Medical Malacology role of snaails in snail borne parasitic diseses

Role of snaails in snail borne parasitic diseses

1. Malacology PAR7001 Prof. Noha Elleboudy

2. STPDs Parasite Snail Intermediate Host Type of Snail Ecology Distribution Intramolluscan Larvae Type of larva coming out Control Strategies

3. Elaborate the medical importance of snails in parasites transmission.   Explain the transmission dynamics and snail\ parasite interaction. Discuss the ecological factors  that influence the distribution and abundance of medically important snails. Elaborate how to detect parasitic infections in snails Design control strategies  for snail-borne diseases. By the end of the lecture, students should be able to: DOI: 10.4172/2161-0525.1000311

4. Snails are invertebrates belonging to the phylum, Mollusca , which is the second-largest animal group. Under this phylum, gastropods are the largest, consisting of snails and slugs . They are characterized by a single spiral shell and a foot for movement.

5. Phylum Mollusca Class Gastropoda Belly - Foot

6. Parts of a Gastropod Shell There are key areas of a gastropod shell that can be useful in identifying and differentiating species. Some of these characteristics include: Protoconch Shell whorl Spire Aperture Outer lip Siphonal Canal Shell Sculpture Chirality

7. What is a shell whorl?  A  shell   whorl  is one 360- degree rotation of this shell spiral. These can often be seen as " layers " down the spire of the shell. Each shell has a single  Body Whorl . This is the largest section of the shell where the gastropods body resided at the latest stage of growth. The smaller shell whorls make up the  Spire  of the shell. 

8. What is a shell aperture? The  aperture  is the primary opening in the shell that the mollusk body, foot, and head enter and exit in order to interact with the environment. Living gastropods have an  operculum , a hard calcified " door " that they can use to plug up the aperture. The operculum allows them to seal of from the outside protecting them from predators or other dangerous environmental conditions.

9. Shell Sculpture The texture on the outside of a shell is called the  shell sculpture . Shell sculpture is typically oriented in one of two ways, parallel or perpendicular to the axis of coiling (shown in red). Sculpture arranged  parallel  to the axis of coiling is called  axial sculpture  while sculpture arranged perpendicular to this axis is  spiral sculpture .

10. What is chirality? . Chirality refers to the direction in which the shell spirals. To determine a shells chirality hold it with the aperture facing you and the spiral of the shell pointing up. If the aperture is on the right side of the shell, it is  Dextral  (right-handed) and if its on the left the shells is  Sinistral  (left-handed). https://www.seahorseandco.com/gastropodshells

11. Evolutionary Significance : Shell coiling is determined by genetic factors and can influence snail anatomy, behavior, and survival . Ecological and Parasitological Implications : The direction of coiling can affect snail-parasite interactions , as it may influence the snail's ability to evade predators or adapt to environmental conditions. P.S. Biomphalaria alexandrina  is  planispiral , meaning its shell is coiled in a flat, disc-like shape. Why Coiling Matters in Snails??

12. The geographical distribution and occurrence of fasciola spp. and their intermediate hosts, snails: Freshwater snail-borne parasitic diseases in Africa 2024 DOI: 10.1186/s41182-024-00632-1 Cailliaudi ?????????? Lymnaea natalensis

13. Types of Medically Important Snails: Freshwater Snails: Biomphalaria spp.: Intermediate hosts for Schistosoma mansoni , the causative agent of intestinal schistosomiasis.  Bulinus spp.: Intermediate hosts for Schistosoma haematobium, responsible for urinary schistosomiasis.     Oncomelania spp.: Intermediate hosts for Schistosoma japonicum, causing Asian intestinal schistosomiasis.   Lymnaea spp.: Intermediate hosts for Fasciola hepatica and Fasciola gigantica , the liver flukes.

14. b. Terrestrial Snails Achatina fulica (Giant African Land Snail): Potential host for Angiostrongylus cantonensis , the rat lungworm, which causes eosinophilic meningitis in humans. Pomacea spp.: Known to transmit Angiostrongylus costaricensis , causing abdominal angiostrongyliasis.   Succinea spp.: Intermediate hosts for Leucochloridium paradoxum , a trematode that infects birds but can be accidentally ingested by humans. c. Brackish-marine Snails Pirenella , Conus

15. Ecological Factors Affecting the Distribution of Freshwater Snails Biotic Factors: Vegetation…. they exhibit higher oxygen tension owing to photosynthesis. Human Influence…Areas of the water body with much human activity always have high snail population for effective infectivity. Food supply Predators……birds, turtles, tortoise, crocodiles, lizards. Abiotic Factors: Ecology of freshwater snails depends on the physical geography of a given region. Land contours, soil composition, hydrography and climate have significant effect on snail ecology and population dynamics

16. Ecology of Medically Important Snails: Habitat : Freshwater snails thrive in slow-moving or stagnant water bodies such as ponds, lakes, and irrigation canals. Terrestrial snails prefer moist environments like forests and agricultural fields.   Climate : Snail populations are highly sensitive to temperature and rainfall. Warm, tropical, and subtropical regions are most conducive to their proliferation.   Human Activity : Agricultural practices, dam construction, and poor sanitation can create ideal habitats for snails, increasing the risk of parasitic transmission.

