Parelaphostrongylus tenuis
Encyclopedia
Parelaphostrongylus tenuis (brainworm or meningeal worm) is a small parasitic nematode
that infects the brain
of many ungulate
s. Its natural host, the white-tailed deer
, is unaffected by its presence; other species
, however, suffer severe neurologic damage that eventually leads to death
. This disease is known as moose sickness
for its frequent occurrence in moose
sharing territory with white-tailed deer.
Parelaphostrongylus tenuis was identified as the cause of moose sickness—a disease known since 1912—by Canadian
biologist
Roy Anderson
in 1963.
http://www.michigan.gov/dnr/0,1607,7-153-10370_12150_12220-26502--,00.html
in blood vessel
s in the venous sinuses and subdural space of a white tailed deer's brain. The eggs are swept up in the blood circulation and they reach the lung
s, where they hatch into first-stage larva
e. Occasionally, the larvae hatch in the brain tissue and enter the blood supply as larvae. In either case, once the larvae are in the lung
s, they enter the air passages. The deer cough
s up and swallow
s the larvae, which pass through the digestive tract and are excreted in the deer's feces
.
The first stage larvae emerge from the manure
and infect snail
s and slug
s that crawl over the deer droppings. These gastropods are infected through their foot. The first intermediate gastropod hosts include:
Once in the gastropod, the larvae develop into their second and third stage. When a deer feeds on vegetation
, an infected snail or slug may be inadvertently ingested. The third-stage larvae emerge in the stomach of the deer, and migrate through the deer's stomach
lining, along the outside curvature of the deer stomach (or abomasum
) and through the abdomen until they reach the spinal cord
. Once in the spine
, they crawl through to the brain, where they grow and the life cycle begins anew. In ungulates other than deer (i.e. aberrant hosts), the mature worms do not produce eggs, and the infected animal becomes severely ill. Classic aberrant hosts are llamas, sheep, moose and some exotic antelope.
The slugs or snails that serve as intermediate hosts
are very small, usually less than 1 cm, and have a predilection to live in the vegetation that deer like to eat. Although the accidental ingestion of an infected slug or snail suggests deer infection is a rare occurrence, especially since Parelaphostrongylus tenuis has been found to only infect roughly one out of 1,200 snails and slugs in the Grand Marais, Minnesota
area, eighty percent of white-tailed deer in the region nonetheless become infected during their first year of life.
It takes 3 to 4 weeks for the first stage larvae to develop into an infective-capable third stage larvae inside the snail or slug.
Nematode
The nematodes or roundworms are the most diverse phylum of pseudocoelomates, and one of the most diverse of all animals. Nematode species are very difficult to distinguish; over 28,000 have been described, of which over 16,000 are parasitic. It has been estimated that the total number of nematode...
that infects the brain
Brain
The brain is the center of the nervous system in all vertebrate and most invertebrate animals—only a few primitive invertebrates such as sponges, jellyfish, sea squirts and starfishes do not have one. It is located in the head, usually close to primary sensory apparatus such as vision, hearing,...
of many ungulate
Ungulate
Ungulates are several groups of mammals, most of which use the tips of their toes, usually hoofed, to sustain their whole body weight while moving. They make up several orders of mammals, of which six to eight survive...
s. Its natural host, the white-tailed deer
White-tailed Deer
The white-tailed deer , also known as the Virginia deer or simply as the whitetail, is a medium-sized deer native to the United States , Canada, Mexico, Central America, and South America as far south as Peru...
, is unaffected by its presence; other species
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
, however, suffer severe neurologic damage that eventually leads to death
Death
Death is the permanent termination of the biological functions that sustain a living organism. Phenomena which commonly bring about death include old age, predation, malnutrition, disease, and accidents or trauma resulting in terminal injury....
. This disease is known as moose sickness
Moose sickness
Moose sickness is a degenerative condition that occurs in moose populations in central and eastern North America that have been infected with the parasitic worm Parelaphostrongylus tenuis. The disease is characterized by stumbling, aimlessness and other odd behavior and is often fatal.The parasite...
for its frequent occurrence in moose
Moose
The moose or Eurasian elk is the largest extant species in the deer family. Moose are distinguished by the palmate antlers of the males; other members of the family have antlers with a dendritic configuration...
sharing territory with white-tailed deer.
