Protothecosis in dogs is caused by a mutant form of green algae by the name Prototheca. This mutated green algae lacks chlorophyll and can therefore not survive on energy from the sun. Dogs with Protothecosis can develop uveitis and retinal detachment, and weight loss is common. The disease is usually disseminated (it spreads from its original point of entry to other parts of the dog’s body). Protothecosis is not only a problem for dogs; the Protothecaalgae can infest other animals as well, including cats, cattle and humans.

What is Prototheca?

Prototheca is the only identified infectious pathogen that is a plant. It is believed to be a mutant form of the algae Chlorella, which is a single-celled green algae with chlorophyll. Unlike Chlorella, Prototheca can not derive energy directly from the sun and must therefore feed on dead and decaying organic matter. Originally, researchers believed the algae to be a type of fungus.

Prototheca is found all over the world, typically in soil and sewage. A lot of dogs are exposed to Prototheca without developing any illness and why some dogs are more prone to Protothecosis is not fully understood. What we do know is that skin wounds increases the risk for the cutaneous versions of the disease in dogs. The disseminated form might be linked to a weakened immune system. Collies are more prone to Protothecosis than other breeds, and female dogs are more easily diseased than male dogs.
The two most common species of Prototheca, at least as far as science know today, are Prototheca wickerhami and Prototheca zopfii. Both species are capable of causing Protothecosis dogs, but Prototheca zopfii is rarely seen in humans suffering from Protothecosis.

Cutaneous and disseminated Protothecosis

There are two known forms of Protothecosis in dogs – disseminated Protothecosis and cutaneous Protothecosis. Cats never develop disseminated Protothecosis; only cutaneous Protothecosis. Cutaneous Protothecosis is limited to the skin; normally as a result of the algae having entered the dog’s body through a skin wound. Symptoms of cutaneous Protothecosis in dogs are soft lumps that form on the skin of the feet, legs, head, nose and ears. Humans can develop both types of Protothecosis, but the disseminated form is normally only seen in patients with a weakened immune system.

Protothecosis symptoms in dogs

Disseminated protothecosis is most commonly seen in dogs, not in cats. The Prototheca algae typically enter the body of the dog via the mouth or nose, and will proceed to the intestines where they will cause infection. From the intestines of the dog, the disease can spread to kidneys, eyes and brain. A dog suffering from protothecosis can suffer from diarrhoea, weight loss, ataxia, retinal detachment, uveitis (eye inflammation), and seizures. The blindness can be acute. The vet can make a definite protothecosis diagnoses for your dog through culture or biopsy, or by testing urine or cerebrospinal fluid.

Protothecosis treatment for dogs

Treating dogs with cutaneous protothecosis is guarded, while the prognosis is much worse for dogs with the disseminated form of protothecosis. This might be partly due to the fact that disseminated protothecosis is hard to recognize and many vets do not realise that the dog is actually suffering from disseminated protothecosis during the first few examinations. This naturally delays treatment for many dogs. When disseminated protothecosis has been diagnosed in a dog, antifungal medication can be successful, but in many cases it will not be enough. When a dog suffers from cutaneous Protothecosis, surgery is usually necessary.