Hospital-based surveillance for Lassa fever in Edo State, Nigeria, 2005-2008.

OBJECTIVES: To estimate the burden of Lassa fever in northern and central Edo, a state in south Nigeria where Lassa fever has been reported. METHODS: Blood samples were obtained from 60 patients hospitalised at the Irrua Specialist Teaching Hospital (ISTH), Irrua, with a clinical suspicion of Lassa fever and from 451 febrile outpatients seen at the ISTH and hospitals in Ekpoma, Iruekpen, Uromi, Auchi and Igarra. All samples were tested retrospectively by Lassa virus-specific RT-PCR. Outpatients were additionally screened for Lassa virus-specific antibodies by indirect immunofluorescent antibody assay. RESULTS: Lassa virus was detected in 25 of 60 (42%) patients with a clinical suspicion of Lassa fever. The disease affected persons of all age groups and with various occupations, including healthcare workers. The clinical picture was dominated by gastrointestinal symptoms. The case fatality rate was 29%. Lassa virus was detected in 2 of 451 (0.44%) febrile outpatients, and 8 (1.8%) were positive for Lassa virus-specific IgG. CONCLUSIONS: Lassa fever contributes to hospital mortality in Edo State. The low prevalence of the disease among outpatients and the low seroprevalence may indicate that the population-level incidence is not high. Surveillance for Lassa fever should focus on the hospitalised patient.

Current molecular epidemiology of Lassa virus in Nigeria.

Recent Lassa virus strains from Nigeria were completely or partially sequenced. Phylogenetic analysis revealed the predominance of lineage II and III strains, the existence of a previously undescribed (sub)lineage in Nigeria, and the directional spread of virus in the southern part of the country. The Bayesian analysis also provided estimates for divergence times within the Lassa virus clade.

Development and evaluation of antibody-capture immunoassays for detection of Lassa virus nucleoprotein-specific immunoglobulin M and G.

BACKGROUND: The classical method for detection of Lassa virus-specific antibodies is the immunofluorescence assay (IFA) using virus-infected cells as antigen. However, IFA requires laboratories of biosafety level 4 for assay production and an experienced investigator to interpret the fluorescence signals. Therefore, we aimed to establish and evaluate enzyme-linked immunosorbent assays (ELISA) using recombinant Lassa virus nucleoprotein (NP) as antigen. METHODOLOGY/PRINCIPAL FINDINGS: The IgM ELISA is based on capturing IgM antibodies using anti-IgM, and the IgG ELISA is based on capturing IgG antibody-antigen complexes using rheumatoid factor or Fc gamma receptor CD32a. Analytical and clinical evaluation was performed with 880 sera from Lassa fever endemic (Nigeria) and non-endemic (Ghana and Germany) areas. Using the IFA as reference method, we observed 91.5-94.3% analytical accuracy of the ELISAs in detecting Lassa virus-specific antibodies. Evaluation of the ELISAs for diagnosis of Lassa fever on admission to hospital in an endemic area revealed a clinical sensitivity for the stand-alone IgM ELISA of 31% (95% CI 25-37) and for combined IgM/IgG detection of 26% (95% CI 21-32) compared to RT-PCR. The specificity of IgM and IgG ELISA was estimated at 96% (95% CI 93-98) and 100% (95% CI 99-100), respectively, in non-Lassa fever patients from non-endemic areas. In patients who seroconverted during follow-up, Lassa virus-specific IgM and IgG developed simultaneously rather than sequentially. Consistent with this finding, isolated IgM reactivity, i.e. IgM in the absence of IgG, had no diagnostic value. CONCLUSIONS/SIGNIFICANCE: The ELISAs are not equivalent to RT-PCR for early diagnosis of Lassa fever; however, they are of value in diagnosing patients at later stage. The IgG ELISA may be useful for epidemiological studies and clinical trials due its high specificity, and the higher throughput rate and easier operation compared to IFA.

