Introduction To Parasitology PDF

Topic 9.0: INTRODUCTION TO PARASITOLOGY    Medical Parasitology is the science dealing with parasites that infect man, causing disease and misery in most countries of the tropics.  They plague billions of people, kill millions annually, and inflict debilitating injurie...

Topic 9.0: INTRODUCTION TO PARASITOLOGY    Medical Parasitology is the science dealing with parasites that infect man, causing disease and misery in most countries of the tropics.  They plague billions of people, kill millions annually, and inflict debilitating injuries such as blindness and disfiguration on additional millions.  World Health Organization estimates that one person in every four harbors parasitic worms On completion of this session the student should be able to: State the general terms used in parasitology State the parasitic form that causes disease in humans and its location in the body Describe the means by which each infection occurs State the sources of parasitic infection Discuss the diagnostic test for parasitic disease Parasitology  The study of parasites Parasites  Defined as an organisms that live on or in other living organism called the host to get food and shelter and cause disease. . Parasitism  Define as symbiotic relationship that is of benefit to one party or symbiont (the parasites) and usually cause harm to another party (host). Symbiosis  A parasitic relationship that depend on each other equally. Or a relationship which each provides for the other the conditions necessary for its continued existence. Obligate parasites  A parasites which is completely dependant on the host. Facultative parasites  An organism that can be parasitic, but does not have to live as parasites. Ectoparasites  Parasites that live on the surface of the host. e.g. mites, tick, bugs and lice. Endoparasites  A parasite that lives inside the body of the host e.g. parasitic protozoa and helminths. Commensal  Living in a relationship in which one organism derives food or other benefits from another organism without hurting or helping it. Host  Define as an organism which harbours the parasites and provides the nourishment and shelter. Definitive host  Define as the host that harbours the sexually mature or adult parasites. Intermediate host  The host that harbours the larval or asexual form of the parasites. Paratenic host  A host which act as a transporting agent for the parasite and in which parasites dose not undergo any development. Compromised host  The host in whose normal defence mechanism has impaired (e.g. AIDS). Pathogen  A parasites which is able to produce disease. Infestation  Present of arthropods on the skin of the host. Pathogenicity  Is the ability of a parasite to produce disease. Zoonosis  Diseases which are transmissible between man and animals Virulence  Refers to the degree of pathogenicity Vector  An agent usually an insect that transmit an infection from one human host to another. Parasite  An organism that is entirely dependent on another organism for it’s survival. It obtains nourishment and shelter from organism on which it thrives. Types of parasite 1. Protozoa 2. Helminths A unicellular organisms Classified as per organ of locomotion Group Genus/species Amoeba Entamoeba histolytica Flagellates Leishmania donovani Giardia lamblia Trichomonas Sporozoa Plasmodium species P. vivax P. falciparum P. ovale P. malariae Toxoplasma species Ciliata Balantidium coli  Multicellular organism. Group Examples Cestodes – tape like Taenia species and segmented. Taenia saginatum (Beef tapeworm) Taenia solium (Pork tapeworm) Diphyllobothrium species Diphyllobothrium canium (Dog tapeworm) Diphyllobothrium latum (Fish tapeworm) Trematodes – flat Fasciola and leaf. Schistosoma Nematodes – Hookworm Elongated cylindrical Roundworm unsegmented. Threadworm Microparasite  Small, unicellular and multiplies within its vertebrate host, often inside cells, e.g. protozoa Macroparasite  Large, multicellular and has no direct reproduction within its vertebrate host, e.g. helminths  Not all protozoa are parasitic.  Can be free-living, e.g. pond water protozoa, only becoming parasites when accidentally gain entrance to the body.  Able to multiply in humans, which contributes to their survival and serious infections to develop from just a single organism.  Transmission in a human's intestine to another human occurs through a fecal-oral route.  Protozoa in humans blood or tissue of are transmitted by an arthropod vector (for example, through the bite of a mosquito or sand fly). Types of protozoa that is infectious to human i. Amoebae o Various size and shape o Move by pseudopodia e..g. Entamoeba Naegleria, Entamoeba histolytica Types of protozoa ii. Flagellates o Possess flagella for locomotion o Whip-like’ extensions of the cell membrane o Include; Haemo flagellates, intestinal flagella e.g. Leishmania, Giarda lambia, Trichomonas Types of protozoa iii. Sporozoa o Produce spore like oocysts o Alteration of generation and host occurs e.g. Plasmodium, Toxoplasma Types of protozoa iv. Ciliates o ‘Hair-like’ extensions of the cell membrane are organ of locomotion e.g. balantidium o Ciliated cells are found in specialized tissues and organs in many other higher life-forms (e.g. human bronchial epithelial cells). Life-cycles o Most protozoa have enormous reproductive potential because they have short generation times, o Undergo rapid sequential development and produce large numbers of progeny by asexual or sexual processes o Responsible for many protozoan infections rapidly causing acute disease syndromes. o May multiply by asexual division or sexual reproduction Life-cycles  Protozoan developmental stages occurring within hosts generally consist of feeding trophozoites, and they may be found intracellularly (within host cells) or extracellularly (in hollow organs, body fluids or interstitial spaces between cells).  