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VetBooks.ir Chapter 75

Trichothecenes

Rhian B. Cope

INTRODUCTION airborne and are associated with “sick building syn-
dromes,” the most important source of veterinary expo-
The foci of this chapter are on: (1) the general toxicologi-
sure is ingestion in food.
cal characteristics of the trichothecene mycotoxins; and
Sources of the toxins: Trichothecenes are produced
(2) the more common problematic trichothecenes encoun-
by several genera of fungi, including Fusarium,
tered in veterinary medicine, i.e., T-2 toxin (a type A
Stachybotrys, Myrothecium, Trichothecium, Trichoderma,
trichothecene), dexoxynivalenol (DON; a type B tricho-
Cephalosporium, Cylindrocarpon, Verticimonosporium,
thecene), stachybotryotoxicosis, myrotheciotoxicosis, and
and Phomopsis (Scott, 1989). The fruiting bodies of
dendrodochiotoxicosis. Of the trichothecenes, DON is
Podostroma cornu-damae, a poisonous mushroom species
probably the most commonly detected in cereal grains
found in Japan and China, also contains trichothecenes
throughout the world (Rotter et al., 1996; CAST, 2003). It
(slatratoxins, verrucarin) and the toxins are also produced
is important to remember: (1) all of the 180-plus members
by the Brazillian plant genus Baccharis spp. However, the
of the trichothecene family should be regarded as toxic to
most medically and economically important source of
domestic animals until proven otherwise; (2) the most
trichothecene mycotoxins in North America is from
common presentation in veterinary medicine is feed
Fusarium spp. fungi. Fusarium spp. are important plant
refusal and associated effects on performance and repro-
pathogens and grain contaminants in temperate regions
duction; and (3) site of first contact irritancy (mouth,
(fusarium head blight in wheat, barley, triticale, and other
eyes, perioral area in the case of ingestion; skin in the
grains).
case of bedding) and ulceration are common.
Factors affecting trichothecene production: The eco-
logical factors likely to increase the level of trichothecene
contamination include: ideal temperatures for fungal

growth (0 50 C depending on species), humidity
General Toxicological Characteristics
($70%), moisture level of the growth medium (10%
Trichothecenes are a family of sesquiterpene mycotoxins 20%; optimum water activity is .0.88), oxygen level in
with the common core chemical structure as shown in the growth medium (fungal growth is heavily oxygen
Fig. 75.1. The 12, 13-epoxy ring structure is important for dependent), substrate type (nutrient composition), mon-
biological activity and toxicity. The presence of hydroxyl soonal weather, unseasonal rains during harvest times,
groups and the structure and position of side chains influ- flash flooding, insect interactions and methods of grain
ence the biological activity. Trichothecenes can be chemi- handling and storage (Adhikari et al., 2017; Smalley and
cally classified into four types based on substitutions at Strong, 1974). Unusually cool weather conditions in late
five positions of the trichothecene skeleton, including summer and early fall, coupled with heavy rainfall in the
Type A, which includes T-2 toxin and HT-2 toxin; upper Midwest of the United States, can result in wide-
Type B including nivalenol and DON; Type C including spread, severe Fusarium infestation and mycotoxin pro-
crotocin; and Type D or macrocyclics. Type A trichothe- duction (Bamburg et al., 1968; Jacobsen et al., 1995; Park
cenes include some of the most toxic trichothecenes: T-2 et al., 1996). Fusarium species vary in toxigenic potential
toxin, its deacetylated metabolite, HT-2 toxin, and by strain, which in turn varies with geographic location.
DAS (or anguidine). The plant synthesis pathways for tri- Environmental conditions can substantially influence the
chothecenes resemble the metabolic pathways for amino types of mycotoxins produced by Fusarium fungi, e.g.,
acid synthesis and fatty acid metabolism. While some DON is produced under conditions of low oxygen tension,
of the toxins, particularly the macrocyclics, can become whereas zearalenone (a nontrichothecene, estrogenic

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