CHICAGO - Infecting mosquitoes with a strain of bacteria known as Wolbachia significantly reduced their ability to transmit the Zika virus, Brazilian researchers have said, raising hope for this biological method of blocking transmission of the deadly virus.

The bacteria has been released in several countries including Australia, Brazil, Indonesia and Vietnam as part of strategies to control dengue, and the new finding shows the method also works with Zika, a close relative of dengue.

Zika has been linked with the birth defect microcephaly that has been sweeping through South and Central America and the Caribbean and making its way north to the United States.  In February the World Health Organization declared Zika a global health emergency. The connection between Zika and microcephaly came to light last fall in Brazil, which has now confirmed more than 1,100 cases of microcephaly that it considers to be related to Zika infections in the mothers.

The new study, by researchers at Brazil’s Oswaldo Cruz Foundation and published in Cell Host & Microbe, takes advantage of the naturally occurring strain of bacteria known as Wolbachia, which live in insect cells and are found in 60 percent of common insects. The method involves inserting the bacteria into mosquito eggs, which then pass the bacteria along to their offspring. “The idea has been to release Aedes mosquitoes with Wolbachia over a period of a few months, so they mate with Aedes mosquitoes ... and over time, replace the mosquito population,” said senior author Luciano Moreira of the Oswaldo Cruz Foundation in Rio de Janerio, which is preparing to host the Olympics this summer. Moreira is part of Eliminate Dengue, a non-profit that is testing the approach in 40 locations around the world.

In the Zika study, the team infected field mosquitoes and Wolbachia-infected mosquitoes with two strains of Zika currently circulating in Brazil.

After two weeks, mosquitoes carrying Wolbachia had fewer particles of the virus in their bodies and saliva - making them less able to infect humans with the virus.

“Wolbachia showed to be as effective on Zika as the most important dengue experiments we did,” Moreira said.

Dr. Jason Rasgon, an entomologist at Penn State University, said in some prior experiments Wolbachia has been shown to suppress transmission of one pathogen but enhance transmission of another. The new finding removes that concern.

Moreira cautioned that the strategy is not 100 percent effective and will not eliminate the virus, saying it should be used as part of an integrated control strategy.

Meanwhile, Brazil’s outbreak of Zika - which has been linked to the devastating microcephaly birth defect in newborns in 1,271 cases since October - has also killed 57 of those babies, authorities said.

The Health Ministry said in that as of April 30, 3,580 suspected cases had been reported and that another 2,492 were ruled out as false alarms.

While 57 babies were known to have died of the condition, another 178 deaths were suspected to have been caused by it, the data showed. Brazil, the epicenter of the mosquito-borne Zika virus outbreak, hosts the 2016 Games in Rio de Janeiro from August 5 to 21.

The virus is blamed for birth defects in babies born to women infected with the virus.

Despite a flurry of research, very little is known about the virus - how long it can hide out in the human body, the degree of risk via sexual transmission, the full list of diseases and disorders it may cause, and all the mosquito types capable of transmitting it.

The recent scientific consensus is that Zika causes microcephaly, a form of severe brain damage in newborns, and adult-onset neurological problems such as Guillain-Barre Syndrome, which can cause paralysis and death.

There is no vaccine or treatment for the virus, which in most people causes only mild symptoms - a rash, joint pain or fever.

Largely contained to Latin America and the Caribbean, Zika’s range is likely to expand as summer arrives in the northern hemisphere - and with it virus-transmitting mosquitoes.