Blue-Green Algae

Pond with an algal bloom

Blue-green algae, or cyanobacterium, grows on the top of water.  If the nutrients are available and the temperature is warm, it can develop into a toxic algal bloom.  Add a little wind to push it all to one side of the water, and you have the perfect setup for a disaster.  Poisoning occurs when an animal drinks the affected water.  This can happen as a result of swimming in the water, ingesting some in the process.

Many species are susceptible, but simple stomached animals (dogs, cats, pigs, humans etc.) are less sensitive than ruminants (cattle, sheep, goats etc.).  Sensitivity also depends on the animal’s size and the amount of toxin it ingests.  Don’t let the fact that dogs are less susceptible than cattle fool you.  Many dogs have died from swimming in water with toxic algal blooms.

Microscopic image of blue-green algae

The toxins tend to fall into one of two groups.  Either they are neurotoxins (affecting the nervous system) or they are hepatotoxins (affecting the liver).  The neurotoxins cause a more rapid onset of clinical signs often within minutes of exposure, whereas the hepatotoxins typically take at least an hour before clinical signs appear.  Both are very dangerous.  Studies have found that animals can consume up to 90% of a lethal dose before they show any clinical signs.  As a result if clinical signs do appear there is a very good chance that without treatment the animal will die.

Affected animals may have muscle tremors, difficulty breathing, or diarrhea.  The most important piece of information necessary to diagnose this is the history of drinking or swimming in water with blue-green algae.

Prevention is clearly the key in blue-green algae poisoning.  If the only access animals have to water is a pond or lake that has algal blooms, the safest solution is to only allow access to the upwind side.  If you are lucky the wind will push enough of it to the other side that there will be no problems.  Don’t let dogs and other small animals swim in water during a bloom.  Avoidance is the best protection.