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A
new threat from
Lyme-disease ticks
The small, unobtrusive
tick called Ixodes scapularis received worldwide medical
attention almost 20 years ago, when it was found to play a crucial
role in the transmission of Lyme disease. Although the ticks
themselves pose no great threat to humans, they carry the disease-causing
spirochete Borrelia burgdorferi and provide the route
of human infection through their bites.
But their culpability
doesn’t end there. In the inaugural issue of the journal
Vector Borne and Zoonotic Diseases, Durland Fish, Ph.D.,
and several colleagues describe a spirochete from I. scapularis
that closely resembles B. burgdorferi but does not match
it in highly sensitive DNA tests carried out by polymerase chain
reaction. The new species of Borrelia was discovered in
I. scapularis nymphs that had previously been fed on mice
known to be free of B. burgdorferi infection. The yet-unnamed
spirochete may infect humans as well, since “all the other
organisms that this tick transmits to mice can also infect people,”
according to Fish, an associate professor of epidemiology. It
is not known what symptoms, if any, such an infection would cause
in humans.
“Our sampling
of I. scapularis … from the field suggests that this
novel Borrelia is widely distributed in nature,”
the study’s authors wrote, and its prevalence is “surprisingly
high in proportion to the total number of Borrelia species
found in these ticks.” They concluded, “These data
suggest that a significant proportion of spirochete-positive
ticks previously thought to be B. burgdorferi by microscopy
is instead this novel Borrelia.” Infection with B.
burgdorferi is responsible for more than 15,000 cases of
Lyme disease each year. Infection with the new Borrelia organism
cannot be found by current Lyme-disease diagnostics—Yale
scientists are now working on a specific test—but it might
well respond to the same treatments as Lyme disease. |
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Chronic
cocaine use may dull responsiveness to brain signals
In a study measuring
the brain’s degree of excitability, the brains of cocaine-dependent
people show an abnormally low response to signals in the region
responsible for muscle movement, according to a recent article
in Biological Psychiatry. The authors, led by Nashatt
N. Boutros, M.D., associate professor of psychiatry, reported
that cocaine addicts and longtime users require significantly
more stimulus to the motor cortex in order to cause the muscles
of their fingers and hands to move. The signals in this study
were delivered on the scalp in the form of transcranial magnetic
stimulation, rapid magnetic pulses from a handheld coil. The
motor threshold, the minimum amount of stimulation needed to
produce movement, ran at a mean of about 41 percent in normal
subjects but about 65 percent in chronic cocaine users.
Cocaine itself
is well known as a drug that excites the brain’s signaling
pathways rather than impeding them, so one might expect that
longtime users of the drug would have the most signal-sensitive
brains of all. Boutros and his colleagues offered two possible
explanations for the higher motor threshold seen in cocaine-dependent
brains. It may reflect either “an adaptation to those effects
of cocaine intoxication that promote cortical excitability and
seizures,” they said, or else tissue damage that has left
this brain region less responsive. In other words, by becoming
less sensitive to signals or less well able to respond to them,
the brain may be attempting to balance out the dangerous hyperresponsiveness
that comes with cocaine use. The next step, said Boutros, will
be to replicate these results in additional cocaine-dependent
subjects, using several different measures of cortical responsiveness. |
