Wildlife Diseases An overview of selected examples

(with tests of your wildlife forensic skills!)

. Many diseases can exist as chronic, often low-level infections (enzootic) or as rapidly-spreading, erruptive infections (epizootic)

Botfly larvaeUgly but not lethal!

Text example:Problem:Hunter reaction

Management:Season Start

Papilloma/fibroma viruses (warts)Ugly but not lethal unless disrupt vision etcUsually attacked by immune system

Avian Pox (Virus) Vector = Mosquito or contact

Mange – caused by mites usually nonlethal,

Sarcoptic mangeCan be lethalOutbreaks in wild canids in N. AmericaMay be of concern for small populations or pop’s ofspecial concern

Dead rabbits or rabbits acting lethargic, easily approached,

or having trouble running

A wildlife forensics quiz

 Symptoms: Hunters should be very suspicious of "lazy" rabbits which are easily killed

Treatment/Management: See text example

Human Concerns: Can be deadly in humans. Rubber gloves should probably be worn when dressing rabbits. The meat of these animals should be thoroughly cooked.

Transmission: bloodsucking arthropods;

In U.S., rabbits source of infection in 90% of human cases of tularemia, 70% of which result from contacts with cottontails. Jackrabbits are an important source of infection in some areas, but are a minor factor nationally. Snowshoe hares comprise less than 1% of the source of human infection.

Toxin or Tularemia - bacterial infection

Dead birds, especially members of the crow/jay family (corvids)

Toxin orWest Nile Virus (WNV)

Encephalitis (inflammation of the brain)Meningitis (inflammation of the lining of brain and spinal cord). 

Transmission: mosquitos  

Symptoms: uncoordinated walking, weakness, lethargy, tremors, and abnormal head posture. Although crows and blue jays account for between 50 and 90 percent of reported avian cases, WNV infection has been identified in over 170 other avian species across North America.

Treatment/Management: monitoring, mosquito eradication

Human Concerns: When the level of virus transmission among birds and mosquitoes becomes high, horses and humans can be incidentally infected. Only 1% of humans bitten actually become infected.

Emaciated, slobbering, wide-legged stance, poor coordination

If Cervid, Chronic Wasting Disease CWD

Agent: prion Prion proteins can be passed in predatorfeces, decaying matter, etc. Prions cause conformational change in other proteins. These are slow to build-up, explaining the time required for symptoms to develop

First recorded in deer in Colorado, has spread to many western states and recently to Wisconsin Attacks central nervous system, leads to emaciation and eventual death

Transmission: unknown

Treatment/Management: Monitoring of brain tissue and containmentRestricted transport of live cervids, and import of nervous tissueReducing density of deer in infected areas

Human concerns: avoid contact with nervous tissue

Malnutrition

Symptoms: Emaciation, lethargic, unsteady, reduced fear response

Don’t rule out other potential factors.

Mass waterfowl deaths, waterfowl weak, easily approached, may act partially paralyzed

Avian cholera – bacteria

Transmission: spread by contact between healthy and ill birds, in an environment contaminated with Pasteurella organisms.

Environmental correlates: Stress appears to be an important factor in breaking down the bird's resistance. Cold, damp weather predisposes birds to this disease and outbreaks are generally seen during the winter months in overwintering waterfowl flocks.

Symptoms: Convulsions, uncoordinated fluttering, stiffness and rapid breathing. Respiratory sound, sneezing and sticky nasal discharges are sometimes observed.

Treatment/Management: : reduce population build-ups, drain infected areas, kill infected populations - controversial!

Human concerns: not transferred to humans

Avian Botulism- toxin produced by Botulinum anaerobic bacteriaThe Salt Lake TribuneArticle Last Updated:10/05/2006 12:52:37 AM MDT   Utah wildlife officials are reporting that an outbreak of type C avian botulism has killed between 10,000 and 15,000 ducks and shorebirds statewide, with the majority of the dead birds on marshes of the Great Salt Lake.

   "During an aerial count in the middle of September, we estimated about 6,000 dead birds," said Tom Aldrich, (DWR). Ecological Correlates: High temps and lots of decaying “meat” as bacterial food source, fluctuating water levels, pesticide kills, etc.

