Dengue

Molecular evolution studies suggest that dengue virus (DENV) evolved 1000 years ago and entered a sustained human–mosquito cycle between 125 and 320 years ago. While it is unlikely that DENV would be used as a biothreat agent, DENV has emerged since World War II as the most important mosquito-borne viral pathogen infecting an estimated 100 million persons each year. Infection with any of the four DENV serotypes (DENV-1, 2, 3, and 4) can be inapparent, result in classic dengue fever with high fever, headache, eye pain and muscle ache, or progress at the time of defervescence to dengue hemorrhagic fever (DHF) characterized by hemorrhagic manifestations and plasma leakage that can lead to shock and death. The immunopathological mechanisms by which DENV causes the clinical features of DHF are intricate and include aberrant humoral and cellular immune responses. Previous DENV infections may predispose to more severe disease by the induction of enhancing antibody and cross-reactive T cells. Treatment is supportive relying upon careful fluid management which can be lifesaving. Prevention currently depends on vector control which has been largely unsuccessful. Several dengue vaccine candidates have advanced to clinical trials to include classically and molecularly attenuated live virus vaccines, chimeric vaccines using dengue and yellow fever virus backbones, and DNA vaccines. Whole virus inactivated and recombinant subunit vaccine candidates should soon enter into clinical testing. Live attenuated DENV vaccines offer the most promise in terms of broad, long-lasting protection, and although they are economical to produce, they may carry the risks of enhanced reactogenicity in recipients with preexisting flavivirus antibodies, adverse events among the immunocompromised, vaccine virus transmission by vector mosquitoes, and the risk of adventitious agents. Chimeric vaccine approaches use the same gene sequence for the nonstructural proteins for each of the four DENV serotypes avoiding the need for attenuating mutations in the structural genes and potentially reducing interference in the replication of the four virus vaccine components within the multivalent vaccine recipient. DNA vaccines, in combination with other approaches, may increase the complexity and effectiveness of the immune response. Whole inactivated virus approaches have been used successfully for other viral diseases, reduce interference issues in multivalent vaccines, and have protected nonhuman primates from viremia following challenge with wild-type virus. Recombinant subunit vaccines have also protected nonhuman primates from viremia and offer a more focused approach in an attempt to tailor antibody and cell-mediated immure responses. While pathogenesis studies seek to dissect immune responses in an attempt to avoid vaccine-related disease enhancement, these risks, which apply to all vaccine approaches, may need to be evaluated empirically.