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Studies on the survival of Ascaris suum eggs under laboratory and simulated field conditions
Veterinary Parasitology 75 Ž1998. 227–234
Studies on the survival of Ascaris suum eggs under laboratory and simulated field conditions C.P.H. Gaasenbeek ) , F.H.M. Borgsteede DLO-Institute for Animal Science and Health, Department of Pathobiology and Epidemiology, Laboratory For Parasitic Diseases, P.O. Box 65, 8200 AB Lelystad, Netherlands Received 10 July 1997; accepted 10 July 1997
Abstract A series of four experiments was carried out to study the survival of Ascaris suum eggs: in a pig slurry unit on a farm, in the laboratory under anaerobic conditions and different relative humidities ŽrH., and under simulated field conditions. Survival of eggs in the pig slurry unit was 20% after four weeks and 0% after 16 weeks. Anaerobic conditions had only a minor influence on survival: after 12 weeks, more than 80% of the eggs could still develop. At high relative humidities Ž100% and 75%., survival was respectively 96% and 62% after 12 weeks. At 47.5% rH, survival dropped to 0% after 10 weeks and at 7.5% rH in 8 weeks. A. suum eggs kept in pig slurry under dry and sunny outdoor conditions survived for 2–4 weeks, whereas under wet and shady conditions, 90% of the eggs were still viable after 8 weeks. q 1998 Elsevier Science B.V. Keywords: Ascaris suum; Pig-nematoda; Humidity; Anaerobic conditions
1. Introduction In the last two decades animal production has increased in the Netherlands and the number of pigs had grown to 14 million in 1994 ŽAnonymous, 1994.. As a result, faecal production on pig farms increased from 9 million tons a year in 1970 to 19 million tons a year in 1994 ŽAnonymous, 1994.. In the Netherlands, pig slurry is applied on agricultural land particularly used for cereal production, on maize fields and on grassland. A surplus of pig slurry is produced in the Eastern and Southern parts of the country. Because of environmental regulations, it is not allowed to apply more slurry than necessary to obtain a maximum crop production. Even application on grassland is )
Corresponding author. Tel.: q31-320-238104; fax: q31-320-238050; e-mail: [email protected]
0304-4017r98r$19.00 q 1998 Elsevier Science B.V. All rights reserved. PII S 0 3 0 4 - 4 0 1 7 Ž 9 7 . 0 0 1 9 8 - 2
228
C.P.H. Gaasenbeek, F.H.M. Borgsteeder Veterinary Parasitology 75 (1998) 227–234
limited to the nutritional need of grass. Hence, the surplus of slurry is stored and distributed to regions with a deficit of nutrition. Slurry may contain free living stages of pathogens and parasitic helminths. The pig is the main host for Ascaris suum, but infections in cattle and sheep are possible. When pig slurry is applied on pasture, it is a possible source of infection. For these ruminants, Enigk et al. Ž1965. reported that A. suum eggs in slurry could survive for more than 37 days at 188C. Several cases of natural A. suum infections have been reported in cattle ŽMcCraw and Lautenslager, 1971; Roneus ´ and Christensson, 1977; McLennan et al., 1974; Borgsteede et al., 1992. and sheep ŽWensvoort, 1962; Brown et al., 1984.. A series of four experiments was carried out to study the survival and development of A. suum eggs: –in pig slurry –under anaerobic conditions –at different relative humidities –under simulated field conditions
2. Materials and methods 2.1. Collection of eggs Adult worms were collected from the intestines of naturally infected pigs at the slaughterhouse and kept in saline for 24 h at 378C. The fluid was sieved Žscreenmesh 32 m m., and the A. suum eggs were stored at 48C in tap water for further use. 2.2. Experiment 1: surÕiÕal of A. suum eggs in pig slurry Forty plastic tubes, 300 mm in height, 20 mm in diameter with twenty holes of 5 mm in diameter were wrapped with 25 m m gauze. The open ends of the tubes were closed with rubber stops. The tubes filled with slurry containing 10,000 A. suum eggs. The tubes were placed in a rack and stored 1.2 m below the surface of a 1.5 m deep pig slurry unit. The contents of this unit was 30 m3. The gauze allowed contact with the surrounding fluid. The experiment started at the end of February, temperature and pH in the pig slurry unit were measured at weekly or fortnightly intervals for a period of 16 weeks. Pairs of tubes were removed from the unit at weekly or fortnightly intervals and survival of eggs was checked. 2.3. Experiment 2: surÕiÕal of A. suum eggs under anaerobic conditions. Twenty-four Petri dishes with 10 ml water and 250 A. suum eggs were placed in Gaspak w jars and stored at 158C. The Gaspak w system is used to exclude the influence of slurry and to create anaerobic conditions. The principle of the Gaspak w system is that oxygen is removed from the jar by catalytic reaction. The catalyst activates hydrogen gas to combine with free oxygen in the jar to form water. Over a period of 12 weeks, pairs of Petri dishes were removed weekly and survival of eggs checked.