17. https://doi.org/10.1038/s41598-022-21306-0 Q Environmental factors affecting snails’ growth and parasitic disease transmission Snail Ecology Q

18. Temperature…27 °C., Sunlight, Rainfall, Water Current, Turbidity, Salinity, Calcium and Magnesium ions, pH … 7.8 to 8.5., Conductivity, Oxygen tension, all can influence the physiological processes of snails https://doi.org/10.1038/s41598-022-21306-0

19. Parasitism Capacity: Snails serve as intermediate hosts for various parasites, particularly trematodes. The parasitism capacity of snails depends on:   Compatibility : Not all snail species are susceptible to all parasites. Specific snail-parasite combinations are required for successful transmission.   Parasite Load : Snails can harbor thousands of larval stages of parasites, which are released into the environment to infect definitive hosts.   Immune Response : Snails have an innate immune system that can sometimes limit parasite development, but many parasites have evolved mechanisms to evade snail defenses.

20. ??????

21. STPDs can be divided into three groups: trematode diseases (by infection of flukes such as liver flukes, intestinal flukes, blood flukes, and lung flukes), nematode diseases (rat lungworm infection), and cestode diseases ( Davainea infection). Non zoonotic

22. Classification of important parasite-transmitting snail species AC ,  Angiostrongylus cantonensis ;  CS ,  Clonorchis sinensis ;  FB ,  Fasciolopsis buski ;  FH ,  Fasciola hepatica ;  OF ,  Opisthorchis felineus ;  OV ,  Opisthorchis viverrini ;  PW ,  Paragonimus westermani ;  SM ,  Schistosoma mansoni ;  SMa ,  Schistosoma malayensis ;  SH ,  Schistosoma haematobium ;  SMe ,  Schistosoma mekongi ;  SJ ,  Schistosoma japonicum Echinostoma ??

23. Snail transmitted parasitic diseases: parasite species, host, parasitic stages, transmission, and pathological lesions DH , definitive host; IH , intermediate host; Mi , miracidium; Sc , sporocyst; R , redia ; C , cercaria; Mc , metacercaria; L1 , 1 st larval stage; L2 , 2 nd larval stage; L3 , 3 rd larval stage aA Ants https://doi.org/10.1007/s00436-023-08021-z MISSING ???????????????

24. Snails/Parasite Interaction: 1. Initial contact 2. Development Inside the Snail 3. Parasite-Induced Changes in Snail Biology 4. Cercarial Release and Transmission

25. 1. Initial contact 1. Initial contact

26. https://doi.org/10.1186/s40249-018-0414-7 Echinostoma ?? L1: first-stage; L2: second-stage ; L3: third-stage larvae 2. Development Inside the Snail

