Ecology and Management of Avian Botulism on the Canadian Prairies

137INTRODUCTIONAlthough blue-green algae (cyanobacteria spp.) are very common in wetl<strong>and</strong>s, <strong>and</strong> mortality <strong>of</strong>waterfowl has been attributed to toxicity from algae, there is very little information on thetoxicity <strong>of</strong> specific toxins for birds, including waterfowl. Algal toxins are <strong>of</strong> two general types:neurotoxins <strong>and</strong> hepatotoxins. In general, hepatotoxic blooms occur more commonly than doneurotoxic blooms (Carmichael et al. 1985). Neurotoxins are associated with Anabaena <strong>and</strong>Aphanizomenon spp. cyanobacteria. One neurotoxin (anatoxin-a) is known to be toxic formallards (Anas platyrhynchos) (Carmichael <strong>and</strong> Biggs 1978) <strong>and</strong> produces clinical signs similarto those produced by cholinesterase-inhibiting insecticides. However, this toxin is not reportedcommonly in Prairie lakes (e.g., Kotak et al. (1993) did not find it in any <strong>of</strong> 39 bloom samplescollected from Alberta lakes <strong>and</strong> dug-outs). Hepatotoxins are produced by a number <strong>of</strong> differentalgae. The most common <strong>of</strong> these are a group <strong>of</strong> toxins called microcystins that are produced byMicrocystis spp., as well as by some other cyanobacteria. Microcystin-LR is likely the mostcommon form <strong>of</strong> microcystin. Kotak et al. (1993) detected microcystin-LR in 37 <strong>of</strong> 39 algalbloom samples collected in Alberta. Microcystin-LR is highly toxic for mammals, causingvery rapid liver damage <strong>and</strong> death within a few hours. The toxic dose for mice byintraperitoneal injection is approximately 50-100 µg/kg. There is very little information ontoxicity <strong>of</strong> microcystins for birds, <strong>and</strong> liver damage <strong>of</strong> the type that occurs in mammals has notbeen described in this group. Gorham (1960) <strong>and</strong> Konst et al. (1965) reported that domesticducks were very resistant to toxins produced by M. aeruginosa. Takahashi <strong>and</strong> Kaya (1993)reported that another microcystin (microcystin-RR) was toxic for quail when injectedintraperitoneally, but it caused enlargement <strong>of</strong> the spleen rather than causing the liver damagethat occurs in mammals.The association between these toxins <strong>and</strong> poisoning <strong>of</strong> birds is confusing, because commonlyoccurring hepatotoxins have not been clearly linked with toxicity in birds, but at least one <strong>of</strong> theless commonly occurring neurotoxins is known to be toxic for ducks. There are about 20 reportsin the literature in which death <strong>of</strong> waterfowl has been associated with a blue-green algal bloom(Wobeser 1997). The cyanobacteria present were characterized poorly in many <strong>of</strong> theseoccurrences, but in 12 <strong>of</strong> 20 occurrences either Anabaena or Aphanizomenon spp. weredescribed, so that neurotoxins may have been present. Microcystis spp. were described in seveninstances, but in three <strong>of</strong> these cases, Anabaena or Aphanizomenon spp. were also present. Theobjective <strong>of</strong> this pilot study was to determine the toxicity <strong>of</strong> purified microcystin-LR(Calbiochem catalogue # 475815) for mallard (Anas platyrhynchos) ducklings.EXPERIMENT 1MethodsDay-old ducklings were obtained from a commercial supplier (Whistling Wings, Hanover,Illinois), held in the laboratory for one week for acclimation, <strong>and</strong> then divided into groups <strong>of</strong> fivebirds for exposure to toxin. Although Microcystin-LR had been successfully isolated fromculture, the yield was less than expected so commercial supplies were used to expedite the study.