Global epidemiology of Zika and Chikungunya virus human infections

Zika virus was discovered in 1947. The first reported case of Zika fever was in a sentinel rhesus monkey in Uganda in 1947, while the first human cases were reported in Nigeria in 1954. Since the first evidence of human infection, Zika was active in several countries in Africa and Asia, as sporadic cases and serological evidence of Zika human infections have been demonstrated in several reports. The outbreak of Zika in Yap Island in 2007 is considered the first emergency of this infection. Since then Zika has spread worldwide with a large ongoing epidemic in South and Central America. A huge concern nowadays is about the relationship between Zika infection and microcephaly and about the sexual transmission of the virus. The first identified outbreak of Chikungunya human infection, with an incidence estimated at 23%, was reported from July 1952 to March 1953 in the Southern Province of the current Tanzania. Since then Chikungunya circulated mainly in continental Africa with limited outbreaks. The virus started to spread east bound involving most of the areas surroundings the Indian Ocean. In 2004/2005 a large outbreak developed in La Reunion a French territory in the Indian Ocean: from this point Chikungunya spread to India and from there, due a viraemic traveller returning from Kerala, to Italy where in the summer of 2007 the first outbreak with local viral transmission in a temperate climate zone occurred. In the following years Chikungunya moved to the Caribbean and South America. Recently also the USA experienced the spread of this virus and a limited outbreak based again on local spreading occurred in the French Department of Var, in August 2017.