Tidskrift/serie: Rapport - Sveriges lantbruksuniversitet, Institutionen för växtskyddsvetenskap
Utgivare: SLU, Institutionen för växtskyddsvetenskap
Redaktör: Berger A.
Författare: Shehata M.A.
Adress: Natural Products Laboratory - Tree Improvement Research Centre - National Council for Scientific Research - P.O.Box 21210, Kitwe, Zambia
Ingår i...: Natural Plants Products as Pesticides. Proceedings from the first National Symposium i Zambia held in Lutsaka, 2nd-5th August of 1994
Titel: Endod plant, Phytolacca dodecandra, and its application in bilharziosis control programme
Nummer (ISBN, ISSN): ISSN 1104-6422, ISRN SLU-VÄXT-R-4-SE
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Three field trials were conducted in Muchinshi stream to determine the molluscicidal potency of endod plant, Phytolacca dodecandra, obtained from Ichimpe plantation. The first trial was applied in 1991 using a high concentration extract of 150 ppm. The second trial was carried out in 1992 using a medium concentration of 75 ppm. In 1993 plant extract with a low concentration (37 5 ppm) was tested. Endod at 75 and 150 ppm reduced the snail population by 98% 24 hours after the application. At 37.5 ppm the snail mortality was 67%.
Schistosomiasis or bilhartziosis is considered to be a public health problem in Zambia and effort is being made to control the disease. From a survey carried out in the Copperbelt (Shehata, unpubl.) and from literature (Boatin et al., 1985) it was shown that both Schistosomum haemotobium (urinary bilhartzia) and S. mansoni (intestinal type) are endemic in Zambia. The increase in human population and the opening of new irrigation areas have increased the need for continuing research to provide more effective and economical methods to control schistosomiasis. At present the application of molluscicides is considered to be the most promising and practical method of controlling the disease transmission. The molluscucidal potency of the endod plant, Phytolacca dodecandra, has been documented by Lugt (1880) and a study has been undertaken in Zimbabwe about peoples' knowledge and practical use of this plant (Ndamba et al., 1989). The present study presents the results from field trials carried out in the Copperbelt Province of Zambia, where plant extract from endod was tested against the snail vectors of bilhartzia.
Munchinshi is an area of about 75 km2 and is situated in the west part of Chingola district, 35 km on the Chingola/Solwezi road. This area was chosen because it has a comparatively high prevalence of both S. haematobium (34%) and S. mansoni (45%) and relatively high densities of the snail vectors Biomphalaria pfeifferi and Bulinus (Physiopsis) globusus in its water course. It also represents one of the virgin areas in Zambia in which no molluscicides or other control measures against the disease have been undertaken.
The site selected for the field trial was a stretch of 1.2 km of the Muchinshi stream inside the boundary of the study area. The stretch was divided equally into 12 stations, 100 m apart. The first station (up stream) served as a control.
The active molluscicidal compounds in P. dodecandra berries are triterpenoids (Fig. 1.). Chemically, they are the acetal derivates of carbohydrates called saponins and produce a foaming aqueous solution. The molluscicidal components in the berries are soluble in water because of the carbohydrate portion.
Preparation of endod extract: Unripe berries (fully grown green) harvested from Ichimpe plantations were used. The berries were allowed to dry in the shade immediately after harvesting for two weeks. The dry berries were stored in plastic bags at room temperature, 20-30°C. The water extract was obtained by soaking the carefully crushed berries in water for 24 hours and then filtered.
Pre-treatment snail survey was undertaken along a one km stretch of the Muchinshi stream to determine the snail population density one day before the application. A dip-net was used as sampling tool.
Application of endod. Three field trials were conducted with the following treatments: Endod extracts of 150 mg/l (1991), 75 mg/l (1992) and 37.5 mg/l (1993). The first part of the experimental stretch was untreated and served as a control (see above). The extract was drip fed into the water for eight hours and allowed to be cartied down stream at a constant concentration. The use of this method is dependent on the velocity of flow (m/s) which is measured. Multiplying the velocity by the area gives the quantity of flow (discharge) in m3/s from which the molluscicide dose was calculated.
Fig. 1. Lemmatoxin-A (Parkhurst et al., 1974).
Endod obtained from the Ichimpe plantation has given encouraging results. Application of 75 and 150 ppm water extracts for eight hours killed 98% of the snail population after 24 hours. On the other hand 37.5 ppm water extract killed only 67% of the snails. The down stream losses on the concentration of saponin were greater than expected under these field conditions. For example, in the case of the 150 ppm treatment the peak concentrations measured at 500, 700, 900 and 1000 m below the application point were 150, 100, 63 and 0 ppm respectively.
