Development of Taenia saginata asiatica metacestodes in SCID mice and its infectivity in human and alternative definitive hosts.

Abstract

Development of Taenia saginata asiatica metacestodes in SCID mice, and its infectivity in humans, golden hamsters, and Mongolian gerbils as alternative definitive hosts, were investigated. Cysticerci were recovered from SCID mice that were subcutaneously injected with hatched oncospheres of T. s. asiatica. The morphological changes of metacestodes were observed. The recovered cysticerci were fed to gerbils, hamsters and humans, to check for their infectivity. Tapeworms were recovered from gerbils and hamsters fed with 20 to 45 week-old cysticerci, and proglottids excretions were observed in human volunteers fed with 45 week-old cysticerci. However, no tapeworms were recovered from gerbils fed with 10 week-old cysticerci. Our results suggest that T. s. asiatica oncospheres needed more than 20 weeks to develop to maturity in SCID mice to be infective to both their natural and alternative definitive hosts.

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Instructions for use
Title
Development of Taenia saginata asiatica metacestodes in SCID
mice and its infectivity in human and alternative definitive
hosts
Author(s)
Chang, S. L.; Nonaka, N.; Kamiya, M.; Kanai, Y.; Ooi, H. K.;
Chung, W. C.; Oku, Y.
CitationParasitology Research, 96(2): 95-101
Issue Date2005-05
Doc URLhttp://hdl.handle.net/2115/765
RightThe original publication is available at www.springerlink.com
Type article (author version)
Additional
Information
Hokkaido University Collection of Scholarly and Academic Papers : HUSCAP

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S. L. Chang, N. Nonaka, M. Kamiya, Y. Kanai, H. K. Ooi, W. C. Chung, Y. Oku

Development of Taenia saginata asiatica metacestodes in SCID mice
and its infectivity in human and alternative definitive hosts


S. L. Chang, N. Nonaka, Y. Kanai, Y. Oku (Corresponding author)
Laboratory of Parasitology, Graduate School of Veterinary Medicine, Hokkaido University, Sapporo
060-0818, Japan.
E-mail address: oku@vetmed.hokudai.ac.jp
Tel. and fax:+81-11-706-5196

M. Kamiya
Laboratory of Environmental Zoology, Department of Biosphere and Environmental Sciences,
Faculty of Environmental Systems, Rakuno Gakuen University, Ebetsu 069-8501, Japan

H. K. Ooi
Department of Veterinary Medicine, National Chung Hsing University, 250 Kuo Kuang Road,
Taiwan

W. C. Chung
Department of Parasitology, Taipei Medical University, 250 Wu Hsing Road, Taipei, Taiwan

Abstract: Development of Taenia saginata asiatica metacestodes in SCID mice and its infectivity
in humans, and in golden hamsters and Mongolian gerbils as alternative definitive hosts, were
investigated. Cysticerci were recovered from SCID mice that were subcutaneously injected with
hatched eggs of T. s. asiatica. The morphological changes of cysticerci were observed. The
recovered cysticerci were by fed to gerbils, hamsters and humans, to check for infectivity.
Tapeworms were recovered from gerbils and hamsters that were fed 20 to 45 week-old cysticerci,
and proglottids excretion were observed in human volunteers fed with 45 week-old cysticerci.
However, no tapeworms were recovered from gerbils fed with 10 week-old cysticerci. Our results
suggest that T. s. asiatica oncospheres needed more than 20 weeks to develop to maturity in SCID
mice to be infective to both their natural and alternative definitive hosts.

Keywords: Taenia saginata asiatica; Metacestode; Cysticercus; SCID mice; Alternative host;
Human infection

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Introduction

Asian taeniasis, caused by Taenia saginata asiatica, was first reported by Oi in 1915 in central
Taiwan (Oi 1915). It has been reported in many other Asian countries such as China (several
provinces), Korea, Indonesia, Thailand, Philippines, Malaysia and Myanmar (Fan et al. 1989, 1990a,
1992a, 1992b; Eom and Rim 1993; Bowles and McManus 1994; Simanjuntak et al. 1997; Zhang et
al. 1999; Fan 2000; Fan et al. 2001; Eom et al. 2002; Ito et al. 2003).
Compared with other human taeniids, the tapeworm of T. s. asiatica has no hook on its rostellum,
which differed from T. solium but is similar to the classical T. saginata (Taenia saginata saginata)
(Fan et al. 1995). However, in the intermediate host, metacestodes of T. s. asiatica parasitize in the
viscera (mostly in the liver) of pigs (Fan et al. 1995; Eom and Rim 2001), whereas T. s. saginata
parasitize in the muscle of cattle (Schmidt and Roberts 2000).
Recently, eggs of T. s. asiatica had been reported to develop into mature cysticerci when injected
into the subcutaneous tissue of severe combined immunodeficiency (SCID) and immunosuppressed
ICR mice (Ito et al. 1997b; Ito and Ito 1999; Wang et al. 1999). The size of the cysticerci recovered
from SCID mice was found to be larger than those in the pigs (Ito et al. 1997a). Moreover, 49% of
the metacestode were seen to be calcified or degenerated in 34 infected pigs at 11 to 97 days
post-infection but no calcification of the metacestodes was observed in the SCID mice at 244 days
post-infection (Wang et al. 2000; Fan et al. 1990c).
Since the SCID mouse has proved to be an experimental intermediate host model for the study of
the development of T. s. asiatica metacestodes, it is necessary to confirm the infectivity of the
cysticerci recovered from SCID mice. Human is the only known natural definitive host of the three
aforementioned human taeniids. In addition, alternative definitive hosts have been used to test for
the infectivity of the cysticerci. Alternative definitive host models for T. solium using golden
hamsters, Mongolian gerbils, chinchillas and gibbons that were orally inoculated with cysticerci
obtained from naturally infected pigs, have been reported. Gravid proglottids were recovered only
from chinchillas and gibbons (Cadigan et al. 1967; Verster 1971, 1974; Maravilla et al. 1998). For T.
s. saginata, sexually mature tapeworms were recovered from gerbils inoculated with cysticerci from
naturally infected cattle (Kamiya et al. 1990). It has also been demonstrated that cysticerci of T.
solium recovered from SCID mice could develop to maturity in hamster albeit only pregravid
tapeworm was observed (Wang et al. 1999). In the present study, we examined the infectivity and
development of T. s. asiatica metacestodes from SCID mice in human and its alternative definitive
hosts, the golden hamsters and Mongolian gerbils.

