Advances in PARASITOLOGY VOLUME 42 Editorial Board C. Bryant Division of Biochemistry and Molecular Biology, The Australian National University, Canberra, ACT 0200, Australia M. Coluzzi Director, Istituto di Parassitologia, Universita Degli Studi di Roma ‘La Sapienza’, P. le A. Moro 5 , 00185 Roma, Italy C. Combes Laboratoire de Biologie Animale, UniversitC de Perpignan, Centre de Biologie et d’Ecologie Tropicale et Mediterraneenne, Avenue de Villeneuve, 66860 Perpignan Cedex, France S.L. James Chief, Parasitology and Tropical Diseases Branch, Division of Microbiology and Infectious Diseases, National Institute for Allergy and Infectious Diseases, Bethesda, MD 20892-7630, USA W.H.R. Lumsden 16A Merchiston Crescent, Edinburgh EHlO 5AX, UK Lord Soulsby of Swaffham Prior Department of Clinical Veterinary Medicine, University of Cambridge, Madingley Road, Cambridge CB3 OES, UK K. Tanabe Laboratory of Biology, Osaka Institute of Technology, 5-16-1 Ohmiya, Asahi-Ku, Osaka 535, Japan P. Wenk Falkenweg 69, D-72076 Tubingen, Germany Advances in PARASITOLOGY Edited by J.R. BAKER Royal Society of Tropical Medicine and Hygiene, London, England R. MULLER International Institute of Parasitology, S t Albans, England and D. ROLLINSON The Natural History Museum, London, England VOLUME 42 ACADEMIC PRESS San Diego London Boston New York Sydney Tokyo Toronto This book is printed on acid-free paper Copyright 0 1999, by ACADEMIC PRESS All Rights Reserved No part of this publication may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopy, recording, or any information storage and retrieval system, without permission in writing from the publisher ISBN 0-12-031742-7 ACADEMIC PRESS 2 6 2 8 Oval Road LONDON NW17DX http:llwww.hbuk.co.uklapl ACADEMIC PRESS 525 B Street, Suite 1900, San Diego, California 921014495, USA http:llwww.apnet.com A catalogue record for this book is available from the British Library Typeset by J&L Composition Ltd, Filey, North Yorkshire Printed in Great Britain by MPG Books Ltd, Bodmin, Cornwall 99 00 01 02 03 04 MP 9 8 7 6 5 4 3 2 1 T. AGATSUMA, Department of Bioresource Chemistry, Obihiro University of Agriculture and Veterinary Medicine, Inada, Obihiro City, Hokkaido 080, Japan J.B. ALARCON,Molecular Parasitology Unit, Australian Centre for International and Tropical Health and Nutrition, Queensland Institute of Medical Research, The Bancroft Centre, PO RBH, Herston, Queensland 4029, Australia M. ALBONICO, Scientific Committee, Ivo de Carneri Foundation, Torino, Italy J. ANDREASSEN, Department of Population Biology, Universitetsparken 15, DK-2 100, Copenhagen, Denmark E.M. BENNET-JENKINS, Centre for the Public Awareness of Science, Faculty of Science, Australian National University, Canberra, ACT 0200, Australia D. BLAIR,Department of Zoology and Tropical Ecology, James Cook University, Townsville, Queensland 48 11, Australia C. BRYANT, Centre for the Public Awareness of Science, Faculty of Science, Australian National University, Canberra, ACT 0200, Australia E.P. CAMARGO, Departmento de Parasitologia, Instituto de Cihcias Biomkdicas, Universidade de SLo Paulo, Av. Lineu Prestes 1374, Cidade Universitaria, 05508-900, SLo Paulo, SP, Brazil D.W.T. CROMPTON, WHO Collaborating Centre for Soil-transmitted Helminthiases, Institute of Biomedical and Life Sciences, University of Glasgow, Glasgow G12 8QQ, U