Harmful algal blooms can be deadly to animals, people

Harmful algal blooms (HABs) are a growing concern in Ohio. From Lake Erie to the Ohio River, HABs are becoming commonplace in many streams, lakes and ponds. Besides being unsightly and sometimes odorous, HABs can produce toxins that can kill animals.

HABs include toxin-producing blue-green algae which are actually photosynthesizing bacteria (gram negative, photoautotrophic prokaryotes), called cyanobacteria. These organisms may produce a number of types of “algal” toxins that can cause skin irritation, illness or even death to pets, livestock and people.

Numerous dog and livestock illnesses and deaths from exposure to HABs have been reported in the U.S. and around the world. As researchers stressed in their March 2003 report to the U.S. House Science Committee’s Subcommittee on Environment, Technology and Standards, the past 30 years has revealed a substantial increase in the rate of occurrence and the duration of harmful algal blooms.1 There have been reports from 50 countries, including at least 27 states in the U.S. of human and animal illnesses linked to algal toxins.

Cyanobacteria Blooms

Cyanobacteria are present in most surface waters including lakes and streams. Excessive growth (blooms) of these organisms can occur any time of the year when an abundance of nutrients (phosphorus and nitrogen) are present in the water. Cyanobacteria blooms increase the possibility of toxin production that may cause illnesses in people and animals.

It is generally thought that most blooms occur in stagnant water in the late summer and early fall when water temperatures are high. However, there are many reports of cyanobacteria blooms developing in the early spring and in slow moving waters, such as the Ohio River. In fact, some species bloom under ice, providing there is sufficient sunlight transmitted through the ice.

HAB Appearance

It is not possible to visually distinguish a toxic cyanobacteria bloom (HAB) from a non-toxic cyanobacteria bloom. Water samples need to be analyzed to determine if the bloom is toxic. An Enzyme-Linked Immuno Sorbent Assay (ELISA) and sonication are used to determine total toxin concentration of some common algal toxins, such as microcystin, a hepatotoxin.

A bloom of cyanobacteria can have many appearances. These organisms can distribute throughout the water or appear as foam or surface scums. Scum color varies and includes white, brown, purple, blue-green and black.. Some scums may appear to be green paint spills, green colonial formations or dots in the water. Some species such as Planktothrix do not generally form a scum, but distribute through the water column giving the water a blue-green or brown appearance. Some algae blooms have a foul or musty odor and others do not.

HAB Toxins

Not all cyanobacteria produce toxins. However HAB blooms can produce single or multiple toxins that include hepatotoxins, neurotoxins and dermatoxins.
See (page 10) Table 7.5-1 http://water.usgs.gov/owq/FieldManual/Chapter7/7.5.pdf listing some cyanobacteria species and the toxins they may produce. Toxins are tasteless, colorless and odorless. Scums usually have higher toxin concentrations.

Some common species that may produce neurotoxins, hepatotoxins AND dermatoxins are Anabaena, Aphanizomenon, Cylindrospermopsis, Lyngbya (Plectonema) Microcystis, and Oscillatoria (Planktothrix).

Those cyanobacteria that can produce toxins do not consistently do so and it is difficult to predict when these organisms will produce toxins at the level that may cause illness. Toxins are usually released gradually to the water during natural cell death or quickly when algaecides are applied to a HAB bloom. When blooms die off and the water looks clear, toxins persist until they are broken down by sunlight or by other bacteria.

Animal Illnesses

Animals are not hesitant about swimming in or ingesting water with algal blooms. They are exposed to HAB toxins by primary contact resulting in skin irritation, and most importantly by ingesting HAB infested waters; eating cyanobacteria on the beach; or licking algae off fur when self grooming after swimming. And since dogs have a smaller body mass, they are likely to experience more adverse illness and even death at lower algal toxin levels.

According to Dr. Michael Carlson, diagnostic toxicologist with the UNL Veterinary Diagnostic Center at the University of Nebraska, hepatotoxins such as microcystin can cause lethargy, vomiting, diarrhea, weakness, pale mucous membranes and death. Animals suffering from the neurotoxin, anatoxin-a poisoning can experience muscle tremors, rigidity, lethargy, respiratory distress, convulsions and death. Victims of the neurotoxin anatoxin-a(s) poisoning can experience salivation, urination, lacrimation, defecation, tremors, dyspnea and convulsions and death.