C.P.H. Gaasenbeek, F.H.M. Borgsteeder Veterinary Parasitology 75 (1998) 227–234
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2.4. Experiment 3: surÕiÕal of A. suum eggs at different relatiÕe humidities Relative humidities of 100%, 77.5%, 47.5% and 7.5% were created using water and different saturated salt solutions respectively. NaCl, K 2 CO 3 and NaOH. Relative humidity was measured monthly with a hygrometer. Sixteen Petri dishes with sand each containing 250 A. suum eggs were placed above saturated salt solution in a preserving jar at 158C for a period of 12 weeks. Pairs of Petri dishes were removed at weekly or fortnightly intervals and survival of eggs was checked. 2.5. Experiment 4: surÕiÕal of A. suum eggs in pig slurry under simulated field conditions Four different conditions ‘dryrshade’, ‘dryrsun’, ‘wetrshade’ and ‘wetrsun’ were created outdoors on plots of 1 m2 . These plots were covered with glass 500 mm above the ground level. Plastic tubes 60 mm in height, 70 mm in diameter and closed at the bottom side with 25 m m gauze contained 80 grams of pig slurry and 10,000 A. suum eggs. Series of twelve of these tubes were placed on the plots. In total, four series were started respectively on 24r4, 8r5, 22r5 and 5r6. Artificial rain showers were given according to the long range average of rainfall in the Netherlands. Temperature was measured on the plots. Pairs of tubes were removed at weekly or fortnightly intervals and survival of eggs was checked. 2.6. Control of the surÕiÕal of A. suum eggs In all experiments, two samples were removed and sieved over a 90 m m and 32 m m sieve. A. suum eggs were concentrated by flotation with ZnSO4 Ždensity 1.33., washed, and incubated in 0.1 M H 2 SO4 for 4 weeks at 278C. The survival was studied by screening one hundred A. suum eggs. The development of eggs was evaluated under a microscope on the basis of morphological changes of germinal cells, presence of viable larvae in the eggs and, eventually, free living larvae.
3. Results 3.1. Experiment 1: surÕiÕal of A. suum eggs in pig slurry The percentage of eggs which was able to develop decreased after four weeks to 80. After 8 and 16 weeks, this percentage was 40 and 0 respectively ŽFig. 1.. The temperature in the pig slurry unit increased gradually from 108C in mid February to 178C in mid June. An average pH of 7.7 was recorded. 3.2. Experiment 2: surÕiÕal of A. suum eggs under anaerobic conditions. The percentage of eggs which could develop after being placed under anaerobic conditions is presented in Fig. 1. More than 80% of the eggs survived for twelve weeks.
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Fig. 1. Survival of Ascaris suum eggs in pig slurry and under anaerobic conditions.
