INTRODUCTION
Anurans include frogs and toads and comprise
of about thirty families (Flament et al., 2011). Research into the helminth parasites of anurans in Rivers State, Nigeria, has
progressed significantly. Akani et al. (2011) pioneered the research examining anuran species from
some residential areas in Port Harcourt, Rivers State, Nigeria. Subsequently,
other researchers including Amuzie et al. (2016), Aisien
et al. (2017a), Amuzie
(2017), Amuzie et
al. (2019) and Okere et al. (2019) conducted studies in several locations of the State.
The anuran species
examined by these researchers included the bufonids (Sclerophrys
spp.), ptychadenids (Ptychadena spp.), hyperolids (Afrixalus spp. and Hyperolius spp.), pipids (Silurana tropicalis, Hymenochirus
sp.), Ranids (Hylarana galamensis) and dicroglossids (Hoplobatrachus occipitalis)
among others. The endo-helminth parasites of these
host species were also documented and a common observation among these reports
is the greater diversity of nematode parasites above other helminth
classes. For instance, Amuzie et al. (2019) reported eight nematode species (Amplicaecum africanum, ascaridia
larvae, Batracocamallanus siluranae, Chabaudus leberrei, Cosmocerca ornata, Oswaldocruzia hoepplii, Rhabdias africanus and two
other Rhabdias
spp.), six trematodes (Prosotocus exovitellosus, Ganeo
africana, Diplodiscus fischthalicus, Metahaematoloechus exoterorchis, Mesocoelium monodi and Mesocoelium sp.), one cestode (Baerietta jaegerskioeldii),
acanthocephalan cystacanths, one pentastomid
(Raillietiella
sp.) and three monogeneans (Polystoma aeschlimanni, P. baeri
and P. pricei).
Among the documented
reports on helminth parasites of anurans from Rivers
State, Nigeria, we found information on anurans from the Ahoada
area of the State in Aisien et al. (2017b) and Amuzie et al. (2019). This present research at Ahoada Main Town and Joinkrama
represent efforts to fully document the species of anurans and their helminth parasites across Rivers State and the entire Niger
Delta region.
MATERIALS AND METHODS
Sample Locations,
Methods and Duration
Anuran samples were taken from two locations:
Ahoada Main Town in Ahoada
East Local Government Area and Joinkrama in Ahoada West Local Government Area, Rivers State, Nigeria.
Samples were collected from both locations using the search and capture
technique from temporary pools of water on grass fields (Plate 1). This was
done between the hours of 8:00 to 10:00pm during each expedition. Sampling was
conducted from May to July, 2018, at Ahaoada Main
Town, and in September, 2020, at Joinkrama. Anurans
were identified after Roedel (2000).
Laboratory
Examination
Anuran samples were transported in wet and aerated
containers to the Entomology and Parasitology Laboratory, Department of Animal
and Environmental Biology, Rivers State University, Port Harcourt, for
examination. They were anesthetized and measured to determine the wet body
weight (using a top-local electronic balance) and snout-vent length (using a metre rule).
They were thereafter dissected for the
isolation of helminth parasites. The lungs,
gastrointestinal tract, urinary bladder and body cavity were examined in Petri
dishes half-filled with 0.9% normal saline solution.
Parasites
were picked up using pipettes and fixed appropriately in well labeled bottles:
nematodes were stretched in hot water and fixed in 70% alcohol; monogeneans, trematodes and cestodes were flattened in 5%formol saline under cover slip
pressure and fixed in the same solution.
Identification
of Helminth Endoparasites
and Computation of Prevalence and Mean Intensity of Infection
The helminth endoparasites were identified with the help of identification
keys (Prudhoe and Bray, 1982; Khalil et
al., 1994) using compound microscopes. The number of helminthes recovered
was recorded per predilection site.
Prevalence
and mean intensity of infection were computed following the formula of Bush et al. (1997).
