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Basics ⬇

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BASICS

Definition!!navigator!!

  • Reported only in horses and donkeys
  • Classically thought to be caused by Trypanosoma equiperdum; however, the position with the trypanozoon group is uncertain, with overlap noted between this and Trypanosoma evansi and Trypanosoma brucei
  • Only a small number of laboratory strains of uncertain origin exist. No recent isolates have been obtained.
  • Venereal-only transmission
  • Tropism for genital mucosa; cannot survive outside host
  • Mortality high; debilitation; predisposition to other diseases

Pathophysiology!!navigator!!

  • Limited to venereal transmission; transmissible by direct contact
  • Requires no vector host; low numbers of organisms in peripheral blood make biting insect transmission unlikely

Systems Affected!!navigator!!

  • Gastrointestinal—weight loss; emaciation
  • Cardiovascular—intense anemia, dependent edema, and urticaria
  • Lymphatic—peripheral lymphadenopathy
  • Nervous—meningoencephalitis, progressive weakness, paresis, and paralysis
  • Musculoskeletal—progressive weakness
  • Reproductive—abortion
  • Ophthalmic—keratoconjunctivitis

Incidence/Prevalence!!navigator!!

  • Enzootic; endemic in Africa, Asia, Central and South America
  • Eradicated in North America
  • Low prevalence in parts of Europe

Signalment!!navigator!!

Breeding mares and stallions.

Signs!!navigator!!

  • Depends on strain and general health of the horse population
  • 3 disease phases recognized:
    • Genital—preputial and vulvar edema and tumefaction
    • Cutaneous—pathognomonic widespread raised cutaneous plaques (round, ovoid, irregular) 1–10 cm in diameter; trunk, neck, chest, shoulders. Edema of mammary gland, limbs, and ventrum also reported
    • Neurologic—neurologic compromise (hindquarter weakness; ataxia, hyperesthesia, and hyperalgia); lower lip droop; anemia of increasing severity during clinical course of disease (normochromic, macrocytic); emaciation, death
  • Approximately 50% of affected animals die of acute disease in 6–8 weeks

Females

  • Severe, edematous vulvar and perineal swelling
  • Mucopurulent vulvar discharge
  • Frequent, painful attempts at urination because of vaginal mucosal irritation
  • Chronic cases develop urticarial subcutaneous plaques in the vulva and surrounding tissues, as well as in the neck and ventral abdomen. These may regress within hours or days to areas of depigmentation
  • Abortion, if pregnant

Males

  • Edema of prepuce, urethral process, penis, testes, and scrotum
  • Paraphimosis may ensue
  • Purulent urethral discharge
  • Inguinal lymph node enlargement
  • Plaques and depigmented lesions, as in females

Causes!!navigator!!

  • Exposure to T. equiperdum
  • Infection occurs across intact genital mucosal barriers

Risk Factors!!navigator!!

  • Presence of asymptomatic carriers
  • The organism periodically may be unrecoverable from the urethra or vagina
  • Transmission is not certain, even from matings with animals known to be infected
  • Transport of horses from areas known to be infected
  • Urethral discharge from intact male
  • Males may serve as noninfected mechanical carriers after breeding of infected females

Diagnosis ⬆ ⬇

Outline

DIAGNOSIS

Differential Diagnosis!!navigator!!

  • Equine herpesvirus 3
  • Equine infectious anemia
  • Equine viral arteritis
  • Endometritis

CBC/Biochemistry/Urinalysis!!navigator!!

  • Acute infection—leukocytosis; other inflammatory changes
  • Chronic, debilitating infection results in anemia and extensive multisystemic disease

Other Laboratory Tests!!navigator!!

Cytology/Histopathology

  • Causative organism in smears of body fluid or lymph node aspirates may yield organism; appears as flagellated protozoan. Mount as a wet film, appears motile with flagellar movement
  • Seminal fluid, mucus from prepuce, and vaginal discharges
  • Histology, immunohistochemistry, IFA

Serology

  • PCR testing recently available. Species differentiation (T. equiperdum versus T. evansi) has been reported
  • CF test is the most widely used and only internationally recognized test; however, developed in 1915
  • Also available––agar gel immunodiffusion, IFA, and ELISA tests

Diagnostic Procedures!!navigator!!

