Blue green algae poisoning is most often seen in western Canada during the hot summer months. The primary manifestation of poisoning in livestock and companion animals is sudden death. There is considerable year to year variation, making poisonings unpredictable. The composition of the algal bloom may include many species of blue green algae such as Dolichospermum (formerly Anabena) and Microcystis. Other species of blue green algae may also be present in the water. In the past, about 75% of the positive tests in PDS have been associated with Dolichospermum algae. The remaining cases have confirmed positive for Microcystis. Prairie Diagnostic Services has been testing water samples for both algal species using sensitive semi-quantitative test strips. This technology may be expanded to include chromatographic methods in the future.
Numerous factors contribute to growth of harmful algal blooms. Hot weather (>20DC), nutrient input (industrial and agricultural run-off, including manure), and stagnant water bodies (such as dugouts and ditches) can contribute. The growth of algae is very dynamic. Toxic algae are also in competition with non-toxic green algae. Toxin production by harmful algal blooms is also unpredictable and can vary substantially. The presence of toxic algae is not sufficient to confirm poisoning since the blue green algae only produce the toxins under certain conditions. To confirm a case of poisoning water samples can be collected and submitted for analysis. The samples should be collected within 24 hours of death. Some of the blue green algae toxins are not stable and disappear rapidly from the water. It is advised to freeze the water before submission to prevent breakdown of the toxin. Submission of about 100 mL of water is sufficient for testing.
In most instances, the toxins cause nervous system stimulation and sudden death with few pathological changes. In the hot sun, rapid decomposition limits further compromises investigation. The Microcystins also cause liver damage which may be evident in the dead animal. Other disease such as anthrax, lead poisoning, nitrate poisoning and insecticide poisoning are also associated with sudden death and should be considered as possible causes. Once the water has been deemed toxic, drinking the water should be avoided. It has been suggested that access to water sources with algal blooms be restricted for up to 2 weeks depending upon temperature and environmental factors. Re-testing the water after 1-2 weeks should be considered.
If you require further information, you may contact Dr. Vanessa Cowan, Veterinary Toxicologist, by email at vanessa.cowan@usask.ca