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HAB Impacts on Domestic AnimalsDeon van der Merwe

HABs

When flying over the central Great Plains on a late afternoon, with the sun hanging low

over the western horizon, the landscape is bejeweled with countless golden reflections from lakes and small ponds. In spite of their beauty and essential role as sources of drinking water for farm animals, the lakes and ponds can be a source of poisoning risk when environmental conditions promote the formation of harmful algal blooms (HABs). The HABs that make it into headlines are generally associated with public waters, and the occasional poisoning of much-loved pets that become poisoned when they visit public lakes. Arguably, however, the biggest impacts in terms of lost labor and income, are suffered by farmers who have to find alternative water sources when ponds become unusable for livestock (Figure 1).

Toxins and Their Effects in Animals The most common toxins produced in HABs worldwide, including the central Great Plains, are microcystins, which are produced by several genera of cyanobacteria including Microcystis, Planktothrix/Oscillatoria, and Anabaena. Microcystins are a family of cyclic heptapeptides that primarily affect the liver and gastrointestinal tract. Microcystins are also irritants, and contact may cause skin rashes, and inflammation of the mucous membranes of the eyes and respiratory system. Symptoms in animals typically start 2-4 hours after exposure. Vomiting is often the first sign seen in dogs, followed by increasing lethargy, weakness, and exercise intolerance. Vomiting is usually

Recent Impacts of Harmful Algal Blooms on Domestic Animals: The Kansas Experience

Figure 1. A typical central Great Plains farm pond used to provide drinking water for livestock.

followed by other signs of gastrointestinal effects, such as abdominal tenderness and diarrhea. Cattle do not vomit. The first signs in cattle are usually indications of abdominal discomfort and diarrhea. In severe cases in any species, the damage to the gastrointestinal mucosa leads to bleeding; this results in a severe, bloody diarrhea. Microcystins are extremely toxic to liver cells, and the liver is the first organ that gets into contact with the toxins after they are absorbed from the gastrointestinal tract. Clinical signs of liver failure are not always obvious, but the appearance of jaundice (yellow discoloration of the mucous membranes) may be seen. Secondary to liver failure,

some animals will develop a bleeding tendency, or neurological abnormalities such as convulsions. When large doses are ingested, liver failure can be rapid and complete, typically resulting in death within a few days. Although microcystins are the most frequent toxins involved in animal poisoning in the central Great Plains, anatoxin-A is also occasionally implicated. It is an alkaloid that is mostly produced by species of Anabaena, but other genera, including Microcystis, Planktothrix/Oscillatoria, Aphanizomenon, Cylindrospermum, and Phormidium may also be involved (Park et al. 1993). It has cholinergic neurotoxic effects that cause abnormal muscle contractions, which become progressively more severe until it results

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in uncontrollable convulsions. Death typically occurs due to failure of the respiratory muscles. The onset and progression following exposure to a large dose is rapid, and animals are often found dead near the source of exposure. No specific antidotes are available for either microcystins or anatoxin-A, and mortality can be high (Puschner and Roegner 2012).

Kansas Cyanotoxin Cases The late summer of 2011 was unusually active in terms of HABs in the central Great Plains, and it was reflected in the unusually high number of water samples submitted to the Kansas State Veterinary Diagnostic Laboratory (KSVDL) that tested positive for toxic species of cyanobacteria. There were 42 HABs identified in private ponds by the end of the summer, compared to 5-15 in a typical year. Most private ponds are never tested. The water samples submitted to the KSVDL represents only a fraction of the total HABs that occur in any given season. The 2011 summer was also unusual in terms of the diversity of cyanobacteria that formed HABs in farm ponds. The vast majority of HABs identified in typical years are caused by Microcystis, but in 2011, only about half (20) of the positive samples contained Microcystis, and 8 of those were part of mixed blooms (Figure 2). During 2011, the predominant cyanobacterial genera, other than Microcystis, were Anabaena and Aphanizomenon. The trend toward increased numbers of identified HABs, and increased diversity of blooms, has continued during the early part of the 2012 season. This increasing trend for HAB formation in farm ponds is a major concern. The relatively small numbers of livestock that actually get poisoned do not convey the real economic impact and hardship suffered by multiple families across the state, when they have to use scarce resources to provide alternative water sources for their livestock. This will often require the sinking of new wells, laying pipes and installing pumps, or trucking water over long distances. These hidden costs associated with HABs are difficult to estimate accurately, but it is a hard reality to those who are affected, and the economic losses can, on occasion,