RESULTS AND
DISCUSSION
Twenty-eight anurans were collected from Ahoada Main Town- Ahoada East-
over the sampling period and included the following species: Hoplobatrachus occipitalis, Ptychadena bibroni, P. oxyrhynchus, P. pumilio, P. mascareniensis and
Hymenochirus sp.
Fourteen helminth parasite species were
isolated from the infected hosts. The parasites were monogeneans
(Polystoma aeschlimanni and P. pricei), digeneans (Mesocoelium monodi, Diplodiscus fischthalicus, Ganeo africana and Metahaematoloechus exoterorchis), cestodes (Cylindrotaenia jaegerskioeldii),
and nematodes (encysted ascaridida larvae (Plate 2), Rhabdias sp., Oswaldocruzia hoepplii, Cosmocerca ornata, Chabaudus leberrei and Amplicaecum africanum).
The overall prevalence
of infection with parasites ranged from 6.25% to 100% (Table 1). Among the monogeneans, Polystoma aeschlimanni infected Ptychadena pumilio at a prevalence of 20% while P. pricei
infected Ptychadena mascareniensis
at a prevalence of 12.5%; mean intensity of infection was two per infected host
for both parasites. The digeneans, Mesocoelium monodi and Metahaematoloechus exoterorchis
infected Ptychadena mascareniensis
and Hoplobatrachus occipitalis,
respectively, at a prevalence of 37.50%. Diplodiscus fischthalicus and Ganeo africana both infected H. occipitalis
at 6.3% prevalence.
The only cestode, Cylindrotaenia jaegerskioeldii, was isolated from P. mascarenienesis at 25% prevalence and
mean intensity of about five parasites per infected host. Among the nematodes,
the highest prevalence of 100% was reached by Ascaridia
larva-2 in Ptychadena oxyrhynchus,
and Amplicaecum africanum in Ptychadena bibroni.
At Joinkrama – Ahoada West LGA- a total of thirty amphibian specimens were
captured and examined for helminth parasites. These
were comprised of toads (Sclerophrys maculata) and
frogs (Hylarana galamensis, Hoplobatrachus occipitalis, Ptychadena bibroni and Ptychadena mascareniensis). A total of ten helminth
species, including members of the Acanthocephala, Cestoda, Trematoda and Nematoda, were recovered from the anuran hosts. The
parasites were namely, acanthocephalan cystacanths (Acanthocephala), Cylindrotaenia jaegerskioeldii (Cestoda), Diplodiscus fischthalicus, Mesocoelium monodi,
Metahaematoloechus exoterorchis
(Trematoda), Amplicaecum africanum, Cosmocerca ornata, Rhabdias sp., Rhabdias africanus and Oswaldocruzia hoepplii (Nematoda).
The acanthocephalan cystacanths were isolated from the body cavity of Ptychadena mascareniensis.
Prevalence of infection was 100.0% and the mean intensity of infection was
seven parasites per infected host. The tapeworm, C. jagerskioeldii, infected only P. bibroni at
a prevalence of 50.0% and mean intensity of one parasite per infected host.
Among the trematodes, Diplodiscus fischthalicus infected only Hoplobatrachus occipitalis
at a prevalence of 11% and mean intensity of one parasite per infected host. Metahaematolechus exoterorchis
infected both H. occipitalis
and Sclerophrys
maculata. However, both prevalence and mean
intensity of infection were higher in H. occipitalis. Whereas prevalence was 88% in H. occipitalis,
it was 33% in S. maculata.
Mean intensity of infection was 13.5 parasites per infected host in H. occipitalis,
and 3.0 parasites per infected host in S.
maculata.
Another trematode, M. monodi, infected H.
galamensis, H. occipitalis
and S. maculata,
at prevalence rates of 20%, 22% and 66%, respectively. Mean intensity of
infection was higher in H. galamensis (11 parasites per infected host), followed
by H. occipitalis
(5.5 parasites per infected host) and Sclerophrys maculata (1.5 parasites per infected host).
