Page 805 - Veterinary Toxicology, Basic and Clinical Principles, 3rd Edition

764 SECTION | XI Bacterial and Cyanobacterial Toxins

VetBooks.ir surface waters (Pearl et al., 2016). Particularly runoff from toxin production during a bloom event. This chapter
focuses on the several types of cyanotoxins known to
nitrogen- and phosphorus-rich fertilizers, soaps, and waste
have the greatest impact on veterinary species and pre-
products has led to significant eutrophication worldwide
(.40% in Europe, Asia, and America) (Bartram et al., sents the current understanding of their toxic mechanisms,
1999; Smith, 2003). As a major consequence of shifting toxicokinetics, and diagnostic and therapeutic approaches
nutrient additions, previously nutrient-limited photosyn- with a focus on veterinary medicine.
thetic microorganisms proliferate. Depending on the lim-
itations of the system and the types of nutrients added, a MICROCYSTINS
few species (generally one or two) outcompete the others,
thereby considerably reducing the heterogeneity of the Produced by multiple cyanobacteria, including species
phytoplankton community. In such conditions, cyanobac- within the genera Microcystis, Anabaena, Planktothrix,
teria often predominate through adaptive processes, and Nostoc, Oscillatoria,and Anabaenopsis,microcystins have
substantial shifts in the microscopic and macroscopic food been detected worldwide (Fromme et al., 2000; Hitzfeld
web may occur. Anoxic conditions can also result in fish et al., 2000; Ballot et al., 2004; Briand et al., 2005; Karlsson
kills, and falling debris from blooms can have profound et al., 2005a; Ndetei and Muhandiki, 2005; Agrawal et al.,
impacts on the invertebrates in the sediment below (Pearl 2006; Chatziefthimiou et al., 2014). Not all strains are capa-
et al., 2001; Havens, 2008). ble of producing microcystins. Microcystins were responsi-
Among the oldest microorganisms, these oxygenic ble for the 2014 drinking water advisory in Toledo, OH
photosynthetic prokaryotes may be organized as indi- (Bullerjahn et al., 2016). In recent years, a useful diagnostic
vidual cells (e.g., Synechococcus), filaments (e.g., tool to test for the presence of toxin-producing genes has
Planktothrix), or colonies (e.g., Microcystis). More than emerged (Hisbergues et al., 2003). Although the reason for
2000 cyanobacterial species belong to four orders based production is not understood, environmental factors, such as
on morphological and morphometric criteria in botanical pH, nutrient concentrations, and water temperature, clearly
code (Anagnostidis and Komarek, 1985); however, classi- trigger production, increasing with water temperature, ele-
fication based on bacterial code defines five sections vated concentrations of phosphorus and nitrogen, iron limi-
through combined use of genetic data, morphological cri- tation, and globally with the growth rate (Briand et al.,
teria, and cellular fission (Rippka et al., 1979). 2005; Downing et al., 2005; Sevilla et al., 2008).
Both pelagic (suspended in the water column) and Microcystin concentrations may be highest when the growth
benthic (along the bottom) cyanobacteria can proliferate of the cyanobacteria is high, but toxin concentrations do not
into blooms. Pelagic blooms, which are easier to visually necessarily correlate with cell count, and toxins may occur
detect because of the evident scum formation at the sur- any time of the year. Although predominantly found in
face, usually occur in mesotrophic and eutrophic ecosys- freshwater, microcystin-producing blooms have also been
tems (concentrations in phosphorus .30 μg/L), during the described in saline ecosystems (Atkins et al., 2001;
summer, in water temperatures greater than 20 C, and in Carmichael and Li, 2006). Beyond exposure to microcystin-

low turbulence. Proliferations of benthic species generally contaminated water, animals are at risk for microcystin
occur during the summer on the surfaces of sediments, exposure through blue-green algae containing dietary sup-
stones, or macrophytes in small oligotrophic rivers or in plements (Bautista et al., 2015; Mittelman et al., 2016).
oligotrophic lakes (Mez et al., 1997). Potent cyclic heptapeptides causing acute hepatotoxi-
In the past, most cases were diagnosed by positive cosis in mammals, microcystins have also been demon-
identification of the algae in the suspect water source strated to be toxic to reptiles, amphibians, and aquatic
along with the occurrence of consistent clinical signs and species, as well as invertebrates and even plant species
pathological findings. However, new analytical methods (McElhiney et al., 2001; Malbrouck and Kestemont,
can now be applied to detect toxins in biological speci- 2006; Nasri et al., 2008; Amado and Monserrat, 2010). In
mens of animals or humans with suspect exposure to toxic freshwater, the toxins are retained inside the cyanobacter-
algal blooms Fig. 57.1illustrates the wide variety in chem- ia and only released upon cell damage, lysis, and death;
ical structures of cyanotoxins and the need for specific destruction of algal mats (either naturally or through the
detection methods (Yuan et al., 2006; Humbert, 2010). application of herbicides) may result in a pulse of micro-
These capabilities will allow for in-depth diagnostic cystin release following destruction of the individual cell
investigations and a better estimate of the true frequency walls. After oral exposure to microcystin-containing
of blue-green algae poisonings in livestock, pets, and algae, the acidic environment of the stomach can result in
wildlife. Table 57.1 provides an overview of cyanobacter- the release of microcystins. Commercially available blue-
ial species known to produce a large number of toxins. green algae food supplements also present a potential
Some species can produce a variety of cyanotoxins and route of oral exposure (Schaeffer et al., 1999; Dietrich
thus it is difficult to predict the nature and the level of the and Hoeger, 2005).