1. Parasitology Unit, Department of Public Health,
2. Department of Biological Sciences, University of Notre Dame, Notre Dame, IN 46556, USA.
3. Department of Ecology and Evolutionary Biology, Yale University, New Haven, CT 06520, USA.
4. Department of Genetics and Molecular Biology, University of Rome “La Sapienza,” P.le Aldo Moro 5, 00185 Rome, Italy.