NEW YORK, Feb 16 (Reuters Health) -- Migratory birds can carry Lyme
disease and Lyme-infected ticks over great distances, researchers report.
Lyme disease is an inflammatory disorder that can cause fever and chills,
neurologic and cardiac complications, and arthritis. Ticks that feed on infected
deer, mice or dogs pick up the bacteria that cause Lyme disease. A bite from an
infected tick can transmit the disease to humans.
Previously, researchers disputed that migratory birds acted as hosts for
Lyme disease, explain Dr. Bjorn Olsen and colleagues of Umea University and
Kalmar County Hospital in Sweden.
But their study, described in the February 17th issue of Nature, found
that birds can in fact carry the disease as a latent infection for several
months before passing it on to ticks.
"Ticks anywhere along a migration route will feed on migrants with
reactivated infections and become infected, in turn passing the disease on to
other organisms," the authors warn.
The current study investigated whether an increase in stress hormones that
occurs during migration could suppress the birds' immune systems enough to lower
their defenses against Borrelia garinii, one of the family of bacteria that
cause Lyme disease.
Nineteen redwing thrushes, a species that is frequently infested by the
ticks that transmit Lyme disease, were divided into two groups and kept in
separate rooms. One room was exposed to light for 12 hours and the other room
was exposed to light for a decreasing length of time, from 12 hours to 3.5 hours
over the first 2 months of the 3-month study, to simulate daylight during
autumn.
The researchers injected 8 of the 10 birds exposed to decreasing amounts
of light and 6 of the 9 birds exposed to constant light, with B. garinii.
By day 50, birds exposed to less light showed increased nocturnal
activity, or migratory restlessness. These birds also gained weight, a
phenomenon that occurs in birds preparing to migrate.
Blood samples taken from birds in both groups revealed that pathogens had
infected birds exposed to decreasing light but not birds exposed to constant
light.
"Our results show that migratory restlessness in redwing thrushes can
reactivate a latent Borrelia infection," Olsen and colleagues conclude.
"As thrushes and other birds often travel great distances during
migration, this reveals a new mechanism for facilitating the long-distance
spread of Lyme disease," they add.
