Page 747 - Veterinary Toxicology, Basic and Clinical Principles, 3rd Edition

712 SECTION | X Avian and Aquatic Toxicology

VetBooks.ir more toxic to pheasants than rats. Dimethoate is metabo- concentration of a mycotoxin in a feed can be quite vari-
able. Therefore, it is important to obtain a number of sam-
lized by pheasants to a toxic metabolite, whereas the toxic
ples that can then be pooled and subsampled. Other
metabolite is detoxified by rats (Pan and Fouts, 1978). In
addition, there are differences between bird species and toxicants for which obtaining representative feed samples
between sexes and ages. Geese, chickens, and turkeys had are critical include drugs; growth promotants such as
similar liver aniline hydroxylase activity compared with ionophores; sodium chloride; and nutritionally important
that of rats, whereas quail and ducks had lower activities minerals such as copper, zinc, and selenium.
(Dalvi et al., 1987). Because malicious poisonings of wild birds are com-
mon, and state or federal laws protect some poisoned
Excretion birds, the potential for litigation should always be of con-
Birds have several unique excretory pathways for xeno- cern. Therefore, it may be critical to obtain and submit
biotics. Many metals are incorporated into feathers, which samples following chain-of-custody procedures.
are subsequently molted. In addition, incorporation of tox-
icants into eggs provides a significant excretory pathway
for female birds.
NATURAL TOXICANTS
GENERAL COMMENTS ABOUT Algal Toxins
DIAGNOSING AVIAN INTOXICATIONS
Cyanobacterial blooms and cyanotoxins have been linked
Although most diagnostic approaches for documenting to the death of animals throughout the world. The more
intoxication in mammals are applicable to birds, there are popular cyanotoxins are anatoxin-a and microcystins, pro-
several unique aspects that bear mentioning. Given the duced by cyanobacteria belonging to various genera such
small size of many birds, obtaining a sufficient amount of as Anabaena, Microcystis, Coelosphaerium, and
sample for testing can sometimes present a challenge. For Plankothrix. There are few documented instances of
example, it is not unusual to be able to obtain only intoxication of birds, mostly in wild birds because they
100 μL (sometimes less) of whole blood or serum ante- are more likely to be exposed to cyanobacterial toxins
mortem for lead and zinc testing, respectively. Quantities than pet birds or poultry given their water sources such as
of gastrointestinal contents or tissues such as liver are lakes, reservoirs, and rivers. However, it is possible that
sometimes limiting, especially if multiple tests are zoo birds or production birds such as poultry, game birds,
desired. The availability of less than optimal sample sizes or waterfowl can be exposed via their water depending on
often decreases the sensitivity of toxicologic testing, so it its source and if conditions conducive to algal blooms are
is possible that low toxicant concentrations are not present. Anatoxin-a(s) was believed to have been the
detected. In the case of wild bird die-offs, pooling of sam- cause of bird mortality in several Danish lakes where
ples from several dead birds is often required. Anabaena lemmermannii dominated the blooms, and ana-
Antemortem, whole blood is most often requested toxin-a(s) was detected (Henriksen et al., 1997). Similarly
from mammals for cholinesterase activity determinations. a bloom of Microcystis aeurginosa in a pond in Japan
However, in birds, there is little cholinesterase activity was believed to have played a role in the death of approx-
that is associated with the red blood cell. Therefore, for imately 20 spot-billed ducks (Matsunaga et al., 1999).
avian species, plasma is preferred. Feathers and egg sam- Clinical signs may vary depending on the cyanotoxin
ples are sometimes useful for diagnosing either exposure though birds are often found dead in mass mortality
to or intoxication from toxicants. events occurring along water sources. Anatoxin-a is a
Investigation of wild bird die-offs is often a challenge potent agonist at nicotinic acetylcholine receptors
from the standpoint that frequently birds are not discov- (nAChRs) and poisoning may result in clinical signs of
ered until significant postmortem autolysis and/or preda- muscle fasciculations or seizures. Microcystins are
tion has occurred. Postmortem autolysis often precludes hepatotoxic, which on ingestion of an acutely toxic dose
thorough pathologic and microbiologic testing. However, can result in fulminant liver failure. Brevetoxins produced
for the vast majority of toxicologic tests, the condition of by the dinoflagellate Karenia brevis has been attributed to
the tissue or fluid sample is of less concern, and severely clinical signs such as disorientation, inability to stand,
autolyzed samples may be perfectly suitable for toxico- ataxia, seizures (Fauquier et al., 2013) and the death of
logic testing. sea birds along the west Florida coast in 2005 and 2006.
As is the case for any suspected intoxication related to Necropsy findings are typically absent in anatoxin intoxi-
feed, it is critical to obtain a representative feed sample. cations whereas microcystins exposed birds may present a
For example, feed-related mycotoxicoses are common hemorrhagic, necrotic, severely jaundiced, and dark-green
concerns in poultry. However, the distribution and colored liver (Matsunaga et al., 1999).