Like most molluscicides endod also acts as a piscicide and many types of fish were killed during ther trials except for crabs and prawns. Although many extra men were distributed along Muchinshi stream to prevent the collection of dead fish, some people managed to collect dead fish for consumption. However, no cases of poisoning were reported during the trials.
This study has demonstrated that Zambian endod, P. dodecandra, used as a water extract successfully reduced the snail population under field conditions and probably also the transmission of schistosomiasis. Health authorities should be aware of the potential benefits from such a snail control programme. As fish and other aquatic organisms are effected by endod, environmental assessment studies on the impact of this product need to be carried out.
Kaitisha: May I ask how you were able to monitor the reduction in number of snails - should the reduction be attributed only to P. dodecandra and to migration and other factors?
Shehata: Post-treatment snail surveys were carried out monthly for at least a year in order to observe the long term effects on the snail population. However, the reduction in number of snails was attributed only to Phytolacca because the results showed that 98% of the snail population was eliminated 24 hours after the application. This was confirmed from the results obtained from untreated area (control) where there was no reduction in number of snails due to any migration.
Mulenga: The chemical also affects non-target organisms e.g. fish, birds, generally riverine organisms. Doesn't this raise high concerns from the environmentalist's point of view?
Shehata: Yes of course it raises high concerns and therefore I am going to do eco-toxicity research work in the near future to know how safe Endod is to the environment.
Mwanaumo: Since Phytolacca is also proved to be spermacidal, what effect does it have on human reproduction, if we continue to drink the water and eat the fish killed by the chemical? Have any studies been done to prove its safety and if not, would it not be a good idea to look at this in the near future?
Shehata: At its molluscicidal concentration Phytolacca does not affect human reproduction. Although it was reported that people collected dead fisk and ate it, no incidents or complaints were reported in connection with the trial. However, further studies are needed to determine the environmental effects of a long term application of endod.
Alick: Do the people who stay along the Muchinshi stream keep livestock? if they do, did you determine whether the chemical i.e. Phytolacca was toxic to the livestock? Secondly, you said that Phytolacca was highly biodegradable, does that mean that even at the time of processing it breaks down or is it after you have applied it into the water?
Shehata: Yes some of them do keep livestock. Before the application period people were told in advance not to use the stream water for their own use or for their cattle during the application period. They stored the water one day before the application was done. No incidents or complaints were reported. Water samples for saponin analysis showed that saponin concentration within the experimental area fluctuated from 50 to 100 ppm during the application period. Thereafter it declined to 0 ppm 12 hours after the application. This means that the material breaks down after the application and not during the processing.
Taguma: What stage of mosquito is controlled by endod, how effective is it and at what concentration?
Shehata: Endod is very effective against the larval stage of the malaria mosquito. At 50 ppm the larvae could be killed by endod in the field.
Luguru: What percentage of the snails spend time on vegetation surrounding the water?
Shehata: Very few snails can move and spend time on vegetation surrounding the water. This only happens when the water is not suitable for the snails.
Mandola: What is the active chemical compound of the endod plant and secondly, how easy is to propagate the plant?
Shehata: Endod plants contain saponins or triterpenoids to which branched trisaceharides are linked at C3. They are the acetal derivatives of carbohydrates or glycosides. The extract contains 12 coumpounds out of only five have been identified. With regard to propagation, seeds are used and the survival of the seedlings after planting was 90%.
Mwangala: Are there any differences in the susceptibility of the two species of snails. It appears that Bulinus sp. is not affected by endod extract?
Shehata: The difference in susceptibility of the two species is not significant. Bulinus sp. was also affected by endod, this was confirmed from large number of dead snails recovered three days after the application.
Mugoya: How did you sample snails in running water and were the standard deviations high or low? Secondly, how did you ensure stability of the saponin concentration in a turbulent system like that of a flowing stream?
Shehata: The dip-net was employed as a sampling tool and the standard deviations were low. The concentration of saponin was stabilized using the drip feeding of the endod for eight hours at a place up stream. This allowed the extract to be carried down stream at a constant concentration. The use of this method is dependent on the velocity of the flow (in/s) which was measured on the spot. Multiplying the velocity by the area gives the quantity of flow (discharge) in cubic meters from which the molluscicide dose was calculated.
Boatin, B.A., Wurapa, F.K. and Ulrich, A.M. 1985. Prevalence and distribution of schistosomiasis in Zambia. Central African Journal of Medicine 31(9): 170- 176.
Lugt, C.B. 1980. Development of molluscicidal potency in the short and long staminate racemes of Phytolacca dodecandra. Planta-Medica 38(1): 68-72.
Ndamba, J., Chandiwana, S.K. and Makaza, N. 1989. Knowledge, attitudes and practices among rural communities in Zimbawe in relation to Phytolacca dodecandra - a plant molluscicide. Social Science and Medicine 28 (12): 1249- 1253.