Blue-green algae poisoning in dogs: symptoms and immediate help

Overview

Despite their name, blue-green algae are bacteria: specifically, cyanobacteria. They occur naturally in bodies of water. Rapid growth can form a bloom on the water's surface. Not all blue-green algae produce toxins.

You cannot distinguish a toxic bloom from a non-toxic one by looking at it. Toxicity is confirmed by laboratory testing. Even clear surface water does not guarantee safety, because toxic mats may grow on the bottom. A dog can be exposed by eating these mats.

Deaths in dogs associated with blue-green algae poisoning have been reported. The severity of symptoms depends on factors including the type of toxin and the exposure. The same term therefore covers several different forms of poisoning.

Some blue-green algae suspended in the water can use gas vesicles to regulate their depth.

Causes

A dog may swallow toxins while drinking or swimming. Toxins can also reach the mouth when a dog licks their coat. Simply leaving the water therefore does not end exposure if algae remain on the coat. Skin exposure can also cause irritation.

Microcystins are common liver toxins. They can cause liver cell death and acute liver failure. Nodularins found in brackish water have similar effects on the liver. Microcystins travel from the digestive tract to the liver in the portal vein blood.

Anatoxins disrupt communication between the nervous system and muscles. This can cause continuous muscle stimulation and eventually paralysis of the breathing muscles. Guanitoxin inhibits the enzyme that breaks down acetylcholine. It can cause both muscle signs and excessive drooling and digestive symptoms.

Some toxins can also damage the kidneys. Toxins may be inside cells or free in the water after cells break down. The disappearance of visible algae therefore does not necessarily remove the danger.

The same species of blue-green algae can produce more than one toxin. Even a toxin-producing strain does not produce toxins continuously. Toxic and non-toxic species may occur together in a bloom.

Microcystins inhibit enzymes that are important for the supporting structure of liver cells. Saxitoxins are nerve toxins that block sodium channels in nerve cells. Cylindrospermopsins can inhibit protein production within cells. The intestinal inflammation they cause may be followed by liver and kidney damage.

Risk factors

Warm, nutrient-rich water favours the growth of blue-green algae. Blooms typically form when the water temperature exceeds 15 °C and sunlight is abundant. Water above 20 °C is one factor that promotes blooms. However, temperature is not a test of whether a waterside area is safe.

In a northern European setting, large surface blooms are typically seen in July and August. Calm weather can allow blue-green algae cells to rise to the surface. Wind can carry the material towards a particular part of the shore. In strong winds, algae may mix into the water and become harder to see.

The risk is particularly associated with lakes, ponds and slow-moving water. However, blue-green algae can also grow in open water tanks and buckets. Poisoning is most common in warm seasons, but exposure is possible throughout the year.

Inputs of phosphorus and nitrogen promote blooms. Blue-green algae also occur in nutrient-rich marine waters. Species that use atmospheric nitrogen can multiply when there is enough phosphorus in the water. Large floating blooms in the Baltic Sea often consist of these species.

Cyanobacteria may also occur in crust-like deposits left on the shore after floodwater recedes.

Typical symptoms

Symptoms depend on which toxin the dog has encountered. Signs caused by nerve toxins can begin within minutes to hours. Signs caused by liver toxins may appear after about 1–2 hours or later. Possible signs include:

• Vomiting or diarrhoea.
• Excessive drooling.
• Abdominal tenderness or loss of appetite.
• Weakness, unsteadiness or collapse.
• Muscle twitching, tremors or stiffness.
• Difficulty breathing or paralysis.
• Seizures.

Liver damage may cause pale mucous membranes, followed later by jaundice or dark urine. Bleeding may develop as the condition progresses. A rash or hives may appear on the skin. In some dogs, symptoms progress extremely quickly to respiratory arrest.

Liver poisoning may also cause loss of appetite and marked lethargy.

Complications and consequences

Extensive liver cell damage can cause circulatory shock. A clotting disorder can lead to widespread bleeding. Nerve toxins can stop breathing within minutes. A dog's condition may therefore deteriorate even during the journey to the practice.

The outlook is serious, particularly for a dog with severe symptoms. However, some dogs survive with intensive care. A dog that survives liver poisoning may be left with chronic liver disease. Recovery from some forms of nerve toxin poisoning may be complete. The outcome cannot be predicted simply from the colour of water containing blue-green algae.

Liver poisoning may also involve damage to the kidney tubules. Prolonged or repeated exposure can also cause chronic harm.

Diagnosis at the vet

As well as assessing symptoms, the vet asks when the dog swam, drank or had other contact with water. An initial diagnosis is based on the exposure history and compatible symptoms. Blue-green staining may be visible on the coat. The possibility of toxic mats on the bottom is considered even if there was no surface bloom.

Blood tests look for signs of organ damage. ALT and alkaline phosphatase (ALP) may rise with liver damage. Bilirubin may also rise. Blood sugar may fall. Potassium and phosphorus levels may increase.

Blood clotting is tested when necessary if there is liver damage. Clotting times may be prolonged. Protein may be present in the urine. Blood albumin may fall at a later stage.

With anatoxin poisoning, routine blood tests and blood counts may show no characteristic changes. Normal basic tests therefore do not replace establishing the exposure history. Low blood acetylcholinesterase activity may support a diagnosis of guanitoxin poisoning.

