The 2016 Olympics could be hit hard after some countries warned pregnant women not to travel to Brazil and major airlines began offering refunds on tickets to the South American country in light of growing fears over the Zika virus.

With the Olympics less than 200 days away – and Rio's annual carnival set to begin in a fortnight – officials in Brazil are desperately trying to curb the spread of the virus, which poses a risk of microcephaly (or abnormally small head and brain) to unborn babies.

The government has increased spending on testing kits, with 500,000 on order, and sent municipal health workersonto the streets ahead of the carnival in a bid to combat the mosquitoes spreading the virus.

In a meeting on 28 January, World Health Organisation director general Dr Margaret Chan warned that the virus was spreading "explosively" across South America.

And with countries including the US – which was expecting 200,000 citizens to travel to Brazil for the Olympics – issuing guidance to pregnant women not to travel to Zika virus risk areas, the numbers of spectators and visitors attending the Olympics and Rio carnival could be drastically reduced.

On its website, the US Center for Disease Control and Prevention issued specialist advice to pregnant women in any trimester, stating: "Consider postponing travel to any area where Zika virus transmission is ongoing."

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More than 4,000 babies in Brazil have been confirmed with microcephaly, with up to 1.5 million in the country thought likely to have contracted the virus.

The Brazilian government earlier in the month declared a state of emergency due to the virus, while other South and Central American countries are also taking steps to combat the disease.