Canine protothecosis is a rare disease caused by Prototheca, a saprophytic achlorophyllus alga. Protothecosis occurs in Europe, Asia, Africa, Oceania, and in North America. The organism affects both humans and animals including dogs, cats and cattle. The organism is ubiquitous in nature and is commonly found in sewage, slime flux of trees and in animal wastes. Despite the abundance of this organism in nature, the incidence of disease is rare. Canine protothecosis is very difficult to treat and is often fatal.
The two species of Protetheca that are known to cause disease in animals are P. zopfii and P. wickerhamii. Protothecosis is an infection that occurs when the organism comes into contact with injured skin or mucosa. It is believed that those animals that have suppressed immune systems or are overwhelmed by a pre-existing disease are at greater risk of infection. Female dogs are more often affected than male dogs. Most cases of protothecosis in the United States are restricted to the Southeast.
Forms of Protothecosis
Protothecosis occurs in two forms: systemic (disseminated) infection and skin infection. The systemic form of protothecosis is most often caused by P. zopfii. Organs commonly infected include the eyes, kidney, liver, heart, large intestines, skeletal muscle, lymph nodes, thyroid, pancreas, and brain. Clinical signs depend on the organ systems involved and the severity of the lesions.
The most commonly reported clinical sign of disseminated protothecosis is intermittent bloody diarrhea. The colon is most often affected. Clinical signs such as neck pain, head tilt, depression, poor movement coordination, circling, and partial paralysis are seen in a large percentage of dogs with systemic protothecosis. Affected dogs generally have red, painful eyes and blindness. On examination, the pupil or cornea appeared cloudy.
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Skin infection is associated with infection by P. wickerhamii organism. This form of protothecosis is less commonly observed. Skin lesions consist of nodules and draining ulcers with crusty discharge on the limbs, trunk and mucosal surfaces. Crusting may be present as well as secondary bacterial infections.
Protothecosis is a difficult disease to treat. Amphotericin B, tetracycline, ketoconazole, itraconazole, fluconazole and clotrimazole have been used to attempt to treat this disease. Unfortunately, these drugs have shown little success in treating systemic protothecosis. Surgery is used to treat both systemic and skin forms of the disease.
- Disseminated Protothecosis in a dog (N07-610). Francesco C. Origgi DVM, PhD Dipl ACVM