A recent report documented the occurrence of dengue virus type-3 infection in a traveler returning from Benin. In their discussion, the authors mentioned the importance of the diagnosis of dengue fever in the presence of other viruses like Lassa fever and yellow fever viruses endemic in the same areas. The authors did not offer any suggestions how to clinically differentiate infections with these viruses. In a patient with pyrexia and hemorrhagic manifestations like mucosal bleeding, Lassa fever is compared with clinical manifestations of dengue and yellow fever very commonly characterized by a sore throat with white exudative patches in the pharynx. Common respiratory system involvement includes cough with underlying bronchitis or pneumonia. In an endemic area, the combination of fever, exudative pharyngitis, retrosternal pain, and proteinuria made it possible to distinguish Lassa fever from other febrile illness with a positive predictive value of 80%. Another common and distinguishing feature is the rapid evolution of sensorineural hearing loss in about 29% of confirmed cases. The hallmark of yellow fever as opposed to dengue and Lassa fever is liver injury which becomes apparent by subclinical transaminase level elevation on days two and three of illness followed by jaundice over several days to a week. Characteristic features of dengue fever are the severe frontal and retrobulbar headaches and the severe myalgia and bone pains.
Clinical distinction of the common viral hemorrhagic fevers in returnees is important because it can guide laboratory investigations and treatment, which in the case of Lassa fever virus infection is the early application of ribavirin. Early application of ribavirin appears critical in Lassa fever because administration of ribavirin within the first 6 days of the onset of fever in patients with high risk of death was associated with a lower mortality of 5% while treatment that started seven or more days after onset of fever had a fatality rate of 26%.