Algal Exposure and Poisoning: Symptoms, Diagnosis, Treatment, and Prevention
Mon, April 19, 2021

Algal Exposure and Poisoning: Symptoms, Diagnosis, Treatment, and Prevention

 

 

As an acute condition, algal poisoning is often fatal caused by high concentrations of cyanobacteria or blue-green algae in drinking water and water used for aquaculture, agriculture, and recreation, said Wayne W. Carmichael, Ph.D., of MSD Veterinary Manual, a trusted source of animal health information. Acute cases of algal poisoning have been documented in humans, not only in animals.

Algal poisoning usually happens during warm seasons when harmful algae bloom rapidly and for a longer period of time. Most cases of poisoning occur when animals drink cyanobacteria-infested freshwater. Aquatic animals, particularly maricultured fish and shrimp are also affected. 

 

Canine Cyanotoxin Poisonings In the US from the 1920s to 2012 (2013)

Lorraine C. Backer and colleagues of biomedical and life sciences journal PMC identified 231 discreet cyanobacteria harmful algal bloom (cyanoHAB) events and 368 cases of cyanotoxin poisoning associated with dogs across the US between the late 1920s and 2012. The authors said that the cyanotoxin poisoning events analyzed in the study were likely to represent a small fraction of cases that occur all over the US every year.

Between 2007 and 2011, Departments of Health and/or Environment from 13 states documented 67 suspected or confirmed cases of canine intoxications associated with HABs. Of these, 87% followed exposure to fresh waters and 1% followed exposure to marine waters. For the remaining nine cases (13%), the exposure source was unknown. Among the cases, exposure was reported as inhalation (13%), ingestion (9%), dermal contact plus ingestion (i.e., swimming, with accompanying ingestion of algae/toxins from swallowing water and/or licking algae off fur) (54%), and unknown (24%).

43% of dogs suffered from gastrointestinal symptoms, including vomiting and diarrhea. Other symptoms included lethargy, which was present in 18% of dogs, and neurological signs (ex: stumbling or change in behavior) (9%). 58% of the canine intoxications were fatal. Of these, 32% were correlated with anatoxin poisoning, 8% to microcystin poisoning, and 13% to exposure to an unspecified cyanotoxin.

Media reports, state and federal agency reports, and published scientific and medical literature between the late 1920s and August 2012 described 115 cyanoHAB-related events. This involved 260 dogs; 83% of the canines died and 17% became ill and then recovered. After identifying 115 poisoning events, Backer and colleagues found that 102 cases were fatal. 39 were associated with the exposure to a specific cyanobacterial species or genus, to mixed genera or toxins, or to a specific cyanotoxin. Among these, 22 fatal poisoning events (58%) involving 76 canines were associated with Anabaena spp. and/or anatoxin-a or anatoxin-a(s).

 

 

10 events (26%) involving 14 dogs were linked to exposure to Microcystis, Anabaena and/or microcystins. Six events (16%) involving eight dogs were correlated to exposure to mixed blooms of Anabaena, Aphanizomenon, and Microcystis and anatoxins/microcystins. One event was linked Lyngbya (possibly L. wollei ) and the neurotoxin neosaxitoxin. There were 30-non fatal poisoning that affected 45 dogs, with 16 events accompanying fatal events. Of the non-fatal events, 17% were associated with the exposure to Anabaena spp. or anatoxin. 3 were linked to mixed blooms of Anabaena, Aphanizomenon, and Microcystis and anatoxins/microcystin, and  1 event was connected to Lyngbya,.

No events were linked to exposure to Microcystis spp. or microcystins. Among the non-fatal cases associated with cyanotoxicosis, 75% co-occurred with fatal cases.  Cyanobacteria/blue-green algae exposure was observed in 12 events (43%) involving 16 dogs. To increase awareness and reporting, including the response to HAB-related events, action plans can include the creation of national maps of historical and current cyanoHAB events and the acquisition of more information about the exposure and clinical aspects of these poisonings to ensure a swift diagnosis and treatment.

 

 

Symptoms of Algal Poisoning

Blue-green algae can produce the toxins microcystins and anatoxins, explained Lynn Buzhardt, DVM, of VCA, an operator of over 1,000 animal hospitals in the US and Canada. Symptoms may depend on which toxin is involved. For example, microcystins affect the liver, leading to organ failure. When the liver is damaged, it cannot filter toxins and metabolic by-products from your dog’s body. Therefore, it can cause toxins to build up, and these toxins cause neurologic signs like disorientation and seizures.

Meanwhile, anatoxins harm the nervous system. Signs manifest within 30 to 60 minutes of exposure. develops overactive secretions leading to drooling and tears. Muscle tremors also occur. Some muscles become rigid while others become paralyzed. When your pet is exposed to anatoxins, death may occur within minutes or hours after being exposed.

 

 

Diagnosis and Treatment for Blue-Green Algae Exposure

There is no antidote for the toxins, said Patricia Wuest of Today’s Veterinary Nurse, the NAVC’s (North American Veterinary Community) official journal. For affected dogs, the prognosis is poor. Hence, aggressive and immediate treatment is needed to ensure your dog’s safety. In some cases, euthanasia is the only option.

Therapy may include intravenous fluids and plasma to replenish electrolytes, regulate blood glucose, support organ function, and prevent shock. Muscle relaxers may also be helpful for patients with muscle tremors. Atropine may aid in the reduction of excess salivation and tearing. Nutraceuticals may aid in supporting a patient’s waning liver function. It can take weeks or months for your dog to recover from algae poisoning. If your dog recovers from cyanobacteria, it will usually suffer from lingering liver damage and other health complications. However, with the help of your veterinarian’s team, your dog can have a good quality of life.

 

 

Preventing Dogs From Blue-Green Algae

ASPCA (American Society for the Prevention of Cruelty to Animals), a non-profit organization dedicated to preventing animal cruelty, said that prevention is key to avoid any complications associated cyanotoxins and any pet toxin. Don’t let your dog drink from stagnant ponds, lakes, or other bodies of water if you see bluish-green hues on the surface or around the edges. Blue-green algae can also stick to your dog’s fur and can be ingested when they groom themselves. Exercise caution before letting your dog swim in a body of water. Then, rinse your dog thoroughly with fresh water. Many public health departments conduct water tests in areas that are susceptible to outbreaks. Check with your local health department if they have posted any news of blue-green algae breakouts.


Blue-green algae are harmful as they produce the toxins microcystins and anatoxins. The prognosis is poor, so consult your veterinarian immediately if your dog is exposed to or comes into contact with cyanobacteria-infested water.