Ukrainian Medical Stomatological Academy Medical Biology department Lecture 11. Topic: MEDICAL AND BIOLOGICAL BASIS OF PARASITISM. PROTOZOA – HUMAN PARASITES Poltava 2021 Plan 1. Parasitology as a branch of biology and medicine. Basis of parasitism. 2. Medical protozoology as a science about protozoans. Subkingdom Protozoa: general characteristics and systematics. 3. General characteristics of the phylum Sarcomastigophora. Medical importance of the representatives of class Lobosea. 4. Phylum Sarcomastigophora, class Zoomastigophorea: general characteristics and medical importance of the representatives. 5. Phylum Арісоmрlеха, class Sporozoa: general characteristics and medical importance of the representatives. 6. Phylum Ciliophora, class Litostomatea: general characteristics and medical importance of the representatives. Recommended literature: 1. Medical Biology : text-book / Bazhora Yu. I., Bylyk R. Ye., Chesnokova M. M. et al. – 2nd ed., revised and updated. – Vinnytsia : Nova Knyha, 2019. – 448 p. 2. Biological peculiarities of the human vital functions. Training text-book on Medical biology (module I) for students of medical and stomatological faculties / S.I. Dubinin, O.V. Ovcharenko, O.V. Klepets et al. – Poltava, 2019. – 79 p. 3. Lazarev K.L. Medical Biology: Text-book. – Second edition. – Simferopol: IAD CSMU, 2003. – 592 p. 4. Medical biology: The study guide of the practical classes course / O.V. Romanenko, O.V. Golovchenko, M.G. Kravchuk, V.M. Grinkevych. – Edited by O.V. Romanenko. – K.: Medicine, 2008. – 304 p. 5. Bekish O.-Y.L. Medical biology: Textbook for students of higher educational establishments. – Vitebsk: VSMU Press, 2003. – 346 p. 6. Green N.P., Stout G.W., Taylor D.I. Biological Science. – Cambridge, 1994. Symbiotic interactions Symbiosis (from Greek sym – together and bios – life) is any type of a close and long- term biological interaction between two different biological species. Parasitism Parasitism is a symbiotic relationship between species, where one organism (parasite) benefits from the relationship and another organism (host) is injured. Parasitology Parasitology is a complex biological science, which carries out diversified studies of parasites and their pathogenic effect on an organism. Medical parasitology is a science dealing with human parasites and diseases caused by them. Branches of medical parasitology: • medical protozoology (studies parasitic protists); • medical helminthology (studies helminths – parasitic worms); • medical arachnoentomology (studies arthropods – agents and vectors of human diseases). Human as a host of parasites It is known for nowadays about 1.5 million species of animals. Of them about 60–65 thousands species are parasites. Humans are hosts to: • nearly 300 species of parasitic worms • over 70 species of protozoans. Objects of Medical parasitology Who is a parasite? Parasite is a species that obtains food and physical protection from a living organism of another species (host) which is usually damaged by it and never benefits from its presence. Characteristics of parasite: • Can penetrate the host to gain entry • Can attach itself to the host • Have protection against immune system of the host • Show degeneration of unnecessary organ systems • Produce vast numbers of eggs to increase a chance of reaching a new host • Use a vector or intermediate host to reach a new host • Produce resistant stages to survive outside the host Types of parasitism by location of parasite Ectoparasite Aberrant parasite Endoparasite by obligatory of parasitic way of life Obligate Facultative by specificity to host Specific Accidental Panxenous (Evryxenous) (occasional) Monoxenous Stenoxenous Heteroxenous by duration of parasitic interaction Permanent Temporary Types of parasites by their location Ectoparasites are parasites that live outside of the host’s body (Example: lice, ticks). Endoparasites live inside the host’ (Example: nematodes and hookworms). Aberrant (erratic) parasites are located in unusual places of the host’s body, where they can not develop or survive (Example: ascaris in ovary; Entamoeba histolytica in liver or lungs). Types of parasites by obligatory of parasitism Obligate parasites are Facultative parasites can completely dependent survive without the host, on the host in order to and only sometimes lead complete their life cycle parasitic way of life (Example: Head lice; (Example: Naegleria fowleri = the vast majority of human ="brain-eating amoeba“; round parasites). worm Strongyloides stercoralis). Types of parasitism by specificity to host Host specific parasites are associated with concrete species of host (hosts): • Monoxenous – have only single host species (Example: amoeba, coccidia, head louse). • Heteroxenous require at least two species