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Tanzania’s farm expansion brings more corn and plague-carrying rats

credit: batwrangler/flickr

Increased food production and use of land for agriculture in Tanzania means more food for the country – and more rats. The northern part of Tanzania saw croplands grow by 70 percent in the past few decades and the number of African rats increase by 20-fold. What is concerning, say a group of researchers, are the diseases carried by the rats.

The plague and Lassa Fever, problems traditionally found in places like Madagascar and West Africa respectively, may pose a greater risk, finds a study published yesterday in the American Journal of Tropical Medicine and Hygiene. While most cases of the plague occur in Madagascar and the Democratic Republic of the Congo, there is a concern that parts of Tanzania could experience more frequent cases due to the increased number of rats that carry the disease.

“The presence of the crop as a food source caused a surge in the population of a rat species known to carry plague. Local farmers often then store this harvested corn next to or inside their homes — baiting in the hungry field rats and increasing opportunities for human infection,” said ecologist Dr. Hillary Young, one of the study’s lead authors. “These kinds of conditions are what breed outbreaks.”

Juxtaposition of agricultural and conserved land. (Photo Credit: Lauren Helgen)

Juxtaposition of agricultural and conserved land. (Photo Credit: Lauren Helgen)

Fortunately, the plague is easily treatable. Of the 8490 cases recorded in Tanzania between 1980 and 2011, 675 resulted in death. If it goes untreated, the plague has a fatality rate of between 30 percent and 60 percent, says the World Health Organization. The hope for Young and her co-authors is that Tanzania will take the steps to be prepared to respond to future outbreaks.

“When you change land from conservation to agriculture there are often these unintended consequences. If you alter the environment you will alter disease dynamics, in any direction,” explained co-author and epidemiologist Dr. Dan Salkeld, in an interview with Humanosphere.  “It is the local context that will determine that.”

The global outlook for the plague is positive, he said. Prior research conducted by Salkeld affirms the findings in a recent study that climate change will contribute to changes in the location of animals which in turn affects the spread of disease. With the case of the plague, climate change will help to reduce cases. Though, the potential for it to be a problem in places where it is rare – take Tanzania for example – will require health systems to adapt and prepare.

Salkeld and Young worked alongside zoologist Dr. Kristofer Helgen on the new research. Salkeld said the interdisciplinary approach to the question of animals, disease and crops in Tanzania helped him consider study methods not often deployed by epidemiologists. Rats were caught in traps and tested in three regions of north central Tanzania, by the team. They were then tested for fleas and pathogens. Few tests were conducted for the plague itself, but the findings focused more on the potential for the rats to carry fleas that carry the plague.

A woodland dormouse. (Photo Credit: Lauren Helgen)

A woodland dormouse. (Photo Credit: Lauren Helgen)

The tests found that the same number of rodents were found in conserved land as there were on agricultural land. The big difference was in the number of African rats (mastomys natalensis). There were 20 times as many African rats living in agricultural sites as opposed to conserved ones. The researchers attributed the difference to the land use. Even further, the rats found on farms were more likely to host fleas known for carrying the plague.

While plague rates have not spiked in a significant way, the increase in plague carrying rats due to farms is reason for future concern. Such a change is something that countries should consider when undertaking large programs and initiatives that change the way land is used.

“In the context of sub-Saharan Africa, these observations are worth particular consideration given the rapid conversion of landscapes to agriculture in this region,” concludes the paper.


About Author

Tom Murphy

Tom Murphy is a New Hampshire-based reporter for Humanosphere. Before joining Humanosphere, Tom founded and edited the aid blog A View From the Cave. His work has appeared in Foreign Policy, the Huffington Post, the Guardian, GlobalPost and Christian Science Monitor. He tweets at @viewfromthecave. Contact him at tmurphy[at]