The second case of Zika infection occurred in a woman with no recent history of travel, suggesting that the virus has started to spread locally. Three others living or working near her workplace has also tested positive, according to the Straits Times report. It is important to keep in mind that approximately 80% of Zika infections result in no symptoms, although these asymptomatic cases can also spread the infection, if a female Aedes mosquito bites them and survives to bite others. So – as with dengue – the number of infected cases is actually 4 to 5 times of those who present with the typical symptoms of fever and rash, with or without mild conjunctivitis and joint pain.
Screenshot of the Straits Times report of local Zika infection
The long term solution to Zika is therefore not isolation (or shunning) of the symptomatic patients who are diagnosed, but either mosquito control/eradication, or a Zika vaccine.
Clinical trials of a candidate Zika vaccine has started in the USA this year. But this is only a Phase 1 trial, meaning that even if the vaccine worked wonderfully, it will be at least 6 years or more before it becomes commercially available.
Our National Environment Agency (NEA) is stepping up efforts at mosquito control, and a pilot trial of Wolbachia is targeted to start in October this year. Wolbachia are a type of bacteria that have evolved to become successful parasites of insects, and may cause a large variety of effects to their hosts (more on this interesting phenomenon in a future post). The ones planned for release by NEA in male Aedes mosquitos are designed to render the female mosquito sterile, laying eggs that will never hatch. There is another novel strategy, using the gene editing tool CRISPR-cas9, that appears very promising, and that has been tried against the mosquito that transmits malaria – it would be great if this could be explored as well.