Trophozoites do not survive long outside of their hosts. Four main modes of transmission:  Direct,  Faecal-oral,  Vector-borne  Predator-prey transmission.  General term meaning worm  Large, multicellular organisms generally visible to the naked eye in their adult stages.  Can be either free-living or parasitic.  In their adult form, helminths cannot multiply in humans Three major assemblages of parasitic helminths:  Nematodes (roundworms)  Cestodes (tapeworms)  Trematodes (flukes) i. Trematodes (Flukes) o Leaf-like, flatworm o Sexes not separate o Incomplete alimentary canal o Do not have a body cavity (acoelomate) e.g. Fasciola, schistosoma, threadworm ii. Nematodes (Roundworm) Elongated, cylindrical nonsegmented Separate male and female fluid-filled internal body cavity (pseudocoelum) e.g. hookworm, roundworm iii. Cestodes (Tapeworm) o Have long flat ribbon-like bodies o Sexes not separated o Alimentary canal absent o Body cavity absent.e.g. Taenia, Echinococcus Life cycle  Form three main life-cycle stages: o eggs, o larvae o adults.  Definitive hosts –habours adult stage  Intermediate or paratenic : may be more than one  Larval stages may be free-living or parasitize invertebrate vectors. The four main modes of transmission:  Faecal-oral,  Transdermal,  Vector-borne  Predator-prey transmission: Parasite infection originate from the following source: 1. Contaminated soil and water o Soil polluted with human excreta acts a source of infection with Ascaris lumbricoides, trichuris trichiura, Ancylostoma duodenale, Necator americanus and Strongyloides stercoralis. o Before acquiring infectivity for man, eggs of these parasites undergo certain development in the soil known as soiled transmitted helminths o Water polluted with human excreta may contain viable cyst of Entamoeba histolytica, Giarda lamblia, Balantidium coli, eggs of Taenia solium and etc. 2. Raw and undercooked pork  Source of Trichinella spiralis,, Taenia saginata and sarcocystis suihominis 3. Blood-sucking insects e.g Anopheles mosquito  Transmit plasmodium spp. 4. Housefly (mechanical carrier)  The source of E.histolytica 5. Dog  Source of Echinococcus granulosus and Toxocara canis 6. Cat  Source of Toxoplasma gondii 7. Man  Source of E. hostolytica, Giarda lamblia, enterobius vermicularis and hymenolepiasis nana 8. Autoinfection  May occur with E.vermicularis and Strongyloides stercoralis leading to hyperinfection The parasites can be acquired by various routes and from various infections; 1. Autoinfection o Threadworm o Strongyloides 2. Water-borne o Ameobiasis o Giardiasis o Free living amoeba o Guineaworm o Roundworm, etc. 3. Vector-borne o Mosquito (malaria, Filariasis) o Sand-fly (kala azar) o Tsetse fly (sleeping sickness) o Reduviid bug (Chaga disease) 4. Through animal o Pig (pork tapeworm) o Cat (toxoplasmosis) o Cow (beef tapeworm) o Dog (hydatid disease) 5. Contaminated food o Amoebiasis o Ascariasis o Toxoplasmosis o Trichinellosis 6. Penetration through skin o Hookworm o Schistosomiasis Strongyloides Mouth  Commonest portal of entry for parasite through: o Contaminated food o Soiled fingers or fomites  The mode of transmission is referred to faecal-oral route Skin  Some parasite can penetrate the unbroken skin of an individual walking over soil contaminated with faeces  Large number of parasite are introduce percutaneously when blood sucking arthropods puncture the skin to feed Sexual contact  Trichomonas vaginalis is transmitted by sexual contact  E. histolytica and G. lamblia may also be transmitted by anal-oral sexual practices among male homosexual Kissing  E. gingivitis is transmitted from person-to-person or contaminated drinking utensils Congenital  Infection with T. gondii and plasmodium spp. May be transmitted from mother to foetus through placenta Inhalation  Airborne eggs of E. vermicularis may be inhaled into the posterior pharynx leading to infection Iatrogenic infection  Malaria parasite may be transmitted by: o Transfusion of blood also known as trophozoite- induced malaria or transfusion malaria (from donor with malaria containing erythrocytic schizogomy o Use of contaminated syringe and needle – may occur in drug addict Traumatic damage  Entry of the following parasites into the skin cause slight physical damage: o Filariform larvae (infective third-stage larva) of Strongyloides stercoralis (threadworm) , Ancylostoma duodenale (Hookworm) o Cercaria larvae (the final, free-swimming larval stage of a