What is protothecosis?

Protothecosis is a rare infection caused by Prototheca, an achlorophyllous (colourless) algae. It can affect the skin, gastrointestinal tract, or nervous system, and requires veterinary testing to confirm the source and extent of infection.

What are the common symptoms of protothecosis?

Common symptoms include decreased appetite, vomiting, diarrhoea, weight loss, and lethargy. If the central nervous system is affected, unsteady gait or seizures may also occur.

What tests does the vet use to confirm the diagnosis?

The vet may arrange blood tests, imaging (X-ray, CT, or MRI), tissue biopsy, or pathogen culture and PCR to confirm the infection and identify the affected areas.

How should I care for my pet at home, and when should I return for a check-up?

Monitor your pet's appetite, water intake, and elimination at home. If symptoms persist or worsen, return to the clinic promptly. Follow your vet's recommendations for subsequent tests and follow-up visits.

How much do the tests and treatment usually cost?

Costs vary by clinic and region — ask your vet for an estimate before proceeding.

Disease Guide

Protothecosis in Dogs & Cats: Symptoms, Diagnosis & Care [2025]

A rare algal infection with poor prognosis and multi-organ involvement

Take 1 minute to check the symptoms first

Last updated: 2026/01/17

Pethealthmap Editorial Team

Sources: AVMA, ISFM, National Taiwan University Veterinary Hospital

When to See a Vet

Seek emergency care immediately

•Continuous seizures that do not stop on their own or loss of consciousness
•Sudden inability to walk or severe lameness with inability to stand
•Prolonged vomiting leading to obvious dehydration and weakness

Schedule a clinic visit soon (within 24–72 hours)

•Persistent loss of appetite for more than two days accompanied by lethargy
•Occasional vomiting or diarrhea but still eating
•Unsteady gait but still able to move short distances

01What Symptoms Indicate Something Is Wrong?

Protothecosis can cause both gastrointestinal and neurological abnormalities in dogs and cats. Symptoms are varied and can progress quickly, so close monitoring is essential.

Decreased appetite or sudden refusal to eat
Frequent vomiting or changes in the nature of vomit
Diarrhoea or changes in stool consistency and frequency
Weight loss or noticeably low energy
Seizures, epileptic-type episodes, or unsteady gait

Seek emergency care immediately if you notice the following symptoms:

⚠️ Continuous seizures that do not stop on their own or loss of responsiveness
⚠️ Sudden inability to walk or severe lameness preventing standing
⚠️ Prolonged vomiting causing obvious dehydration and weakness

02How to Assess Abnormal Signs at Home: Key Observations and Emergency Criteria

Observing and recording key information at home helps your vet quickly assess the condition and clarify the timeline of illness.

Note when symptoms first appeared and how long they have lasted
Track daily changes in food and water intake
Record videos of vomiting episodes or abnormal walking on your phone
Record the frequency, colour, and consistency of bowel movements
List all current medications and supplements

03How Will the Vet Diagnose the Condition? Common Diagnostic Tests

After arrival, the vet will perform a systematic examination and arrange blood tests, imaging, or specialist diagnostics as needed to identify the cause.

Full physical examination and neurological function assessment

Blood and biochemistry tests to assess infection and organ function

Imaging studies (X-ray, ultrasound, or CT/MRI)

Tissue biopsy to confirm the source of the lesion

Pathogen testing (culture or PCR) to identify the infectious agent

04How Is Protothecosis Treated? Medication, Diet, and Home Care Guide

Treatment depends on the severity and extent of infection, combining targeted therapy with supportive care, and requires regular follow-up to monitor response.

The vet will design a medication and supportive care plan based on test results
Maintain hydration and nutrition, adjusting diet as necessary
Schedule follow-up visits as directed to monitor symptoms and test results
Repeat blood tests or imaging if needed to assess improvement
Monitor temperature, appetite, and elimination at home for any worsening

05What to Prepare Before the Vet Visit: Key Information to Help Diagnose Quickly

Record the date symptoms started and daily changes

List all current medications, supplements, and dosages

Bring videos of vomiting, abnormal gait, and photos of stools to the appointment

Bring any previous relevant test results or imaging reports if available

Call ahead to book an appointment and arrange any specialist referrals or tests

This content is for reference only and cannot replace a professional veterinary diagnosis. If your pet shows signs of illness, please seek veterinary care promptly.