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article imagePlague alert: How agriculture could trigger problems in Africa Special

By Tim Sandle     Feb 25, 2015 in Science
A warning has been sounded that methods deployed to increase food production in East Africa could increase the risk of plague, possibly to epidemic levels.
According to a new study, the conversion of natural lands into croplands, which is happening at a relatively fast pace, is affecting the local rodents. By examining patterns in northern Tanzania, scientists have noted that rodent populations have increased by almost two-thirds. More importantly, many of these rodents are infested with plague-carrying fleas. Humans are infected when they are bitten by fleas, causing swelling of the lymph nodes and sometimes causing pneumonia.
The bubonic version of the disease leads to swollen lymph nodes. This form, if caught in time, can be treated with antibiotics. However, with the deadliest form — pneumonic — this attacks the lungs and is invariably fatal,
In terms of specific activities, the creation of maize fields has led to a 20-times increase in the population of the African rat (Mastomys natalensis.) This species of rat is renowned for being a carrier of the fleas that can be infected with the plague causing bacterium (Yersinia pestis.) There is also an association with the rats and Lassa fever.
It stands that the more rats there are, along with more human communities that are located near to the converted fields, then the chance of human-to-rat close contact increases. Areas where maize is stored are likely to be particularly vulnerable.
Discussing these issues, Hillary Young, PhD, a community ecologist at the University of California, Santa Barbara, told Digital Journal: “We found that introducing maize production in natural areas appears to create a perfect storm for plague transmission.”
She went on to add: “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.”
And most importantly Young states: “These kinds of conditions are what breed outbreaks.”
In terms of the human-to-rat contact, the scientist explains: “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.”
The issue is important because plague has been affecting other parts of Africa, notably in the Democratic Republic of Congo and Mozambique. The World Health Organization has set up a national task force to help manage these outbreaks, and the cost of control is rising. With Tanzania itself there have been sporadic cases since 1980.
The findings have been published in the American Journal of Tropical Medicine and Hygiene. The report is headed “Effects of Land Use on Plague (Yersinia pestis) Activity in Rodents in Tanzania.”
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