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OPEN ACCESS Research Journal of Parasitology
ISSN 1816-4943
DOI: 10.3923/jp.2017.8.18
Research Article
Population Abundance and Bionomics of Snail Intermediate
Hosts of Trematode Parasites in Nasarawa State, Nigeria
1E.M. Abe, 2A. Ombugadu, 3A.S. Oluwole, 4H.L. Njila, 3,5 H.O. Mogaji, 3A.A. Adeniran, 1Y.H. Guo, 1S.Z. Li,
1X.N. Zhou and 3U.F. Ekpo
1Chinese Centre for Disease Control and Prevention, WHO Collaborating Centre for Tropical Diseases, National Institute of Parasitic Diseases,
Shanghai, China
2Department of Zoology, Federal University Lafia, Nasarawa State, P.M.B. 146, Lafia, Nigeria
3Department of Pure and Applied Zoology, Federal University of Agriculture Abeokuta, P.M.B. 2240, Abeokuta, Nigeria
4Department of Science Laboratory Technology, Faculty of Natural Sciences, University of Jos, P.M.B. 2084, Nigeria
5Department of Animal and Environmental Biology, Federal University Oye-Ekiti, Ekiti State, Nigeria
Abstract
Background and Objective: Snail intermediate hosts play active role in the transmission of trematode parasites. Hence, this study
assessed 105 water bodies across Nasarawa State, Nigeria for snail hosts bionomics and abundance between July, 2012 and August, 2013.
Methodology: Snail hosts were sampled monthly in water bodies across Nasarawa State. Snail sampling was done using hand-held
scooping net for 45 min and identified using shell morphology. They were screened for patent infection through exposure to sunlight
individually for 2 h in a petri-dish that contains aged tap water and checked for cercarial shedding in the laboratory under a dissecting
microscope. Identification was confirmed at the Natural History Museum, London snail reference laboratory. Vegetation samples were
collected from each sampling site and identified. The physico-chemical parameters including pH, dissolved oxygen, conductivity and
temperature of water bodies sampled for snails were obtained using hand-held meter (Combo-Hanna). Results: A to ta l o f 97 7 s na i l h os ts
were collected from the studied sites. Five different snail hosts of trematode parasites including
Bulinus globosus
,
Bulinus forskalii
,
Biomphalaria pfeifferi
,
Lymnaea natalensis
and
Indoplanorbis exutus
were sampled. Highest snail collection was 153 (15.66%)
in Akwanga Local Government Area, followed by 138 (14.12%) in Lafia LGA and the least was 12 (1.23%) in Nasarawa Eggon LGA.
Percentage distribution of the five snail hosts population is as follows:
B. globosus
(50.15%),
B. forskalii
(23.75%),
L. natalensis
(15.15%),
B. pfeifferi
(7.47%) and
I. exutus
(3.48%). Using R Console software version 3.2.2, one way ANOVA shows significant difference in snails
mean abundance across species (F520 = 20.48, adjusted R2 = 0.1295, p<0.0001). The pH is only significant parameter influencing the pooled
abundance of the five identified snail hosts in the studied water bodies across Nasarawa State. Influence of physico-chemical parameters
on individual species abundance shows that temperature was significant for
B. globosus
abundance, pH was significant for
B. forskalii
,
B. pfeifferi
and
L. natalensis
while pH and dissolved oxygen were significant for
I. exutus
abundance in the sampled water bodies.
Conclusion: Information on snail bionomics is vital for effective snail control programme.
Key words: Population, abundance, bionomics, snail intermediate hosts
Received: September 13, 2016 Accepted: November 16, 2016 Published: December 15, 2016
Citation: E.M. Abe, A. Ombugadu, A.S. Oluwole, H.L. Njila, H.O. Mogaji, A.A. Adeniran, Y.H. Guo, S.Z. Li, X.N. Zhou and U.F. Ekpo, 2017. Population
abundance and bionomics of snail intermediate hosts of trematode parasites in Nasarawa state, Nigeria. Res. J. Parasitol., 12: 8-18.
