PRAIA/LONDON (Reuters) - Florzinha Amado is eight months pregnant and trying to stay calm about whether the Zika virus infection she contracted at 21 weeks could have harmed her unborn child.

The exterior of Agostinho Neto Hospital, in Praia, Cape Verde, February 11, 2016. To match HEALTH-ZIKA/AFRICA REUTERS/Julio Rodrigues

But Amado isn’t Brazilian. She lives on the volcanic archipelago of Cape Verde, 570 km (350 miles) west of Senegal, and is one of 100 pregnant women in the capital of Praia who have contracted Zika there.

Their fears, and those of West African authorities seeking to prepare the region’s defenses, are shared by global health experts who say it could have unknown consequences in countries ill-equipped for another public health emergency following the Ebola epidemic.

Zika, a mosquito-borne virus, was first identified by two Scots, virologist George Dick and entomologist Alexander Haddow, in a forest near Entebbe in Uganda in 1947.

The disease itself is mild and 80 percent of those infected do not feel ill, but it has shot to the top of the global health agenda after an outbreak in Brazil was suspected of causing a spike in birth defects.

And now, nearly 70 years after its discovery in mainland Africa, it is threatening to return to its roots - this time apparently in a changed form causing large-scale outbreaks.

“Cape Verde has historical links with Brazil and it seems very likely it has got there from Brazil,” said Nick Beeching of Liverpool School of Tropical Medicine, a Zika expert for the European Society of Clinical Microbiology and Infectious Diseases.

According to new data from Cape Verde’s health ministry, more than 7,000 cases of Zika have been recorded in the country since the beginning of the epidemic in October 2015, with heavier than normal rains last summer boosting mosquito numbers.

Beeching believes it is highly probable Zika will soon be back on the African mainland, thanks to regular flight connections from the Atlantic islands, potentially triggering a new chain of transmission.

Regional health officials told Reuters they were most worried about Zika being exported to Senegal or Guinea Bissau, which shares the same Portuguese heritage as Cape Verde.

A regional meeting on Zika took place in Dakar on Feb. 9, with African and Western partners discussing preparations for possible imported cases, according to officials.

Abdoulaye Bousso, the coordinator of the health emergency operations center in Senegal, said his country had an active surveillance program with several “sentinel sites” being established as early warning points for an outbreak.

“We do not have cases in the country currently but the risk is there,” he said.

MANY MOSQUITOES

Africa is fertile ground for Zika. Researchers have found more than 20 different mosquito species carrying the virus there, although whether they all transmit the disease effectively to humans is unclear.

Ultimately, how much damage Zika may cause on this vast continent will depend on the level of immunity among African populations - and that hinges, crucially, on the extent to which Zika’s genetic make-up has mutated on its round-the-world trip.

A warning from World Health Organization experts in a paper published online on Feb. 9 that the virus “appears to have changed in character” is heightening concerns.

The exact nature of the shift has yet to be unraveled but Mary Kay Kindhauser and colleagues said Zika had altered as it moved through Asia - from an infection causing limited cases of mild illness to one leading to large outbreaks and, from 2013 onwards, linked to babies born with neurological disorders and abnormally small heads.

Jimmy Whitworth, a British-based researcher now at the London School of Hygiene and Tropical Medicine who studied Zika in Uganda back when it was still a “virological curiosity”, said the ground was shifting and the risks increasing.

“There are a few genetic differences between the African and Asian lineages, and it looks like the Asian lineages may be better able to transmit and flourish in a human population,” he told Reuters.

What this means on the ground is uncertain. In theory, there may be some cross-protection between different Zika strains, which could protect Africans from the latest version.

But Beeching noted that dengue fever, a closely related mosquito-borne virus, had four recognized strains and there was only limited and temporary cross-protection between them. “We just don’t know how Zika will spread if it gets to Africa,” he said.

Another big question is why there is no apparent link in Africa between Zika and birth defects, since the continent has been home to sporadic cases of Zika for decades, if not centuries or millennia.

It may be that any past cases of small heads in newborns, known as microcephaly, or of the neurological condition Guillain-Barre syndrome may have been missed in Africa given its limited healthcare infrastructure.

But Whitworth hopes to go back and take a retrospective look, since countries including Malawi, Kenya and Uganda have good population records, head measurement data and serum banks that should make checks possible.

Back in Cape Verde’s Central Hospital in Praia, clinical director Maria do Ceu says there is so far no evidence from scans of any microcephaly among the country’s infected mothers-to-be, who are due to deliver their first babies this month.

Amado is optimistic. “The doctor encouraged me to do morphological ultrasound and told me that I am okay,” she said. “It happened suddenly. I started having blotchy skin and then I went to the maternity ward. I was followed up and thank God everything is fine.”