Parelaphostrongylus tenuis was identified as the cause of moose sickness—a disease known since 1912—by Canadian
Canada
Canada is a North American country consisting of ten provinces and three territories. Located in the northern part of the continent, it extends from the Atlantic Ocean in the east to the Pacific Ocean in the west, and northward into the Arctic Ocean...
biologist
Biologist
A biologist is a scientist devoted to and producing results in biology through the study of life. Typically biologists study organisms and their relationship to their environment. Biologists involved in basic research attempt to discover underlying mechanisms that govern how organisms work...
Roy Anderson
Roy Anderson
Roy Anderson or Andersson may refer to:* Sir Roy M. Anderson , former rector of Imperial College* Roy Anderson , character from television sitcom The Office* Roy Andersson , Swedish film director...
in 1963.
Significance
The worm is of no public health significance since it is not infective to humans, and meat of infected animals is safe for human consumption. The parasite may be of some importance to veterinarians since sheep and goats are susceptible.http://www.michigan.gov/dnr/0,1607,7-153-10370_12150_12220-26502--,00.html
Life cycle
The life cycle of Parelaphostrongylus tenuis begins when female worms lay their eggsEgg (biology)
An egg is an organic vessel in which an embryo first begins to develop. In most birds, reptiles, insects, molluscs, fish, and monotremes, an egg is the zygote, resulting from fertilization of the ovum, which is expelled from the body and permitted to develop outside the body until the developing...
in blood vessel
Blood vessel
The blood vessels are the part of the circulatory system that transports blood throughout the body. There are three major types of blood vessels: the arteries, which carry the blood away from the heart; the capillaries, which enable the actual exchange of water and chemicals between the blood and...
s in the venous sinuses and subdural space of a white tailed deer's brain. The eggs are swept up in the blood circulation and they reach the lung
Lung
The lung is the essential respiration organ in many air-breathing animals, including most tetrapods, a few fish and a few snails. In mammals and the more complex life forms, the two lungs are located near the backbone on either side of the heart...
s, where they hatch into first-stage larva
Larva
A larva is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle...
e. Occasionally, the larvae hatch in the brain tissue and enter the blood supply as larvae. In either case, once the larvae are in the lung
Lung
The lung is the essential respiration organ in many air-breathing animals, including most tetrapods, a few fish and a few snails. In mammals and the more complex life forms, the two lungs are located near the backbone on either side of the heart...
s, they enter the air passages. The deer cough
Cough
A cough is a sudden and often repetitively occurring reflex which helps to clear the large breathing passages from secretions, irritants, foreign particles and microbes...
s up and swallow
Swallow
The swallows and martins are a group of passerine birds in the family Hirundinidae which are characterised by their adaptation to aerial feeding...
s the larvae, which pass through the digestive tract and are excreted in the deer's feces
Feces
Feces, faeces, or fæces is a waste product from an animal's digestive tract expelled through the anus or cloaca during defecation.-Etymology:...
.
The first stage larvae emerge from the manure
Manure
Manure is organic matter used as organic fertilizer in agriculture. Manures contribute to the fertility of the soil by adding organic matter and nutrients, such as nitrogen, that are trapped by bacteria in the soil...
and infect snail
Snail
Snail is a common name applied to most of the members of the molluscan class Gastropoda that have coiled shells in the adult stage. When the word is used in its most general sense, it includes sea snails, land snails and freshwater snails. The word snail without any qualifier is however more often...
s and slug
Slug
Slug is a common name that is normally applied to any gastropod mollusc that lacks a shell, has a very reduced shell, or has a small internal shell...
s that crawl over the deer droppings. These gastropods are infected through their foot. The first intermediate gastropod hosts include:
- Anguispira alternataAnguispira alternataAnguispira alternata, common name the flamed disc or flamed tigersnail, is a species of air-breathing land snail, a terrestrial pulmonate gastropod mollusk in the family Discidae, the disk snails....
- Arion circumscriptusArion circumscriptusArion circumscriptus, common name Brown-banded arion, is a species of air-breathing land slug, a terrestrial pulmonate gastropod mollusk in the family Arionidae.- Distribution :This species occurs in countries and islands including:...
- Discus cronkhitei
- Deroceras laeveDeroceras laeveDeroceras laeve, the marsh slug, is a species of small air-breathing land slug, a terrestrial pulmonate gastropod mollusk in the family Agriolimacidae.-Distribution:...
