Image caption Colombian health officials have been closely monitoring the situation in Brazil

Health officials in Colombia are warning that as many as 600 babies could be born with microcephaly this year.

With the second highest rate of Zika virus infections after Brazil, Colombia has more than 2,000 pregnant women showing symptoms.

Microcephaly is the condition in which babies are born with brains that are smaller than normal.

The Colombian authorities have watched events in Brazil.

They say they are determined to avoid another tragedy on the same scale.

As in Brazil, large parts of the country host the Aedes aegypti mosquito blamed for spreading the virus and face similar conditions of tropical heat, surface water and poor sanitation.

One of the worst-affected areas in Colombia is the northern state of Atlantico with its densely-populated industrial centre of Barranquilla.

No cases of microcephaly have been reported so far but the state's Health Secretary, Armando de la Hoz, told the BBC that the potential for harm from the Zika outbreak had now made it the top health priority.

"Based on Brazilian projections, we have estimated that in Colombia for this year we will have approximately 600 births with microcephaly.

"Therefore each of the women that are pregnant have a specific health care protocol - with permanent follow-up so we can confirm in utero before the microcephaly is present at birth."

Early months

Under a plan developed late last year, when the first cases emerged, pregnant women are encouraged to report any symptoms of Zika and their pregnancies are then followed carefully.

The aim is to gather as much data as possible on the spread of the virus and of its assumed links with microcephaly.

Clara Inez Collazos, in her ninth month of pregnancy, is among those being monitored closely. We watched her giving the latest of many blood samples.

She said she became pregnant last May and then started developing symptoms of Zika during November and December.

"I didn't know I had it but when I had the symptoms I went to the doctor and I was really already coming out of the disease. They gave me the medication that I needed and he also recommended the mandatory ultrasounds.

"Thank God everything was ok. I was already over the first months which are the most dangerous.

"The truth is that only now I have come to realise how dangerous this illness is, because at this point the illness is not so spread out as it is in Brazil with all the kids with microcephaly. So just now we're understanding what this really is."

The blood samples are sent for analysis by a specialist laboratory in the capital Bogota and the results then take about three weeks to be returned - so, as in Brazil, there is a desperate need for a faster system of diagnosis.

Alarm bells

Nerys Jimenez, two months pregnant, is one of many waiting for results.

She said: "For three days I had fever, my body was aching, my eyes were red, and I had a rash.

"I'm feeling better now but I have persistent headache, it is a splitting headache that doesn't go away.

"A lot of people have told me that if I have Zika my baby can be born deformed because of the illness."

As in many parts of Latin America, with carnival season just getting under way, authorities in Barranquilla are braced for an upsurge in Zika infections.

Huge crowds are due to gather in the narrow streets to enjoy the spectacle and, despite intense spraying by insecticide in recent days, there is a constant risk of widespread biting by mosquitoes.

And there is a new concern as well. A case of sexual transmission, confirmed by the US authorities in Texas earlier this week, has rung alarm bells here.

As the city's health secretary, Mr de la Hoz puts it, the carnival is part of a culture which is open to sexual experiences.

"With the information we are getting from the US, with Zika being transmitted via sexual encounters, we need to multiply our efforts to avoid people contracting the disease in this way."

The city is providing condoms but there is no guarantee they will be used.

One member of a carnival dance troupe, Margarita Mendoza, said that people shed their inhibitions during the festival.

"People lose their sense, lose her mind, go crazy, we try to help with condoms but the people have the last word they choose if wear a condom or not."