Zika Virus Was in Brazil a Year Before It Was Detected

The Brazilian outbreak likely started from a single introduction of the virus into the Americas, in mid-2013, finds genetic analysis.

The Zika virus was likely circulating in Brazil for more than a year before it was detected, according to a new genetic analysis of a small number of Zika samples from Brazil.

Researchers also found that the Brazilian outbreak likely started from a single introduction of the virus into the Americas, in mid-2013. Airline data from that time show an upsurge in the number of people traveling to the country, particularly from areas where Zika was circulating. Moreover, the timing lines up with when Zika virus outbreaks were occurring in the Pacific islands.

The findings suggest that, contrary to previous speculations, fans who attended the FIFA World Cup or a championship canoe race, held in Brazil in 2014, aren't to blame for bringing the virus into the country. Most likely, the virus arrived before these events, and was circulating in Brazil for months without being recognized, the researchers found. [Zika Virus News: Complete Coverage of The Outbreak]

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The high degree of genetic similarity among the samples that the researchers looked at in their study points to a single introduction of the virus. And, by considering both the small genetic differences among the virus samples, and the average rate at which such genetic changes are expected to happen, the researchers were able to calculate that the introduction happened sometime in 2013.

"If the Zika virus epidemic in Brazil did, indeed, arise from a single introduction, then the virus must have circulated in the country for at least 12 months prior to the first case being reported in May 2015," the researchers wrote in the study, published today (March 24) in the journal Science.

Martin Hibberd, a professor of emerging infectious diseases at London School of Hygiene & Tropical Medicine who was not involved in the new study, noted that "the introduction of one Zika virus leading to a widespread outbreak may seem surprising."

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"However, the modeling of other Zika outbreaks, and also the highly-related Dengue outbreaks, suggest that this is not unusual," Hibberd said. "In the right conditions, with sufficient mosquitoes and closely packed humans, the virus can spread rapidly."

Zika virus was first identified in rhesus monkeys in Uganda in 1947, and the first human cases were reported in 1952. Since then, Zika outbreaks have occurred in Africa and Asia, according to the World Health Organization. Between 2013 and 2014, outbreaks of the virus were reported in several Pacific islands, including French Polynesia and Tahiti.

In May 2015, Brazil became the first country in the Americas to report a Zika virus outbreak. So far, about 30,000 cases have been reported in Brazil, and outbreaks have also been seen in several other countries in South and Central America, and the Caribbean.

The aim of the new study was to understand when and how Zika virus entered the Americas. The researchers analyzed the Zika gene sequences from seven samples of the virus collected in Brazil, including one from a blood donor, one from a fatal adult case and one from a newborn with microencephaly, a congenital condition linked to the virus.

They also looked at airline flight data from all of the countries with reported Zika virus outbreaks between 2012 and the end of 2014.

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They found little genetic variability among the samples. Moreover, a comparison of these sequences to other existing Zika genome sequences from samples taken in nine other countries revealed that the samples collected in the Americas were closely related to each other and share an ancestor with the Zika strain that circulated in French Polynesia in November 2013.

Similarities among the seven samples from Brazil suggest that all of the cases were caused by viruses with a single origin, meaning the virus made a single introduction into the region, the researchers said.

Oliver Pybus, an evolutionary biologist at the University of Oxford in the United Kingdom and a co-author of the study, told Science that someone infected during the 2013 Zika epidemic in French Polynesia might have introduced the virus to Brazil.

The researchers found that the timing of the virus's likely introduction to Brazil, as revealed by their genetic analysis, coincided with a surge in the number of travelers arriving in Brazil from Zika-affected countries. There were 3,775 passengers per month entering Brazil in early 2013, but 5,754 monthly travelers a year later.

Zika is spread by mosquitoes in the Aedes genus, which live on almost every continent. Most people infected with Zika virus don't have symptoms. [The 9 Deadliest Viruses on Earth]

People who travel to another part of the world may be bitten by mosquitoes, thus beginning a new chain of transmission in that region.

