2Institute of Ecology and Environmental Studies, Obafemi Awolowo University, Ile-Ife, Nigeria
3Department of Biology, Adeyemi College of Education, Ondo, Nigeria
The aims of the study were to (i) identify the freshwater snail species in the River Basin; (ii) ascertain their infection patterns density and distribution in correlation with S. haematobium transmission in the study area.
Materials and Methods: Each of the randomly selected seven sites was sampled for snails once every month for a period of twelve months(May 2006 - April 2007) using a standard manual search. The number of each snail species was counted to determine the number of each species or genera per month per site. The established local intermediate host species were measured and examined for schistosomia infection using the lightexposure method and crushing method.
Result: The only local intermediate hosts of S. Haematobium and S. Mansoni in Aponmu-Lona River Basin were Bulinus globosus and Biomphalaria preifferi respectively. Out of the seven sites sampled, Bulinus globosus was found only in three sites (3, 4, 5) while biomphalaria pfeifferi was found in five sites (1, 2, 5, 6, and 7). In the twelve-month (May 2006 – April 2007), period of study a total of 6018 snails were collected,the total number of Bulinus globosus was 112 (1.86%) and Bimophalaria pfeifferi was 747 (12.4%). Only 5 out of 112 Bulinus globosus examined for trematode infection were found shedding trematode cercariae. The overall rates of schistosome cercaria shedding of Bulinus globosus were 4.5%.No infection was recorded during the Biomphalaria snails examined.
Conclusion: This study found not that both the density and prevalence of schistosoma infection Bulinus globosus was in December. It is recommended that any control activity may be targeted towards the peak period in December when water level was low with a view to reducing the transmission status in Aponmu-Lona Community.
Keywords: S. Haematobium; Bulinus globosus; Biomphalaria pfeifferi; Urinary schsitosomiasis Aponmu-Lona River Basin; Nigeria;
Aponmu-Lona River Basin has a catchment area of approximately 900 km within the southwestern climatic belt of Nigeria. Its major tributaries are rivers Owena and Anu figure 2. The soil is generally composed of crystline acid rock of the ferruginious tropical type that has been moderately to strongly leach with low hummus content [20]. The substratum is characteristically swampy and banks covered by low to tall grasses.
Most water-related activities in the community take place in the river. These activities include palm oil milling, washing clothes, cooking utensil, and cassava tubers, fermentation of cassava tuber, and fishing, swimming and bathing [1].
The number of each snail species was counted to determine the number of each species or genera per month per site. The established local intermediate host species were measured and examined for Schistosoma infection using the light exposure method. The sizes (i.e. height x width for globose and diameter for discoid) snails were measured using a fine Vanier caliper.
Height or length which represents the longest distance between apex and base is measured for globose shells while width is the maximum distance across the shell (globose or discoid).
Site |
B. globosus |
M. tuberculata |
P. freethi |
B. pfeifferi |
L. ovum |
P. ovate |
I. exustus |
Type B |
Total |
% Over all Total |
S1 |
0 |
0 |
118 |
308 |
3 |
22 |
0 |
0 |
451 |
7.49 |
S2 |
0 |
1,124 |
100 |
170 |
13 |
0 |
8 |
0 |
1,415 |
23.51 |
S3 |
63 |
966 |
264 |
0 |
0 |
0 |
13 |
0 |
1,306 |
21.70 |
S4 |
41 |
554 |
313 |
0 |
2 |
0 |
0 |
0 |
910 |
15.12 |
S5 |
8 |
928 |
401 |
122 |
5 |
15 |
2 |
0 |
1,481 |
24.61 |
S6 |
0 |
63 |
132 |
6 |
8 |
0 |
2 |
6 |
217 |
3.61 |
S7 |
0 |
63 |
7 |
141 |
0 |
10 |
11 |
6 |
238 |
3.95 |
P-value |
<0.00 |
<0.00 |
