This is the moment in history when Bangladeshi medical science marked a milestone by successfully completing the remarkable surgery separating the ten-month-old pygopagus twins Tofa and Tahura. Twenty-four doctors spent nine hours inside an operating theatre operating on the spine of the twins.

The head of the World Health Organization warns that the Zika outbreak would likely worsen before nations besieged by the mosquito-borne virus linked to thousands of birth defects in Brazil see relief.

Brazil is planning to fight the Zika virus by zapping millions of male mosquitoes with gamma rays to sterilize them and stop the spread of the virus linked to thousands of birth defects.

The Zika virus may be particularly adept at entrenching itself in parts of the body that are shielded from the immune system, making it harder to fight off and possibly lengthening the timeframe in which it can be transmitted, top US experts say.

The World Health Organization's emergency committee will debate whether a Zika virus outbreak suspected of causing a surge in serious birth defects in South America should be considered a global health emergency.

Brazil President Dilma Rousseff has called on the whole of Brazilian society to help combat the spread of the Zika virus, which has been linked to birth defects.