Prevalence of Lassa Virus Disease (LVD) in Nigerian children with fever or fever and convulsions in an endemic area.

BACKGROUND: Convulsions with fever in children are a common neurologic emergency in the tropics, and determining the contribution of endemic viral infections can be challenging. In particular, there is a dearth of data on the prevalence and clinical differentiation of Lassa virus disease (LVD) in febrile children in endemic areas of Nigeria, which has multiple lineages of the virus. The aim of this study was to determine the prevalence and presentation of LVD in febrile children with and without convulsions. METHODOLOGY/PRINCIPAL FINDINGS: This was a prospective study of consecutive febrile children aged ≥1 month- 15 years admitted to the Children's Emergency Room of Irrua Specialist Teaching Hospital over a period of 1 year. Febrile children with convulsions (Cases) were compared with those without convulsions (Controls). LVD was defined by the presence of a positive Lassa virus RT-PCR test. Rates were compared between groups using χ2 or Fisher's exact tests and p <0.05 taken as significant. 373 (40.9%) of 913 admissions had fever. Of these, 108/373 (29%) presented with convulsions. The overall prevalence of LVD was 13/373 (3.5%; 95% CI = 1.9%, 5.7%) in febrile admissions, 3/108 (2.8%) in Cases and 10/265 (3.8%) in Controls [(Odds Ratio (95% Confidence Interval) (OR (95% CI)) of LVD in Cases versus Controls = 0.73 (0.2, 2.7)]. Only vomiting (OR (95% CI) = 0.09 (0.01, 0.70)) and bleeding (OR (95% CI) = 39.56 (8.52, 183.7)) were significantly associated with an increased prevalence of LVD. CONCLUSIONS/SIGNIFICANCE: LVD is an important cause of fever, including undifferentiated fever in children in endemic areas, but it is not significantly associated with convulsions associated with fever. Its prevalence, and lack of clinical differentiation on presentation, underscores the importance of a high index of suspicion in diagnosis. Screening of febrile children with undifferentiated fever in endemic areas for LVD could be an important medical and public health control measure.

Molecular diagnostics for lassa fever at Irrua specialist teaching hospital, Nigeria: lessons learnt from two years of laboratory operation.

BACKGROUND: Lassa fever is a viral hemorrhagic fever endemic in West Africa. However, none of the hospitals in the endemic areas of Nigeria has the capacity to perform Lassa virus diagnostics. Case identification and management solely relies on non-specific clinical criteria. The Irrua Specialist Teaching Hospital (ISTH) in the central senatorial district of Edo State struggled with this challenge for many years. METHODOLOGY/PRINCIPAL FINDINGS: A laboratory for molecular diagnosis of Lassa fever, complying with basic standards of diagnostic PCR facilities, was established at ISTH in 2008. During 2009 through 2010, samples of 1,650 suspected cases were processed, of which 198 (12%) tested positive by Lassa virus RT-PCR. No remarkable demographic differences were observed between PCR-positive and negative patients. The case fatality rate for Lassa fever was 31%. Nearly two thirds of confirmed cases attended the emergency departments of ISTH. The time window for therapeutic intervention was extremely short, as 50% of the fatal cases died within 2 days of hospitalization--often before ribavirin treatment could be commenced. Fatal Lassa fever cases were older (p = 0.005), had lower body temperature (p<0.0001), and had higher creatinine (p<0.0001) and blood urea levels (p<0.0001) than survivors. Lassa fever incidence in the hospital followed a seasonal pattern with a peak between November and March. Lassa virus sequences obtained from the patients originating from Edo State formed--within lineage II--a separate clade that could be further subdivided into three clusters. CONCLUSIONS/SIGNIFICANCE: Lassa fever case management was improved at a tertiary health institution in Nigeria through establishment of a laboratory for routine diagnostics of Lassa virus. Data collected in two years of operation demonstrate that Lassa fever is a serious public health problem in Edo State and reveal new insights into the disease in hospitalized patients.