Corresponding Author: E.M. Abe, Chinese Centre for Disease Control and Prevention, WHO Collaborating Centre for Tropical Diseases,
National Institute of Parasitic Diseases, Shanghai, China
Copyright: © 2017 E.M. Abe
et al
. This is an open access article distributed under the terms of the creative commons attribution License, which permits
unrestricted use, distribution and reproduction in any medium, provided the original author and source are credited.
Competing Interest: The authors have declared that no competing interest exists.
Data Availability: All relevant data are within the paper and its supporting information files.
Res. J. Parasitol., 12 (1): 8-18, 2017
INTRODUCTION
Snails are invertebrate animals found in freshwater and
other ecological niches1. Some of these snails (especially the
freshwater species of the subclass Pulmonata) are important
in the epidemiology of snail-borne diseases in the tropic and
subtropic regions of the world because they are known to
serve as intermediate host of parasites of medical and
veterinary importance2.
The continued transmission of schistosomiasis and other
snail-borne diseases are enhanced by the distribution of snail
intermediate hosts that are required for the trematode
parasites to thrive in areas characterized with continued
neglect, poor sanitation and lack of quality infrastructure such
as sanitary facilities and access to good potable water
sources3-6.
The implementation of preventive chemotherapy is the
major control effort in place to reduce the morbidity of
schistosomiasis that is endemic in many parts of Nigeria but
has not been very successful due to re-infection after
treatment7,8. Though, several studies7,9-12 and intervention
measures have been carried out to curtail the distribution and
transmission of the snail-borne diseases caused by trematode
parasites in Nigeria. However, there is dearth of reliable data
on snail intermediate hosts distribution, abundance and
bionomics in most areas known to be endemic for
schistosomiasis and other snail-borne diseases in Nigeria.
Snail intermediate hosts are important in the
epidemiology of schistosomiasis and other snail-borne
diseases2 because of their unique role in facilitating the
development of the infective cercariae which penetrate
human skin in water for further development13.
Hence, this makes snail host studies crucial for effective
control of schistosomiasis and other snail-borne diseases
whose control and elimination is one of the main goals of the
World Health Organization as declared in the resolution
passed at the World Health Assembly (WHA 65.21) in 2012.
Therefore, this study assessed the population abundance
and bionomics of snail intermediate hosts of trematode
parasites in Nasarawa State, Nigeria with a view to providing
information that will help initiate and set-up an effective snail
host control programme in Nasarawa state.
MATERIALS AND METHODS
Study area: The study was carried ou t in 105 wat er bo dies
across 12 local government areas of Nasarawa state,
North central Nigeria (Fig. 1). The LGAs surveyed for
snail intermediate hosts include; Awe, Akwanga, Karu,
Keana, Keffi, Kokona, Lafia, Nasarawa, Nasarawa-Eggon, Obi,
Toto and Wamba LGAs. Nasarawa State has a total land area of
27,137.8 km2 and it shares borders in the west with the Federal
Capital Territory, Abuja, in North with Nasarawa state lies
within the Guinea Savannah region and has tropical climate
with moderate rainfall (annual mean rainfall of 1311:75 cm).
The state is made up of plain lands and hills measuring up to
300 ft a.s.l., at some points (http://www.canuk. org.uk/about
nigeria.aspx., 2011).
Snail sampling: Snail intermediate hosts were sampled
monthly from 105 water bodies across 12 LGAs of Nasarawa
state, North central Nigeria between July, 2012 and August,
2013. The sites were visited in the morning for snail hosts
collection. Snail sampling was done using hand-held scooping
net (diameter: 18 cm and 0.2 mm mesh) supported by a frame
mounted on a 2 m long handle for 45 min in each of the water
bodies sampled for collection. Manual search with visual
inspection and hand-picking was also employed along the
length of the water bodies at various sites. Collections were
made in water bodies with visible water contacts and areas
without apparent water contacts were also sampled for snails.
