Comparative Parasitology 67(2) 2000 - Peru State College

Several horses, all with unknown antiparasitic
treatment, were examined at necropsy in Kentucky,
U.S.A., in 1998 in a prevalence survey
for various species of internal parasites. Specimens
of 2 species were atypical. One was the
cecal tapeworm, Anoplocephala perfoliata
(Goeze, 1782) Blanchard, 1848. The other was
the eyeworm, Thelazia lacrymalis (Gurlt, 1831)
Raillet and Henry, 1910.
The usual habitat of A. perfoliata in the horse
is the large intestine, mainly the cecum. In past
surveys of dead horses in Kentucky, prevalence
of A. perfoliata was about 50-60% and no differences
in infection with age of the horse were
found (Benton and Lyons, 1994). Detrimental
effects of A. perfoliata are not always evident.
Some of the problems, mainly at the attachment
sites of the tapeworms, are ulceration, inflammation,
edema, and a resulting diphtheritic
membrane (Proudman and Trees, 1999). Possible
life-threatening effects attributed to A. perfoliata
are intussusception, perforation, and hypertrophied
small intestine (Proudman and
Trees, 1999).
Among 265 A. perfoliata found in a 29-yearold
Thoroughbred gelding in the present study
were 2 atypical specimens joined together at the
midportion (Fig. 1). Possibly there had been incomplete
separation of 2 eggs during embryogenesis.
Alternatively, in early development,
there may have been injury to 1 specimen, and
the other somehow partially invaded the afflicted
individual. The authors were unable to find any
reference in the literature to this type of anomaly
in A. perfoliata. However, several other types of
abnormalities, including 1-4 extra suckers on
the scolex and tri- and tetraradiate strobila, have
been reported for A. perfoliata (Lyons et al.,
1997).
Thelazia lacrymalis uses muscid flies, e.g.,
Musca autumnalis (deGeer, 1776), as intermediate
hosts. Negative effects caused by 7". lacrymalis
are usually limited to conjunctivitis and
excessive lacrimation (Patton and McCracken,
1981). In past surveys for T. lacrymalis, about
40-50% of horses under 5-6 years of age were
infected; older horses had much lower prevalences
(Lyons et al., 1986). This eyeworm species
is associated with several parts of the eyes,
including the lacrimal glands, lacrimal ducts,
conjunctival sac, and nictitating membrane
gland plus ducts. Typically, females in most
groups of nematodes have a double or bifurcate
RESEARCH NOTES 259
Figure 1. Anomalous Anoplocephala perfoliata:
2 specimens joined in midportion, 1 smaller (S)
than the other. Scale bar = 10.0 mm.
reproductive system consisting of a vulva, vagina,
and 2 uteri (Fig. 2A) and 2 ovaries. In the
present study, 1 of 3 female T. lacrymalis recovered
from the eyes of a yearling male Thoroughbred
had 3 uteri (Fig. 2B). This aberration
was observed by chance, because all female T.
lacrymalis in the survey were examined for the
presence of embryos with the aid of a compound
microscope. The specimen with the 3 uteri accidentally
ruptured at the location shown in the
accompanying photomicrograph (Fig. 2B),
which was taken to record the embryos. Later,
it was realized that the presence of 3 uteri was
not normal. No references could be found regarding
such an anomaly in T. lacrymalis. Hyman
(1951) mentioned that polydelphic female
nematodes may have more than 2, and as many
as 10 or 11, ovaries and uteri. This situation occurs
particularly in the Physalopteridae, which
are spirurids (Hyman, 1951). Thelazia spp.,
while also spirurids, are in a different family.
Chandler (1924) found 3 instead of the usual 2
ovaries and uteri in the ascarid, Ascaris lumbricoides
(Linnaeus, 1758), and considered this
highly unusual.
Causes of anomalies of internal parasites are
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