What is Zika virus?
The Zika virus (ZIKV) is an arbovirus that carries the name of a forest near Kampala, Uganda. The virus was first identified in rhesus monkeys in 1947 and was further isolated in humans in Uganda and Tanzania in 1952. The transmission is mostly vectorial by mosquitoes, Aedes aegypti (also known to spread dengue virus and chikungunya virus). In addition, direct interhuman transmission has also been documented through intrauterine transmission resulting in congenital infection, intrapartum transmission from a viremic mother to her newborn, sexual transmission and blood transfusion. The first large documented ZIKV outbreak was reported from Yap State, Federated States of Micronesia in 2007 wherein 73% of the population aged ≥3 years is estimated to have been infected. Subsequent outbreaks have been reported in South-east Asia. During outbreaks, humans are the primary amplifying host for Zika virus. An estimated 80% of persons who are infected with Zika virus are asymptomatic. Symptomatic disease generally is mild and characterized by acute onset of fever, maculopapular rash, arthralgia, or nonpurulent conjunctivitis. Symptoms usually last from several days to 1 week.
Current scenario of Zika virus
In April 2015, the recent and current outbreak in Brazil has attracted attention all round the world. An estimated 1 million individuals have been infected by ZIKV; and there has been a 20 fold increase in cases of newborn microcephaly (corresponding to a prevalence of 99.7 per 100 000 live births). This recent increase in the prevalence of microcephaly has been strongly suspected of being associated with ZIKV congenital infection, with the virus found in the amniotic fluid of 2 pregnant women whose newborns presented with a reduced head circumference (perinatal transmission). Recent findings also suggest that such congenital infections are known to cause visual abnormality in 34.5% children. Due to concerns of microcephaly associated with maternal Zika virus infection, fetuses and infants of women infected with Zika virus during pregnancy should be evaluated for possible congenital infection and neurologic abnormalities. Phylogenetic studies on these ZIKV strains revealed close proximity to Asian lineage.
Bangladesh Confirms first case of Zika Virus
Clinical symptoms of Zika virus and diagnostic algorithm
- Approximately 20% ZIKV infected individuals become symptomatic lasting for several days to a week. Characteristic clinical findings are acute onset of fever with maculopapular rash, arthralgia, or conjunctivitis myalgia and headache.
- The diagnosis of Zika virus infection can be made through both molecular and serological testing, molecular testing is the preferred test (which is useful to detect the virus only in the initial days of an acute infection). This includes reverse transcription-polymerase chain reaction (RT-PCR) for viral RNA, and should be performed on serum specimens. To detect congenital infections, serum samples should be collected from the umbilical cord or directly from the infant within 2 days of birth.
- IgM ELISA for Zika virus and Dengue virus should be performed on infant serum, infant CSF, and maternal serum; however, results of these assays can be falsely positive because of cross-reacting antibodies.
Management of ZIKV infections
No specific antiviral treatment is available for Zika virus infections and no vaccine against Zika virus is available. In case of infants with congenital ZIKV infections, treatment is supportive and should address specific neurodevelopmental issues.
Tiered algorithm for arbovirus detection for suspected cases of chikungunya, dengue, or Zika. (Testing only performed if travel history indicates travel to affected area.)
PRNT*: Plaque reduction neutralization tests for Zika virus
- Due to entensive cross-reactivity in flavivirus serological assays, for samples collected <7 days post illness onset, molecular detection should be performed first.
- Perform if sample > 4 days after symptom onset
- Extensive cross-reactivity would be expected in samples from DENV/ZIKV circulation areas. A positive IgM assay with either antigen should be confirmed by using PRNT against both ZIKV anf DENV as well as any other flavivirus (eg. SLEV, ZIKV, WNV, etc.) that might be found in that geographic area (including travel areas)
- PRNT should include any flavivirus(eg. SLEV, ZIKV, WNV. etc.) that might be found in that geographic area(including travel areas).
1. Centres for Disease Control and Prevention. Interim guidelines for the evaluation and testing of infants with possible congenital zika virus infection – United States, 2016. MMWR. 2016;65(3):63-67.
2. Musso D, et al. Rapid spread of emerging Zika virus in the Pacific area. Clin Microbiol Infect. 2014;20:O595-O596.
3. Centres for Disease Control and Prevention. Zika virus spreads to new areas – region of the America’s, May 2015 – January 2016. MMWR. 2016;65(3):55-58.
4.Freitas BDP, et al. Ocular findings in infants with microcephaly associated with presumed zika virus congenital infection in Salvador, Brazil. JAMA Opthalmol. 2016; doi:10.1001/jamaophthalmol.2016.0267.