trematode parasite) of Schistosoma haematobium, S. mansoni and S. japonicum Traumatic damage …cont…  Migration of several helminth to organs such as: o Lungs produces traumatic damage of the pulmonary capillaries leading to extravasation of blood into the lungs  Eggs of S. haematobium and S. mansoni causes extensive damage with haemorrhage as they escape the vesical and mesenteric venules into the lumen of the urinary bladder and intestinal canal Traumatic damage …cont…  Attachment of hookworm (A. duodenale and Necator americanus) causing traumatic damage of the villi and oozing of blood at the site of attachment  Lumbricoides and T saginata may produce intestinal obstruction  Ascaris can : o Occlude lumen of the of the appendix or common bile duct o May cause perforation of the intestinal wall o May penetrate into the parenchyma of liver and the lungs Lytic necrosis  E. histolytica secretes lytic enzyme which lyses tissue for its nutritional needs and helps to penetrate into tissue of the colon and extraintestinal viscera  Obligate intracellular parasites, e.g. Plasmodium spp., Leishmania spp. Trypanosoma cruzi and Taxoplasma gondii cause necrosis of host cell during their growth and multiplication. Competition for specific nutrients  Diphyllobothrium latum (fish Tapeworm) competes with the host for vitamin B12 leading to parasitic-induced pernicious anaemia. Inflammatory reaction  Iron-deficiency, pernicious and haemolytic anaemia develops in patient with hookworm disease, diphyllobothriasis and malaria.  E. histolytica may produce inflammation of the large intestine leading to formation of amoebic granuloma or amoeboma Allergic manifestation  In certain helminthic infections the normal secretions and excretion of the growing larvae and product release from dead cells may give rise to: o Schistosomes cause cercarial dermatitis and eosinophilia. o D. medinensis and T. spiralis infection cause urticarial and eosinophilia. o Rupture of hydatid cyst may precipitate anaphylaxis. Neoplasia  Parasitic infection may contribute to the development of neoplastic growth, e.g o C. sinensis and Opisthorchis viverrini have associated with cholangiocarcinoma o S. haematobium with vesical carcinoma Main classes of antibodies (immunoglobulin)  IgM – first to appear marking the presence of acute infection  IgG – most abundant types in parasitic infection  IgE- high in the presence of helminth and Ectoparasite  In most of the parasitic infection immunity last only till original infection remain active known as concomitant immunity.  Protective immune response to parasitic infection: o Cytotoxic T (Tc) cells o Natural killer (NK) cells o Activated macrophages o Antibody (produced by B-cell)  Immunocompromised host are vulnerable to infections. These include:  Acquired immunodeficiency syndrome (AIDS)  Transplant patient  Cancer patients  Patient receiving steroid Parasites known to cause serious infection in these individual include:  Protozoans toxoplasma Gondii  Pneumocystis carini in AIDS  Cryptosporidium parvum  Isospora belli  Cyclospora cayetanesis  Species of microsporidia  Helminth strongyloides steroratis  Wash hands with soap and water o before eating o before food prep o after touching raw meat o after using the toilet o after changing a diaper or caring for someone who is sick o after touching an animal or animal waste  Never eat raw or undercooked meat or poultry.  Avoid cross-contamination during food prep by keeping meat separate from other foods.  Disinfect all cutting boards, utensils, and countertops that touched raw meat.  Don’t walk barefoot in places where soil may be contaminated by faeces.  Clean up animal waste.  When traveling, be sure to: o Be aware of how your food is prepared. o Drink only bottled water. o Carry hand sanitizer. Soap and water is best, but if you don’t have access to soap and running water it can help prevent parasitic worm infection.  Practice safe sex, using a condom.  The preventive use of chloroquine (Nivaquine) for long periods when travelling in areas where malaria is endemic Purpose  To establish or exclude diagnoses.  To assess the severity of the disease process and formulate a prognosis.  To monitor the progress of the disorder.  To monitor the effectiveness of the treatment Accuracy in Laboratory Testing The following are required o The doctor’s order must be transcribed onto the correct requisition form. o All information must be written on the form including patent’s name, ID number, physician’s name, date and time of specimen collection o Pertinent data that could influence the test’s results must be included. o Collection of the specimen from the correct client must be confirmed by checking the identification band. o Laboratory results must be placed in the correct medical record.. General Guidelines o Universal precautions are always used for collecting and handling specimens. o Specimens are transported in bio-hazard bags ALWAYS! o Transport specimens immediately to the laboratory A fecal (stool) exam, also called an ova and parasite test (O&P)  This test is used to find parasites that cause diarrhea, loose or watery stools, cramping, flatulence (gas) and other abdominal illness.  