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Information for Veterinarians

Dog drinking from lake

Pet Illnesses and Harmful Algal Blooms

The assortment of cyanotoxins released during Harmful Algal Blooms (HABs) can be dangerous to animals as well as humans. Algal blooms can be recognized by abnormal water coloring (blue, green, brown, yellow, orange and red) and the appearance of a foam, mats or scum floating in the water. Not all algal blooms are harmful, but it is not possible to tell if a bloom is harmful just by looking at it.  Since pet owners often allow their animals to drink from and swim in these water bodies, pets have an increased risk of cyanotoxin exposure. The different hepatotoxins, neurotoxins, and dermatoxins can lead to a wide range of symptoms that without veterinary attention may lead to serious illness or death. It is important to report any HAB-related illness to your local health district.

ODH has developed a quick reference poster for diagnosis and treatment of animals exposed to harmful algal blooms for veterinarians and a fact sheet on pet exposure to harmful algal blooms for pet owners.  A PDF of the poster can be found here and a PDF of the fact sheet here.

Reporting a HAB-related Animal Illness 

Report any suspected, probable, or confirmed cases to your local health district. Consult the comprehensive search tool to find the contact information for your district. https://odhgateway.odh.ohio.gov/lhdinformationsystem/Directory/GetMyLHD

After reporting to the local district, fill out the “Harmful Algal Bloom-related Animal Illness Report” found on this page. Once completed, submit document to the Ohio Department of Health Bureau of Environmental Health and Radiation Protection. Contact information is provided below:

Ohio Department of Health
Bureau of Environmental Health and Radiation Protection
246 N High St, Columbus, Ohio 43215
Phone: (614) 644-1390
Email: BEH@odh.ohio.gov

HAB Exposure Routes

Symptoms depend on the type of toxin and exposure route: dermal, ingestion or inhalation.  Pet exposure to cyanotoxins typically occurs after swimming or drinking from contaminated water. Other exposures occur when animals lick their fur after swimming or by eating the surface scum on the beach.  The severity of the illness depends on the amount of water and algal cells ingested, the animal’s body size, the amount of food in the animal’s stomach, and the sensitivity of the species and individual animal. 

Common cyanotoxins are listed in the table below:

Toxin Type
Microcystin Hepatotoxin
Cylindrospermopsin Hepatotoxin
Anatoxin-a Neurotoxin
Saxitoxin Neurotoxin
Lyngbyatoxin Dermatoxin

Clinical Features of HAB-Related Illness


Exposure Route

Onset Time

Likely Symptoms

Differential Diagnosis

Possible Laboratory or Other Findings



Minutes to days

Acute depression

Weakness & incoordination

Loss of appetite

Excessive drooling

Vomiting & diarrhea

Abdominal tenderness


Dark urine


Nonsteroidal anti-inflammatories



Sago/cycad palm

Metals: copper, zinc, iron

Xylitol (dogs only)


Other hepatotoxins

Elevated bile acids & liver enzymes




Prolonged clotting times

Presence of toxin in biological specimens collected from ill animals

Blue-green staining of fur or hair



Minutes to hours

Excessive drooling

Apprehension & anxiousness


Muscle twitching


Respiratory failure



Chlorinated hydrocarbon




Other neurotoxins

Presence of toxin in biological specimens collected from ill animals

Blue-green staining of fur or hair


Skin contact

Minutes to hours



Allergic reactions

Other dermal allergens

Blue-green staining of fur or hair

Treatment Options

There is no antidote when treating cyanotoxins, all medical care is supportive. The contaminated water source should be identified, and access to it removed. 

The common cyanotoxins have a steep dose-response curve, increasing recovery chance of affected animals1. Treatment approaches vary by toxin and animal. The following are general recommendations used to reduce symptoms and support recovery:

  • Induce vomiting.
    • If done within first two hours of ingestion, may minimize absorption of toxins.
  • Administer activated charcoal slurry1.
    • This will bind toxins in the gut to reduce absorption of toxins.
  • Monitor liver function.
  • Be aggressive with fluids and corticosteroids to support liver function and prevent shock4.
  • Neurological symptoms may require seizure control and ventilator support.
  • Oral Cholestyramine may be effective at treating microcystin poisoning in addition to supportive care2, but this treatment is considered experimental.
  • Bile acid transport blockers such as cyclosporin A, rifampin, and silymarin have effectively prevented hepatotoxicity when injected prior to microcystin dosing1.
  • Intravenous milk thistle (Silybum mariamum) application has demonstrated experimental success in general liver protection from hepatotoxins3.
  • Animals should have fur or other exposed areas cleaned and be removed from places of direct sunlight.​


  1. The Merck Veterinary Manual, “Overview of Algal Poisoning”: https://www.merckvetmanual.com/toxicology/algal-poisoning/overview-of-algal-poisoning
  2. Rankin KA, Alroy KA, Kudela RM, Oates SC, Murray MJ, Miller MA. Treatment of cyanobacterial (microcystin) toxicosis using oral cholestyramine: case report of a dog from Montana. Toxins (Basel). 2013; 5(6):1051-1063.
  3. Hackett ES, Twedt DC, Gustafson DL. Milk thistle and its derivative compounds: a review of opportunities for treatment of liver disease. Journal of Veterinary Internal Medicine. 2013; 27(1):10-16.
  4. Minnesota Department of Health, Harmful Algal Blooms and Pets https://www.health.state.mn.us/diseases/hab/animal.html

Testing for Cyanotoxins

Testing vomitus or stomach contents from affected animals are most valuable, but is not readily available in the state of Ohio.

The Ohio Department of Agriculture (ODA) can perform histopathology on sections of formalin-fixed liver, kidney and brain tissue to support a diagnosis. Contact ODA for specifics. For more information on histopathology for HAB associated illness contact ODA, ADDL (614) 728-6220 or at animal@agri.ohio.gov. 

Questions and Advice for Pet Owners

Use the following questions to help determine whether an animal has been exposed:  

  • Has your animal been exposed to an outdoor water body within 48 hours of symptom onset?
  • If known, what type of interaction did your pet have with the water source (ingestion of water, swimming, etc.)?
  • Was your pet bathed following exposure to the water body?
  • Did your pet ingest any health supplements that may contain blue-green algae derived ingredients?
  • Is your pet experiencing any of the symptoms described in the clinical features table shown above?


Use the Pet owners may inquire on how to reduce risk of exposure to HAB-associated illnesses:

  • app to track HAB advisories in Ohio. Access BeachGuard here.
  • Keep people, pets and livestock out of water with blooms. “When in doubt, keep them out.”
  • If your pets do enter the water, be sure to rinse them off with clean, fresh, HAB-free water so they do not lick algae off their fur or skin where toxins may be present.
  • Do not let your pet eat algae off the beach as toxins may be present.
  • Do not water lawns, gardens, or golf course with water from HAB-impacted lakes or ponds.
  • Follow posted water body closures announced by state agencies or local public health authorities. 


For additional information, refer to the "Harmful Algal Blooms: Information for Pet Owners" fact sheet found here (عربى中文DeutschEspañol).