Top US health experts said on Friday that Zika virus could be specifically skilled in establishing itself in body parts that are shielded from immune system, which makes it tougher to battle off and could probably lengthen the timeframe in which it can be transmit.

Researchers said that Zika virus can be found in semen for over two months after a person has contracted infection, adding to the proof of the presence of the virus in fetal brain tissue, placenta and amniotic fluid.

The efforts of the researchers are a part of an international race of understanding the risks linked to Zika. The virus is a rapidly spreading mosquito-borne virus that is thought to be associated with thousands of birth defects’ cases in Brazil.

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

He said that all these are the things that need to be examined carefully in natural history and case-control studies.

Fauci said that the virus’ persistence in the body reminded of the findings during the 2014 Ebola outbreak, which was the worst recorded ever. The highly deadly virus stayed in semen and eye fluid for months in individual patients.

The virus generally causes just mild symptoms, and mostly may not result in illness. Zika’s link to the birth defect microcephaly and to neurological disorder Guillain-Barre syndrome has caused an alarm in public health officials, though a link has not been proved so far. On February 1, the World Health Organization declared the virus a global health emergency.