BRAZIL (Reuters) - They look harmless enough, but these guppies are the latest weapon in Brazil's all out war on the Zika virus.

The fish feed off the larvae of the Aedes mosquitos that transmit Zika, and officials are using them to help stop the disease from spreading.

Rio de Janeiro municipal health worker Fabio Freitas says the guppies are being deployed in stagnant pools and hard to reach areas. "The advantage of using the fish is that there is a large area that we are unable to treat, and the fish take care of the larva," he said.

The need to kill the mosquitos has become urgent in Brazil.

The Zika virus has been linked to birth defects in babies.

Authorities suspect that Zika is responsible for at least 4,400 cases of microcephaly, a condition marked by abnormally small head size that can result in developmental problems.

Guppies have been used throughout the world as a natural method to control outbreaks of other mosquito-borne diseases such as malaria.

"The fish is very resilient, it lives in places where there is a lot of sewerage, a lot of organic material, where other species of fish would not survive," said Mr Freitas.

With millions of people at risk as Zika spreads across the Americas, health officials will need every ally they can get to stop the virus, which still has no treatment or vaccine.