3.3. Experiment 3: surÕiÕal of A. suum eggs at different relatiÕe humidities The survival of eggs which were kept at a relative humidity of 100% and 77.5% respectively, was 96% and 62% after 12 weeks. Fig. 2 shows a constant decrease of the percentage development of the eggs kept at 47.5 rH, and an even faster decrease at 7.5. 3.4. Experiment 4: surÕiÕal of A. suum eggs in pig slurry under simulated field conditions Fig. 3 presents the percentage of the eggs which could develop after being exposed to the earlier described four simulated field conditions. It was shown that 90% of the eggs in all series developed after being exposed for 3 weeks to the ‘dryrshade’ condition,
Fig. 2. Survival of Ascaris suum eggs at different relative humidities.
Fig. 3. Survival of Ascaris suum eggs in pig slurry under simulated field conditions.
C.P.H. Gaasenbeek, F.H.M. Borgsteeder Veterinary Parasitology 75 (1998) 227–234 231
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C.P.H. Gaasenbeek, F.H.M. Borgsteeder Veterinary Parasitology 75 (1998) 227–234
and 40% after 8 weeks exposure in the series started in April and the beginning of May. The ‘dryrshade’ series exposed in late May and in the beginning of June showed a lower survival and none of the eggs were viable after 8 weeks. Under ‘dryrsun’ conditions the development of A. suum eggs decreased dramatically from the very beginning of the experiment. Dryness must be the factor who killed the eggs, because under ‘wetrsun’ conditions, the eggs survived longer. The temperature of the ‘sun’ conditions shows a 10–20% higher level as under ‘shade’ conditions. The average weektemperature under ‘sun’ conditions did not increase above 258C. In contrast, all series under ‘wetrshade’ conditions showed a survival of 90% or more. A. suum eggs exposed to ‘wetrsun’ conditions ŽFig. 3. showed in all series a development between 60% and 80%, with the exception of the series which started in June, when only 40% of the eggs were able to develop after 8 weeks.
4. Discussion This experiment was designed to obtain insight into some of the factors which influence the survival of A. suum eggs. A. suum eggs can survive for more than 3 months in pig slurry at temperatures between 108C and 178C. Persson Ž1974., and Enigk Ž1980. obtained the same results both with cattle and with pig slurry. Our study confirms these results. However, the longer eggs stay in the slurry, the higher the percentage of eggs that did not survive. It was demonstrated that anaerobic conditions hardly influences the development of A. suum eggs over a 12 week period. Enigk et al. Ž1965. found the same results. They reported a development of 70% after 12 weeks. In contrast to the results of Enigk Ž1979. more than 75% of A. suum eggs survived 6 weeks at a rH of 100%, 77.5% and 47.5% respectively. In the grazing season a rH between 47.5% and 100% is common in our country. Small parts of a pasture have microclimates in which these values occur and they are very important for the survival of A. suum eggs. In the experiment under simulated field conditions, the contribution of only the temperature for killing A. suum eggs was less important. Combination of dryness and sun killed A. suum eggs within a few weeks, while ‘wetrshade’ conditions provided optimal circumstances for eggs to survive. More than 50% of A. suum eggs Žexcept under ‘dryrsun’ conditions. survived longer than 6 weeks under several simulated field conditions. These environmental conditions may commonly occur in the beginning of the grazing season when slurry is applied. A. suum eggs did not develop in pig slurry ŽEnigk et al., 1965., so embryonation will take place when slurry is applied on the pasture and eventually spread by rain showers. A rapid embryonation of A. suum eggs was reported during June, July and August ŽStevenson, 1979.. In the Netherlands, slurry is applied on grassland by soil injection under restricted emission conditions. On clay and peat soils application is the whole year around allowed. On sandy soils, application is prohibited from September to February. Restricted emission application does not prevent A. suum contamination of grassland. Grazing within 4 weeks after application can provide the transmission to other animals.
