Yellow fever, Zika, Dengue, and Chikungunya are all viruses that are transmitted by the Aedes aegypti mosquito. The virus, in the saliva of the mosquito, is transmitted to humans when probing or feeding.
All of these diseases can become very serious. Only yellow fever can be prevented by vaccination. Insect bite prevention is essential when travelling where local transmission exists. Protective measures such as long sleeved clothing, and using a DEET or picaridin repellent are an excellent idea during the day, when this mosquito is active.
In the case of Zika, sexual transmission is also possible and the World Health Organization recommends safer sex practices or abstinence during and for 4 weeks after returning from an area where local transmission of Zika occurs.