22nd October 2017
Chasing Away Mosquitoes
Eco-friendly chemical repellent
Image: Muhammad Mahdi Karim
Vector borne zoonotic diseases take a heavy toll on human lives. Synthetic repellents are effective but have undesirable effects on other organisms and on the environment. Eco-friendly botanicals are suitable alternatives. However, low persistence and lack of proper quality control make commercialization difficult. The morbidity and mortality due to these vectors, meanwhile, necessitate immediate action.
Researchers from the DRDO collaborated with the Dibrugarh University to assess the repellency of ethyl anthranilate on mosquitoes – Aedes aegypti, Anopheles stephensi and Culex quinquefasciatus. Ethyl anthranilate activates an ionotropic receptor hormone – Ir40a – found exclusively in many agricultural pests and disease vectors, including mosquitoes and head lice.
The researchers asked selected human volunteers aged 25-35 to refrain from alcohol, caffeine, and fragrances. The volunteers were exposed to 5-7 day old adult female mosquitoes.
The team then performed a repellent bioassay and spatial repellency study of ethyl anthranilate against a popular repellent – N,N-diethyl phenylacetamide – as control.
In all assays, ethyl anthranilate outperformed the control. In the test chamber, ethyl anthranilate was effective for two hours. Ethyl anthranilate successfully repelled all three mosquito species.
The Food and Drug Administration, the WHO and the European Food Safety Authority have certified ethyl anthranilate non-toxic and eco-friendly. Now, it is up to entrepreneurs to translate the lab results into a management tool for the buzzy vectors that carry malaria, filaria, japanese encephalitis, dengue, chikungunya and other diseases.
Acta Tropica, 174: 56-63 (2017)
S Suresh Ramanan
Molecular targets for vaccines
Zika virus infection in pregnant women results in abnormal brain development in newborns. This virus, transmitted by mosquito bite, is on the rise and, therefore, vaccine development is a high priority. However, the fast evolving nature of the virus poses a challenge for the development of an effective vaccine.
Researchers from the IISc, Bengaluru, and the AIIMS, New Delhi, recently published a report on the analysis of hereditary material in collaboration with scientists in California. They looked into the RNA of forty-six strains of the Zika virus.
By comparing the RNA and protein sequences of these viruses, the scientists inferred that the Zika virus strain in Asia is of African origin. Two distinct Asian strains evolved, one 88 years ago and the other 34 years ago. They detected 16 amino acid substitutions in the strain that caused the recent epidemic.
They also found that a hundred and thirty seven regions in viral proteins are highly conserved. These conserved proteins are useful as targets for vaccine development. So the scientists went on to identify the best two targets for vaccine development. Now that the targets are clear, effective vaccines against the Zika virus are only a matter of time.
The Zika virus was first discovered in 1947. It has taken seventy years for this first step to develop effective vaccines. However, now, it seems likely that the days of Zika virus infections are numbered.
Infection Genetics and Evolution, 51: 74-85 (2017)