In January, Colombia saw an unusual increase in cases of Guillain-Barre Syndrome, a rare disorder where a person's immune system attacks the nervous system, in some cases temporarily paralyzing the body and requiring hospitalization.
As in neighboring Brazil and Venezuela, the uptick in Colombia happened at the same time as a local Zika outbreak, leading experts to begin searching for a connection. Researchers have since rushed to find out more, and a new report published Wednesday in the New England Journal of Medicine outlines the most compelling evidence to date linking the mosquito-borne virus to the debilitating disorder.
The study analyzed 68 patients with Guillain-Barre syndrome this year at six Colombian hospitals. Researchers determined the presence of Zika infection in those patients offered enough evidence to support the idea that the virus sparks the onset of the syndrome.
"The fact that we found Zika infection in those patients is good evidence that Zika may contribute to development of the disease," said Beatriz Parra, one of the study's authors and a researcher at Universidad del Valle in Colombia. As she explained, the evidence strongly supports a link between Zika and Guillain-Barre syndrome.
Specifically, the study found 97 percent of the patients exhibited Zika-related symptoms. A total of 42 participants were lab-tested for the virus and 40 percent were positive. Getting lab results for the entire group was complicated by the fact that the most definitive testing method for Zika is only effective up to about one week after infection. On average, the report concluded, Guillain-Barre set in about seven days after Zika infection.
While this rate was enough for the paper's authors to decide evidence supported connection, it's not yet enough to confirm Zika infection causes Guillain-Barre syndrome and there's still a lot more experts have to figure out, according to Parra.
"This evidence supports the need to continue research to try to understand which people develop this complication after they get infected with Zika. No one knows," she said. While her team was able to demonstrate a link, more needs to be done to strengthen and understand that link.
Until now, much of the recent evidence has been anecdotal and based on Guillain-Barre syndrome cases increasing after Zika virus descended on the population in Colombia and other countries. An unprecedented outbreak of the virus hit Brazil in the spring of 2015 and has since spread to dozens of countries around the world, where it is now causing a relatively new set of health complications and birth defects.
For the most part, Guillain-Barre impacts adults, a different course for a virus that's become synonymous with causing birth defects like microcephaly — when a child is born with a small head and underdeveloped brain. This rare neurological condition in newborns has been linked to mothers infected with the virus during pregnancy. Parra said Guillain-Barre has been seen in children, but at smaller rates, and no children were included in the study.
Zika has been around since the 1940s, but it wasn't until a 2013 outbreak in French Polynesia that Guillain-Barre cases appeared to increased in tandem. A case control study of 42 patients from that outbreak was the first, and until now the only, to find evidence associating the two issues. Colombia reported 86 cases of Guillain-Barre in the first five weeks of 2016, compared to typical monthly average of 20 cases. As of August the country reported at least 320 cases.
In an editorial response to the latest study, Cleveland Clinic neurologist Dr. Jennifer A. Frontera wrote, "As is true with most clinical studies, proving a causal relationship between [Zika] infection and the Guillain-Barre Syndrome is challenging."
As she explained, the study found "consistent, specific, temporal relationship" between the two, but concluding that Zika itself triggers Guillain-Barre will be more challenging. Typically, people develop the disorder in the days or weeks immediately after a viral or bacterial infection. The infection triggers the immune system response that inadvertently wreaks havoc on the nervous system.
There are many different known causes of Guillain-Barre syndrome, such as the chickenpox virus and the bacterial foodborne illness known as Campylobacter, adding to the complications of determining the link with Zika.
"Somebody may be coincidentally infected with any pathogen and end up with Guillain-Barre syndrome, so proving infection and having Guillain-Barre syndrome at the same time doesn't prove that infection caused it," said Dr. Dean Blumberg, an associate professor and the chief of pediatric infectious diseases at University of California-Davis Children's Hospital.
Blumberg said the new study from Colombia is an important but preliminary step in investigating a link that will be hard to prove. For more conclusive results, researchers will need to perform larger studies with control groups. Subsequently, epidemiological studies would be required to examine how Zika virus triggers Guillain-Barre — Does the virus trigger an immune response attack on the nervous system or does it directly attack and kill neurons?
With the considerable burden Guillain-Barre places on patients, doctors, families, and the health system as a whole, Parra said an important next step in research will also be determining the risk for the syndrome after contracting Zika.
"All this information that we and others are gathering is crucial info that the health system needs to handle the Zika epidemic and provide better care for the people," she said, warning that the health system could get overwhelmed by an uptick in Guillain-Barre syndrome, Zika-inspired or not. "It's not prepared; it's never prepared for that."