Chikungunya virus is a disease spread by mosquitoes, and causes flu-like symptoms. It is increasing in concern and although it is rare to die from it, the joint pain it causes can last for months. Insect repellent can help deter mosquitoes but not much else can be done as a precaution. The disease is native to East Africa and occasionally is introduced and quickly eradicated.
Tap water is safe to drink in most areas of the Seychelles, but water quality is variable in undeveloped areas. It is recommended to drink bottled water only and to avoid bodies of fresh water like lakes, rivers, ponds, etc.