Medically Important Arthropods PDF
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Pradip K. Chaudhary
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This document provides an overview of medically important arthropods, including their classification, roles in disease transmission, and effects on human health. It covers topics like disease transmission, direct effects on humans (bites and stings), infestations, and economic impacts. It details several examples of medically important arthropods.
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Pradip K. Chaudhary Medically Important Arthropods Arthropods are a diverse group of invertebrates with jointed legs, a segmented body, and an exoskeleton made of chitin. Medically important arthropods are those that directly or indirectly affect human health. These organism...
Pradip K. Chaudhary Medically Important Arthropods Arthropods are a diverse group of invertebrates with jointed legs, a segmented body, and an exoskeleton made of chitin. Medically important arthropods are those that directly or indirectly affect human health. These organisms can act as vectors, transmitting diseases to humans and animals, or cause harm through their bites, stings, or other interactions. They belong to the phylum Arthropoda, which includes insects, arachnids, crustaceans, and myriapods. Arthropods are of immense concern in public health due to their role in the transmission of several parasitic, viral, and bacterial diseases. They also cause allergic reactions, infestations, and in some cases, venom-induced complications. Classification On the basis of locomotory organs, Phylum Arthropoda classified as Class 1: Crustacea Class 2: Myriapoda Five pairs of walking legs. Many pairs of walking legs. E.g Palaemon (Prawn), Cancer (crab), E.g Julus (Millipede), Scolopendra Daphnia etc (Centipede) etc. Class 3: Insecta or hexapoda Class 4: Arachnida Three pairs of walking legs (6 legs). Four pairs of walking legs. E.g Periplaneta americana (Cockroach), E.g Aranea (Spider), Palamaneus Pieris (Butterfly), Bombyx mori (Moth or (Scorpion), Ixodex (tick), Chorioptes silkworm), Apis indica (Honey bee) (Mite) etc. Musca (House fly) etc. Some examples of medically important arthropods Mangemite (Sarcoptes scabiei) Sand flies (Phlebotomus argentipes), Cockroaches (Periplaneta americana) Human louse (Pediculus humanus), Houseflies (Musca nebulo), Bed bug (Cimex), Mosquitoes (Culex, Anopheles and Aedes), Fleas (Xenopsylla cheopis) Public Health Importance of Medically Important Arthropods Disease Transmission (Vector Role): Arthropods act as vectors for diseases caused by viruses (e.g., dengue, Zika), bacteria (e.g., Lyme disease, plague), and parasites (e.g., malaria, leishmaniasis). Direct Effects on Humans: Bites and stings can cause skin irritation, allergic reactions, anaphylaxis, or venom-induced systemic effects. Examples: Bee stings, spider bites, and scorpion stings. Infestations: Infestations such as scabies (mites) and pediculosis (lice) can lead to significant discomfort, secondary infections, and societal stigma. Economic and Social Impact: Diseases transmitted by arthropods can lead to loss of productivity, increased healthcare costs, and strain on public health systems, especially in endemic regions. Role as Irritant Pests: Some arthropods, even without transmitting diseases, disrupt human activity and living conditions, such as bed bugs (Cimex lectularius). Pradip K. Chaudhary Mangemite (Sarcoptes scabiei) Systemic position Distribution: worldwide distribution Phylum: Arthopoda Habit and Habitat: the parasites bore down and live below the skin making Class: Arachnida a gap in the soft regions where they lay eggs. They are most common in Order: Acarina protected parts of the skin, e.g. between the digits and on hands and arms. Family: Sacroptidae Males are short-lived and remain on the surface of the skin. Genus: Sarcoptes Morphology: Species: scabiei Sarcoptes (mite) are microscopic and slightly round consisting of cuticle lining with numerous wavy parallel or hairs. The adult female is longer than male. The body is dorso-ventrally flattened bearing long pointed spines that are sensory in function. The anterior region consists of false head or gnathosoma which bears a pair of chelicerae and a pair of three jointed triangular pedipalpi. It has no eyes or trachea. There are four pairs of short and thick legs. Anterior two pairs of legs are stronger and project beyond the body and