December 11, 2008 — Agricultural Research
Service (ARS) scientists are tracking how the dissemination of the
parasite Trichinella spiralis throughout Europe, North Africa and the
Americas was facilitated by human travel and the transportation of
T. spiralis lurks in the muscle tissue of a wide range of mammals
and can infect humans who consume undercooked meat contaminated with
the parasite. It is no longer a major threat to the U.S. food supply,
but it does persist in some European countries.
Ben Rosenthal, Dante Zarlenga and Detiger Dunams work at the ARS
Animal Parasitic Diseases Laboratory in Beltsville, Md. They used
Trichinella DNA collected from 28 countries on four continents to
evaluate potential links between parasite hosts, geographic
distribution and species diversity.
Over time, the genetic traits of a pathogen may shift as the
pathogen expands beyond its original range and becomes isolated.
Geographic barriers prevent contact between the new populations, and
these barriers support the development and maintenance of unique
genetic mutations within each group.
These mutations, in turn, can be used to trace the links between
individuals in each population. They can also be compared with
populations that have dispersed to other areas.
Although T. spiralis is believed to be at least 20 million years
old, the scientists were surprised to find that parasite samples from
Europe, North Africa and the Americas had remarkably uniform DNAs. In
fact, statistical analyses grouped all 44 samples from all evaluated
regions into a single "Western" group of T. spiralis, due to the high
degree of genetic similarity.
This evidence suggests that the T. spiralis found in Europe first
evolved after the domestication of swine. Settlers on their way to the
New World and elsewhere traveled with swine for food, and some of these
pigs were infected with T. spiralis.
The team concluded that human travel was the primary source of
disseminating T. spiralis throughout the New World. They also believe
that these migration patterns explain the limited range of genetic
diversity observed in the European, North African and the American
isolates of T. spiralis.
Source : USDA/Agricultural Research Service