C ol le c te d s n ai l s w er e tr a ns p o rt e d t o t h e la b or at o ry wh e re t he y
were washed, identified and snail host population was
recorded for each site.
Screening for patent infection: The snails were exposed to
sunlight individually for 2 h in a petri-dish that contains aged
tap water. They were screened for cercarial shedding in the
laboratory under a dissecting microscope.
Morphological identification of vector snails: The snails
were identified using shell morphology according to
Brown and Kristensen14. This was achieved by holding the
snail shell with the apex (pointed edge) pointing upward.
When the aperture (shell opening below the body whorl)
opens to the right, it is termed dextral but when the
aperture opens to the left it is termed sinitral. More so, the
sculptural marking on the snail shell was considered during
identification. Other shell components considered during
identification include number of whorls, shape of the shell,
type of apex (sharp or blunt) and shape of the peristome on
the aperture. The snail intermediate hosts identification
was confirmed at the Department of Life Sciences snail
reference laboratory, Natural History Museum, Cromwell road,
London.
Sampling of vegetation from the water bodies: Vegetation
samples were collected from each sampling site and
9
Res. J. Parasitol., 12 (1): 8-18, 2017
Fig. 1: Map of Nigeria showing Nasarawa state
identified. Identification of aquatic vegetation samples
collected from the sampling sites was carried out according to
Arbonnier15 and was confirmed using reference specimen
from the Department of Botany, Benue State University,
Makurdi, Benue State, Nigeria.
Water physico-chemical parameters: The physico-chemical
parameters including pH, dissolved oxygen, conductivity and
temperature of water bodies sampled for freshwater snail
intermediate hosts were obtained by dipping the hand-held
portable meter (Combo HANNA, USA) inside the water bodies
for 5 min staying in one spot while the meter reading is taken
and recorded. The physico-chemical parameters for each
sampling site were recorded accordingly.
Data analysis: Data obtained was analyzed using R
Console software version 3.2.2. One way analysis of
variance (ANOVA) was used to compare the mean
abundance of snails between snail species. Two way analysis
of variance (ANOVA) was used to determine the abundance
of snails in relation to snail species and physico-chemical
parameters. Pearson's product-moment correlation was
used to determine the association between the numbers
of snails and physico-chemical parameters. The p<0.05 was
considered statistically significant. In addition, SPSS software
(version 17, USA) was used to carry out descriptive analysis of
the study.
RESULTS
Distribution and abundance of snail intermediate hosts
in selected water bodies in Nasarawa state: A total of
977 freshwater snail intermediate hosts were collected from
the 105 studied water bodies sampled for snails in the 12 LGAs
across Nasarawa state between July, 2012 and August, 2013.
Five different snail hosts of trematode parasites including
Bulinus globosus
,
Bulinus forskalii
,
Biomphalaria pfeifferi
,
Lymnaea natalensis
and
Indoplanorbis exutus
were
identified using shell morphology shown in Fig. 2. Highest
snail abundance of 153 (15.66%) were collected from 14 water
10
N
Rivers
Nassarawa State
0 10 20 40 60 80 km
Res. J. Parasitol., 12 (1): 8-18, 2017
Fig. 2(a-e): Shell samples of snail intermediate hosts snails sampled in water bodies across Nasarawa state, Nigeria,
(a)
Biomphalaria pfeifferi
, (b)
Bulinus globosus
, (c)
Indoplanorbis exutus
, (d)
Bulinus forskalii
and (e)
Lymnaea
natalensis
Table 1: Snail hosts population collected from sampling sites across Nasarawa state
LGA No. of location
B. globosus B. forskalii B. pfeifferi L. natalensis L. exutus
Total
Awe 3 15 20 13 0 0 48
Obi 5 8 17 0 3 0 28
Lafia 10 22 30 18 37 31 138
Akwanga 14 51 56 11 35 0 153
Keffi 12 43 28 4 13 0 88
N. Eggon 1 11 0 1 0 0 12
Wamba 9 54 12 21 37 3 127
Keana 11 47 2 0 1 0 50
Kokona 10 63 48 0 7 0 118
Karu 10 33 4 0 6 0 43
Nasarawa 10 66 1 0 7 0 74
Toto 10 77 14 5 2 0 98
Total 105 490 (50.15%) 232 (23.75%) 73 (7.47%) 148 (15.15%) 34 (3.48%) 977
bodies in Akwanga local government area, 138 (14.12%)
from 10 water bodies in Lafia LGA and 12 (1.23%) from one
water body in Nasarawa Eggon LGA resp ecti vely as shown
in Table 1. The percentage population distribution of
the five snail intermediate hosts depicted
B. globosus
(50.15%),
B. forskalii
(23.75%),
L. natalensis
(15.15%),
B. pfeifferi
(7.47%) and
L. exutus
(3.48%) as shown in Table 1.
