Brazil has declared an end to its public health emergency over the Zika virus, 18 months after a surge in cases drew headlines around the world.

The mosquito-borne virus wasn't considered a major health threat until the 2015 outbreak revealed that Zika may lead to severe birth defects.

One of those defects, microcephaly, causes babies to be born with skulls much smaller than average.

Photos of babies with the defect spread panic around the Western Hemisphere and the globe, as the virus was reported in dozens of countries. Many would-be travellers cancelled their trips to Zika-infected places.

The US Center for Disease Control and Prevention and others recommended that women who were pregnant avoid travel to affected areas.

The concern spread even more widely when health officials said it could also be transmitted through sexual contact with an infected person.

The health scare came just as Brazil, the epicenter of the outbreak, was preparing to host the 2016 Olympics, raising concerns the Games could help spread the virus. One athlete, a Spanish wind surfer, said she got Zika while training in Brazil ahead of the Games.

In response to the outbreak, Brazil launched a mosquito-eradication campaign. The Ministry of Health said those efforts have helped dramatically reduce cases of Zika.

From January through mid-April, the Ministry of Health recorded 95 percent fewer cases than during the same period last year. The incidence of microcephaly has fallen as well.

The World Health Organization lifted its own world health emergency in November, even while saying the virus remained a threat.

"The end of the emergency doesn't mean the end of surveillance or assistance" to affected families, said Adeilson Cavalcante, the secretary for health surveillance at Brazil's Ministry of Health.

"The Health Ministry and other organisations involved in this area will maintain a policy of fighting Zika, dengue and chikungunya."

All three diseases are carried by the Aedes aegypti mosquito.

But the WHO has warned that Zika is "here to stay", even as the number of reported cases drops, and that fighting the disease will be an ongoing battle.

Adriana Melo, the Brazilian doctor who raised alarm bells in the early days of the outbreak about a link between Zika and birth defects, said the lifting of the emergency was expected following the decline in number of cases.

"The important thing now is that we don't forget the victims," said Melo.