Advanced molecular genetic profiling of freshwater snails and schistosomes to characterise and to compare schistosomiasis transmission in Malawi and Saudi Arabia.

Alharbi, Mohammad
(2022) Advanced molecular genetic profiling of freshwater snails and schistosomes to characterise and to compare schistosomiasis transmission in Malawi and Saudi Arabia. PhD thesis, University of Liverpool.

[img] Text
201006500_March2022.pdf - Unspecified
Access to this file is embargoed until 1 January 2024.

Download (112MB)


My thesis implemented molecular methods of snail and schistosome identification in a novel attempt to better understand schistosomiasis transmission in Malawi and Saudi Arabia, respectively. I investigated several factors that may play important roles within and between the two country settings. I conducted several malacological surveys, three in Malawi and two in Saudi Arabia, measuring key environmental variables, mapping snail and parasite populations and thereafter using molecular characterisation methods, for example, by PCR-RFLP, DNA sequencing, microsatellite markers and phylogenetic tree construction methods. With regard to Malawi, novel snail distribution maps of various planorbid snail species, with focus upon Biomphalaria and Bulinus, were presented. I also noted the presence of Lymnaea, conducting basic DNA typing. Most importantly, the spread of Biomphalaria pfeifferi, a keystone intermediate host for Schistosoma mansoni, between 2017 and 2019, was confirmed. Assembled molecular evidence pointed towards a recent populational founder effect for this species as it exhibited low genetic diversity at all loci inspected. By real-time PCR, the prevalence of S. mansoni within Bi. pfeifferi was 18% and underpins the newly appreciated environmental risk of intestinal schistosomiasis transmission within Lake Malawi. Similarly, DNA evidence confirmed the presence of Bulinus globosus but newly reported the presence of Bulinus africanus and two, as of yet, poorly known species within the Bu. africanus species group. These can now be better recognised and more easily detected with a PCR-RFLP assay of the cox1 using double digestion with HaeIII and SacI restriction enzymes. By real-time PCR the prevalence of Schistosoma haematobium within snails was 28%. Furthermore, characterisation of available miracidia, using a combination of mitochondrial and nuclear loci, from locally infected children identified the presence of novel schistosome hybrids of S. haematobium-mattheei as well as characterised group IV S. mansoni. With regard to Saudi Arabia, the presence of Bi. pfeifferi, and not Bi. arabica, was confirmed; snails presenting with limited microsatellite variation but were slightly genetically divergent to those from Africa and Madagascar. Although no Biomphalaria was found shedding schistosome cercariae, real-time PCR analysis suggested some 13% were infected with S. mansoni. Molecular characterisation also confirmed the presence of Bu. forskalii, never before confirmed locally. Information within my thesis is of direct use to national schistosomiasis control planning by providing up-to-date information on snail and schistosomes distributions in each country. Moreover, I have helped to clarify previously cryptic aspects within the snail-schistosome relationship in each country.

Item Type: Thesis (PhD)
Divisions: Faculty of Health and Life Sciences
Depositing User: Symplectic Admin
Date Deposited: 15 Dec 2022 16:21
Last Modified: 18 Jan 2023 20:45
DOI: 10.17638/03164424
  • Russell Stothard,