provided with terminal stalked suckers. Posterior two pairs of legs are shorter and attached more ventrally and carry long bristles. Mode of Infection Fertilized females are infective and take place by close personal contact Diseases Sarcoptes is an unpleasant dangerous ectoparasite which causes scabies to produce severe irritation and may lead to eczema in Human. The larval mites cause follicular papules and a distinct kind of itching. Systemic position Control Measures Phylum: Arthopoda it is controlled by the treatment with benzyl benzoate (Proscabin) or by sulphur. Class: Insecta However sulphur causes dermatitis. Order: Orthoptera Family: Blattidae Cockroaches (Periplaneta americana) Genus: Periplaneta Distribution: worldwide distribution especially tropics and subtropics region. Species: americana Habit and Habitat: generally found in dark and warm places in the kitchen and storehouses. It is nocturanal and omnivorous animal, comes out at night in search of food. It feeds on bread, rice, ghee, oil paper etc. it act as scavengers for clean our places. Morphology: The body is dorsoventrally flattened and segmented. The male is smaller than the Pradip K. Chaudhary female. The body is deep brown in color, covered by hard and chitinous exoskeleton. The body is divided into three parts- head, thorax and abdomen. The head is triangular in shape and bears a pair of long antenna and compound eyes. The mouth parts are adapted for biting and chewing. The thorax is formed by three segments- prothorax, mesothorax and metathorax. Each segment bears a pair of segmented legs. The meso and metathorax bear each pair of wings. The anterior part of wings called tegmina or elytra. The abdomen is consisted of 10 segments, end part is anus. 10th segment is a segmental anal circus while in male 9th sternum bears non-segmented anal styles. Sexes are separate. Sexes can be distinguished by anal style in 9th segment of a male. Diseases These harm human beings by chewing our clothes, books, and leather wares. Control Measures it is controlled by spraying insecticides such as DDT, Pyrethrin, Gammexane, and other pesticides. Houseflies (Musca nebulo) Systemic position Distribution: cosmopolitan distribution. Phylum: Arthopoda Habit and Habitat: Class: Insecta Active insect found around human habitations and dirty places. It flies freely from one Order: Diptera place to another and feed human debris and decaying organic matter. It is dangerous Family: Muscidae house pest as it serves as a carrier of many diseases. Genus: Musca Morphology: Species: nebulo Shape, size and coloration: oval shape, measuring about 6-8 mm in length. It has dark grey body with yellowish tinge on ventral side having four longitudinal lines on thorax and one black streak on abdomen. Body divisions: divided into three parts: head, thorax and abdomen. Head: small, semicircular and bears a pair of short flexible and highly sensitive antennae (chemoreptors), one pair of large, prominent, spherical compound eyes. Mouths parts are of the sponging type, adapted only to suck liquid food but not pierce the tissues. Thorax: indistinctly segmented and bears a pair of strong, membranous wings dorsally and three parts of jointed legs ventrally, wings are two pairs. Legs are covered with hair. Each leg consists of coxa, trochanter, femur, tibia and five jointed tarsus with paired of curved claws. Between claws have glandular pad called pulvilli that secretes sticky fluid which helps to walk and ceiling. Abdomen: made up of ten segments. In females these segments form ovipositor to help in reproduction. In the males, the last abdominal segment serves as external genitalia and the 9th segment bears a pair of claspers for copulation. The last segment bears anal cerci in both males and females. Diseases Housefly is a harmful insect as it carries the pathogen of a number of dangerous and infectious diseases of man. The houseflies carry many pathogenic micro-organisms like bacteria, protozoans and their spores. Some very dangerous and even fatal diseases, spread by houseflies are dysentery, anthrax, diarrhoea, typhoid, tuberculosis, cholera etc. Control Measures Pradip K. Chaudhary Destruction of adult flies by mechanical or chemical method (spraying pyrethrum, tugone etc). Prevention of breeding houseflies by mechanical or chemical method (sprinkling lime, formalin etc). Mosquitoes (Culex, Anopheles and Aedes) Systemic position Distribution: occurs in damp and marshy areas throughout the