Cape Verde's health ministry said on Sunday concerns prompted by a U.S. travel alert were overblown and that the number of cases of the Zika virus in the West African island nation was on the decline.

The U.S. Centers for Disease Control (CDC) extended its travel warning on Friday to a further eight countries or territories — including Cape Verde — that pose a risk of infection with Zika, bringing the total to 22.

Zika is a mosquito-borne virus spreading through the Caribbean and Latin America. Only about 20 percent of infected cases display symptoms, which are usually mild and include fever, joint pain and conjunctivitis.

But the CDC says it can be spread from pregnant women to fetuses and has been linked to a birth defect called microcephaly, in which babies are born with abnormally small heads and sometimes brain damage.

Jorge Barreto, the representative for Cape Verde's National Directorate of Health, said the warning did not constitute a travel ban but was intended to persuade women who are pregnant or who may become pregnant to take precautions.

"The Ministry of Health believes that maybe there was a misunderstanding in the interpretation of the recommendation issued by the CDC," said Barreto.

"We have seen a decrease in terms of notification of Zika cases. Last week we recorded 126 cases and the week before there were 212 cases."

The Cape Verde government says it believes the virus was imported from Brazil.

Cape Verde reported about 4,700 suspected cases of Zika virus between the end of September and Dec. 6, the majority of cases in the capital. About 30 cases involving pregnant women are being monitored, according to the World Health Organization.

The economy of Cape Verde, a tiny archipelago of islands off the coast of West Africa, is heavily reliant on tourism.