The Zika virus may be particularly adept at entrenching itself in parts of the body that are shielded from the immune system, making it harder to fight off and possibly lengthening the time frame in which it can be transmitted, top U.S. experts said on Friday.

Researchers reported that the virus can be detected in semen for 62 days after a person is infected, adding to evidence of the virus's presence in fetal brain tissue, placenta and amniotic fluid. Their work is part of an international race to understand the risks associated with Zika, a rapidly spreading mosquito-borne virus thought to be linked to thousands of cases of birth defects in Brazil.

"Right now, we know it's in the blood for a very limited period of time, measured in a week to at most 10 days. We know now, as we accumulate experience, it can be seen in the seminal fluid. We're not exactly sure after the infection clears, where else it would be," Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases said.