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Schistosoma mekongi and Schistosoma japonicum: Differences in the distribution of eggs in the viscera of mice
Parasitology International 56 (2007) 239 – 241 www.elsevier.com/locate/parint
Short communication
Schistosoma mekongi and Schistosoma japonicum: Differences in the distribution of eggs in the viscera of mice Yoshinori Hirose a , Jun Matsumoto a , Masashi Kirinoki a , Mizuho Shimada a , Yuichi Chigusa a , Satoshi Nakamura b , Muth Sinuon c , Duong Socheat c , Viroj Kitikoon d , Hajime Matsuda a,⁎ b
a Department of Tropical Medicine and Parasitology, Dokkyo Medical University School of Medicine, Mibu, Shimotsuga, Tochigi 321-0293, Japan Department of Appropriate Technology Development and Transfer, Research Institute, International Medical Center of Japan, Shinjuku, Tokyo 162-0052, Japan c National Centre for Parasitology, Entomology and Malaria Control, Ministry of Health, #372 Monivong Blvd, Phnom Penh, Cambodia d Department of Social and Environmental Medicine, Faculty of Tropical Medicine, Mahidol University, 420/6 Rajvithi Road, Bangkok 1044, Thailand
Received 31 July 2006; received in revised form 17 March 2007; accepted 31 March 2007 Available online 6 April 2007
Abstract The difference in the distribution of Schistosoma eggs in the viscera has not been clearly elucidated in the two closely related species Schistosoma japonicum and Schistosoma mekongi. In this study, we quantitatively compared the distribution of eggs in mice infected with the two species. In S. mekongi-infected mice, 56.6% to 69.4% of total eggs were found in the distal small intestine 9 to 15 weeks after infection, while in S. japonicum-infected mice, 48.8% to 71.8% of eggs were found in the proximal small intestine during the same period. There were significantly more eggs in the liver in mice infected with S. japonicum than in those infected with S. mekongi. The number of adult worms recovered did not differ between the two species during the study period. The total number of eggs laid in the tissues also did not differ between the two species at 12 to 15 weeks postinfection, but in the earlier period the total number of eggs was significantly fewer in S. mekongi-infected than in S. japonicum-infected mice, suggesting the delayed maturation of the former compared with the latter. These results clearly show that S. japonicum and S. mekongi exhibit different oviposition behavior in their hosts. © 2007 Published by Elsevier Ireland Ltd. Keywords: Schistosoma japonicum; Schistosoma mekongi; Proximal small intestine; Distal small intestine
Schistosomiasis mekongi is endemic in the lower Mekong River basin in Laos, Cambodia, and northern Thailand. The first human schistosomiasis case in the basin was reported from Laos by Vic-Dupont et al. in 1957 [1], followed by a case in Cambodia. These cases were described as Schistosoma japonicumlike infections until Voge et al. established the new species Schistosoma mekongi in 1978 [2]. A WHO survey in 1966– 67 revealed that Khong Island was an endemic area of schistosomiasis mekongi, with a 12% infection rate [3,4]. The intermediate host of S. mekongi was identified as Lithoglyphopsis aperta (Hydrobiidae), which was renamed Tricula aperta [5] and then Neotricula aperta [6]. Voge et al.
