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n Suid-Afrikaanse Tydskrif vir Natuurwetenskap en Tegnologie - Verspreiding en habitats van drie lewerbot-tussengashere in Suid-Afrika en die gesondheidsimplikasies daarvan : navorsings- en oorsigartikel - : navorsings- en oorsigartikel

Volume 27, Issue 1
  • ISSN : 0254-3486
  • E-ISSN: 2222-4173

Abstract


Account is given of the distribution and habitats of the three species currently on record in the National Freshwater Snail Collection (NFSC) of South Africa. A total number of 616, 353 and 202 loci (1/th square degrees) was respectively recorded for and . The number of loci in which the collection sites of each species was located, was distributed in intervals of mean annual air temperature and rainfall, as well as intervals of mean altitude. A temperature index was calculated for all mollusc species in the database and the results used to rank them in order of their association with low to high climatic temperatures. Chi-square and effect size values were calculated to determine the significance in differences between frequencies of occurrence of each species in, on, or at the different options for each of the variables investigated and also to determine the significance of the differences between the three species.
None of the three species were well represented in the arid regions of the Northern, Western and Eastern Cape Province, and only was reported from Lesotho. is the most widespread of the three species, while the distribution of displays a sporadic and limited pattern. The alien invader species was first reported from South Africa in the early 1940's but was so successful in its invasion of water-bodies in South Africa that it is currently considered the third most widespread freshwater snail in the country.
was the only one of the three species not recovered from all 14 water-body types represented in the database. The largest number of samples of by far, was yielded by marshes while the largest number of samples of the other two species was collected in rivers, streams and dams. The highest percentage occurrence of all three species was in habitats in which the water conditions were described as permanent, standing, fresh and clear. Although the highest percentage of samples of all three species was reported from loci that fell within the interval ranging from 16-20oC, a significant number of samples of came from loci falling within the 11-15oC interval.
In view of the fact that species are well known as intermediate hosts for liver fluke in South Africa and elsewhere in the world, the widespread occurrence of these snails could have considerable health and economic consequences. is the most important and probably the only intermediate host of , the most common liverfluke in Africa but has been reliably reported only from Lesotho where its traditional intermediate host, is widespread. However, the epidemiology of fasciolosis in South Africa has been complicated by the invasion of many water-bodies by because this species has proved to be a successful host for where it had been introduced elsewhere in the world. To our knowledge its role in South Africa in this respect has not yet been evaluated. Due to the fact that no statistics are available in print, the results of positive serological tests on cattle herds all over South Africa were used to compile a map depicting the possible occurrence of species in livestock in this country.
Although human infections with in Africa was considered as very rare in 1975 the situation has changed. It is considered an underrated and underreported disease in humans in Ethiopia and in Egypt an increase in cases of fasciolosis and prevalences as high as 12.8% in humans have also recently been reported. To our knowledge the only cases of human fasciolosis reported in literature for South Africa were from northern KwaZulu-Natal where infections were found in 22 out of 7 569 school children examined in 1981. Efforts to obtain recent statistics on human infections from various persons and authorities were totally unsuccessful. In view of statistics available for elsewhere in the world, it would be unwise to assume that no problems exist in this regard in South Africa. The number of people suffering from fasciolosis was already estimated at 2.4 million in 61 countries in 1995 and another 180 million at risk of becoming infected, with the highest prevalences reported from Bolivia, China, Ecuador, Egypt, France, Iran, Peru and Portugal.
The results of recent serological assays for the detection of fasciolosis in cattle herds in selected areas in South Africa indicated positive cases from localities that closely correspond to the geographical distribution of the three species in this country. According to reports in the literature, the high prevalence of fasciolosis in livestock in the highlands of Ethiopia could have serious health implications for people in the area because they have to use the same water resources. In many rural areas in South Africa local populations also have no other options than to share natural water resources with their livestock. In most instances these water bodies harbour at least one of the species which can maintain the life cycle of fasciola. Under such conditions residents could daily be exposed to the risk of becoming infected.
It is a matter of concern that epidemiological research with regard to human fasciolosis is such a neglected subject in South Africa. In our opinion epidemiological surveys should be conducted to determine the prevalence of human fasciolosis in specific areas which could be selected on the basis of using the geographical distribution of the three species as guidelines. Efforts should also be made to conduct surveys to update the geographical distribution of the snail intermediate hosts and awareness programmes should be launched in rural areas at risk.

Hierdie artikel fokus op die geografiese verspreiding en habitats van drie spesies soos weerspieël deur monsters wat tans in die databasis van die Nasionale Varswaterslakversameling (NVWSV) op rekord is. Die totale getal lokusse (1/ vierkantegraad) wat tans vir , ('n eksotiese indringerspesie) en op rekord is, is onderskeidelik 616, 353 en 202. is die enigste van die drie spesies wat nie in al die waterliggaamtipes verteenwoordig was nie en is die meeste keer in moerasse versamel. Daarenteen is die meeste monsters van die ander twee spesies in riviere, spruite en damme versamel. Omdat -spesies wêreldwyd daarvoor bekend is dat hulle as tussengashere vir -spesies (lewerbot) kan optree, hou die wye verspreiding van drie verskillende spesies van hierdie genus in Suid-Afrika gesondheidsimplikasies in. Geen statistiek oor die prevalensie van fasciolose onder mens en dier in Suid-Afrika is na ons wete gepubliseer nie. Ongepubliseerde data dui egter daarop dat die voorkoms van fasciolose onder vee grootliks met die geografiese verspreiding van die betrokke spesies ooreenstem. Na aanleiding van die toenemende voorkoms en dikwels hoë prevalensie van fasciolose onder mense wat vir elders in Afrika en die wêreld gerapporteer word, word kommer uitgespreek oor die lae prioriteit wat navorsing met betrekking tot hierdie parasitiese siekte in die besonder, maar slakgedraagde helmint-infeksies oor die algemeen, tans in Suid-Afrika geniet. Epidemiologiese ondersoeke en die instelling van bewusmakingsprogramme word bepleit.

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/content/aknat/27/1/EJC20423
2008-03-01
2019-08-26

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