Blue-green algae, or cyanobacteria, are bacteria capable of photosynthesis. They play a crucial role in the nitrogen cycle by converting atmospheric nitrogen into a form usable by plants and other organisms. However, under certain conditions, such as warm temperatures and high nutrient levels (phosphorus and nitrogen), cyanobacteria can proliferate rapidly, leading to harmful algal blooms. These blooms produce toxins known as cyanotoxins, which are harmful to livestock, aquatic life, pets, and humans. Agricultural runoff is often a critical source of nutrient pollution contributing to these blooms.
Clinical Signs:
- Pale mucous membranes
- Diarrhea
- Vomiting
- Weakness
- Death
Postmortem Findings:
- Icterus
- Liver damage (intrahepatic hemorrhage, acute diffuse hepatic necrosis)
- Renal tubular necrosis
Diagnosis of algal poisoning is often based on clinical signs, necropsy findings, and a history of exposure to contaminated water sources, such as ponds, lakes, reservoirs, or slow-moving streams.
The Texas A&M Veterinary Medical Diagnostic Laboratory (TVMDL) offers microscopic examination of water (Toxicology Evaluation – Test Code: 1068) to identify blue-green algae. In the summer of 2024, the laboratory saw numerous blue-green algae cases across Texas due to drought conditions and sporadic rainfalls. The lab helped clients identify potentially dangerous water sources by examining samples for blue-green algae before animals could consume the contaminated water. Unfortunately, in many cases, the confirmation came too late, with clinical and postmortem findings indicating exposure to cyanotoxins.
Preventing algal poisoning in animals involves monitoring and providing fresh, clean water. If a water source is contaminated, it is best to block animal access until the algal bloom is controlled or cleared. The safest remediation option is to replace or replenish the water with fresh, clean water from another source to dilute the algae and reduce the nutrient load. However, this is often not feasible. Another option is using herbicides, such as copper sulfate, which is effective and cost-efficient but must be used carefully to avoid copper toxicity in aquatic life and livestock. Long-term control of algal blooms requires minimizing nitrogen and phosphorus pollution.
References:
- Puschner B, Roegner A. Cyanobacteria (blue-green algae) toxins. In: Gupta R, ed. Veterinary Toxicology basic and Clinical Principles. 3rd ed. Waltham, MA: Elsevier Inc.; 2018:763-773.
- Sebbag L, Smee N, van der Merwe D, et al. Liver failure in a dog following suspected ingestion of blue-green algae (Microcystis spp.): a case report and review of the toxin. J Am Anim Hosp Assoc 2013;49:342-326.
