Aedes Mosquito
Aedes mosquitos that can transmit the Zika virus are native in some parts of the United States, but not widespread throughout the country. CDC

After a man in Italy was reported to have signs of Zika virus in his semen six months after exposure, scientists are questioning whether the virus is reproducing itself in the male genital tract.

An Italian man in his early 40s reported Zika symptoms after a two-week trip to Haiti. Ninety-one days after his symptoms began, the Zika virus was still present in his urine, saliva and sperm, and 181 days later, his sperm still tested positive for the virus. Previously, the longest registered positive testing was 93 days.

The World Health Organisation is looking into the doctor’s report, and evaluating whether guidelines for preventing Zika’s spread needed to be reevaluated.

Something very similar happened with the Ebola outbreak last year: Long after it was thought to have passed, a woman reported Ebola symptoms weeks after having unprotected sex with a man who’d been hospitalized for Ebola months prior. Testicles are the perfect hiding spot for viruses like Zika and Ebola, because they are protected from the immune system by a wall of cells called the blood-testis barrier.

As Zika virus reaches the U.S., with cases in Florida and casualties in Texas earlier this week, doctors are working to develop vaccines to stop the outbreak.

[h/t BBC]