Zika: The Expanding and Deepening Threat

Marc Gozlan, MD


November 14, 2016

A few days later, on March 15, 2016, a retrospective analysis of the 2013-2015 outbreak in French Polynesia found that the biggest risk for microcephaly in fetuses and neonates was in the first trimester of pregnancy.[41] This study also reported a lower incidence of microcephaly of about 1% (95 per 10 000 infected women) compared with brain birth defects linked to other viral maternal infections, such as cytomegalovirus (13%) and congenital rubella syndrome (38%-100%). Nevertheless, such a risk was a major important public health issue when the incidence of Zika virus in the general population could be very high during a large outbreak.

Meanwhile, it appeared that active Zika virus could also be found in the urine. Clinicians from Martinique reported viruria in two cases of GBS that occurred in this French territory in January 2016, at the beginning of the Zika virus outbreak.[42] The viruria persisted for longer than 15 days after symptom onset, at a time when viremia was negative.[42]

One week later, Italian researchers reported the isolation of infectious Zika virus in the urine and saliva collected from a patient during acute Zika virus infection who developed a febrile illness after returning from the Dominican Republic to Italy in January 2016.[43] The patient had prolonged shedding of Zika virus RNA in urine and saliva for up to 29 days after symptom onset.[43]

Mid-March 2016. A phylogenetic analysis was published that suggest a single introduction of Zika virus into the Americas, estimated to have occurred between May and December 2013. This finding indicated that the Zika virus strain, belonging to the Asian lineage, had been circulating in Brazil more than 1 year before the first case of Zika virus infection was reported in 2015.[44] This estimated date of origin coincided with major events in the Brazilian cultural calendar that were associated with increased numbers of air travel passengers to Brazil from Zika virus-endemic areas in Pacific Islands. This study also observed a correlation between incidence of microcephaly and week 17 of pregnancy, and week 14 for suspected cases of severe microcephaly.[44]

Among some possible explanations proposed for why Zika virus emerged and caused an outbreak in Brazil, one relied on a high density of human-biting mosquitoes and the immunologically naive status of populations in the Americas compared with African and Asian countries, where Zika virus had been circulating for decades and where widespread immunity against this virus most likely existed.[45,46]

In light of these latest scientific findings about the link between Zika virus infection in pregnancy and fetal microcephaly, on March 25, 2016, the CDC updated their interim guidance for preventing sexual transmission with information about how long men and women should consider using condoms or not having sex.[47] The CDC recommended that women wait at least 8 weeks after their symptoms first appeared before trying to get pregnant. Concerning men, the delay before having unprotected sex was increased from at least 8 weeks (previous guidance) to at least 6 months after the last possible exposure.[47] Finally, for men and women without symptoms of Zika virus but who had possible exposure to Zika from recent travel or sexual contact, the CDC recommended for couples trying to conceive to wait at least 8 weeks.[47]

At the end of March 2016, cases of microcephaly had been reported in Brazil, Cape Verde, Colombia, Martinique, and Panama, as well as French Polynesia.[48] (Figure 4).

Figure 4. Timeline of introduction of Zika virus in the Americas, 2015-2016.[48] Courtesy of the World Health Organization.


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