TTeexxttbbooookk ooff MMEEDDIICCAALL PPAARRAASSIITTOOLLOOGGYY ANTONI VAN LEEUWENHOEK Born: 24.10.1632 - Died: 30.8.1723 Delft-Holland This man, born poor, with little education, a draper in his hometown of Delft had surprising visitors! They included great men of science as well as the Royalty like the Tsar Peter the Great, Frederick the Great of Prussia and King James II of England. This was due to his hobby of grinding fine lenses through which he looked at various objects and brought forth the wonder world of small things that none had seen before. He kept clear descriptions and accurate drawings of what he saw and communicated them to the Royal Society in London. A strict check convinced the Society of their authenticity. The unlettered Antoni was elected a Fellow of the Royal Society! The papers sent by him over decades can still be seen in the Philosophical Transactions of the Royal Society. The discoveries he made are legion. He described the first protozoan pathogen Giardia. He also discovered many types of bacteria, human and animal spermatozoa and eggs of various animals realizing their importance in reproduction. He could not recognize the significance of the different types of bacteria and to him, they were just ‘little animalcules’. His fault was in being much before the time, for it took two centuries more for people to accept the microbial origin of infectious diseases. But that should not deter us from acknowledging the great contributions made by Leeuwenhoek to Biology and many other branches of Science. He was truly the Founder of Microbiology. TTeexxttbbooookk ooff MMEEDDIICCAALL PPAARRAASSIITTOOLLOOGGYY SIXTH EDITION CK Jayaram Paniker MD Formerly Director and Professor of Microbiology and Principal, Medical College Calicut Dean, Faculty of Medicine Calicut University Emeritus Medical Scientist Indian Council of Medical Research JAYPEE BROTHERS MEDICAL PUBLISHERS (P) LTD New Delhi Published by Jitendar P Vij Jaypee Brothers Medical Publishers (P) Ltd EMCA House, 23/23B Ansari Road, Daryaganj New Delhi 110 002, India Phones: +91-11-23272143, +91-11-23272703, +91-11-23282021, +91-11-23245672 Fax: +91-11-23276490, +91-11-23245683 e-mail: [email protected] Visit our website: www.jaypeebrothers.com Branches • 2/B Akruti Society, Jodhpur Gam Road, Satellite Ahmedabad 380 015, Phone: +91-079-30988717, +91-079-26926233 • 202 Batavia Chambers, 8 Kumara Krupa Road, Kumara Park East Bangalore 560 001, Phones: +91-80-22285971, +91-80-22382956, +91-80-30614073 Tele Fax: +91-80-22281761 e-mail: [email protected] • 282 IIIrd Floor, Khaleel Shirazi Estate, Fountain Plaza, Pantheon Road Chennai 600 008, Phones: +91-44-28262665, +91-44-28269897 Fax: +91-44-28262331 e-mail: [email protected] • 4-2-1067/1-3, Ist Floor, Balaji Building, Ramkote, Cross Road Hyderabad 500 095, Phones: +91-40-55610020, +91-40-24758498 Fax: +91-40-24758499 e-mail: [email protected] • “KURUVI BUILDING”, 1st Floor, Plot/Door No. 41/3098-B &B1, St. Vincent Road Kochi 682 018, Ph: +91-0484-4036109 e-mail: [email protected] • 1A Indian Mirror Street, Wellington Square Kolkata 700 013, Phones: +91-33-22456075, +91-33-22451926 Fax: +91-33-22456075 e-mail: [email protected] • 106 Amit Industrial Estate, 61 Dr SS Rao Road, Near MGM Hospital, Parel Mumbai 400 012, Phones: +91-22-24124863, +91-22-24104532, +91-22-30926896 Fax: +91-22-24160828 e-mail: [email protected] • “KAMALPUSHPA”, 38 Reshimbag, Opp. Mohota Science College, Umred Road Nagpur 440 009, Phones: +91-712-3945220, +91-712-2704275 e-mail: [email protected] Textbook of Medical Parasitology © 2007, CK Jayaram Paniker All rights reserved. No part of this publication should be reproduced, stored in a retrieval system, or transmitted in any form or by any means: electronic, mechanical, photocopying, recording, or otherwise, without the prior written permission of the author and the publisher. This book has been published in good faith that the material provided by author is original. Every effort is made to ensure accuracy of material, but the publisher, printer and author will not be held responsible for any inadvertent error(s). In case of any dispute, all legal matters to be settled under Delhi jurisdiction only. First Edition: 1988 Second Edition: 1989, Reprint: 1991 Third Edition: 1993, Fourth Edition: 1997, Reprint: 1999 Fifth Edition: 2002, Reprint: 2003, 2004 Sixth Edition: 2007 ISBN 81-8061-937-0 Typeset at JPBMP typesetting unit Printed at Ajanta Offset Preface to the Sixth Edition This, the 6th edition ot the Textbook of Medical Parasitology comes after 18 years of its birth, which is a milestone! In India, an 18 year-old can vote and choose who is to rule the land. By the same analogy, this book has come of age and can decide its own fate. Till now the Author was guided largely by the views of the students and teachers using the book. While they were generally happy with the narrative style, many had asked for improvements in pictures, both in their numbers and quality. So the emphasis this time has been here. Several pictures have been added, many in pretty colours, hoping they may attract and arrest the readers’ attention. The ultimate judges of a textbook are the students and the teachers. As in the past, we solicit their opinion and suggestions for improving the quality of the book. Shanthi, East Hill Road CK Jayaram Paniker Calicut-673006 (Kerala) Preface to the First Edition Parasitic infections continue to account for a large part of human illness. Antimicrobial drugs and vaccines that have made possible the effective control of most bacterial and viral diseases have not been as successful against parasitic infections. The numbers of persons afflicted by parasites run into many millions. Malaria still affects over 500 millions, pinworm and whipworm 500 millions each, hookworm 800 millions and roundworm a billion persons. Filariasis, leishmaniasis and schistosomiasis remain serious public health problems. Infections due to opportunist parasites are becoming increasingly evident in the affluent countries. In recent years there has been a resurgence in the study of parasitic infections. Much new knowledge has been gained making possible precise diagnosis and more effective control of parasites and the diseases they cause. This textbook attempts to present the essential information on parasites and parasitic diseases, with emphasis on pathogenesis, epidemiology, diagnosis and control. Every effort has been made to incorporate recent advances in the subject. It is hoped that medical students, teachers and physicians will find this book useful. Their comments and suggestions for improvement of the book will be most welcome. SHANTHI, East Hill Road CK Jayaram Paniker Calicut, Kerala 673 006 Contents 1. General Introduction............................................................................................... 