Colombia is one of the countries at the front line of the Zika crisis. It has also seen an alarming number of cases of Guillain-Barre syndrome - which can cause devastating paralysis. Scientists are cautious of making a direct connection between the two, but on the frontline the panic is real - and growing.
Imagine losing control over the muscles in your body. It starts with pins and needles in your feet. You lose feeling in your legs. Then you can't even blink. Victims of Guillain-Barre can sometimes show the whites of their eyes, as if they are the living dead. And, in the worst cases, it can mean you can no longer breathe.
Fabian Medina, 22, should be in the prime of his life but he has the vitality of a man of 90. He's recovering from the paralysis after two weeks in intensive care.
If he hadn't been on ventilation, he would be dead. When I ask Fabian if he has children, he struggles to lift up one finger. Then, with a curling gesture, he describes the roundness of a pregnant woman's belly and starts to weep.
His wife Karen, three months pregnant, has had Zika; the symptoms were mild, the consequence yet to be known. "My fear," she explains, "is that on the news they say your baby can be deformed. I am really frightened and pray to God that nothing bad will happen to it."
What might be seen when a baby is born is causing great anxiety in South America: terrifying birth deformities where babies are born missing the front part of their brains, known as microcephaly.
The prime suspect for the birth deformities is the Zika virus - originally from Africa, now plaguing South America. Zika, carried by the Aedes Egypti mosquito, is suspected of causing 400 confirmed cases of microcephaly in Brazil. Many doctors in Colombia believe that Zika is also causing the paralysis.
Others are sceptical about linking Zika with Guillain-Barre syndrome. WHO spokesman Christian Lindmeier said: "We must really be cautious and not mix the two too much," as the link has not yet been proven by experts.
Here in Cucuta on the front line it's taken for granted.
No doubting that Zika is moving north. The outbreak of the creeping paralysis in Colombia started in October but it won't be until June that it will be known if there will be an increase in babies born with microcephaly. In Cucuta and the surrounding area, there are 27 cases of paralysis and 27,000 cases of Zika across the whole of Colombia.
For the moment, there is no treatment and no vaccine. The only way of not contracting the disease is prevention, wearing long-sleeved shirts and trousers and dousing yourself with mosquito repellent.
Terrified of catching Zika, I ended up smelling like a chemical factory and, with my trousers tucked into my socks, looked like Tintin. The contrast with the locals was comic. Everybody dresses as if they are at the beach. In the tropical heat, that makes sense. With Zika, it doesn't.
The disease was first identified in Uganda in 1947 but traditionally Zika was seen as a mild viral fever. It was then seen in South East Asia and the Pacific Islands. Now it is in South America, and there multiple reports of paralysis and birth defects.
Dr Marco Fonseca is a neuro-surgeon in Cucuta. "It looks like the virus changed in some way," he told me. "I'm afraid there is some change in the genome. This is Zika-plus. A mutation."
Dr Fonseca doesn't rule out environmental factors and is waiting for the definitive answer from the biologists and the epidemiologists.
Other scientists are considering the possibility that Zika is behaving the same as it has in the past, but that the consequences are different because it is in densely-populated areas.
Dr Fonseca suspects that the spread of the disease was fuelled by the football World Cup in 2014. Will the Brazil Olympics hasten it further, to California, to southern Europe? He said: "It's going to go to California. With the Olympics it will go a little faster."
The Colombian authorities are trying hard to raise awareness of the dangers from Zika. Next door to a school in Cucuta, a public health official found buckets of water full of wriggling mosquito larvae.
John Sweeney was reporting for BBC Newsnight - you can watch his full report here
More on the Zika crisis:
What you need to know Key questions answered about the virus and its spread
Key unanswered questions The many things we do not know about Zika
Travel advice Countries affected and what you should do
The mosquito behind spread of virus What we know about the insect
Abortion dilemma Laws and practices in Catholic Latin America