However, there was a significant difference (F520 = 20.48,
adjusted R2 = 0.1295, p<0.0001) in the mean population
abundance of snails in relation to species (Fig. 3).
Relationship between abundance of snail hosts and
physico-chemical parameters: The relationship between
overall abundance of snail hosts and physico-chemical
parameters revealed that pH is the only significant
parameter (t = 1.2799, df = 103, p = 0.2034, r = 0.1251254)
influencing abundance of snails in water bodies in
Nasarawa state (Fig. 3b). However, there was a negative
relationship between temperature (t = -0.78008, df = 103,
p = 0.4371, r = -0.07663712), conductivity (t = -1.6071,
df = 103, p = 0.1111, r = -0.1564073) and dissolved
11
(a) (b) (c)
(d) (e)
Res. J. Parasitol., 12 (1): 8-18, 2017
7
6
5
4
3
2
1
0
Mean abundance of snails ±SE
B. forskalii
B. globosus
B. pfeifferi
I. exutus
L. natalensis
Fig. 3: Mean abundance of snail hosts in selected water bodies of Nasarawa state
Fig. 4(a-d): Association between abundance of snail hosts and physico-chemical parameters, (a) Temperature (EC), (b) pH,
(c) Conductivity (µS) and (d) Dissolved oxygen (ppm)
oxygen (t = -1.6162, df = 103, p = 0.1091, r = -0.1572659) on
abundance of snails (Fig. 4a, c, d).
Relationship between individual snail abundance
and physico-chemical parameters: The influence of
physico-chemical parameters on individual snails abundance
depicted temperature to be significant for
B. globosus
(t = 0.18054, df = 103, p = 0.8571, r = 0.01778615) as shown in
Fig. 5a. However, there was negative relationship between
abundance of
B. globosus
and pH (t = -1.2215, df = 103,
p = 0.2247, r = -0.119497), conductivity (t = -0.87934, df = 103,
p = 0.3813, r = -0.08632097) and dissolved oxygen
(t = -0.80974, df = 103, p = 0.42, r = -0.07953352) as shown in
Fig. 5b-d, only pH positively influenced
B. fo rsk al ii
,
B. pfeifferi
,
12
30
15
0
30
15
0
15 20 25 30 6 7 8 9 10
0 200 400 600 800 0 100 200 300 400
(a) (b)
(c) (d)
No. of snails
No. of snails
30
15
0
30
15
0
No. of snails
No. of snails
Res. J. Parasitol., 12 (1): 8-18, 2017
Fig. 5(a-d): Association between abundance of
B. globosus
and physico-chemical parameters, (a) Temperature (EC), (b) pH,
(c) Conductivity (µS) and (d) Dissolved oxygen (ppm)
Fig. 6(a-d): Association between abundance of
B. forskalii
and physico-chemical parameters, (a) Temperature (EC), (b) pH,
(c) Conductivity (µS) and (d) Dissolved oxygen (ppm)
L. natalensis
, while
L. exutus
associated positively with
pH and dissolved oxygen as shown in Fig. 5-9,
respectively.