Five nematode species
were recovered from the specimens examined in this project. Amplicaecum africanum was found only in Sclerophrys maculata;
prevalence and mean intensity of infection were 33% and 3.0, respectively. Cosmocerca ornata was
isolated from four of the five host species examined. These were H. galamensis, H. occipitalis, P. bibroni and S. maculata,
and both prevalence and mean intensity of infection were highest in S. maculata.
Two species of Rhabdias were
isolated, Rhabdias africanus
from S. maculata
and an unidentified species from Hylarana galamensis. Oswaldocruzia hoepplii was isolated from Ptychadena bibroni at a prevalence of 100% and mean intensity of
infection was 1.5 parasites per infected host (Table 2).
The anuran composition at
both locations were similar being comprised of species such as Hoplobatracchus occipitalis, Ptychadena bibroni and Ptychadena mascareniensis.
Ptychadena oxyrhynchus,
P. pumilio
and Hymenochirus
sp. were
only encountered at Ahoada Main Town, whereas Sclerophrys maculata and Hylarana galamensis
were found only at Joinkrama. This disparity is thought
to be due to the short duration of sampling at both locations because similar
altered habitats have been reported to support all of these species (Amuzie and Akani, 2017; Amuzie et al.,
2019). Habitat structure affects anuran diversity as a result of its effect on
the availability of preferred niches of varying species of anurans (Pearman, 1997). The undisturbed rainforest would be
expected to hold a higher diversity of amphibian species than anthropogenically disturbed landscapes (Ernst et al., 2007).
Anthropogenic
alterations also affect parasite dynamics enhancing or reducing prevalence as
the case may be. For instance, Roznik et al. (2015) reported that removal of
rainforest canopy cover reduced the prevalence of the fungus Batrachochytrium dendrobatidis
in the rainforest frogs, Litoria rheocola. The
parasites reported in the anuran samples examined in the present research reflect
the parasite fauna of these anurans from other locations of Rivers State,
Nigeria. The monogeneans, Polystoma aeschlimanni and P. pricei are specific to Ptychadena pumilio and P. mascareniensis,
respectively and have been reported from locations such as Rumuji-Emohua
(Okere et al.,
2019), Agbada and Rumuesara
(Amuzie and Akani, 2017),
and Ogoniland (Amuzie and Aisien, 2018). Here, they were encountered in Ptychadena
species from Ahoada Main Town but were absent in
those from Joinkrama. This could be due to short
sampling duration. However, Joinkrama experiences
seasonal flooding accumulating waste and debris which could make the
environment unsuitable for monogeneans.
The digenean, Mesocoelium monodi, is a cosmopolitan species being reported from
varying species of anurans –both frogs and toads- (Robert et al., 2018; Amuzie et al., 2020a). Other digeneans, such as,
Diplodiscus fischthalicus, Ganeo africana and Metahaematoloechus
spp. are usually isolated from Hoplobatrachus occipitalis (Amuzie and Ekerette, 2019). Nematode parasites are usually reported to
be more diverse in terms of species richness in most researches on parasites of
anurans in Nigeria. This is attributed to their ubiquitous nature, resilience
of nematode eggs to adverse environmental conditions and direct mode of
transmission of several nematode species. In this research, the lung-dwelling Rhabdias spp. were encountered as well as intestinal nematodes (Amplicaecum africanum, Cosmocerca ornata, Chabaudus leberrei and Oswaldocruzia hoepplii) and
the ascaridida larvae which reside in the body
cavity. These have also been reported by previous authors from other locations
in the Niger Delta region (Robert et al.,
2018; Okere et
al., 2019; Amuzie et al., 2020b).
CONCLUSION
The common anuran species of Ahoada area of Rivers State, Nigeria, has been found to
include the species Hoplobatracchus occipitalis, Ptychadena bibroni, Ptychadena mascareniensis,
Ptychadena oxyrhynchus, P. pumilio, Hymenochirus sp.,
Sclerophrys maculata and Hylarana galamensis.
Their associated endohelminth parasites include
acanthocephalan cystacanths, cestodes,
digeneans and nematodes. The altered nature of the
habitats surveyed is thought to have influenced both the anuran and endohelminth parasites diversity recorded.
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