Lassa fever is an acute viral haemorrhagic illness caused by Lassa virus, a member of the arenavirus family of viruses. It is transmitted to humans from contacts ...Home/Healthtopics/LassafeverOverviewLassafeverisanacuteviralhaemorrhagicillnesscausedbyLassavirus,amemberofthearenavirusfamilyofviruses.  HumansusuallybecomeinfectedwithLassavirusthroughexposuretofoodorhouseholditemscontaminatedwithurineorfaecesofinfectedMastomysrats.ThediseaseisendemicintherodentpopulationinpartsofWestAfrica.  LassafeverisknowntobeendemicinBenin,Ghana,Guinea,Liberia,Mali,SierraLeone,TogoandNigeria,butprobablyexistsinotherWestAfricancountriesaswell.  Person-to-personinfectionsandlaboratorytransmissioncanalsooccur,particularlyinhealthcaresettingsintheabsenceofadequateinfectionpreventionandcontrolmeasures.  Diagnosisandprompttreatmentareessential.Theoverallcase-fatalityrateis1%.AmongpatientswhoarehospitalizedwithsevereclinicalpresentationofLassafever,case-fatalityisestimatedataround15%.Earlysupportivecarewithrehydrationandsymptomatictreatmentimprovessurvival. About80%ofpeoplewhobecomeinfectedwithLassavirushavenosymptoms.1in5infectionsresultinseveredisease,wherethevirusaffectsseveralorganssuchastheliver,spleenandkidneys.   SymptomsTheincubationperiodofLassafeverrangesfrom2–21days.Theonset,whenitissymptomatic,isusuallygradual,startingwithfever,generalweaknessandmalaise.Afterafewdays,headache,sorethroat,musclepain,chestpain,nausea,vomiting,diarrhoea,cough,andabdominalpainmayfollow.Inseverecasesfacialswelling,fluidinthelungcavity,bleedingfromthemouth,nose,vaginaorgastrointestinaltractandlowbloodpressuremaydevelop. Proteinmaybenotedintheurine.Shock,seizures,tremor,disorientationandcomamaybeseeninthelaterstages.Deafnessoccursin25%ofrecoveredpatients.Inhalfofthesecases,hearingreturnspartiallyafter1–3months.Transienthairlossandgaitdisturbancemayoccurduringrecovery. Deathusuallyoccurswithin14daysinfatalcases.Thediseaseisseverelateinpregnancy,withmaternaldeathand/orfoetallossinmorethan80%ofcasesduri