Proc. Helminthol. Soc. Wash.
54(2), 1987, pp. 262-263
Research Note
Excystment in the Plerocercus Metacestode of Otobothrium insigne
(Cestoda: Trypanorhyncha)
MICHAEL B. HILDRETH' AND ROBERT R. LAZZARA
Department of Biology, Tulane University, New Orleans, Louisiana 70118
loc. cit.). The various incubations were conducted at 37°C in fish saline (Hanks' basal salt
solution plus 0.3% [w/v] NaCl as recommended
The physico-chemical factors that cause evag- by Wolf and Quimby [1969, pages 253-305 in
ination or excystment of the tapeworm scolex W. S. Hoar and D. J. Randall, eds., Fish Physfrom its metacestode bladder have been studied iology, Vol. 3, Academic Press, New York]. Befor several different metacestodes from the order cause we were unable to acquire shark pepsin,
Cyclophyllidea (e.g., cysticercoid and cysticercus trypsin, and bile salts, we used commercially premetacestodes). Yet, little is known of the factors pared mammalian enzymes and bile salts (crysresponsible for evagination or excystment in oth- talline porcine pepsin, crystalline bovine trypsin,
er types of metacestodes. Because members of and porcine bile salts; from Sigma Chemical Co.).
the order Trypanorhyncha utilize a very different In the absence of available data on concentralife cycle than cyclophyllidians, we chose to ex- tions of trypsin and bile salts in the spiral valve
amine the factors necessary for excystment in the of sharks, we used concentrations (0.5% trypsin
trypanorhynch metacestode (termed a plerocer- and 0.3% bile salts [w/v]) found to be optimum
cus) of Otobothrium insigne Linton, 1905.
for scolex evagination in hymenolepid cysticerThe adult of O. insigne has been reported from coids (Rothman, 1959, Experimental Parasitolthe spiral valve of Carcharhinus obscurus sharks ogy 8:336-364).
(Linton, 1905, Bulletin of the Bureau of Fisheries
The results of the excystment study are sum[for 1904] 24:321-428); the plerocercus stage has marized in Table 1. A 2.0% solution of pepsin
been reported from the skeletal musculature of at a pH of 2.0 failed to excyst any of the scoleces;
Ariusfelis catfish (Hildreth and Lumsden, 1985, however, a 0.5% solution of trypsin (pH 7.6)
Proceedings of the Helminthological Society of produced excystment of all the scoleces within
Washington 52:44-50). This plerocercus consists 90 min. The addition of bile salts into the trypsin
of a juvenile scolex surrounded by a blastocyst. solution decreased the time needed for 100% exThe blastocyst consists of a thick outer wall, a cystment from 90 min to 60 min. Excystment
fluid-filled blastocyst cavity, and a thin inner wall did not occur in control plerocerci incubated in
(Hildreth and Lumsden, 1987, Journal of Par- fish saline at a pH of either 2.0 or 7.6.
asitology 73:400-410). The juvenile scolex lies
The process of excystment in the trypsin/bile
within a second cavity, the receptaculum scole- salt-treated plerocerci initially involves partial
cis, formed by the blastocyst's inner wall. Once
the plerocercus is transferred to its definitive host,
the juvenile scolex must excyst from the blas- Table 1. Effect of digestive agents on excystment of
tocyst before it can attach to the spiral value.
Otobothrium insigne plerocerci.
We tested 2 digestive agents present in the
% excysted at each
stomach (low pH and pepsin) and 2 digestive
time period
agents present in the spiral valve (trypsin and
30
60
90
120
bile salts) in order to determine if 1 or more of
'Digestive" conditions
min min
min
min
these factors may cause excystment in vitro. Plerocerci were obtained from naturally infected cat- 2.0% Pepsin at pH 2.0
0
0
0
0
(N = 25)
fish as described by Hildreth and Lumsden (1985,
KEY WORDS:
tion.
blastocyst digestion, blastocyst func-
'Present address: Department of Comparative Biosciences, School of Veterinary Medicine, University of
Wisconsin, Madison, Wisconsin 53706.