C.P.H. Gaasenbeek, F.H.M. Borgsteeder Veterinary Parasitology 75 (1998) 227–234
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Thus, contact with viable A. suum eggs is possible and may cause pneumonia in cattle ŽBorgsteede et al., 1992.. In slurry, factors such as anaerobic conditions, alkaline pH and rH hardly influenced the development of A. suum eggs. Other factors that destroy A. suum eggs must be of more importance. Helle et al. Ž1989. reported that larval development in nematode larvae cultures from sheep faeces was blocked by sprinkling with sheep urine and suggested that it was mainly caused by ammonia. Burden and Ginnivan Ž1978. and Juris et al. Ž1992. reported that thermophilic fermentation and a temperature of 558C killed A. suum eggs within one hour. Persson Ž1973. and Olsen Ž1984. have developed systems to destroy A. suum eggs and other parasitic stages based on aeration and thermophilic fermentation. Tharaldsen and Helle Ž1989. concluded that the temperature should be maintained above 40–458C for a period of at least 25 days to obtain adequate killing of A suum eggs. In order to ensure total killing of A. suum eggs and other parasitic stages in slurry which can infect cattle or sheep, it is necessary to use such suitable techniques to treat slurry before application. References Anonymous, 1994. Landbouwcijfers 1994. Agricultural Economics Research Institute and the Netherlands Central Bureau of Statistics, The Haque, Netherlands. Borgsteede, F.H.M., de Leeuw, W.A., Dijkstra, Th., Alsma, G., de Vries, W., 1992. Ascaris suum infecties als oorzaak van klinische problemen bij runderen? Tijdschr. Diergeneeskd. 117, 296–298. Brown, D., Hinton, M., Wright, A.I., 1984. Parasitic liver damage in lambs with particular reference to the migrating larvae of Ascaris suum. Vet. Rec. 115, 300–303. Burden, D.J., Ginnivan, M.J., 1978. The destruction of pig helminth ova and larvae in a slurry treatment process. Vet. Rec. 103, 373–375. Enigk, K., 1979. Resistenz der Dauerformen von Endoparasiten der Haustiere. Berl. Munch. Tieraerztl. ¨ Wochenschr. 92, 491–497. Enigk, K., 1980. Vernichtung parasitarer Entwicklungsformen in Flussigmist. Berl. Munch. Tieraerztl. ¨ ¨ ¨ Wochenschr. 93, 379–384. Enigk, K., Hildebrandt, J., Tietjen, C., 1965. Die Lebensdauer von Helmintheneier und -larven in Schwemmist. Berl. Munch. Tieraerztl. Wochenschr. 6, 102–106. ¨ Helle, O., Velle, W., Tharaldsen, J., 1989. Effect of ovine urine and some of its components on viability of nematode eggs and larvae in sheep faeces. Vet. Parasitol. 32, 349–354. Juris, P., Plachy, P., Toth, F., Venglovsky, J., 1992. Effect of biofermentation of pig slurry on Ascaris suum eggs. Helminthologia 29, 155–159. McCraw, B.M., Lautenslager, J.P., 1971. Pneumonia in calves associated with migrating Ascaris suum larvae. Can. Vet. J. 12, 87–90. McLennan, M.W., Humphris, R.B., Rac, R., 1974. Ascaris suum pneumonia in cattle. Aus. Vet. J. 50, 266–268. Olsen, J.E., 1984. The effect of mesophilic or thermophilic anaerobic digestion of slurry on the survival of pathogenic bacteria, indicator bacteria and intestinal parasites. Bioenergy 84. In: Egneus, H., Ellegard, A. ŽEds.., Procs. conf. June 15–21, Vol. 3. Goteborg Sweden, pp. 401–405. Persson, L., 1973. The destruction of parasites in liquid cattle manure by aeration using the Licom system. Zbl. Vet. Med. B 20, 289–303. Persson, L., 1974. The bionomics of parasite eggs and larvae in manure, soil and fodder; a literature review. Nor. Vet. Med. 26, 1–24. Roneus, ´ O., Christensson, D., 1977. Mature Ascaris suum in naturally infected calves. Vet. Parasitol. 3, 371–375.
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Stevenson, P., 1979. The influence of environmental temperature on the rate of development of Ascaris suum eggs in Great Britain. Res. in Vet. Sci. 27, 193–196. Tharaldsen, J., Helle, O., 1989. Survival of parasite eggs in livestock slurry utilized for compost heat. Acta Agric. Scand. 39, 381–387. Wensvoort, P., 1962. Spontaneous Ascaris lumbricoides infection in lambs. Tijdschr. Diergeneesk. 87, 260–262.
