Short communication: Lassa fever in Sierra Leone: UN peacekeepers are at risk.

Abstract

Lassa fever is endemic in much of West Africa, particularly in Guinea, Sierra Leone and Liberia. The conflict and population migrations in this part of the world have led to the deployment of United Nations (UN) forces who are at risk of infection. We describe a Lassa case in this group. On July 12th 2000, a member of the Indian contingent of the United Nations Mission in Sierra Leone (UNAMSIL) peacekeeping forces stationed in Daru, Kailahun District, developed the clinical symptoms of Lassa fever ( McCormick et al. 1987 ). He presented with persistent fever (103–104 °F), myalgia, headache, abdominal pain, hypotension and facial flushing. On the eighth day he developed exudative tonsillar patches, subconjunctival haemorrhage, facial oedema and ecchymosis, then developed bilateral pleural effusions and started to bleed from venipuncture sites. He was treated for 10 days with intravenous ribavirin in the UNAMSIL referral hospital in Freetown, and survived. Presently no diagnostic facilities for Lassa fever are available in Sierra Leone, and the disease often does not present with specific symptoms allowing an early clinical diagnosis. The European Community supports a research project for the surveillance of Lassa fever, yellow fever and Ebola in Côte d’Ivoire and the Republic of Guinea. Coordinated by Epicentre, laboratory back up is provided by the University of Marburg, the Pasteur Institute in Paris and the Bernhard Nocht Institute, Hamburg. After a field investigation in Daru, UNAMSIL sent serum samples from the suspected Lassa case, possible contacts and from healthy villagers by helicopter to the project laboratory in Conakry. The samples were subjected to two different Reverse Transcription/PCR reactions (targeting the glycoprotein (GP) ( Demby et al. 1994), and nucleoprotein (NP) ( ter Meulen et al. 1998) genes) and indirect immunofluorescence for detection of anti-Lassa IgM and IgG antibodies. Lassa-IgM antibodies were detected in three consecutive serum samples of the Daru case and in pleural exudate, with IgM titres ranging from 1:40 to > 1:320. IgG antibody titres ranged from undetectable to > 1:640. Viral RNA was detected only in the first serum sample, taken on day three of ribavirin treatment, and Lassa virus was successfully isolated in Marburg (biosafety level 4). Sequencing of the PCR products revealed 93% homology for the GP gene with the prototypic Lassa virus strain Josiah from Sierra Leone, and 94% for the NP gene. On the aminoacid level, homologies were 97% for both GP and NP. Nine staff members of the Indian contingent who were considered contacts of the index case tested negative both in PCR and immunofluorescence. All four samples collected from male inhabitants of villages surrounding the UNAMSIL camp were PCR and IgM negative, but three samples tested positive for IgG (titres up to 1:160), consistent with the presence of Lassa transmission in that area. Lassa fever is endemic in many regions of Sierra Leone and can be transmitted to humans through food contaminated by rodent excreta or aerosolized rodent urine. UN peacekeepers are now protected by measures to reduce human-rodent contact (proper food storage, rodent control). Prompt ribavirin treatment of clinically suspected Lassa cases remains mandatory in endemic areas, since the drug is effective only if given early in the course of the disease. However, rapid laboratory confirmation of suspected cases is desirable for clinical and epidemiological purposes. Until diagnostic facilities can be re-established in Sierra Leone, the facility in Conakry can provide screening of suspected Lassa fever cases.