Overview of Medical Entomology Lecture PDF

Overview of Medical Entomology Topic 1/Lecture 1 Date 28/01/25  Archaea Bacteri Eukarya a Archaeabacteri Eubacteria Animalia Plantae Fungi...

Overview of Medical Entomology Topic 1/Lecture 1 Date 28/01/25  Archaea Bacteri Eukarya a Archaeabacteri Eubacteria Animalia Plantae Fungi Protista a Porifer Cnidaria Plathyhelminth Nematod Annelid Mollusc Echinodermat Chordat Arthropoda a e a a a a a  Objectives Students should be able to:  Define the term “medical entomology”.  List common characteristics unique to arthropods.  List the subphyla within the phylum Arthropoda.  Give examples of arthropods of medical importance.  Describe the transmission of arthropod borne disease agents.  Medical Entomology – Definition of Terms Entomology: It is the scientific study of insects. Arthropods: They are invertebrate animals with jointed-legs. Fig 1: Examples of arthropods Medical Entomology: The study of arthropods of medical importance.  General Characteristics of Arthropods They have jointed legs referred to as appendages. Body covered with exoskeleton which is made up of a tough and rigid substance known as chitin. Growth is by molting. Bilaterally symmetrical body sub-divided into segments. Body cavity between the alimentary canal and the body wall. Open circulatory system that works by diffusion unlike the arteries and veins in higher animals like humans which are the closed type. Have ventral ladder type of nervous system.  Classification of phylum Arthropoda - Subphylum Chelicerata Chelicerates are largely terrestrial arthropods except the sea spider and horseshoe crabs. They lack antennae. They possess a set of chelicerae (clawed appendages) which are used to grab and shred food. There are three classes: ClassArachnida Class Pycnogonida Class Meristomata Classification of phylum Arthropoda - Subphylum Chelicerata The Class Arachnida Approximately 65,000 described species. Terrestrial chelicerates e.g. spider, scorpion, mites. Absence of antennae and wings. They are characterized by having two body regions, a cephalothorax and an abdomen. They also have 6 pairs of appendages: 4 pairs of legs and 2 pairs of mouthpart appendages, the first are called chelicerae. The second pair of mouthpart appendages are called pedipalps. Classification of phylum Arthropoda - Subphylum Chelicerata cont’d Class Meristomata Marine aquatic form Include extinct sea horse and extant horse shoe crabs Prosoma bears ten eyes with six pairs of appendages One pair forms the chelicera. Five form the walking legs. Classification of phylum Arthropoda - Subphylum Chelicerata cont’d Class Pycnogonida There are more than 1,300 species that belong to this class. Pycnogonids are considered as sea spiders. They are marine arthropods. Long legs with small body. Body divided into two: cephalothorax and abdomen. Abdomen bears no appendages. Four pairs of walking legs. Some may have additional appendages. A pair of chelicerae use to grasp prey Appendage for reproductive and sensory functions.  Classification of phylum Arthropoda - Subphylum Myriapoda Myriapods, e.g. centipedes and millipede, are land-dwelling arthropods. This group contains over 13,000 species. They have elongated worm-liked bodies. They have a single pair of antennae. They have multiple jointed legs between 10 to 200 pairs of legs. There are four classes: Class Chilopoda Class Diplopoda Class Pauropoda Class Symphyla Classification of phylum Arthropoda - Subphylum Myriapoda cont’d Class Chilopoda Chilopods includes the centipedes. They are dorso-ventrally flattened. Their body consists of a head and trunk. The head bears a pair of antennae and three pairs of ventral mouth parts (mandibles, first maxillae, and second maxillae) There are two pairs of simple eyes. The trunk appendages of the first pair are developed as strong, conspicuous, stinging fangs, used to poison the prey and for defense. Each segment of the trunk bears a single pair of legs. Classification of phylum Arthropoda - Subphylum Myriapoda cont’d Class Diplopoda Diplopoda includes the millipedes. These are cylindrical animals with a head and trunk. The head appendages include antennae, mandibles, one pair of maxillae. The trunk has 25-100 or more segments with each segment bearing two pair of appendages. A fusion occurs between two segments all along the body except on the first trunk segment. Simple eyes if present, although many have no eyes  Classification of phylum Arthropoda - Subphylum Myriapoda cont’d Class Pauropoda Terrestrial and live in soil. Body soft and cylindrical. First instar has only three pairs of legs, with number of legs increase in each molt. Eyes absent. Antennae are branched.  Classification of phylum Arthropoda - Subphylum Myriapoda cont’d Class Symphyla (garden centipedes) Symphylans are terrestrial soil dwelling arthropods. They are small, blind, fast-running myriapods which can be very abundant in soil and forest litter. Translucent, lack body pigment and are 2–9 mm long, delicate, white, and soft- bodied. Body divided into head and trunk. Juveniles have six pairs of legs with additional pair added at each molt. Eyes absent. Antennae is long and segmented.  Classification of phylum Arthropoda - Subphylum Crustacea There exist about 67,000 species of crustaceans. They are aquatic organisms with the majority found in the oceans. The crustacean body is clearly divided into a head, an abdomen, and a thorax. Usually, the head is fused with the thorax to form cephalothorax. The dorsal side of the cephalothorax region is covered by a carapace (a shield- like plate). This feature is shared with chelicerates The head region bears two pairs of antennae and three pairs of feeding appendages: a pair of mandibles and two pairs of maxillae. The crustacean head also contains two compound eyes. The thorax contains the walking legs and feeding legs (maxillipeds). The front pairs of appendages are often modified into claw-bearing appendages. The abdomen contains the swimming legs. These appendages produce water currents that pass over the gills for respiration. Female crustaceans typically use swimmerets to hold onto eggs for brooding, or keeping the eggs with them until they are ready to hatch. The abdomen also contains the tail appendages, uropod and telson.  