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Before Zika was detected in Brazil, cases could have been mistaken for dengue fever or chikungunya, which produce very similar symptoms. "It's very hard to distinguish these three illnesses from each other," said Dr. Amesh Adalja, an infectious-disease specialist at the University of Pittsburgh who wasn't involved with the new study.

"This is something that people had suspected - that maybe the virus was circulating for a while before the cases were reported," Adalja told Live Science.

Originally published on Live Science.

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A health employee takes part in a spraying day against the Aedes Aegypty mosquito in El Valle in Caracas, the capital of Venezuela, on Jan. 28, 2016.

Rarely has anyone looked at a potentially fatal infectious disease and exclaimed, "Now, that is a thing of beauty." One sculptor, however, has taken bacteria and viruses from their invisible world and placed them in ours.

Artist Luke Jerram has created a collection of glass artwork in the shape microorganisms -- bacteria and viruses no less that have the potential to infect or even kill human beings. By bringing these microscopic marauders to the light, Jerram demystifies these otherwise unknowable microorganisms. And using glass as a medium reinforces not only the fragility of the work, but also our own in the face of these diseases.

In this slide show, take a closer look at some of the highlights from Jerram's glass microbiology collection.

Turning HIV into a work of art is a seemingly impossible task. The virus is responsible for the deaths of an estimated 34 million people worldwide since the epidemic was first reported in 1981, according to UNAIDS, the joint United Nations Programme on HIV/AIDS.

The HIV virus sculpture was the first Jerram built for his collection.

If there's one disease that has plagued humankind throughout its history, it's malaria. In 2010, the World Health Organization estimated that more than 200 million people were infected with the disease, mostly in poverty-stricken regions of sub-Saharan Africa, but also parts of South America and Southeast Asia.

Malaria is transmitted through mosquito bites. Mosquito nets, insect repellant and pesticides are all effective means of prevention, but only for those with the available resources and access to afford them.

Looking at this spindly sculpture might make you the slightest bit queasy, and for good reason. E. coli is represented by this glass artwork. Although most E. coli strains are in fact harmless to humans, the strains we're most acquainted with are the ones that cause food poisoning.

This alien-looking sculpture is actually T4 Bacteriophage, a virus that targets E. coli bacteria.

Bacteriophages are small viruses that attach to the cell membrane of bacteria. The virus injects its DNA into the bacteria, which then produces replicas of the virus, filling the bacterium until it bursts.

If this model is giving you that nostalgic feeling of plagues past, you might not be surprised to find out that this work represents Severe acute respiratory syndrome, or SARS.

SARS made global headlines in 2003 when people in 37 countries and nearly reached pandemic levels. Although coverage of the illness was widely criticized for overstating the threat, nearly 9,000 were infected with the disease, with had a nearly 10 percent fatality rate.

Swine flu, shown here, was another contagious disease that drew global attention that Jerram selected for his exhibition, but this time it was personal. According to his website, Jerram came down with swine flu and constructed the sculpture "with a fever whilst swallowing my Tamiflu tablets every few hours."

Swine flu, or H1N1 strain of the influenza virus, made global headlines in 2009 as the next potential major flu epidemic. Though common among pigs, swine flu is rarely transmitted among humans. When it does infect a human, however, the symptoms associated with the virus, typical of other flu strains, are particularly acute.

Given just how common the Human Papilloma Virus (HPV) is among humans, you'd think this virus, pictured here, wouldn't be so controversial. In fact, it isn't, but the use of a vaccine to prevent the infection, which can lead to certain kinds of cancers in women.

Because the virus can be transmitted sexually, however, the idea of vaccinations, particularly compulsory ones for children -- the vaccine is in fact intended only for people 25 and younger -- generated a considerable pushback, despite the obvious benefits of the treatment.

Hand, foot and mouth disease might not get a lot of press, but these disease outbreaks are in fact fairly common, particularly among infants and children. Occasionally, they can be fatal. Symptoms are similar to the flu, with the exception of sores that can appear all over the body, but particularly the hands, feet and mouth of the carrier.

This final entry is an unrealized future mutation for a disease that doesn't exist yet. Look for it in a contaminated water main, food source or loving pet near you. (But seriously, don't.)