By Cas van der Made
For the past months, the Zika virus has been and is still a popular topic of interest among both the media and scientists. In February of this year, the World Health Organization declared the disease caused by the Zika virus as a “Public Health Emergency of International Concern” as it had supposedly already spread to twenty countries in the Americas. Until then, most people had never even known the virus existed. History tells us that the mosquito-borne flavivirus was first identified in humans in 1952 in Uganda and Tanzania, with subsequent outbreaks in Africa, the Americas, Asia and the Pacific. In September 2015, researchers in Brazil observed an increase in the number of infants born with microcephaly in those areas in which the Zika virus was encountered earlier that year. This initial figure of reported cases rose exponentially in the following months to over 4300, although this estimate is most probably biased by overreporting and misdiagnosis. Nevertheless, these results warranted further investigation of the still largely unknown symptomatology and complications of a Zika virus infection.
A recent review published in the New England Journal of Medicine (NEJM) has aimed to recapitulate the knowledge that has been gained so far on transmission, symptomatology, diagnosis and treatment. In Africa, the Zika virus circulates in a transmission cycle between nonhuman primates and certain forest-dwelling species of aedes mosquitoes. However, in suburban and urban settings, Zika virus is transmitted in a human–mosquito–human transmission cycle, mostly involving A. aegypti mosquitoes. Additionally, Zika virus can be transmitted sexually and from the pregnant mother to the fetus, as viral RNA has been identified in the brains and placentas of children born with microcephaly. The often mild and nonspecific clinical manifestations resemble those inflicted by other tropical infections such as dengue and include fever, skin rash, conjunctivitis, arthralgia and headache. Moreover, the infection has been associated with the occurrence of the Guillain-Barré syndrome. The most feared complications include fetal congenital anomalies such as microcephaly, although the full spectrum remains elusive. A definitive diagnoses is made by detecting viral nucleic acid by RT-PCR and IgM antibodies by MAC-ELISA, although cross-reactivity with other flaviviridiae complicates serologic assessment. As no Zika virus vaccine exists, treatment focuses on the symptoms itself and on prevention and control measures to avoid mosquito bites, reducing sexual transmission and controlling of the mosquito vector.
In conclusion, the current incidence of Zika virus is difficult to estimate as the symptoms are often nonspecific and generally mild, laboratory diagnosis is not uniformly available, and flavivirus antibody cross-reactivity complicates serologic assessment in dengue-endemic areas. However, the virus is expected to spread. Therefore, rapidly tackling the remaining research gaps is essential to develop better diagnostic tools, effective treatment and protective vaccines.
Lyle R. Petersen et al., N Engl J Med 2016; 374:1552-1563