A strain of dengue fever not seen in parts of the Pacific for more than 40 years has been reported in the Federated States of Micronesia.
An alert was issued by the Secretariat of the Pacific Community after the discovery of the DENV-2 virus.
The Manager of Disease Surveillance Research and Control unit for the SPC, Dr Yvan Souares, says for some islands it hasn't been circulated in the 1990s, but in others, it hasn't been seen since the early 1970's.
He says that may make some people who haven't been exposed to the strain before more susceptible.
"The second aspect of it is the dengue two strain, depending on various genotypes - and this is something that we still don't know - can have a different pathogenic effect. That is, causing more severe forms of dengue hemorrhagic fever."
Dr Yvan Souares says the fact that the Pacific is entering the rainy and hotter season, as well as the holiday season when people move around the region, could see the virus spread.