Top 6 Cervid Diseases

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Chronic wasting disease can have infection rates of 79% in captive deer herds.

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Nearly 80% of white-tailed deer are infected with the meningeal worm in endemic regions.

Zuku's Top 6 Cervid Conditions To Know For NAVLE® Success:

  1. Chronic wasting disease (CWD)

    Occurence of CWD in free-ranging animals as of March 2019

    Histopathology of an elk with CWD showing spongiform changes (arrows) in the medulla oblongata

    Location of the obex, the most useful specimen in testing for CWD

    • Classic case:
      • White-tailed deer, mule deer, elk, and moose
      • Due to the long incubation period, affected animals are over 16 mos of age
      • Weight loss
      • Behavioral changes: Somnolence, pacing, loss of fear of humans, hyperexcitability
      • Neurologic signs: Ataxia (especially pelvic limbs), head tremors, drooping ears
      • Polydipsia/polyuria
      • Aspiration pneumonia is common
    • Dx:
      • Etiology: Misfolded prion protein (PrPCWD)
      • Immunohistochemistry (preferred), ELISA (screening), or western blot at USDA-certified laboratories:
        • Retropharyngeal lymph node (especially in mule and white-tailed deer)
        • Obex
      • Surveillance:
        • Heads provided by hunters
        • Biopsies:
          • Tonsil
          • Retropharyngeal lymph node
          • Recto-anal mucosa-associated lymphoid tissue (RAMALT)
    • Rx:
      • No treatment
      • Control:
        • Voluntary National CWD Herd Certification Program:
          • Either by state or by herd owner
          • Fencing requirements
          • Individual animal identification
          • Testing of all animals that die after 12 mos of age
        • Surface disinfection:
          • 50% bleach for 30-60 min
          • 1 M sodium hydroxide for 60 min
        • Carcass disposal:
          • Incineration
          • Alkaline digestion
    • Pearls:
      • First case was seen in a mule deer from northern Colorado in 1967
      • Click here to see the distribution of CWD by species in free-range (Jan 2015) and farmed (Dec 2013) cervids
      • Horizontal transmission via ingestion of urine or feces on forage
      • REPORTABLE

  2. Parelaphostrongylus tenuis (meningeal worm)

    Elk (wapiti) are aberrant hosts of P. tenuis and are likely to show clinical signs

    Snails are intermediate host of P. tenuis

    • Classic case:
      • Usually asymptomatic in white-tailed deer
      • Aberrant cervid hosts are symptomatic (moose, mule deer, elk, or caribou)
      • CNS signs depend on area of CNS affected:
        • Lumbar weakness
        • Ataxia
        • Circling
        • Abnormal head positions
        • Paralysis
        • Slow movement
        • Less wary of humans
        • +/- Cortical blindness
      • May see a temporary remission
    • Dx:
      • Etiology: P. tenuis, a metastrongyle
      • Cerebrospinal fluid analysis (CSF):
        • Pleocytosis: May or may not be eosinophilic
        • Elevated protein
        • +/- Xanthochromia
      • Necropsy: See long, threadlike adult P. tenuis in subdural space in white-tailed deer; but are in CNS parenchyma of aberrant hosts
    • Rx:
      • Fenbendazole or ivermectin
    • Pearls:
      • Life cycle:
        • Adult worms lay eggs in white-tailed deer dura mater
        • Eggs hatch into L1 larvae and are carried to lungs
        • Larvae migrate up the bronchial tree and are swallowed
        • Larvae exit the deer in the mucous coating of the deer's fecal pellets
        • Snails and slugs feed on the mucous coating and become intermediate hosts where L2 and L3 larvae develop
        • White-tailed deer (or an aberrant host) ingest intermediate hosts (snails and slugs) or their slime secretions as they graze

  3. Hemorrhagic diseases (bluetongue and epizootic hemorrhagic disease)

    The biting midge (Culicoides spp.) is the most common vector of EHDV and bluetongue

    Bluetongue in a sheep

    Bluetongue viral particles in a cell visualized under transmission electron micrography (TEM)

