The World Health Organization (WHO) and partners established a definition of what constitutes an outbreak, endemic transmission, and the interruption of mosquito-borne transmission in order to better characterize the level of transmission of Zika virus infection (Table 1, Fig. 2). This classification system was put into use as of the situation report of 7 July 2016.
As of 20 July 2016, 65 countries and territories (Fig. 1, Table 1) have reported evidence of mosquito-borne Zika virus transmission since 2007 (62 of these countries and territories have reported evidence of mosquito-borne Zika virus transmission since 2015):
- 48 countries and territories with a first reported outbreak from 2015 onwards (Table 1).
- Four countries are classified as having possible endemic transmission or have reported evidence of local mosquito-borne Zika infections in 2016.
- 3 countries and territories have reported evidence of local mosquito-borne Zika infections in or before 2015, but without documentation of cases in 2016, or with the outbreak terminated.
No new country or territory has reported mosquito-borne Zika virus transmission in the week to 20 July 2016.
Eleven countries have reported evidence of person-to-person transmission of Zika virus, probably via a sexual route (Table 2).
One case of Zika virus infection, whose mode of transmission is currently being investigated, was recently reported in the United States of America. The case is a family contact of an individual who died in June. The blood samples of the deceased case were found to have high amounts of Zika virus, more than 100 000 times higher than what has been found in other samples of infected people.
The first documented case of female-to-male sexual transmission of Zika virus infection was reported in the United States of America on 15 July 2016.
As of 20 July 2016, 13 countries or territories have reported microcephaly and other central nervous system (CNS) malformations potentially associated with Zika virus infection or suggestive of congenital infection. Three of those countries reported microcephaly cases born from mothers with a recent travel history to Zika-affected countries in the WHO Region of the Americas (Table 3).
As of 20 July 2016, the United States Centers for Disease Control and Prevention (US-CDC) reported nine live-born infants with birth defects and six pregnancy losses with birth defects with laboratory evidence of Zika virus infection.
As of 20 July 2016, 15 countries and territories worldwide have reported an increased incidence of Guillain-Barré syndrome (GBS) and/or laboratory confirmation of a Zika virus infection among GBS cases (Table 4).
Based on research to date, there is scientific consensus that Zika virus is a cause of microcephaly and GBS.
In Guinea-Bissau, on 29 June 2016, Institute Pasteur Dakar (IPD) confirmed that four of 12 samples tested positive for Zika by PCR. All 12 samples tested negative against IgM Zika. Four additional samples were sent to IPD on 1 July for gene sequencing and the results are still pending.
The government of Guinea-Bissau with support from the WHO Country Office (WCO) is demonstrating strong leadership in response to these findings. The WCO has availed funds to support the logistical needs of the response activities. A multidisciplinary assessment mission to Guinea-Bissau is planned for the last week of July and will support the investigation of the outbreak and assess the level of preparedness in Guinea-Bissau.
The global Strategic Response Framework launched by WHO in February 2016 encompasses surveillance, response activities and research. An interim report4 describing some of the key activities being undertaken jointly by WHO and international, regional and national partners in response to this public health emergency was published on 27 May 2016. A revised strategy for the period of July 2016 to December 2017 was published on 17 June.
WHO has developed advice and information on diverse topics in the context of Zika virus. 6 WHO’s latest information materials, news and resources to support corporate and programmatic risk communication and community engagement are available online.