The US Centers for Disease Control and Prevention (CDC) and the UK Health Security Agency (UKHSA) have issued travel health advisories warning travelers about the growing risks of mosquito-borne diseases, including chikungunya and yellow fever.The CDC has issued a Level 2 Travel Health Notice for Costa Rica following a chikungunya outbreak, while UK health authorities have alerted travelers about rising imported chikungunya cases and yellow fever activity across multiple countries.CDC Issues Level 2 Travel Health NoticeThe CDC warned American travelers to "practice enhanced precautions" after Costa Rica reported a chikungunya outbreak.On July 1, Costa Rica's Ministry of Health declared an active outbreak in the oceanside community of Playa Langosta in the western province of Guanacaste..An epidemiological survey identified 45 suspected cases, of which four were laboratory confirmed, while 17 others were considered likely linked to the outbreak.According to the US Embassy in Costa Rica, the cases include both Costa Rican nationals and foreign visitors. The embassy said local transmission means the virus is now circulating among the local mosquito population rather than being limited to infected travelers.Costa Rica has reported 16 total cases this year, with the previous reported case dating back to 2017.UKHSA Warns Over Rising Chikungunya CasesThe UK Health Security Agency issued a warning for holidaymakers travelling to affected regions as imported chikungunya cases continue to rise."Are you, or someone you know, heading off on a tropical trip? It's worth being aware of chikungunya, a mosquito-borne virus that can cause severe joint pain. Check out our blog post to learn how to stay protected," the UKHSA said in a post on X.UKHSA reported 112 confirmed and probable chikungunya cases among travelers returning to England, Wales and Northern Ireland in 2024—almost one and a half times the number reported in 2023."Travel to India accounted for the majority of these cases, followed by travel to Pakistan and Brazil – all popular destinations for people travelling from the UK," the agency added.Yellow Fever Alert Issued for Multiple CountriesThe UK government-backed Travel Health Pro has also warned travelers about increasing yellow fever activity.Since the beginning of 2026, 95 confirmed yellow fever cases have been reported globally.Confirmed cases have been reported in:BoliviaBrazilColombiaEcuadorPeruVenezuelaBurkina FasoCentral African RepublicCameroonThe advisory noted that 2025 recorded a 5.6-fold increase in yellow fever cases compared with 2024.What Is Chikungunya?Chikungunya is a mosquito-borne viral disease transmitted primarily by Aedes aegypti and Aedes albopictus mosquitoes, the same mosquitoes that spread dengue fever.Symptoms usually appear three to seven days after an infected mosquito bite and include:Sudden feverSevere joint painHeadacheNauseaFatigueRash (in about half of cases)Unlike dengue, chikungunya can leave lingering effects, with joint pain and fatigue lasting for weeks, months or even years.People at higher risk of severe illness include:NewbornsOlder adultsPeople with hypertensionPeople with diabetesPeople with heart diseaseThe mosquitoes responsible for spreading chikungunya commonly breed in stagnant water found in overhead tanks, coolers and unused containers.What Is Yellow Fever?Yellow fever is a viral disease transmitted through the bite of infected mosquitoes. The infection can be severe and may become fatal in some cases if not managed appropriately. Vaccination is recommended before travelling to certain affected regions.Initial SymptomsFeverChillsSevere headacheBack painGeneral body achesNauseaVomitingFatigueWeaknessSevere SymptomsHigh feverYellowing of the skin or eyes (jaundice)BleedingShockOrgan failure