A Review on Dengue Vaccine Development.

Dengue virus (DENV) has become a global health threat with about half of the world's population at risk of infection. Although the disease caused by DENV is self-limiting in the first infection, the antibody-dependent enhancement (ADE) effect increases the mortality in the second infection with a heterotypic virus. Since there is no specific efficient medicine in treatment, it is urgent to develop vaccines to prevent infection and disease progression. Currently, only a live attenuated vaccine, chimeric yellow fever 17D-tetravalent dengue vaccine (CYD-TDV), has been licensed for clinical use in some countries, and many candidate vaccines are still under research and development. This review discusses the progress, strengths, and weaknesses of the five types of vaccines including live attenuated vaccine, inactivated virus vaccine, recombinant subunit vaccine, viral vectored vaccine, and DNA vaccine.

Application of the Scorpion Neurotoxin AaIT against Insect Pests.

Androctonus australis Hector insect toxin (AaIT), an insect-selective toxin, was identified in the venom of the scorpion Androctonus australis. The exclusive and specific target of the toxin is the voltage-gated sodium channels of the insect, resulting in fast excitatory paralysis and even death. Because of its strict toxic selectivity and high bioactivity, AaIT has been widely used in experiments exploring pest bio-control. Recombinant expression of AaIT in a baculovirus or a fungus can increase their virulence to insect pests and diseases vectors. Likewise, transgenic plants expressing AaIT have notable anti-insect activity. AaIT is an efficient toxin and has great potential to be used in the development of commercial insecticides.

Expression of Bacillus thuringiensis toxin Cyt2Ba in the entomopathogenic fungus Beauveria bassiana increases its virulence towards Aedes mosquitoes.

BACKGROUND: The entomopathogenic fungus Beauveria bassiana has been widely used to kill mosquito larvae and adults in the laboratory and field. However, its slow action of killing has hampered its widespread application. In our study, the B. bassiana fungus was genetically modified to express the Bacillus thuringiensis (Bt) toxin Cyt2Ba to improve its efficacy in killing mosquitoes. METHODOLOGY/PRINCIPAL FINDINGS: The efficacy of the wild type (WT) of B. bassiana and a transgenic strain expressing Cyt2Ba toxin (Bb-Cyt2Ba) was evaluated against larval and adult Aedes mosquitoes (Aedes aegypti and Aedes albopictus) using insect bioassays. The Bb-Cyt2Ba displayed increased virulence against larval and adult Aedes mosquitoes compared with the WT: for Ae. aegypti adults, the median lethal time (LT50) was decreased by 33% at the concentration of 1× 108 conidia/ml, 19% at 1× 107 conidia/ml and 47% at 1× 106 conidia/ml. The LT50 for Ae. albopictus adults was reduced by 20%, 23% and 29% at the same concentrations, respectively. The LT50 for Ae. aegypti larvae was decreased by 42% at 1× 107 conidia/ml and 25% at 1× 106 conidia/ml, and that for Ae. albopictus larvae was reduced by 33% and 31% at the same concentrations, respectively. In addition, infection with Bb-Cyt2Ba resulted in a dramatic reduction in the fecundity of Aedes mosquitoes. CONCLUSIONS/SIGNIFICANCE: In conclusion, our study demonstrated that the virulence of B. bassiana against mosquitoes can be significantly improved by introducing the Bt toxin gene Cyt2Ba into the genome to express the exogenous toxin in the fungus. The transgenic strain Bb-Cyt2Ba significantly reduced the survival and fecundity of Ae. aegypti and Ae. albopictus compared with the WT strain, which suggested that this recombinant B. bassiana has great potential for use in mosquito control.

[Larvicidal activity of recombinant Escherichia coli expressing scorpion neurotoxin AaIT or B.t.i toxin Cyt2Ba against mosquito larvae and formulations for enhancing the effects].

OBJECTIVE: To assess the larvicidal effects of recombinant Escherichia coli expressing scorpion neurotoxin AaIT or Bacillus thuringiensis subsp israelensis (B.t.i) toxin Cyt2Ba against the second instar larvae of Culex pipiensquinquefasciatus and Aedes albopictus and compare different formulations for their larvicidal effects. METHODS: The AaIT- or Cyt2Ba-coding sequences were cloned into pET28a(+) and the recombinant plasmids were transformed into E. coli BL21(DE3). After induction with IPTG, the recombinant proteins expressed by the recombinant E. coli were detected and identified by SDS-PAGE and Western blotting, respectively. The larvicidal activity of the bacterial suspension was tested at different concentrations against mosquitoes. The effective engineered bacteria were prepared into dry powder with different formulations, and their larvicidal activity was tested. RESULTS: AaIT and Cyt2Ba proteins were successfully expressed in E. coli. The recombinant AaIT protein showed no virulence to the mosquito larvae. The suspension of the recombinant E. coli expressing Cyt2Ba protein exhibited a stronger killing effect on Aedes albopictus larvae than on Culex pipiens quinquefasciatus larvae at 48 h (P<0.001) with LC50 of 3.00×106 cells/mL and 1.25×107 cells/mL, respectively. The dry powder of the engineered bacteria formulated with yeast extract, wheat flour or white pepper powder at the mass ratio of 1:1 showed the strongest killing effect on mosquito larvae (P=0.044), and the formulation with white pepper powder produced a stronger killing effect than formulations with yeast extract or wheat flour (P=0.002). CONCLUSION: The B.t.i Cyt2Ba protein expressed in E. coli BL21(DE3) shows a good larvicidal activity against mosquitoes, and appropriate formulations of the engineered bacteria can enhance its efficiency in mosquito control.