Introduction to Medical Parasitology PDF - BNU 2024

Faculty of Medicine PMP Module Parasitology lecture Introduction to Medical Parasitology Prof. Nagwa S.M. Aly Professor of Medical Parasitology, Benha University& BNU, Egypt. By the end of this lecture, the student will : Des...

Faculty of Medicine PMP Module Parasitology lecture Introduction to Medical Parasitology Prof. Nagwa S.M. Aly Professor of Medical Parasitology, Benha University& BNU, Egypt. By the end of this lecture, the student will : Describe some definitions of parasitism. Explain the general concepts of parasitology. Differentiate between different types of hosts. Discuss host parasite relationship (types, definitions, examples). Describe Effects of parasites on their hosts 2  Why do medical students still need to learn parasitology? 1. Seven of 10 major human tropical diseases are parasitic. (African trypanosomiasis, Dengue, Leishmaniasis, Malaria, Schistosomiasis, Tuberculosis, Chagas disease, Leprosy, Lymphatic filariasis, Onchocerciasis). 2. The increased travel of the population. 3. Immunosuppression becomes more widespread. 4. Modifications of the environment.  Terms used in Parasitology Parasite: An organism living temporarily or permanently in or on another larger organism (Host) to have shelter and /or nutrition. Parasitology: A science that deals with an organism (Parasite) that lives in or on another organism. Parasitology has traditionally been limited to parasitic helminths, protozoa, and arthropods, as well as those species of arthropods that serve as vectors for parasites. Medical Parasitology: The study of parasites that are capable of causing disease in man. 4  Host: An organism that harbors the parasite. Types of Hosts: ❑Definitive host: Depending on the parasitic species, it is either a host that harbors the adult stage, the most highly developed form of the parasite, or the sexually mature stage of a parasite, and fertilization takes place in it. ❑Intermediate host: Is a host harboring sexually immature or larval stage of a parasite and in which no fertilization takes place. ❑ Reservoir host: The animal that holds the same species of parasites as man, constitutes a source of infection to man, and ensures the continuity of the parasite life cycle. ❑ Carrier host: A host harboring a parasite but exhibiting no clinical signs or symptoms. N.B. Man can act as both DH. And IH. i.e. in H. nana infection 5  Vector: Any arthropod that transports a parasite from an infected to a non-infected host. Biological vectors Mechanical Vectors  Habitat: The tissue or organ in which the adult stage of parasite exists in the host. Infection: Invasion of the body by any pathogenic organism “except” arthropods. Infestation: The establishment of arthropods upon or within a host. 7  Prepatent (Biological) Incubation Period: It is the time elapsing between initial infection with the parasite and demonstration of the parasites or their stages in excreta, blood, aspirate, and other diagnostic material. Clinical Incubation Period: It is the interval between exposure to infection and the appearance of the earliest manifestation. Autoinfection: A situation where the infected individual acts as a source for hyperinfection to himself. 9  Infective Stage: The stage of parasite that can transmit the infection to DH and it is capable of entering the host and continuing development within the host. Diagnostic Stage: ✓it is the stage of a parasite that can be detected in stool, blood, urine, or other human body secretions. Zoonosis: Diseases of animals that are transmittable to man.  Basic Concepts in Medical Parasitology In medical parasitology, each of the medically important parasite is discussed through: 1. Disease, Geographical distribution 2. Morphology, Life cycle 3. Pathology, Clinical manifestations of infection 4. Diagnosis, treatment 5. Preventive/control measures of parasites.  Geographical distribution: Once we are clear about the geographical distribution and conditions favoring survival in relation to different parasites, effective preventive and control measures can more easily be devised and implemented. Morphology: This is especially important in the diagnosis of infection and differentiation between pathogenic and non-pathogenic organisms. 13 Life cycle of parasites: Life cycle can either be - simple, when only one host is involved, or - complex, involving one or more intermediate hosts. A parasite’s life cycle could be classified into two common phases: 1) inside the human body: ✓ It provides an understanding of the symptomatology and pathology of the parasite. ✓ It is essential for selection of method of diagnosis and tratment. 2) outside of the human body: It provides information relevant to epidemiology, prevention, and control.  Mode of Transmission: It provides important information relevant to prevention and control. 1) Direct mode of transmission (the parasite doesn’t require biological vectors and/or intermediate host): ✓ Ingestion by mouth, ✓ Inhalation during respiration, ✓Sexual, √ Blood transfusion, ✓ Direct skin penetration, ✓Congenital (transplacental), ✓ Trans-mammary (breast milk) and autoinfection. 