Molecular Epidemiology of Lassa Fever in Edo State, Nigeria.

Lassa fever is an acute, severe, often fatal, febrile illness; estimated to affect about 100,000 persons per year in West Africa. It is caused by Lassa virus, a single-stranded RNA virus which belongs to the virus family Arenaviridae. In Nigeria, the current epidemiological situation is less clear as there has been no active surveillance system in place. A hospital-based study was conducted in Edo State, South-South Nigeria where outbreaks has been frequently reported. This study was from November, 2005 to December, 2008 and it was to investigate the epidemiology and clinical presentation of Lassa fever. Blood collected from patients clinically suspected to have Lassa fever were tested for Lassa virus ribonucleic acid (RNA) by Reverse Transcriptase Polymerase Chain Reaction (RT-PCR). Also, although there is great diversity of Lassa virus in Nigeria, only one full-length L RNA sequence and five S RNA sequences are known. To fill this gap, S and L RNA of six Lassa virus strains isolated from different areas of Nigeria were completely sequenced. These six and a large number of novel partial sequences were subjected to phylogenetic analysis. Lassa fever was laboratory confirmed in 62 (23.2%) of the 267 patients. Of these 267 patients, 103 (38.6%) were female, 160 (60.0%) were male and the sex of 4 (1.4%) was not recorded. However Lassa fever was found in 37 (59.7%) male and 25 (40.3%) female. The mean age for positive patients was 31.1 years (the youngest patient with Lassa fever was one year, 3 months old and the oldest was 70 years old). Geographically, patients were seen from the three senatorial districts of the state with the highest number of laboratory confirmed cases from the central senatorial district. Of the 62 positive patients, 41 (66%) patients were seen in the dry season and 21 (34%) in the rainy season. A wide spectrum of clinical manifestations was observed in patients with Lassa fever. They ranged from fever, nausea, vomiting, abdominal pain, headache, sore throat, cough, malaise, chest pain, diarrhoea, muscle pain, back pain, stiff neck, haemorrhage (bleeding), jaundice, oedema, conjunctivitis and convulsion. Bleeding was observed in 12 (19%) of the patients with acute Lassa fever and deafness occurred in 2 (3%) of them. Clinical presentations between those with Lassa fever and other febrile illnesses were essentially indistinguishable. Thirty-five (56%) of the 62 positive patients recovered and were discharged from the hospital, 18 (29%) died and 1 (1.6%) was referred to another hospital and the outcome of 8 (12.9%) was not recorded. The overall case-fatality rate for those with Lassa fever was 24.2%. Lassa fever is still largely widespread in Edo State but still typically difficult to distinguish clinically; and it is feared that this picture might be the same for other regions of Nigeria. This study suggests that there is still significant genetic variation among Lassa virus strains and this has enormous implications for molecular diagnosis especially with an antigen-based serology and the Polymerase Chain Reaction (PCR), which has been extensively shown in previous studies to be sensitive. Phylogenetic analysis revealed a predominance of lineage II and III strains, existence of a previously un-described sub-lineage in Nigeria, and directional spread of virus in the southern part of the country. The novel sequences will aid in the design of molecular detection assays for Lassa virus.
A Thesis Submitted to the School of Postgraduate Studies, University of Lagos.
Lassa Fever , Molecular Epidemiology , Arenaviridae , Research Subject Categories::MEDICINE::Microbiology, immunology, infectious diseases::Microbiology
Ehichioya, D.U (2012), Molecular Epidemiology of Lassa Fever in Edo State, Nigeria. A Thesis Submitted to University of Lagos School of Postgraduate Studies Phd Thesis and Dissertation, 140pp.