Researchers Exploit Cattle Pathogen's Genomic
By Jan Suszkiw
February 8, 2007
With genomic "maps" in
hand, Agricultural Research Service (ARS)
scientists are plotting new ways to protect cattle from cellular attack by
A. marginale is a primarily tick-borne bacterium that invades and
destroys the red blood cells of cattle and other ruminant hosts. Severe
infections cause anemia, weight loss and death. Between 50,000 and 100,000 U.S.
cattle succumb to it annually. Those surviving the diseaseknown as
anaplasmosisbecome lifelong carriers that can endanger other herd members
and impede U.S. cattle trade.
Although antibiotics can kill A. marginale, a long-sought alternative
strategy has been to develop a vaccine to keep the bacterium from infecting
cattle in the first place. However, vaccination has been dogged by safety
issues and uneven performance. A chief reason is A. marginale's ability
to reconfigure its surface proteins and evade detection by the animals' immune
systems, according to
S. Kappmeyer, a geneticist in the ARS Animal Diseases Research Unit (ADRU)
at Pullman, Wash.
Now the jig could be up, thanks to Kappmeyer and colleagues' success in
determining the nucleic acid sequence for the genome of the bacterium's St.
Maries strain, which is tick-transmitted. His fellow "decoders"
include ADRU research leader
Knowles, other scientists in the unit, and a team led by Guy Palmer at
Washington State University-Pullman.
The advance, first reported in January 2005, has enabled the researchers to
identify 70 percent of A. marginale's genes, including those encoding
for two protein superfamilies. Many superfamily proteins reside on the
bacterium's outer surface, where the host's immune system searches for them in
order to mount a defensive response.
According to Lowell, the discovery raises the prospect of devising new
vaccines that will help the immune systems of cattle to better recognize the
bacterium's protein-shuffling shenanigans, and to flag them with antibodies
that mobilize pathogen-eating cells.
more about the research in the February 2007 issue of Agricultural
ARS is the U.S. Department of
Agriculture's chief scientific research agency.