By Amanda Koch, MPH, Waterborne Diseases Epidemiologist and Rachel Klos, DVM, MPH, State Public Health Veterinarian, Wisconsin Department of Health Services
The season for algal blooms has begun, which means you and your clients might be seeing stagnant areas of lakes, rivers and ponds affected by high concentrations of cyanobacteria, popularly known as blue-green algae. Cyanobacteria are photosynthetic bacteria naturally found in surface water in Wisconsin and across the world.
When cyanobacteria grow to very high concentrations, they can create a localized accumulation, called a bloom. Blooms can take on different appearances depending on which species of cyanobacteria are present and their concentrations in the water. Some species of cyanobacteria produce cyanotoxins which can cause adverse health effects in humans and animals. Generally, the riskiest bloom conditions exist when cell concentrations are high, such as when the water looks like green pea soup or colorful spilled latex paint. Dogs can experience severe symptoms after ingesting water with elevated toxin concentrations because of their relatively small size and tendency to ingest more water than people.
Unfortunately, there are no pathognomonic signs or symptoms associated with cyanotoxin poisoning. Different cyanotoxins target different body systems but include hepatotoxins, nephrotoxins, neurotoxins and dermal toxins. For example, microcystin targets the liver while anatoxin-a targets the nervous system. Signs will vary according to toxins present, but can include diarrhea or vomiting, drooling or foaming at the mouth, or neurologic signs like muscle twitching. Collapse and sudden death can also occur. These signs, accompanied by exposure to a bloom, may be reason to consider cyanotoxin poisoning.
Steps your clients can take to prevent cyanotoxin poisoning include:
• Knowing what a bloom looks like and avoiding contact.
• Keeping pets and livestock away from water if they see signs of cyanobacteria.
• Immediately washing off an animal if it gets into water with a bloom.
• Calling their veterinarian if an animal becomes sick.
A veterinary reference card with additional clinical information can be downloaded from the Centers for Disease Control and Prevention’s website at
The Wisconsin Department of Health Services (DHS) Harmful Algal Blooms (HAB) Program has been collecting and investigating reports of cyanotoxin-related illnesses in humans and animals since the inception of the program in 2008. Reports of dog illnesses or deaths suspected to be due to cyanotoxin poisoning are investigated by state health officials.
Veterinarians who think they may have a case of cyanotoxin poisoning in a dog, or other animal, are urged to report the case to the DHS HAB Program. Reports can be made by:
• Calling 608-266-1120
• Completing the HAB Illness or Sighting Survey available online at https://www.dhs.wisconsin.gov/water/bg-algae/index.htm
Additional information about blue-green algae, pictures of blooms, information for veterinarians and a dog safety fact sheet for owners can be found on the HAB Program website. Go to https://www.dhs.wisconsin.gov/ and search algae.