The vertebrate hosts of the virus were primarily monkeys in a so-called enzootic mosquito-monkey-mosquito cycle, with only occasional transmission to humans. Before the current pandemic began in 2007,<unk>  "rarely caused recognized 'spillover' infections in humans, even in highly enzootic areas". Infrequently, however, other arboviruses have become established as a human disease and spread in a mosquito–human–mosquito cycle, like the yellow fever virus and the dengue fever virus (both flaviviruses), and the chikungunya virus (a togavirus). Though the reason for the pandemic is unknown, dengue, a related arbovirus that infects the same species of mosquito vectors, is known in particular to be intensified by urbanization and globalization.<unk>  is primarily spread by Aedes aegypti mosquitoes, and can also be transmitted through sexual contact or blood transfusions. The basic reproduction number (R0, a measure of transmissibility) of<unk>  has been estimated to be between 1.4 and 6.6 . In 2015, news reports drew attention to the rapid spread of<unk>  in Latin America and the Caribbean. At that time, the Pan American Health Organization published a list of countries and territories that experienced "local<unk>  transmission" comprising Barbados, Bolivia, Brazil, Colombia, the Dominican Republic, Ecuador, El Salvador, French Guiana, Guadeloupe, Guatemala, Guyana, Haiti, Honduras, Martinique, Mexico, Panama, Paraguay, Puerto Rico, Saint Martin, Suriname, and Venezuela. By August 2016, more than 50 countries had experienced active (local) transmission of<unk> . Mosquito Global Aedes aegypti predicted distribution. The map depicts the probability of occurrence (blue=none, red=highest occurrence).<unk>  is primarily spread by the female Aedes aegypti mosquito, which is active mostly in the daytime. The mosquitos must feed on blood to lay eggs. The virus has also been isolated from a number of arboreal mosquito species in the genus Aedes, such as A. africanus, A. apicoargenteus, A. furcifer, A. hensilli, A. luteocephalus, and A. vittatus, with an extrinsic incubation period in mosquitoes around 10 days. The true extent of the vectors is still unknown.<unk>  has been detected in many more species of Aedes, along with Anopheles coustani, Mansonia uniformis, and Culex perfuscus, although this alone does not incriminate them as vectors. To detect the presence of the virus usually requires genetic material to be analysed in a lab using the technique RT-PCR. A much cheaper and faster method involves shining a light at the head and thorax of the mosquito, and detecting chemical compounds characteristic of the virus using near-infrared spectroscopy. Transmission by A. albopictus, the tiger mosquito, was reported from a 2007 urban outbreak in Gabon, where it had newly invaded the country and become the primary vector for the concomitant chikungunya and dengue virus outbreaks. New outbreaks can occur if a person carrying the virus travels to another region where A. albopictus is common. The potential societal risk of<unk>  can be delimited by the distribution of the mosquito species that transmit it. The global distribution of the most cited carrier of<unk> , A. aegypti, is expanding due to global trade and travel. A. aegypti distribution is now the most extensive ever recorded – on parts of all continents except Antarctica, including North America and even the European periphery (Madeira, the Netherlands, and the northeastern Black Sea coast). A mosquito population capable of carrying<unk>  has been found in a Capitol Hill neighborhood of Washington, DC, and genetic evidence suggests they survived at least four consecutive winters in the region. The study authors conclude that mosquitos are adapting for persistence in a northern climate.<unk>  appears to be contagious via mosquitoes for around a week after infection. The virus is thought to be infectious for a longer period of time after infection (at least 2 weeks) when transmitted via semen. Research into its ecological niche suggests that<unk>  may be influenced to a greater degree by changes in precipitation and temperature than dengue, making it more likely to be confined to tropical areas. However, rising global temperatures would allow for the disease vector to expand their range further north, allowing<unk>  to follow. Sexual<unk>  can be transmitted from men and women to their sexual partners; most known cases involve transmission from symptomatic men to women. As of April 2016, sexual transmission of<unk>  has been documented in six countries – Argentina, Australia, France, Italy, New Zealand, and the United States – during the 2015 outbreak. ZIKV can persist in semen for several months, with viral RNA detected up to one year. The virus replicates in the human testis, where it infects several cell types including testicular macrophages, peritubular cells and germ cells, the spermatozoa precursors. Semen parameters can be altered in patients for several weeks post-symptoms onset, and spermatozoa can be infectious. Since October 2016, the CDC has advised men who have traveled to an area with<unk>  should use condoms or not have sex for at least six months after their return as the virus is still transmissible even if symptoms never develop. Pregnancy<unk>  can spread by vertical (or "mother-to-child") transmission, during pregnancy or at delivery. An infection during pregnancy has been linked to changes in neuronal development of the unborn child. Severe progressions of infection have been linked to the development of microcephaly in the unborn child, while mild infections potentially can lead to neurocognitive disorders later in life. Congenital brain abnormalities other than microcephaly have also been reported after a<unk>  outbreak. Studies in mice have suggested that maternal immunity to dengue virus may enhance fetal infection with<unk> , worsen the microcephaly phenotype and/or enhance damage during pregnancy, but it is unknown whether this occurs in humans. Blood transfusion , two cases of<unk>  transmission through blood transfusions have been reported globally, both from Brazil, after which the US Food and Drug Administration (FDA) recommended screening blood donors and deferring high-risk donors for 4 weeks. A potential risk had been suspected based on a blood-donor screening study during the French Polynesian<unk>  outbreak, in which 2.8% (42) of donors from November 2013 and February 2014 tested positive for<unk>  RNA and were all asymptomatic at the time of blood donation. Eleven of the positive donors reported symptoms of<unk>  fever after their donation, but only three of 34 samples grew in culture.
Zika virus
West Nile virus
Sepik virus
Western equine encephalitis virus
Venezuelan equine encephalitis virus
Dengue virus
Muju virus
Rabies virus