Figure 2. An accumulation of pond scum, formed by a Microcystis aeruginosa bloom, on the downwind shore of a pond. Such pond conditions are extremely hazardous for livestock and pets.

be devastating when large groups of livestock become poisoned. Pet poisonings are more widely recognized, compared to livestock poisonings, because pet poisoning cases often involve publicly accessible lakes, which tends to generate much more media interest. At Milford Lake in North Central Kansas, a large Microcystis aeruginosa HAB persisted for most of summer 2011and had extremely high, localized microcystin concentrations of up to 126,000 µg/L (Van der Merwe et al. 2012). Seven cases of suspected or confirmed microcystin poisonings occurred in dogs, including 5 deaths, at Milford Lake during the 2011 bloom. Rapidly changing HAB conditions, including rapidly shifting cyanobacterial concentrations depending on wind speed and direction, make it difficult to predict the risk to dogs and other pets during HABs. For example, a water sample collected at the site of poisoning of one of the lethal cases at Milford Lake, within one day of the exposure, actually showed a safe water concentration of microcystins (0.5 µg/L). The high susceptibility of dogs to poisoning is related to their scavenging behavior. Dogs may seek out and find pockets of rotting algal scum along the lake shore, and some dogs will consume

such material, which may contain extremely high toxin concentrations.

Risk Avoidance Increasing trends in HAB formation may be difficult to control, but it is important that the general public be made aware of the potential poisoning risk associated with HABs. Proactive risk avoidance based on an appropriate level of awareness of the potential for poisoning, at the individual stockman and pet owner level, will be the key to preventing poisoning in domestic animals. All available avenues for generating public awareness should be used, including the news media, extension publications, and the posting of advisory and warning signs where HABs have been confirmed. Success will be silent, seen only in the absence of tragic headlines reporting the poisoning of pets and livestock.

ReferencesCodd, G.A., C. Edwards, K.A. Beattie,

W.M. Barr and G.J. Gunn. 1992, Fatal attraction to cyanobacteria? Nature, 359:110-111.

Park H.D., M.F. Watanabe, K. Harda,H. Nagai, M. Suzuki, M. Watanabe and H. Hayashi. 1993. Hepatotoxin

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(microcystin) and neurotoxin (anatoxin-a) contained in natural blooms and strains of cyanobacteria from Japanese freshwaters. Nat Toxins, 1(6):353-60. PubMed PMID: 8167957.

Puschner, B. and A. Roegner. 2012. Cyanobacterial (blue-green algae) toxins. In: Veterinary Toxicology Basic and Clinical Principles, Second Edition, Gupta, R.C. (Ed), pp. 953-965.

Van der Merwe, D., L. Sebbag, J.C. Nietfeld, M.T. Aubel, A. Foss and E. Carney. 2012. Investigation of a Microcystis aeruginosa cyanobacterial freshwater harmful algal bloom associated with acute microcystin

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toxicosis in a dog. J Vet Diagn Invest, 24(4):679-687.

Deon van der Merwe heads the toxicology section of the Kansas State Veterinary Diagnostic Laboratory. He teaches veterinary toxicology, and environmental toxicology at Kansas State University. His research interests include clinical veterinary toxicology, analytical toxicology, and toxicokinetics. x

Lake and Reservoir ManagementA scientific publication of NALMS published up to four times per year solicits articles of a scientific nature, including case studies.

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