UPDATE 2-WHO says on watch for spread of Zika virus to Africa, Asia
* UN health agency sets up global response unit
* Calls for developing better diagnostics to detect virus
* Some 20-30 monitoring sites could be set up in poor countries
* Learning lessons from Ebola outbreak -senior WHO official
* Mosquito carrying Zika virus seen reaching Asia, Africa (Recasts, adds details, quotes)
By Stephanie Nebehay
GENEVA, Feb 2 (Reuters) - The Zika virus linked to a microcephaly outbreak in Latin America could spread to Africa and Asia, and the World Health Organization will set up monitoring sites in the poorest countries with the highest birth rates, it said on Tuesday.
The WHO on Monday declared an international public health emergency due to Zika's link to thousands of recent birth defects in Brazil.
It called for the urgent development of better diagnostic tests to detect the virus in pregnant women and newborn babies. Seen as a relatively rare condition, the virus may lead to babies being born with small heads and often experiencing neurological disorders and learning disabilities. Continuación...