| Nasal Leeches of Waterfowl |
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| Causative Agent |
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A leech of the genus Theromyzon that feeds directly on blood
from the nasal passages, trachea and
mucous
membranes
of the eyes of migratory waterfowl.
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Other species of leeches feed on other exposed surfaces of
waterfowl.
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| Images |
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Click on images to enlarge. |
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Nasal leeches are often visible as they infest external nasal
passages. |
Nasal leeches also infest
the nasal sinuses. |
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| Distribution |
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Geographic: |
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Common on birds north of the 30th parallel and in western
North America.
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Seasonality: |
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Peak infestations occur during the spring and summer months when leeches
are actively seeking potential hosts and reproducing.
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Winter slows the metabolic rate and activity of leeches.
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| Hosts |
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Many aquatic birds are affected; commonly dabbling ducks (e.g.,
mallard, teal, wigeon, northern shoveler, etc.) and swans.
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| Signs and Symptoms |
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Leeches are 10-45 mm long when fully engorged, and are dark yellow to
olive in color.
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Free-living leeches are green with patterns of spots on the top surface.
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Birds with leeches protruding from the nostrils or attached to the
mucous membranes of the eyes are easily recognized at a distance with binoculars.
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Leeches may become so engorged with blood that they resemble sacks of
blood.
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Infected birds may vigorously shake their heads, scratching at their
bills with their feet, or sneeze in an attempt to dislodge leeches.
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Leeches lodged in the nostrils and respiratory tract can cause labored
breathing and gaping (breathing with an open bill) similar to that
seen in birds affected by
Aspergillus infection.
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Feeding leeches can lead to
extensive damage and
inflammation of the lining of the nasal
cavity.
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Severe infestations of the
eye can result in temporary blindness.
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Leeches protruding from the
nostrils or attached to the eyes can be removed with forceps.
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| Meat Edible? |
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Meat is edible but, if considerable blood-loss has occurred from leech
infestation, the quality of meat may be decreased.
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| Human Health Concerns and
Risk Reduction |
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Theromyzon
leeches feed exclusively on
birds and are not considered a threat to humans.
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| Samples for Diagnosis |
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Nasal leeches often cannot be observed externally, so submitting the
entire carcass is warranted.
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Nasal leeches will depart from a dead bird or may move to other areas of
the bird, making them difficult to see. Leeches found on the carcass
should be submitted as well for identification.
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Leeches can be shipped live in pond water and maintained for several
months in a refrigerator.
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| Similar Diseases |
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Similar breathing
difficulty is observed in birds with
aspergillosis
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| Further Reading |
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Tuggle B.N. 2001. Nasal leeches. Pp. 245-248 in
Field Manual of Wildlife Diseases: General Field Procedures and Diseases
of Birds. M. Friend, J.C. Franson (Tech. eds.), E.A. Ciganovich
(ed.). Biological Resources Division Information and Technology
Report 1999-001. U.S. Department of the
Interior and U.S. Geological Survey. Washington, DC. (Chapter
in PDF Format)
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