MIM 33 Introduction to Parasitology (Fall 2024) PDF

MIM 33 Introduction to Parasitology Blood & Tissue Protozoa...

MIM 33 Introduction to Parasitology Blood & Tissue Protozoa Terri S. Hamrick, PhD Office #167 (910) 893-1705 [email protected] The copyrighted materials available in this class are for educational use only. One copy per student is permitted for educational purposes. Redistribution is not permitted. MIM –Block 1 Fall 2024 https://www.grc.org/biology-of-spirochetes-conference/2024/  Readings 1. Lippincott’s Illustrated Reviews: Microbiology, Cornelissen, NA and Hobbs, MM (editors) 2019, 4th ed. Wolters Kluwer. Chapter 21 2. W. Levinson, 2022, Review of Medical Microbiology and Immunology 18th Ed., Chapters 52. Learning objectives 1. Describe the basic classification of medically important helminths and protozoa. 2. Define definitive, intermediate, and dead-end hosts, reservoirs, and vectors in parasite life cycles. 3. Explain the general protozoal replication cycles and identify their metabolic active and dormant phases. 4. Describe the morphological characteristics, clinical manifestations, epidemiology, and diagnosis of Trichomonas vaginalis/trichomoniasis. 5. Identify the definitive host, dead-end host, and reservoir/intermediate host of Toxoplasma gondii. 6. Explain the life cycle of T. gondii and describe the biological significances and morphological characteristics of oocyst, trophozoite, and tissue cyst during the course of an infection. 7. Describe the clinical manifestations and diagnosis of toxoplasmosis. 8. Identify, compare, and contrast the etiologies, vectors, and reservoirs of the two common blood protozoa infections. 9. Explain the pathogenesis of malaria and relate the parasite’s life cycle to transmission and clinical manifestations. 10. Compare and contrast the diagnostic findings and clinical manifestations in P. falciparum and P. vivax malarias. 3 Presentation Outline Basic parasitology Urogenital protozoa: Trichomonas vaginalis Tissue protozoa: Toxoplasma gondii Blood protozoa: Plasmodium sp.  Helminth: Protozoa: multicellular single-celled worms 5 Terminology Hosts Definitive host: adult and sexual cycle Intermediate host: asexual cycle or larva stage Dead-end host: parasite not transmitted to others Reservoir: habitat or population of organisms that can transmit to others. Could be humans, animals, or the environment Vector: an organism (usually an insect) that is responsible for transmission. It might be important for the parasite life-cycle. 6  Helminths: Worms Macroscopic Cestodes (tapeworms) Ribbon-like, segmented worms; intestine Individual species generally inhabit a Trematodes (flukes) specific location (often Small, flat, leaf-like worms; various organs intestine), some may Freshwater snails, intermediate host disseminate to vital Nematodes (roundworms) organs Nonsegmented worms Mode of transmission varies with species: Ingestion of larvae in raw or undercooked meat Ingestion of eggs in feces Transmission by insect bites Direct skin penetration 7  Intestinal Protozoa Urogenital Blood and tissues Unicellular, eukaryotic organisms; cell membrane, only Some have dormant, environmentally stable cysts Classified by infection site and mode of locomotion Note: eukaryotic– so not as many unique targets for Tx. Microscopic 8  Life Cycle and Replication of Protozoa Many are unable to withstand desiccation in the external environment Transmission depends mostly on arthropod vectors or direct contact Phases: (can have specific terms for different protozoa) Trophozoite: active form, grows and replicates by binary fission within the host Cyst: dormant, non-replicating form adapted for survival Presentation Outline Basic parasitology Urogenital protozoa: Trichomonas vaginalis Tissue protozoa: Toxoplasma gondii Blood protozoa: Plasmodium sp. Trichomonas vaginalis Single-celled, pear-shaped with ruffled, undulating membrane edge and flagella Most common protozoal urogenital tract infection of humans No cyst form Not a reportable STI Sexually transmitted Not routinely screened for except in Humans only natural host specific circumstances 11  Trichomoniasis Women: vaginitis, frothy creamy (yellow), malodorous discharge; itchy and burning Increased pH associated with infection Men: majority asymptomatic; mild urethritis, epididymitis, or prostatitis in 10% Associated HIV infections and pelvic inflammatory diseases. Reinfection very common.  