Studies on the survival of Ascaris suum eggs under laboratory and simulated field conditions C.P.H. Gaasenbeek ) , F.H.M. Borgsteede DLO-Institute for Animal Science and Health, Department of Pathobiology and Epidemiology, Laboratory For Parasitic Diseases, P.O. Box 65, 8200 AB Lelystad, Netherlands Received 10 July 1997; accepted 10 July 1997
Abstract A series of four experiments was carried out to study the survival of Ascaris suum eggs: in a pig slurry unit on a farm, in the laboratory under anaerobic conditions and different relative humidities ŽrH., and under simulated field conditions. Survival of eggs in the pig slurry unit was 20% after four weeks and 0% after 16 weeks. Anaerobic conditions had only a minor influence on survival: after 12 weeks, more than 80% of the eggs could still develop. At high relative humidities Ž100% and 75%., survival was respectively 96% and 62% after 12 weeks. At 47.5% rH, survival dropped to 0% after 10 weeks and at 7.5% rH in 8 weeks. A. suum eggs kept in pig slurry under dry and sunny outdoor conditions survived for 2–4 weeks, whereas under wet and shady conditions, 90% of the eggs were still viable after 8 weeks. q 1998 Elsevier Science B.V. Keywords: Ascaris suum; Pig-nematoda; Humidity; Anaerobic conditions
1. Introduction In the last two decades animal production has increased in the Netherlands and the number of pigs had grown to 14 million in 1994 ŽAnonymous, 1994.. As a result, faecal production on pig farms increased from 9 million tons a year in 1970 to 19 million tons a year in 1994 ŽAnonymous, 1994.. In the Netherlands, pig slurry is applied on agricultural land particularly used for cereal production, on maize fields and on grassland. A surplus of pig slurry is produced in the Eastern and Southern parts of the country. Because of environmental regulations, it is not allowed to apply more slurry than necessary to obtain a maximum crop production. Even application on grassland is )
Corresponding author. Tel.: q31-320-238104; fax: q31-320-238050; e-mail: [email protected]
0304-4017r98r$19.00 q 1998 Elsevier Science B.V. All rights reserved. PII S 0 3 0 4 - 4 0 1 7 Ž 9 7 . 0 0 1 9 8 - 2
228
C.P.H. Gaasenbeek, F.H.M. Borgsteeder Veterinary Parasitology 75 (1998) 227–234
limited to the nutritional need of grass. Hence, the surplus of slurry is stored and distributed to regions with a deficit of nutrition. Slurry may contain free living stages of pathogens and parasitic helminths. The pig is the main host for Ascaris suum, but infections in cattle and sheep are possible. When pig slurry is applied on pasture, it is a possible source of infection. For these ruminants, Enigk et al. Ž1965. reported that A. suum eggs in slurry could survive for more than 37 days at 188C. Several cases of natural A. suum infections have been reported in cattle ŽMcCraw and Lautenslager, 1971; Roneus ´ and Christensson, 1977; McLennan et al., 1974; Borgsteede et al., 1992. and sheep ŽWensvoort, 1962; Brown et al., 1984.. A series of four experiments was carried out to study the survival and development of A. suum eggs: –in pig slurry –under anaerobic conditions –at different relative humidities –under simulated field conditions
2. Materials and methods 2.1. Collection of eggs Adult worms were collected from the intestines of naturally infected pigs at the slaughterhouse and kept in saline for 24 h at 378C. The fluid was sieved Žscreenmesh 32 m m., and the A. suum eggs were stored at 48C in tap water for further use. 2.2. Experiment 1: surÕiÕal of A. suum eggs in pig slurry Forty plastic tubes, 300 mm in height, 20 mm in diameter with twenty holes of 5 mm in diameter were wrapped with 25 m m gauze. The open ends of the tubes were closed with rubber stops. The tubes filled with slurry containing 10,000 A. suum eggs. The tubes were placed in a rack and stored 1.2 m below the surface of a 1.5 m deep pig slurry unit. The contents of this unit was 30 m3. The gauze allowed contact with the surrounding fluid. The experiment started at the end of February, temperature and pH in the pig slurry unit were measured at weekly or fortnightly intervals for a period of 16 weeks. Pairs of tubes were removed from the unit at weekly or fortnightly intervals and survival of eggs was checked. 2.3. Experiment 2: surÕiÕal of A. suum eggs under anaerobic conditions. Twenty-four Petri dishes with 10 ml water and 250 A. suum eggs were placed in Gaspak w jars and stored at 158C. The Gaspak w system is used to exclude the influence of slurry and to create anaerobic conditions. The principle of the Gaspak w system is that oxygen is removed from the jar by catalytic reaction. The catalyst activates hydrogen gas to combine with free oxygen in the jar to form water. Over a period of 12 weeks, pairs of Petri dishes were removed weekly and survival of eggs checked.