world but are mostly Phylum: Arthopoda abundant in tropics and subtropics. Class: Insecta Habit and Habitat: Order: Diptera Nocturnal insects, only the females suck blood of warm-blooded vertebrates for feeding Family: Culicidae and hence posseses piercing and sucking type of mouthparts. However, males posseses Genus: Culex or only sucking type of mouthparts and feed the nectar of flowers. Anopheles or Aedes Morphology: Shape, size and coloration: body is small (3-6 mm in length), soft, slender and covered with scales. Body is greyish black. Wings of Anopheles carry dark spot while Aedes has a black and white striped body. Body divisions: divided into three parts: head, thorax and abdomen. Head: small, bears a pair of compound eyes and a pair of feathery antennae. Mouth parts form a long piercing and sucking tubular proboscis. Male and females are easily differentiated by form of antennae and maxillary palps. In Anopheles, palps slightly long as proboscis but in males their ends are club shaped. In Culex, palps are much shorter than proboscis is in female but slightly longer in male. Thorax: consists of very small prothorax, large mesothorax and small metathorax. Single pair legs and wings are present. Wings are sensory in function and produces characteristics sound. Abdomen: slender and have 10 segmented, 9th segment bears genital pore. The abdomen is specialized for food digestion and egg development. Diseases Malaria: caused by species of Plasmodium carried by female Anopheles. Dengue fever: caused by virus and carried by Culex fatigans and Aedes. Elephantiasis: caused by W. bancrofti and carrid by Cules fatigans. Yellow fever: caused by virus and carried by Aedes. Elephantiasis: caused by virus and spread by Culex and Aedes. Control Measures Destruction of adult flies by mechanical or chemical method (spraying pyrethrum, tugone etc). Prevention of breeding houseflies by mechanical or chemical method (sprinkling lime, formalin etc). Destruction of larvae and pupae. Protection from mosquitos. Pradip K. Chaudhary General concept of Integrated vector management (IVM) approaches Vector and Reservoirs The living being which carries or transmits the pathogen from an infected person to a healthy person is called a Vector. For examples; sand fly is a vector for disease Kala Azar because it carries the pathogen Leishmania donovani. The site where the parasites or pathogen are mainly live is known as a reservoir. Usually vertebrates like cattles, pig, dog etc. are the hosts. Reservoir Vector It stores the pathogen or parasite inside the body. It transmits or carries parasites or pathogens. It harms the host of reservoirs. It does not harm the vector. It lives for a long time so that life cycle is completed It lives for a short time and life cycle is not competed in a vector Examples: higher animals mostly mammals such as Examples are invertebrates or lower animals such as man, dog, pig, sheep etc are the potential mostly insects-housefly, mosquitoes, sand fly, flea reservoirs. etc are vectors. Vector Control Strategy/ Methods of Control Habitat/Environmental control: removing or reducing areas where vectors easily breed can help limit population growth. E.g., stagnant water removal, destruction of old tires etc can reduce areas of excessive vector incidence. Chemical control: various insecticides, larvicides, rodenticides and repellents can be used to control vectors. E.g., larvicides can be used in mosquito breeding zones. The uses of pesticides for vector control which proven to be highly effective and used Integrated Vector Management (IVM) framework. Biological control: the use of natural vector predators such as bacterial toxins or botanical compounds can help control vector populations. Eg. Various microorganisms are used. Reducing contact: limiting exposure to insects or animals that are known disease vectors can reduce infection risks significantly. E.g. bed nets, window screens on homes etc used. Importance of Vector Control For some diseases there is no effective cure such as Dengue fever, sleeping sickness, Japanese encephalitis, yellow fever etc; vector control remains the only way to protect populations. Both prevention through vector control and treatment are needed to protect populations. WHO recommends integrated method to combat multiples diseases at once through "Integrated Vector Management" (IVM). IVM is improve the efficacy, cost-effectiveness, ecological soundness and sustainable control of disease vectors.