27. Trematode Snail Intermediate Host Type of Snail Bionomics Distribution Ecology Intramolluscan Larvae Control Strategies Schistosoma mansoni Biomphalaria spp. Planorbid snail Freshwater, prefers slow-moving or stagnant water. Africa, South America, Caribbean. Found in ponds, lakes, irrigation canals. Miracidium → Sporocyst → Cercaria Molluscicides, environmental management, health education. Schistosoma haematobium Bulinus spp. Planorbid snail Freshwater, prefers slow-moving or stagnant water. Africa, Middle East. Found in ponds, lakes, irrigation canals. Miracidium → Sporocyst → Cercaria Molluscicides, environmental management, health education. Schistosoma japonicum Oncomelania spp. Pomatiopsid snail Amphibious, found in marshes, rice fields, and irrigation ditches. China, Philippines, Indonesia. Thrives in muddy, vegetation-rich environments. Miracidium → Sporocyst → Cercaria Snail control, improved sanitation, health education. Fasciola hepatica Lymnaea truncatula Lymnaeid snail Freshwater, prefers shallow, slow-moving water with vegetation. Worldwide (temperate regions). Found in ponds, ditches, and wet meadows. Miracidium → Sporocyst → Redia → Cercaria Molluscicides, drainage of habitats, livestock treatment. Fasciola gigantica Lymnaea natalensis Lymnaeid snail Freshwater, prefers warm, slow-moving water with vegetation. Africa, Asia. Found in ponds, lakes, and irrigation canals. Miracidium → Sporocyst → Redia → Cercaria Molluscicides, environmental management, livestock treatment. Paragonimus westermani Semisulcospira spp. Thiarid snail Freshwater, prefers fast-flowing streams and rivers. Asia (China, Korea, Japan). Found in rocky, fast-flowing freshwater habitats. Miracidium → Sporocyst → Redia → Cercaria Snail control, cooking crustaceans thoroughly, health education. Clonorchis sinensis Bithynia spp. Bithyniid snail Freshwater, prefers slow-moving or stagnant water. East Asia (China, Korea, Vietnam). Found in ponds, lakes, and rice fields. Miracidium → Sporocyst → Redia → Cercaria Snail control, proper cooking of fish, health education. Opisthorchis viverrini Bithynia spp. Bithyniid snail Freshwater, prefers slow-moving or stagnant water. Southeast Asia (Thailand, Laos). Found in ponds, lakes, and rice fields. Miracidium → Sporocyst → Redia → Cercaria Snail control, proper cooking of fish, health education. Echinostoma spp. Lymnaea spp. ,  Biomphalaria spp. Lymnaeid/Planorbid snail Freshwater, prefers slow-moving or stagnant water. Worldwide (tropical/subtropical). Found in ponds, lakes, and irrigation canals. Miracidium → Sporocyst → Redia → Cercaria Snail control, proper cooking of second intermediate hosts, health education. Heterophyes heterophyes Pirenella spp. Cerithiid snail Brackish water, prefers estuaries and coastal lagoons. Middle East, North Africa. Found in brackish water habitats with vegetation. Miracidium → Sporocyst → Redia → Cercaria Snail control, proper cooking of fish, health education. Metagonimus yokogawai Semisulcospira spp. Thiarid snail Freshwater, prefers fast-flowing streams and rivers. East Asia (Japan, Korea, China). Found in rocky, fast-flowing freshwater habitats. Miracidium → Sporocyst → Redia → Cercaria Snail control, proper cooking of fish, health education. Watsonius watsoni Bulinus spp. Planorbid snail Freshwater, prefers slow-moving or stagnant water. Africa. Found in ponds, lakes, and irrigation canals. Miracidium → Sporocyst → Redia → Cercaria Snail control, improved sanitation, health education. Nanophyetus salmincola Oxytrema silicula Pleurocerid snail Freshwater, prefers cool, fast-flowing streams. North America (Pacific Northwest). Found in cold, clear streams with rocky substrates. Miracidium → Sporocyst → Redia → Cercaria Snail control, proper cooking of fish, health education. Dicrocoelium dendriticum Cionella spp. ,  Zebrina spp. Land snail Terrestrial, prefers dry, grassy habitats. Worldwide (temperate regions). Found in grasslands and pastures. Miracidium → Sporocyst → Redia → Cercaria Control of land snails, treatment of