0.5% Trypsin at pH 7.6
(N= 15)
0.5% Trypsin and 0.3% bile
salts at pH 7.6 (N = 25)
262
Copyright © 2011, The Helminthological Society of Washington
0
27
100
100
52
100
100
100
263
Table 2. Effect of pH on juvenile scolex viability of
Otobothrium insigne.
% viability at each
time period
Scolex condition*
pH
30
min
60
min
90
min
120
min
Manually excysted
Manually excysted
Within blastocyst
2.0
2.5
2.0
0
100
100
0
40
100
0
40
100
0
20
100
* N = 25 scoleces/group.
digestion of the blastocyst outer wall; the juvenile
scolex then eventually penetrates through the inner wall and weakened portions of the outer wall.
Histological observations of paraffin sections
from pepsin/HCl-treated, trypsin/bile salt-treated, and untreated plerocerci showed that the pepsin/HCl solution caused no apparent change in
the blastocyst wall; in contrast, the trypsin/bile
salt solution digested away areas of the blastocyst-wall tegument and portions of the subtegumental muscle.
We also tested the ability of juvenile scoleces
to survive pH values approximating those found
in the shark stomach (i.e., pH less than 2.5; Williams, 1971, Symposia of the British Society for
Parasitology 8:43-77). Plerocerci and manually
excysted juvenile scoleces were incubated at 18°C
in fish saline with pH values of 2.0 and 2.5 (pH
adjusted with HC1). Results for this study are
summarized in Table 2. None of the juvenile
scoleces that lacked blastocysts survived the 30min incubation at a pH of 2; a few survived for
2 hr at a pH of 2.5. One hundred percent of the
blastocyst-enclosed scoleces survived the 2-hr
incubation period at pH 2. These scoleces were
then transferred to fish saline and removed from
their blastocysts; all but 3 of these scoleces remained viable after 30 days in fish saline plus a
mixture of amino acids (20 ml/liter; 50 x MEM
Essential Amino Acid Solution; Grand Island
Biological Co.).
Because pepsin/pH 2 treatment does not cause
excystment of the scoleces in vitro, and because
manually excysted scoleces do not survive in a
low pH in vitro, we speculate that in vivo excystment occurs after the plerocerci leave the
stomach.The ability of trypsin/bile salt treatment to digest the blastocyst outerwall and thereby cause excystment additionally suggests that
excystment occurs in the spiral valve. We also
speculate that one function of the blastocyst is
to shield the juvenile scolex from the acidic environment of the shark's stomach during the scolex's passage to the spiral valve.
Proc. Helminthol. Soc. Wash.
54(2), 1987, pp. 263-265
Research Note
Observations on the Surface of Taenia solium Following
Treatment with Niclosamide
PAZ MARIA SALAZAR-SCHETTINO, l IRENE DE HARO ARTEAGA,' MARIETTA VooE,2
AND ADELA Ruiz HERNANDEZ'
1 Departmento de Ecologia Humana, Facultad de Medicina, Universidad Nacional Autonoma de Mexico,
04510 Mexico, D. F. and
2 Deceased, School of Medicine, University of California, Los Angeles
KEY WORDS: Cestoda, treatment, scanning electron
microscopy.
Studies on the effect of niclosamide on cestodes have shown that the effect of the administration of a curative dose produces the partial
digestion of scolex and proglottids (Goodman et
al., 1980, The Pharmacological Basis of Therapeutics, MacMillan, New York, 1,019 pp.). Histological studies of Taenia solium proglottids after exposure to niclosamide have revealed
vacuolization of the segments (Martinez et al.,
1971, Revista de Investigacion en Salud Publica,
Mexico 31:152-162). Vacuolization of the te-
Copyright © 2011, The Helminthological Society of Washington