By | 2011-08-04

Prototheca zopfii and Prototheca wickerhatnii

Algae: Cause

Three species have been recognized within the genus Prototheca: P. stagnosa, P. wickerhatnii, and P. zopfii; a fourth species, P. salmonis, has been proposed. Of these three species, P. wickerhatnii and P. zopfii have demonstrated pathogenicity. Prototheca spp. are ubiquitous in nature and are found in sewage systems, soil, lakes, rivers, ponds, and in feces. The organism has been documented to cause disease in dogs and cats and a variety of other species. P. wickerhamii is the causative organism in virtually all instances of cutaneous protothecosis, and P. zopfii is the causative organism in most instances of disseminated disease.

Algae: Pathophysiology

Cutaneous infection with granuloma formation is the most common manifestation of protothecosis in most species, including cats and humans. Dissemination does not readily occur in cats or humans, but the infection readily disseminates to distant sites in dogs.

Clinical examination

Of the 26 canine cases reported in the veterinary literature, 20 either had ocular signs on presentation or developed them later. Sixteen cases had gastrointestinal signs, usually colitis-type diarrhea, vomiting, and weight loss. Six cases had neurologic signs in the form of paresis, head tilt, cervical pain, circling, and ataxia. P. zopfii accounts for most of the cases of canine disseminated protothecosis.

Diagnosis of Algae

Contrast radiography or abdominal ultra-sonography may reveal diffuse colonic wall thickening or obstruction, but these are nonspecific findings. Fecal parasitologic examination is generally of little use in demonstrating the organism, but exfoliative cytology, histology, or both readily identifies the organism. Aqueous or vitreous centesis can also be performed in dogs with ocular pathology and is generally useful in documenting organisms in the ocular fluid.

Treatment of Algae

The management of systemic protothecosis has been challenging in all animal species. Amphotericin B and itraconazole (5 mg / kg orally, twice a day for 1 month and then 5 mg / kg orally, once a day thereafter) have been used in several patients. Short-term improvement was reported in orjly two dogs.


Like pythiosis, the prognosis for protothecosis is grave. The course of the disease is so insidious that, by the time a definitive diagnosis has been reached, the organism has often disseminated throughout the body.