Nasal Leeches

Nasal Leeches of Waterfowl

Causative Agent

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.
Other species of leeches feed on other exposed surfaces of waterfowl.

Distribution

Geographic:

Seasonality:

Peak infestations occur during the spring and summer months when leeches are actively seeking potential hosts and reproducing.
Winter slows the metabolic rate and activity of leeches.

Click on a photo to enlarge.

Nasal leeches are often visible infesting external nasal passages.

Nasal leeches also infest the nasal sinuses.

Hosts

Many aquatic birds are affected; commonly dabbling ducks (e.g., mallard, teal, wigeon, northern shoveler, etc.) and swans

Signs and Symptoms

Leeches are 10-45 mm long when fully engorged, dark yellow to olive in colour.
Free-living leeches are green with patterns of spots on the top surface.
Birds with leeches protruding from the nostrils or attached to the mucous membranes of the eyes are easily recognized at a distance with binoculars.
Leeches may become so engorged with blood that they resemble sacks of blood.
Infected birds may vigorously shake their heads, scratching at their bills with their feet, or sneeze in an attempt to dislodge leeches.
Leeches lodged in the nostrils and respiratory tract can cause laboured breathing and gaping (breathing with an open bill) similar to that seen in birds affected with Aspergillus infection.
Feeding leeches can lead to extensive damage and inflammation of the lining of the nasal cavity.
Severe infestations of the eye can result in temporary blindness.
Leeches protruding from the nostrils or attached to the eyes can be removed with forceps.

Meat Edible?

Meat is edible, but if considerable blood-loss has occurred from leech infestation the quality of meat may be decreased.

Human Health Concerns and Risk Reduction

Theromyzon leeches feed exclusively on birds and are not considered a threat to humans.

Samples for Diagnosis

Nasal leeches often cannot be observed externally, so submitting the entire carcass is warranted.
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.
Leeches can be shipped live in pond water and maintained for several months in a refrigerator.

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