University of KhartoumFaculty of Medical Laboratory Sciences

Department of Parasitology & Medical Entomology(4th level-Medical Entomology Course)

Overview of Medical Entomology Course

Arwa Elaagip

Lecturer, Medical Entomologist

Aims, Objectives and outcomes

• This course will provide the fundamental information necessary for understanding the role of arthropod vectors in the transmission of different pathogens to human and livestock.

• The course further enhances the knowledge of their breeding biology and control measure.

Aims, Objectives and outcomes

• Following a general review of the morphology, life cycle and classification of arthropods, individual groups of medical importance are considered in detail in regard to the recognition of important species, the epidemiology and pathogenesis of associated diseases, and the principles and methods of vector control.

Medical Entomology Course Contents

• Introduction to Medical Entomology.

• General classification of Arthropods.

• The main taxonomic frame of classification.

• Morphological characteristics of arthropods.

Medical Entomology Course Contents

• Anatomy & physiology of insects:

The digestive system.

The reproductive system.

The respiratory system.

The nervous system.

The circulatory system.

Medical Entomology Course Contents

• Vectors of diseases: Mosquitoes. Sand flies. Tsetse flies. House flies and Blow flies. Black Flies. Horse Flies. Lice. Fleas. Bugs. Cockroaches. Ticks. Mites.

Introduction to Medical Entomology

Arthropods: An overview

• Arthropods display an amazing diversity and abundance.

• They make up more than 85% of all known animal species.

• They are highly successful group of animals in diversity of structure and function.

Arthropods: An overview

Arthropods: Morphology

• Bilaterally symmetrical.

• Segmented body: that allows movement.

• Paired, jointed appendages: that allows extensive specialization.

• Exoskeleton or cuticle or tegument: hard protective covering.

Classification of Arthropods

The main taxonomic frame of classification

KingdomPhylumSubphylum

ClassSubclass

OrderSuborderSuperfamily

FamilySubfamily

TribeGenus

SubgenusSpecies

Classification of Phylum Arthropoda

• Subphylum: Chelicerata

• Subphylum: Myriapoda

• Subphylum: Crustacea

• Subphylum: Hexapoda

Subphylum: Chelicerata

Chelicerata

• Arachnids include spiders, scorpions, ticks and mites.

• They all have:

• 2 body segments - cephalothorax and abdomen

• 8 legs

• no antennae

Spider

Solphugidae

Scorpion

False Scorpion

Ticks

Mites

Subphylum: Myriapoda

Myriapoda

• Chilopods: which include centipedes, all have:

• many body segments

• 1 pair legs /body segment

• 1 pair antennae

• poison jaws

Ce

nti

pe

de

s

Myriapoda

• Diplopods: which include millipedes, all possess:

• Many body segments

• 2 pair legs /body segment

• 1 pair antennae

Millipedes

Subphylum: Crustacea

Crustacea

• Crustaceans: include crabs, prawns, barnacles etc.

• Their features are:

• Varied number of body segments - usually there is a head, thorax and abdomen but there is much fusion, reduction and modification of segments

• Varied number of legs

• 2 pair antennae

Bro

od

ch

amb

er

Daphnia

Subphylum: Hexapoda

Hexapoda

• Insects such as beetles, wasps and cockroaches all have:

• 3 body segments

• 6 legs

• 1 pair antennae

Arthropods: Medical importance

• Arthropods may affect human health directly or indirectly.

• Only a small percentage are medically important.

• Most arthropods are benign as far as their effects on humans are concerned and are extremely important components in ecological communities.

Arthropods: Direct effects

• There are six major categories of direct

effects from arthropods:

1. Annoyance (and blood loss)

2. Dermatitis

Scabies mite

Source :A Colour Atlas of Clinical Parasitology. Tomio Yamaguchi.Translation : Lesmana Padmasutra, dkk.

Scabies Mites

Predilection sites of Scabies in manSource : Basic Clinical Parasitology. 1994. Neva F.A. & Brown H.W.

3. Entomophobia

4. Envenomization

5. Allergic reactions

6. Myiasis

Arthropods: Indirect effects

• Disease transmission.

• More important than any other effect produced by medical and veterinary pests.

Entomology

Entomology: Definition

• Entomology: Branch of zoology dealing with the scientific study of insects, including their taxonomy, morphology, physiology, and ecology.

