Increase in Lyme disease mirrors drop in red fox numbers: study

Jun 18, 2012
The decline of the red fox coincides with a rise in cases of Lyme disease. Credit: Taal Levi

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 , reveal that although deer populations have stabilized, 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 , such as white-footed mice, short-tailed shrews, and Eastern chipmunks, all of which transmit Lyme disease bacteria to ticks.

Dwindling numbers of red foxes, the authors suggest, might be attributed to growing populations of coyotes, now top predators in some eastern regions where wolves and 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, published this week online. Coyotes can and will kill foxes and more significantly, Levi said, "foxes often don't build dens when coyotes are around."

Levi and his UCSC co-authors, A. Marm Kilpatrick, assistant professor of ecology and ; Marc Mangel, distinguished professor in applied mathematics and statistics; and Chris Wilmers, assistant professor of environmental studies, 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 there is now an abundance of coyotes," said Levi, who has just begun a position as a researcher at the Carey Institute for Ecosystems Studies in the hotspot for Lyme disease, Duchess County, north of New York City. There he works as a postdoctoral research fellow with Lyme disease expert Rick Ostfeld, who literally wrote the book on Lyme disease, Lyme Disease Ecology of a Complex System.

Lyme disease was first reported in Old Lyme, Conn. in 1975. Ticks pick up the bacteria when they bite infected mice and later infect other animals including humans. Levi said tick nymphs, about the size of a sesame seed, carry the bacteria and are so small that many people who contract Lyme disease never knew they were bitten.

Lyme disease can be treated with antibiotics if discovered early, however long term patients may suffer muscle and joint pain.

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More information: “Deer, predators, and the emergence of Lyme disease,” by Taal Levi, et al., PNAS, 2012.

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User comments : 3

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Doug_Huffman
not rated yet Jun 18, 2012
A sesame seed is 4 mm long maximum, 2mm wide and 1 mm thick. Ixodes scapularis nymph is ~1.5 mm longest. The disinformation on size contributes to lack of recognition and longer duration engorgement.
tpb
3.7 / 5 (3) Jun 18, 2012
OMG, this is one of the first articles I've seen on Phys.org that doesn't blame global warming, when it easily could have.
alfie_null
5 / 5 (1) Jun 19, 2012
Need more wolves. And so on.

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