Page 804 - Veterinary Toxicology, Basic and Clinical Principles, 3rd Edition

VetBooks.ir Chapter 57

Cyanobacterial (Blue-Green Algae)

Toxins

Birgit Puschner

INTRODUCTION suspect cyanotoxin poisoning cases of humans and ani-
mals requires extensive effort from both toxicologists and
Freshwater cyanobacterial blooms hold the potential to
clinicians, and resources are often not readily available.
significantly impact the health of both animal and human
New cyanotoxins are continuously being discovered, and
populations utilizing surface waters for drinking water,
oral bioavailability and toxicity data are often unavailable.
daily living, and recreation worldwide. In addition to the
It is probable that poisonings are more common in ani-
often visually stunning nature of these proliferations of
mals than in humans due to animals’ greater direct depen-
cyanobacterial species, the blooms can result in the pro-
dence and contact with surface waters.
duction of a variety of compounds, from malodorous ones
Pursuant to several major human intoxications in
that affect the taste of the water to dermal and gastrointes-
Australia, Europe, and Brazil (Falconer and Humpage,
tinal irritants and severe neurotoxicants, gastrointestinal
2005), in 1998 the World Health Organization (WHO) pro-
toxicants, and hepatotoxicants. Among the 2000 species
posed a guidance value for the maximum permissible con-
identified through morphological criteria, more than 80
centration of 1 μg/L free and cell bound MC-LR in
are known to be toxigenic, and as assays for detection and
potable water sources for microcystin-LR, the most com-
toxicity continue to improve, this number will continue to
monly reported cyanotoxin worldwide. Water sanitation
grow. George Francis first reported a toxigenic bloom in
agencies in many countries in Europe, North America
the journal Nature in 1878. He reported a “poisonous
(Canada), South America (Brazil), and Oceania (Australia
Australian lake” with “a thick scum like green oil paint”
and New Zealand) adopted these guidelines. In addition, as
and vividly described acute intoxications of sheep, horses,
a result of a tragedy in 1996 in which more than 100 patients
dogs, and pigs. Analysis of archeological evidence cou-
at a hemodialysis clinic received inadequately treated drink-
pled with evolving understanding of modern blooms have
ing water (Azevedo et al., 2002), most of whom developed
begun to implicate the role of cyanotoxin poisoning in
acute liver failure as a result of being exposed to cyanotox-
more widespread mammalian die-offs dating back to the
ins, Brazil has adopted more comprehensive and stringent
Pleistocene age (i.e., approximately 150,000 years BC;
guidelines to include other cyanotoxins (Burch, 2008).
Braun and Pfeiffer, 2002), and even a controversial
Awareness of imminent health risks for wild and domestic
hypothesis about the role of cyanobacteria in the various
terrestrial vertebrates has increased during approximately
mass extinction events has begun to emerge (Castle and
the past decade, in part due to veterinary case reports; how-
Rodgers, 2009).
ever, the extent and heterogeneity of the impact are still far
Since Francis’s publication in 1878, numerous case
from understood. Veterinarians thus have the opportunity to
reports describing animal morbidity and mortality after
substantially deepen the understanding of the impact of
exposure to cyanotoxins have been published (Bautista
these cyanotoxins on animal and human populations alike.
et al., 2015; Naegeli et al., 1997; Puschner et al., 1998,
2008, 2010; Gugger et al., 2005; Moore et al., 2016;
Nasri et al., 2008; Wood et al., 2010). The frequency of BACKGROUND
cyanotoxins poisoning in animals is likely underreported
due to lack of methods to confirm exposure; in addition, Cyanobacterial blooms are predicted to become more
geographical distribution of these case reports is likely severe and widespread with climate change if land use
biased by available resources. Diagnostic confirmation of practices are not altered to minimize nutrient input to
Veterinary Toxicology. DOI: http://dx.doi.org/10.1016/B978-0-12-811410-0.00057-X
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