Medical Parasitology The main aim of medical Parasitology course is to provide the student with knowledge, comprehension and methods of application of medical Parasitology in practical life. • 1. Describe the morphological characteristics, life cycles, methods of transmission of medically important helminthes. • 2. Mention the morphological characteristics, life cycles, methods of transmission of medically important Protozoa. • 3. Describe the morphological characteristics, life cycles and recognize diseases caused or transmitted by medically important Arthropods. • 4. Discuss clinical picture associated with parasitic infections. • 5. List the different diagnostic techniques for detecting parasites. • 6. Outline the plan of treatment of each parasitic disease. • 7. Interpret different clinical presentations and correlate them to suspected parasites. • 8. Differentiate and compare similar stages of different parasites. • 9. Choose the most suitable diagnostic technique for each parasitic problem • 10. Use the light microscopy . • 1 1.Examine mounted slides and identify different parasites • 12.Examine laboratory specimens . • 13. Interpret the results of examination of parasitic specimens. Introduction to parasitology Objectives • 1- Aims to focus on general parasitological terms that will be discussed later on during the course. • 2-Gives general idea about life cycle, methods of infection and different harmful effects caused by parasitic infection. Introduction • A parasite is an organism which lives on or within another organism called a host from which it obtains food and protection. Parasites vary according to their biological habits and can be divided into: Type of the parasite Definition Example 1-Obligatory organisms that cannot Plasmodium and parasites exist Oxyuris without a host 2-Facultative parasites organisms that can either Strongyloides live freely in soil or water or as parasites in hosts when unfavorable environmental conditions occur 3-Accidental parasites free living organisms which larvae of flies accidentally enter the human body by ingested and live in the mistake intestine of man 4-Temporary visits its host from one Soft tick parasite time to another for feeding Type of the parasite Definition Example 5-Specific parasite affects only one species of Enterobius host 6-Coprozoic (Spurious) Foreign organisms or Paramecium parasites stages of non human parasites which have been swallowed and pass through the intestine in feces without causing infection 7- Ectoparasite parasite which lives on the Pediculus outside of the host 8- Endoparasite parasite which lives within Ancylostoma the body of the host HOSTS Type of the host Definition Example Definitive in which the adult stage of man a definitive host for the Ascaris parasite lives, or in which sexual reproduction takes place Intermediate in which the immature or pigs act as intermediate larval stage of the parasite hosts for Taenia solium. is found, or in which the parasite multiplies asexually Reservoir when a parasite utilizes a Pigs are reservoir hosts for wide range of animal hosts Balantidium besides man, such animals represent the reservoir hosts of the particular parasite and act as a continuous source for human infection Type of the host Definition Example Paratenic (transport) in which the parasite does fish 2nd intermediate host not undergo any for Medina worm. developmental changes Amplifier is an intermediate host in snail 1st intermediate host which asexual for Schistosoma multiplications occur Vector is a host that transmits Fleas act as vectors for parasites from one host to Pasteurella another. It is usually pestis from rodents to man. arthropod Medical Protozoology • Objectives • Focus on morphological characters, life cycle, pathogenesis, clinical picture (Symptomatology), laboratory procedures, lines of treatment and prevention with control strategy of different protozoa affecting human beings. MEDICAL PROTOZOOLOGY • Protozoa: These are unicellular organisms that occur singly or in colony formation. Each protozoan is a complete unit capable of performing all functions. a) Morphology: Protozoa have wide range of size (1-150μ). The structure of protozoan cell is formed of a cytoplasmic body and a nucleus. 1. Cytoplasm: a. Ectoplasm: The outer hyaline layer that is responsible for ingestion of food, excretion, respiration, protection and sensation. -Some structures develop from ectoplasm as: - Organs of locomotion; pseudopodia, flagella and cilia. - Organs for food intake or excretion; peristome, cytostome and cytopyge. b. Endoplasm: The inner granular part of cytoplasm that is responsible for nutrition and reproduction. The endoplasm contains number of structures as: food vacuoles, foreign bodies, contractile vacuoles and chromatoid bodies. 