*Steve Ensley is with the department of veterinary diagnostic and production animal medicine at Iowa State University.

BLUE-green algae are commonly found in lakes, ponds, rivers and streams during the summer and autumn. Blue-green algae, also known as cyanobacteria, are actually bacteria that originated billions of years ago.

Blue-green algae can form dense algal blooms that create mats on the water surface or tint the water a blue-green color. Blue-green algae blooms can develop following storms, when surface runoff containing phosphorus and nitrogen enters the water. Blooms can be especially large when storm events are followed by prolonged periods of hot temperatures.

Cyanotoxins are not produced all of the time, and there is no easy way to tell when blue-green algae are producing these toxins and when they are not.

Blue-green algae can pose health concerns to people, livestock, pets and wildlife because they can produce neurologic and liver toxins. During blue-green algae blooms, toxin concentrations can reach very high levels and can produce severe adverse reactions, including human and livestock fatalities if that water is consumed. Because it is difficult to predict toxicity from these algal blooms, it is best to not let animals consume water or swim in water that is "pea soup" green in color.

Blue-green algae may start forming slightly below the surface and may not be visible but are still as toxic. Dermatological issues have also been associated with cyanotoxin exposure.

Toxins

Blue-green algae can produce neurotoxins such as anatoxin, saxitoxin and beta-methylamino-L-alanine that are extremely toxic and can be fatal within a few minutes.

Occasionally, livestock are found dead next to water with blue-green algae blooms. Clinical signs of neurotoxicity are rapid onset of rigidity and muscle tremors, followed by paralysis, cyanosis and death. Poisoning with the neurotoxin does not result in gross or microscopic lesions.

Blue-green algae also can produce hepatotoxins, such as microcystins, nodularins and cylindrospermonsins, that are toxic but do not kill livestock as rapidly as neurotoxins. Clinical signs associated with hepatotoxins include gastrointestinal tract disturbances like abdominal pain and diarrhea. This is followed by weakness, lack of responsiveness and death. In the liver, destruction of hepatocytes occurs soon after ingestion.

Rapid necrosis of the liver cells often results in severe hemorrhaging into the liver, which can cause shock and death. If death due to shock does not occur, then death from liver failure often results within 24 hours. Secondary (hepatogenous) photo-sensitization can occur after ingestion. Upon gross examination, the liver often is enlarged, swollen and dark red. In some cases, there is significant edema around the gall bladder. There can be massive liver necrosis with severe intrahepatic hemorrhage.

Toxicosis due to neurotoxins or hepatotoxins is diagnosed based on history of exposure to blue-green algae, clinical signs, the presence of blue-green algae in the gastrointestinal tract and gross and histological liver lesions for hepatotoxins only. In cases of suspected blue-green algae poisoning, the algae should be collected from the suspected water source soon after the incident.

Water should be collected on the leeward side of the body of water sampled. One quart of water should be collected for toxin identification. An additional quart of water should be collected for identification of algae. Both samples should be refrigerated or kept on ice and transported to an analytical laboratory as soon as possible. Great care should be taken to ensure the safety of the collectors.

Avoidance

Various techniques have been used to reduce blue-green algae blooms in lakes and ponds. Installing an aeration or mixing device to create turbulence reduces the competitive advantage of blue-green algae by not allowing them to regulate their depth in the water column.

Reducing nutrient runoff into the water also will reduce the abundance of blue-green algae because they thrive in systems with high nutrient concentrations. Reducing nitrogen and phosphorus fertilizer applications and establishing vegetated buffer strips around the lake/pond or inflowing streams are two ways to minimize nutrient loading into the system.

Algaecides such as copper sulfate can be effective at mitigating algae blooms. However, they should be applied carefully as they can harm fish and wildlife and rupture algae cells, which can release lethal levels of toxins. Furthermore, copper can accumulate in the water or sediment and cause problems.

Barley straw extract also can be used to prevent the formation of blue-green algae blooms. In this treatment, barley straw is placed loosely in a mesh bag and suspended within the affected lake or pond. Barley straw should be applied before algal blooms develop because the compounds released by the straw are more effective in preventing algae growth than in killing the algae already present. The straw becomes active within a month and will continue to inhibit algae growth for up to six months.

Monitoring blue-green algal bloom development for the presence of toxigenic species is a way to provide an early warning for cyanotoxin risk. Traditional microscopic identification of these microorganisms, however, is time consuming and does not distinguish toxigenic strains from nontoxigenic strains and may not detect the presence of toxigenic cyanobacteria at a very early stage.

The Iowa State University Veterinary Diagnostic Laboratory has developed a polymerase chain reaction-based method that detects the presence of Microcystis spp. and allows for a rapid determination of the presence of toxigenic Microcystis in any water source. The new test is available now. Practitioners are encouraged to contact the Iowa State Veterinary Diagnostic laboratory for details on sampling and proper testing procedures.

The Bottom Line

Blue-green algae can pose health concerns to people, livestock, pets and wildlife because they can produce neurologic and liver toxins. During blue-green algae blooms, toxin concentrations can reach very high levels and can produce severe adverse reactions — including human and livestock fatalities — if that water is consumed.

Volume:88 Issue:09