Classification of phylum Arthropoda - Subphylum Crustacea cont’d There are six classes Class Branchiopoda, e.g. brine shrimp. Class Remipedia e.g. bind crustacean. Class Chephlocandua e.g. horse shoe. Class Maxillopoda e.g. Barnacles Class Ostraloda e.g. seed shrimps Class Malacostraca e.g. crabs, lobsters, shrimps  Classification of phylum Arthropoda - Subphylum Crustacea cont’d Class Branchiopoda Mostly freshwater. Leaf-like appendages for respiration, f ilter feeding and locomotion. There are more than 2,000 described species. Includes three orders: Anostraca: No carapace e.g. fairy and brine shrimp. Notostraca: Carapace forms a large dorsal shield e.g. Tadpole shrimp. Diplostraca: Carapace covers the body below the head e.g. Daphnia.  Classification of phylum Arthropoda - Subphylum Crustacea Class Remipedia There are only 10 known living species. All found in caves connected to the sea. Primitive body plan i.e. an elongated body divided into head and trunk. M o r e t h a n 30 se gm e n t s, a n d e a c h h a s biramous legs. Antennules are also biramous. Remipedes do not have a carapace. Swimming appendages lateral on the body segments.  Classification of phylum Arthropoda - Subphylum Crustacea cont’d Class Chephlocaridia Known as horse shoe shrimps. Only 12 species known. Elongated body with large head. Eyes, carapace, abdominal appendages absent. Thorax made up of 10 segments.  Classification of phylum Arthropoda - Subphylum Crustacea Class Maxillopoda Maxillopoda is a large class of mostly small crustaceans (typically 0.5–2 mm) with over 14,000 described species. A typical maxillopod has a head made up of f iv e segments: a thorax consisting of six segments and an abdomen with four segments. There are no appendages on the abdomen. Example are Copepods and barnacles.  Classification of phylum Arthropoda - Subphylum Crustacea Class Ostracoda Referred to us seed shrimps. Live in various niches; ocean platform, sea f loor, fresh water ponds, humid forest soils. About 33,000 species have been identified. Ostracods have a modif ie d bivalved carapace that totally encloses the body in a clam-like fashion. They have signif ic antly reduced bodies with two pairs o f ante nnae , two pairs o f mo uthpar t appendages, three pairs of leg-like thoracic appendages, and a pair of furcal claws. Both the f irst and second antennae (antennules, antennae) are well developed and are the most conspicuous appendages, protruding beyond the carapace. Most ostracods are very small. Classification of phylum Arthropoda - Subphylum Crustacea Class Malacostraca Most Malacostraca have three body regions: A head of five segments fused to a thorax of eight segments An abdomen of six segments.  Classification of phylum Arthropoda - Subphylum Hexapoda Hexapods are characterized by the presence of a head, thorax, and abdomen and a single pair of antennae. The thorax bears the wings as well as six legs in three pairs. Examples are ants, cockroaches, butterflies, and flies— Two classes Class Insecta (Winged insects) Class Entognatha (wingless insects)  Arthropods of Medical Importance Arthropods of medical importance are those species of arthropods that directly or indirectly affect human health. Class: Maxillopoda Copepods  Reduviid bug Rat flea Sand flea Sandflies Cyclops Trombiculid mites Itch mite Soft ticks  Transmission of arthropod borne disease agents Mechanical disease transmission: Disease agents are carried from one host to another by arthropods through the body parts (example wings, hairs, feces, vomitus, etc.). In this type of disease transmission no change takes place in the number, form or developmental stages of the organism, but simply deposited in the body, food or drink of the host. There is no multiplication or development of the pathogen within the vector's body. The house f ly, Musca domestica can mechanically transmit vibrio cholerae, the disease agent for cholera. Biological disease transmission: The disease agent will exhibit changes in form and or number of developmental stages in the arthropod before entry to the host. Propagative biological transmission: The disease-agent reproduces in the arthropod but undergoes no further development; examples are the plague bacillus in the f lea and the yellow fever virus in the mosquito. Cyco-developmental: Only the developmental stage (form) of the disease agent is changed (small to big, immature to matured stage, etc.), while the number of the pathogenic organism remains constant. Example filarial worms that cause filariasis. The worm must spend a portion of their life cycle in their mosquito vectors although they reproduce elsewhere. Cyclo-propagative: This type of disease transmission is a combination of both propagative and cyclo-developmental; whereby the disease pathogen undertakes a change both in number and developmental form (stage). Example, Plasmodium spp. transmitted by mosquitoes which cause malaria. Transovarial transmission: The transmission of an infectious agent from parent to offspring via their eggs which subsequently results in infectious adult arthropods, Rickettsia spp. Transmitted by lice that cause typhus.  Practice questions Define the term ‘medical entomology’. What are arthropods? State five features unique to arthropods. List the subphyla of phylum Arthropoda? How will you distinguish organisms belonging to each of the subphylum? Give three examples of organisms in each of the subphylum. Give one example of organism in each of the following classes. (refer to all the classes the lecture covered). List the classes of arthropods that are of medical importance. Outline three distinguish features unique to each of the class? With given examples, explain the various transmission route of arthropod borne disease. Give ten examples of arthropods and two diseases they transmit. State three importance for studying medical entomology. END OF LECTURE