⁎ Corresponding author. Tel.: +81 282 87 2134; fax: +81 282 86 6431. E-mail address: [email protected] (H. Matsuda). 1383-5769/$ - see front matter © 2007 Published by Elsevier Ireland Ltd. doi:10.1016/j.parint.2007.03.004
[2] reported that the Mekong schistosome differed from S. japonicum in the size of embryonated eggs and the length of the prepatent period in the mammalian host. Unlike S. japonicum, S. mekongi develops poorly in rabbits [7]. In human schistosomiasis japonica, the typical network pattern is observed in ultrasonographic images of the liver, while in S. mekongi infection little change is detectable in the liver parenchyma except for portal vein thickening [8,9]. The difference in the morbidity suggests that there may be a difference in the site of oviposition between S. japonicum and S. mekongi. Previous studies indicated that, in S. mekongi infection, the site of the heaviest concentration of eggs in mice is usually the distal small intestine [7], while in S. japonicum infection, the majority of eggs are laid in the proximal small intestine [10]. To the best of our knowledge, however, there have been no quantitative comparative studies of the oviposition
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sites between S. mekongi and S. japonicum in the same host species. The purpose of the present study was therefore to evaluate quantitatively the difference in oviposition sites in mice between S. mekongi and S. japonicum. S. mekongi (Laotian strain) was maintained in N. aperta snails and ICR mice, and S. japonicum (Yamanashi strain) was maintained in O. nosophora snails and ICR mice in our laboratory as described previously [11]. Four-week-old female ddY mice were each infected via the percutaneous route with 40 cercariae of S. mekongi or S. japonicum [12]. Groups of five mice each were killed 6, 9, 12, and 15 weeks after infection, and the number of worm pairs was counted under a microscope after collection with a perfusion technique [13]. The intestine was removed and divided into three sections: proximal small intestine (duodenum to anterior half of small intestine), distal small intestine (posterior half of small intestine to terminal ileum), and the large intestine (cecum and colon to rectum). The liver and the 3 segments of the intestine were placed in plastic tubes with 50 mL of 5% KOH solution and digested at 37 °C for 4 h [10]. The digested solutions were mixed well, centrifuged at 1710 ×g for 5 min at room temperature, and the supernatant was discarded. The volumes of the remaining sediment were adjusted to 10 mL (S. mekongi) or 40 mL (S. japonicum) with distilled water and stored in a refrigerator after the addition of 5% sodium azide (1 drop of reagent/1 mL sample). An aliquot (0.02 mL) of each sediment was examined under a microscope, and the number of eggs was counted in 6 (S. japonicum) or 5 replicates (S. mekongi). In the examination, immature eggs, mature eggs, shells, and calcified eggs were counted. The number of eggs in the liver and intestine was divided by the number of worm pairs recovered to give the mean number of eggs per worm pair. Microsoft Excel was used to calculate the geometric mean and SE. The Wilcoxon–Mann–Whitney test and Student's t-test were used to assess the significance of differences. The total number, i.e., the sum of the number of eggs in the liver and intestine, laid per worm pair was significantly fewer in
S. mekongi-infected than in S. japonicum-infected mice at 6 and 9 weeks postinfection, although that difference was no longer observed at 12 and 15 weeks postinfection. The tissue/organ distribution of S. mekongi eggs showed that the most eggs were laid in the distal small intestine, and the number was significantly greater (P b 0.001) than those in the liver, proximal small intestine, and large intestine from 9 to 15 weeks after infection. The number of eggs in the distal small intestine accounted for 56.6% to 69.4% of the total. In contrast, in S. japonicum infection, the majority of eggs (38.4% to 71.8% of the total) were found in the proximal small intestine, and the number was significantly greater (P b 0.05 at 6 weeks, P b 0.001 at 9–15 weeks) than those in the liver, distal small intestine, and large intestine from 6 to 15 weeks after infection. The number of eggs in the liver was significantly greater in S. japonicum than in S. mekongi infection at 6, 9, 12, and 15 weeks postinfection (P b 0.001). There was no statistical difference in the number of worm pairs recovered from mice infected with S. japonicum and those infected with S. mekongi during the entire study period (Table 1). In a previous study of the oviposition sites of schistosome eggs in albino mice infected with S. japonicum, 81% of eggs were found in the small intestine, 11% in the liver, and 7% in the large intestine [14]. Amano and Oshima [10] further reported that 61.8% of S. japonicum eggs were found in the proximal small intestine 15 weeks after infection in female ddY mice. On the other hand, in dogs infected with S. mekongi, eggs were more common in the ileum than in the colon [15]. Moore and Sandground [16] stated that the localization of the worms in the alimentary canal varied with the host species. The present comparative study in the same host species clearly showed that the preferred site of oviposition differs between S. mekongi and S. japonicum. In our study, 71.8% of S. japonicum eggs and 58.3% of S. mekongi eggs were seen in the proximal small intestine and in the distal small intestine, respectively, 15 weeks after infection, consistent with previous reports [7,10,15]. It has been suggested that there are differences in ultrasound images
Table 1 Numbers of Schistosoma mekongi eggs and Schistosoma japonicum eggs per worm pair in different tissues in mice at weeks 6, 9, 12, and 15 after infection Tissue site
Week 6 (mean ± SE)
(%)
Week 9 (mean ± SE)
(%)
Week 12 (mean ± SE)
(%)
Week 15 (mean ± SE)
(%)
S. mekongi Worm pairs per mouse Liver Proximal small intestine Distal small intestine Large intestine Total
10.2 ± 2.08 1,004 ± 127 184 ± 56 1,935 ± 201 1,761 ± 232 4,884 ± 315 a
20.6 3.8 39.6 36.1 100
8.4 ± 1.08 3,141 ± 203 4,933 ± 559 19,468 ± 1072⁎⁎⁎ 6,847 ± 913 34,389 ± 833a
9.1 14.3 56.6 19.9 100
6.2 ± 1.16 3,376 ± 420 5,064 ± 1422 29,982 ± 3840⁎⁎⁎ 4,777 ± 857 43,200 ± 4198
7.8 11.7 69.4 11.1 100
3.8 ± 0.73 5,010 ± 389 9,052 ± 2,837 36,211 ± 2,707⁎⁎⁎ 11,887 ± 985 62,160 ± 1555
8.1 14.6 58.3 19.1 100
S. japonium Worm pairs per mouse Liver Proximal small intestine Distal small intestine Large intestine Total
8.0 ± 1.87 5,463 ± 463 9,459 ± 469⁎ 7,905 ± 427 1,800 ± 235 24,627 ± 924a
22.2 38.4 32.1 7.3 100
7.2 ± 1.74 8,815 ± 723 32,574 ± 3311⁎⁎⁎ 11,724 ± 849 2,142 ± 550 55,256 ± 3223a
16.0 59.0 21.2 3.9 100
5.0 ± 0.55 8,737 ± 760 26,616 ± 1627⁎⁎⁎ 11,682 ± 2014 7,504 ± 2167 54,540 ± 4,669
16.0 48.8 21.4 13.8 100
±7.2 ± 2.24 ±8,033 ± 1,084 ±52,023 ± 7,844⁎⁎⁎ ±10,791 ± 1,313 ±1,581 ± 243 ±72,428 ± 7,730
11.1 71.8 14.9 2.2 100
All data are expressed as mean ± SE (n = 5). ⁎, ⁎⁎⁎Significantly different from other tissues at the same time after infection (⁎P b 0.05, ⁎⁎⁎ P b 0.001). a Significant differences between S. mekongi and S. japonicum at the same time after infection (P b 0.001).
Y. Hirose et al. / Parasitology International 56 (2007) 239–241
of the liver between schistosomiasis japonicum and schistosomiasis mekongi: the former exhibits more severe liver parenchymal changes than the latter [8]. In this respect, it is interesting to note that the number of eggs in the liver was significantly greater in S. japonicum than in S. mekongi infection. However, it is as yet unclear whether the oviposition sites of S. mekongi and S. japonicum vary due to the parasite strain and the intensity of infection, as suggested by Hsü and Hsü [14]. It has been reported that the eggs of S. mekongi are laid and mature later than those of S. japonicum [7]. In the present study, the total number of eggs laid per worm pair in the early period of infection was significantly fewer in S. mekongi infection than in S. japonicum infection, although the number of worms recovered did not differ significantly between the two species. Thus, it appears that the sexual maturity of S. mekongi is delayed compared with that of S. japonicum in the final host. Taken together, the present results show that S. japonicum and S. mekongi exhibit different oviposition behavior in their mammalian hosts. This will help in understanding the difference in morbidity after infection with the two closely related Schistosoma species. Acknowledgements This study was supported in part by grants for emerging and reemerging infectious diseases from the Ministry of Health, Labor and Welfare, Japan; Sasakawa Memorial Health Foundation; and Ohyama Health Foundation Inc. This study was also supported by the Ministry of Education, Culture, Sports, Science and Technology, Japan, in the project entitled “Sustainable Co-existence of Human, Nature and the Earth” under Research Revolution 2002 (RR2002). References [1] Vic-Dupont BE, Soubrane J, Halle B, Richir C. Bilharziose à Schistosoma japonicum à forme hépato-splénique révéléé par une grande hématémèse. Bull Mem Soc Med Hop Paris 1957;73:933–41 [in French].
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[2] Voge M, Bruckner D, Bruce JI. Schistosoma mekongi sp. n. from man and animals, compared with four geographic strains of Schistosoma japonicum. J Parasitol 1978;64:577–84. [3] Harinasuta C. Introduction: schistosomiasis in Asia. The Mekong schistosome. Malacol Rev 1980(Suppl 2):1–8. [4] Iijima T, Garcia RG. Preliminary survey for schistosomiasis in south Laos. Assignment report, vol. 67. WHO/Bilh; 1967. p. 64. [5] Davis GM, Kitikoon V, Temcharoen P. Monograph on ‘Lithoglyphopsis’aperta, the snail host of Mekong River schistosomiasis. Malacologia 1976;15:241–87. [6] Davis GM, Rao NVS, Hoagland KE. In search of Tricula defined, and a new genus described. Proc Natl Acad Sci Philadelphia 1986;138:426–42. [7] Byram JE, Von Lichtenberg F. Experimental infection with Schistosoma mekongi in laboratory animals: parasitological and pathological findings. The Mekong schistosome. Malacol Rev 1980(Suppl 2):125–59. [8] Hatz C. The use of ultrasound in Schistosomiasis. Adv Parasitol 2001;48: 226–84. [9] Chigusa Y, Ohmae H, Otake H, Keang H, Sinuon M, Saem C, et al. Effects of repeated praziquantel treatment on schistosomiasis mekongi morbidity as detected by ultrasonography. Parasitol Int 2006;55:261–5. [10] Amano T, Oshima T. A quantitative study of Schistosoma japonicum egg production in ddY mice. Jpn J Parasitol 1987;36:383–9. [11] Sasaki Y, Kirinoki M, Chigusa Y. Comparative studies of the defense mechanism against Schistosoma japonicum of schistosome-susceptible and -resistant Oncomelania nosophora. Parasitol Int 2005;54:157–65. [12] Maeda S, Irie Y, Yasuraoka K. Resistance of mice to secondary infection with Schistosoma japonicum, with special reference to neutrophil enriched response to schistosomula in the skin to immune mice. Jpn J Exp Med 1982;52:111–8. [13] Duvall RH, Dewitt WB. An improved perfusion technique for recovering adult Schistosomes from laboratory animals. Am J Trop Med Hyg 1967;16:483–6. [14] Hsü HF, Hsü SYL. Distribution of eggs of different geographic strains of Schistosoma japonicum in the viscera of infected hamsters and mice. Am J Trop Med Hyg 1960;9:240–7. [15] Iijima T, Lo C, Ito Y. Studies on schistosomiasis in the Mekong Basin I. Morphological observation of the schistosomes and detection of their reservoir hosts. Jpn J Parasitol 1971;20:24–33. [16] Moore DV, Sandground JH. The relative egg producing capacity of Schistosoma mansoni and Schistosoma japonicum. Am J Trop Med Hyg 1956;5:831–40.
Short communication
Schistosoma mekongi and Schistosoma japonicum: Differences in the distribution of eggs in the viscera of mice Yoshinori Hirose a , Jun Matsumoto a , Masashi Kirinoki a , Mizuho Shimada a , Yuichi Chigusa a , Satoshi Nakamura b , Muth Sinuon c , Duong Socheat c , Viroj Kitikoon d , Hajime Matsuda a,⁎ b
a Department of Tropical Medicine and Parasitology, Dokkyo Medical University School of Medicine, Mibu, Shimotsuga, Tochigi 321-0293, Japan Department of Appropriate Technology Development and Transfer, Research Institute, International Medical Center of Japan, Shinjuku, Tokyo 162-0052, Japan c National Centre for Parasitology, Entomology and Malaria Control, Ministry of Health, #372 Monivong Blvd, Phnom Penh, Cambodia d Department of Social and Environmental Medicine, Faculty of Tropical Medicine, Mahidol University, 420/6 Rajvithi Road, Bangkok 1044, Thailand
Received 31 July 2006; received in revised form 17 March 2007; accepted 31 March 2007 Available online 6 April 2007
Abstract The difference in the distribution of Schistosoma eggs in the viscera has not been clearly elucidated in the two closely related species Schistosoma japonicum and Schistosoma mekongi. In this study, we quantitatively compared the distribution of eggs in mice infected with the two species. In S. mekongi-infected mice, 56.6% to 69.4% of total eggs were found in the distal small intestine 9 to 15 weeks after infection, while in S. japonicum-infected mice, 48.8% to 71.8% of eggs were found in the proximal small intestine during the same period. There were significantly more eggs in the liver in mice infected with S. japonicum than in those infected with S. mekongi. The number of adult worms recovered did not differ between the two species during the study period. The total number of eggs laid in the tissues also did not differ between the two species at 12 to 15 weeks postinfection, but in the earlier period the total number of eggs was significantly fewer in S. mekongi-infected than in S. japonicum-infected mice, suggesting the delayed maturation of the former compared with the latter. These results clearly show that S. japonicum and S. mekongi exhibit different oviposition behavior in their hosts. © 2007 Published by Elsevier Ireland Ltd. Keywords: Schistosoma japonicum; Schistosoma mekongi; Proximal small intestine; Distal small intestine
Schistosomiasis mekongi is endemic in the lower Mekong River basin in Laos, Cambodia, and northern Thailand. The first human schistosomiasis case in the basin was reported from Laos by Vic-Dupont et al. in 1957 [1], followed by a case in Cambodia. These cases were described as Schistosoma japonicumlike infections until Voge et al. established the new species Schistosoma mekongi in 1978 [2]. A WHO survey in 1966– 67 revealed that Khong Island was an endemic area of schistosomiasis mekongi, with a 12% infection rate [3,4]. The intermediate host of S. mekongi was identified as Lithoglyphopsis aperta (Hydrobiidae), which was renamed Tricula aperta [5] and then Neotricula aperta [6]. Voge et al.
⁎ Corresponding author. Tel.: +81 282 87 2134; fax: +81 282 86 6431. E-mail address: [email protected] (H. Matsuda). 1383-5769/$ - see front matter © 2007 Published by Elsevier Ireland Ltd. doi:10.1016/j.parint.2007.03.004
[2] reported that the Mekong schistosome differed from S. japonicum in the size of embryonated eggs and the length of the prepatent period in the mammalian host. Unlike S. japonicum, S. mekongi develops poorly in rabbits [7]. In human schistosomiasis japonica, the typical network pattern is observed in ultrasonographic images of the liver, while in S. mekongi infection little change is detectable in the liver parenchyma except for portal vein thickening [8,9]. The difference in the morbidity suggests that there may be a difference in the site of oviposition between S. japonicum and S. mekongi. Previous studies indicated that, in S. mekongi infection, the site of the heaviest concentration of eggs in mice is usually the distal small intestine [7], while in S. japonicum infection, the majority of eggs are laid in the proximal small intestine [10]. To the best of our knowledge, however, there have been no quantitative comparative studies of the oviposition
240
Y. Hirose et al. / Parasitology International 56 (2007) 239–241
sites between S. mekongi and S. japonicum in the same host species. The purpose of the present study was therefore to evaluate quantitatively the difference in oviposition sites in mice between S. mekongi and S. japonicum. S. mekongi (Laotian strain) was maintained in N. aperta snails and ICR mice, and S. japonicum (Yamanashi strain) was maintained in O. nosophora snails and ICR mice in our laboratory as described previously [11]. Four-week-old female ddY mice were each infected via the percutaneous route with 40 cercariae of S. mekongi or S. japonicum [12]. Groups of five mice each were killed 6, 9, 12, and 15 weeks after infection, and the number of worm pairs was counted under a microscope after collection with a perfusion technique [13]. The intestine was removed and divided into three sections: proximal small intestine (duodenum to anterior half of small intestine), distal small intestine (posterior half of small intestine to terminal ileum), and the large intestine (cecum and colon to rectum). The liver and the 3 segments of the intestine were placed in plastic tubes with 50 mL of 5% KOH solution and digested at 37 °C for 4 h [10]. The digested solutions were mixed well, centrifuged at 1710 ×g for 5 min at room temperature, and the supernatant was discarded. The volumes of the remaining sediment were adjusted to 10 mL (S. mekongi) or 40 mL (S. japonicum) with distilled water and stored in a refrigerator after the addition of 5% sodium azide (1 drop of reagent/1 mL sample). An aliquot (0.02 mL) of each sediment was examined under a microscope, and the number of eggs was counted in 6 (S. japonicum) or 5 replicates (S. mekongi). In the examination, immature eggs, mature eggs, shells, and calcified eggs were counted. The number of eggs in the liver and intestine was divided by the number of worm pairs recovered to give the mean number of eggs per worm pair. Microsoft Excel was used to calculate the geometric mean and SE. The Wilcoxon–Mann–Whitney test and Student's t-test were used to assess the significance of differences. The total number, i.e., the sum of the number of eggs in the liver and intestine, laid per worm pair was significantly fewer in
S. mekongi-infected than in S. japonicum-infected mice at 6 and 9 weeks postinfection, although that difference was no longer observed at 12 and 15 weeks postinfection. The tissue/organ distribution of S. mekongi eggs showed that the most eggs were laid in the distal small intestine, and the number was significantly greater (P b 0.001) than those in the liver, proximal small intestine, and large intestine from 9 to 15 weeks after infection. The number of eggs in the distal small intestine accounted for 56.6% to 69.4% of the total. In contrast, in S. japonicum infection, the majority of eggs (38.4% to 71.8% of the total) were found in the proximal small intestine, and the number was significantly greater (P b 0.05 at 6 weeks, P b 0.001 at 9–15 weeks) than those in the liver, distal small intestine, and large intestine from 6 to 15 weeks after infection. The number of eggs in the liver was significantly greater in S. japonicum than in S. mekongi infection at 6, 9, 12, and 15 weeks postinfection (P b 0.001). There was no statistical difference in the number of worm pairs recovered from mice infected with S. japonicum and those infected with S. mekongi during the entire study period (Table 1). In a previous study of the oviposition sites of schistosome eggs in albino mice infected with S. japonicum, 81% of eggs were found in the small intestine, 11% in the liver, and 7% in the large intestine [14]. Amano and Oshima [10] further reported that 61.8% of S. japonicum eggs were found in the proximal small intestine 15 weeks after infection in female ddY mice. On the other hand, in dogs infected with S. mekongi, eggs were more common in the ileum than in the colon [15]. Moore and Sandground [16] stated that the localization of the worms in the alimentary canal varied with the host species. The present comparative study in the same host species clearly showed that the preferred site of oviposition differs between S. mekongi and S. japonicum. In our study, 71.8% of S. japonicum eggs and 58.3% of S. mekongi eggs were seen in the proximal small intestine and in the distal small intestine, respectively, 15 weeks after infection, consistent with previous reports [7,10,15]. It has been suggested that there are differences in ultrasound images
Table 1 Numbers of Schistosoma mekongi eggs and Schistosoma japonicum eggs per worm pair in different tissues in mice at weeks 6, 9, 12, and 15 after infection Tissue site
Week 6 (mean ± SE)
(%)
Week 9 (mean ± SE)
(%)
Week 12 (mean ± SE)
(%)
Week 15 (mean ± SE)
(%)
S. mekongi Worm pairs per mouse Liver Proximal small intestine Distal small intestine Large intestine Total
10.2 ± 2.08 1,004 ± 127 184 ± 56 1,935 ± 201 1,761 ± 232 4,884 ± 315 a
20.6 3.8 39.6 36.1 100
8.4 ± 1.08 3,141 ± 203 4,933 ± 559 19,468 ± 1072⁎⁎⁎ 6,847 ± 913 34,389 ± 833a
9.1 14.3 56.6 19.9 100
6.2 ± 1.16 3,376 ± 420 5,064 ± 1422 29,982 ± 3840⁎⁎⁎ 4,777 ± 857 43,200 ± 4198
7.8 11.7 69.4 11.1 100
3.8 ± 0.73 5,010 ± 389 9,052 ± 2,837 36,211 ± 2,707⁎⁎⁎ 11,887 ± 985 62,160 ± 1555
8.1 14.6 58.3 19.1 100
S. japonium Worm pairs per mouse Liver Proximal small intestine Distal small intestine Large intestine Total
8.0 ± 1.87 5,463 ± 463 9,459 ± 469⁎ 7,905 ± 427 1,800 ± 235 24,627 ± 924a
22.2 38.4 32.1 7.3 100
7.2 ± 1.74 8,815 ± 723 32,574 ± 3311⁎⁎⁎ 11,724 ± 849 2,142 ± 550 55,256 ± 3223a
16.0 59.0 21.2 3.9 100
5.0 ± 0.55 8,737 ± 760 26,616 ± 1627⁎⁎⁎ 11,682 ± 2014 7,504 ± 2167 54,540 ± 4,669
16.0 48.8 21.4 13.8 100
±7.2 ± 2.24 ±8,033 ± 1,084 ±52,023 ± 7,844⁎⁎⁎ ±10,791 ± 1,313 ±1,581 ± 243 ±72,428 ± 7,730
11.1 71.8 14.9 2.2 100
All data are expressed as mean ± SE (n = 5). ⁎, ⁎⁎⁎Significantly different from other tissues at the same time after infection (⁎P b 0.05, ⁎⁎⁎ P b 0.001). a Significant differences between S. mekongi and S. japonicum at the same time after infection (P b 0.001).
