Behavior of Schistosoma mansoni cercariae

Introduction
The cercariae of most trematode species exhibit very specific characteristic behavior patterns. Learning to distinguish normal from abnormal cercarial behavior is very important, since abnormal cercarial behavior likely indicates problem areas that might adversely affect the outcome of experiments.

Equipment

• Dissecting microscope
• 200 ml glass beaker

Materials and reagents

• Artificial pond H2O (see recipe in SRC SOPs)

Procedure
Indications of normal behavior

• S. mansoni cercariae typically will swim to the surface of the water, rest momentarily and sink down partially in the water column before swimming again. Some may also sink to the bottom of the container and lie quiescent before they resume swimming. The body of the cercaria is the trailing part of the swimming organism, led vertically by the vigorous movement of the tail.

Indications of abnormal behavior

• Cercariae that swim continuously without stopping. In the most extreme situation, this continual movement is quickly followed by their sinking to the bottom of the container. High chlorine levels are one major contributor to this behavior.
• Cercariae that lie on the bottom of the container and cannot be stimulated to move by quickly changing the light. Soluble products released by rotifers (order Bdelloidea) are frequently responsible for this behavior. This behavior may also indicate poor water quality.

Comments
Recognizing the normal and abnormal behavior of free-swimming cercariae can give the investigator valuable insight into an underappreciated aspect of the organism that may greatly impact the outcome of their experiments. Cercariae are extremely sensitive to innumerable physical and chemical agents. Among the more common contaminants in laboratories are high chlorine levels and byproducts of commensals such as rotifers. The resulting altered behavior of the cercariae limits and/or may completely inhibit their skin penetration capability.

References
1. Haas, W., Haberl, B., Schmalfuss, G., and Khayyal, M.T. 1994. Schistosoma haematobium cercarial host-finding and host-recognition differs from that of S. mansoni. Journal of Parasitology 80: 345-353.
2. Krakower, C.A. 1940. Some observations of the effects of physical and chemical agents on the cercariae of Schistosoma mansoni. The Puerto Rico Journal of Public health and Tropical Medicine 16: 26-44.
3. Lewis, F.A., Stirewalt, M.A., Souza, C.P., and Gazzinelli, G. 1986. Large-scale laboratory maintenance of Schistosoma mansoni, with observations on three schistosome/snail host combinations. Journal of Parasitology 72: 813-829.
4. Sirewalt, M. and Lewis, F.A. 1981. Schistosoma mansoni: effect of rotifers on cercarial output, motility and infectivity. International Journal for Parasitology 11: 301-308.
5. Tucker, M. S., Karunaratne, L. B., Lewis, F. A., Frietas, T. C., and Liang, Y-S. 2013. Schistosomiasis, in Current Protocols in Immunology 19.1.1-19.1.57, John Wiley and Sons, Inc., (R. Coico, Ed). Published online November 2013 in Wiley Online Library (wileyonlinelibrary.com). doi: 10.1002/0471142735.im1901s103.

For further technical information, contact André Miller at amiller@afbr-bri.com