Zika virus fight a 'long journey': WHO chief

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.