  • Diagnosis complicated by inconsistent presence of characteristic lesions, low numbers of organisms, short-lived parasitemia
  • In the nervous form, the organism can be recovered from the lumbar and sacral spinal cord, sciatic and obturator nerves, and cerebrospinal fluid

Pathologic Findings!!navigator!!

Primarily emaciation with enlargement of lymph nodes, spleen, liver; periportal infiltrations in liver; and petechial hemorrhages in kidney.

Treatment ⬆ ⬇

Outline

TREATMENT

Appropriate Health Care!!navigator!!

  • International regulations impose slaughter of CF-positive horses
  • May be successful if treated early in the course of disease
  • Chronic cases in particular are unresponsive to treatment

Client Education!!navigator!!

Recovered treated animals may become asymptomatic carriers.

Medications ⬆ ⬇

Outline

MEDICATIONS

Drug(s) of Choice!!navigator!!

Quinapyramine sulfate—5 mg/kg divided doses SC.

Alternative Drugs!!navigator!!

  • Diminazene diaceturate—7 mg/kg as 5% solution injected SC; repeat at half-dose 24 h later
  • Suramin—10 mg/kg IV 2 or 3 times at weekly intervals
  • 4-Melaminophenylarsine dihydrochloride—0.25–0.5 mg/kg/day for up to 6 days

Follow-up ⬆ ⬇

Outline

FOLLOW-UP

Patient Monitoring!!navigator!!

  • Body weight and condition
  • CBC
  • Neurologic examination

Prevention/Avoidance!!navigator!!

  • Prohibit movement of horses from infected areas
  • Control breeding practices
  • Eradication–serologic testing with slaughter of infected animals
  • Consecutive negative tests at least 1 month apart indicate freedom from disease

Possible Complications!!navigator!!

Multisystemic nature of the disease predisposes to multisystem failure.

Expected Course and Prognosis!!navigator!!

  • Incubation period—1 week to 3 months
  • Approximately 50% of affected animals die of acute disease in 6–8 weeks
  • Course of disease—usually 1–2 months but may last for 2–4 years

Miscellaneous ⬆ ⬇

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MISCELLANEOUS

Pregnancy/Fertility/Breeding!!navigator!!

Abortion

Abbreviations!!navigator!!

  • CF = complement fixation
  • ELISA = enzyme-linked immunosorbent assay
  • IFA = immunofluorescent assay
  • PCR = polymerase chain reaction

Suggested Reading ⬆ ⬇

Barrowman PR. Observations on the transmission, immunology, clinical signs and chemotherapy of dourine (Trypanosoma equiperdum infection) in horses, with special reference to cerebrospinal fluid. Onderstepoort J Vet Res 1976;43:55–66.

Claes F, Buscher P, Touratier L, Goddeeris BM. Trypanosoma equiperdum—master of disguise or historical mistake? Trends Parasitol 2005;21:316–321.

Clausen PH, Chuluun S, Sodnomdarjaa R, et al. A field study to estimate the prevalence of Trypanosoma equiperdum in Mongolian horses. Vet Parasitol 2003;115:9–18.

Hagebock JM, Chieves L, Frerichs WM, Miller CD. Evaluation of agar gel immunodiffusion and indirect fluorescent antibody assays as supplemental tests for dourine in equids. Am J Vet Res 1993;54:1201–1208.

Hagos A, Goddeeris BM, Yilkal K, et al. Efficacy of Cymelarsan® and Diminasan® against Trypanosoma equiperdum infections in mice and horses. Vet Parasitol 2010;171:200–206.

Pascucci I, Di Provvido A, Cammà C, et al. Diagnosis of dourine in outbreaks in Italy. Vet Parasitol 2013;193:30–38.

Vulpiani MP, Carvelli A, Giansante D, et al. Reemergence of dourine in Italy: clinical cases in some positive horses. J Equine Vet Sci 2013;33:468–474.

Author(s) ⬆

Author: Peter R. Morresey

Consulting Editor: Carla L. Carleton