Travelers to tropical areas may encounter the Zika virus. Zika results in a relatively mild disease. Recent studies from Brazil indicate pregnant women are at risk for fetal brain
abnormality and microcephaly. This week the CDC has recommended that all pregnant women consider postponing travel to areas where Zika virus transmission is ongoing. Local transmission of Zika virus has not yet been reported in Florida or the continental United States.
Zika (named for the Zika forest in Uganda), dengue, and yellow fever are all of the genus Flaviviruses (yellow viruses). These particular Flaviviruses evolved in Africa where they circulate through primate reservoirs. Their spread depends on exposure to the Aedes mosquito (the vector). They are blood-borne and can (rarely) also spread by blood transfusions or sexual contact. Under favorable circumstances returning travelers infected with these particular Flaviviruses are capable of introducing human reservoirs of infection into their communities.
tiger mosquito (Aedes albopictus)
yellow fever mosquito (Aedes aegypti)
Of special concern is the tiger mosquito Aedes albopictus. It is a very aggressive daytime biter and has in recent years been expanding its range rapidly across North America and worldwide.
Historically yellow fever outbreaks with autochthonous (locally acquired) human to human transmission by Aedes mosquitoes have occurred in Florida. An interesting account is given in Yellow Fever at Miami: The Epidemic of 1899. Then, as now, the outbreaks were associated with travelers from a known focus. Likewise, autochthonous dengue appeared in Key West in 2009 presumably related to returning travelers.
Around 3000 chikungunya cases (a closely related alphavirus with the same mosquito vectors) were reported in 2013–2015 in the US, mostly in travelers. Eleven cases of autochthonous chikungunya were reported in 2014 in South Florida (p 1137).
These outbreaks have been limited by good mosquito control and reduced mosquito exposure because of air conditioning, window screens, insect repellents and clothing. A vaccine against yellow fever was developed by 1937. It confers lifelong immunity after a single dose. Zika, chikungunya, and dengue vaccines are at various stages of development.