livestock, health education. Trematode Snail Intermediate Host Type of Snail Bionomics Distribution Ecology Intramolluscan Larvae Control Strategies Schistosoma mansoni Biomphalaria spp. Planorbid snail Freshwater, prefers slow-moving or stagnant water. Africa, South America, Caribbean. Found in ponds, lakes, irrigation canals. Sporocyst → Cercaria Molluscicides, environmental management, health education. Schistosoma haematobium Bulinus spp. Planorbid snail Freshwater, prefers slow-moving or stagnant water. Africa, Middle East. Found in ponds, lakes, irrigation canals. Sporocyst → Cercaria Molluscicides, environmental management, health education. Schistosoma japonicum Oncomelania spp. Pomatiopsid snail Amphibious , found in marshes, rice fields, and irrigation ditches. Diocious China, Philippines, Indonesia. Thrives in muddy, vegetation-rich environments. Sporocyst → Cercaria Snail control, improved sanitation, health education. Fasciola hepatica Lymnaea truncatula Lymnaeid snail Freshwater, prefers shallow, slow-moving water with vegetation. Worldwide (temperate regions). Found in ponds, ditches, and wet meadows. Sporocyst → Redia → Cercaria Molluscicides, drainage of habitats, livestock treatment. Fasciola gigantica Lymnaea natalensis Lymnaeid snail Freshwater, prefers warm, slow-moving water with vegetation. Africa, Asia. Found in ponds, lakes, and irrigation canals. Sporocyst → Redia → Cercaria Molluscicides, environmental management, livestock treatment. Paragonimus westermani Semisulcospira spp. Thiarid snail Freshwater, prefers fast-flowing streams and rivers. Diocious Asia (China, Korea, Japan). Found in rocky, fast-flowing freshwater habitats. Sporocyst → Redia → Cercaria Snail control, cooking crustaceans thoroughly, health education. Clonorchis sinensis Bithynia spp. Bithyniid snail Freshwater, prefers slow-moving or stagnant water. East Asia (China, Korea, Vietnam). Found in ponds, lakes, and rice fields. Miracidium → Sporocyst → Redia → Cercaria Snail control, proper cooking of fish, health education. Opisthorchis viverrini Bithynia spp. Bithyniid snail Freshwater, prefers slow-moving or stagnant water. Southeast Asia (Thailand, Laos). Found in ponds, lakes, and rice fields. Miracidium → Sporocyst → Redia → Cercaria Snail control, proper cooking of fish, health education. Echinostoma spp. Lymnaea spp., Biomphalaria spp. Lymnaeid/Planorbid snail Freshwater, prefers slow-moving or stagnant water. Worldwide (tropical/subtropical). Found in ponds, lakes, and irrigation canals. Sporocyst → Redia → Cercaria Snail control, proper cooking of second intermediate hosts, health education. Heterophyes heterophyes Pirenella spp. Cerithiid snail Brackish water, prefers estuaries and coastal lagoons. Bottom feeder resistant to molluscides Middle East, North Africa. Found in brackish water habitats with vegetation. Miracidium → Sporocyst → Redia → Cercaria Snail control, proper cooking of fish, health education. Metagonimus yokogawai Semisulcospira spp. Thiarid snail Freshwater, prefers fast-flowing streams and rivers. East Asia (Japan, Korea, China). Found in rocky, fast-flowing freshwater habitats. Miracidium → Sporocyst → Redia → Cercaria Snail control, proper cooking of fish, health education. Watsonius watsoni Bulinus spp. Planorbid snail Freshwater, prefers slow-moving or stagnant water. Africa. Found in ponds, lakes, and irrigation canals. Sporocyst → Redia → Cercaria Snail control, improved sanitation, health education. Nanophyetus salmincola Oxytrema silicula Pleurocerid snail Freshwater, prefers cool, fast-flowing streams. North America (Pacific Northwest). Found in cold, clear streams with rocky substrates. Miracidium → Sporocyst → Redia → Cercaria Snail control, proper cooking of fish, health education. Dicrocoelium dendriticum Cionella spp., Zebrina spp. Land snail Terrestrial, prefers dry, grassy habitats. Worldwide (temperate regions). Found in grasslands and pastures. Miracidium → Sporocyst → Cercaria Control of land snails, treatment of livestock, health education. IH

