Diseases / List of Parasitic Diseases / Disease description:

Leech Infection in Waterfowl








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General and References

Disease Summary

WATERFOWL Infestation with blood-feeding leeches, usually in the nasal cavity or around the eyes. Can be fatal in downies.

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Alternative Names (Synonyms)

  • Duck leech infestation
  • Nasal leech infestation

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Disease Type

Parasitic - Leeches, Pentastomes and Crustacea

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Infectious/Non-Infectious Agent associated with the Disease

Theromyzon spp. (Theromyzon rude, T. occidentalis, T. trizonaire , T. biannulatum North America (USA & Canada), Theromyzon tessulatum (Protoclepsis tessellata) UK, T. tessulatum and T. maculosum, Europe, T. cooperi, Africa. Haementeria (Placobdella) costata Europe and around Mediterranean, Black and Caspian seas.

Infective "Taxa"

Non-infective agents


Physical agents

-- Indirect / Secondary

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Disease Author

Debra Bourne
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Major References / Reviews

Code and Title List

B10.26.w5:- Zoo & Wild Animal Medicine, 2nd Edition
B11.34.w2, B11.37.w5:- BSAVA Manual of Raptors, Pigeons and Waterfowl
B13.46. w1:- Avian Medicine: Principles and Application
B15:- Diseases of Wild Waterfowl
B18: Diseases of Gamebirds and Wildfowl
B34:- Bird Diseases
B36.34.w34:- Field Manual of Wildlife Diseases
B37.x.w1:- Handbook of Avian Medicine
J3.85.w3:- Veterinary Record
J7.28.w1, J7.30.w1, J7.30.w2, J7.33.w1:- Wildfowl
P4.1992.w1:- Proceedings Association of Avian Veterinarians

Other References

Code and Title List

B9.6.w1:- The Swans
B91:- Catalogue of Helminths of Waterfowl
J1.22.w1:- Journal of Wildlife Diseases
J3.62.w1, J3.85.w2, J3.129.w1, J3.129.w2, J3.124.w1, J3.124.w2:- Veterinary Record
J4.99.w1:- Journal of the American Veterinary Medical Association
J7.3.w1:- Wildfowl
J11.23.w1:-Journal of Parasitology

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Clinical Characteristics and Pathology

Detailed Clinical and Pathological Characteristics


  • Leeches may be visible protruding from nasal cavity or attached to the eye. Leeches have also been reported on the feet and plumage. May be large numbers present.
  • Pathogenesis of disease and death is unclear. May be related to blood loss (anaemia), immunological reaction, mucosal irritation, asphyxiation (physical blockage of airways), secondary bacterial infection, toxicity of leech excretions e.g. ammonia, salt, dehydration (as may leave water to escape leeches) (B15, B37.x.w1).

Clinical Characteristics

  • Visible leeches protruding from the nares or eye (on conjunctiva, below nictitating membrane), or on other areas of the body, particularly non-feathered areas.
  • Head-shaking, scratching and bill cleaning ‘sneezing’ movements in water. Affected birds may appear distressed and irritated, and may be reluctant to feed. Rhinitis. Laboured breathing may be seen with heavy respiratory tract burdens of leeches. Haemorrhage may occur from the nares. May produce anaemia and reduced growth rate.
  • Syndrome with paralysis, ocular irritation, dyspnoea, diarrhoea and deaths recorded with Theromyzon cooperi in South Africa (B15).
  • Conjunctivitis, keratitis, ocular discharge, sometimes a fibrinocaseous cast over eye, corneal opacity, and collapse of globe. Temporary blindness and sometimes permanent reduction in vision (J3.67.w1, J7.28.w1).
  • Aerial head scratching seen in American green-winged teal Anas crecca carolinensis (J7.30.w1).
  • Debilitating. Deaths mainly of juveniles, from blood loss and asphyxiation.

N.B. May be associated with other diseases e.g. botulism (Avian Botulism).

(J1.22.w1, J3.85.w3, J3.129.w1, J4.99.w1, J7.28.w1, J7.30.w2, J7.33.w1, B9.6.w1, B10.26.w1, B11.37.w5, B13.46.w1, B15, B18, B36.34.w34, B37.x.w1, P4.1992.w1)


WATERFOWL Infestation may occur in as little as 1 hour after exposure. Individual leeches may be engorged after 2.5 hours (J3.62.w1). Deaths have been recorded 7-14 hours after exposure to leeches (B15).

Mortality / Morbidity

WATERFOWL Infection is common. Mortality has been reported mainly in juveniles and in association with other diseases. Deaths may be related to asphyxiation, excessive bleeding, or brain damage when leeches move into air spaces in the skull. May also predispose to bacterial infection, predation, impede feeding etc. (J1.22.w1, J3.62.w1, J7.28.w1 J7.30.w2, J7.33.w1, B10.26.w1, B15, B36.34.w34, B37.x.w1).