The relationship between abundance of
B. forskalii
show positive relationship with pH (t = 1.7405, df = 103,
p = 0.08476, r = 0.1690258) as shown in Fig. 6b. However,
there was negative relationship between abundance of
B. forskalii
and temperature (t = -0.37604, df = 103,
p = 0.7077, r = -0.03702709), conductivity (t = -0.8889,
df = 103, p = 0.3761, r = -0.08725173) and dissolved oxygen
(t = -1.2513, df = 103, p = 0.2136, r = -0.1223722) as shown in
Fig. 6a, c and d respectively.
The relationship between abundance of
B. pfeifferi
show positive relationship with pH (t = 0.78966, df = 103,
p = 0.4315, r = 0.0775727) as shown in Fig. 7b. However, there
was negative relationship between abundance of
B. pfeifferi
and temperature (t = -0.68815, df = 103, p = 0.4929,
r = -0.06765054), conductivity (t = -0.10506, df = 103,
p = 0.9165, r = -0.01035155) and dissolved oxygen
(t = -0.11369, df = 103, p = 0.9097, r = -0.01120115) as shown
in Fig. 7a, c and d respectively.
The relationship between abundance of
L. natalensis
show positive relationship with pH (t = 1.0074, df = 103,
p = 0.3161, r = 0.09877464) as shown in Fig. 8b. However,
there was negative relationship between abundance of
L. natalensis
and temperature (t = -0.34155, df = 103,
p = 0.7334, r = -0.03363489), conductivity (t = -0.74611,
df = 103, p = 0.4573, r = -0.07331823) and dissolved oxygen
(t = -0.56748, df = 103, p = 0.5716, r = -0.05582867) as shown
in Fig. 8a, c and d respectively.
The relationship between abundance of
L. exutus
show positive relationship with pH (t = 0.94449, df = 103,
13
20
10
0
15 20 25 30 6 7 8 9 10
0 200 400 600 800 0 100 200 300 400
(a) (b)
(c) (d)
No. of B. globosus
20
10
0
20
10
0
20
10
0
No. of B. globosus
No. of B. globosus No. of B. globosus
25
10
0
15 20 25 30 6 7 8 9 10
0 200 400 600 800 0 100 200 300 400
(a) (b)
(c) (d)
No. of B. forskalii No. of B. forskalii
No. of B. forskalii
No. of B. forskalii
25
10
0
25
10
0
25
10
0
Res. J. Parasitol., 12 (1): 8-18, 2017
Fig. 7(a-d): Association between abundance of
B. pfeifferi
and physico-chemical parameters, (a) Temperature (EC), (b) pH,
(c) Conductivity (µS) and (d) Dissolved oxygen (ppm)
Fig. 8(a-d): Association between abundance of
L. natalensis
and physico-chemical parameters, (a) Temperature (EC), (b) pH,
(c) Conductivity (µS) and (d) Dissolved oxygen (ppm)
Table 2: Snail hosts distribution in five habitats sampled in Nasarawa state
Habitats
--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Snail species River Stream Pool Dam Waterfall Total
Bulinus globosus
264 196 3 17 10 490
Bulinus forskalii
98 108 14 0 12 232
Biomphalaria pfeifferi
20 50 3 0 0 73
Lymnaea natalensis
49 93 6 0 0 148
Indoplanorbis exutus
28 6 0 0 0 34
Total 459 (46.98%) 453 (46.37%) 26 (2.66%) 17 (1.74%) 22 (2.25%) 977
p = 0.3471, r = 0.09266254) as shown in Fig. 8b. However,
there was negative relationship between abundance of
L. exutus
and temperature (t = -1.0302, df = 103, p = 0.3053,
r = -0.1009874, Fig. 9a). Conductivity (t = -0.30554, df = 103,
p = 0.7606, r = -0.03009178, Fig. 9c) and dissolved oxygen
(t = 0.037408, df = 103, p = 0.9702, r = 0.003685925, Fig. 9d) as
shown in Fig. 9a, c and d respectively.