28. The hemolymph of Biomphalaria snail vectors of schistosomiasis supports a diverse microbiome doi:10.1111/1462-2920.15303. Li, P., Hong, J., Yuan, Z. et al. Gut microbiota in parasite-transmitting gastropods. Infect Dis Poverty 12, 105 (2023). https://doi.org/10.1186/s40249-023-01159-z The gut microbiome can modulate the interaction between snails and parasites, influencing the outcome of infection. Microbiome Q 2. Inside the Snail

29. The potential functions and influencing factors of gastropod gut microbiota https://doi.org/10.1016/j.pt.2024.01.002 Snail microbiota and snail–schistosome interactions: axenic and gnotobiotic technologies

30. DOI:  10.1016/j.pt.2017.07.006 Key components of the snail immune system include:   Hemocytes : Immune cells that play a central role in phagocytosis, encapsulation, and the production of reactive oxygen species (ROS).   Pattern Recognition Receptors ( PRRs ): Proteins that recognize pathogen-associated molecular patterns ( PAMPs ) on the surface of invaders.   Reactive Oxygen Species (ROS): Toxic molecules produced by hemocytes to kill pathogens.   Antimicrobial Peptides (AMPs): Small proteins that disrupt the membranes of pathogens.

31. Discus the ability of parasites to evade or suppress the snail's immune system Q

32. Immune Evasion Strategies of Parasitic Larvae Molecular Mimicry Secretion of Immunomodulatory Molecules Disruption of Hemocyte Function Manipulation of Host Signaling Pathways Physical Barriers Antigenic Variation DOI:  10.1016/j.pt.2017.07.006 Glycosylation pattern

33. https://doi.org/10.1186/s13071-023-06011-9 Partial immune responses triggered by pathogen invasion in  biomphalaria glabrata . Several immune-related factors and their mechanisms of action have been reported in smooth-bore snails. Bgtlr , as a crucial transmembrane PRR, mediates immune signaling in haemocytes through intracellular transduction . Soluble immune factors like bgfrep , bgtep , and biomphalysin interact to initiate cytotoxic effects (perforation of pathogen cell membranes or release of cytotoxic substances) and opsonization , culminating in pathogen elimination via cell phagocytosis. Additionally, the chemoattractant factor bgmif induces haemocyte migration and proliferation, potentially contributing to encapsulation response pathogen-associated molecular patterns Pattern Recognition Receptors Fibrinogen related proteins

34. Examples of Immune Evasion in Specific Parasites a . Schistosoma spp. Schistosoma mansoni and other schistosomes produce antioxidant enzymes to neutralize ROS generated by snail hemocytes. They also secrete proteins that inhibit hemocyte adhesion and phagocytosis.  b. Fasciola spp. Fasciola hepatica produces cathepsin proteases that degrade host immune molecules and tissues. It also secretes molecules that modulate the snail's TGF-β pathway, suppressing immune responses.   c. Echinostoma spp . Echinostomes produce proteins that disrupt hemocyte function and prevent encapsulation.  They also secrete molecules that inhibit the production of antimicrobial peptides .  

35. Q: Compare snail and human immune responses to schistosomes. Snail immunity Human immunity FREPs  (fibrinogen-related proteins) target sporocysts Th2 response  (IL-4, IL-13) drives granuloma formation Hemocyte encapsulation  (ROS/nitric oxide) Eosinophil-mediated  larval killing No adaptive memory The innate immune system may produce an enhanced secondary response to a pathogen Partial resistance  after repeated exposure ( IgE role) Paradox:  Snails lack antibodies but evolve FREPs; humans have antibodies but suffer chronic immunopathology.

36. The presence of parasitic larvae can significantly alter the biology and behavior of the snail host. These changes often benefit the parasite by enhancing its transmission.  a . Physiological Changes Castration : Many trematodes cause partial or complete castration of the snail by consuming its reproductive tissues. This redirects the snail's energy toward parasite development.   Metabolic Alterations : Infected snails often exhibit changes in metabolism, including increased glucose levels, which may benefit the parasite.   3. Parasite-Induced Changes in Snail Biology

37. b. Behavioral Changes Altered Movement : Infected snails may exhibit erratic or unusual movement patterns, increasing their exposure to predators (definitive hosts).   Phototaxis : Some infected snails become more attracted to light, bringing them closer to the water surface where cercariae can be released and dispersed.   c. Immunological Suppression Parasites often secrete molecules that modulate the snail's immune system, preventing it from effectively eliminating the infection. For example, some trematodes produce antioxidant enzymes to neutralize the snail's reactive oxygen species.  

38. The final stage of the snail-parasite interaction involves the release of cercariae into the environment, where they seek out the definitive host (Schistosoma).   Timing of Release : Cercarial release is often synchronized with the activity patterns of the definitive host. For example, cercariae of Schistosoma spp. are typically released during the day when humans are more likely to be in contact with water.   Environmental Cues : Factors such as light, temperature, and water turbulence can trigger cercarial release.   Infectivity : Cercariae are highly infectious and can penetrate the skin of the definitive host within minutes of contact. 4. Cercarial Release and Transmission

39. Detection of parasitic infections in snails: Microscopic methods Snail crushing Cercarial shedding test DNA‑based methods : Conventional PCR and real‑time polymerase chain reaction (RT‑PCR) and Loop‑mediated amplification (LAMP). Antibody‑based methods Protein barcode‑based methods : MALDI‑TOF MS. https://doi.org/10.1186/s41182-024-00632-1

40. Detection of parasitic infections in snails:

41. Demonstrating the multiple aspects of a one-health approach for STPDs. IH, intermediate host; PH, paratenic host

42. Human health Animal health Environmental Cross sector a. Public Health Education & Awareness Community engagement   Hygiene promotion   Mass drug administration (MDA)   b. Improved Sanitation & Safe Water Access Latrine construction  , Water treatment a. Veterinary Surveillance & Treatment Deworming livestock  Monitoring zoonotic trematodes  b. Livestock Management Grazing control to prevent livestock from contaminating water sources. Alternative water sources  a. Snail Habitat Modification b. Biological Control c. Chemical Control a. Integrated Surveillance & Reporting Joint human-animal-environment monitoring  for snail and parasite trends. Geographic Information Systems (GIS)  to map high-risk zones. b. Multi-Sectoral Coordination Ministries of Health, Agriculture, and Environment  working together. Community participation  in snail control programs. c. Research & Innovation Development of eco-friendly molluscicides . Vaccine research  for livestock (e.g.,  Fasciola  vaccines). One Health

43. While snails can serve as hosts for disease-causing parasites, it is important to note that they also play important roles in ecosystems as food sources for other animals and as decomposers; they consume the dead and decaying vegetation, snails play a role in soil formation. As environmental clean-up crews, snails’ nutrient-cycling activity extends also to fungi, and they also act as water-quality indicators Therefore, any efforts to control snail populations and STPDs should be implemented in a naturally responsible manner and considered in conjunction with the current epidemiological situation in the endemic areas.