This test looks for ova (eggs) or the parasite.  Specimen for parasitic examination must be collected properly and transported to the laboratory without delay.  Improper specimen collection can lead to inability to identify parasites or incorrect interpretation of result.  Faecal should be collected in clean, wide mouthed container with tight fitting lid and sealed in plastic bag for transportation.  Allspecimens should be collected before radiologic, antibiotic therapy and antidiarrheal medication to prevent interference in detection or identification of parasites.  If therapy has began stool should not be collected until 5 - 7days after completion of therapy.  Prevent contamination of stool specimen with urine or water which might harm existing organism of introducing free living organism from the environment  Pre-therapy specimen for intestinal parasite’ o A series of 3 specimen to be collected on alternate days (within no more than 10 day interval) o 6 specimen may be ordered if intestinal amoeba is suspected (should be completed within no more than 14 days) (If any stool tested positive, the remaining series is unnecessary)  Post-therapy stool specimen for protozoan infection o A series 3 specimen - to confirm effectiveness of treatment  Cellophane tape preps or scotch tape test commonly procedure for the recovery of Enterobius vermicularis (pinworm) egg.  The adult female Enterobius vermicularis migrates out of the anus at night and deposits the eggs over the perianal area.  Specimen should be collected in the morning before patient baths or defecate.  Daily consecutive specimens at least 4 should be obtained before the patient is considered infection free.  May be ordered on patient with suspected amebiasis or maybe performed to monitor progress of disease.  Procedure for recovery of Entamoeba histolytica  Others commonly recovered during sigmoidoscopy include: o Cryptosporidium parvum or Giardia lamblia o Helminths  Specimen of choice for recovery of the eggs of the lung fluke, Paragonimus westermani.  Specimen should be collected in the early morning and delivered to the laboratory in a tight seal sterile container  A proper specimen should be from the lower respiratory tract.  Scrapping of the mouth to examine for Entamoeba gingivalis and Trichomonas tenax which cause parasitic infection of the mouth.  Nasal discharge is collected and examined for presence of Naegleria fowleri  Obtained specimen in a sterile container.  Tissue biopsy for patient suspected of cutaneous parasitic infections to examine for Leishmania braziliensis  Skinsnips to examine for Onchocerca volvulus  To examine for Schistosoma haematobium eggs.  Also indicated for detection of microfilariae  Trichomonas vaginalis trophozoites are often recovered in the urinary sediment of infected female and male  Urethral and vagina discharge are examined for the presence of Trichomonas vaginalis  Theaspiration of cerebrospinal fluid (CSF) from the subarachnoid space. Also called spinal tap.  CSF is examined for Naegleria, Toxoplasma, trypanosome. Patient with these infection will exhibit symptoms of meningitis  Specimen of choice for recovery of plasmodium species, Babesia species, trypanosome, microfilariae. Thick and thin blood smear should be prepared.  Blood samples can be obtained from fingertip, earlobe or venepuncture  Wuchereria bancrofti, Brugia malayi exhibit a nocturnal periodicity – therefore collect sample after 10 pm (most microfilariae are present.  The slides should be clean, unscratched and grease –free. Slides should be alcohol- cleaned and dried before using Specimen types Possible parasites Cellophane tape prep Enterobius vermicularis eggs (pinworms) Sigmoidoscopy material Entamoeba histolytica Intestinal protozoa Cryptosporidium parvum Sputum Paragonimus westermani Strongyloides stercoralis Ascaris lumbercoides Hookworm Entamoeba histolytica Echinococcus species Specimen types Possible parasites Aspirates Giardia lambia Duodenal Isospora belli Strongyloides stercoralis Cyrptosporidium parvum Liver or lung abscess Entamoeba histolytica Liver or lung cyst Echinococcus species Bronchoscopy material Pneumocystis carinii Toxoplasma gondii Cyrptosporidium parvum Specimen types Possible parasites Urine Schistosoma haematobium Microfilariae Trichomonas vaginalis Urethral discharge Trichomonas vaginalis Vaginal discharge Trichomonas vaginalis Prostatic secretions Trichomonas vaginalis Nasal discharge Naegleria fowleri Mouth scrapping Entamoeba gingivalis Trichomonas tenax Corneal scrapping Acanthamoeba species Specimen types Possible parasites Specimen types Possible parasites Tissue biopsy Skin ulcer Leishmania species Skin snip Onchocerca volvulus Mansonella streptococcus Lymph node Leishmania species Bone marrow Leishmania species Trypanosoma species Toxoplasma gondii Muscle Trichinella spiralis Specimen types Possible parasites Blood Plasmodium species Babesia species Leishmania species Trypanosoma species Microfilariae Skin tests Performed by intradermal injection of parasitic antigens and are read as follows 1. Immediate Reveal wheal and flare response Hypersensitivity reaction within 30 minutes