Monthly distribution and population of snail
intermediate hosts in water bodies sampled across 12 LGAs
in Nasarawa state are shown in Fig. 10 and 11 respectively.
Snail collection was highest in June, 2013 while the least
collection was made in October, 2012.
The distribution chart indicates that
B. globosus
occurred highest, it was found in all the 12 local government
areas surveyed for snail intermediate hosts of trematode
parasites across Nasarawa state while
I. exutus
only occurred
in three studied sites across two local government areas of
Nasarawa state.
Table 2 shows that (459) 46.98% snails were
collected from the rivers, streams 453 (46.37%), pools
14
15 20 25 30 6 7 8 9 10
0 200 400 600 800 0 100 200 300 400
(a) (b)
(c) (d)
No. of L. natalensis
No. of L. natalensis
No. of L. natalensis
No. of L. natalensis
10
0
10
0
10
0
10
0
8
4
0
15 20 25 30 6 7 8 9 10
0 200 400 600 800 0 100 200 300 400
(a) (b)
(c) (d)
No. of B. pfeifferi
No. of B. pfeifferi
No. of B. pfeifferi No. of B. pfeifferi
8
4
0
8
4
0
8
4
0
Res. J. Parasitol., 12 (1): 8-18, 2017
90
80
70
60
50
40
30
20
10
0
Population
Awe
Obi
Lafia
Akwanga
Keffi
N. Eggon
Wam b a
Keana
Kokona
Karu
Nasarawa
Toto
B. globosus
B. forskalii
B. pfeiffei
L. natelensis
L. exutus
LGA
250
200
150
100
50
0
Jul-2012
Aug-2012
Sept-2012
Oct-2012
Nov-2012
Dec-2012
Jan-2013
Feb-2013
Mar-2013
Apr-2013
May-2013
Jun-2013
Jul-2013
Aug-2013
Population
Months
Fig. 9(a-d): Association between abundance of
I. exutus
and physico-chemical parameters, (a) Temperature (EC), (b) pH, (c)
Conductivity (µS) and (d) Dissolved oxygen (ppm)
Fig. 10: Population of snail intermediate hosts across 12 LGAs surveyed in Nasarawa state
Fig. 11: Monthly distribution of snail intermediate hosts snails in Nasarawa State
15
25
10
0
15 20 25 30 6 7 8 9 10
0 200 400 600 800 0 100 200 300 400
(a) (b)
(c) (d)
No. of I. exutus No. of I. exutus
No. of I. exutus No. of I. exutus
25
10
0
25
10
0
25
10
0
Res. J. Parasitol., 12 (1): 8-18, 2017
Table 3: Different snail sizes and shell types collected in water bodies across Nasarawa State
Snail species Mean shell sizes (mm) Shell types Characteristics
Bulinus globosus
4.4×3.0 Globose (Sinistral) Height and width of shell are about the same
Bulinus forskalii
5.0×2.5 Turetted (Sinistral) Height is many times greater than the width
Biomphalaria pfeifferi
4.6×3.7 Discoid Shell is coiled in one plane
Lymnaea natalensis
5.0×2.7 Conical (Dextral) Height of shell is larger than the width and the spire is cone shaped
Indoplanorbis exutus
4.9×4.5 Discoid Shell is coiled in one plane
Table 4: Vegetation samples identified at sites sampled for snail intermediate
hosts across Nasarawa state
Plant species
Ipomoea aquatic
Azolla punata
Nymphaea lotus
Acroceras zizanoides
Mimosa pudica
Panicum muticum
Pistia stratiotes
Ludwigia
spp.
Diplazia esculentum
Commelina diffusa
Echinochloa colonum
Convolvulus arvensis
Panotum
spp.
Elaeis guineensis
26 (2.66%), waterfall 22 (2.25%) and dam 17 (1.74%)
across Nasarawa state.