- one of three most infected hosts - Deroceras reticulatumDeroceras reticulatumDeroceras reticulatum, common names "grey field slug" and "grey garden slug", is a species of small air-breathing land slug, a terrestrial pulmonate gastropod mollusk in the family Agriolimacidae...
- Haplotrema concavumHaplotrema concavumHaplotrema concavum, gray-footed lancetooth, is a species of predatory air-breathing land snail, a terrestrial pulmonate gastropod mollusk in the family Haplotrematidae.- Feeding habits :...
- Mesodon thyroidusMesodon thyroidusMesodon thyroidus is a species of air-breathing land snail, a terrestrial gastropod mollusk in the family Polygyridae.-External links:* on the UF / IFAS Featured Creatures Web site...
- Stenotrema fraternum
- Triodopsis albolabris
- Triodopsis notata
- Zonitoides arboreusZonitoides arboreusZonitoides arboreus is species of small air-breathing land snail, a terrestrial pulmonate gastropod mollusk in the family Gastrodontidae.-Distribution:The native distribution of Zonitoides arboreus includes:* North America...
- one of three most infected hosts - Zonitoides nitidusZonitoides nitidusZonitoides nitidus is a species of small, air-breathing land snail, a terrestrial pulmonate gastropod mollusk in the family Gastrodontidae.Zonitoides nitidus is the type species of the genus Zonitoides.-Distribution:...
- one of three most infected hosts
Once in the gastropod, the larvae develop into their second and third stage. When a deer feeds on vegetation
Vegetation
Vegetation is a general term for the plant life of a region; it refers to the ground cover provided by plants. It is a general term, without specific reference to particular taxa, life forms, structure, spatial extent, or any other specific botanical or geographic characteristics. It is broader...
, an infected snail or slug may be inadvertently ingested. The third-stage larvae emerge in the stomach of the deer, and migrate through the deer's stomach
Stomach
The stomach is a muscular, hollow, dilated part of the alimentary canal which functions as an important organ of the digestive tract in some animals, including vertebrates, echinoderms, insects , and molluscs. It is involved in the second phase of digestion, following mastication .The stomach is...
lining, along the outside curvature of the deer stomach (or abomasum
Abomasum
The abomasum, also known as the maw, and the rennet-bag, and the read, is the fourth and final stomach compartment in ruminants. It secretes rennin - the artificial form of which is called rennet, and is used in cheese creation....
) and through the abdomen until they reach the spinal cord
Spinal cord
The spinal cord is a long, thin, tubular bundle of nervous tissue and support cells that extends from the brain . The brain and spinal cord together make up the central nervous system...
. Once in the spine
Vertebral column
In human anatomy, the vertebral column is a column usually consisting of 24 articulating vertebrae, and 9 fused vertebrae in the sacrum and the coccyx. It is situated in the dorsal aspect of the torso, separated by intervertebral discs...
, they crawl through to the brain, where they grow and the life cycle begins anew. In ungulates other than deer (i.e. aberrant hosts), the mature worms do not produce eggs, and the infected animal becomes severely ill. Classic aberrant hosts are llamas, sheep, moose and some exotic antelope.
The slugs or snails that serve as intermediate hosts
Host (biology)
In biology, a host is an organism that harbors a parasite, or a mutual or commensal symbiont, typically providing nourishment and shelter. In botany, a host plant is one that supplies food resources and substrate for certain insects or other fauna...
are very small, usually less than 1 cm, and have a predilection to live in the vegetation that deer like to eat. Although the accidental ingestion of an infected slug or snail suggests deer infection is a rare occurrence, especially since Parelaphostrongylus tenuis has been found to only infect roughly one out of 1,200 snails and slugs in the Grand Marais, Minnesota
Grand Marais, Minnesota
Grand Marais is a city in Cook County, Minnesota, United States. The population was 1,351 at the 2010 census. It is also the county seat of Cook County...
area, eighty percent of white-tailed deer in the region nonetheless become infected during their first year of life.
Timeline
The time between infection with third stage larvae and completion of the cycle by passing first stage larvae in the feces is 80–90 days. This is called the prepatent period.It takes 3 to 4 weeks for the first stage larvae to develop into an infective-capable third stage larvae inside the snail or slug.