Cheyenne Conrad

Schistomsoma Echinostoma

4 different small molecules were identified as the exclusive stimuli attracting miracidia

Only 2 studies controlled pH

Miracidia were exposed to artificially high concentrations of ‘attractants’ (Snail conditioned water)

Some miracidial responses to snail attractants could have been induced by toxic effects, rather than being examples of seeking behavior

This study addressed two main questions:

What mechanism of chemo-orientation do miracidia and cercariae use to respond to snail cues?

What kind of molecules are they responding to?

The Choice-chambers:

Miracidia and cercariae were exposed to concentration gradients of chemical compounds

Their chemo-orientation response was observed

Results:Chemotaxis

Increase of turning

Turnback swim

Miracidia

S. mansoni No Yes Yes

S. haemotobium No Yes Yes

S. japonicum Yes No Yes

T. ocellata No Yes Yes

F. hepatica no Yes Yes

Cercariae

E. revolutum No No Yes

P. echinatum No No Yes

H. conoideum yes No No

Results:

Miracidia show 2 types of orientation mechanism

Cercariae show only 1 type of orientation mechanism

Snail host cues are macromolecules

Specificity in miracidial host-finding?

Results: S. mansoni (Egyptian strain) was

significantly more attracted to snail conditioned water of their compatible host snail species

Miracidia of two Brazilian S. mansoni strains did not show such preference

Specificity in miracidial host-finding?

Results: S. japonicum miracidia could not

distinguish between their host snail O. hupensis and B. glabrata during chemo-orientation

S. japonicum only attached to O. hupensis

Different Schistosome strains may achieve different levels of host specificity during chemo-orientation of miracidia

The macromolecule cues may be snail-strain specific

Higher levels of specificity may be attained during miracidial attachment and penetration

Employ different chemo-orientation mechanisms than miracidia

They respond to small molecules

The swimming movements of miracidia and cercariae may make chemotactic behavior difficult

Miracidia are attracted to snail macromolecules, and are able to employ 2 different types of chemo-orientation

Cercariae are attracted to small molecules, and are only capable of one type of chemo-orientation mechanism

Miracidia are the better host finders

Miracida-snail relationships are phylogenetically older

Some degree of specificity during host-finding, but specificity is also determined by attachment and penetration stages

Haas, W, B. Haberl, M. Kalbe, M. Körner. 1995. Snail-host-finding by Miracidia and Cercariae: Chemical Host Cues. Parasitology Today 11: 468-472