Zika virus in the Americas: A New Global Health Emergency

ZIKV is a member of the flavivirus family, which also includes Yellow fever virus, Dengue virus, Japanese encephalitis virus, and West Nile virus. Virions are spherical (40-50 nm in diameter) with a positive-sense, nonsegmented, single-stranded RNA genome (~10.8 Kb). This virus has two lineages (or genotypes) different, African and Asian lineages. Information regarding pathogenesis of ZIKV is scarce but mosquito-borne flaviviruses could replicate in dendritic cells near the site of inoculation and spread to lymph nodes and the bloodstream. To date, ZIKV RNA has been detected in blood, urine, semen, saliva, cerebrospinal fluid, amniotic fluid, and breast milk [4-6].

ZIKV is a member of the flavivirus family, which also includes Yellow fever virus, Dengue virus, Japanese encephalitis virus, and West Nile virus. Virions are spherical (40-50 nm in diameter) with a positive-sense, nonsegmented, single-stranded RNA genome (~10.8 Kb). This virus has two lineages (or genotypes) different, African and Asian lineages. Information regarding pathogenesis of ZIKV is scarce but mosquito-borne flaviviruses could replicate in dendritic cells near the site of inoculation and spread to lymph nodes and the bloodstream. To date, ZIKV RNA has been detected in blood, urine, semen, saliva, cerebrospinal fluid, amniotic fluid, and breast milk [4][5][6].
ZIKV is transmitted to humans primarily through the bite of infected mosquitos, Aedes aegypti and Aedes albopictus [6,7]. The disease is benign and self-limiting, with a high proportion (75-80%) of asymptomatic cases. The incubation period is short (7-12 days). People infected with ZIKV have symptoms that can include mild fever, skin rashes, conjunctivitis, muscle and joint pain, malaise or headache [4,5]. The illness is usually mild, with symptoms lasting from several days to a week. The diagnosis of infection ZIKV is performed in serum samples collected during the first week of infection using molecular methods such as RT-PCR to detect viral RNA. Specific IgM antibodies (ZIKV-IgM) can then be detected 4 days after onset of the infection but can give cross-react with other flaviviruses such as Dengue virus and Yellow fever virus [6,[8][9][10].
ZIKV was known as a zoonotic pathogen with sporadic human infections in Africa and Southeastern Asia. This virus was first identified in 1947 in sentinel monkey that was being used to monitor for Yellow fever virus in Uganda [4][5][6][8][9][10][11]. For over 50 years, few cases are reported in areas of Africa, Southeast Asia, and the Pacific Islands. The first large outbreak of disease caused by ZIKV was reported from Micronesia [11]. From 2007-2016, ZIKV was documented in 61 countries worldwide (Table 1).   [11].
Human ZIKV infection appears to have changed in character while expanding its geographical range. The change is from an endemic infection causing mild illness to an infection causing large outbreaks, probably linked with neurological disorders including congenital microcephaly (CM) and Guillain-Barré syndrome (GBS).
There is a possible association between ZIKV and CM in newborn with maternal ZIKV infection. Infants with CM can have neurological sequelae, seizure, intellectual disability, vision or hearing problems, and developmental problems. [3,11]. In the last six months, an increase of this neurological condition has been reported in Brazil (944 cases). Other countries that have reported cases were Cabo Verde (2 cases), Colombia (32), French Polynesia (8), Martinique (1) and Panama (1) [11].
The incidence of neurological symptoms associated with ZIKV infection is a distinctive feature. Some adults with ZIKV and neurologic conditions like GBS were also described [5,12]. Thirteen countries have reported an increased incidence of GBS potentially related to ZIKV infection: Brazil, Colombia, Dominican Republic, El Salvador, French Guiana, French Polinesia, Haiti, Honduras, Martinique, Panama, Puerto Rico, Suriname, and Venezuela [11].
Vector-borne diseases account for 22% of the estimated global burden of communicable diseases. No effective vaccine or medication is available for some diseases, and vector control is the only option. Prevention of ZIKV infection is to avoid mosquito bites. The use of air conditioning systems, mosquito nets, appropriate clothing that covers the entire body, and applying insect repellents are the main preventive measures. In particular, WHO recommends that pregnant women avoid travel to endemic areas with ZIKV. The sexual partners of pregnant women, living in or returning from areas with the virus, should use safer sexual practices or abstinence from sexual activity for the pregnancy [4,6,11,13,14].
At present, information regarding ZIKV is scarce. To prevent and control ZIKV infection in humans, we must understand the viral pathogenesis, the lineages circulating, the modes of transmission (mosquito-borne transmission and person-to-person transmission), the risks associated with infection, the impact of climate change in the vectors, the etiology of neurological disorders, and the natural history of ZIKV disease.