Are Freshwater Snails, Melanoides sp. and Invasive Tarebia granifera (Gastropoda: Thiaridae) Suitable Intermediate Hosts for Calicophoron microbothrium (Trematoda: Paramphistomoidea)? An Experimental Study

Abstract

Prosobranch snails and adult Paramphistomoidea flukes were collected from water bodies and cattle abattoir located in Mpumalanga province of South Africa, respectively. The snails were identified based on morphological characters as well as the ITS-2 and 16S markers as Melanoides sp. and Tarebia granifera, respectively, and the Paramphistomoidea flukes were identified as Calicophoron microbothrium using the ITS-1/5.8S/ITS-2 marker. After confirming identification, the snails were bred to first filial generation (F1) under laboratory conditions. Ninety snails were randomly selected from the laboratory-bred F1 snails and 25 Melanoides sp. and 20 T. granifera were exposed to C. microbothrium miracidia, and the same numbers were maintained as non-exposed controls. Results showed that C. microbothrium successfully established in Melanoides sp. and produced cercariae, and the prepatent period recorded was 21 days. Three snails shed cercariae at day 21 postexposure (PE), and rediae and free cercariae were detected in the soft tissues of one snail on dissection at day 44 PE. The same fluke did not establish in T. granifera. Melanoides sp. started producing offspring at day 7 PE, and T. granifera at day 14 PE. In conclusion, our results showed that Melanoides sp. used in this study is a suitable intermediate host for C. microbothrium under experimental conditions, and given the wide distribution of this snail species, it is important to determine its role in the natural transmission of other Calicophoron species that have been reported in South Africa.

Keywords: Calicophoron microbothrium; Melanoides spp.; Melanoides tuberculata; Melanoides victoriae; Tarebia granifera; Thiaridae; experimental infectivity.

Figure 1

Neighbor-joining tree based on the 399-nucleotide sequence of the ITS-2, confirming the identity of Melanoides sp. (MT1-3) (in bold) collected from Mpumalanga province of South Africa and their relationship with other Melanoides species obtained from the NCBI GenBank database. The support value indicated on the nodes follows the order neighbor-joining bootstrap value/maximum likelihood bootstrap value/Bayesian inference posterior probability.

Figure 2

Neighbor-joining tree based on the 481-nucleotide sequence of the 16S rDNA, confirming the identity of Tarebia granifera (TG1–4) (in bold) collected from Mpumalanga province of South Africa and their relationship with other Thiaridae species obtained from the NCBI GenBank database. The support value indicated on the nodes follows the order neighbor-joining bootstrap value/maximum likelihood bootstrap value/Bayesian inference posterior probability.

Figure 3

Neighbor-joining tree based on the 373-nucleotide sequence of the ITS-1/5.8S/ITS-2 marker, confirming the identity of amphistomes from Mpumalanga province (in bold) as Calicophoron microbothrium and their relationship with Calicophoron species obtained from the NCBI GenBank database. The support value indicated on the nodes follows the order neighbor-joining bootstrap value/maximum likelihood bootstrap value/Bayesian inference posterior probability.