Introduction to Parasitology

1. Introduction to Parasitology

2. Medical parasitologydeals with parasites which cause human infections and diseases they produce.

3. Taxonomic classification of protozoa

4. Class Lobosea • Class Zoomastigophorea • Class Sporozoa • Class Ciliophora Medical Protozoology • Class Nematoda • Class Trematoda • Class Cestoda Medical Helminthology

5. A parasite: “a living organism that acquires some of its basic nutritional requirements through its intimate contact with another living organism”. • Parasites may be simple unicellular or complex multicellular. • Protozoa: unicellular organisms, e.g. Plasmodium • Metazoa:multicellular organisms, e.g. helminths (worms) and arthropods (ticks, lice)

6. An endoparasite: “a parasite that lives within another living organism” – e.g. malaria, Giardia • An ectoparasite: “a parasite that lives on the external surface of another living organism” – e.g. lice, ticks • Vector: “a living carrier (e.g.an arthropod) that transports a pathogenic organism from an infected to a non-infected host”. Eg; female Anopheles mosquito that transmits malaria

7. Endoparasite

8. Ectoparasite

9. Host: “the organism in, or on, which the parasite lives and causes harm” • Definitive host: “the organism in which the adult or sexually mature stage of the parasite lives” • Intermediate host: “the organism in which the parasite lives during a period of its development only”

10. Reservoir hosts: the vertebrate hosts which harbour the same species of parasite at same stage as a human host. They are an important source of infection in epidemiology.

11. Life cycle Life cycleis the process of a parasite’s growth, development and reproduction, which proceeds in one or more different hosts depending on the species of parasites. Infective Stageis a stage when a parasite can invade human body and live in it .

12. Alternation of Generation: In life cycles of some parasites, there are the regular alternations of sexual and asexual reproductions , this phenomenon is called alternation of generation, such as the life cycle of Plasmodium vivax.

13. Mechanical Transmission: Arthropods play a role in the transportation of pathogens, which is not indispensable for the disease transmission.

14. Biological Transmission: Pathogens have to spend a part of their life cycle in the vector arthropods in which they multiply or develop into the infective stage and then invade the human body under the help of the arthropod, such as Anopheles mosquitoes transmit malaria.

15. Protozoans Microscopic single celled organisms • Amoeba Eg; Entamoeba. Endolimax, Naegleria, Acanthamoeba • Ciliates Balantidiumcoli Flagellates Giardialamblia, Trypanosome sp. Trichomonasvaginalis Sporozoa Plasmodium Toxoplasma

16. Examples of important intestinal protozoa Transmitted by the faecal-oral route • Giardialamblia: live in small intestine and results in malabsorption • Entamoebahistolytica: may invade the colon and cause bloody diarrhoea – amoebic dysentery. Also causes ameobic liver abscess. • Cryptosporidium parvum: prevalent in immunocompromised • Balantidiumcoli: a large motile ciliated parasite that lives in the colon of pigs, humans and rodents and can lead to colonic ulceration • . Electron micrograph of G. lamblia trophozoites (feeding stage) Typical flask-shaped ulcer due to E. histolytica in the colonic mucosa

17. Taxonomic classification of helminths

18. Cestodes • Intestinal - (“tapeworms”) • Taeniasaginata • acquired by ingestion of contaminated, uncooked beef • a common infection but causes minimal symptoms • Taeniasolium • acquired by ingestion of contaminated, uncooked pork that contains cystercerci • Less common, but causes cystercicosis – a systemic disease where cysticerciencyst in muscles and in the brain

19. 2. Systemic • Echinococcusgranulosus(dog tapeworm) and Echinicoccusmultilocularis (rodent tapeworm) • Hydatid disease occurs when the larval stages of these organisms are ingested

20. Fasciola hepatica (liver fluke)- Primarily, a parasite of sheep, humans become infected when they ingest metacercariae that have encysted on watercress. The adult trematode lives in the intra-hepatic bile ducts of the liver. “Fascioliasis” can lead to severe anaemia in humans Examples of important metazoa –trematodes (flukes) Intestinal Fasciolopsisbuski

21. Ascaris (roundworm) Found world-wide in conditions of poor hygiene, transmitted by the faecal- oral route Adult worms lives in the small intestine Nematodes – intestinal nematodes • Trichuris (whipworm) • A soil transmitted helminth • Ancylostoma and Necator (hookworms) • A major cause of anaemia in the tropics • Strongyloides • inhabits the small bowel • infection more severe in immunospressed people (e.g. HIV/AIDS, malnutrition, intercurrentdisease • Enterobius (pinworm or threadworm) • found mainly in children Heavy intestinal infections may occur with Ascaris. Adult worms can be several cms long.

22. Examples for systemic nematodes Filaria including: • Wuchereriabancrofti – The major causative agent of lymphatic filariasis • Brugiamalayi – Another microfilarial parasite that causes lymphatic filariasis

23. Parasites’ Harms to Man • Mechanical effects • Depriving nourishment from hosts • Toxic effect • Immuno-pathological lesion

24. Pathogenesis: • 1. Source of infection • infected persons • carriers • animals

25. 2. Mode of transmission • ingestion • Through skin contact • Vectors • direct • 3. Susceptible host • immunity

26. Diagnosis of Parasitic Infections: 1. Clinical diagnosis 2. Laboratory diagnosis

27. Laboratory diagnosis: Demonstration of parasite Culture Animal inoculation Skin tests Serological test Molecular method

28. Demonstration of parasite Specimen: Blood Stool Urine Genital specimen CSF Sputum Tissue biopsy Aspirated fluid

29. Treatment of Parasitic Infections: 1. Medical and surgical 2. Chemotherapy 3. Adequate nutrition

30. Prevention and Control: 1. Reduction in sources 2. Education 3. Destruction and/or control of reservoir hosts and vector