Viruses and the Environment To Audrey, Wendy and Elaine Viruses and the Environment J.1. Cooper o. F. MacCallum Natural Environment Research Council, Institute ofVirology Oxford, UK SPRINGER-SCIENCE+BUSINESS MEDIA, B.V. © 19841.1. Cooper and F.O. MacCallum Originally published by Chapman and Hall in 1984 ISBN 978-94-015-7703-8 ISBN 978-94-015-7701-4 (eBook) DOI 10.1007/978-94-015-7701-4 This title is available in both hardbound and paperback editions. The paperback edition is sold subject to the condition that it shall not, by way of trade or otherwise, be lent, re-sold, hired out, or otherwise circulated without the publisher' s prior consent in any form of binding or cover other than that in which it is published and without a similar condition including this condition being imposed on the subsequent purchaser. All rights reserved. No part ofthis book may be reprinted, or reproduced or utilized in any form or by any electronic, mechanical or other means, now known or hereafter invented, including photocopying and recording, or in any information storage and retrieval system, without permission in writing from the Publisher. British Library Cataloguing in Publication Data Cooper, I.!. Viruses and the environment.-(Science paperback) 1. Viruses 2. Environmental health I. Tide II. MacCallum F.O. 576' .64 QR360 ISBN 978-94-015-7703-8 oe Library Congress Cataloging in Publication Data Cooper, I. I. Viruses and the environment. (Science paperbacks; 192) Bibliography: p. Includes index. 1. Viruses. I. MacCallum, F. O. II. Tide. III. Series. [DNLM: 1. Viruses. 2. Virus diseases - Transmission. WC 500 C777v] QR360.C65 1984 576' .64 84-14302 ISBN 978-94-015-7703-8 Contents Acknowledgements ix 1 The nature of vimses 1 Introduction 1 Virus characteristics 2 Agents that were confused with viruses and how they differ 6 Virus names 7 Virus classification 8 Some approved virus taxa 10 Poxviridae 10 Herpesviridae 10 Iridoviridae 10 Parvoviridae 11 Papovaviridae 11 Geminiviruses 11 Reoviridae 11 Togaviridae 12 Orthomyxoviridae 13 Paramyxoviridae 13 Rhabdoviridae 14 Bunyaviridae 14 Retroviridae 1S Picornaviridae IS Caliciviridae 16 Cucumovirusus 16 Luteoviruses 16 VI V iruses and the environment Closteroviruses 17 Tobamoviruses 17 Potyviruses 17 Potexviruses 18 Ungrouped viruses 18 Polymorphism, a consequence of multiple infection 18 Quasi-genetic interactions resulting from heterozygosity 20 Appendix - Virus families and groups recognized by International Committee on Taxonomy ofViruses 24 2 Exposure to viruses and some consequences 27 Inoculation 27 Infection 28 Invasion 29 Responses to the challenge 32 Virus Transmission 34 Vertical transmission 34 Vertical transmission in vertebrates 34 Vertical transmission in seed plants 38 Vertical transmission in lower plants 41 Contact spread in plants 43 Virus transmission by fungi 45 Contact spread of viruses in vertebrates 46 Viruses in food 47 3 Viruses associated with invertebrates 50 Introduction 50 Invertebrates as virus vectors 50 Nematodes as virus vectors 52 Insects as virus vectors 56 Homoptera 56 Feeding habits 59 Virus retention and relationships with vectors 60 Heteroptera 65 Thysanoptera 66 Coleoptera 66 Diptera 67 Mechanical virus-vector association 67 Circulative-propagative association 68 Acarina as virus vectors 69 Contents Vll As vectors for plant pathogenic viruses 69 As vectors of viruses pathogenic for vertebrates 70 Vertical transmission of viruses in insects and ticks 72 The range of insect-pathogenic viruses 73 Consequences of virus introduction into invertebrate populations 78 Reactions to infection 80 Perennation of inocula 81 Viruses in soil 83 Occurrence of natural antibodies to invertebrate viruses in wild and domesticated animals 86 Viruses infecting other invertebrates 87 4 Viruses and the terrestrial environment 89 The range of viruses in terrestrial vertebrates 89 The range of viruses in terrestrial plants 90 Factors affecting the occurrence of viruses 90 Geographical distribution 90 Rainfall 94 Temperature 95 Natural diversity and the biological components 97 The concept of host range 97 Factors facilitating acquisition of novel hosts 100 Yellow fever 100 Kyasanur forest disease 104 The broadcasting of viruses 109 In the air 109 On the wind 109 Viruses broadcast because of cornmerce or science 111 Epidemics, prospect and retrospect 114 5 Viruses in aquatic environments 117 Introduction 117 Indigenous sources of viruses 118 Some extraneous sources of virus contamination 119 The fate of virus-contaminated sewage 121 Agricultural use of waste water 123 Viruses in drinking water 124 The fate of sewage sludge 125 The contamination of seawater 126 Vlll V iruses and the environment 6 Strategies of virus maintenance in communities 128 Introduction 128 Agricultural plant populations 131 Naturally regenerating populations 133 Vertebrate populations 134 Application of predator-prey models to virus-host dynamics 135 Regulation of population growth by viruses 138 The influence of immunities on virus maintenance in populations 141 Some problems in modelling multicellular virus-host systems 144 Unicellular populations in virus dynamics 145 The optimum maintenance strategy: speculation about the cost and benefits of co-evolution 150 Conclusion 155 References 158 Author Index 171 Sub;ect Index 176 Acknowledgements Grateful acknowledgement for suggestions and comments is due to Drs R.M. Anderson, M.L. Edwards, K.A. Harrap, N. Moore and T.W. Tinsley, and to Miss S. Mackenzie and P.R. Massaiski for constructive criticism of certain sections of the text. We are indebted to Mrs Joyce Bald, Miss Marlina Rowland and particularly Miss Gail Davies for cheerfully typing the text. We are grateful to the authors and publishers who gave permission to reproduce illustrations and regret that not all such material has, in the event, been included. Chapter 1 The nature ofviruses INTRODUCTION Viruses are ubiquitous yet when plants, animals and other biota are in their natural environments, it is commonplace for virus replication to occur in hosts that show no detectable abnormality. In many instances, these inapparent (sometimes called latent or silent) infections are potentially hazardous for Man, his domestic animals or his crops. From time to time, drastic environmental changes occur and whether these are attributable to natural phenomena or result from human interference (agriculture, forestry, urbanization, war) one consequence is liable to be a catastrophic increase in disease incidence (epidemics). Analyses of epidemics have furthered understanding of the complex interplay of factors that modify host susceptibility/sensitivity on the one hand, while influencing the abundance, virulence and invasiveness of the viruses on the other. Often this experience has also given insight into the private lives of virus populations that wax and wane in response to the constant fluctuations in their micro-environments - out of sight and usually out of mind. Commonly, the unmanaged components of the environment are the sources of contagion - wild plants, including weeds in relation to agriculturallhorticultural crops, migratory birds or commensal rodents in human infections. Invertebrates, usually arthropods, are the omnipresent go-betweens. However, virus transmission may be independently achieved by contact or when the virus infects reproductive organs, e.g. plant seed and pollen, fungal spores, animal spermatazoa and ova. Alternatively, or additionally, the genetic constituents (genomes) of viruses may become intimately associated and replicate in harmony with the genomes of their hosts. There is a