What are the causative organism of chikungunya/dengue/yellow fever?

Chikungunya is a relatively rare form of viral fever caused by an alphavirus that is spread by mosquito bites.

Dengue is a mosquito-borne disease caused by a flavivirus. Dengue fever usually results in the abrupt onset of high fever, headache, myalgias, arthralgias, lymphadenopathy, and a rash that appears with a 2nd temperature rise after an afebrile period. Respiratory symptoms, such as cough, sore throat, and rhinorrhea, can occur. Dengue can also cause potentially fatal hemorrhagic fever with bleeding tendency and shock. Diagnosis involves PCR and serologic testing. Treatment is symptomatic, including meticulously adjusted intravascular volume replacement.

Yellow fever is a mosquito-borne flavivirus infection endemic in tropical South America and sub-Saharan Africa. Symptoms may include sudden onset of fever, relative bradycardia, headache, and, if severe, jaundice, hemorrhage, and multiple organ failure. Diagnosis is with viral culture and serologic tests. Prevention involves vaccination and mosquito control. Treatment is supportive.
Please see the web pages for more details on Chikungunya, Dengue fever and Yellow fever.