Sidebar: Elk Restoration Projects and the Meningeal Worm
Any animal restoration project is a study in ecological complexity. The arrival of a new species, even if it has lived in the restoration area in the past, sets in motion a whole array of interactions. The animal’s diet changes the food web. The animal’s behavior changes the habitat. The animal potentially brings with it diseases, parasites, and insects that were previously unknown in the area. And the animal becomes a host to diseases, parasites, or insects that it has not encountered before.
Elk restorations in the eastern part of the United States have sometimes failed in part due to a parasite called meningeal worm (Parelaphostrongylus tenuis), or brain worm, which lives in the east, but is unknown in the west.
The meningeal worm is a parasite that affects white-tailed deer, elk, and other cervids. The parasite causes little, if any, damage in its usual host, white-tailed deer. But when the parasite infects elk, it is often fatal. The parasite has a multistage life cycle that begins in the feces of white-tailed deer, passes into snails and slugs, and then to deer or elk when the animals ingest an infected snail or slug while feeding. Once in the cervid, the parasite migrates to the spinal cord, and then into the brain, where it mates and lays eggs. The eggs are deposited in veins, carried to the lungs, then to the throat, where they are swallowed. From here, the eggs are shed with the feces, and the life cycle begins again. The exact distribution of the meningeal worm is unknown, but in general it occurs east of 100 degrees west longitude (which runs through the middle of Nebraska).
Elk restoration projects were attempted in ten states east of the Mississippi between the turn of the century and 1990. Eight of these failed. These restoration efforts were not well documented, but deaths due to meningeal worms played a part in the failure of perhaps half of them. Other problems were lack of good habitat, conflicts over crop degradation, or illegal hunting. (Elk restoration succeeded in Michigan and Pennsylvania.)
Some of the restorations involved relatively
small numbers of elk, and small herds are more vulnerable
to problems—whether poaching, parasites, or poor reproduction
due to animals dispersing too far from one another. That’s
one of the reasons the Kentucky project brought in so many
animals. “We were using mass quantities of elk, huge
numbers comparatively speaking,” Maehr says. “The
other restoration efforts relied on handfuls of animals
to get things going. No one will ever know why they didn’t
make it. But when you start with a much larger group of
animals they tend to do better.”
Maehr is planning to study the affects of meningeal worm
in the Kentucky elk, particularly those ages one to three,
pending funding. “There are some hints that this parasite
is more problematic in that age group,” he says. “We
don’t know much about their ecology and demographics.”
At least five, and perhaps more, of the elk born into the
Kentucky herd in 1998 have died of meningeal worm. These
animals were not radio-collared, so the actual number may
be higher.
Still, Maehr doesn’t think the brain worm will spell disaster for the Kentucky elk. “There’s still a question mark because of that young cohort,” he says. “But all indications are that the herd continues to grow and expand.”
—Mary-Russell Roberson
ZooGoer 32(3) 2003. Copyright 2003
Friends of the National Zoo.
All rights reserved.
