Corynebacterium pseudotuberculosis Infection of Horses and Cattle
(Pigeon breast, Pigeon fever, False strangles, Dry land distemper) |  |
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In horses,
C
pseudotuberculosis
causes
ulcerative lymphangitis (an infection of the lower limbs), chronic abscesses in the pectoral region, and contagious acne. It is one of the most common and economically important infectious diseases of horses in California and is increasing in prevalence in other dry, western states of the USA. In cattle, the bacteria causes ventral lymphadenitis, abscesses, and ulcerative dermatitis. Sporadic outbreaks have occurred in cattle in the western USA. Large, ulcerative skin
lesions and lymphangitis may occur in 2-5% of cows. Location on the animal is variable. Healing often occurs without treatment or with limited topical treatment. Abortion and mastitis may also occur. Rarely, visceral involvement has been reported. |
| Pathogenesis and Clinical Findings: |
| The onset of ulcerative lymphangitis in horses is slow and usually manifests by painful inflammation, nodules, and ulcers, especially in the region of the fetlock; occasionally, the edematous swelling can extend up the entire limb. The exudate is odorless, thick, greenish white, and blood tinged. Usually, only one leg is involved. Lesions and swelling progress slowly, and the condition can become chronic with relapses. |
| In the southwestern USA,
C
pseudotuberculosis
infection in horses is seasonal, with a peak incidence in late summer and fall. Infection results in abscessation of the lower pectoral region or ventral abdominal wall with secondary dissemination to internal organs. Clinical signs include diffuse or localized swellings, ventral pitting edema, ventral midline dermatitis, lameness, draining abscesses or tracts, fever, weight loss, and depression. Leukocytosis and neutrophilia may be present. A marked or prolonged fever
indicates untoward sequelae—chronic discharge, multiple or internal abscessation, or systemic infection with abortion. Abscesses can be large, up to 20 cm in diameter before rupturing, and take months to resolve. Weight loss, colic, or ataxia may be signs of internal abscesses. Dermatitis lesions are painful and mildly pruritic with alopecia, exudation, crusting, and ulceration. |
| The bacteria probably enter via skin wounds including IM injections, arthropod vectors such as
Habronema
spp
larva and stable flies, and contact with fomites such as contaminated tack and grooming equipment. Unhygienic and wet conditions predispose animals to infection, particularly of the lower legs and ventral region. However, the disease also occurs under excellent management conditions. |
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| Diagnosis: |
| Isolation of
C
pseudotuberculosis
from lesions is necessary for confirmation. In all forms of lymphangitis in horses, samples for culture include aspirates of abscesses, swabs of purulent exudate beneath crusts associated with folliculitis, and punch biopsies. Differential diagnoses include pyoderma, abscesses, lymphangitis from other bacteria (eg,
Staphylococcus
aureus
,
Rhodococcus
equi
,
Streptococcus
spp
, or
Dermatophilus
spp
), dermatophytosis, sporotrichosis, equine cryptococcosis, North American blastomycosis, and onchocerciasis. |
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| Treatment: |
| Lymphangitis and early abscess swellings are treated with hot packs, poultices, or hydrotherapy. Abscesses are lanced and flushed with iodine solution. Large abscesses require surgery. Skin lesions and grossly contaminated limbs are scrubbed daily with an iodophor shampoo. Penicillin or trimethoprim-sulfa combinations have been given; however, antimicrobial treatment may prolong the disease by delaying abscess maturation. Phenylbutazone relieves pain and swelling. General
supportive and nursing care is indicated. If treatment is successful, the swelling gradually recedes over days or weeks. Severe or untreated cases often become chronic, and fibrosis and induration of the leg occurs. An experimental bacterin-toxoid was not effective in field trials. |
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