When it comes to most toxicities, most kill slowly. In other words, it takes several hours before clinical signs are seen and days before organ injury or multi-organ dysfunction is seen. Not so with blue-green algae toxicity in dogs (and other species).
Cyanobacteria (also known as blue-green algae) are microscopic bacteria found in freshwater lakes, streams, ponds and brackish water ecosystems. They can produce toxins (such as microcystins and anatoxins) that affect people, livestock and pets that swim in and drink from the algae-contaminated water. Blue-green algae grow and colonize to form “blooms” that give the water a blue-green appearance or a “pea soup” like color. It can also appear as blue or green “paint” on the surface of the water. Because the algae float, they may be blown by the wind into thick, concentrated mats near the shore, thus making them easily accessible to livestock, pets and people. Algal concentrations vary throughout the year, but are most abundant during periods of hot weather in mid- to late-summer months and are most likely to be found in nutrient-rich water. While most blue-green algae blooms do not produce toxins, it is not possible to determine the presence of toxins without testing.3 Thus, all blooms should be considered potentially toxic. Very small exposures, such a few mouthfuls of algae-contaminated water, may result in fatal poisoning.
Dogs that enjoy swimming and playing in lakes and ponds on hot summer days may be exposed to blue-green algae. Clinical signs of poisoning are dependent on the toxin involved. Microcystins can result in liver damage or failure.3 Signs of hepatic injury include vomiting, diarrhea, melena, weakness, pallor, icterus, seizures, hepatic encephalopathy, and shock. Death generally follows within days as a result of liver failure. Clinicopathologic blood testing often reveals normal to elevated liver enzymes, hypoalbuminemia, hypoglycemia, hypocholesterolemia, coagulopathy (e.g., prolonged prothrombin and partial thromboplastin blood levels), and a low BUN. Treatment includes aggressive IV fluid therapy, colloid administration (e.g., Hetastarch), antibiotic therapy, anti-emetics, dextrose supplementation, Vitamin K1 administration (if coagulopathic), hepatoprotectants (e.g., SAM-e), and plasma transfusions (if coagulopathic).
Anatoxins result in neurotoxicity evidenced by excessive secretions (e.g., salivation, lacrimation, etc.), neurologic signs (including muscle tremors, muscle rigidity, paralysis, etc.), and cyanosis (due to bronchosecretions).3 Anatoxins are a naturally-occurring, irreversible, acetylcholinesterase inhibitor and lead to increased acetylcholine concentrations in the synapses.3 Death follows within minutes to hours of exposure as a result of respiratory paralysis. Livestock that graze around affected ponds or lakes and are able to drink from them are often found dead near the water source. Treatment includes atropine, muscle relaxants, anticonvulsants (e.g., phenobarbital, benzodiazepine), oxygen therapy, and supportive and symptomatic care.
As the prognosis for a pet surviving a toxic exposure to blue-green algae is very poor once clinical signs have occurred, immediate veterinary intervention is needed. If the exposure was recent and the animal has no clinical signs, immediate decontamination (induction of emesis) is recommended. Stomach contents should be saved for possible analysis. Bathing is recommended for all animals with dermal exposures. Protective clothing should be worn by owners or veterinary staff that are exposed to poisoned animals (e.g., during the bathing process to remove the blue-green algae). Further care includes aggressive monitoring with symptomatic and supportive care of the critically ill patient. There is no antidote for the toxins produced by blue-green algae.
When in doubt, the ASPCA Animal Poison Control Center should be contacted for life saving care!