The highest levels of ZIka virus are found in male testes, scientists have revealed.

Experts developed a mouse model for testing vaccines and treatments to battle Zika.

The mouse model mimics the infection in humans – and they discovered a high concentration of the virus in the brain and spinal cord.

That is consistent with evidence showing that the mosquito-borne virus causes neurological defects in human fetuses.

The discovery of high Zika concentrations in testes, however, adds further fuel to the theory that the virus can be spread sexually.

The finding comes just weeks after the Centers for Disease Control urged couples planning a pregnancy to wait to conceive if the male partner has been exposed to Zika.

Lead study author Dr Michael Diamond, of the Washington University School of Medicine in St Louis, said: ‘We looked for evidence of Zika in the mouse testes mostly as an afterthought, due to mounting evidence of sexual transmission and were surprised that viral levels were the highest we saw in any tissues.

‘We are now doing subsequent tests to determine how long those viral levels are sustained, which could help us estimate the length of time Zika can be transmitted sexually.’

The study was published in the journal Cell Host & Microbe.