More research is needed before officials can make a definitive connection between birth defects and the Zika virus.

FOX's Alex Hein reports:

This is Housecall for Health.

Evidence is building for the theory that Zika can cause newborn brain defects, but nailing a definitive link will neither be simple nor swift.

Specialists say picking apart numerous potential connections between mothers who show evidence of infection and babies born with microcephaly will require precision and patience.

One expert said the timing depends on how definitive officials want to be.

Part of the challenge is the difficulty of ruling other things out, microcephaly is known to be linked to some parasitic and bacterial diseases as well as rubella, herpes, HIV, and exposure to some chemicals.

The current outbreak began in 2015 and has spread to over 20 countries in the Americas, prompting the World Health Organization to declare the virus and its suspected links to birth defects a global emergency.

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Housecall for Health, I'm Alex Hein, FOX News.