Bill Gates was in London on Wednesday for the Annual Meeting of his Grand Challenges initiatives. He indicated – subtly enough to avoid outcry or litigation – that Britain’s vote to leave the European Union was unwise but was really there to voice his support for causes closer to the heart of the Bill and Melinda Gates Foundation (BMGF). These include clean energy and climate change and he called for more “high risk” private investors to help bring abundant, affordable electricity to emerging economies in the most environmentally friendly way.
His other notable passion is the elimination of pandemics. The BMGF has very nearly eradicated polio and Bill Gates claimed, on a previous visit to London in 2015, that he thought both polio and malaria could be wiped out by 2030. Bill and Melinda Gates first pledged their support and a considerable donation to malaria back in 1999, a year before their Foundation was established, so mosquitoes have become something of an area of expertise for them over the past 17 years.
In his speech on Wednesday, Mr Gates announced a new $18 million investment to which the foundation will contribute, along with the Wellcome Trust and various governments. The money will be used to halt the spread of mosquito-borne diseases including the Zika virus.
Unlike the Oxitec solution reported by Rockfire in September, which introduces a self-limiting gene that could, if widely used, affect mosquito populations, the BMGF/Wellcome research focuses on a naturally-occurring bacterium, Wolbachia, that is found in many other insect species including spiders and fruit flies but not in the mosquitoes that carry diseases such as Zika, dengue and yellow fever. 
There are many interesting things about Wolbachia, not least that they like to set up their centre of operations in the reproductive organs of their host insects where, once installed, they reduce the host’s chances of continuing its line by means of various ingenious manipulations including the conversion of infected males into females. More pertinent, however, to the Gates-Wellcome research, is that Zika, Dengue and other viruses fail to thrive where a Wolbachia infection is present. So, by introducing Wolbachia to the mosquito population, it is hoped that the bacteria will triumph where other antiparasitics have so far failed.
Small scale trials have been held in Australia, Indonesia, Vietnam and Latin America and the results are promising. With this new £18m donation, Wolbachia-infected mosquitoes will be released in Medellin, Colombia and in Rio de Janeiro, Brazil. Brazil has been the principal focus of the virus, not just because it has registered the highest rates of infection: 165,907 reported cases by July 2016 – but also because it has had at least 1749 cases of associated microcephaly confirmed. Colombia has registered the second highest number of infections but a mere 18 cases of associated microcephaly have been recorded. The reasons for this discrepancy are disputed, with optimists suggesting that Colombian women have been more assiduous in avoiding pregnancy since the outbreak of the virus while pessimists fear that the true extent of infection in Brazil has, to date, been vastly underestimated.
If the latter is the case, the Wolbachia bacteria will be more welcome than ever.
 Telegraph. We could wipe out polio by 2019 says Bill Gates. 23 June 2015. www.telegraph.co.uk
 Ars Technica. Gonad-chomping parasite may block transmission of dengue fever. 24 August 2011. Arstechnica.com
 World Health Organization. Pan American Health Organization. Zika Epidemiological Update. 29 July 2016. www.paho.org
 The Washington Post. Colombia offers the possibility that the Zika epidemic may not be as bad as feared. 13 July 2016. www.washingtonpost.com