Zika Spread Inconspicuously in South America for Months, According to New Research


Research published in Nature on May 24, suggests that the Zika virus has been circulating in the Americas silently for far longer than previously thought.

The Zika virus has been said to be circulating in South America since 2014, and with no surefire infection prevention methods, infection is imminent for many of those living in Zika-endemic regions. Now, a study supported by the National Institutes of Health’s (NIH) National Institute of Allergy and Infectious Diseases (NIAID) indicates that the Zika virus had been spreading in the Americas earlier than previously thought. This information may affect not only the estimate of infected individuals, but also the geographic range of infection.

According to research recently published in Nature, the mosquito-borne virus may have been silently spreading for nearly a year in some parts of South America before health officials were able to detect it in 2014. In addition, using genetic sequencing, these researchers were able to track how the virus mutated into its current clades as it spread across geographic borders.

The researchers set out to “gain a deeper understanding of the viral populations underpinning the [Zika virus] epidemic by extensive genome sequencing of the virus directly from samples collected as part of ongoing surveillance.” However, the samples the researchers were working with were not intended for viral genetic sequencing, and so they had to utilize “innovative sequencing approaches,” which they detail in their findings.

To reach their goal, the group “sequenced and assembled complete or partial genomes” from 110 out of 229 samples collected from individuals living in 10 different countries that were affected by the epidemic—the “largest collection to date,” according to an NIH press release. The researchers went on to phylogenetically analyze these samples “together with 64 published genomes available on NCBI GenBank” and other publicly available genomes.

The changes observed in the viral genome as it spread across the Americas suggest that the virus was able to spread quickly when it first hit Brazil and started infecting residents, which the researchers described as an “immunologically naïve population,” as well as tourists. This likely occurred “in early 2014 (95% credible interval (CI) August 2013 to July 2014).”

Afterwards, the virus mutated into 4 distinct clades; the first 3 clusters included genomes from Colombia, Honduras and Puerto Rico, with the last “consisting entirely of genomes from patients who contracted the [Zika virus] in 1 of 3 Caribbean countries (the Dominican Republic, Jamaica, and Haiti) or the continental United States.”

Last year in the United States, the Zika virus outbreak reached Florida and Texas, but those weren’t the only areas to report Zika infection. Many individuals in other states were reported to have been infected during travels to other Zika-endemic regions. Only 20% of individuals infected with the Zika virus present with symptoms, which are usually mild, making infection with the virus nonthreatening in most individuals. However, the Zika virus is known to cause neurological complications, such as microcephaly and loss of hearing, in congenitally infected fetuses, and Guillain-Barré syndrome in some adults.

Those infected within the United States included 1471 pregnant women, and a total of 64 of the infants born to these women were afflicted with Zika congenital syndrome. According to The New York Times, half of these infants were born to mothers in New York.

Because of the severity of the complications associated with Zika virus infection, researchers are working against the clock to create effective vaccines and efficient diagnostic tests that would slow the spread of the virus, by hindering individuals unaware of their infection status from spreading infection, either through sexual contact, or by other means.

The researchers wrote, “Determining when the [Zika virus] arrived in specific regions helps to elucidate the spread of the outbreak and track rising incidence of possible complications of [Zika virus] infection,” and this information can aid in the development of diagnostic tests and help advance surveillance efforts.

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