An obscure and non-fatal disease has been spreading among some Western Pacific islands.  Joseph Popiolkowski reports from Hong Kong warmer weather and heavy rains have led to an increase in mosquito-borne illnesses in the region.

Health officials are tracking incidents of a rare, but mild, disease known as Zika on Yap Island, which is part of Micronesia.

Zika's symptoms - skin rash, conjunctivitis, and joint pain - are similar to the more serious and common dengue fever, which has infected tens of thousands of people in Southeast Asia this year.

Dr. Takeshi Kasai, an advisor on communicable diseases for the World Health Organization, says the similarity between the two diseases initially caused confusion among health officials.

"Originally this is reported as dengue-like illness," Dr. Kasai said.  "But later we identified this is not dengue, but the virus called Zika virus causing this disease."

Outbreaks of dengue fever are ongoing in Cambodia, Singapore, and the Philippines.  Kasai says dengue is mostly reported between July and September, but this year has occurred earlier in the year and in greater densities.

Experts say this could be due to unusually wet and warm weather, which has resulted in a rise in diseases spread by mosquitoes such as Zika and dengue.

There have been no hospitalizations or deaths from Zika, which was first discovered in an Ugandan jungle in 1947.

Kasai said anecdotal reports, not yet confirmed, suggest isolated cases of Zika have occurred in Malaysia and Indonesia.  Scientists are monitoring the emergence of the Zika infection and tracing its possible spread from Pacific islands into Southeast Asia.