CUCUTÁ —Colombia has been unable to control the Aedes aegypti, the mosquito that spreads the Zika virus, chikungunya and dengue fever. The failure to control the insect is perhaps most evident here in Cúcuta, a damp city on the Venezuelan border.

The Aedes aegypti, or yellow fever mosquito, seems to have made a particularly fierce appearance in Cúcuta. In 2014, 27,000 people here caught chikungunya — which leads to fever and joint pains — one of the highest rates in the country, and now some 2,000 residents have Zika. The Health Ministry qualifies the city as the most infected in the country alongside Girardot and Barranquilla.

I have heard from my own family members here who have suffered the pains of this illness. What, we ask, has made the capital of the Norte de Santander department so attractive to this mosquito?

It is not yet clear. In fact health authorities are not even working with consistent figures. While the national Health Ministry reports 1,917 cases, the local health secretariat has mentioned 2,300 cases and Aristides Hernández, president of ANTHOC, the regional branch of the health worker's union, says more than 200,000 people in Cúcuta and its surroundings, one third of the district's population, are infected with Zika.

"I get these figures from the field work I do every day, observing and watching people who come into health centers," Hernández says. "It is a mistake going only by the number of registered patients, as many go back home while others don't even go to the doctor since they know what they're going to be told. Everyone is treating this like a viral infection and we already know it's already way past that."

The Health Ministry's epidemics chief Claudia Cuéllar gives clues on what might be happening. "Environmental circulation, or the way the wind moves in the frontier zone, the sun and generally the climate conditions favor more breeding grounds. We know that if the mosquito rises beyond 2,200 meters above sea level, it can't adapt as it only lives in hot zones."

Judith Ortega, the Cúcuta Health Secretary, admits that officials do not know why the city has had the most cases of chikungunya and now, Zika, since it has a temperature similar to many other cities in Colombia, which have lower infection rates. "On Jan. 22, the number of infections reached 2,300," she said. Ortega adds that the effects of fumigation last just one week, so blocking the virus's advance depends on private action like "cleaning yards and leaving no stagnant water."

Is next week too late?

In fact, in its efforts to reverse the situation in 2014, local authorities invested in some imported tools to boost fumigation against chikungunya, but these remained under lock somewhere for months, because moving them around was expensive. Hernández of ANTHOC says the result is "there has been no efforts to restrict" the mosquitos. "We can show that none of the three machines works. The new local administration says it is working with the Health Ministry to get the insecticide needed to renew fumigation.

New measures are being taken as a result of alarm over the Zika virus, insists Ortega, with a massive "clear-out" day with cleaning and recycling firms, whereby households are expected to bring out all trash or items from their yards that might be serving as breeding grounds for the mosquitos. "We are also fumigating particular points, but the initiative will be more aggressive" during the collection days, she said, "Hopefully, by late next week."

People continue to move about outside as normal, including pregnant women, children and the elderly. "Why go to a clinic when they will tell you the same as anyone else?" says Claudia Sandoval. "People know what they have to do, and are doing what they can. At least Zika is much weaker than chikungunya," she adds.