In October 2015, a team of researchers at the University of Wisconsin-Madison and Universidad de Sucre in Colombia ran the first tests confirming the presence of Zika virus transmission in the South American country. In a study published today [Jan 26, 2016] in the journal Emerging Infectious Diseases, the team documents a disease trajectory that started with nine positive patients and has now spread to more than 13,000 infected individuals in that country. 

"Colombia is now only second to Brazil in the number of known Zika infections," says study lead author Matthew Aliota, a research scientist in the UW-Madison School of Veterinary Medicine (SVM).

Zika virus, which spreads among humans via mosquitoes, causes illness characterized like many other viral infections by fever, rash and joint pain. Officials estimate that four out of five people who contract the virus do not get sick and the virus is rarely fatal. However, pregnant women in Brazil infected with Zika have given birth to babies with small heads and underdeveloped brains, a condition called microcephaly.

"If you're pregnant or planning on being pregnant, absolutely, cancel your vacation," says Aliota, echoing the Centers for Disease Control and Prevention warning that pregnant women not travel to the more than 20 countries now known to have active Zika transmission, like Brazil, Colombia, Ecuador and in the Caribbean. In these countries, mosquitoes are spreading the virus to people.

For the Colombian finding, Aliota and his research team, which includes Jorge Osorio, professor of pathobiological sciences at SVM, and two visiting doctoral students from Colombia, tested samples from 22 patients for the genetic fingerprints of Zika, dengue and chikungunya viruses.

Nine came back positive for Zika virus. Now, 13,500 cases have been identified in Colombia. The researchers' findings highlight the need for better, more accurate laboratory diagnosis of Zika virus.

The symptoms of Zika virus are "really nonspecific and it overlaps with a lot of things, especially with dengue virus and chikungunya," says Aliota. "It's hard when someone comes in with a fever and a rash to narrow it down."

Zika virus was first found in Uganda in 1947 but remained limited to Africa and Southeast Asia for decades. But in 2007, an outbreak occurred in the Pacific Islands and recently the virus began to spread in the Western Hemisphere.

"Historically, Zika virus has just caused mild disease, but as it moved into the New World, in Brazil, we started to notice these more serious consequences associated with it," says Aliota. "There is a lot that is unknown."