Water can be tested for blue-green algae toxins to support the diagnosis. Identifying cyanobacteria under a microscope does not by itself show that toxins were present in the water. Specialist laboratories can measure individual toxins. Toxins can also be sought in suitable samples from the animal, such as urine or stomach contents.

Antibody-based ELISA tests are available for some toxins, such as microcystin and anatoxin. Specialist methods can also identify nodularin and saxitoxins. The choice of sample depends on the suspected toxin.

Treatment

The vet prescribes treatment and medication. There is no universal antidote that counteracts all blue-green algae toxins. Treatment focuses on ending exposure and supporting vital functions. Rinsing with clean water removes algae from the coat and reduces further exposure through licking.

Early treatment in a dog that is well may include emptying the stomach. Inducing vomiting or carrying out other decontamination procedures may be unsafe in a critically ill dog. Owners should not try to induce vomiting or start medication at home on their own initiative.

Intravenous fluids support the circulation. Oxygen is given if breathing is difficult. Paralysis of the breathing muscles may require mechanical ventilation. Seizures and muscle tremors are treated with suitable medication.

Glucose and electrolyte levels are corrected as needed. Severe bleeding or a clotting disorder may require blood or plasma products. Anti-sickness medicines and medicines to support liver function may also be used. Body temperature, fluid balance and electrolyte levels are monitored during treatment.

Activated charcoal may help with microcystin exposure, but colestyramine is considered a better option. Activated charcoal may have limited effectiveness against this group of toxins. The type of toxin therefore affects the choice of medication. Medicines such as atropine may be used cautiously for severe signs caused by guanitoxin.

Blood tests are monitored during treatment, which is adjusted according to the results and the dog's condition. The dog may need hospital care and continuous monitoring. After symptoms improve, follow-up focuses particularly on possible ongoing liver disease.

If necessary, the coat can also be washed with shampoo and rinsed with clean water. However, the urgency of treatment depends on the dog's condition, and washing at home does not replace veterinary help.

Prevention

Do not allow your dog to drink or swim in water containing, or suspected of containing, blue-green algae. Take clean drinking water on outings. Physically prevent access to risky water when necessary. Do not leave water standing for long periods in containers or pools in your garden.

Blue-green algae may look like greenish particles, thick soup or paint. Blue-green algae material generally cannot be lifted out with a stick in the way that filamentous algae can. However, a mat that has broken away from the bottom is an exception. Stay away from visible blooms even if the species is uncertain.

Boiling water containing blue-green algae does not remove harmful compounds. Do not use that water to wash your dog either. Toxins may remain in water for weeks after the cyanobacterial cells die. Treatment to control algae therefore does not automatically make the water safe. Remember other poisoning hazards for dogs too.

Blue-green algae may also appear as brown, red or pale material. The water may smell of decaying plant matter. However, the absence of a smell does not identify whether toxins are present.

If water is left standing in a glass, blue-green algae particles may rise to the surface. Conifer pollen can resemble blue-green algae. Pollen is generally yellow or yellowish-brown, rather than greenish. It is often also visible on jetties or tables. These observations help with identification but do not show that the water is free of toxins.

Important for dog owners

Tell the practice the name of the body of water, the location on the shore, the time of exposure and what your dog did in the water. Photograph the water and any material stuck to the coat if you can do so safely without delaying treatment. A photograph does not establish toxicity. Note when the first symptoms began and how they progressed. Keep other animals away from the same shore too.

Rinse the exposed coat with clean water and prevent licking during transport. Do not return to collect samples before arranging help for your dog. If a sample is needed, agree how to collect it with the practice. A suitable water sample should represent the water the dog actually swallowed and include material from the bloom. Check current warnings for the shore before your next outing.

Frequently asked questions

Can a dog be poisoned just by licking their coat?

Yes. A coat soaked in water containing blue-green algae can carry toxins into a dog's mouth when they lick it. Rinse the coat with clean water and contact a vet immediately. Do not wait at home for symptoms to develop. The toxin may affect the liver or nervous system.

Is clear water always safe?

No. Toxic cyanobacterial mats can grow on the bottom even when the water above is clear. The position of cyanobacterial cells in the water also varies. A dog with symptoms after water exposure needs examination even if you saw no green material at all on the surface.

Does boiling make water containing blue-green algae safe to drink?

No. Boiling does not break down the harmful compounds. Do not give the water to your dog to drink or use it to wash them. Toxins may remain in the water for weeks after cyanobacterial cells die. Use safe, clean water on outings and prevent access to a suspect shore.

How quickly do symptoms begin?

Signs caused by nerve toxins may begin within minutes or a few hours. Signs caused by liver toxins may appear after about 1–2 hours or later. The onset depends on the toxin and the exposure. If you suspect exposure, do not wait for this time window: contact a vet immediately.

Is there an antidote for blue-green algae poisoning?

There is no universal antidote that eliminates blue-green algae toxins. Treatment supports breathing, circulation and damaged organs, while reducing further exposure. Targeted medicines may be used for particular symptoms, but choosing them and assessing their safety is always the treating vet's responsibility.

Can a dog be left with permanent damage?

Yes. A dog that survives liver poisoning may be left with chronic liver disease. Recovery from some forms of nerve toxin poisoning may be complete. Follow-up tests and monitoring after discharge are arranged according to the organ damage and response to treatment, even if visible symptoms have improved.