Diagnosis and Management of Trichomoniasis § No serologic test § Vaginal pH and microscopy § Specimens: urethral (males) or vaginal (female) swab § Microscopic detection of motile, flagellated trophozoites in FRESH wet preparations of secretions for women; inexpensive but low sensitivity. § Nucleic acid amplification tests (NAATs) are highly specific and sensitive. § Treatment: metronidazole § Hint: protozoans and anaerobes § Partners are treated together § Women are often tested again after Tx Presentation Outline Basic parasitology Urogenital protozoa: Trichomonas vaginalis Tissue protozoa: Toxoplasma gondii Blood protozoa: Plasmodium sp.  Toxoplasma gondii Intracellular sporozoan Infects vertebrate species– cats are the definitive host Immunocompromised: Primary infection: Latent infection for life reactivation (CNS usually asymptomatic abscess-like) Some immunocompetent: acute systemic infection or ocular disease 15  Life Cycle of Toxoplasma oocysts gondii § Definitive host: domestic cats and their relatives Tissue Cyst § Dead-end host: with bradyzoites human § Reservoir: any worm-blood animals; environment oocysts  Transmission of Toxoplasma gondii § Cats ingest toxo (any form): parasite infects gut epithelium and reproduces § Cats excrete infectious oocytes in feces (note: oocysts require1-5 days to become infectious) § Intermediate hosts acquire the infection (infective oocysts) § Oocysts transform into tachyzoites (fast-growing trophozoites) after ingestion. Tachyzoites develop into tissue cyst bradyzoites (slow-growing) /cystozoites in neural and muscle tissue. § Humans can become infected by: 1. Eating undercooked meat of animals harboring tissue cysts 2. Exposure to food or water contaminated with cat feces or environmental samples 3. Drinking unpasteurized milk, contaminate seafood (raw) 4. Blood transfusion or organ transplantation 5. Transplacentally from mother to fetus  Oocysts of Toxoplasma gondii Sexual reproduction takes place in the intestinal epithelium of the cat host, and oocysts are shed unsporulated in the feces (blue arrow and panel A). In the environment, oocysts sporulate and become infective (red arrow and panel B) Ingestion of the sporozoites in oocyst à infection The main form spread by fecal- oral route Can be destroyed at >66oC. Dubey JPLindsay DS, Speer CA. 1998. Clin Microbiol Rev 11:.https://doi.org/10.1128/cmr.11.2.267 Tachyzoites/Trophozoites of Toxoplasma gondii Trophozoites in a Asexual, proliferative form macrophage Responsible for tissue invasion and clinical diseases Can NOT survive digestive activity in the stomach This is not the form to acquire the infection  Tissue Cysts of Toxoplasma gondii § Most commonly found in the brain and skeletal and cardiac muscles of the infected hosts § Consists of bradyzoites– more resistant to acid § Latent cysts can revert and release invasive trophozoites when host is immunocompromised) Spherical cyst in the Elongated cyst in the brain cardiac muscle of an AIDS patient  Clinical Significances of T. gondii 50% US population are infected; the infection remains inactive unless the person becomes immunosuppressed. Clinical Manifestations: Mononucleosis-like syndrome: lymphadenopathy; mild Congenital infection when the mother is infected acutely during pregnancy Encephalitis or myocarditis (in immunocompromised hosts; high mortality). Infections during pregnancy Tachyzoites cross the placenta following primary maternal infection Congenital toxoplasmosis is often asymptomatic at birth Symptomatic: Moderate disease: intracranial calcifications, peripheral retinochoroiditis Severe disease: multiorgan, hydrocephalus, macular retinochoroiditis Treatment initiated after confirmation: choice PCR of regimen is complicated. 