Whereas Aedes aegypti is able to transmit Zika, dengue, yellow fever and the chikungunya virus, Anopheles arabiensis is a vector of malaria. Microbide, with headquarters in the Dublin Docklands Innovation Park, develops and markets biodegradable aldehyde-based biocides. It applies a patented method to induce stable complexes of aldehydes with surfactant micelles. In these complexes, aldehydes are less volatile and more effective. The reactive carbonyl groups of the aldehydes point to the surface of the solution and react with moieties in biological molecules, thus interfering with their function.
The openly accessible analyses of larvicidal activity were done in 2009 in collaboration with the South African Bureau of Standards Entomology Laboratory in Johannesburg. “When we heard of the Zika outbreak, we immediately pulled out our ‘old’ data,” said Mary Skelly, one of the company’s directors. “Our laboratory tests showed efficient killing of Aedes aegypti larvae at neutral pH by micelled glutaraldehyde at concentrations between 50 and 20,000 ppm, and of Anopheles arabiensis larvae at concentrations between 50 and 400 ppm. With micelled adipaldehyde, we also observed larvicidal activity.”
Glutaraldehyde is a well tried and tested disinfectant, which kills all forms of microbial life. Both glutaraldehyde and adipaldehyde are crosslinking agents. This activity might also kill the larvae. Adult mosquitos are not affected by the larvicides. “Our formulations are suitable for treating items, which collect water such as old tyres or flowerpots. They are also useful in treating latrines, puddles, ponds, riverbanks, streams and lagoons,” said Skelly. “The ingredients of Microbide’s larvicides are biodegradable and neither caustic nor cumulative. For operators applying the spray, basic industrial respiratory masks are recommended. We anticipate that microbes and other immature insects could be adversely affected by our larvicidal formulations,” the manager added.
To date, outbreaks of Zika virus have been recorded in Africa, the Americas, Asia and the Pacific. Between January 2007 and March 2016, transmission of the virus was documented in 61 countries and territories. The flavivirus is transmitted not only by infected mosquitos but also sexually and via the transfusion of virus-containing blood. It was first isolated in 1947 from a rhesus monkey in the Zika forest, Uganda. The first human cases were observed in 1952. Two virus lineages, the African and the Asian lineage, have been identified. The latter has recently emerged in the Pacific and the Americas.
The outbreaks from 2013 to 2015 in French Polynesia and Brazil suggest that the virus may cause the autoimmune disease Guillain-Barré syndrome, and may be teratogenic. It is thought to damage the brain of human embryos causing microcephaly. In February 2016, the WHO declared the potential damaging effects of Zika virus infections a Public Health Emergency of International Concern. Scientists showed that the virus infected human neural progenitor cells derived from induced pluripotent stem cells, promoted cell death, and interfered with the cell cycle and gene expression. The structure of the mature virus has recently been resolved. Vaccines are currently under development.
By signing the Statement on Data Sharing in Public Health Emergencies, Microbide is joining forces with science academies, research funders, public health and research institutions, NGOs and publishers in the fight against the virus. The signatories commit themselves to the sharing of quality-assured interim and final data as rapidly and widely as possible. The associated journals will make all the content concerning the Zika virus openly accessible. Data or preprints deposited for unrestricted dissemination ahead of manuscript submission can still be published in these journals.
As a next step, Microbide will commission trials with water-filled buckets in the mosquitos’ natural environment. The buckets will be treated with larvicides or serve as controls, and will be monitored for mosquito eggs and larvae. “We want to find out how frequently we have to spray in certain areas and how the local climate affects the larvicidal activity. We will test micelled dialdehyde formulations, monoaldehyde formulations and a combination formulation,” explained Skelly. “With our biocides and data, we hope soon to be able to control the mosquito vector and thus help to reduce the transmission of the Zika virus,” she added.