C.P.H. Gaasenbeek, F.H.M. Borgsteeder Veterinary Parasitology 75 (1998) 227–234
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2.4. Experiment 3: surÕiÕal of A. suum eggs at different relatiÕe humidities Relative humidities of 100%, 77.5%, 47.5% and 7.5% were created using water and different saturated salt solutions respectively. NaCl, K 2 CO 3 and NaOH. Relative humidity was measured monthly with a hygrometer. Sixteen Petri dishes with sand each containing 250 A. suum eggs were placed above saturated salt solution in a preserving jar at 158C for a period of 12 weeks. Pairs of Petri dishes were removed at weekly or fortnightly intervals and survival of eggs was checked. 2.5. Experiment 4: surÕiÕal of A. suum eggs in pig slurry under simulated field conditions Four different conditions ‘dryrshade’, ‘dryrsun’, ‘wetrshade’ and ‘wetrsun’ were created outdoors on plots of 1 m2 . These plots were covered with glass 500 mm above the ground level. Plastic tubes 60 mm in height, 70 mm in diameter and closed at the bottom side with 25 m m gauze contained 80 grams of pig slurry and 10,000 A. suum eggs. Series of twelve of these tubes were placed on the plots. In total, four series were started respectively on 24r4, 8r5, 22r5 and 5r6. Artificial rain showers were given according to the long range average of rainfall in the Netherlands. Temperature was measured on the plots. Pairs of tubes were removed at weekly or fortnightly intervals and survival of eggs was checked. 2.6. Control of the surÕiÕal of A. suum eggs In all experiments, two samples were removed and sieved over a 90 m m and 32 m m sieve. A. suum eggs were concentrated by flotation with ZnSO4 Ždensity 1.33., washed, and incubated in 0.1 M H 2 SO4 for 4 weeks at 278C. The survival was studied by screening one hundred A. suum eggs. The development of eggs was evaluated under a microscope on the basis of morphological changes of germinal cells, presence of viable larvae in the eggs and, eventually, free living larvae.
3. Results 3.1. Experiment 1: surÕiÕal of A. suum eggs in pig slurry The percentage of eggs which was able to develop decreased after four weeks to 80. After 8 and 16 weeks, this percentage was 40 and 0 respectively ŽFig. 1.. The temperature in the pig slurry unit increased gradually from 108C in mid February to 178C in mid June. An average pH of 7.7 was recorded. 3.2. Experiment 2: surÕiÕal of A. suum eggs under anaerobic conditions. The percentage of eggs which could develop after being placed under anaerobic conditions is presented in Fig. 1. More than 80% of the eggs survived for twelve weeks.
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C.P.H. Gaasenbeek, F.H.M. Borgsteeder Veterinary Parasitology 75 (1998) 227–234
Fig. 1. Survival of Ascaris suum eggs in pig slurry and under anaerobic conditions.
