% had other symptoms as well as their gastro-intestinal disorder. Higher attack rates were noted in those taking package holidays. Inexperience of travel, smoking, more southerly travel and younger age (particularly those between 20- and 29-years-old) were other contributing factors. A similar pattern emerged from a I year study of hospital in-patients with travel related admissions. Serological studies of 470 travellers showed that 20% had incomplete immunity to poliomyelitis; 25% of those tested (312 travellers) had serological evidence of typhoid immunisation, I.9% (of 760 travellers) had antibodies to Legionella pneumophila, 64% (5II travellers tested) had antibodies to hepatitis A, 87% (288 tested) had adequate levels of tetanus antitoxin but only 40% of the 225 travellers tested had adequate levels of diphtheria antitoxin. Amongst a subgroup of 645 travellers the travel agent was the most frequently consulted source of pre-travel health advice. This carries particular significance for the dissemination of relevant advice in view of the inadequacies found from study of the health information in travel brochures. These findings, viewed against the perspective of the continuing growth in international travel, means that travellers, the medical profession, the travel trade, health educators, global health agencies and health authorities in those countries accepting and encouraging tourists, will be required to recognise the health implications of further tourism development if this problem of illness associated with travel is to be brought under control.

Hepatitis B infections after gynaecological surgery

When acute hepatitis B developed in 3 patients who had had gynaecological surgery, the surgeon was found to be a carrier of hepatitis B e antigen. Of 268 patients operated on by this surgeon in one hospital, 247 were screened for markers of recent or current hepatitis B. 22 (9%) had such markers, associated with symptoms in 5. The operations carrying greatest risk of infection were hysterectomy (10/42) and caesarean section (10/51). These findings strengthen the case for vaccination of all surgeons and medical students against hepatitis B.

No evidence for increased risk of Lassa fever infection in hospital staff

A prospective serological study was undertaken in hospital personnel who care for Lassa fever (LF) patients in an endemic region of Sierra Leone, West Africa. Among personnel from three hospitals where barrier nursing is practised, antibody prevalence and seroconversion by age and sex were consistently equal to or lower than those of persons in nearby village populations. No group among hospital personnel evaluated by age, sex, contact, or occupational exposure was at higher risk than another. Hospital staff in Sierra Leone who care for LF patients using simple barrier nursing methods have no higher risk of infection than the local population. These findings support the proposal that patients with LF in non-endemic countries need not be confined to isolators.

Patients with suspected Lassa fever in London during 1984: problems in their management at St Thomas's Hospital

During 1984, 23 patients in whom a diagnosis of viral haemorrhagic fever was considered presented to the accident and emergency department at St Thomas's Hospital. There were no confirmed cases of viral haemorrhagic fever. Nine patients were transferred to Coppett's Wood Hospital, the nearest specially designated high security isolation unit. Malaria was the final diagnosis in 14, and in six this diagnosis was confirmed only after examining repeated smears at Coppett's Wood Hospital. Transferral of patients to such units is time consuming, expensive, and often unnecessary. Specially designated isolation units in district general hospitals and all teaching hospitals would simplify and improve the care not only of patients with a possible viral haemorrhagic fever but also patients with tuberculosis, multiply resistant staphylococcal infections, and viral infections that may be hazardous if transmitted to immunocompromised patients.

A case of Lassa fever: clinical and virological findings

Five days after arriving in London from Jos a young Nigerian women developed a severe and prolonged illness that proved to be Lassa fever. Virus was not detected in urine during the first three weeks but then appeared and reached a peak during the sixth week, with continuing excretion for 67 days after the onset of illness. Laboratory investigations showed evidence of extensive tissue damage and disturbance of clotting, but there was no serious bleeding and she eventually made a complete recovery despite a high sustained viraemia and severe liver damage. Convalescent serum was used in treatment but it was difficult to assess its contribution to the favourable outcome.