The case of a man in the United Kingdom who had Zika virus a few years ago provides even more evidence that the virus can be transmitted through sex, according to a new report.

Researchers found the virus in the man's semen nearly nine weeks after he became ill, the report said.

"Our data may indicate prolonged presence of [Zika] virus in semen, which, in turn, could indicate a prolonged potential for sexual transmission," the researchers, from Public Health England, part of the U.K.'s Department of Health, write in an article to be published in the May issue of the journal Emerging Infectious Diseases.

The Zika virus, which is currently spreading in more than 20 countries in Central and South America, is usually transmitted by mosquitoes. But several recent reports suggest that in rare cases, the virus can be transmitted through sex. Earlier this month, health officials said a person in Dallas appeared to have contracted the virus after having sex with a man who had recently traveled to Venezuela, where Zika is spreading.

Health officials are concerned about a strong link between Zika virus infection during pregnancy and a birth defect called microcephaly, in which babies are born with abnormally small heads and face lifelong cognitive impairments. [Zika Virus FAQs: Top Questions Answered]

The new report describes the case of a 68-year-old British man who traveled to the Pacific islands in 2014, when an outbreak of Zika virus was occuring there. When he returned home, he developed a fever, fatigue and a rash. The man tested negative for dengue fever and chikungunya virus, but positive for Zika virus.

After the man recovered, the researchers conducted follow-up tests for the virus, to see if it had lingered in his blood, urine or semen. The virus had disappeared from his blood and urine, but it could still be found in the semen 62 days after the man's illness started.

"These findings could inform decisions regarding what control methods are implemented and which specimen types are best suited for diagnostic detection," the researchers said.

Last week, the Centers for Disease Control and Prevention issued a warning about the potential for Zika virus to spread during sex. The agency said that men who have pregnant partners, and have recently traveled to an area where Zika is spreading, should should abstain from sex or use condoms until the end of their partner's pregnancy.