2. Nucleus • It is the most important structure, as it regulates the various functions and reproduction. It is formed of: a. Nuclear membrane. b. Nuclear sap (nucleoplasm). c. Chromatin granules. d. Karyosome (nucleolus): It is a DNA containing body, situated centrally or peripherally within the nucleus. b)Life cycle: 1. Simple life cycle: Intestinal and luminal protozoa require only one host, within which they multiply asexually, and transfer from one host to another directly. 2. Complex life cycle: Most blood and tissue parasites pass alternatively in a vertebrate and an invertebrate host, this is called alternation of generation (i.e. transmission is indirect). The sexual multiplication occurs in one host and the asexual multiplication in another host. Classification of Protozoa 1. Phylum: Sarcomastigophora (Amoebae and Flagellates): a. Sub-phylum: Sarcodina (Amoebae): i. Parasitic Amoeba. ii. Free-living Amoeba. b. Sub-phylum: Mastigophora (Flagellates): i. Intestinal and uro-genital flagellates e.g. Giardia intestinalis, Dientamoeba fragilis (Amoeba-like flagellate), and Trichomonas vaginalis. ii. Blood and tissue (haemo-somatic) flagellates: Leishmania and Trypanosoma species. 2. Phylum: Ciliophora, e.g. Balantidium coli. 3. Phylum: Apicomplexa (Sporozoa or Coccidia), e.g. Plasmodium, Toxoplasma gondii, Cryptosporidium parvum, Cystoisospora belli and Cyclospora cayetanensis. SARCOMASTIGOPHORA Sarcodina (Amoebae) Entamoeba histolytica Geographical distribution: Worldwide distribution especially in tropical areas and poor communities. Morphology: Entamoeba histolytica has 3 stages: 1. Trophozoite (Vegetative or growing stage): - Size: 10-60 μ (average 20 μ). - Shape: Irregular outline with finger like pseudopodia and active movement. - Cytoplasm: It is formed of outer clear hyaline, refractile ectoplasm and inner granular endoplasm containing nucleus, food vacuoles, erythrocytes (RBCs), occasionally bacteria, and tissue debris. - Nucleus: It has centrally located fine karyosome and peripheral chromatin dots arranged regularly at the inner side of the nuclear membrane. • 2. Precyst: - Smaller than the trophozoite but larger than cyst (10-20 μ). - Rounded or oval with blunt pseudopodia and sluggish movement. - No food vacuoles or RBCs. - It contains a single nucleus similar to that of the trophozoite. • 3. Cyst: - It is rounded, 10-15 μ in diameter. - Has smooth refractile cyst wall. - The early cyst contains glycogen vacuoles and 1-4 chromatoid bodies which are sausage-shaped with rounded ends. - They are formed of RNA & DNA, and represent stored proteins which are consumed with repeated nuclear division. - Immature cysts may be mono- or bi-nucleated. - Mature cysts contain 4 nuclei formed by mitotic division. - Nuclei are similar to that of the vegetative form. • Life cycle: Habitat: a. Trophozoite: Inhabits the wall and lumen of the large intestine, with extra-intestinal metastases (liver, lung and brain, etc.). b. Cyst: Inhabits the lumen of the large intestine. Definitive host: Man. - Intermediate host: No. - Reservoir hosts: Dogs, rats and monkeys. - Infective stage: Mature quadrinucleated cyst. Mode of infection: • Ingestion of mature quadrinucleated E. histolytica cysts in contaminated food or drink, or through infected food handlers. • Mechanical transmission by flies and cockroaches. • Autoinfection: fecal-oral route (hand to mouth contact). - On ingestion, the trophozoites disintegrate in the stomach, while only the mature cysts resist the stomach acidity and pass to the small intestine. - The cyst wall is digested by action of trypsin and excystation occurs in the proximal small intestine, where metacystic stage escapes and divides into 8 small amoebae. - These trophozoites move down to the ilio-caecal region, multiply by binary fission, and then pass to the lumen of colon, where they may remain, feeding on starch or mucus and pass in liquid stool. - They may undergo encystation and cysts pass with formed stool. - Also, trophozoite may invade the wall of large intestine by their lytic secretion(Histolysin) to invade the host tissues through blood vessels (extra-intestinal invasion). Pathogenesis: • E. histolytica causes intestinal and extra- intestinal amoebiasis. • E. histolytica lives in large intestine usually as a commensal without producing any clinical manifestation, but sometimes they become pathogenic and attack the mucosa (10% of cases). Life cycle of E. histolytica • Pathogenesis: - Entamoeba trophozoites attach themselves to the surface epithelium aided by an enzyme called E. histolytica lectin and start crawling over the mucosa. -Trophozoites secrete cytolytic enzymes; haemolysins and pore-forming enzymes (amoeba pore), which lead to necrosis of epithelial cells with pore