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HE305NTH5C D5SEASES

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HE305NTH5C D5SEASESHE30

    DIRECTORATE OF LEARNING SYSTEMS

    DISTANCE EDUCATION PROGRAMME

    COMMUNICABLE DISEASES COURSE

    Unit 12

    Helminthic Diseases

    Allan and Nesta

    Ferguson Trust

Unit 5: Helminthic Diseases

    A distance learning course of the Directorate of Learning Systems (AMREF)

? 2007 African Medical Research Foundation (AMREF)

    This course is distributed under the Creative Common Attribution-Share Alike 3.0 license. Any part of this unit including the illustrations may be copied, reproduced or adapted to meet the needs of local health workers, for teaching purposes, provided proper citation is accorded AMREF. If you alter, transform, or build upon this work, you may distribute the resulting work only under the same, similar or a compatible license. AMREF would be grateful to learn how you are using this course and welcomes constructive comments and suggestions. Please address any correspondence to:

The African Medical and Research Foundation (AMREF)

    Directorate of Learning Systems

    P O Box 27691 00506, Nairobi, Kenya

    Tel: +254 (20) 6993000

    Fax: +254 (20) 609518

    Email: amreftraining@amrefhq.org

    Website: www.amref.org

Writer: Dr Peter Ngwatu

    Chief Editor: Anna Mwangi

    Cover design: Bruce Kynes

    Technical Co-ordinator: Joan Mutero

    The African Medical Research Foundation (AMREF) wishes to acknowledge the contributions of the Commonwealth of Learning (COL) and the Allan and Nesta Ferguson Trust whose financial assistance made the development of this course possible.

Contents

    INTRODUCTION ___________________________________________________ 1 SPECIFIC OBJECTIVES .................................................................................................................... 1 SECTION 1: OVERVIEW OF HELMINTHIC DISEASES _____________________ 2 SECTION 2: DICEASES CAUSED BY NEMATODES (ROUNDWORMS) _________ 4 ASCARIASIAS ............................................................................................................................. 4 Life cycle of Ascaris Lumbricoides _________________________________________________ 5 Clinical features of Ascariasis _____________________________________________________ 6 Diagnosis _____________________________________________________________________ 7 Management __________________________________________________________________ 7 Prevention and Control __________________________________________________________ 8 Life Cycle of Enterobius Vermicularis ______________________________________________ 10 Clinical Features of Enterobiasis _________________________________________________ 11 Diagnosis ____________________________________________________________________ 11 Management _________________________________________________________________ 11 Prevention and Control _________________________________________________________ 12 TRICHURIASIS ......................................................................................................................... 12 Lifecycle of Trichuris Trichiura ___________________________________________________ 12 Clinical Features of Trichuris Trichiura ____________________________________________ 13 Diagnosis ____________________________________________________________________ 13 Management _________________________________________________________________ 13 Prevention and Control _________________________________________________________ 14 HOOKWORM DISEASE .................................................................................................................. 14 Life Cycle of Hookworms________________________________________________________ 15 Clinical Features of the Hookworm ________________________________________________ 16 Diagnosis ____________________________________________________________________ 17 Management _________________________________________________________________ 18 Prevention and Control _________________________________________________________ 18 STRONGYLOIDIASIS .............................................................................................................. 19 Lifecycle of Strongyloides Stercoralis ______________________________________________ 20 Clinical Features of Strongyloidiasis ______________________________________________ 21 Diagnosis ____________________________________________________________________ 22 Treatment ____________________________________________________________________ 22 Prevention and Control _________________________________________________________ 22 TRICHINOSIS ........................................................................................................................... 22 Life Cycle of Trichinella Spiralis __________________________________________________ 23 Clinical Features of Trichinosis __________________________________________________ 23 Diagnosis ____________________________________________________________________ 24 Management _________________________________________________________________ 24 Prevention and Control _________________________________________________________ 24 CESTODE INFECTIONS ____________________________________________ 25 TAENIA SAGINATA ....................................................................................................................... 26 Life cycle of Taenia Saginata_____________________________________________________ 26 Clinical Features ______________________________________________________________ 27 Diagnosis ____________________________________________________________________ 27 Management _________________________________________________________________ 28 Prevention and Control _________________________________________________________ 28 TAENIA SOLIUM ........................................................................................................................... 29 Clinical Features ______________________________________________________________ 29 Management _________________________________________________________________ 29 Prevention and Control _________________________________________________________ 30 HYDATIDOSIS (ECHINOCOCCOSIS) OR HYDATID DISEASE ............................................................ 31 Life Cycle ____________________________________________________________________ 31

