Download B. burgdoferi - SERC-Carleton

Lyme Disease: A Novel Vaccine
Erik Williams1
Carleton College
On the rise?
B. burgdoferi, the most common vector-borne bacteria in the United States, is the causative agent in Lyme disease. In
2006, 19,931 cases of Lyme Disease were reported to the United States Center for Disease Control, yielding an
average of 30.2 cases per 100,000 people in the ten states where Lyme disease is most prevalent. This is over twice
the ratio reported 10 years ago. Nearly all of these cases occurred in 3 areas: northeastern U.S. from Maryland to
Maine, parts of the upper mid-west in Wisconsin and Minnesota, and parts of northern California and southern
Oregon.
a
Creation of Vaccine
E. Coli were genetically modified to produce the B. burgdoferi surface protein OspA. When this protein is
eaten, mice create antibodies against it. OspA is only on the surface of B. burgdoferi when the bacteria is in
ticks. So, when ticks feed on immunized mice, they pick up some of the antibody against OspA and the
bacteria is cleared from the ticks. (Tsao 2001) The vaccine can be inserted into tasty bait. (G-Solecki 2005)
Fieldwork
b
I performed fieldwork at several sites in Western Pennsylvania. Several important factors were determined by
creating an 8x8 grids of Sherman live-traps, each 50 feet apart, baited with oats.
First, I determined the Minimum Number Alive (MNA) of Peromyscus mice, chipmunks and short-tailed
shrews. Second, the amount of ticks on each mouse was determined by counting the number of ticks on the
head and ears of each trapped mouse. Third, the presence of bacteria in mice was determined by bringing mice
into the lab, and putting them in mesh cages above water buckets overnight. As ticks finished feeding, they
dropped off the mice, and were brought into the lab and analyzed to determine infection.
From this fieldwork, these sites were evaluated as areas where the vaccine could be deployed and have a
significant impact on B. burgdoferi prevalence in the region.
Figure 1 (a) Graph of steady increase in incidence of Lyme disease in the U.S. (b) Location of reported cases.
Labwork
Goals
At the University of Pennsylvania, attempts are being made to test
the effectiveness of vaccinating wild animals against the
transmission of Lyme disease to ticks. Since ticks transmit B.
burgdoferi to other animals and humans, this will prevent a
substantial number of infections. The goal of Dr. Dusty Brisson’s
Figure 3 After each vaccine treatment, spirochete
lab is to deploy this edible vaccine in the forest, where animals
transmission to ticks goes down between 10-fold
and 100-fold. (Tsao 2001)
will consume it. If they successfully immunize forest animals,
there will be a reduction of human Lyme disease risk.
Since mice are a main natural reservoir for B. burgdoferi in many ecologies, and are easily tested in labs, the
current vaccine is targeted at these animals. Before the vaccine can be deployed, several field sites must be
investigated to determine infection prevalence in the mouse population. However, preliminary trials have
shown that non-mouse animals contribute significantly to the number of infected ticks. For this technique to be
completely successful, either a broadly targeted vaccine will be needed, or multiple specific ones.
In the lab, I analyzed many ticks from previous sites to determine
spirochete infection. DNA from the gut of each tick was extracted,
and spirochete DNA was specifically amplified by PCR. The
resulting DNA was run through a gel. Infection could be determined
by the presence of a prominent band of B. burgdoferi DNA of a
certain size on the gel.
Figure 4 Example of gel used to
determine tick infection.
Acknowledgments
I thank Dr. Dusty Brisson for this opportunity, and Parris Humphrey for his
guidance. This work was supported by the Kolenkow/Reitz Fund.
References
“Reported Cases of Lyme Disease--United States." Lyme Disease. Center for Disease Control. <http://www.cdc.gov/ncidod/dvbid/lyme/>.
Gomes-Solecki, Maria, and Dustin Brisson. "Oral vaccine that breaks the transmission cycle of the Lyme disease spirochete can be
delivered via bait." ScienceDirect.com (2005).
Tsao, Jean, and Durland Fish. "OspA Immunization Decreases Transmission of Borrelia burgdorferi Spirochetes from Infected Peromyscus
leucopus Mice to Larval Ixodes scapularis Ticks." Vector Borne and Zootonic Diseases 1 (2001): 65-75.
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