ALBANY, NY: The First Presbyterian Church was the location
of the March Save the Pine Bush vegetarian dinner which featured
the excellent presentation on biodiversity and Lyme Disease
by Kathleen LoGiudice, PhD.
Dr. LoGiudice opened her remarks by saying that the battle
over Crossgates Mall made a big impression on her in high school.
She was pleased that Save the Pine Bush was still fighting after
all of these years. In the beginning of her presentation, she
posed the question, “does an increase in the biodiversity
decrease the risk of Lyme disease?”
Lyme disease is caused by the spirochete, Borrelia burgdorferi.
The first symptom (in some but not all people) is a distinctive-looking
bull’s-eye rash, which is caused by the reproduction of
the spirochete. In the early stages, Lyme disease is easily
treated by the use of anti-biotics. Left untreated, Lyme disease
can have serous effects, including arthritis, extreme fatigue,
and heart and central nervous system problems. Lyme disease
is difficult to treat once such symptoms appear.
Borrelia burgdorferi lives in the black-legged tick. The tick
has three life stages: larvae, nymph and adult. Because Lyme
disease is not passed down from adult tick to the tick eggs,
all tick larvae are hatched without harboring Borrelia burgdorferi.
In order to transmit Lyme disease, the tick must become infected
during its lifetime.
The tick has three blood meals, one at each life-stage. During
the larval stage, the ticks will feed on a variety of hosts,
including mice, shrews and birds. After its blood meal, the
larva drop off the host into the leaf litter. Being bit by a
larval tick poses no risk to humans, because no larval tick
is infected with Lyme disease.
If a larval tick bites a host that is infected with Lyme disease,
then during its next phase, as a nymph, the tick can pass Lyme
Disease on to the next host. It is ticks in the nymph stage
which pose the most risk to humans.
Adult ticks feed mainly on deer.
It is the prevalence of Lyme disease among tick nymphs that
predicts the risk of Lyme disease for humans.
Dr. LoGiudice created a mathematical model to predict the effects
of biodiversity on the prevalence of Lyme disease.
To do this, she first had to determine the percentage of larval
ticks who feed on various hosts who became infected with Lyme
disease. In the laboratory, she determined that 92% of larval
ticks that fed on infected white-footed mice became infected.
However, when testing larval ticks in the field, she found that
only 38% of the ticks were infected, which means the ticks were
feeding on other hosts which did not transmit Lyme disease as
well as the white-footed mouse.
In her experiment, she measured how likely ticks were to become
infected by various host animals. To do this, animals were trapped
(or in the case of deer, killed) and kept in the laboratory
for 72 hours in individual cages. The cages were suspended over
a dish of water. During the 72 hour period, ticks would drop
from the host animal. (Other, less pleasant things dropped off
too - but Dr. LoGiudice did not go into a lot details about
this more disagreeable part of the research!) The ticks were
counted and tested for the prevalence of Lyme disease.
Once these brave animals did their duty in the laboratory, they
were returned to the site from which they were captured. A local
farmer donated the deer. The farmer had a problem with deer
eating his corn, so he would shoot the deer. He then donated
the deer meat to an organization for the homeless, and give
the head, hide and feet to Dr. LoGiudice for analysis.
Dr. LoGiudice then created a chart showing the expected nymphal
tick infection based on the animal host. So, if all of the animals
in the forest were white-footed mice, 92% of the ticks would
be infected with Lyme disease. However, other animal hosts are
not as good at passing on the infection, so as these animals
are added to the forest, the rate of infection declines.
For example, the eastern chipmunk was the next most competent
at passing on Lyme disease to ticks with 55% of ticks getting
Lyme disease from chipmunks. This mathematical model indicates
that the more species, the more biodiversity, the less risk
of Lyme disease.
This chart shows that as species are added
to an ecosystem,
the rate of animals infected with Lyme Disease declines.
She also cited a study by Allen, Keesing and Ostfeld on the
Effect of Forest Fragmentation on Lyme Disease Risk. This study
was very small, but it tended to indicate that Lyme disease
was more prevalent in small forest fragments, than in large
Dr. LoGiudice then posed the question: Does Sprawl promote Lyme
A = Sprawl creates habitat fragments
B = Habitat fragmentation reduces biodiverstiy
C = Reduction of biodiverstiy increase Lyme disease risk
So, then does A = C; Sprawl increases Lyme disease risk?
Dr. LoGiudice answered this question with a resounding “Maybe
. . ”
There are many assumptions in the model Dr. LoGiudice proposes
including that diversity declines in predictable manner. In
the decline of biodiverstiy, which species are lost first? What
if there is a different set of rules to remove species? What
if species are lost in relation to their body mass? Applying
different rules for the loss of biodiversity would create a
very different looking chart. Dr. LoGiudice’s chart adds
animals in order of their ability to pass on Lyme disease. She
also showed us a chart that shows animals in relation to their
body size and the chart looked very different.
More study is needed. Dr. LoGiudice does not want the same
mistakes made about the effects of biodiverstiy on human health
made that were made with the issues of acidic lakes in the Adirondacks
and global warming. Because early studies of these subjects
showed there may be a problem, corporations that would be adversely
affected obfuscated the issues by attacking the science before
definitive answers came in. Still, in the public mind, despite
the now overwhelming scientific evidence of problems, people
still don’t understand the issues. Dr. LoGiudice does
not believe we should run right out and and change our zoning
laws until we have definitive answers on how biodiverstiy affects