1 2. Protozoa: General Features .................................................................................. 10 3. Amoebae.................................................................................................................... 14 4. Flagellates ................................................................................................................. 36 5. Malaria Parasites..................................................................................................... 65 6. Miscellaneous Sporozoa and Microspora ........................................................ 96 7. Ciliate Protozoa..................................................................................................... 111 8. Helminths: General Features............................................................................. 113 9. Trematodes: Flukes............................................................................................... 116 10. Cestodes: Tapeworms........................................................................................... 138 11. Nematodes: General Features............................................................................ 158 12. Trichinella Spiralis............................................................................................... 161 13. Whipworm.............................................................................................................. 165 14. Strongyloides......................................................................................................... 169 15. Hookworm.............................................................................................................. 175 16. Pinworm.................................................................................................................. 183 17. Roundworm............................................................................................................ 188 18. Filarial Worms ....................................................................................................... 195 19. Guinea Worm ........................................................................................................ 213 20. Miscellaneous Nematodes.................................................................................. 217 21. Diagnostic Methods in Parasitology............................................................... 221 Index.......................................................................................................................... 233 General Introduction 1 CHAPTER 1 General Introduction The earliest agents of human infection to have been observed were helminthic parasites. The common roundworm, often passed live and wriggling in stools, or emerging from the nostril of an infected child, would surely have caught the attention of ancient humans and could have been associated with illness. However, in some cultures the worms were considered as even useful, helping in the digestion of food. According to an old Chinese belief, a person had to have at least three worms to be in good health! Intestinal worms and their empirical remedies were apparently known from early antiquity in different parts of the world. The well-preserved body of a young man who died on the snow-clad Alps mountain some 5300 years ago was discovered in 1991. Whipworm eggs were identified in the colonic contents. A pouch tied to the body contained plant materials with anthelmintic properties. This finding takes the history of human helminthic infection back to over five millennia. In more recent times, parasites have figured in various milestones along the story of infectious disease. The first description of a human pathogenic microbe was given by the pioneer microscopist Leeuwenhoek in 1681, when he observed Giardia in his own stools and communicated to the Royal Society of London, unmistakably accurate diagrams of the protozoan parasite. In the 19th century, when the silkworm disease Pebrine caused devastating epidemics in Southern Europe, Louis Pasteur was requested to investigate it. Pasteur’s results published in 1870 served to control the disease, which was caused by a microsporidian parasite. This was the first instance of a scientific study on a protozoal disease, leading to its control and prevention. This also was Pasteur’s first introduction to applied microbiology. With the coming of colonialism, interest in parasitic diseases suddenly soared as many of the tropical countries could be penetrated only after controlling parasitic infections like malaria, kala-azar, amoebiasis, trypanosomiasis and schistosomiasis. Their aetiological agents were identified and control measures introduced. A seminal discovery was made in 1878 by Patrick Manson about the role of mosquitoes in filariasis. This was the first evidence of vector transmission. Soon afterwards, Laveran in Algeria discovered the malarial parasite (1880) and Ronald Ross in Secunderabad, 2 Textbook of Medical Parasitology India showed its transmission by mosquitoes (1897). A large number of vector borne diseases have since been identified. This provided a new approach to disease control, by targeting the vectors. Many parasitic infections are associated with overcrowding, poor sanitation, contaminated food and water, undernutrition and other poverty-related factors. They were considered the concern of the developing countries only. While this is generally true, the rich nations are not exempt, and infact there are some parasites like the pinworm which