While mosquitoes are the vector, the main reservoir species remains unknown, though serological evidence has been found in both West African monkeys and rodents.

[53] It is difficult to diagnose Zika virus infection based on clinical signs and symptoms alone due to overlaps with other arboviruses that are endemic to similar areas.

[19][54] The US Centers for Disease Control and Prevention (CDC) advises that "based on the typical clinical features, the differential diagnosis for Zika virus infection is broad.

In addition to dengue, other considerations include leptospirosis, malaria, rickettsia, group A streptococcus, rubella, measles, and parvovirus, enterovirus, adenovirus, and alphavirus infections (e.g., chikungunya, Mayaro, Ross River, Barmah Forest, O'nyong'nyong, and Sindbis viruses).

[61] Due to the difficulties with ordering and interpreting tests for Zika virus, the CDC also recommends that healthcare providers contact their local health department for assistance.

[73] Male partners of pregnant women and couples contemplating pregnancy who must travel to areas where Zika is active are advised to use condoms or abstain from sex.

[4][94] The fetus of a pregnant woman who has Zika fever may die or be born with congenital central nervous system malformations, like microcephaly.

[4] In April 1947, as part of studies sponsored by the Rockefeller Foundation into yellow fever, 6 caged rhesus monkeys were placed in the canopy of the Zika Forest of Uganda.

[33][103] As of July 2019, evidence of local transmission from mosquitoes to humans has been reported in a total of 87 countries from four of six WHO Regions; African, Americas, South-East Asia and Western Pacific.

[107] It was first detected in the Western Hemisphere in February 2014, and rapidly spread throughout South and Central America, reaching Mexico in November 2015.

[113] According to the Brazilian Health Ministry, as of November 2015 there was no official count of the number of people infected with the virus in Brazil, since the disease is not subject to compulsory notification.

[122] In February 2016, WHO declared the outbreak a Public Health Emergency of International Concern as evidence grew that Zika is a cause of birth defects and neurological problems.

[19][123][124][125] In April 2016, WHO stated there is a scientific consensus, based on preliminary evidence, that Zika is a cause of microcephaly in infants and Guillain–Barré syndrome in adults.

[133] Following the initial Zika outbreak in Northeastern Brazil in May 2015, physicians observed a tremendous surge of reports of infants born with microcephaly, with 20 times the number of expected cases.

[134][135] Many of these cases have since been confirmed, leading WHO officials to project that approximately 2,500 infants will be found to have been born in Brazil with Zika-related microcephaly.

[144] In November 2015, the Zika virus was isolated in a newborn baby from the northeastern state of Ceará, Brazil, with microcephaly and other congenital disorders.

[19][145] An analysis of 574 cases of microcephaly in Brazil during 2015 and the first week of 2016, reported in March 2016, found an association with maternal illness involving rash and fever during the first trimester of pregnancy.

[146] In January 2016, a baby in Oahu, Hawaii, was born with microcephaly, the first case in the United States of brain damage linked to the virus.

The mother, who had probably acquired the virus while traveling in Brazil in May 2015 during the early stages of her pregnancy, had reported her bout of Zika.

[148] In one study in Pernambuco state in Brazil, about 40 percent of babies with Zika-related microcephaly also had scarring of the retina with spots, or pigment alteration.

[149] On 20 February 2016, Brazilian scientists announced that they had successfully sequenced the Zika virus genome and expressed hope that this would help in both developing a vaccine and in determining the nature of any link to birth defects.

[154] The Brazilian government also refuted conspiracy theories that chickenpox and rubella vaccinations or genetically modified mosquitoes were causing increases in microcephaly.

[155] This means that not only can the virus cross the placental barrier, but also the antibodies produced by the mother can reach the fetus, which suggests that vertical transmission is plausible in these cases.

One other study published in March 2016 by Mlakar and colleagues analyzed autopsy tissues from a fetus with microcephaly that was probably related to Zika virus; researchers found ZIKV in the brain tissue and suggested that the brain injuries were probably associated with the virus, which also shed a light on the vertical transmission theory.

[165][29] The main roles of brain stem cells are to proliferate until the correct number is achieved, and then to produce neurons through the process of neurogenesis.

There is some evidence that Zika virus may directly or indirectly interfere with mitotic function, this may play a role in altering cell proliferation.

[19][170] A strain of Wolbachia helped to reduce the vector competence of the Zika virus in infected Aedes aegypti released in Medellin, Colombia.

[171] Gene drive is a technique for changing wild populations, for instance to combat insects so they cannot transmit diseases (in particular mosquitoes in the cases of malaria and Zika).

[172] Another method which been researched aims to render male mosquitoes infertile by nuclear radiation in the hope to reduce populations; this is done with a cobalt-60 gamma cell irradiator.

[173] In 2016 the World Health Organization encouraged field trials of transgenic male Aedes aegypti mosquitoes developed by Oxitec to try to halt the spread of the Zika virus.