44. Controlling snail populations is critical for reducing the transmission of SBPDs. Strategies include:

45. Control Measures   a. Environmental Management (ecological = physical control) Habitat Modification: Draining stagnant water, improving irrigation systems, and removing vegetation to reduce snail habitats.  Mechanical Removal and Dredging. Barriers as Screens and Filters, Snail Traps. Sanitation: Proper waste disposal and access to clean water to minimize human-snail contact.  Concreting Canals and Ditches. Water Flow Management.

46. Control Measures b. Biological Control Predators : Introducing natural predators like fish, ducks, or other mollusk-eating species.  Competitors : Using non-host snails to compete with medically important species. Pathogens and Parasites : Nematodes, Bacteria and Fungi, Trematodes Plant-Based Control : Endod (Phytolacca dodecandra ), Neem ( Azadirachta indica), Solanum spp.  

47. Aspect Physical Control Biological Control Effectiveness Immediate reduction in snail populations Slower but sustainable reduction in snail populations Environmental Impact Generally low, but habitat modification can disrupt ecosystems Environmentally friendly, promotes ecological balance Cost Can be labor-intensive and costly (e.g., dredging, concreting canals) Lower cost, especially if using natural predators or competitors Sustainability May require ongoing maintenance (e.g., periodic dredging) Sustainable, as natural predators or competitors can establish long-term control Target Specificity Non-specific, may affect non-target organisms Can be specific to snails, depending on the control agent used Implementation Requires infrastructure and labor Requires knowledge of local ecology and careful selection of control agents

48. c. Chemical Control Molluscicides: Chemicals are used to kill snails, but their use must be carefully managed to avoid environmental harm.     Advantages of using molluscicides: Direct interruption of snail-to-human transmission The desirable, but not essential, involvement of the community A reasonable efficiency and cost of product The simple equipment can also be used for the control of other vectors While good supervision is essential, the methods of application are simple and do not require specialized operational schemes. 6. Selection of foci for application can usually be based on the patterns of water use by the local population

49. D isadvantages of using molluscicides in eliminating a STPDs: 1. Repeated reapplication is necessary, because snail eradication is often not possible. 2. Time demands of implementation and evaluation of control are greater than for MDA. 3. The impact on Schistosoma infection and morbidity is delayed relative to drug therapy. 4. Uniform dispersal and area coverage is difficult to achieve. 5. The cost of labor is foremost when doing repeated treatments. 6. Well-informed technical capacity is required to decide appropriate application. 7. Collateral molluscicide effects on amphibians and fish must be openly addressed and effectively minimized to meet public concerns about safety and environmental impact.

50. Most of the molluscicides can induce the injury of snail soft tissues and influence the activity of key enzymes , leading to the changes of a serial of physiological and biochemical characteristics, and finally resulting in the death of snails bayluscide It is effective against snails and their eggs, miracidia and cercariae at low concentrations and within a few hours but Niclosamide is, however, harmful to non-target aquatic fauna such as fish and frogs, which would limit its use.

51. Plant molluscicides Disadvantages : (1) low content of the active ingredients result in low molluscicidal activity; (2) Regional limitations for some specific molluscicidal plants; (3 ) High cost and complicated extraction process; (4) Environmental pollution because of the application of fresh Molluscicidal plants. DOI:10.1371/journal.pntd.0003657

52. Integrated Approach For effective and sustainable control of medically important snails, a combination of  physical ,  biological , and  chemical  methods is often recommended. This integrated approach minimizes the risk of resistance, reduces environmental impact, and ensures long-term control of snail populations.

53. Transgenic snails vs. Gene Drives . 2018 Aug 15;3(3):86. doi :  10.3390/tropicalmed3030086 Treading the Path towards Genetic Control of Snail Resistance to Schistosome Infection Q CRISPR-edited snails with  enhanced FREP expression  to block sporocyst development.