are more prevalent in the West. A major drawback in the fight against parasitic diseases is the inability to prevent them by immunisation. No effective vaccine is currently available against any parasitic disease. However, host immunity is decisive in determining the course of many parasitic infections. Increased susceptibility to many parasitic infections is a conse- quence of immunodeficiency, as in the HIV infected. Many new parasitic infections have been identified in AIDS patients in the developed countries. Control and eradication programmes had been carried out against some important parasitic diseases, such as malaria and filariasis, with varying degrees of success. But in many cases the benefits gained could not be maintained and the situation has reverted to the original level or worse.This has been due to slackening of control measures or due to drug resistance in the parasite or its vector. By mid-twentieth century, with dramatic advances in antibiotics and chemotherapy, insecticides and antiparasitic drugs, and increased affluence and improved lifestyles, all infectious diseases seemed amenable to control. Great dreams of eradicating infectious diseases were entertained and when global eradication of the great scourge smallpox became a reality, euphoria prevailed. Then came nemesis, with microbes rebounding. Antibiotics and antipesticides lost their efficacy, faced with microbial and vector resistance. New emerging diseases became a serious threat. The HIV pandemic provided a fertile field for old and new pathogens to spread. This applies equally to parasitic infections as to bacterial, viral or mycotic infections. In this context a new enhanced interest attaches to the study of human parasites. PARASITISM Medical parasitology deals with the parasites which cause human infections and the diseases they produce. Parasites are organisms that infect other living beings. They live in or on the body of another living being, the host and obtain shelter and nourishment from it. They multiply or undergo development in the host. Parasitism arose early in the course of biological evolution. Some organisms, instead of remaining as free-living forms deriving nourishment from raw materials in the environment, learned to use the bodies of other organisms as readymade food. One manner of achieving this is by predation, where larger animals prey on smaller ones which they kill and eat. Another is saprophytism (from Sapros, Greek for decayed), in which organisms feed on the dead and decaying bodies of animals, plants and other organic matter and help to decompose them. Parasitism is a more durable and intimate association in which the parasite establishes itself in or on the living body of the General Introduction 3 host, being physically and physiologically dependent on it for at least part of its life cycle. This may or may not lead to disease in the host. Parasites which live in complete harmony with the host, without causing any damage to it are called commensals, while those which cause disease are called pathogens. This distinction is however not absolute, as many commensals can act as facultative or opportunist pathogens when the host resistance is lowered. Rarely, even free-living organisms may become pathogenic under special circumstances. The discipline of parasitology, by tradition deals only with parasites belonging to the animal kingdom. Though bacteria, fungi and viruses are also parasitic, they are excluded from the purview of ‘parasitology.’ Human parasites may be either unicellular microbes (protozoa), or larger organisms (metazoa), some of which may be many metres in size. Parasites may be classified as ectoparasites or endoparasites. Ectoparasites inhabit the body surface only, without penetrating into the tissues. Lice, ticks, mites and other haematophagous arthropods are examples of ectoparasites. They are important as vectors transmitting pathogenic microbes. The term infestation is often employed for parasitisation with ectoparasites in place of the term infection used with reference to endoparasites. Endoparasites live within the body of the host. All protozoan and helminthic parasites of humans are endoparasites. Parasites may pass their life cycles in more than one host. The host in which the adult stage lives or the sexual mode of reproduction takes place is called the definitive host. The species in which the larval stage of the parasite lives or the asexual multiplication takes place is called the intermediate host. Man is the definitive host for most human parasitic infections (e.g. filaria, roundworm, hookworm), but is the intermediate host in some instances (e.g. malaria, hydatid disease). A vertebrate host in which a parasite merely remains viable without development or multiplication is called a paratenic host. Such a host may serve to pass on the infection to another and so is sometimes called a transport host. Parasites infecting humans may be proliferous or nonproliferous. Proliferous parasites are those that proliferate in the human body so that the parasite originally introduced multiplies many fold to cause high intensity of infection. Protozoan parasites are proliferous. On the other hand, most adult helminths do not multiply in the human body. They are nonproliferous. High intensity of infection results from repeated infection as in roundworm, or from high multiplicity of initial infection as in trichinosis. A few helminths, such as Strongyloides stercoralis and Hymenolepis nana multiply in the human host. Parasitic infections which humans acquire from animals are known as zoonotic infections or zoonoses. In most of these, the parasite lives normally in cycles involving domestic or wild animals, domestic zoonoses and feral or sylvatic zoonoses respectively without affecting humans. Human infections are only accidental events and may not profit the parasite because the chain of transmission is usually broken with human infection. The vertebrate species in which the parasite passes its life cycle and which may act as the source of human infection is called the reservoir host. Intermediate hosts in which metazoan parasites undergo multiplication are called amplifier hosts.