Dr. Carlson emphasizes that time can be critical because some exposures to HABs can produce life-threatening illnesses within a half-hour of ingestion, while other exposure may take several hours to days. Time for illness expression is dependent upon the dose of toxin ingested, but other factors are also involved.

In September, 1976, four dogs reportedly died after ingesting water from Long Lake near Spokane, during an Anabaena bloom. And then in 1982, two hunting dogs died after exposure to a cyanobacterial bloom in Moses Lake. In 1989, five cats died after exposure to a cyanobacterial bloom west of the Cascade Mountains. And in 2007, two dogs and two hunting dogs died after exposure to a cyanbacterial bloom in Potholes Reservoir, Washington. 3

Other states such as Minnesota, Nebraska, Oregon, Vermont, and Missouri have reported dog deaths from exposure to algal toxins.

—Linda Merchant-Masonbrink, Ohio EPA HAB Coordinator

Clinical Findings, Diagnosis, and Treatment:
See the Merck Veterinary Manual 2008 online at :

Use these resources to make your clients aware of the prevalence of HABs, how to identify and avoid them, and what to do if a pet is exposed:

Pets & Algae Poster

HAB Informational Brochure

Michael P. Carlson, PhD
Diagnostic Toxicologist/Analytical Chemist
Lincoln, NE
(402) 472-8459 (office)
(402) 472-8448 (lab)

Ronald C. Reupert, DVM
Animal Health Care Center North
Rhinelander, WI
(715) 365-8387

Report Blooms
• Ohio EPA HAB Coordinator
(614) 644-2001

Report Illnesses From HABs (After ImmediateTreatment)
For Animal:
• State Veterinarian (614) 728-6220 or (800) 300-9755
For Human:
• Ohio Department of Health, Bureau of Environmental Health (614) 466-1390

References Cited:

2USGS: Guidelines for Design and Sampling for cyanobacterial Toxin and Taste-and-Odor Studies in Lakes and Reservoirs. Jennifer L. Graham, Keith A. Loftin, Andrew C. Ziegler, and Michael T. Meyer. 2008

3 Washington State Department of Health, Division of Environmental Health, Office of Environmental Health, Safety and Toxicologyhttp://www.doh.wa.gov/ehp/algae/faqs.htm#Should_pets_or_livestock_drink_or_swim_in_water_containing_algal_blooms

Additional References:
Backer, L.C. 2002. Cyanobacterial harmful algal blooms (cyanoHABs): Developing a public health response. Lake and Reservoir Management 18: 20-31.
Briand, J.F., et al., Health hazards for terrestrial vertebrates from toxic cyanobacteria in surface water ecosystems. Vet Res, 2003. 34(4), 361-77.
Carbis, C.R., et al., A biochemical profile for predicting the chronic exposure of sheep to Microcystis aeruginosa, an hepatotoxic species of blue-green alga. Res Vet Sci, 1994. 57(3), 310-6.

