BUENOS AIRES — Rat feces between desks, in the playground and just beneath the blackboard in Buenos Aires schools. Dead rats in gardens in the waterside district of Belgrano, just blocks away from the new Mitre overhead railway. Grey rats as big as cats, crossing General Hornos Ave. outside the Constitución station.

It seems like the pesky rodents are everywhere this year, as indicated by the five schools that had to suspend classes because of infestations, the increasing number of shops reporting rat problems, and a 50% increase in Buenos Aires in calls to exterminators.

The city's environment office says it made 10,533 rat control visits in the first five months of 2019 roughly 70 a day compared to 5,297 for those same months in 2018. Experts have given one main reason for the proliferation: public works.

"Rat behavior is being affected by all the construction going on," says Olga Suárez of the City Rodents Ecology Lab (Laboratorio de ecología de roedores urbanos) at the University of Buenos Aires and a member of CONICET, Argentina's state-run scientific research agency. "Public works mean earth movements, which increase the movements of rodents," she adds.

What Suárez can't say with any certainty is whether there's been an actual increase in the number of rats in Buenos Aires. "There's no rat census," she says. Nor any reliable means, really, of counting them. But yes, in terms of dispersion, something seems to be afoot, the rodent expert adds. "Rats move in response to resource availability. Food, water and refuge. If they have them, movements are limited, but if one of these is altered, they will disperse."

Buenos Aires has been in the grip of a construction frenzy of late, and this has its correlation with rat movements. "They have their nests in the ground. If there is digging to install sewerage or to build or any other task involving excavations, these will destroy burrows and cause rats to move," says Suárez. This could have been controlled, she adds, if just before digging or works start, the presence and activity of rodents were checked.

Gonzalo Fariña, head of Antiplaga Norte, an extermination company, says that in the private sector, people are required to eradicate rats before beginning any demolition work, but questions whether the state takes the same precautions. He also notes that rats have spread into schools. "This is certainly because they lost their burrows and are invading, looking for another place to live," he says.

Rains flood their burrows and the rats have to move.

A female rat can have on average of between nine and 10 pups, perhaps twice a year. There are three types of rats in Buenos Aires: the brown rat, black rat and domestic mouse. The first lives in the ground, uses water, penetrates through sewerage and drain pipes and is seen especially in waterside districts and the Río de la Plata and Riachuelo estuaries. The second is an "overhead" rat, seen on cables, roofs and trees on which it makes its home. The last and smaller one is usually seen in homes and shops.

Whether it is true or not, the overall public perception right now is that there are more rats, with an increase in reported sightings and complaints in the first half of this year compared to 2018. There was a peak in January and February following the hantavirus outbreak in the south of the country.

"People became more alert," the city's Environment Ministry says. The agency says it follows up every complaint, and undertakes weekly inspections and preventive actions in critical areas where there is construction work.

Rain may be another factor in the dispersions. "Rains flood their burrows and the rats have to move," Olga Suárez explains. The national weather office measured slightly less rain in the January to late June period in Buenos Aires compared to the same period 2018, though June itself may have been the rainiest June since 1906.

Whatever the reason, residents want the authorities to take action. They know, after all, that the rodents carry a range of pathogens, viruses, fungi and parasites.

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