Morpho-molecular mechanisms study of photodynamic therapy and curcumin larvicide action on wild mosquitoes larvae of genusAedes
Authors: Araújo BP , Silva EA , Rosa LP , Inada NM , Iermak I , Romano RA , Mezzacappo NF , Melo FF , Silva FC , Rocha MP , Silva RAA , Galantini MPL , Silveira EA , Garbuio M 
Published: July 2020

Introduction

Until the first two weeks of October 2019, 1.489,457 probable dengue cases have been reported in Brazil, with an incidence rate of 708.8 cases per 100 thousand inhabitants. Still in 2019, in the same period, 123.407 probable cases of chikungunya were reported, with 15 deaths confirmed by clinical and epidemiological criteria. Regarding Zika, in that period, 10.441 probable cases were recorded, been the northeast region with the highest number of notifications, followed by the midwest one. It is well known that current policies to control the vectors of those arboviruses are not effective. Studies for use of light-activated photosensitizers as an alternative to conventional insecticides for sustainable control of mosquitoes vector such asAedes(dengue, yellow fever, chikungunya, zika),Anopheles(malaria),Culex(yellow fever) can already be found showing advantages over conventional insecticides (efficacy, safety, non-mutagenicity and fast degradation).

Objective

To evaluate the effectiveness of Photodynamic Therapy (PDT), mediated by curcumin and blue LED (460nm) in mortality of wild mosquitoes larvae of genusAedesand also to verify, through confocal microscopy, how the photosensitizer internalizes in larvae organism. In addition to evaluating the action of PDT on the larvae with Raman spectroscopy and histological technique.

Materials and methods

Ovitraps were placed in the city of Vitória da Conquista, Bahia, and the larvae collected in stages L2 and L3 were fed for 24 hours with curcumin in concentrations of 10, 20 and 50% mixed with fish feed and then subjected to irradiation with blue LED for 2h (22mW / cm2and 158.4 J / cm2). The larvae were placed in a container with dechlorinated water and mortality was monitored for 24 and 48 hours. Control groups in which only the larvae were exposed to blue LED for 2 hours and in which the larvae were only fed with fish feed mixed with curcumin (10, 20 and 50%) were included in the study, in addition to the group without treatment. All experiments were repeated after a 2-month interval to confirm the results, totaling 240 tests (tests 1 and 2, n = 15) between groups PDT 10%, PDT 20%, PDT 50%, curcumin 10%, curcumin 20%, curcumin 50%, blue LED and untreated group. The larvae belonging to the PDT 20% group, 20% curcumin, blue LED and control were submitted to histological slides, confocal microscopy and Raman spectroscopy. Larvae mortality rates were compared between groups using univariate descriptive analysis.

Results

All PDT groups showed larvicidal activity, with the PDT group 20% showing the highest larval mortality in the shortest time. The images from confocal microscopy by laser scanning showed that curcumin was distributed throughout the digestive system of larvae and the analysis by Raman microspectroscopy have shown patterns of alteration and cell death, corroborated by histological sections.

Conclusion

It was concluded that PDT in all concentrations was effective in larval mortality, with PDT 20% having the best activity with mortality of 100% in 24 hours.