Transmission: Waterfowl ingest toxin from substrate or ingest maggots that magnified toxin concentrations

Other Symptoms: paralysis of infected animals

Treatment/Management: Control amt of decaying matterControl water fluctuationsRemove carcasses rapidlyRemove powerlines over water (collision kills)

Human concerns: toxin destroyed in cooking meat

Avian Plague (Duck Viral Enteritus) (DVE) Herpes virus - Entered US in 1972, cases growing since.

Differentially impacts specific species pintails resistant, blue-winged teal highly susceptible

Ecological correlates: not known

Symptoms: Listless, loss of appetite, bloody discharge from the bill and vent, watery diarrhea

Transmission : contact

Treatment/Management: Contain or destroy infected flocks – controversial!!! Text example in California

Human concerns: not transferred to humans

In waterfowl a dose as small as 1 pellet can result in anemia, while 5 or more pellets can result in death due to heart attack or muscle paralysis.

Symptoms: lowered food intake, weakness, weight loss, drooping wings, inability to fly, and green watery diarrhea. Necropsy may reveal a cracked, green-stained, peeling gizzard lining, with or without lead shot present.

Treatment/Management:: Chelation of infected birds (lead-binding chemicals). Shift to steel shot has greatly reduced this in USAFishing sinkers still problematic

MERCURY Great Salt Lake: For teal and shovelers, adults should eat no more than two 8-ounce meals per month, and young children and women who are pregnant or may become pregnant should have no more than one 4-ounce meal per month, the advisory says. Women of child-bearing age and children should not eat goldeneye at all, while other adults ought to limit their consumption to one 8-ounce meal of goldeneye a month.

Lead Poisoning

Spasmodic twitching and muscle quivering, body trembling. Convulsions and/or blind staggers. Jerkiness in gait, tremors, and convulsions

Convulsions, uncoordinated fluttering, stiffness and rapid breathing, listlessness, shivering

Listless, loss of appetite, may have a bloody discharge from the bill and vent, develop a great thirst and exhibit a watery diarrhea.

Uncoordinated walking, weakness, lethargy, tremors, and abnormal head posture

Note that symptoms for differing diseases often similar:e.g. Avian botulism, cholera, DVE, lead poisoning,

Often disease may have key symptom, but not always expressed

Aspergillosus – Fungal

Ecological correlates: moisture favoring moldy grain, grass

Transmission: Inhalation of fungal spores

Symptoms: Weak, emaciated, gasping, fungal tissue in respiratory tract

Treatment/management: removal of moldy food sources (bird feeders, crops in fields)

Human Concerns: can inhale spores from air sacs but usually dangerous only to those already immunocompromised

Free-living birds in the orders Anseriformes (ducks, geese, swans) and Charadriiformes (gulls, terns, shore birds) have traditionally been considered the natural reservoirs for avian influenza viruses (AIVs)

Before 2005, no evidence that highly pathogenic avian influenza (HPAI) was maintained in wild bird populations.

In 2005, outbreaks involved large numbers of wild birds with subsequent spread of viruses to Europe and Africa probably by migratory birds.

Many types of AIV’s, only some highly pathogenic. Low pathogenicity types present in most birds. HPAIVs may kill large numbers of domestic birds and potentially humans.

Management: Monitoring and rapid response in destroying infected birds

Avian Influenza (Bird Flu)

What are these suffering from? They look healthy to me…

Could be suffering:

Brucellosis* Early malnutritionEarly chronic wasting diseaseLiver flukesLungwormTapeworm

Or a host of others! So not all animals, not all diseasesshow symptoms at all times

*See text for this

Ultimately a manager must determine the role disease plays in the system they are managing by answering several basic questions:

1. Is it an important, natural, density dependent factor (dashed line) or is it density independent (solid line)?

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Population Density

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If density dependent could indicate crowding or increased stress in small populations

2. Does it affect the overall population health in a positive way? (the tapeworm-moose-wolf interaction described in text)

Wolf MooseTapeworm forms cysts in lungsWorse the older the moose gets

Wolf feces with tapeworm eggs. Contaminate forage & water

Wolf eats moose, ingests

Result: Wolves prey more on older moose!

3. Is the disease an unnatural event due to human alteration of habitat, vectors,

population densities or other factors?

4. Does the disease threaten the health or viability of populations of special concern?

(e.g. Parvovirus and wolves, distemper and black-footed ferrets)