Protothecosis in Dogs

Protothecosis in Dogs - Symptoms, Causes, Diagnosis, Treatment, Recovery, Management, Cost

What are Protothecosis?

Protothecosis is a disease which, as noted above, can affect humans, dogs, cats and cattle.  It enters the body usually through injured skin, the gastrointestinal tract or the nose and begins to develop, spreading to other parts of the body of the host like the eyes, skin or kidneys.  

The most susceptible are the aged and sick hosts, having immune systems which are already challenged.  The disease is generally found to be fatal to the host.

Protothecosis is defined as a rather rare and uncommon disease which is caused by a type of algae, infecting humans, dogs, cats, and cattle but is not considered a zoonotic disease.

Symptoms of Protothecosis in Dogs

The most common symptoms of this rare disease are what you might suspect knowing that it tends to develop in the gastrointestinal system as well as a few you might not suspect:

  • Intermittent bloody diarrhea or black, tarry feces
  • Weight loss
  • Vomiting
  • Straining when defecating
  • If affecting the eyes, you‚Äôll see inflammation (redness in the ‚Äúwhite‚ÄĚ of the eye), pain and blindness - may be bilateral or unilateral
  • Neurological symptoms - Head tilt, loss of muscle control, lethargy, circling, gait problems, seizures, paralysis
  • Skin problems - Nodules, draining ulcers, thickening of outer layer of skin, lymph gland involvement, skin irritations which evolve into full fledged infections


There are two types of protothecosis in dogs:

  • Systemic - This form of protothecosis can spread virtually to any part of the body of the host, affecting various tissue types and major and vital organs
  • Cutaneous - This form is less common than the systemic form; it is the only form found in cats

Causes of Protothecosis in Dogs

The offending type of algae which can be found in sewage, animal waste and tree slime, can also be found in water and soil which have been contaminated by these substances.  The algae types which have been found responsible for protothecosis in dogs are Prototheca zopfii and Prototheca wickerhamii, and the disease has been found in these areas:

  • North America¬†
  • Europe
  • Asia
  • The Pacific Islands
  • Africa
  • Australia

Most of the cases found in the United States have been found in the Southeastern states in animals having a compromised immune system due to age or other systemic disease.  This is a fungal infection which can kill its host.

Diagnosis of Protothecosis in Dogs

The diagnostic process will involve you, your veterinary professional and a local laboratory.  Your vet will need a complete history from you which includes the symptoms you’ve noticed, the duration and the severity of those symptoms.  You will likely also need to provide the treating vet with a health history and vaccinations unless that information is available to him.  He will also most likely need dietary regimens with any changes made in it with the reasons for those changes, and lifestyle routine like where does your pet sleep, exercise and play.  

Because the symptoms of protothecosis in dogs are similar to many other GI and systemic maladies, the vet will need to rule out those other potential causes for your pet’s illness and clinical signs.  You should expect that he will do his physical examination and then order some blood testing, abdominal x-rays (if the symptoms are GI related) and collection of urine and fecal samples with the potential of scrapings from the rectal area of your pet.  These samples will be evaluated microscopically and cultures may also be ordered from them.

An eye examination will likely also be done since this disease is known to seriously affect the retinal tissues of the eye, causing retinal detachment, retinal pigment changes and blindness.  Spinal fluid and vitreous and aqueous samples (from the eyes) may be needed as well. Once the testing results are collected and analysed, an appropriate  treatment plan will be developed and initiated.

Treatment of Protothecosis in Dogs

If protothecosis is found, some sort of antifungal treatment will likely be needed in an attempt to rid your family pet of the fungal infection. Most animals who are found to be afflicted with protothecosis are in a very poor condition by the time veterinary medical attention is sought. The fungal infection is transported throughout the body by the bloodstream and it progresses at a fairly rapid rate, often with severe loss of muscular control being the most feared symptom.  The treatment options will include, as noted above, an antifungal treatment which has been found to work to slow the progression of the disease but will not cure it.  

A medication called Amphotericin can be given intravenously but there is significant potential for damage to the kidneys with this treatment. If this option is recommended for implementation, expect that your pet will be hospitalized and you should also expect that the treatment will be prolonged.  Sometimes antibiotic medications are administered along with the antifungals to deal with bacterial infections which are present as the disease progresses.

If the cutaneous form of protothecosis is found, the most frequent treatment recommended is the surgical removal of any skin lesions associated with the disease in addition to drug therapy.

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Recovery of Protothecosis in Dogs

Recovery from protothecosis is generally not a given.  This is a rare disease and, because it can progress with symptoms and clinical signs which are so similar to other canine diseases, it is often not found quickly enough to save the pet.  It is often recommended that one carefully consider the treatment options given by the veterinary professional and expect that any treatments recommended will be lengthy as there is no quick resolution to this fungal disease situation.  

The best outcome may be to slow the progression of the disease, allowing you and your family more time with your beloved canine family member.  Remember, in this health situation as well as everyday you have with your family pet, generous amounts of the three A’s: affection, affirmation and attention will be well received by your pet.

Protothecosis Questions and Advice from Veterinary Professionals


cocker mix






0 found this helpful


0 found this helpful

My dog has been diagnosed with this infection. After losing his sight and an enucleation the eye was biopsied and the infection found. There are no internist in my area willing to see me. I have been referred to a university. In the meantime, I have another dog in the house and am concerned about the impact on him. He shows no symptoms of illness. Is this infection communicable between family pets or humans?

Sept. 29, 2017

0 Recommendations

Protothecosis may infection dogs, humans, cats and cows but infections are rare and usually only occur in immunocompromised animals. There is little information about Protothecosis and treatment can be unrewarding from a medical management point of view; it would be best to consult with a University to help with treatment and overall management. Regards Dr Callum Turner DVM

Sept. 30, 2017

We had a dog that was diagnosed with this and passed over a year ago. It started as diarrhea but progressed to take his sight. By the time we identified it - he was in bad shape. We have another dog now and fear that the fungi is in the soil. Any advice as to treatment of the soil? Is it possible to identify the fungi by soil testing?

Dec. 14, 2017

Ken C.

I think my service dog has this.I think I do as well. We were sabatoged by my ex roommate/landlord with black mold, a 50 gallon fish tank that had not been cleaned and had severe swampy water and she had to go away to the vet for 2 weeks while I healed and moved. Her stool is very abnormal with long black hairs. Ideas? I'm on disability and HUD.

May 31, 2018

Cristen O.

I commented and there was much more going on there and he is a chemist.

May 31, 2018

Cristen O.

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