The morphology of the identified snail hosts is
summarized in Table 3, the summary shows the mean shell
sizes, characteristics and shell types and these include
globose, turreted, discoid and conical shells. Aquatic plant
species collected from the sites sampled for snail intermediate
hosts are shown in Table 4.
DISCUSSION
Narasawa state is known to be endemic for
schistosomiasis16,17, which is a major public health concern
among the snail-borne diseases. Pulmonate snail hosts play
active role in the continued transmission of these snail-borne
diseases in environment where there is lack of basic
infrastructure and also facilitated by human activities18.
The pooled abundance of the five snail intermediate hosts
identified in this study is influenced by pH of the water bodies
sampled for their presence and abundance. Assessment of
water physico-chemical parameters on individual snail host
shows that temperature was significant for
B. globosus
abundance in water bodies sampled in Nasarawa state.
Giovanelli
et al
.19 emphasized the effects of temperature on
snail population, which could have adverse effects on snail
intermediate hosts abundance and distribution at extreme
periods. In addition, temperature is recognized as important
in the freshwater biotope, especially its influence on snail
hosts distribution and abundance20. The pH was significant
for
B. forskalii
,
B. pfeifferi
and
L. natalensis
while pH and
dissolved oxygen were significant for
L. exutus
abund ance in
the sampled water bodies. Dissolved oxygen play significant
role in the population abundance of freshwater snails, if there
is low dissolved oxygen in water, the feeding rate of the snails
might be affected and this may result to death if it happens for
a long period21. The distribution and abundance of snail
intermediate hosts may be attributed to the availability of
food materials and aquatic plants used as oviposition sites,
14 aquatic plants were identified at sites where snail hosts
were sampled. Water bodies rich in organic and silt matters
are known to support populations of macro-invertebrates
because of reduction in water current and serves as
substratum for attachment by the snails, which help them
from being washed away by water current22. The favourable
effect of vegetation on snail habitat preference was confirmed
by the fact that most snails in their various habitats were
attached to aquatic plants. Imafidon23, Obureke
et al
.24 and
Amali25 had previously reported the influence of aquatic
vegetations on the distribution of snails of medical
importance.
The reduction in the snail population at the beginning of
this study in July, 2012 to early 2013 was due to flooding
experienced in most part of Nigeria including Nasarawa state
which extended to late raining season of that year. This might
have washed the snail hosts away. However, they resurfaced
at the start of the rains in 2013.
The lack of infected snail hosts among the population of
the five snail hosts of trematode parasites identified is quite
surprising but the presence of these important snail species in
water bodies sampled at communities of Nasarawa state
poses serious danger and risk of potential transmission of
snail-borne diseases across the state. Therefore, it is important
to educate the inhabitants of the communities where these
water bodies are found on the need to embrace good sanitary
culture and avoid indiscriminate disposal of human wastes
into them. Should an infected person dispose their waste into
these water bodies with the right snail hosts, this could trigger
the transmission of snail-borne diseases in such areas.
Our inability to identify snail intermediate hosts with
molecular method is the limitation of this study. However, we
16
Res. J. Parasitol., 12 (1): 8-18, 2017
will improve on this aspect in future studies but it is also
important to stress that studying the bionomics and
population abundance of freshwater snail intermediate hosts
improves our understanding on the ecology and population
dynamics of these important snail species. Assessing
freshwater snail intermediate hosts bionomics is essential to
understanding their ecology and distribution pattern on local
scales across the country. In addition, such information is
important because the different environmental and physico-
chemical factors play important role in their survival across the
different environment where they are found26.
CONCLUSION
Hence, such information is needed to plan effective snail
control programme in order to complement schistosomiasis
and other snail-borne diseases control programme in
Nasarawa state.
ACKNOWLEDGMENTS
This study was supported by the National Special
Science and Technology Project for Major Infectious Diseases
of China (Grant No. 2012ZX10004-220, 2016ZX10004222-004),
China-UK Global Health Support Program (GHSP No. 202708).
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