Overview 

Freshwater harmful algal blooms (HABs), also known as blue-green algae, are overgrowths of a type of bacteria called cyanobacteria. Cyanobacteria can produce numerous types of toxins, some of which are poisonous to animals. HABs are most commonly found in stagnant water sources such as lakes and ponds. Exposure to toxins produced by these bacteria can be life-threatening to dogs, humans, or other animals. There is no antidote for blue-green algae poisoning and it can be rapidly fatal. If you think your pet may have been exposed to a HAB, rinse their fur with fresh water, call a pet poison control hotline, and bring them to a veterinary hospital immediately

There is no way to tell the difference visually if a particular bloom is toxic or non-toxic. If you suspect that there may be a possible HAB, public health authorities should be alerted at your local or state health department.

Causes 

Blue-green algae poisoning occurs when dogs drink or swim in water contaminated by a harmful algal bloom. HABs are an overgrowth of cyanobacteria that can produce numerous types of toxins (cyanotoxins). The two most serious types of cyanotoxins, called microcystin and anatoxin, can cause liver or neurologic injury. Shock, liver failure, respiratory arrest, and even death can occur. 

Algal blooms can be found in warm weather, after periods of lack of rain, and in stagnant water. They may appear as either blue-green or red-brown colored blooms, mats, foam, or scum on the water. The water may also smell of rotting plant material. 

Clinical signs 

The clinical signs for cyanobacteria toxicosis will vary depending on the toxin. The two most dangerous toxins affect the nervous system and the liver. The clinical signs can develop rapidly or over several hours and may include any of the following:

• Vomiting 

• Diarrhea 

• Weakness 

• Pale gums 

• Collapse  

• Drooling 

• Muscle tremors 

• Difficulty breathing 

• Muscle rigidity  

• Paralysis 

• Seizures  

• Sudden death 

Diagnosis 

An initial diagnosis is made based on presenting clinical signs and a history of exposure to water that may have contained an algal bloom. Water may be tested for cyanobacteria toxins to confirm a diagnosis. Your veterinarian will recommend blood work to look for signs of organ injury. They may also test for blood clotting abnormalities if the liver is damaged.

Treatment 

Initiating treatment as early as possible after exposure to blue-green algae is critical. There is no specific antidote for cyanotoxins, and treatment is intensive supportive care for patients in shock or respiratory arrest. Treatments may include:

• IV fluids 

• Oxygen 

• Anti-seizure medication  

• Electrolytes and glucose  

• Blood products (e.g., whole blood or fresh frozen plasma) 

Additional treatments may include anti-nausea medications, antibiotics, liver supplements, muscle relaxants, and atropine. Your veterinarian will monitor blood work during treatment and adjust medications as necessary. 

Decontamination of patients exposed to blue-green algae may not be performed because the patients are usually in critical condition by the time they arrive at the hospital. If the patient is stable early after exposure, decontaminating may include bathing, inducing a patient to vomit, stomach pumping (gastric lavage), activated charcoal, or a medication called cholestyramine. Activated charcoal may not be as effective for microcystins (liver cyanotoxin).

Outcome 

Blue-green algae poisoning can be devastating. Many patients exposed to the liver or neuro cyanotoxins may not survive before arriving at a veterinary hospital. Patients often require intensive care and hospitalization with a poor prognosis. Treatment should be initiated as soon as possible to improve the chances of survival.  Even if a dog survives the initial exposure to liver cyanotoxins, they can suffer from chronic liver disease thereafter. 

Prevention 

• Avoid drinking from or walking and swimming in water that has visible algal blooms, scum, or foam on the surface or has an odor. 
• Check local advisories for warnings before visiting a particular body of water. 
• Remove stagnant water (plant containers, birdbaths, fountains, etc.) to prevent HAB growth around the home. 
• If you think your pet may have been exposed to a HAB, rinse their fur with fresh water and bring them to a veterinary hospital immediately