I suspect there may be a relation between tsunami and chikungunya?

You may be right. "surge of outbreaks in the islands have occurred at the end of 2004 and beginning 2005, after the Tsunami of December 2004. This could be simply a coincidence or perhaps linked to environmental changes after the Tsunami. " See: http://www.natureseychelles.org/~naturese/component/content/38-news/commentary/136-climate-change-and-chikungunya?Itemid=63.
Arbovirus. Tsunamis cause flooding and standing water which leas to more mosquito breeding and more mosquito borne diseases.