In October 2015, Brazilian health authorities notified the World Health Organization that an alarming number of Brazilian babies had been born with microcephaly, a rare, debilitating birth defect with lifelong consequences.
Researchers quickly linked the spike in birth defects to the outbreak of a little-known tropical disease called Zika virus, which is transmitted by mosquito.
Since its discovery in Uganda in 1947, Zika virus has popped up in different African and Asian countries, but no widespread outbreaks had occurred until 2013, when the virus infected an estimated 11 percent of the population of French Polynesia and spread to neighboring Pacific islands.
Then, in 2014, Brazil hosted a series of international sporting events ― the FIFA World Cup and the Va’a World Elite & Club Sprint Championships canoe race. Researchers suspect that this is when people from the Pacific islands who were infected with Zika virus first introduced it to South America.
Since then, the virus has spread across South and Central America, as well as the Caribbean ― reaching as far as the U.S. territory of Puerto Rico.
So far, two people have tested positive for the virus in Spain, three in the U.K. and approximately a dozen people in the U.S. since 2015. The virus has also been linked to a microcephalic baby born in Hawaii.
However, it’s important to note that the U.S. and European cases of the virus were acquired by travelers who had recently visited areas already affected by Zika. The virus has not necessarily reached the places where these people were diagnosed.
Here’s what you need to know about the virus and where it has traveled.
Zika Virus Is In Central And South America
As of Feb. 23, the U.S. Centers for Disease Control and Prevention have graded 34 countries and territories with a “Level 2” travel health warning because of reports of local Zika virus transmission. This means travelers should be extra vigilant to protect themselves from mosquito bites and prevent Zika.
The countries and territories are: American Samoa, Aruba, Barbados, Bolivia, Bonaire, Brazil, Cape Verde, Colombia, Costa Rica, Curacao, Dominican Republic, Ecuador, El Salvador, French Guiana, Guadeloupe, Guatemala, Guyana, Haiti, Honduras, Jamaica, Martinique, Mexico, Nicaragua, Panama, Paraguay, Puerto Rico, Saint Martin, Samoa, Suriname, the Marshall Islands, Tonga, Trinidad and Tobago, Venezuela and the U.S. Virgin Islands.
Pregnant Women Are Most Affected
The CDC warning, issued Friday morning, advises pregnant women in any trimester to avoid traveling to these areas, if possible. Women who want to become pregnant should also first consult with a health care provider before going.
If travel is unavoidable, the CDC says, pregnant women and women who want to become pregnant should follow the strictest protocols to guard against mosquito bites. This means using products with active ingredients like DEET or picaridin on exposed skin. (The CDC says these products are considered safe for pregnant and breastfeeding women.)
The agency also advises wearing long sleeves and pants and sleeping in air-conditioned, screened-in rooms.
Zika Travels Well
Zika virus started popping up across Africa and in some Asian countries in the decades after it was discovered. However, because the virus’ symptoms seemed relatively mild -- temporary fever, rash, joint pain and red eyes -- it wasn’t considered much of a threat compared to other mosquito-borne diseases.
That started to change in 2007, when Zika virus broke out in Yap, an island in the southwestern Pacific Ocean. It was the first time the virus had been found outside the African or Asian continents, researcher Edward Hayes noted at the time. While the symptoms were again relatively mild, Hayes said the outbreak should “prompt awareness of the potential for ZIKV to spread to other Pacific Islands and the Americas.”
Then, as Hayes predicted, French Polynesia suffered a large outbreak of Zika virus in 2013. This time, however, it also happened to coincide with a 20-fold increase in Guillain-Barré syndrome, a rare autoimmune disorder in which the body’s immune system attacks the nerves, causing tingling, muscle weakness and even temporary paralysis in the worst cases.
Zika Virus May Have A Devastating Effect On Babies
Zika virus made its way to the Americas by 2015, and Brazil bore the brunt of the outbreak. As many as 1.5 million people in Brazil contracted Zika virus that year, and an alarming potential side effect of the virus began to emerge.
The Zika virus outbreak seemed to coincide with a sharp increase in babies born with a birth defect called microcephaly, which is when the brain doesn't develop normally in the womb and babies are born with abnormally small heads. This can have lifelong consequences for the child, including intellectual disabilities, developmental delays and seizures.
From 2010 to 2014, Brazil had seen an average of 156 babies born every year with microcephaly. But from October 2015 to January 2016, that number had spiked to over 4,000 babies. Researchers suspected that these infants may have been infected with Zika virus when in the womb, and that the virus may have adversely affected their development.
Like French Polynesia, Brazil has experienced an uptick in Guillain-Barré syndrome. However, Brazilian officials have not been able to quantify it because the condition was previously so rare that health officials saw no need to record cases, reports The New York Times. To date, there is no vaccine or cure for Zika virus.
Here's What Could Happen Next
Researchers are still confirming the link between Zika virus and conditions like microcephaly and Guillain-Barré syndrome, but countries where the virus is widespread -- including Brazil, Colombia and El Salvador -- are already advising women to delay pregnancy. Jamaica issued a similar warning, but hasn't seen a single case of Zika virus case yet. However, Jamaican officials assume it will arrive soon because it's already endemic in neighboring countries, The Associated Press reports.
While people in the U.S. have already been diagnosed with Zika virus, they are though to have contracted the disease while traveling abroad. The mother of the baby born with microcephaly in Hawaii likely contracted the virus while she was in Brazil.
Yet based on the migration of other mosquito-borne diseases, it may only be a matter of time before states like Texas, Florida and Hawaii start seeing cases that emerge locally, experts say.
The migratory patterns of the mosquitos that carry the Zika virus, as well as global travel patterns, may mean Zika will continue to spread before the outbreak dies out. Experts say that the best way to guard against Zika is to wage war on mosquitoes by eliminating stagnant pools of water where they breed and by fumigating areas with mosquito repellant.
Graphics by Alissa Scheller for The Huffington Post.
This story was updated with more information about other Zika virus cases in the U.K.
This story was updated Feb. 3 with new graphics that depict the most recent update on microcephaly cases in Brazil. It has also added new places where Zika virus transmission is ongoing.
Also on HuffPost: