- Email: [email protected]
Schistosoma japonicum eggs survive passage through dogs and chickens
Veterinary Parasitology 140 (2006) 362–365 www.elsevier.com/locate/vetpar
Short communication
Schistosoma japonicum eggs survive passage through dogs and chickens Tianping Wang a, Fengfeng Wang a, Lei Zhu a, Shiqing Zhang a, Niels Ørnbjerg b, Maria V. Johansen b,* b
a Anhui Institute of Parasitic Diseases, No. 207 Dongjiao Road, Wuhu 241000, Anhui, PR China DBL-Institute for Health Research and Development, Jaegersborg Alle´ 1D, DK-2920 Charlottenlund, Denmark
Received 14 December 2005; received in revised form 22 March 2006; accepted 22 March 2006
Abstract The present study sought to elucidate whether Schistosoma japonicum eggs could survive a passage through dogs and chickens. Three dogs and three chickens were used for the experiment. The dogs were allowed to eat goat faeces containing 80 S. japonicum eggs per gram. The chickens were given 2 ml of water containing more than 100 S. japonicum eggs per ml. The hatchability of the eggs was 51.8% prior to administration. All faeces were collected for 3 days from the dogs and for 2 days from the chickens and egg excretion and hatchability were measured. The results showed that nearly 50% of the eggs administered to the dogs were recovered in the faeces during the first 2 days and during the first 25 h 39% of the recovered eggs were viable and able to hatch. In the chickens 9% of the administered eggs were recovered within 27 h and within the first 3.5 h after administration 19% of the recovered eggs were viable and able to hatch. The results suggest that both dogs and chickens may act as transport hosts for S. japonicum in endemic areas. # 2006 Elsevier B.V. All rights reserved. Keywords: Schistosoma japonicum; Transport host; Dog; Chicken
1. Introduction Schistosoma japonicum is a zoonotic trematode with an indirect lifecycle and with more than 40 mammalian species acting as definitive hosts (Chen, 1993). Transmission is dependent on whether eggs excreted in faeces of the host reach fresh water so that * Corresponding author. Tel.: +45 77 32 77 43; fax: +45 77 32 77 33. E-mail address: [email protected] (M.V. Johansen).
they can hatch. Most mammalian hosts do not defecate directly in water (except cattle and water buffaloes). Hence for the Schistosoma eggs to reach fresh water, the faecal material must somehow be transported into the water following deposition. This can be facilitated by e.g. rain, flooding, eggs in faeces attached to wheels of vehicles, or cattle stepping in other animals’ faeces on their way to a water body. However, unlike the African schistosomes, S. japonicum is transmitted by amphibious snails, Oncomelania hupensis, which are found in the grass and mud in the wetlands, thus to
0304-4017/$ – see front matter # 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.vetpar.2006.03.026
T. Wang et al. / Veterinary Parasitology 140 (2006) 362–365
keep the transmission going only very little fresh water is required. Hence, the present study sought to investigate whether dogs (a definitive host) and chickens (not a definitive host) could act as transport hosts for S. japonicum.
2. Materials and methods One goat naturally infected with S. japonicum was purchased from an endemic area of Anhui province, China. On the day of the administration of eggs to the dogs and chickens, 10 g of goat faeces was obtained to estimate intensity of infection and hatchability of the eggs using a miracidial hatching technique (Ministry of Health, 2000). Three dogs (one male and two female) of a local domestic breed were used in this study. The dogs were 4-months old and weighing approximately 5 kg each. The dogs were purchased from a schistosomiasis nonendemic area. Three female chickens, 6-month old and weighing approximately 1 kg each were also used. All animals were kept at the research animal facilities at Anhui Institute of Parasitic Diseases. The chickens were fed commercial pellets and Chinese green vegetables. The dogs were fed commercial food and rice. Water was provided ad libitum. Prior to the experiment miracidial hatching tests were performed on faeces from the dogs to confirm their S. japonicum free status. The three dogs were provided with 20, 75 and 60 g goat faeces, respectively containing 80 S. japonicum eggs per gram. The dogs had eaten all faeces within 20 min although the dogs had not been starved prior to the feeding. For the chicken experiment, S. japonicum eggs were obtained from the goat faeces. Twenty-gram fresh goat faeces were dissolved in cold, dechlorinated tap water followed by filtration through 250 and 45 mm sieves. Residual material from the 45 mm sieve was re-suspended in dechlorinated tap water in a 250 ml sedimentation flask and left for 30 min. The supernatant was removed leaving 10 ml sedimentation. The number of eggs per ml was determined as the mean of 3 egg counts in 200 ml of the sediment suspension. Using a syringe, 2–6 ml of water containing an estimated 242, 296 and 1221 S. japonicum eggs were administrated to each chicken, respectively, followed by administration of water. The chickens
363
were subsequently observed closely for signs of regurgitation of the inoculum. All faecal samples from the animals were collected for 2 (chicken) or 3 (dogs) days after administration of the eggs and examined by miracidial hatching test (Ministry of Health, 2000). For this test, the faecal samples were suspended and left to sediment twice in dechlorinated tap water followed by transfer to a flask and incubated under strong artificial illumination at 25 8C. The presence of miracidia was assessed 1, 3 and 5 h after incubation. If miracidia were found 5 h after incubation, assessment was continued every second hour until no miracidia were seen. After completion of the miracidial hatching test the sediment was transferred to counting chambers and the number of non-hatched eggs was recorded using a light microscopy. After the experiment the chickens were killed by cervical dislocation whereas the dogs were adopted as pets. Data were coded and analyzed using SPSS software. Chi-square test was used to compare hatchability before and after passage in either dogs or chickens. A significance level of P < 0.05 was used.
3. Results The intensity of infection in the goat was 80 eggs per gram faeces (eggsg-1) and the hatchability was 51.8% (413/798). Fig. 1 shows the egg recovery and the hatching as a percentage of the total number of eggs administered to the three dogs and three chickens. The estimated total number of eggs administered to the 3 dogs was 12,313, of which 6102 (49.6%) were
Fig. 1. Percent of eggs recovered and hatched out of the total number of eggs administered to three dogs and three chickens. Hatchability of the eggs was 51.8% prior to administration.
364
T. Wang et al. / Veterinary Parasitology 140 (2006) 362–365
recovered from faeces. Of the eggs recovered from the 3 dogs 35.6% (2174/6102) were able to hatch. However, hatchability did significantly decline following the passage through the dogs when compared to the hatchability of the eggs in the fresh goat faeces (x2 = 77.6, P < 0.01). The first defecation took place 5 h after egg ingestion while the last took place 49 h after ingestion. Dog 1 received approximately 1540 eggs of which 366 were excreted at first defecation (25 h after ingestion) and 325 were excreted at second defecation (48 h after ingestion). Only at the first defecation did any of the recovered eggs hatch (59%). Dog 2 ingested approximately 5985 eggs and at its first defecation 5 h after ingestion 1811 eggs were found. Out of these, 44% hatched. At the second defecation 12 h after ingestion 1097 eggs were excreted of which 56% hatched. At the third (23 h) and fourth (46 h) defecation 15 eggs were found each time but none were able to hatch. Dog 3 ingested approximately 4788 eggs. At its first defecation 11 h after ingestion 2070 eggs were recovered of which 19% hatched. The second defecation occurred after 23 h. Of the 227 eggs recovered, 74% hatched. At the dog’s third defecation 49 h after ingestion 176 eggs were recovered but none of these hatched. The total number of eggs administered to the 3 chickens was 1759 of which 156 were recovered (8.9%). Like with the dogs, viable eggs were recovered from all chickens and the mean proportion of recovered eggs, which hatched was 19.2% (30/156). The hatchability of the eggs was significantly lower compared to eggs in the donor goat faeces (x2 = 54.2, P < 0.01). The first eggs appeared in faeces 40 min after administration and the last time eggs were observed was 26.5 h after administration. Chicken 1 received 242 eggs and at first defecation 40 min later 16 eggs were recovered of which 13 hatched (81.3%). Hereafter no miracidia were recorded but in total 11 eggs were found, the last one 18 h after administration. Chicken 2 got 296 eggs. Two hours after administration three eggs were found of which two hatched and 1 h later another three eggs were found. Chicken 3 received 1221 eggs. At the first defecation 1 h after administration neither eggs nor miracidia were recovered. However, 2 h after administration 4 miracidia and 3 eggs were recovered and 1.5 h later 11 miracidia and 23 eggs were found. Thereafter no more eggs were found.
4. Discussion The results showed that nearly 50% of the eggs administered to the dogs were recovered in the faeces during the first 2 days and after the first 25 h, 39% of the recovered eggs were viable and able to hatch. In the chickens 9% of the administered eggs were recovered within 27 h and within the first 3.5 h after administration 19% of the recovered eggs hatched. Although the number of eggs and their viability were reduced following intestinal passage, both dogs and chickens proved to be possible transport hosts for S. japonicum. In China dogs have traditionally been used as watchdogs but in the past decades pet dogs have become more and more common, especially in the countryside (Wang et al., 1998). This change has resulted in an increase in non-restrained dogs roaming freely in the villages. Promiscuous defecation by humans and domestic animals combined with dog’s habit of coprophagy have lead to the hypothesis that dogs may play a role as mechanical transmitter of S. japonicum eggs as have been seen for several other helminths (Traub et al., 2002). However, if the passage through the dog reduces the viability of S. japonicum this would theoretically also reduce transmission. On the other hand, dog’s free roaming and indiscrete defecation does increase the likelihood that the eggs would be deposited in snail-infested wetlands. Hence, the role of the dog as transport host as well as a definitive host needs to be further assessed. Chickens are very common in most Chinese villages and are most often allowed to roam freely. Although their roaming range is more limited than the dogs their chance of entering snail habitats is high (Chen and Ye, 2005). However, chicken do not have the same habit of coprophagy as dogs and although the present study showed that they can act as transmitters, the study also showed that the intestinal passage reduced the hatchability significantly. Hence the chickens might play a minor role in transmission of S. japonicum. However, in the present study the dogs and chickens were not infected in the same way, hence it cannot be excluded that some viable eggs have hatched during the processing of infection material for the chickens leaving a higher proportion of eggs not able to hatch passing through the chickens as compared to the dogs.
T. Wang et al. / Veterinary Parasitology 140 (2006) 362–365
Further studies should be undertaken to elucidate the actual role of various animals for transmission of S. japonicum. Pigs are known to be coprophagous and whether they like dogs play a double role as both actual host and transport host deserve further investigations. Likewise, in areas where wild life is abundant like in Indonesia, their role in transmission should be considered. References Chen, M.G., 1993. Schistosoma japonicum and S. japonicum-like infections: epidemiology, clinical and pathological aspects. In:
365
Jordan, P., Webbe, G., Sturrock, R.F. (Eds.), Human Schistosomiasis. CAB International, Oxon, UK, pp. 242–243. Chen, X.Z., Ye, J.L., 2005. Highly effective techniques for raising native chickens. China Poult. 27, 20–21 (in Chinese only). Ministry of Health, China, 2000. Manual for Schistosomiasis Control. Shanghai Science and Technique Publisher, Shanghai, China, pp. 77–78, 218–220, 288 pp. (in Chinese only). Traub, R.J., Robertson, I.D., Irwin, P., Mencke, N., Thompson, R.C., 2002. The role of dogs in transmission of gastrointestinal parasites in a remote tea-growing community in northeastern India. Am. J. Trop. Med. Hyg. 67, 539–545. Wang, T.P., Ge, J.H., Wu, W.D., Zhang, S.Q., Lu, D.B., Zhang, G.H., He, J.C., Xiao, X., Zhu, C.G., Fang, G.R., 1998. Infection sources of schistosomiasis and their role in the transmission in lake and marshland regions in Anhui province. Chin. J. Parasitic Dis. Contr. 11, 196–199 (in Chinese, English abstract).
Short communication
Schistosoma japonicum eggs survive passage through dogs and chickens Tianping Wang a, Fengfeng Wang a, Lei Zhu a, Shiqing Zhang a, Niels Ørnbjerg b, Maria V. Johansen b,* b
a Anhui Institute of Parasitic Diseases, No. 207 Dongjiao Road, Wuhu 241000, Anhui, PR China DBL-Institute for Health Research and Development, Jaegersborg Alle´ 1D, DK-2920 Charlottenlund, Denmark
Received 14 December 2005; received in revised form 22 March 2006; accepted 22 March 2006
Abstract The present study sought to elucidate whether Schistosoma japonicum eggs could survive a passage through dogs and chickens. Three dogs and three chickens were used for the experiment. The dogs were allowed to eat goat faeces containing 80 S. japonicum eggs per gram. The chickens were given 2 ml of water containing more than 100 S. japonicum eggs per ml. The hatchability of the eggs was 51.8% prior to administration. All faeces were collected for 3 days from the dogs and for 2 days from the chickens and egg excretion and hatchability were measured. The results showed that nearly 50% of the eggs administered to the dogs were recovered in the faeces during the first 2 days and during the first 25 h 39% of the recovered eggs were viable and able to hatch. In the chickens 9% of the administered eggs were recovered within 27 h and within the first 3.5 h after administration 19% of the recovered eggs were viable and able to hatch. The results suggest that both dogs and chickens may act as transport hosts for S. japonicum in endemic areas. # 2006 Elsevier B.V. All rights reserved. Keywords: Schistosoma japonicum; Transport host; Dog; Chicken
1. Introduction Schistosoma japonicum is a zoonotic trematode with an indirect lifecycle and with more than 40 mammalian species acting as definitive hosts (Chen, 1993). Transmission is dependent on whether eggs excreted in faeces of the host reach fresh water so that * Corresponding author. Tel.: +45 77 32 77 43; fax: +45 77 32 77 33. E-mail address: [email protected] (M.V. Johansen).
they can hatch. Most mammalian hosts do not defecate directly in water (except cattle and water buffaloes). Hence for the Schistosoma eggs to reach fresh water, the faecal material must somehow be transported into the water following deposition. This can be facilitated by e.g. rain, flooding, eggs in faeces attached to wheels of vehicles, or cattle stepping in other animals’ faeces on their way to a water body. However, unlike the African schistosomes, S. japonicum is transmitted by amphibious snails, Oncomelania hupensis, which are found in the grass and mud in the wetlands, thus to
0304-4017/$ – see front matter # 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.vetpar.2006.03.026
T. Wang et al. / Veterinary Parasitology 140 (2006) 362–365
keep the transmission going only very little fresh water is required. Hence, the present study sought to investigate whether dogs (a definitive host) and chickens (not a definitive host) could act as transport hosts for S. japonicum.
2. Materials and methods One goat naturally infected with S. japonicum was purchased from an endemic area of Anhui province, China. On the day of the administration of eggs to the dogs and chickens, 10 g of goat faeces was obtained to estimate intensity of infection and hatchability of the eggs using a miracidial hatching technique (Ministry of Health, 2000). Three dogs (one male and two female) of a local domestic breed were used in this study. The dogs were 4-months old and weighing approximately 5 kg each. The dogs were purchased from a schistosomiasis nonendemic area. Three female chickens, 6-month old and weighing approximately 1 kg each were also used. All animals were kept at the research animal facilities at Anhui Institute of Parasitic Diseases. The chickens were fed commercial pellets and Chinese green vegetables. The dogs were fed commercial food and rice. Water was provided ad libitum. Prior to the experiment miracidial hatching tests were performed on faeces from the dogs to confirm their S. japonicum free status. The three dogs were provided with 20, 75 and 60 g goat faeces, respectively containing 80 S. japonicum eggs per gram. The dogs had eaten all faeces within 20 min although the dogs had not been starved prior to the feeding. For the chicken experiment, S. japonicum eggs were obtained from the goat faeces. Twenty-gram fresh goat faeces were dissolved in cold, dechlorinated tap water followed by filtration through 250 and 45 mm sieves. Residual material from the 45 mm sieve was re-suspended in dechlorinated tap water in a 250 ml sedimentation flask and left for 30 min. The supernatant was removed leaving 10 ml sedimentation. The number of eggs per ml was determined as the mean of 3 egg counts in 200 ml of the sediment suspension. Using a syringe, 2–6 ml of water containing an estimated 242, 296 and 1221 S. japonicum eggs were administrated to each chicken, respectively, followed by administration of water. The chickens
363
were subsequently observed closely for signs of regurgitation of the inoculum. All faecal samples from the animals were collected for 2 (chicken) or 3 (dogs) days after administration of the eggs and examined by miracidial hatching test (Ministry of Health, 2000). For this test, the faecal samples were suspended and left to sediment twice in dechlorinated tap water followed by transfer to a flask and incubated under strong artificial illumination at 25 8C. The presence of miracidia was assessed 1, 3 and 5 h after incubation. If miracidia were found 5 h after incubation, assessment was continued every second hour until no miracidia were seen. After completion of the miracidial hatching test the sediment was transferred to counting chambers and the number of non-hatched eggs was recorded using a light microscopy. After the experiment the chickens were killed by cervical dislocation whereas the dogs were adopted as pets. Data were coded and analyzed using SPSS software. Chi-square test was used to compare hatchability before and after passage in either dogs or chickens. A significance level of P < 0.05 was used.
3. Results The intensity of infection in the goat was 80 eggs per gram faeces (eggsg-1) and the hatchability was 51.8% (413/798). Fig. 1 shows the egg recovery and the hatching as a percentage of the total number of eggs administered to the three dogs and three chickens. The estimated total number of eggs administered to the 3 dogs was 12,313, of which 6102 (49.6%) were
Fig. 1. Percent of eggs recovered and hatched out of the total number of eggs administered to three dogs and three chickens. Hatchability of the eggs was 51.8% prior to administration.
364
T. Wang et al. / Veterinary Parasitology 140 (2006) 362–365
recovered from faeces. Of the eggs recovered from the 3 dogs 35.6% (2174/6102) were able to hatch. However, hatchability did significantly decline following the passage through the dogs when compared to the hatchability of the eggs in the fresh goat faeces (x2 = 77.6, P < 0.01). The first defecation took place 5 h after egg ingestion while the last took place 49 h after ingestion. Dog 1 received approximately 1540 eggs of which 366 were excreted at first defecation (25 h after ingestion) and 325 were excreted at second defecation (48 h after ingestion). Only at the first defecation did any of the recovered eggs hatch (59%). Dog 2 ingested approximately 5985 eggs and at its first defecation 5 h after ingestion 1811 eggs were found. Out of these, 44% hatched. At the second defecation 12 h after ingestion 1097 eggs were excreted of which 56% hatched. At the third (23 h) and fourth (46 h) defecation 15 eggs were found each time but none were able to hatch. Dog 3 ingested approximately 4788 eggs. At its first defecation 11 h after ingestion 2070 eggs were recovered of which 19% hatched. The second defecation occurred after 23 h. Of the 227 eggs recovered, 74% hatched. At the dog’s third defecation 49 h after ingestion 176 eggs were recovered but none of these hatched. The total number of eggs administered to the 3 chickens was 1759 of which 156 were recovered (8.9%). Like with the dogs, viable eggs were recovered from all chickens and the mean proportion of recovered eggs, which hatched was 19.2% (30/156). The hatchability of the eggs was significantly lower compared to eggs in the donor goat faeces (x2 = 54.2, P < 0.01). The first eggs appeared in faeces 40 min after administration and the last time eggs were observed was 26.5 h after administration. Chicken 1 received 242 eggs and at first defecation 40 min later 16 eggs were recovered of which 13 hatched (81.3%). Hereafter no miracidia were recorded but in total 11 eggs were found, the last one 18 h after administration. Chicken 2 got 296 eggs. Two hours after administration three eggs were found of which two hatched and 1 h later another three eggs were found. Chicken 3 received 1221 eggs. At the first defecation 1 h after administration neither eggs nor miracidia were recovered. However, 2 h after administration 4 miracidia and 3 eggs were recovered and 1.5 h later 11 miracidia and 23 eggs were found. Thereafter no more eggs were found.
4. Discussion The results showed that nearly 50% of the eggs administered to the dogs were recovered in the faeces during the first 2 days and after the first 25 h, 39% of the recovered eggs were viable and able to hatch. In the chickens 9% of the administered eggs were recovered within 27 h and within the first 3.5 h after administration 19% of the recovered eggs hatched. Although the number of eggs and their viability were reduced following intestinal passage, both dogs and chickens proved to be possible transport hosts for S. japonicum. In China dogs have traditionally been used as watchdogs but in the past decades pet dogs have become more and more common, especially in the countryside (Wang et al., 1998). This change has resulted in an increase in non-restrained dogs roaming freely in the villages. Promiscuous defecation by humans and domestic animals combined with dog’s habit of coprophagy have lead to the hypothesis that dogs may play a role as mechanical transmitter of S. japonicum eggs as have been seen for several other helminths (Traub et al., 2002). However, if the passage through the dog reduces the viability of S. japonicum this would theoretically also reduce transmission. On the other hand, dog’s free roaming and indiscrete defecation does increase the likelihood that the eggs would be deposited in snail-infested wetlands. Hence, the role of the dog as transport host as well as a definitive host needs to be further assessed. Chickens are very common in most Chinese villages and are most often allowed to roam freely. Although their roaming range is more limited than the dogs their chance of entering snail habitats is high (Chen and Ye, 2005). However, chicken do not have the same habit of coprophagy as dogs and although the present study showed that they can act as transmitters, the study also showed that the intestinal passage reduced the hatchability significantly. Hence the chickens might play a minor role in transmission of S. japonicum. However, in the present study the dogs and chickens were not infected in the same way, hence it cannot be excluded that some viable eggs have hatched during the processing of infection material for the chickens leaving a higher proportion of eggs not able to hatch passing through the chickens as compared to the dogs.
T. Wang et al. / Veterinary Parasitology 140 (2006) 362–365
Further studies should be undertaken to elucidate the actual role of various animals for transmission of S. japonicum. Pigs are known to be coprophagous and whether they like dogs play a double role as both actual host and transport host deserve further investigations. Likewise, in areas where wild life is abundant like in Indonesia, their role in transmission should be considered. References Chen, M.G., 1993. Schistosoma japonicum and S. japonicum-like infections: epidemiology, clinical and pathological aspects. In:
365
Jordan, P., Webbe, G., Sturrock, R.F. (Eds.), Human Schistosomiasis. CAB International, Oxon, UK, pp. 242–243. Chen, X.Z., Ye, J.L., 2005. Highly effective techniques for raising native chickens. China Poult. 27, 20–21 (in Chinese only). Ministry of Health, China, 2000. Manual for Schistosomiasis Control. Shanghai Science and Technique Publisher, Shanghai, China, pp. 77–78, 218–220, 288 pp. (in Chinese only). Traub, R.J., Robertson, I.D., Irwin, P., Mencke, N., Thompson, R.C., 2002. The role of dogs in transmission of gastrointestinal parasites in a remote tea-growing community in northeastern India. Am. J. Trop. Med. Hyg. 67, 539–545. Wang, T.P., Ge, J.H., Wu, W.D., Zhang, S.Q., Lu, D.B., Zhang, G.H., He, J.C., Xiao, X., Zhu, C.G., Fang, G.R., 1998. Infection sources of schistosomiasis and their role in the transmission in lake and marshland regions in Anhui province. Chin. J. Parasitic Dis. Contr. 11, 196–199 (in Chinese, English abstract).