Aquatic snails are the intermediate hosts of the disease schistosomiasis.
Irrigation schemes have often provided a favourable habitat for these
snails, but rapidly flowing water will carry them away.
The research established 23 stations in irrigation canals and monitored
snail numbers and water velocity at these points. A maximum tolerable
velocity for the snail Bulinus truncatus of 0.23 m/s was established,
corresponding to 0.13 m/sat snail height. Aquatic weed did not invalidate
this velocity, but the use of a single control velocity was found to be
over-simplistic. The long-term mean velocity was found to be the best
measure for snail control when velocity varied with time.
Using specially designed filter-traps, snails being carried along by the
flow were intercepted and counted. Attempts to relate these counts to
velocity revealed daily and seasonal cycles of numbers of snails detaching.
Snails in 130 syphon boxes were monitored and the number of snails compared
with water velocity. The maximum velocity tolerated here was lower than in
the canals. Turbulence theory was examined to explain the difference.
The fieldwork was largely carried out in the Tessaout Amont Irrigation
Scheme in Morocco.
Recommendations are made for the design, operation and maintenance of
irrigation schemes, if velocity is to be considered as a snail control.

Water velocity as a control of aquatic snails in concrete canal systems for irrigation

The survival of Bulinus truncatus buried in mud under experimental outdoor conditions

OF THESIS Title of the Thesis : STUDIES ON Indoplanorbis exustus AND ITS ASSOCIATED SCHISTOSOMES Research pertaining to the Degree programme : DOCTOR OF PHYLOSOPHY in VETERINARY PARASITOLOGY Name of the Scholar: : Dr. Kamal Hashan Bulbul Roll No. : 2013-VDK-20 Name and Designation of the Major Adviser: : Dr. Manoranjan Das Professor Department of Parasitology College of Veterinary Science Assam Agricultural University Khanapara, Guwahati-781 022 Department where research work was conducted : Department of Parasitology College of Veterinary Science Assam Agricultural University Khanapara, Guwahati-781 022 Name of the University : Assam Agricultural University Total number of Pages : 223 Total number of Tables : 83 Total number of Figures : 99 Year of submission : July, 2016

STUDIES ON Indoplanorbis exustus AND ITS ASSOCIATED SCHISTOSOMES

A study of the distribution and population of Lymnaea gedrosiana in relation to the transmission of Ornithobilharzia turkestanicum in various habitats was carried out in Khuzestan. Populations were higher in canals and swamps than in ponds, with peaks in spring and autumn and low densities in summer and winter. The reproductive capacity of L. gedrosiana was higher in running water than in stagnant water. The peak reproduction rates occurred in spring and autumn and reproduction continued at a low level in summer but was nil in winter. Infection with O. turkestanicum was higher in large than in small snails (0.1 %, 0.5% and 1.1% in snails measuring 0.6 mm, 6–10 mm and 10–14 mm respectively). In canals and swamps transmission occurred throughout the year, with a peak in late summer in the former and early summer in the latter. In ponds, most transmission probably occurred in spring and autumn. Drains played a very minor role in transmission.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0022149X00022720

Observations on Lymnaea gedrosiana, the intermediate host of Ornithobilharzia turkestanicum in Khuzestan, Iran.

Freshwater snails act as intermediate hosts (IH) for schistosomiasis, a tropical disease affecting over 200 million people worldwide. Despite their medical importance, an extensive understanding of IH snail ecology remains absent. Especially data on the tolerance limits to different abiotic factors are fragmented and incomplete. Consequently, the construction of accurate species distribution models to identify snail habitats and guide targeted snail control efforts remains difficult. Here, we compiled a summary on the tolerance limits to abiotic factors of African IH snails of human schistosomiasis. A systematic search on Web of Science, PubMed, and Embase identified 45 relevant studies. Synthesis of these studies indicates that research efforts differ greatly between IH snail species, life stages, and abiotic factors. The importance of each abiotic factor in determining snail presence and abundance is discussed. Furthermore, attention was drawn to knowledge gaps and the lack of standardised experimental designs, which impedes comparisons between studies. This in turn prevents us from making firm conclusions and calls for best practices adopted by all malacologists. In doing so, IH snail ecological data could serve as a basis to assess schistosomiasis risk and guide snail control efforts in order to support schistosomiasis control.

J. Massoud

Papers

The ability of Bulinus truncatus, Biomphalaria alexandrina and Lymnaea gedrosiana to survive out of water in the laboratory.