Lyme disease is an emerging infectious disease caused by at least three species of bacteria. It is generally transmitted to humans from a natural reservoir among rodents by ticks that feed on both sets of hosts. A continued increase of Lyme disease in the United States, once linked to a recovering deer population, may instead be explained by a decline of the red fox, UC Santa Cruz researchers suggest in a new study. The team's findings, published in the Proceedings of the National Academy of Sciences, reveal that although deer populations have stabilized, Lyme disease has increased across the northeastern and midwestern United States over the past three decades. The increase coincides with shrinking populations of the red fox, which feeds on small mammals, such as white-footed mice, short-tailed shrews, and Eastern chipmunks, all of which transmit Lyme disease bacteria to ticks.
Lyme disease is an emerging infectious disease caused by at least three species of bacteria. It is generally transmitted to humans from a natural reservoir among rodents by ticks that feed on both sets of hosts. A continued increase of Lyme disease in the United States, once linked to a recovering deer population, may instead be explained by a decline of the red fox, UC Santa Cruz researchers suggest in a new study. The team's findings, published in the Proceedings of the National Academy of Sciences, reveal that although deer populations have stabilized, Lyme disease has increased across the northeastern and midwestern United States over the past three decades. The increase coincides with shrinking populations of the red fox, which feeds on small mammals, such as white-footed mice, short-tailed shrews, and Eastern chipmunks, all of which transmit Lyme disease bacteria to ticks.
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Dwindling numbers of red foxes, the authors suggest, might be attributed to growing populations of coyotes, now the top predators in some eastern regions where wolves and mountain lions are extinct.
"A new top predator has entered the northeast and has strong impact on the ecosystem," said Taal Levi, a recent UCSC Ph.D. graduate in environmental studies. Levi is the lead author of Deer, Predators, and the Emergence of Lyme Disease. Coyotes can and will kill foxes and more significantly, Levi said, "foxes often don't build dens when coyotes are around."
More significantly is that fewer coyotes will inhabit an area once populated by more foxes, Levi said. The greater number of foxes would have consumed a larger number of small, tick-bearing animals than the coyotes that replace them.
The study used an extensive dataset from five states as well as mathematical models to determine why Lyme disease continues to rise despite stabilized numbers of deer, long known to act as reproductive hosts for adult ticks that carry Lyme disease bacteria.
The loss of red foxes can result in an increase in the abundance of the smaller animals that serve as hosts for bacteria-carrying ticks. Red foxes may have once kept those populations under control.
"We found that where there once was an abundance of red foxes there is now an abundance of coyotes," said Levi.
Lyme disease was first reported in Old Lyme, Connecticut in 1975. Lyme disease can affect multiple body systems and produce a range of symptoms. Not all patients with Lyme disease will have all symptoms, and many of the symptoms are not specific to Lyme disease, but can occur with other diseases as well. The incubation period from infection to the onset of symptoms is usually one to two weeks, but can be much shorter (days), or much longer (months to years).
For further information see Lyme and Foxes.
Bull's Eye image via Wikipedia.
