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Basics ⬇

Basics

Overview

  • Prototheca wickerhamii and P. zopfii-single-celled achlorophyllous blue-green algae (Chlorophyta) that can cause disease in warm-blooded animals.
  • Humans and cats-usually localized infection of the skin or gastrointestinal tract.
  • Dogs-usually colitis.

Systems Affected

  • Skin/Exocrine
  • Gastrointestinal
  • Nervous
  • Ophthalmic

Signalment

  • Dogs-young, female adult, medium- to large-breed dogs, boxer and collie are overrepresented.
  • Cats-uncommon, usually cutaneous form.

Signs

Historical Findings

Dogs

  • Intermittent and chronic large bowel diarrhea with fresh blood.
  • Chronic weight loss.
  • Acute onset blindness.
  • Neurologic disease; deafness, seizures, ataxia.
  • Cutaneous lesions.

Cats

Chronic cutaneous or mucous membrane ulceration with few systemic signs.

Physical Examination Findings

Dogs

  • Gastrointestinal, ocular, or neurologic disease most common.
  • Severe weight loss and debilitation.
  • Hemorrhagic colitis, vomiting, anorexia.
  • Blindness due to chorioretinitis and/or detached retinas.
  • CNS-depression, ataxia, vestibular signs, siezures and/or paresis.
  • Cutaneous-ulcers and crusts on the extremities and mucosal surfaces.

Cats

Large cutaneous nodules on the face or limbs.

Causes & Risk Factors

  • Dogs-usually P. zopfii; P. wickerhamii infection may also occur.
  • Cats-usually P. wickerhamii.
  • Basis for the pathogenicity of Prototheca sp. unknown, likely traumatic inoculation.
  • Organism-ecologic niche is raw and treated sewage; contaminants of water, soil, and food; occasionally isolated from fecal samples from healthy individuals.
  • Dogs and humans-depressed cell-mediated immunity may predispose to gastrointestinal and disseminated infections with P. zopfii.
  • Cats-no known predisposing factors.

Diagnosis ⬆ ⬇

Diagnosis

Differential Diagnosis

  • Systemic-histoplasmosis, blastomycosis, cryptococcosis, pythiosis.
  • Cutaneous-systemic and subcutaneous mycoses; mycobacterioses, neoplasia, L-form bacterial infection, actinomycosis.

CBC/Biochemistry/Urinalysis

  • Dogs-often normal; depends on organ system affected; organism occasionally seen in urine sediment.
  • Cats-almost always normal.

Other Laboratory Tests

CSF tap-pleocytosis with mononuclear cells; increased protein; organisms.

Diagnostic Procedures

Cytology

  • Definitive diagnostic test; gram's iodine solution.
  • Rectal or colonic mucosa, vitreous humor, CSF, cutaneous aspirations.
  • Organisms-unicellular, non-pigmented, oval or round cell walls often appear folded; diagnostic characteristic is endospore formation with internal septation in two planes.

Culture

  • Blood agar or Sabouraud's dextrose agar (without cycloheximide) at 25–37°C (77–97°F) white or creamy, smooth colonies within 48 hours.
  • Specific identification by selective agars or biochemical tests in culture (susceptibility to clotrimazole, sugar and alcohol assimilation tests) or immunohistochemistry.

Polymerase Chain Reaction (PCR) Assays

PCR and DNA to determine species; specimens can be taken from biopsies, CSF or urine.

Pathologic Findings

Dogs

  • Small granulomatous foci or hemorrhagic ulcers-found in many organs, especially kidneys; identification of organisms is diagnosed.
  • Nodular thickening of the gastrointestinal mucosa with ulceration.
  • Nonspecific inflammatory foci surrounding organisms or pyogranulomas-poorly organized; mixed with other inflammatory cells.

Cats

Cutaneous masses-localized; extend deep into subcutaneous tissues; consist of granulomatous inflammation and mixed-cell inflammation; made up primarily by organisms.

Treatment ⬆ ⬇

Treatment

Medications ⬆ ⬇

Medications

Drug(s)

  • Amphotericin B-use for localized disease after surgical excision; 0.25–0.5 mg/kg IV three times weekly or until a total dose of 8 mg/kg; lipid formulation 1 mg/kg every other day until 12 mg/kg cumulative; concurrent administration of tetracycline or amikacin may provide synergistic effect; lipid formulations may be more efficacious and less toxic for cutaneous disease; reported effective for ocular disease.
  • Ketoconazole, fluconazole, and itraconazole (5–10 mg/kg PO q12h)-may use with amphotericin B, or as sole agents for less life-threatening disease.
  • Alternative treatments-clotrimazole (locally for P. wickerhamii); potassium iodide.
  • Amphotericin B cream or clotrimazole enemas for colitis.

Follow-Up ⬆ ⬇

Follow-Up

Expected Course and Prognosis

  • Difficult to eradicate with drug therapy.
  • No definitive therapeutic protocol.
  • Dogs-prognosis guarded to grave (median survival 4 months).
  • Cats-prognosis fair to good for cutaneous disease if lesions completely excised.

Miscellaneous ⬆

Miscellaneous

Zoonotic Potential

None

Abbreviations

  • CNS = central nervous system
  • CSF = cerebrospinal fluid

Internet Resources

Author Mitchell D. Song

Consulting Editor Alexander H. Werner

Client Education Handout Available Online

Suggested Reading

Lane LV, Meinkoth JH, Bunker J, et al. Disseminated protothecosis diagnosed by evaluation of CSF in a dog. Vet Clin Pathol 2012, 41(1):147–152.

Mercuriali E, Bottero E, Abramo F, et al. Canine protothecosis in the North of Italy: 4 cases (2009–2011), 22nd ECVIM-CA Congress 2012.