54. Gene Editing in the Control of Medically Important Snails a. Disrupting Parasite Development Targeting Snail Genes Essential for Parasite Survival : Gene editing can be used to knock out or modify genes in snails that are essential for the development of parasites Example: Knocking out genes involved in the snail's immune response or metabolism that are required for parasite survival. Creating Resistant Snail Strains : Gene editing can be used to create snail strains that are resistant to parasitic infections. b.  Population Suppression Sterile Snail Production : Gene editing can be used to create sterile snails by disrupting genes essential for reproduction. Releasing sterile snails into the wild can reduce the overall population of medically important snails. Example: Using CRISPR to knock out genes involved in gametogenesis or embryogenesis. Gene Drives : Gene drives can be used to spread genes that reduce snail fertility or viability through wild populations, potentially leading to population suppression or elimination. Example: Using CRISPR-based gene drives to spread a sterility gene in  Biomphalaria glabrata  populations.

55. c. Enhancing Snail Immunity Boosting Immune Responses : Gene editing can be used to enhance the snail's natural immune response to parasites, making them less susceptible to infection. Example: Overexpressing genes involved in the production of antimicrobial peptides or reactive oxygen species (ROS). d. Studying Snail-Parasite Interactions Functional Genomics : Gene editing can be used to study the role of specific genes in snail-parasite interactions, providing insights into potential targets for control. Example: Knocking out genes involved in the snail's immune response to identify those that are critical for parasite development.  Gene Editing Tools for Snail Control--Challenges in Gene Editing----Examples

56. https://doi.org/10.1080/20477724.2020.1731667

57. What are the operating procedures to optimally target snails? How to achieve the best molluscicide effect? (https://doi.org/10.1007/s00436-021-07288-4) Q

58. Bioindicators of Environmental Quality Model Organisms in Immunological and Parasitological Research Biological Control Agents Testing Natural Molluscicides and Larvicides Pharmacological and Molecular Studies Biomphalaria snails have several beneficial uses, particularly in scientific research and disease control:

59. Snail Mucin Moisturizing, wound healing, anti-inflammatory effects, antimicrobial , improve skin hydration and barrier function also aiding scar healing https://doi.org/10.1111/jocd.16269 Snail extract for skin: A review of uses, projections, and limitations

60. HOMEWORK

61. What are the types of cercaria in medically important snails???? Q https://doi.org/10.12980/jclm.5.2017J7-161

62. Type of Cercaria Key Characteristics Development Taxa Importance Snail Hosts Monostome Cercariae - No ventral sucker or pharynx - Simple tail - 2-3 eyespots - Adhesive organs Develop in rediae, encyst in the open Families: Notocotylidae, Pronocephalidae, Mesometridae, Microscaphididae No medical or veterinary importance Bellamya unicolor ,  Biomphalaria alexandrina ,  Bithynia goryi ,  Cleopatra bulimoides ,  Melanoides tuberculata , etc Gymnocephalous Cercariae - Straight, slender tail - Two equal suckers - No stylet or spiny collar Develop in rediae, encyst on objects or in fishes Family: Fasciolidae (and others) Veterinary importance (e.g.,  Fasciola  spp.) Biomphalaria alexandrina ,   Bithynia sp. ,  Cleopatra bulimoides ,  Galba truncatula ,  Radix natalensis , etc. Echinostome Cercariae - Head collar with spines - No eyespots - Two types of glands (penetration, paraesophageal) Develop in rediae, encyst in invertebrates or vertebrates Family: Echinostomatidae Veterinary importance; antagonistic to other trematodes (e.g., schistosomes) Biomphalaria alexandrina ,  Bulinus truncatus ,  Cleopatra bulimoides ,  Radix natalensis , etc. Stylet Cercariae (Xiphidiocercariae) - Stylet in oral sucker - Four subtypes: ornatae, virgulate, ubiquita, armatae Develop in sporocysts, encyst in invertebrates, amphibians, or reptiles Families: Haematolocchidae, Macroderoididae, Allassogonoporidae, etc. No medical or veterinary importance Bellamya unicolor ,   Biomphalaria alexandrina ,  Bulinus truncatus ,  Cleopatra bulimoides ,  Melanoides tuberculata , etc. Paramphistomoid Cercariae - Large ventral sucker - Small, unbranched tail - Two eyespots Develop in rediae, encyst on objects or in tadpoles Superfamily: Paramphistomoidea Veterinary importance (e.g.,  Paramphistomum  spp.) Biomphalaria alexandrina ,  Bulinus forskalii ,  Bulinus truncatus ,  Cleopatra bulimoides Furcocercous Cercariae - Forked tail (brevifurcate or longifurcate) - Five subtypes (e.g., lophocercous, brevifurcate, etc.) Develop in sporocysts or rediae, encyst in vertebrates or penetrate directly Families: Schistosomatidae, Clinostomatidae, Strigeidae, Diplostomatidae Medical and veterinary importance (e.g.,  Schistosoma  spp.) Biomphalaria alexandrina ,  Bulinus truncatus ,  Cleopatra bulimoides ,  Melanoides tuberculata , etc. Opisthorchioid Cercariae - Unforked tail with finfolds - Vestigial or absent ventral sucker - Eyespots Develop in rediae , encyst in fishes or amphibians Superfamily: Opisthorchioidea (e.g., Heterophyidae , Opisthorchiidae ) Medical importance (e.g.,  Heterophyes heterophyes ,  Clonorchis sinensis ) Pirenella conica ,  Cleopatra bulimoides ,  Melanoides tuberculata ,  Radix natalensis Cystophorous Cercariae - Large tail with a chamber (caudal cyst) - Body can withdraw into the tail Develop in rediae (rarely sporocysts), encyst in aquatic organisms Families: Gorgoderidae, Hemiuridae No medical or veterinary importance Biomphalaria alexandrina