  • Leeches in nares, sinuses, conjunctival sacs, sometimes pharynx, and trachea, rarely in bronchi; 'verminous pneumonia' has been described. Up to 35mm in length. Nasal passages may be blocked with leeches and blood. N.B. 1) may not be found at PME as may have left host; 2) may have moved further into respiratory tract after death.
  • Secondary bacterial infection may occur, also anaemia.
  • Kerato-conjunctivitis, sometimes severe, permanent ocular damage such as corneal opacity and collapse of eyeball have also been reported (J3.67.w1).

(J1.22.w1, J3.85.w3, J4.99.w1, J7.28.w1, J7.30.w2, J7.33.w1, B9.6.w1, B15, B36.34.w34, P4.1992.w1).

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Human Health Considerations

Theromyzon species are parasites of birds. Haementeria costata is mainly a parasite of Emys orbicularis - European terrapin - but may be found on humans and other mammals as well as waterfowl and frogs (J7.33.w1).

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Susceptibility / Transmission

General information on Susceptibility / Transmission

  • All species of Anatidae are presumed susceptible; however geese are affected less frequently than ducks or swans and some species such as trumpeter swans Cygnus buccinator may be particularly susceptible.
  • Infection is more frequent and more pathogenic in juveniles than adults. In some areas effect of leeches on downies may be sufficient to prevent youngsters being raised.
  • In adults, leech infestation may be associated with weakness due to other problems, such as botulism.

(J3.85.w3, J4.99.w1, B11.37.w5, B15, B36.34.w34, B37.x.w1, P4.1992.w1).

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Disease / Agent has been reported in either the wild or in captivity in:

  • Mallard Anas platyrhynchos, Carolina duck (wood duck) Aix sponsa, South African (Cape) shelduck Tadorna cana, Northern pintail Anas acuta, domestic Aylesbury duck Anas platyrhynchos domesticus (J3.85.w3).
  • Mute swan Cygnus olor, Chinese goose Anser cygnoides domesticus, cape shelduck Tadorna cana, Falkland flightless steamer duck Tachyeres brachypterus, northern pintail Anas acuta, (green-winged) teal Anas crecca, mallard Anas platyrhynchos, (Eurasian) wigeon Anas penelope, European eider Somateria mollissima, Carolina (wood duck) Aix sponsa, muscovy duck Cairina moschata, harlequin duck Histrionicus histrionicus, long-tailed duck Clangula hyemalis, white-headed duck Oxyura leucocephala in the UK (J7.33.w1).
  • Falkland flightless steamerduck Tachyeres brachypterus (J7.3.w1).
  • Green-winged teal Anas crecca in Alberta, Canada (J7.30.w1).
  • European (Common) eider Somateria mollissima (J7.30.w2).
  • Blue-winged teal Anas (querquedula) discors in Iowa, USA (J11.23.w1).
  • Domestic ducks, muscovy ducks, geese (J3.62.w1).
  • Chinese geese (Anser cygnoides domesticus) ocular infection, UK (J3.67.w1).
  • Trumpeter swan Cygnus buccinator (J1.22.w1).
  • Muscovy ducklings in the UK (J3.85.w2).
  • Black-necked swan Cygnus melanocoryphus in the UK (J3.129.w1).
  • Mute swan Cygnus olor, black swan Cygnus atratus (B9.6.w1).
  • Trumpeter swan Cygnus buccinator, yellow-billed duck Anas undulata (B15).
  • Whistling swan Cygnus columbianus, Trumpeter swan Cygnus (cygnus) buccinator, White-fronted goose Anser albifrons frontalis, Lesser snow goose Anser caerulescens caerulescens, Canada goose Branta canadensis, Pintail Anas acuta, American green-winged teal Anas crecca carolinensis, Mallard Anas platyrhynchos, Gadwall Anas strepera, American wigeon Anas americana, Blue-winged teal Anas discors, Shoveler Anas clypeata, Canvasback Aythya valisineria, Redhead Aythya americana, Ring-necked duck Aythya collaris, Lesser scaup Aythya affinis, Surf scoter Melanitta perspicillata, American white-winged scoter Melanitta fusca deglandi, Bufflehead Bucephala albeola, Ruddy duck Oxyura jamaicensis jamaicensis in North America (J7.28.w1)
  • Northern pintail Anas acuta, (green-winged) teal Anas crecca, Mallard Anas platyrhynchos, American wigeon Anas americana, Northern shoveler Anas clypeata, Ring-necked duck Aythya collaris, Canvasback Aythya valisineria, Redhead Aythya americana, Lesser scaup Aythya affinis, Bufflehead Bucephala albeola, Gadwall Anas strepera, Ruddy duck Oxyura jamaicensis, White-winged scoter Melanitta fusca, Surf scoter Melanitta perspicillata, Trumpeter swan Cygnus buccinator, and Tundra swan Cygnus columbianus (B36.34.w34).
  • Anser anser domesticus - Domestic goose (Theromyzon tessulatum), Anser cygnoides domesticus - Chinese goose (Theromyzon tessulatum), Cygnus atratus - Black swan, Cygnus olor - Mute swan, Tachyeres spp. (Theromyzon tessulatum), Anas platyrhynchos - Mallard, (Theromyzon maculosum, Theromyzon tessulatum), Anas crecca - Common teal (Theromyzon tessulatum)Anas discors - Blue-winged teal (Theromyzon occidentale), Anas penelope - Eurasian wigeon (Theromyzon tessulatum), Aythya americana - Redhead (Theromyzon occidentale), Aythya fuligula - Tufted duck (Theromyzon tessulatum), Cairina moschata domesticus - Domestic muscovy duck (Theromyzon tessulatum), Clangula hyemalis - Long-tailed duck (Theromyzon tessulatum). (B91)