     Clinical features ______________________________________________________________ 32

    Diagnosis ____________________________________________________________________ 33 Management _________________________________________________________________ 33 Prevention and Control _________________________________________________________ 34 DIPHYLLOBOTHRIUM LATUM ...................................................................................................... 34 Life Cycle ____________________________________________________________________ 34 Clinical Features ______________________________________________________________ 34 Diagnosis ____________________________________________________________________ 35 Management _________________________________________________________________ 35 Prevention and Control _________________________________________________________ 35 HYMENOLEPSIS NANA .................................................................................................................. 35 Life Cycle ____________________________________________________________________ 36 Diagnosis ____________________________________________________________________ 36 Management _________________________________________________________________ 36 Prevention and Control _________________________________________________________ 36 TUTOR MARKED ASSIGNMENT ________________________ 错误;未定义书签。38

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INTRODUCTION

    Welcome to the twelfth unit of this course. In the previous unit, you learnt about the diseases that are caused by faecal-oral contamination, but we said we would exclude those diseases that are caused by worms. Now, this is where you will learn about helminthes, commonly referred to as worms. This unit has quite a number of similarities with the previous one as helminthic diseases also occur due to poor sanitation. As you will see later in this unit, some of the worms also infect man via the faecal-oral route.

    The simplified classification of helminthic parasites of man includes cestodes (tapeworms), trematodes (flukes) and nematodes (roundworms). The cestodes and some nematodes pass through the human intestine during their life cycle. The trematodes that are a problem in Africa are the schistosoma species which mainly affect blood vessels. As you may recall, we already covered schistosomiasis in Unit 8 on vector borne diseases. Similarly, the nematodes in which the adults develop in human tissues such as Wuchereria and Onchocerca have already been covered in that unit on vector borne diseases.

    In this unit, therefore, we will cover the helminthes that affect the intestines. As we begin the unit, we will look first at the classification of helminthes and then tackle the individual worms. For each worm, we will cover the epidemiology, life cycle, diagnosis of the helminthic diseases it causes (laboratory findings and clinical features), management and lastly, ways of prevention and control.

Specific Objectives

By the end of this unit you should be able to:

    ; List the worms of medical importance in Africa;

    ; Describe the classification and epidemiology of helminthes;

    ; Describe the life cycles of helminthes that affect humans;

    ; Diagnose helminthic diseases;

    ; Manage a patient with a helminthic disease;

    ; Plan for interventions to prevent and control helminthic infections.

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Section 1: Overview Of Helminthic Diseases

    As we saw from the introduction, the worms of medical importance in many parts of Africa can be divided into three groups: cestodes (tapeworms), trematodes (flukes) and nematodes (roundworms). However, according to their shape, worms are divided into two groups: flat or round. The flukes and the tapeworms are included in the group of the flatworms or Platyhelminthes. This is because they are usually

    flattened, bilaterally symmetrical, have no true body cavities, and are hermaphrodite. On the other hand, roundworms are zoologically distinct, more tubular and simple but the sexes are distinct. This is illustrated in Figure 1 below.

     Helminthes

    Platyhelminthes Nematodes

     (Flatworms) (Roundworms)

Cestodes Trematodes Mature in man Fail to mature

    (Tapeworms) (Flukes) in man

     Adults in intestine (Larva migrans)

    Adults in man Intestine Ascaris

     Taenia saginata Fasciolopsis Trichuris Cutaneous

     Diphyllobothrium latum Metagonimus Ancylostoma Ancylostoma

     Hymenolepis nana Heterophyes Necator Strongyloides

     Strongyloides Visceral

    Adults and larvae in man Liver Enterobius Toxocara

     Taenia solium Fasciola Trichinella

    Larvae in man Opisthorchis

     Echinococcus granulosus Adults in tissues

     Lung Wuchereria

     Paragonimus Brugia

     Blood vessels Loa

     Schistosoma species Onchocerca

     Dracunculus

    Figure 1: A simplified classification of helminthic parasites of man

    Adult tapeworms have no digestive systems. However, they absorb nutrients directly from the hosts gut contents through their surfaces. An adult tapeworm has a small head (scolex) with two or four suckers and usually a circle of hooks by which it

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    attaches to the hosts intestinal wall. It also has a body (strobila) which is generally long and tape like and consists of many units also referred to as proglottids. It is from the tape like structure of its body that the tapeworm gets its name. The larval stages occur in various organs and tissues of vertebrate intermediate hosts.