2) Indirect Mode of transmission (the parasite requires biological vectors and/or intermediate hosts).  Host parasite relationship: Once the infecting organism is introduced into the body of the host, it reacts in different ways and their relation will be one of the following types: 1) Commensalism: one organism lives at the expense of another which is not affected. 2) Parasitism: one organism lives At the expense of another which is affected. 3) Mutualism: Both organisms in associate are benefited. 3) Parasitism: The sequalae of parasitism could be one of the following: a) Carrier state - a perfect host-parasite relationship where tissue destruction by a parasite is balanced with the host’s tissue repair. At this point the parasite and the host live harmoniously, i.e. they are at equilibrium. b) Disease state - this is due to an imperfect host-parasite relationship where the parasite dominates the upper hand. It can result either from lower resistance of the host or a higher pathogenicity of the parasite. c) Parasite destruction – occurs when the host takes the upper hand. 17  Opportunistic parasites: Parasites which cause mild disease in immunologically healthy individuals, but they cause severe disease in immuno-deficient hosts. e.g., Pneumocystis carnii, Toxcoplasma gondii, Isospora belli. 18  Effects of parasites on their hosts A Parasite can affect the host in a number of ways such as: 1) Consumption of the nutritive elements of the host. e.g., Diphyllobothrium latum selectively remove vitamin B12. 2) Obstruction of passages e.g., Ascaris may cause intestinal obstruction. 3) Bleeding e.g. Schistosomes eggs. 4) Destruction of tissues: e.g. Leishmania donovani. 5) Compression of organs, e.g. Hydatid cysts in liver, brain cause pressure. 6) Opening pathway to secondary infections e.g. Ulcer formed as a result of Dracunculus medinensis infection exposes to Bacterial, Viral infection. 7) Transmission of pathogens to man, e.g., lice transmitting Rickettsia. 8) Predisposition to malignancy e.g., Infection with bilharziasis predisposes to malignancy. 9) Immunological reactions that may cause: Inflammation and fibrosis. e.g. liver or urinary tract fibrosis after deposition of the ova of schistosomes. Allergy development, e.g. bite of arthropod causing itching Anaphylactic shock e.g. due to rupture of Echinococcus granulosus cyst. Destruction of tissues. e.g. blood cells destruction in malignant malaria. Protection from reinfection e.g. Leishmania.  Host susceptibility factors Not all parasitic infection causes disease of clinical significance. Both host and parasitic factors are involved. - Host factors include: Parasite factors include: 1) Genetic constitution, 1. Strain of the parasite and adaptation to human host. 2) Age, 2. Parasite load. 3) Sex, 3. Site occupied in the body. 4) Level of immunity, 4. Metabolic process of the parasite, 5) Malnutrition, particularly the nature of any waste products or 6) Intensity and frequency of infections, toxins produced by the parasite during its growth and reproduction. 7) Lifestyle and occupation and 8) Presence of co-existing disease or conditions which reduces immunity e.g. AIDs.  Prevention and control of parasitic infection Preventive measures designed to break the transmission cycle are important to successful parasitic eradication. Such measures include: a) Reduction of the source of infection by Chemotherapy. b) Sanitary control of drinking water and food. c) Proper waste disposal. d) Control the vector population e) Protective clothing that would prevent vectors bite. f) Good personal hygiene. g) Avoidance of unprotected sexual practices h) Vaccination : as in malaria (under trials) Classification of Parasites Nomenclature Animal parasites are classified according to the “International Code of Zoological Nomenclature”. Each parasite belongs to a phylum, class, order, family, genus and species. the first name is that of the genus to which the organism belongs (capital letter), and the second is that of the species (small letter). e.g. Ascaris lumbricoides.  Taxonomic classification of medically important parasites of man belong to the kingdom of Animalia and most parasites are members of 4 phyla: 1- Phylum Protozoa (unicellular parasites) 2- Phylum Platyhelminthes (flat worms) 3-Phylum Nemathelminthes (round worms) 4-Phylum Arthropoda (body has exoskeleton, segmented and attached to appendages) Thank YOU  Quiz Match a. The tissue or organ in which the adult stage of parasite exists in the host. 1. Infection: b. Invasion of the body by any pathogenic organism “except” 2. Infestation: arthropods. 3. Habitat: c. The establishment of arthropods upon or within a host. 4. Diagnostic Stage: d. The stage of parasite that can transmit infection to DH 5. Infective Stage: e. It is the stage of a parasite that can be detected in stool, blood, or other human body secretions. 28