There is enough cropland in existence to feed the entire world and then some, if only we could curb food waste and meat consumption, among other things . In the near term, though, creating more farmland often seems like the easiest solution to getting more food. In East Africa, however, a big push into expanding cropland may have led to an unintended consequences: the plague.

There have been periodic outbreaks of the plague–caused by bacterium called Yersinia pestis–in Tanzania over the past few decades. At the same time, the amount of cropland in the country has increased dramatically. This is not necessarily a coincidence.

In a new study, published in the American Journal of Tropical Medicine and Hygiene, researchers turned their attention to rats in northern Tanzania, where they found that conversion of natural lands into cropland for maize was linked to nearly double the number of rats burdened with plague-carrying fleas. The conditions for an outbreak are ripe: Farmers often store the corn they’ve harvested in or near their homes, potentially attracting nearby rats–and therefore fleas–that can transmit the virus to human.

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“The rats that persist in human areas are also particularly competent hosts for plague, as well as likely to interact with humans. Together, these changes increase the opportunities for humans to be bitten by plague-infected fleas,” explains Hillary Young, a community ecologist at the University of California, Santa Barbara, and one of the study’s lead authors, in a statement.

Between 1980 and 2011, 675 people in Tanzania died from the plague. That number could easily increase as more natural land is converted to make room for crops–and not just in Tanzania. Sub-Saharan Africa contains 50% of the planet’s arable land.

Keep in mind that the plague isn’t as deadly or as easily transmissible as other recent virus epidemics, like Ebola, but it’s still dangerous. Last year, the Ebola death rate rose to 70%; the plague is 30% to 60% fatal if untreated, but can be treated with antibiotics.