    • Classic case: These 2 diseases are clinically inidistinguishable
      • White-tailed deer are most severely affected
      • Loss of fear of humans
      • Hypersalivation
      • Anorexia, lethargy
      • Marked head and neck edema
      • Bloody diarrhea
      • Fever
      • Tachycardia
      • Hyperpnea
      • Cyanosis, mucous membrane edema
      • Swelling and hyperemia of conjunctiva
      • Erosions and ulcerations of the oral cavity
      • Cyanosis
      • Death usually within 36 h or may follow a chronic course of several weeks
      • Dead deer due to epizootic hemorrhagic disease are often found in water, presumably an attempt to decrease their body temperature
      • Chronic disease signs:
        • Emaciation
        • Crawling on knees or chest due to sloughing of hoof wall
    • Dx:
      • Etiology:
        • Bluetongue: Bluetongue virus
        • Epizootic hemorrhagic disease: Epizootic hemorrhagic disease virus (EHDV), an Orbivirus closely related to, but genetically distinct from, the bluetongue virus
      • Viral identification: Blood, spleen, lymph nodes, lungs
        • Immunofluorescence
        • Sandwich ELISAs
        • RT-PCR
      • Serology: Paired serum samples 10-14 d apart
        • ELISAs (some may not distinguish from bluetongue from EHDV)
        • AGID (cannot distinguish EHDV from bluetongue virus)
      • Click here to see post-mortem images of EHDV from deer
    • Rx:
      • Supportive care only
      • Prevention:
        • Avoid swampy areas where biting midges are common
        • Insecticides or insect repellents
        • Stabling from dusk to dawn
        • Custom vaccines for EHDV and the bluetongue virus are now available for deer, however, there is little information on their efficacy
    • Pearls:
      • Insect vector is usually the biting midge (Culicoides spp.)
      • No evidence of zoonotic potential
      • Reportable in some states

  4. Tuberculosis

    Typical granulomatous tuberculosis lesions (in a wild boar)

    1000X of Ziehl Neelsen stained specimen showing Mycobacterium in pink

    • Classic case:
      • Abscessed lymph nodes, particularly the medial retropharyngeal lymph node
      • Lymphadenopathy
      • Emaciation
      • Respiratory distress
    • Dx:
    • Rx:
      • No treatment
      • Control:
        • Test and slaughter
        • Test and segregate
    • Pearls:
      • Deer typically have abscesses rather than the granulomas that are typical of tuberculosis in other species
      • ZOONOTIC

  5. Brucellosis
    • Classic case:
      • Moose:
        • Usually asymptomatic
        • Abortion in second half of gestation
        • Retained placenta
      • Elk:

        Bursitis in a caribou secondary to brucellosis

        • Usually asymptomatic
        • Abortion in second half of gestation
        • Retained placenta
        • Hygromas or bursitis
      • Caribou/reindeer:
    • Dx:
      • Etiology: B. suis , B. abortus , or B. melitensis
      • Plate agglutination test
      • Click here to see purulent exudate from the carpus of a caribou with a B. suis infection
    • Rx:
      • Antibiotics may be used but are not practical
      • Test and slaughter
      • Prevention:
        • Vaccination (strain RB51 "plus" and strain 82)
        • Negative Brucella test within 30 days before interstate transport
    • Pearls:
      • Wildlife are more likely to contract brucellosis from domesticated animals, rather than vice versa
      • In the US, brucellosis often occurs in elk and moose; less often in deer
      • Remember that horses can get brucellosis too, in the form of fistulous withers
      • ZOONOTIC

  6. Malignant catarrhal fever

    Sheep are endemic for OHV-2 and are a source of malignant catarrhal fever in cervids

    • Classic case:
      • White-tailed deer, mule deer, elk
      • Nearly 100% mortality; death usually occurs within 48 h with few clinical signs
      • Depression, weakness
      • Hemorrhagic diarrhea
      • Hematuria
      • Weight loss
      • Sloughing of hoof walls
      • Visual impairment due to corneal opacity
      • Alopecia with crusting, hyperkeratosis, and ulceration
      • Sudden death
      • +/- Neurologic signs (abnormal behavior, apathy, ataxia)
    • Dx:
      • Etiologies:
        • Ovine herpesvirus 2 (OHV-2)
        • Gammaherpesvirus of unknown origin closely related to both the alcelaphine herpesvirus 1 (AHV-1) of wildebeests and OHV-2 of sheep
      • ELISA or immunoblotting (may not pick up antibodies in the acute phase)
    • Rx:
      • No treatment
      • Prevention:
        • Do not farm deer or elk near sheep, sheep pastures, or lamb feedlots (at least 0.6 miles (1 km) away)
        • Be cautious of fomite transmission from sheep
    • Pearls:
      • AHV-1 and OHV-2 are nonpathogenic to wildebeests and sheep, respectively
      • OHV-2 is endemic in most sheep

Images courtesy of Michael Gäbler (Fallow deer), Joel C. Watts (CWD histopathology), CDC (CWD map), Mad Max (snail), US Fish and Wildlife Service/Jim Leupold (elk), Alan R. Walker (biting midge), Fourrure (bluetongue in a sheep), Livestock Industries, CSIRO (bluetongue TEM), David Risco/PLOS ONE (TB lesions in a wild boar), CDC/George P. Kubica (Mycobacterium microscopy), Wildlife Alaska (brucellosis in caribou), USDA (location of obex and sheep), Fry1989 (deer crossing sign), and Martin Falbisoner (red deer at top).