63. Image examples for snail and parasite categories. For snail categories, (A-1,A-2): Biomphalaria . (B-1,B-2): Bulinus . (C-1,C-2): Radix natalensis . (D-1,D-2): Melanoides spp. HS, Human- schisto ; NHS1, Nonhuman- schisto forktail type I; NHS2, Nonhuman- schisto forktail type II; AM, Amphistome cercariae; BO, Schistosoma bovis ; EC, Echinostome cercariae; GY, Gymnocephalus cercariae; ME, Metacercaria; PP, Parapleurolophocercous cercariae; PT, Parthenitae ; XI, Xiphidiocercariae . https://doi.org/10.3389/fpubh.2021.642895

64. The brevifurcate apharyngeate distome type The brevifurcate apharyngeate monostome , the longifurcate pharyngeate distome type, and the longifurcate pharyngeate monostome type have no medical or veterinary importance

65. HOMEWORK What factors influence the susceptibility of snails to parasitic infections? How do parasites manipulate snail behavior to enhance transmission? What role do snail immune cells (hemocytes) play in combating parasitic infections? How do parasites evade the snail's immune system? What are the ecological consequences of snail-parasite interactions? What are the methods for controlling snail populations?

66. HOMEWORK 7. What are the challenges of using molluscicides for snail control? 8. How can biological control be used to manage snail populations? 9. What role does community engagement play in snail control? 10. What are the potential benefits of genetic approaches to snail control? 11. What are the ethical considerations of using genetic methods for snail control? 12. How can integrated approaches improve snail control?

67. HOMEWORK 1. Discuss the medical importance of snails in the transmission of parasitic diseases, including examples of specific parasites and their impact on human health. 2. Analyze the interaction between snails and parasites, focusing on the stages of initial contact, development inside the snail, parasite-induced changes in snail biology, and cercarial release. 3. Evaluate the ecological factors that influence the distribution and abundance of medically important snails, considering both biotic and abiotic elements. 4. Describe and compare the different methods available for detecting parasitic infections in snails, discussing their advantages and limitations. 5. Design a comprehensive strategy for controlling snail-borne diseases, incorporating environmental management, biological control, chemical control, and community engagement approaches.

68. HOMEWORK 6. Examine the role of snail immune cells (hemocytes) in combating parasitic infections and discuss how parasites have evolved mechanisms to evade or suppress the snail's immune system. 7. Assess the potential benefits and challenges of using genetic approaches, such as gene editing and gene drives, for controlling snail populations and preventing parasite transmission. 8. Discuss the ecological consequences of snail-parasite interactions and their implications for ecosystem dynamics and biodiversity. 9. Compare and contrast the effectiveness, environmental impact, cost, sustainability, and target specificity of physical, biological, and chemical control methods for managing snail populations.

69. HOMEWORK 10. Evaluate the ethical considerations and potential risks associated with using genetic methods for snail control, including gene editing and transgenic snails. 11. Analyze the role of community engagement and public health education in successful snail control programs and their integration into a One Health approach. 12. Discuss the challenges of using molluscicides for snail control, including environmental concerns, application difficulties, and the need for repeated treatments. 13. Explore the potential applications of snail mucin in dermatology and wound healing, considering its properties and limitations. 14. Describe the different types of cercariae found in medically important snails, their characteristics, development, and significance in disease transmission. 15. Critically evaluate the prospects and limitations of integrated approaches combining multiple strategies for improved snail control and prevention of snail-borne diseases.

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