Zika Virus Spreading in Latin America, Raising Concerns

Lara C. Pullen, PhD

December 16, 2015

On November 26, the World Health Organization reported that national health authorities in Mexico had documented three cases of Zika virus infection in that country. Zika fever results from the Aedes mosquito-borne viral disease caused by Zika virus and presents as a mild fever, rash, and headaches. However, recent increases in microcephaly among infants born to women infected with Zika virus have raised concerns that the infection may not be as benign as previously thought.

In 2014, Zika virus was documented in Chile — the first incidence of the infection in Latin America. As of the most recent data, the countries in Latin America that have reports of Zika virus infections now include Brazil, Guatemala, El Salvador, Paraguay, Venezuela, Mexico, Colombia, Chile, and Panama.

"Zika virus infection is one of the emerging infectious diseases," William Schaffner, MD, chairman of the Department of Preventive Medicine at Vanderbilt University School of Medicine in Nashville, Tennessee, explained to Medscape Medical News. The mosquito-transmitted virus is generally considered to cause a troublesome, but transient, illness that resembles dengue fever or chikungunya. Patients who contract Zika virus are more apt to have conjunctivitis, however.

Physicians in Brazil noted that Zika virus infections of pregnant women are associated with central nervous system problems in the developing fetus, specifically microcephaly.

According to the Pan American Health Association, the incidence of microcephaly in Brazil has increased 20-fold between 2014 and 2015. As of November 30, there had been 1248 cases (99.7/100,000 live births) relative to the prevalence of 5.7 cases/100,000 live births reported in 2010.

At the moment, however, the link between Zika virus infection and microcephaly appears to be a temporal one.

Although the relationship is not clearly described, the concern is real. "People are now looking at this possibility pretty seriously," Dr Schaffner said. Data from case control studies have not yet, however, been reported.

Mosquitoes as Vectors

Although originally limited to Micronesia and the Cook Islands, Zika is now much more widespread. "Any traveller from the US who goes to these countries could experience an infection with this virus or dengue virus or chikungunya virus," noted Abelardo Moncayo, PhD, director of the Vector-Borne Diseases Program at the Tennessee Department of Health in Nashville, in an interview with Medscape Medical News.

Officials do not know whether mosquitoes have the capacity to spread Zika virus into the United States or whether travelers can bring the virus to the United States. Dr Moncayo does note the possibility, however, that the virus could spread to states in the Deep South, such as Florida.

Zika virus and chikungunya virus likely probably both spread as a result of a traveler visiting an area where the virus was endemic. "You need humans in the equation," explained Dr Moncayo, "as opposed to the West Nile Virus, where you do not." This is because the West Nile Virus is maintained in the wildlife population.

West Nile Virus can be spread via wildlife hosts and does not require an accessible human population to act as a reservoir. The wildlife reservoir also allows the West Nile Virus to be present year after year, despite modifications of human behavior.

Physicians are worried not only about the spread of Zika virus but also about the possibility of an outbreak. Dr Schaffner noted that if the virus has the capacity to spread similar to that of chikungunya, there is a public health concern.

Dr Moncayo clarified, however, that although it is theoretically possible for mosquitoes to spread Zika virus throughout the United States, an outbreak is unlikely. This is because individuals in the United States, for the most part, have relatively good housing with air conditioning with closed doors or open doors with screens. In both cases, the housing limits contact between humans and mosquitoes, thereby disrupting the transmission of the virus.

To this point, last year saw a high number of chikungunya infections in the United States that caused concern among public health officials. This year, however, the number of chikungunya infections in the United States has plummeted.

Physician Response

"Doctors should be aware of it. I don't think there is much to do right now," Dr Schaffner explained.

Physicians are becoming better at recognizing the symptoms of a Zika virus infection, which are very similar to those of dengue and chikungunya. Patients with such symptoms and the appropriate travel history should be tested for Zika virus infection, and the presence of an infection should be documented. In addition, physicians should keep in mind the possibility of a connection between a Zika virus infection and microcephaly.

Dr Schaffner suggests that physicians also ask mothers of newborns with microcephaly whether they traveled during their pregnancy. If the patient did travel during the first and second trimester, then the physician may want to consider contacting the state health department. Dr Schaffner also suggested that pregnant women traveling to countries where Zika virus is now endemic should obtain insect repellent and use it appropriately.

Dr Schaffner and Dr Moncayo have disclosed no relevant financial relationships.

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