<0.00 |
<0.00 |
|
|
|
|
|
|
TOTAL |
112 |
3,698 |
1,335 |
747 |
31 |
47 |
36 |
12 |
6,018 |
100 |
% of Overall of Total |
1.86 |
61.45 |
22.18 |
12.41 |
0.52 |
0.78 |
0.60 |
0.20 |
100 |
|
MONTH |
|
|
|
|
|
|
|
|
|
|
May |
3 |
113 |
56 |
74 |
0 |
8 |
0 |
0 |
254 |
4.22 |
June |
5 |
69 |
76 |
91 |
0 |
10 |
1 |
0 |
252 |
4.19 |
July |
2 |
88 |
67 |
36 |
0 |
11 |
6 |
0 |
210 |
3.49 |
August |
4 |
128 |
73 |
54 |
5 |
17 |
15 |
0 |
296 |
4.92 |
September |
7 |
190 |
57 |
31 |
1 |
0 |
2 |
0 |
288 |
4.79 |
October |
11 |
314 |
124 |
37 |
0 |
0 |
6 |
0 |
492 |
8.18 |
November |
7 |
354 |
163 |
10 |
4 |
0 |
3 |
0 |
541 |
8.99 |
December |
36 |
1,452 |
312 |
108 |
8 |
0 |
3 |
3 |
1,922 |
31.94 |
January |
14 |
276 |
213 |
57 |
0 |
0 |
0 |
1 |
561 |
9.32 |
February |
14 |
278 |
76 |
118 |
5 |
1 |
0 |
3 |
495 |
8.23 |
March |
4 |
171 |
83 |
61 |
3 |
0 |
0 |
2 |
324 |
5.38 |
April |
5 |
265 |
35 |
70 |
5 |
0 |
0 |
3 |
383 |
6.36 |
TOTAL |
112 |
3,698 |
1,335 |
747 |
31 |
47 |
36 |
12 |
6,018 |
100 |
Out of the 112 Bulinus globosus snails collected and examined for trematode infection, only 5 (4.5%) were found shedding trematode cercariae table 2. all the 5 snails shedding cercaria were >3 mm long and none of the snails < 3 mm size range. Thus only B. globosus snails greater than 3 mm were found shedding cercarae and no infection was recorded among the Biomphalaria snails examined. Three cercarial types recovered from the infected snails were amphistome cercaria cercariaeum cercaria figure 4, ornate xiphidiocercaria and brevifurcate apharyngeate distome cercaria.
Species |
Size class (mm) |
Number collected |
Number infected |
% of total collection |
% infection with trematodes |
Bulinus globosus |
<3 |
71 |
0 |
63.4 |
0 |
Biomphalaria pfeifferi |
<3 |
364 |
0 |
48.7 |
0 |
The observed unimoda pattern of density variation agrees with the report of several workers from Southwest [9,10] and southeast [27]. Nigeria. However, it differed from the bimodal pattern recorded in Yola [3] and Oyan Reservoir [18] Nigeria; Lake Volta, Ghana [11,14] and Lake Kariba, Zambia [10]. In all these reports, however, snail density maxima occurred at different periods of the year as a result of variations in local physico-chemical and biological conditions of the particular ecosystem [23]. Probably as a result of this, several of the reports emphasized the importance of a good knowledge of local patterns of seasonal variation in environmental factors in planning sustainable control programmes.
This study was carried out as part of a larger investigation, to elucidate media speculations that widespread haematuria in Aponmu-Lona was caused by an outbreak of urinary schistosomiasis. The findings of this investigation that B. globosus, an established intermediate host species in Southwest Nigeria [9] were shedding schistosome type cercaria is an indication of active schistosomiasis transmission of the disease in the river. This conclusion is further supported by the widespread and heavy intensity patterns of human infection reported by a complementary investigation on human infection [19].
The findings of this investigation provided a strong baseline data not only for understanding schistosomiasis transmission in Apomu-Lona and environs, but also for planning an effective first line control programme against the disease in the area and elsewhere with similar problems. To this end, the investigation has provided a clear trend in both spatial and seasonal distribution of human infection, ecology of snails including B. globosus, the local intermediate host species in the area and human water contact patterns in relation to behavioural patterns that drive the various transmission activities. This information is indispensable in sustainable integrated schistosomiasis control.
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