Insight: Proving Zika guilty - A long and painstaking task

Rosana Vieira Alves holds her 4-month-old daughter Luana Vieira, who was born with microcephaly, as her daughter Laiane Sophia looks on at their home in Olinda, Brazil, February 2, 2016. REUTERS/Ueslei Marcelino

LONDON, Feb 24 (Reuters) - Evidence is building for the theory that Zika can cause newborn brain defects and the World Health Organization is promising more answers in weeks, but nailing a definitive link will be neither simple nor swift.

Picking apart numerous potential connections between mothers who show evidence of infection with the mosquito-borne virus and babies born with microcephaly, in which the head is abnormally small, will require precision and patience, specialists say.