WATERFOWL Host Species List

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Disease / Agent has been specifically reported in Free-ranging populations of:

  • Green-winged teal Anas crecca in Alberta, Canada (J7.30.w1).
  • Blue-winged teal Anas (Querquedula) discors in Iowa, USA (J11.23.w1).
  • Trumpeter swans Cygnus buccinator in Yellowstone National Park, USA (J1.22.w1).

WATERFOWL Host Species List

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General Information on Environmental Factors/Events and Seasonality

  • Associated with many fresh waters not including fast-running streams.
  • Leeches are most active and seeking hosts in spring and summer; opportunistic infestation may occur on ice-free waters in winter.
  • Infections may be most pathogenic in late-hatched ducklings which are still very young in late summer when leeches are numerous.
  • Outbreaks in the UK may be more common in warm summers.
  • Nasal leech infestations of waterfowl are most commonly observed in northern areas because these parasites are better adapted to cold-water lakes.

(J3.62.w1, J3.85.w2, J7.33.w1, B36.34.w34).

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Regions / Countries where the Infectious Agent or Disease has been recorded

North America, Europe including the UK, Africa (J7.28.w1, J7.33.w1, B15, B36.34.w34).

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Regions / Countries where the Infectious Agent or Disease has been recorded in Free-ranging populations

North America (J1.30.w1, J7.30.w1, J11.23.w).

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General Investigation / Diagnosis

General Information on Investigation / Diagnosis

  • Examination of eyes, nostrils, nasal cavity, pharynx, trachea for the presence of leeches (10-45 mm long if engorged, amber/olive to red if engorged, four pairs of eyes). Also check rest of body as may move later. (B15, B36.34.w34, B37.x.w1)
  • Leeches found on carcasses should be kept in cold water, or preserved by fixing in 10% formalin while being kept straightened between two glass slides for 3-12 minutes, allowed to fix for another 12 hours, then transferred to 5% formalin, and sent to an appropriate parasitologist for identification. (B36.34.w34).
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Similar Diseases (Differential Diagnosis)

WATERFOWL Other leeches may be present as an incidental finding on or in the carcass at post mortem examination (B15).

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Treatment and Control

Specific Medical Treatment

  • Ivermectin 0.02ml/kg or 200g/kg, orally, subcutaneous or intramuscular (B11.34.w2, B11.37.w5, B37.x.w1).
  • Dip ends of protruding leeches in ivermectin (10µ g/ml) (gradually become flaccid and fall out), or apply as nasal drops (J3.124.w2).
  • Ophthalmic antibiotic ointment if required for secondary bacterial infection (J3.85.w2).
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General Nursing and Surgical Techniques

  • Removal of visible leeches manually using forceps; proxymetacaine hydrochloride (Ophthaine, Ciba-Geigy) applied to surface loosens hold, assists in removal.
  • Dunking head in warm water or 10-20% sodium chloride (salt water) encourages leeches to leave nasal passages; repeat several times if necessary. Weak acidic solutions e.g. vinegar may also be effective.
  • Provision of salt water may allow birds to 'sneeze out' relaxed leeches).

(J3.85.w2, J7.28.w1, J7.30.w2, J7.33.w1, B36.34.w34, B37.x.w1, P4.1992.w1)

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Preventative Measures

Vaccination WATERFOWL --
Prophylactic Treatment


Related Techniques


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Environmental and Population Control Measures

General Environment Changes, Cleaning and Disinfection


  • Control in natural ponds is difficult.
  • Keeping all hosts off an area for 1-2 years may be effective but is usually impractical.
  • It may be possible to reduce leech populations by keeping the water level of a pond high in winter, waiting until a hard freeze, then lowering the water level – leeches in shoreline mud should freeze with the mud and be killed (J3.129.w2).
  • In concrete ponds, drain and clean out and disinfect e.g. with potassium permanganate.

(J3.85.w2, B10.26.w1, B13.46.w1, B37.x.w1).

Population Control Measures WATERFOWL Restrict access of waterfowl, particularly juveniles, to waters with known infestation (B11.37.w5, B15).
Isolation, Quarantine and Screening WATERFOWL --
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