3.3. Experiment 3: surÕiÕal of A. suum eggs at different relatiÕe humidities The survival of eggs which were kept at a relative humidity of 100% and 77.5% respectively, was 96% and 62% after 12 weeks. Fig. 2 shows a constant decrease of the percentage development of the eggs kept at 47.5 rH, and an even faster decrease at 7.5. 3.4. Experiment 4: surÕiÕal of A. suum eggs in pig slurry under simulated field conditions Fig. 3 presents the percentage of the eggs which could develop after being exposed to the earlier described four simulated field conditions. It was shown that 90% of the eggs in all series developed after being exposed for 3 weeks to the ‘dryrshade’ condition,
Fig. 2. Survival of Ascaris suum eggs at different relative humidities.
Fig. 3. Survival of Ascaris suum eggs in pig slurry under simulated field conditions.
C.P.H. Gaasenbeek, F.H.M. Borgsteeder Veterinary Parasitology 75 (1998) 227–234 231
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C.P.H. Gaasenbeek, F.H.M. Borgsteeder Veterinary Parasitology 75 (1998) 227–234
and 40% after 8 weeks exposure in the series started in April and the beginning of May. The ‘dryrshade’ series exposed in late May and in the beginning of June showed a lower survival and none of the eggs were viable after 8 weeks. Under ‘dryrsun’ conditions the development of A. suum eggs decreased dramatically from the very beginning of the experiment. Dryness must be the factor who killed the eggs, because under ‘wetrsun’ conditions, the eggs survived longer. The temperature of the ‘sun’ conditions shows a 10–20% higher level as under ‘shade’ conditions. The average weektemperature under ‘sun’ conditions did not increase above 258C. In contrast, all series under ‘wetrshade’ conditions showed a survival of 90% or more. A. suum eggs exposed to ‘wetrsun’ conditions ŽFig. 3. showed in all series a development between 60% and 80%, with the exception of the series which started in June, when only 40% of the eggs were able to develop after 8 weeks.
4. Discussion This experiment was designed to obtain insight into some of the factors which influence the survival of A. suum eggs. A. suum eggs can survive for more than 3 months in pig slurry at temperatures between 108C and 178C. Persson Ž1974., and Enigk Ž1980. obtained the same results both with cattle and with pig slurry. Our study confirms these results. However, the longer eggs stay in the slurry, the higher the percentage of eggs that did not survive. It was demonstrated that anaerobic conditions hardly influences the development of A. suum eggs over a 12 week period. Enigk et al. Ž1965. found the same results. They reported a development of 70% after 12 weeks. In contrast to the results of Enigk Ž1979. more than 75% of A. suum eggs survived 6 weeks at a rH of 100%, 77.5% and 47.5% respectively. In the grazing season a rH between 47.5% and 100% is common in our country. Small parts of a pasture have microclimates in which these values occur and they are very important for the survival of A. suum eggs. In the experiment under simulated field conditions, the contribution of only the temperature for killing A. suum eggs was less important. Combination of dryness and sun killed A. suum eggs within a few weeks, while ‘wetrshade’ conditions provided optimal circumstances for eggs to survive. More than 50% of A. suum eggs Žexcept under ‘dryrsun’ conditions. survived longer than 6 weeks under several simulated field conditions. These environmental conditions may commonly occur in the beginning of the grazing season when slurry is applied. A. suum eggs did not develop in pig slurry ŽEnigk et al., 1965., so embryonation will take place when slurry is applied on the pasture and eventually spread by rain showers. A rapid embryonation of A. suum eggs was reported during June, July and August ŽStevenson, 1979.. In the Netherlands, slurry is applied on grassland by soil injection under restricted emission conditions. On clay and peat soils application is the whole year around allowed. On sandy soils, application is prohibited from September to February. Restricted emission application does not prevent A. suum contamination of grassland. Grazing within 4 weeks after application can provide the transmission to other animals.
