AFP

BRASÍLIA

The head of the World Health Organization warned Tuesday that the fight against Zika, a mosquito-transmitted virus linked to serious birth defects, will be long and complex.

“The Zika virus is very tricky, very tenacious, very difficult. And so is the Aedes aegypti mosquito,” WHO chief Margaret Chan said in the Brazilian capital Brasilia. “We have learnt lessons from dengue and from chikungunya outbreaks in the past, so we should expect to see more cases, we should expect this is going to be a long journey.”

Brazil is at the center of a Zika outbreak and the virus is strongly suspected of causing a spike in microcephaly, a congenital condition that causes abnormally small heads and hampers brain development. Cases of active Zika transmission have been reported in 28 countries and territories in the Americas and Caribbean, with 1.5 million in Brazil, the hardest-hit country.

Countries throughout the region have launched massive operations to eliminate pools of stagnant water where the mosquitoes, which also spread dengue and chikungunya viruses, can breed. There is currently no cure or vaccine against the Zika virus . The WHO had previously warned that the virus’s spread could be “explosive,” infecting up to four million people. Moreover, US health authorities are investigating 14 new cases of Zika virus that may have been transmitted sexually, suggesting a larger role than previously considered for the spread of the mosquito-borne virus.

Several of the cases involve pregnant women, the US Centers for Disease Control and Prevention warned Tuesday.

The agency reiterated its call for people to use condoms or practice abstinence when living in or traveling to the more than 20 nations and territories in Latin America and the Caribbean affected by the Zika virus . The virus is suspected to have played a role in a spike of birth defects in Brazil.

“In all events for which information is available, travelers were men and reported symptom onset was within two weeks before the non-traveling female partner’s symptoms began,” the CDC report said.

“These new reports suggest sexual transmission may be a more likely means of transmission for Zika virus than previously considered.” Experts still consider Zika a primarily mosquito-borne virus, and urge people to avoid bites by applying insect repellent, using bed nets and wearing long sleeves and pants.

The United States reported its first case of sexually transmitted Zika virus in early February, after a man traveled to Venezuela then returned to Texas and infected a partner who had not traveled there. “In two of the new suspected sexual transmission events, Zika virus infection has been confirmed in women whose only known risk factor was sexual contact with an ill male partner who had recently traveled to an area with local Zika virus transmission,” said the CDC. “Testing for the male partners is still pending.”

The CDC said the 14 cases, “like previously reported cases of sexual transmission involve possible transmission of the virus from men to their sex partners.” Health officials currently have “no evidence that women can transmit Zika virus to their sex partners; however, more research is needed to understand this issue.”