    The roundworms have a complete digestive system with a mouth and anus. Hookworms, ascaris, trichuris and strongyloides are all soil-transmitted helminthes.

    Enterobius is transmitted directly by the faecaloral route. The final host of all the

    worms is man except for the dog tapeworm for which the human is an accidental intermediate host. The eggs of all the intestinal worms are excreted in stools.

    Sanitary disposal of human faeces is the preventive measure of choice because it will control most of these worm diseases with the exception of the hydatid disease, enterobius and schistosomiasis.

     Take Note

    Intestinal worms are a problem of poor sanitation.

    

    Proper disposal of faeces is one of the most difficult preventive measures to achieve because the cooperation of every member of the community, including children is necessary. When even just one person does not dispose of stools properly, transmission will continue. Building of latrines is not helpful if they are not properly used. Health education has to be given to members of the community so that they can change their attitudes and behaviour about human waste disposal. Because of the lack of proper latrines and the attitudes of people, it will take some time before worm diseases are controlled in many parts of Africa.

    As most worm infestations are asymptomatic, or treated at health centres or dispensaries, there are few figures on their real prevalence in the community. Much of the transmission of helminthes is through children who often do not use latrines or at least, not to the same extent as their parents. Most of the helminthic diseases occur in children, except perhaps for hookworm anaemia and taeniasis which equally

    affects adults.

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    We will now look at individual worms. We shall first discuss the various roundworms and the diseases they cause and then we shall look at the flatworms and the diseases they cause.

    Section 2: Diseases Caused By Nematodes (Roundworms)

    Take a sheet of paper and make a list of the following:

    1. Name all roundworms that you know of.

    2. Name the respective diseases that they cause.

    As you read through Section 2, keep on comparing your lists to find out if they are

    correct

    To start with, let us learn about a common condition known as ascariasis which is caused by the largest intestinal roundworm.

Ascariasias

Ascariasis is an infection caused by Ascaris Lumbricoides, the largest intestinal

    roundworm, reaching up to 40cm in length. It lives in the small intestine and the female produces up to 200,000 eggs which pass with feaces daily. It is one of the commonest nematode infestations of the small intestine. It does not appear to depend so much on the climate, although it is more perennial in the damp and humid areas of the tropics. This explains why ascariasis is common in all areas of Africa. Have you ever seen an Ascaris worm? The photograph in Figure 2 below depicts an Ascaris worm that was passed by a five year old girl.

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    Figure 2: A photograph of an Ascaris worm

Life cycle of Ascaris Lumbricoides

    Infection with the Ascaris parasite results when a person swallows food containing eggs of this parasite. The eggs have to be embryonated in soil before they are infective for a period of 8-50 days. The soil must be loose and not too dry. Oxygen must be available and the temperatures over 15 ?C.

    The embryonated eggs hatch when swallowed by a human being. The eggs can also pass through the gastrointestinal tract of animals and remain infective. The usual vehicle is fruit or other food eaten raw. Unwashed hands and children picking up things from the floor or ground and putting them into the mouth are common ways of acquiring Ascaris. In communities that use human faeces as manure, the possibility of ingesting the eggs from foodstuffs grown using this manure is very high. This is especially after consumption of vegetables which are sometimes eaten raw or half cooked. Eggs can survive adverse circumstances for a long time, and embryonated eggs can be carried away from the contaminated place into houses by feet, footwear or in the dust by wind. Temperatures above 60?C are necessary to destroy the eggs.

    To reach maturity the larvae need to pass through the lungs (see figure 3). The larvae penetrate the intestinal wall and reach the liver via the portal system. From the liver they are carried through the right side of the heart into the lungs. Here they

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    penetrate into the airways and pass via the bronchiole, bronchi and trachea to the pharynx. Then they are swallowed, return to the gastrointestinal tract and settle in the jejunum where they develop into adult worms. Between 2 to 3 months elapse between entry into the body and egg production. The life span of an adult worm is about 1 to 2 years.

During the lung phase, eosinophilia develops. This eosinophilia is temporary if no

    new infestation occurs. The migration phase may be associated with fever, cough, wheezing shortness of breath and allergic dermatitis. Lung migration may also cause pneumonia.

Figure 3: Lung passage of the ascaris larvae

Clinical features of Ascariasis

    Except for the temporary symptoms during larval migration through the lungs, infection with a few ascaris is usually asymptomatic or if symptoms are present, they are not characteristic. There may be vague abdominal discomfort. Occasionally a worm may leave the body (in vomitus or stools) upsetting the patient and the family. Complications may occur in very heavy infections or due to wandering worms.

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