Diseases Threatening CT's Birds

Links are provided if you wish to learn more about a disease.

West Nile Virus

  • Wild birds serve as the reservoir for WNV

    • Transmitted among wild birds (and humans, among other mammals) primarily by mosquitoes

    • Most birds do not become sick if infected - but some do, ESPECIALLY crows and blue jays

      • Though since WNV was discovered in the United States in 1999, the virus has been detected in over 300 species of dead birds

  • Majority of birds do not show symptoms, but some may include: 

    • Uncoordinated walking, lethargy, tremors, inability to fly,  rapid weight loss, green waste, blindness, lack of awareness, head droop, and abnormal body posture

Avian Cholera

  • Contagious infection due to bacterium Pasteurella multocida

    • Different strains, but in wild birds, primarily one strain: Type 1

    • Transmitted by bird-to-bird contact, contact with secretions or feces of infected birds, or ingestion of food or water containing the bacteria

  • Signs:

    • Convulsions, swimming in circles, throwing head back between wings, erratic flight, and miscalculated landing attempts

    • Mucous discharge from mouth or nose; soiling or matting of feathers, eyes, and bill; pasty or blood-stained droppings

  • Often see cases with large numbers of dead birds in good body condition with few, if any, sick birds present

Avian Botulism

  • Paralytic disease caused by ingestion of toxin produced by the bacterium Clostridium botulinum

    • Widespread in soil and requires warm temperatures

    • Waterfowl, turkeys, pheasants and most wild birds may be affected if they ingest the toxin directly or may eat invertebrates containing it

  • Signs:

    • Paralysis of wings and legs; cannot control third eyelid, neck muscles, and other muscles

  • Birds with paralyzed neck muscles cannot hold their heads up and often drown (see picture)

    • Death can also result from water deprivation, electrolyte imbalance, respiratory failure, or predation


Duck Viral Enteritis

aka Duck Plague

  • Acute, highly contagious disease of ducks, geese, and swans of all ages, characterized by sudden death, high mortality (particularly among older ducks), and hemorrhages and necrosis in internal organs

  • Caused by duck herpesvirus 1 (anatid herpesvirus 1) through direct contact or contaminated water

  • Signs:

    • Unable to stand, show weakness and depression

    • Nasal discharge, watery or bloody diarrhea

    • Ducklings frequently show dehydration and weight loss, as well as blue beaks and blood-stained vents

    • Dead males may have prolapse of the penis



aka House Finch Conjuvitis

  • Caused by the bacterium Mycoplasma gallisepticum, well-known for causing chronic respiratory tract disease in domestic poultry and gamebirds

    • Was not recognized as potentially important pathogen of wild birds until it decimated House Finch populations in the eastern United States in the mid-1990s

  • Signs:

    • Puffy or swollen eyes, crusty appearing eyelids, cloudy fluid drainage

    • Rubbing eyes on branches and birdfeeder surfaces, remaining on ground or at birdfeeder after other birds have left, colliding with stationary objects due to impaired vision


  • Caused by inhalation of spores of fungi in the Aspergillus group, of which A. fumigatus is the primary species responsible for infections in wild birds

  • All species of birds susceptible

    • Majority of reported cases occur in waterfowl, raptors, and gulls

  • Can cause acute or chronic illness

    • Acute:

      • Will die quickly from respiratory distress

      • May exhibit lethargy, dehydration, loss of appetite, diarrhea, gasping for breath

    • Chronic:

      • May exhibit loss of body condition, lethargy, difficulty flying and breathing, vomiting, and diarrhea

      • May also show signs of neurological disease

    • Both may also have fungus growing on respiratory tissues that resembles bread mold




aka Rice Breast Disease

  • Parasitic infection caused by a protozoan, different per species

    • Commonly Sarcocystis rileyi in waterfowl

      • Especially dabbling ducks (mallard, pintail, shoveler, teal, black duck, gadwall, and widgeon)

    • Ingest eggs of parasite in food or water

      • When eggs hatch, parasites move to form cysts at skeletal muscles

  • Waterfowl affected usually do not look or act sick and generally the disease is not fatal

  • Occasionally, severe infections may cause muscle loss with resultant lameness or weakness, making them more susceptible to predation

Avian Pox

  • Caused by several different strains of avipoxvirus

  • Affects variety of birds, including upland gamebirds, songbirds, marine birds, the parrot family, and raptors

  • Transmission via direct contact with infected birds, ingestion of contaminated food, water or surfaces 

    • Insects, especially mosquitoes, can also act as mechanical vectors

  • Two forms: cutaneous pox (most common) and diphtheritic ("wet") pox

    • Cutaneous:

      • Wart-like growths, sometimes in large clusters, occur around the eyes, beak, legs - any non-feathered skin

      • Leads to difficulty seeing, breathing, feeding, or perching

    • Diphtheritic:

      • Growths form in mouth, throat, trachea and lungs resulting in difficulty breathing or swallowing.

    • Birds with either form of pox may appear weak and emaciated


Lymphoproliferative Disease Virus (LPDV)

  • Emerged in US in 2012

    • Much has yet to be researched

    • Believed to be in wild turkey populations throughout eastern US

  • Some turkeys carry the virus without becoming ill, while other turkeys can develop tumors on the head and feet, can ultimately die from it

    • Look very similar to Avian Pox tumors

      • Cannot tell the difference without testing

      • May even be both!

Avian Salmonellosis

  • Bacterial disease caused by Salmonella typhimurium

  • Spread by direct contact between birds, from contaminated surfaces/environments, food or water

    • Outbreaks often associated with bird feeding stations

  • Songbirds, European starlings, blackbirds, common grackles, and mourning doves are most commonly affected.

  • No definitive signs

    • Some may be carriers and appear healthy

    • Others may have lethargy, ruffled feathers, droopy head, shivering, diarrhea, loss of appetite, and maybe arthritis

      • Eventually coma and death

Southeastern Cooperative Wildlife Disease Study