of host to complete the life cycle (Example: malaria plasmodium, liver fluke). • Stenoxenous – have narrow host range, prefer a certain host species, but can be parasitic on others (Example: scabies of man and horse). • Panxenous (evryxenous) – have wide range of hosts (Example: Toxoplasma gondii, mosquitoes). Accidental (occasional) parasites attack an unusual host (Example: dog roundworm, Toxocara canis, which may infect humans). Types of parasites by duration of parasitic interaction Permanent parasites Temporary parasites are are those that spend seen in or on the body of their entire life cycle the host only for certain in or on the body of the periods of time (short or host long duration) (Example: lice). (Example: mosquitoes and bugs). Who is a host? Host – is an organism that harbors the parasite, providing its nourishment and shelter. Characteristics of a host: • Usually larger than parasite • Has higher organization • Never benefits. Effects of parasites on host Depriving the host of nutrition: pathogens utilize nutrition from host environment for their development and reproduction. Hookworm → Suck blood → Anemia Mechanical effects: • Entering the cells: Some protozoa → live and reproduce in host’s cells → rupturing of cells. • Migration or penetration through tissue or organ: hookworm’s or Ascaris larvae in blood → the wall of capillary of lung and alveoli → mechanical damage (Pneumonitis) Ascaris perforates intestine walls → peritonitis) / obstruction (ileus) • Blockage and pressure: - the intestinal lumen can be blocked by worms. - hydatid cyst in liver may reach volumes of 1–2 litres → severe damage of organ. Toxic and allergic effect: in contrast to bacterial toxin, parasitic toxins have minimal role in pathogenesis. Proteolytic enzyme → Necrosis / ulcer; Parasite metabolites → antigen → Immune system → Immune response → Allergy / Hypersensitivity / Anaphylaxis (is harmful to host, or even fatal). Effects of host on parasites Types of hosts • Definitive (primary) host (DH): that harbours the adult or sexually mature stages of the parasite (or in whom sexual reproduction occurs). (Example: in the majority of human parasitic infections man is DH). • Intermediate (secondary) host (IH): that harbours larval or sexually immature stages of the parasite (or in whom asexual reproduction occurs). (Example: man is IH of malaria parasites and in hydatid disease). • Additional host is the second intermediate host, when in some cases larval development requires more than one hosts. • Reservoir host (RH): that harbours the same species and same stages of the parasite as a man and is therefore, a reservoir source of infection for man. (Example: sheeps are RH for Fasciola hepatica). Types of the life cycle of parasite Life cycle is the whole process of parasite’s growing and developing. Direct (simple) life-cycle: when a parasite requires only one host to complete its development. It is a life cycle with one host. Indirect (complex ) life cycle: when a parasite requires two hosts (definitive and intermediate) to complete its development. It is life cycle with more than one host. Host-parasite relationship Infection is the result of entry and development within the body of any injurious organism regardless of its size. Once the infecting organism is introduced into the body of the host, it reacts in different ways and this could result in: • Carrier state → parasite and host are at equilibrium. • Disease state → parasite dominates under host due to – lower resistance of the host – a higher pathogenicity of parasite. • Parasite destruction → host takes upper the parasite. The sources of parasitic infections • Man: Patient (Persons who have parasites in their body and show clinical symptoms) or Carrier (Persons who have parasites in their body, not show symptoms). • Animal: Reservoir host (Animals that harbors the same species of parasites as man. Sometimes, the parasites in animals can transmit into human). • Vectors: an arthropod that transmites the infection from one infected organism to another. Routes of parasitic infections Routes of parasitic infections VECTOR Vectors any agent which carries an infectious pathogen of parasites into another living organism Specific Mechanical vector vector an arthropod, which transmits transmits parasitic some stages of parasites forms of the inside its body parasite (cysts, (tsetsefly, mosquitoes) eggs, larvae) on Inoculation Contamination external parts of their body (flies, introduction of introduction of cockroaches) infecting agent in infection with fecal wound through matter into the the bite of an wound caused by a infected vector bite of infected Specific Nonspecific vector The mode of transmission may be only through the vector There may be another mode of transmission