"The spread of Zika... (is) the price being paid for a massive policy failure that dropped the ball on mosquito control in the 1970s," WHO chief Margaret Chan told the opening of the UN health agency's annual assembly.
Those failures have allowed the mosquito-borne virus to spread rapidly and create "a significant threat to global health," Chan told some 3,000 delegates gathered from WHO's 194 member countries.
Experts agree that Zika is behind a surge in Latin America in cases of the birth defect microcephaly -- babies born with abnormally small heads and brains -- after their mothers were infected with the virus.
Programmes in the 1950s and 60s targeted the aegypti in a bid to prevent the spread of dengue and yellow fever, which it also spreads, and all but eradicated the mosquito species from Central and South America.
But when the programmes were discontinued in the 1970s, the mosquito returned.
Chan also decried policy failures in the realm of reproductive rights.
With the virus now present in 60 countries, countless women who may want to delay pregnancy have no access to contraception, and even fewer to abortion.
Chan pointed out that Latin America and the Caribbean "have the highest proportion of unintended pregnancies anywhere in the world."
"With no vaccines and no reliable and widely available diagnostic tests to protect women of childbearing age, all we can offer is advice," she told the assembly.
In Brazil, the hardest-hit country, more than 1.5 million people have been infected with Zika, and nearly 1,400 cases of microcephaly have been registered since the outbreak began last year.
Researchers estimate that a woman infected with Zika during pregnancy has a one-percent chance of giving birth to a baby with the birth defect. Zika is not new. The African strain of the virus was discovered in Uganda's tropical Zika forest in 1947, and an Asian strain has long circulated on that continent, without sparking concern.
On its own Zika is fairly benign, like a bad cold or a mild flu.
