Zika: The Expanding and Deepening Threat

Marc Gozlan, MD


November 14, 2016

On February 1, 2016, the World Health Organization (WHO) declared that the recent association of Zika infection with clusters of microcephaly and other neurologic disorders constituted a Public Health Emergency of International Concern. At that time, the Zika virus had emerged in 25 countries and territories in south and central America.

A lot has happened since then. The past months have shown that the current Zika virus epidemic has become a major challenge for the medical and scientific communities.

This article reviews the global efforts and progress made from February 2016 in medical and scientific research related to the epidemiology and pathogenesis of Zika virus, and the neurologic disorders and fetal/birth abnormalities that include microcephaly. The following is an update of our previous article on the history of Zika as an emerging virus.

The objective of this narrative review is to present how the current Zika outbreak has been a paradigmatic example of how quickly clinical, epidemiologic, and basic information on Zika virus and Zika virus disease has been collected and disseminated among the scientific and medical communities.

The amount of this new knowledge is impressive, as is the high level of global concern surrounding the threat from this virus. These factors have changed the views on a pathogen which was considered until recently to be of relatively minor importance. Previously considered harmless, Zika virus disease has now been re-profiled as a serious disease—indeed, a global threat.

History of the Zika Virus Since the Beginning of 2016

Figure 1. The Zika virus, highly magnified. Courtesy of the Centers for Disease Control and Prevention.

February 2016

February 2, 2016. An investigation by health officials in Dallas County, Texas, identified a case of sexual transmission of Zika virus. The case concerned a man (patient A) with recent travel to Venezuela, an area of active Zika virus transmission, and his nontraveling male partner (patient B). At that time, there was only one previous case report of sexual transmission of Zika virus.[1]

The Dallas case report, which was published 3 months later in the Morbidity and Mortality Weekly Report (MMWR),[1] indicated that Zika virus can be transmitted through anal sex as well as vaginal sex, which is not surprising. It appeared that patient B's exposures occurred both before and just after the initial appearance of symptoms (fever, pruritic rash, conjunctivitis) in patient A, at a time when Zika viremia seems to be highest.

On February 5, a few days after Dallas health officials announced these two sexually transmitted Zika virus cases, the Centers for Disease Control and Prevention (CDC) released interim guidelines for the prevention of sexual transmission of Zika virus and healthcare providers caring for pregnant women and women of reproductive age with possible Zika virus exposure.[3,4] The CDC advised that "men who reside in or have traveled to an area of active Zika virus transmission who are concerned about sexual transmission of Zika virus might consider abstaining from sexual activity or using condoms consistently and correctly during sex." But at that time, the CDC said that "testing of men for the purpose of assessing risk for sexual transmission is not recommended."[4] The CDC needed to "learn more about the incidence and duration of seminal shedding from infected men before considering the utility and availability of testing in this context."

In these guidelines,[4] the CDC emphasized that mosquito bites were still the primary mode of Zika virus transmission, Zika virus being a mosquito-borne flavivirus primarily transmitted by Aedes aegypti mosquitoes. They also continued to hammer home two messages: (1) Infection with Zika virus is asymptomatic in an estimated 80% of cases,[4] and (2) when Zika virus does cause illness, symptoms are generally mild and self-limited.

At that time in early February, the CDC was aware of 51 cases of Zika illness in the continental United States, 50 of which were linked to travel and one in Dallas due to apparent sexual transmission.[5] The CDC had also heard of 21 cases in Puerto Rico—20 locally acquired, and one from travel elsewhere. Among all of those cases, there were seven pregnant women: six in the continental United States and one in Puerto Rico.[5] Only one case of Guillain-Barré syndrome (GBS) had been reported among the infected people in the United States.[5]


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