Zika is caused by Zika virus (ZIKV, a single-stranded RNA virus of the Flavivirus genus from the Flaviviridae family. ZIKV strains are divided into two major lineages: the African lineage and the Asian/American lineage. These two lineages differ in around 90% of their nucleotide sequence. Strains belonging to the Asian/American lineage have been isolated in Southeast Asia, in the Pacific Islands, and in the Americas. Within the Asian/American lineage, the strains from the Americas have formed a new American cluster.

ZIKV is predominantly transmitted by the Aedes mosquitoes, with humans representing the amplifying host. A sylvatic cycle of transmission also exists and involves non-human primates and arboreal zoophilic Aedes mosquitoes from African and Asian forests. ZIKV can also be transmitted from human to human through sexual transmission, blood transfusion, ocular transmission, or vertical transmission from mother to fetus. Clinically, the majority of ZIKV infections are asymptomatic, however some may present with fever, rash, arthritis and/or arthralgia and/or myalgia, which are typically self-limiting. 

ZIKV was first isolated from a sentinel rhesus monkey in the Zika Forest in Uganda in 1947 and from Aedes africanus mosquitoes in 1948. The first human infection was recorded in Nigeria in 1954. In Asia, the virus was isolated in Malaysia in 1966 from Aedes aegypti mosquitoes, and the first human infections were reported in 1977 in Central Java, Indonesia. Prior to the outbreak in Yap State (part of the Federated States of Micronesia) in 2007, where an estimated 75% of the residents were infected, only 14 human cases had been confirmed.

The world was made aware of the alarming public health problem of ZIKV infection when Brazil reported a large outbreak in March 2015, and its subsequent direct association with Guillain-Barré syndrome and microcephaly. By August 31, 2016, 72 countries and territories had observed local ZIKV transmission. In the Americas alone, over 500 000 locally acquired cases had been reported up to September 1, 2016. In November 2016, the WHO declared ZIKV infection a Public Health Emergency of International Concern (PHEIC), and two years later, ZIKV was listed as a priority disease in WHO’s R&D Blueprint on preparedness for infectious disease outbreaks. The 2016 ZIKV epidemic propelled global efforts to develop diagnostic tests, vaccines and therapeutics. 

In Malaysia, ever since the ZIKV was isolated in Aedes aegypti mosquitoes in 1966, serological evidence of ZIKV infections were reported in human and non-human primates in 1996 and 1997. The first ZIKV active case in Malaysia was reported in September 2016; a Malaysian woman with fever and facial rash a week after returning from a visit to Singapore. The first local infection was detected in a 61-year-old man from Kota Kinabalu. In Malaysia, ZIKV infection was not widespread compared to outbreaks in countries nearby such as Singapore and Thailand. To date, only 8 laboratory-confirmed cases with active surveillance were reported.

There is no treatment available for ZIKV infection or its associated diseases. Transmission persists in several countries but generally the incidence and testing for ZIKV are low globally from 2018 to the present, which stalled many development efforts. The public health value for a Zika vaccine is to prevent prenatal ZIKV infection and congenital ZIKV syndrome, resulting in microcephaly, other nervous system malformations and pregnancy-related complications. Effective vaccine and monoclonal antibody treatment is still a public health priority, especially for persons who can become pregnant and who live or travel in ZIKV-endemic regions.