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Thus, contact with viable A. suum eggs is possible and may cause pneumonia in cattle ŽBorgsteede et al., 1992.. In slurry, factors such as anaerobic conditions, alkaline pH and rH hardly influenced the development of A. suum eggs. Other factors that destroy A. suum eggs must be of more importance. Helle et al. Ž1989. reported that larval development in nematode larvae cultures from sheep faeces was blocked by sprinkling with sheep urine and suggested that it was mainly caused by ammonia. Burden and Ginnivan Ž1978. and Juris et al. Ž1992. reported that thermophilic fermentation and a temperature of 558C killed A. suum eggs within one hour. Persson Ž1973. and Olsen Ž1984. have developed systems to destroy A. suum eggs and other parasitic stages based on aeration and thermophilic fermentation. Tharaldsen and Helle Ž1989. concluded that the temperature should be maintained above 40–458C for a period of at least 25 days to obtain adequate killing of A suum eggs. In order to ensure total killing of A. suum eggs and other parasitic stages in slurry which can infect cattle or sheep, it is necessary to use such suitable techniques to treat slurry before application. References Anonymous, 1994. Landbouwcijfers 1994. Agricultural Economics Research Institute and the Netherlands Central Bureau of Statistics, The Haque, Netherlands. Borgsteede, F.H.M., de Leeuw, W.A., Dijkstra, Th., Alsma, G., de Vries, W., 1992. Ascaris suum infecties als oorzaak van klinische problemen bij runderen? Tijdschr. Diergeneeskd. 117, 296–298. Brown, D., Hinton, M., Wright, A.I., 1984. Parasitic liver damage in lambs with particular reference to the migrating larvae of Ascaris suum. Vet. Rec. 115, 300–303. Burden, D.J., Ginnivan, M.J., 1978. The destruction of pig helminth ova and larvae in a slurry treatment process. Vet. Rec. 103, 373–375. Enigk, K., 1979. Resistenz der Dauerformen von Endoparasiten der Haustiere. Berl. Munch. Tieraerztl. ¨ Wochenschr. 92, 491–497. Enigk, K., 1980. Vernichtung parasitarer Entwicklungsformen in Flussigmist. Berl. Munch. Tieraerztl. ¨ ¨ ¨ Wochenschr. 93, 379–384. Enigk, K., Hildebrandt, J., Tietjen, C., 1965. Die Lebensdauer von Helmintheneier und -larven in Schwemmist. Berl. Munch. Tieraerztl. Wochenschr. 6, 102–106. ¨ Helle, O., Velle, W., Tharaldsen, J., 1989. Effect of ovine urine and some of its components on viability of nematode eggs and larvae in sheep faeces. Vet. Parasitol. 32, 349–354. Juris, P., Plachy, P., Toth, F., Venglovsky, J., 1992. Effect of biofermentation of pig slurry on Ascaris suum eggs. Helminthologia 29, 155–159. McCraw, B.M., Lautenslager, J.P., 1971. Pneumonia in calves associated with migrating Ascaris suum larvae. Can. Vet. J. 12, 87–90. McLennan, M.W., Humphris, R.B., Rac, R., 1974. Ascaris suum pneumonia in cattle. Aus. Vet. J. 50, 266–268. Olsen, J.E., 1984. The effect of mesophilic or thermophilic anaerobic digestion of slurry on the survival of pathogenic bacteria, indicator bacteria and intestinal parasites. Bioenergy 84. In: Egneus, H., Ellegard, A. ŽEds.., Procs. conf. June 15–21, Vol. 3. Goteborg Sweden, pp. 401–405. Persson, L., 1973. The destruction of parasites in liquid cattle manure by aeration using the Licom system. Zbl. Vet. Med. B 20, 289–303. Persson, L., 1974. The bionomics of parasite eggs and larvae in manure, soil and fodder; a literature review. Nor. Vet. Med. 26, 1–24. Roneus, ´ O., Christensson, D., 1977. Mature Ascaris suum in naturally infected calves. Vet. Parasitol. 3, 371–375.
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Stevenson, P., 1979. The influence of environmental temperature on the rate of development of Ascaris suum eggs in Great Britain. Res. in Vet. Sci. 27, 193–196. Tharaldsen, J., Helle, O., 1989. Survival of parasite eggs in livestock slurry utilized for compost heat. Acta Agric. Scand. 39, 381–387. Wensvoort, P., 1962. Spontaneous Ascaris lumbricoides infection in lambs. Tijdschr. Diergeneesk. 87, 260–262.