Introduction to Medical Parasitology

Transcription

1 Introduction to Medical Parasitology Lecture I Medical Parasitology Course (MLAB 362) Dr. Mohamed A. El-Sakhawy 1 Suggested Textbooks 1. Cheesbrough (2009), District Laboratory Practice in Tropical Countries. Part 1, Second Edition. 2. Kayser (2005), Medical Microbiology. Thieme. Basic Clinical Parasitology, Harold W. Brown Pranklin. A. Nevs. Appleton. & Lange 251 Vanezant. St. Conneticut. USA. Garcia L.S. (1999) practical guide to diagnostic parasitology American society for microbiology Practical Animal Biology, Vol. II, Systematic Zoology By Al- Hussaini and Demian, Twentieth Edition 2005, Dar Al- Maaref, Cairo. 2 1

2 Electronic Materials, Web Sites etc Parasites online : Official website of the British Society for Parasitology. Offer information about the society and its activities as well as links to relevant parasitological sites. Official website of the American Society of Parasitologists. Offer information about the society and its activities as well as links to relevant parasitological sites. 3 Course Assessment Quizzes and assignments 10% Midterm Exams (2 exams) 20 % Lab notebook and activity 5% Lab midterm exam 10% Lab final exam 15% Final exam 40% 4 2

3 Learning Outcomes After completing this course, you should be able to: 1- Discuss how important parasites can be classified according to kingdom and phylum 2- State the meaning of commonly-used terms 3- Describe how parasitic infections affect communities in poor countries and that knowledge of their life cycle is necessary for effective prevention and control 4- Discuss the epidemiology, basic life cycle, clinical presentation, management and control of some important parasitic infections 5 Clinical Parasitology: Is the study of parasites which infect humans Conceptions related to medical parasitology Relationships between parasite and host The basic factors of transmission of parasitic diseases The preventive measures of parasitic diseases 6 3

4 Clinical Parasitology includes Parasites Parasitic diseases Prevention Transmission Treatment Diagnosis Pathogenesis Life Cycle Morphology 7 Symbiosis Is the relationship between two living things (animals) and two living things live together which involving protection or other advantages to one or both partner. Commensalism Mutualism Parasitism* 8 4

5 Commensalism Both partners are able to lead independent lives, but one may gain advantage from the association when they are together and least not damage to the other. Mutualism An association which is beneficial to both living things. 9 Parasitism An association which is beneficial to one partner and harmful to the other partner. The former that is beneficial to is called parasite, the latter that is harmful to is called host. Human / Hookworm 10 5

6 Parasite and the type of parasites Parasite: It is an animal that is dependent on another animal (host) for its survival. Type of parasites Protozoa Nematodes Parasites Helminths Trematodes Endo- Cestodes Arthropods Ecto- 11 Endoparasite and ectoparasite A parasite which lives in or on the body of the host is called endoparasite (protozoa and heminthes) or ectoparasite (arthropods). 12 6

7 Host and type of host Host : An organism that harbors the parasite usually larger than the parasite. Intermediate host : The host harboring the larvae or asexual stage of parasite. Final host : The host harboring adult or sexual stage of parasite. Reservoir host : Animals harboring the same species of parasites as man. Potential sources of human infection. 13 Life cycle and type of life cycle Life cycle: Is the whole process of parasite growing and developing. The direct life-cycle: Only one host (no intermediate host). The indirect life cycle: Life cycle with more than one host (intermediat host and final host). 14 7

8 Effects of parasites on the host Depriving the host of essential substance Hookworm Suck blood Anemia Mechanical effects of parasites on the host Ascaris Toxic and allergy effect Perforate/Obstruction E.h Proteolytic enzyme Necrosis Parasite antigen Immune system e.g Anaphylaxix (Type I hypersensitivity) Immune response Allergy/ Hypersensitivity 15 Effects of the host on the parasites The host can produce certain degree resistance to parasites in human body or re-infection. The resistance (Immunity) is not very strong. In general, It don t wipe out parasites completely, but may limit the number of parasites and establish balance with parasites. Innate immunity Acquired immunity 16 8