Carbis, C.R., et al., Recovery of hepatic function and latent mortalities in sheep exposed to the blue-green alga Microcystis aeruginosa. The Veterinary Record, 1995. 137(1), 12-15.
Chorus, I., I. Falconer, H.J. Salas, and J. Bartram. 2000. Health risks caused by freshwater cyanobacteria in recreational waters. Journal of Toxicology and Environmental Health, Part B 3: 323-347.
Codd, G.A., et al., Fatal attraction to cyanobacteria? Nature, 1992. 359(6391), 110-1.
DeVries, S.E.,et al.Clinical and pathologic findings of blue-green algae (Microcystis aeruginosa) intoxication in a dog. Journal of Veterinary Diagnostic Investigation, 1993. 5(3), 403.
Dillenberg, H.O. and M.K. Dehnel, Toxic waterbloom in Saskatchewan, 1959. Can Med Assoc J, 1960. 83, 1151-4.
Edwards, C., Beattie, K.A., Scrimgeour, C.M., Codd, G.A., 1992. Identification of anatoxin-a in benthic cyanobacteria (blue-green algae) and in associated dog poisonings at Loch Insh, Scotland. Toxicon 30, 1167–1175.
Falconer, I.R., Humpage, A., 1996. Tumour promotion by cyanobacterial toxins. Phycologia 35, 74–79.
Falconer, I.R., et al., Effect of the cyanobacterial (blue-green algal) toxins from Microcystis aeruginosa on isolated enterocytes from the chicken small intestine. Toxicon, 1992. 30(7),790-3.
Fitzgerald, S.D. and R.H. Poppenga, Toxicosis due to microcystin hepatotoxins in three Holstein heifers. J Vet Diagn Invest, 1993. 5(4), 651-653.
Frazier, K., et al., Microcystin toxicosis in cattle due to overgrowth of blue-green algae. Vet Hum Toxicol, 1998. 40(1), 23-4.
Furey, A., et al.,1997. Identification of a microcystin in benthic cyanobacteria linked to cattle deaths on alpine pastures in Switzerland. Eur. J. Phycol. 32, 111–117.
Galey, F.D., et al., Blue-green algae (Microcystis aeruginosa) hepatotoxicosis in dairy cows. Am J Vet Res, 1987. 48(9), 1415-20
Gunn, G.J. et al. Fatal canine neurotoxicosis attributed to blue-green algae (cyanobacteria). Veterinary Record, 1992 130, 301-302
Haider, S., N. Vijay, P. Viswanathan, and P. Kakkar. 2003. Cyanobacterial toxins: a growing environmental concern. Chemosphere 52: 1-21.
Kerr, L.A., C.P. McCoy, and D. Eaves, Blue-green algae toxicosis in five dairy cows. J Am Vet Med Assoc, 1987. 191(7), 829-30.
Lopez Rodas, V. and E. Costas, Preference of mice to consume Microcystis aeruginosa (toxin-producing cyanobacteria): a possible explanation for numerous fatalities of livestock and wildlife. Res Vet Sci, 1999. 67(1), 107-10.
McBarron, E.J. et al. Toxicity to livestock of the blue-green algae Anabaena circinalis. Australian Veterinary Journal, 1975. 51 (12).
Mez, K., et al., Identification of a microcystin in benthic cyanobacteria linked to cattle deaths on alpine pastures in Switzerland. European Journal of Phycology, 1997. 32, 111-117.
Puschner, B., et al., Blue-green algae toxicosis in cattle. J Am Vet Med Assoc, 1998. 213(11), 1605-7, 1571.
Senior, V.E., Algal poisoning in Saskatchewan. Can J Comp Med, 1960. 24, 26-31.
Short, S.B. and C. Edwards, Blue-green algae toxicoses in Oklahoma. Vet Hum Toxicol, 1990. 32, 558-560.

Wood, S., et al. First report of homoanatoxin-a and associated dog neurotoxicosis in New Zealand. Toxicon 50 (2007), 292-301.
WHO, Toxic Cyanobacteria in Water: A guide to their public health consequences, monitoring and management. 1999, Routledge: London and New York.

Microscopic Images of Cyanobacteria:
Web Links for More Information:
Ohio EPA Harmful Algal Bloom and Algal Toxin web site -

Division of Environmental Health, Office of Environmental Health, Safety, and Toxicology – Cyanobacterial Toxins and Symptoms -

Microcystins: A brief overview of their toxicity and effects, with special reference to fish, wildlife and livestock -http://www.oehha.ca.gov/ecotox/documents/Microcystin031209.pdf

Toxicology Summary - http://cal.vet.upenn.edu/projects/poison/cases/case2/c2toxsum/c2toxsum.htm

Centers for Disease Control and Prevention (CDC) HABISS program Web site - http://www.cdc.gov/hab/

World Health Organization (WHO) cyanobacterial toxins Web site -http://www.who.int/water_sanitation_health/diseases/cyanobacteria/en/

Comments are closed.