Microscopic evaluation of sporocyst development in live Biomphalaria glabrata

Introduction
The successive intramolluscan stages of schistosome development are called primary (mother) and secondary (daughter) sporocysts. The black mantle pigmentation in field-collected  B.glabrata makes intramolluscan stages difficult to detect using a dissecting microscope. Many laboratories, therefore, use albino B. glabrata snails for routine S. mansoni propagation. Both primary and secondary sporocysts may be detected after they develop in the snails, and well before cercariae begin to emerge from these snails.

Equipment
Dissecting microscope
Strong light source, preferably with transmitted and reflective light

Materials and reagents
Featherweight forceps
Petri dishes
Aged tap water

Procedure
Identification of primary (mother) sporocysts

• 10-14 days after miracidial exposure, remove snails from the maintenance incubator, and place them in a petri dish with a sufficient amount of water to cover the shell.
• Using transmitted light, examine the snail as it crawls around the dish. A primary sporocyst is more easily detected as an abnormal swelling in the edge of the headfoot and/or in the one of the tentacles.

Identification of secondary (daughter) sporocysts

• Approximately 3 weeks after miracidial exposure, remove snails from the maintenance incubator and place them in a petri dish with a sufficient amount of water to cover the shell.
• Secondary sporocysts can be seen in various snail tissues. With reflective light, they can be visualized most readily as gray patches in the hepatopancreas area. Some sporocysts that have not yet reached the hepatopancreas may be seen (using transmitted light)  in the mantle and appear as small vermiform, coiled organisms.

Follow-up comments/recommendations
The ability to detect the presence of developed primary and/or developing secondary sporocysts within the snail almost invariably assures one that cercariae will emerge later in the course of the infection. Consistent sporocyst detection requires time and experience (i.e., lack of  detection doesn’t necessarily mean the snail is uninfected. One must then rely on eventual emergence of cercariae). Fixation of the snails (See SOP Fixing Biomphalaria glabrata snails for dissection) makes the developing sporocysts readily apparent.

References
Newton, W.L. 1955. The establishment of a strain of Australorbis glabratus which combines albinism and high susceptibility to infection with Schistosoma mansoni Journal of Parasitology 41: 526-528.