9 The source of the infection Patient: Persons who have parasites in their body and show clinical symptoms. Carrier: Persons who have parasites in their Reservoir host: body, not show symptoms. Animals that harbors the same species of parasites as man. Sometimes, the parasites in animals can transmit into human. 17 The routes of transmission I Congenital transmission: From mother to infant. Toxoplasmosis Contact transmission: Direct contact---trichomonas vaginalis Indirect contact---ascaris lumbricodes Food transmission: The infectious stage of parasites contaminated food / The meat of the intermediate hosts containing infectious stage of parasites. 18 9

10 The routes of transmission II Water transmission: Drink or contact the water contaminated the infectious stage of parasites. Soil transmission: Contamination of the soil by feces containing the certain stage of parasites and this stage can develop into stage. Arthropod transmission: Vectors of certain parasitic diseases. 19 The avenues of invasion Digestive tract: Most common avenue of entrance. (Food/ Water transmission) Skin: Infective larvae perforate skin and reach to body and establish infection. (soil/ water transmission) Blood: Bloodsucking insects containing infective parasites bite the skin and inject parasites into human blood. (Arthropod transmission---malaria)

11 The prevention measures of the parasitic diseases Controlling the source of the infection. ----Treatment of the patients, carriers and reservoir hosts. Intervention at the routes of transmission ----Managing feces and water resource, controlling or eliminating vectors and intermediate hosts. Protecting the susceptible hosts. ----Paying attention to personal hygiene, changing bad eating habit, taking medicine. 21 Taxonomic classification of parasitic organisms The classification of parasites is controversial - there is no universally accepted system Parasites form part of the animal kingdom which comprises some 800,000 identified species categorised into 33 phyla The parasitic organisms that are of importance for human health are eukaryotes - they have a well defined chromosome in a nuclear membrane (as opposed to prokaryotes which have no nuclear membrane, e.g. bacteria) 22 11

12 Taxonomic classification of parasitic organisms Parasites are classified into 2 sub-kingdoms: protozoa (unicellular) and metazoa (multicellular) Protozoan (unicellular) parasites are classified according to morphology and means of locomotion. There are 45,000 protozoa species. Most species that cause human disease belong to the phyla sarcomastigophora and apicomplexa Metazoa (multicellular) include the worms (helminths) and arthropoda (posses an external skeleton) e.g. ticks, lice Note that the genus starts with a capital letter and the species is always written in italics, e.g. Plasmodium 23 falciparum, Giardia lamblia Taxonomic classification of protozoa Sub kingdom Phylum Sub-phylum Genusexamples Speciesexamples Protozoa Sarcomastigophora further divided into Sarcodina-- - move by pseudopodia Entamoeba E. histolytica Mastigophora move by flagella Giardia G. lamblia Apicomplexa no organelle of locomotion Plasmodium P. falciparum, P. vivax, P. malariae, P. ovale Ciliophora move by cillia Balantidium B. coli Microspora Spore-forming Enterocyto-zoa E. bienusi 24 12

13 Examples of important intestinal protozoa Transmitted by the faecal-oral route and cause diarrhoea Giardia lamblia: world-wide distribution, lives in the small intestine and results in malabsorption Entamoeba histolytica: may invade the colon and cause bloody diarrhoea amoebic dysentery. Also causes ameobic liver abscess. Cryptosporidium parvum: more prevalent in the immunocompromised Cyclospora cyatenensis - parasitises the small intestinal mucosa and may cause diarrhoea for several weeks Balantidium coli: a large motile ciliated parasite that lives in the colon of pigs, humans and rodents and can lead to colonic ulceration Enterocytozoon bienusi: a microsporidian that parasitises the small intestine. Also more common in the immunocompromised. Electron micrograph of G. lamblia trophozoites (feeding stage) Typical flask-shaped ulcer due to E. histolytica in the colonic mucosa 25 Examples of important systemic protozoa Detected in the blood Plasmodium: the cause of malaria. There are 4 species that infect man: P. falciparum, P. vivax, P. ovale and P. malariae Typical lesion of cutaneous leishmaniasis Tsetse fly the vector of African trypanosomiasis It has a painful bite! Toxoplasma gondii: transmitted by the ingestion of oocysts from cat faeces. Infection can lead to ocular problems and is also a cause of neonatal toxoplasmosis Leishmania: transmitted by sand flies, can lead to visceral, cutaneous and mucocutaneous leishmaniasis Trypanosoma: haemoflagellates which cause In Africa - sleeping sickness (transmitted by the Tsetse fly) In South America - Chagas disease (transmitted by the Reduviid bug) 26 13