Y. Hirose et al. / Parasitology International 56 (2007) 239–241
of the liver between schistosomiasis japonicum and schistosomiasis mekongi: the former exhibits more severe liver parenchymal changes than the latter [8]. In this respect, it is interesting to note that the number of eggs in the liver was significantly greater in S. japonicum than in S. mekongi infection. However, it is as yet unclear whether the oviposition sites of S. mekongi and S. japonicum vary due to the parasite strain and the intensity of infection, as suggested by Hsü and Hsü [14]. It has been reported that the eggs of S. mekongi are laid and mature later than those of S. japonicum [7]. In the present study, the total number of eggs laid per worm pair in the early period of infection was significantly fewer in S. mekongi infection than in S. japonicum infection, although the number of worms recovered did not differ significantly between the two species. Thus, it appears that the sexual maturity of S. mekongi is delayed compared with that of S. japonicum in the final host. Taken together, the present results show that S. japonicum and S. mekongi exhibit different oviposition behavior in their mammalian hosts. This will help in understanding the difference in morbidity after infection with the two closely related Schistosoma species. Acknowledgements This study was supported in part by grants for emerging and reemerging infectious diseases from the Ministry of Health, Labor and Welfare, Japan; Sasakawa Memorial Health Foundation; and Ohyama Health Foundation Inc. This study was also supported by the Ministry of Education, Culture, Sports, Science and Technology, Japan, in the project entitled “Sustainable Co-existence of Human, Nature and the Earth” under Research Revolution 2002 (RR2002). References [1] Vic-Dupont BE, Soubrane J, Halle B, Richir C. Bilharziose à Schistosoma japonicum à forme hépato-splénique révéléé par une grande hématémèse. Bull Mem Soc Med Hop Paris 1957;73:933–41 [in French].
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[2] Voge M, Bruckner D, Bruce JI. Schistosoma mekongi sp. n. from man and animals, compared with four geographic strains of Schistosoma japonicum. J Parasitol 1978;64:577–84. [3] Harinasuta C. Introduction: schistosomiasis in Asia. The Mekong schistosome. Malacol Rev 1980(Suppl 2):1–8. [4] Iijima T, Garcia RG. Preliminary survey for schistosomiasis in south Laos. Assignment report, vol. 67. WHO/Bilh; 1967. p. 64. [5] Davis GM, Kitikoon V, Temcharoen P. Monograph on ‘Lithoglyphopsis’aperta, the snail host of Mekong River schistosomiasis. Malacologia 1976;15:241–87. [6] Davis GM, Rao NVS, Hoagland KE. In search of Tricula defined, and a new genus described. Proc Natl Acad Sci Philadelphia 1986;138:426–42. [7] Byram JE, Von Lichtenberg F. Experimental infection with Schistosoma mekongi in laboratory animals: parasitological and pathological findings. The Mekong schistosome. Malacol Rev 1980(Suppl 2):125–59. [8] Hatz C. The use of ultrasound in Schistosomiasis. Adv Parasitol 2001;48: 226–84. [9] Chigusa Y, Ohmae H, Otake H, Keang H, Sinuon M, Saem C, et al. Effects of repeated praziquantel treatment on schistosomiasis mekongi morbidity as detected by ultrasonography. Parasitol Int 2006;55:261–5. [10] Amano T, Oshima T. A quantitative study of Schistosoma japonicum egg production in ddY mice. Jpn J Parasitol 1987;36:383–9. [11] Sasaki Y, Kirinoki M, Chigusa Y. Comparative studies of the defense mechanism against Schistosoma japonicum of schistosome-susceptible and -resistant Oncomelania nosophora. Parasitol Int 2005;54:157–65. [12] Maeda S, Irie Y, Yasuraoka K. Resistance of mice to secondary infection with Schistosoma japonicum, with special reference to neutrophil enriched response to schistosomula in the skin to immune mice. Jpn J Exp Med 1982;52:111–8. [13] Duvall RH, Dewitt WB. An improved perfusion technique for recovering adult Schistosomes from laboratory animals. Am J Trop Med Hyg 1967;16:483–6. [14] Hsü HF, Hsü SYL. Distribution of eggs of different geographic strains of Schistosoma japonicum in the viscera of infected hamsters and mice. Am J Trop Med Hyg 1960;9:240–7. [15] Iijima T, Lo C, Ito Y. Studies on schistosomiasis in the Mekong Basin I. Morphological observation of the schistosomes and detection of their reservoir hosts. Jpn J Parasitol 1971;20:24–33. [16] Moore DV, Sandground JH. The relative egg producing capacity of Schistosoma mansoni and Schistosoma japonicum. Am J Trop Med Hyg 1956;5:831–40.