Entomology: Introduction

• Insects are comprise about 1,5 million known species, representing about three fourths of all the classified animal species.

• Insects are studied because of their importance as pollinators for fruit crops; as carriers of bacterial, viral, and fungal diseases; as parasites of humans or livestock; as destroyers of economically important plants; or as predators of other destructive insects.

Insects: Introduction

• Their abundance, short life cycle, reproductive potential and small size allow scientific experiments to be set up, monitored and duplicated with relative ease in almost any location.

• Much of the basic understanding of genetics, population ecology, and evolution has resulted from experimentation with insects.

Insects: Future Food

Insects: Culture

Insects: Styles & Fashion

Insects Morphology & Life Cycle

Insects: Characteristics

• THREE distinct body regions:

• Head (feeding, sensory, CNS)

• Thorax (locomotion, respiration)

• Abdomen (feeding, reproduction)

Insects: Characteristics

Metamorphosis

• Metamorphosis: changes in form from the first stage (egg) in the life cycle of an arthropod to the adult form.

• Can be:

Ametabolous

Holometabolous (complete metamorphosis).

Hemimetabolous (incomplete metamorphosis).

Ametabolous Development

YoungEgg Adult

Holometabolous

• Holometabolous: (complete metamorphosis) arthropod development from egg to adult in which the body form changes completely in appearance.

• Eggs - Larva - Pupa - Adults

Hemimetabolous

• Hemimetabolous (incomplete metamorphosis) describes the development from egg to adult which is gradual, passing through one or more nymphal stages.

• Eggs - Nymphs- Adults

Medical Entomology

Medical Entomology: Definition

• Medical Entomology: The branch of science that deals with insects that cause disease or that serve as vectors of organisms that cause disease in humans.

Concepts in Vector-Borne Disease

Modes of transmission

Two modes of transmission

• Mechanical

• Biological

Biological Transmission

• The transmission of disease organisms with biological involvement between the vector and parasite.

• Example: Plasmodium inside Anopheles

Mechanical Transmission

• The transmission where there is no multiplication or cyclic development of the etiological agent (parasite or pathogen), it being merely passively carried by the vector.

• Example: housefly – trachoma virus and dysenteries by their feet, vomit or faeces.

Biological Vector

• An arthropod vector in whose body the infecting organism develops or multiplies before becoming infective to the recipient individual.

Mechanical Vector

• An arthropod vector which transmit an infective organism from one host to another but which is not essential to the life cycle of the parasite.

Modes of Biological Transmission

1. Propagative mode

2. Cyclico propagative

3. Cyclico developmental

4. Transovarian mode

Modes of Biological Transmission

Propagative transmission

• Transmission is preceded by multiplication

of disease agents inside the body of vector

• Example: Multiplication of Yersinia pestis

inside the body of fleas.

Modes of Biological Transmission

Cyclico propagative

• Transmission is preceded by growth and

multiplication of disease agents inside the

body of insect vector

• Example : Plasmodium inside Anopheles

Modes of Biological Transmission

Cyclico developmental

• Transmission is preceded by development of parasites without multiplication

• Example: Filarial worm inside the body of Culex mosquito, where microfilaria worm develop into (L-1) larva, and finally into (L-2 or L-3) larva

Modes of Biological Transmission

Transovarian

• Transmission through the next generation

• Example : Dengue virus inside the body ofAedes mosquitoes

Types of Hosts

• Dead end Host (A host from which infectious agents are not transmitted to other susceptible hosts).

• Definitive Host (The organism in which a parasite passes its adult and sexual existence).

• Reservoir Host (A host that serves as a source of infection and potential reinfection of humans and as a means of sustaining a parasite when it is not infecting humans).

• Intermediate Host (The organism in which a parasite passes its larval or nonsexual existence).

Types of Vectors

• Primary vector

• Secondary vector

Vector Biting Activity

• Nocturnal – night feeder

• Diurnal – day feeder

• Crepuscular

Host Specificity (Blood meal Source)

• Anthropophilic

• Ornithophilic

• Zoophilic

Vector Feeding Location

• Exophagic – feed outdoor

• Endophagic – feed indoor

• Exophilic – rest outdoor after feeding

• Endophilic – rest indoor after feeding

Incubation Periods

• Extrinsic incubation period - in arthropod vector

• Intrinsic incubation period - in vertebrate host

THANKS