14 Taxonomic classification of helminths Sub kingdom Phylum Class Genus examples Metazoa Nematodes Round worms; appear round in cross section, they have body cavities, a straight alimentary canal and an anus Ascaris (roundworm) Trichuris (whipworm) Ancylostoma (hookworm) Necator (hookworm) Enterobius (pinworm or threadworm) Strongyloides Platyhelminthes Flat worms; dorsoventrally flattened, no body cavity and, if present, the alimentary canal is blind ending Cestodes Adult tapeworms are found in the intestine of their host They have a head (scolex) with sucking organs, a segmented body but no alimentary canal Each body segment is hermaphrodite Taenia (tapeworm) 27 Trematodes Non-segmented, usually leafshaped, with two suckers but no distinct head They have an alimentary canal and are usually hermaphrodite and leaf shaped Schistosomes are the exception. They are thread-like, and have separate sexes Fasciolopsis (liver fluke) Schistosoma (not leaf shaped!) Examples of important metazoa intestinal nematodes Trichuris (whipworm) A soil transmitted helminth prevalent in warm, humid conditions Can cause diarrhoea, rectal prolapse and anaemia in heavily-infected people 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, intercurrent disease) Ascaris (roundworm) Found world-wide in conditions of poor hygiene, transmitted by the faecal- oral route Adult worms lives in the small intestine Causes eosinophilia Enterobius (pinworm or threadworm) prevalent in cold and temperate climates but rare in the tropics found mainly in children Heavy intestinal infections may occur with Ascaris. Adult worms can be several cms long

15 Filaria including: Examples of important metazoa systemic nematodes Onchocerca volvulus Transmitted by the simulium black fly, this microfilarial parasite can cause visual impairment, blindness and severe itching of the skin in those infected Wuchereria bancrofti The major causative agent of lymphatic filariasis Brugia malayi Another microfilarial parasite that causes lymphatic filariasis Toxocara A world-wide infection of dogs and cats Human infection occurs when embryonated eggs are ingested from dog or cat faeces It is common in children and can cause visceral larva migrans (VLM) 29 Examples of important flatworms - cestodes Intestinal - ( tapeworms ) Taenia saginata worldwide acquired by ingestion of contaminated, uncooked beef a common infection but causes minimal symptoms Taenia solium worldwide acquired by ingestion of contaminated, uncooked pork that contains cystercerci Less common, but causes cystercicosis a systemic disease where cysticerci encyst in muscles and in the brain may lead to epilepsy 2. Systemic Echinococcus granulosus (dog tapeworm) and Echinicoccus multilocularis (rodent tapeworm) Hydatid disease occurs when the larval stages of these organisms are ingested The larvae may develop in the human host and cause spaceoccupying lesions in several organs, e.g. liver, brain 30 15

16 Examples of important metazoa trematodes (flukes) Intestinal Fasciolopsis buski - A common parasite of humans and pigs in South- east Asia. This parasite is one of the largest trematodes to infect man (8cm in length) and lives in the upper intestine. Chronic infection leads to inflammation, ulceration and haemorrhage of the small intestine Adult Fasciolopsis buski trematode Dr. Peter Darben, Queensland University of Technology 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 Clonorchis sinensis (liver fluke)- Widespread in China, Japan, Korea and Taiwan, this parasite is acquired by ingestion of infective metacercariae in raw or pickled fish Paragonimus westermani ( lung fluke)- Widespread in the Far East and South east Asia, the parasite is acquired by ingestion of infective metacercariae in raw or pickled crustaceans Schistosoma haematobium, S. mansoni and S. japonicum see below