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Materials and Methods

Parasite

Proglottids of T. s. asiatica adult worm were collected from a Taiwanese aborigine patient after
deworming with atabrine (Quinacrine) (Fan et al. 1990b). The worms were kept at 4˚C in saline
until used.

Development of metacestodes in SCID mice

Eggs were collected from gravid proglottids. Embryophores were removed by incubating the
eggs in 10 % sodium hypochlorite for 10 minutes, and the oncospheres were washed 5 times in
sterile saline. Eighteen SCID mice (C.B-17/Icr-scidJcl, female) purchased from a commercial
source (CLEA, Tokyo, Japan) were subcutaneously inoculated with 20,000 and 40,000 oncospheres
and intraperitoneally with 18,600 oncospheres of T. s. asiatica, respectively (Table 1). The SCID
mice were kept in sterile cages and wood chips used as bedding. The mice were provided with
autoclaved drinking water and commercial pellet food (CLEA, Tokyo, Japan) ad libitum. All the
inoculated SCID mice were sacrificed under ethyl ether anaesthesia at 10, 20, 21, 24 and 45 weeks
after inoculation. To check the evagination rate, cysticerci were incubated in calf bile in 37˚C for 1
hour. For morphological observation, evaginated cysticerci were relaxed in the refrigerator (4˚C) in
saline overnight, fixed in 70% alcohol and cleared in glycerin.

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Table 1 Recovery rates of T. s. asiatica metacestodes from eighteen SCID mice subcutaneously
inoculated with oncospheres
Oncospheres SCID Mice Metacestodes recovery
Number Source a Inoculation
route
Inoculation
dose
Number Age of
autopsy
(weeks)
Average Range
Recovery
rate (%)
A Subcutaneous20,000 5 12, 20 133.6 20-218 0.1-1.1
Intraperitoneal 18,600 5 12, 20 10.8 0-50 0-0.3
B Subcutaneous 40,000 3 24, 62 153.6 1-450 0.003-1.1
Subcutaneous 20,000 5 10-45 814.2 174-2,000 b 0.9-6.4
a Source A: Eggs collected from worms after deworm treatment in December, 2003 and inoculated
into mice on January 9, 2004.
a Source B: Eggs collected from worms after deworm treatment in April, 2004 and inoculated in
May, 2004.
bThe number of recovered metacestodes from 1 (2000 metacestodes were recovered) of the 5 mice
was estimated by the dilution method, and the other samples were counted without diluting.

Development of tapeworms in human and alternative definitive hosts

Three human volunteers (1 female, volunteer A; age 30, 2 males, volunteer B and volunteer C;
age 26 and 51 years old) each swallowed five 45-week-old cysticerci that were obtained from the
SCID mice. After eating the cysticerci, the human volunteers checked their feces daily for the
presence of proglottids. Fifty-five 3-week-old male golden hamsters were purchased from a
commercial breeder (SLC, Shizuoka, Japan) and used for the experiment after 3 weeks
acclimatization (Table 2). The hamsters were divided into 2 groups, designated H1 and H2, and then
orally inoculated with 20 or 24 week-old cysticerci, respectively. Eighty-one 5 to 11 week-old male
and female Mongolian gerbils raised in our laboratory, were used for the experiment (Table 2). The
gerbils were orally inoculated with 10, 20, 21 and 45 week-old cysticerci and divided into 4 groups,
namely G1, G2, G3 and G4. The animals were injected subcutaneously with prednisolone acetate at
different schedules as shown in Table 2. They were then orally inoculated with cysticerci of T. s.
asiatica obtained from the SCID mice by stomach tubes and fed commercial pellet food (CLEA,
Tokyo, Japan) and water ad libitum. Animals were sacrificed under ethyl ether anaesthesia at 2 to
146 days post inoculation (DPI) and tapeworms were collected from their intestines. After relaxing
the worm in saline at 4˚C overnight, the worms were fixed in 70% ethanol, stained with
acid-carmine and observed under light microscope.