22  Diagnosis of Toxoplasmosis T. gondii serologic profile (TSP): Assays for different isotypes of antibodies (IgM, IgE, IgA, IgG); attention to increasing titers is essential to differentiate past and recent infections. Acute (primary, recent): IgG? IgM? Confirmatory IgG 2 weeks later Reactivation: Usually IgM negative and IgG positive (Might also need PCR test) (sometimes IgM stays around) Presentation Outline Basic parasitology Urogenital protozoa: Trichomonas vaginalis Tissue protozoa: Toxoplasma gondii Blood protozoa: Plasmodium sp.  BLOOD PROTOZOA INFECTIONS ORGANISM Human cell RESERVOI MODE OF CLINICAL (disease) infected R TRANSMISSION MANIFESTATIONS Vector-borne by the Fever and chills Plasmodium Infected female Anopheles with red blood cell sp. (malaria) Red blood cells humans mosquito lysis Fever and chills Babesia sp. Rodents, Vector-borne by with red blood cell Red blood cells (babesiosis) deer, mice Ixodes tick lysis  Babesia Plasmodium Ring-form Pleomorphic tends to be (vary in shape uniform and size) Not Can be vacuolated vacuolated Pigmented No pigment 26  Malaria In 2022, the global tally of malaria cases reached 249 million Natural disasters, climate change, extreme weather can all affect the behavior and survival of the malaria-carrying Anopheles mosquito Malaria disease– cyclic fevers, headache, anemia, splenomegaly.  Malarial Parasites: Plasmodium sp Four species of the Plasmodium protozoa (humans) Species distribution varies by geography Utilize humans almost exclusively as intermediate host P. falciparum: most dangerous; infect RBCs in all stages P. vivax Milder forms; infect young P. ovale or old RBCs P. malariae Note: P. knowlesi zoonotic malaria in people – normally in simians  General sequence: Ø Anopheles mosquito Ø Bite (mosquito is the vector) Ø Liver (a sexual reproduction) Ø Red blood cells– growth (asexual reproduction), rupture of RBCs, re-entry to RBCs (cyclic fevers) Ø Gametogenesis Ø Picked up by a mosquito (sexual reproduction of plasmodium) Different species of Plasmodium behave differently throughout the life cycle sequence Don’t learn the drugs now. 29 Organism Transmission Cyclic fever Liver phase Blood Smear Diagnosis P. malariae Anopheles 72-hr fever Not dormant Blood smear; trophozoite ring in mosquito cycle RBC RDT P. vivax Anopheles 48-hr fever Dormant form Blood smear with trophozoites and P. ovale mosquito cycle (hypnozoite) Schüffner stippling (small red granules) within RBC cytoplasm RDT P. falciparum Anopheles Severe, irregular Not dormant Blood smear with trophozoite ring mosquito pattern; (headphone- shaped) within RBC; parasitized RBCs crescent-shaped gametocytes may occlude RDT capillaries Babesia sp. Ixodes tick Fever and None Blood smear: ring form, and hemolytic anemia “maltese cross”; PCR (asplenia increases risk of severe disease) Malaria: Rapid diagnostic tests (RDT) are available and can ID species PCR for malaria in reference labs 30  Lab Diagnosis of Malaria Detection of the parasite inside red blood using blood smear (gold standard) Serologic tests not helpful Rapid diagnostic tests PCR would be sensitive but not quick enough in the clinical setting Gametocytes Definitions: Sporozoites: the version injected from the mosquito– infect hepatocytes Merozoites: the result of asexual reproduction- in the liver to infect RBCs; in the RBCs to infect new RBCs Hypnozoite: dormant liver version (P. vivax and P. ovale) Trophozoites: in the red blood cells– they are the form that causes disease Schizont: collection of the replicating parasites (liver schizont, erythrocytic schizont) Gametocytes: the male and female versions of the parasite 32  Life Cycle and Transmission Of Plasmodium qAnopheles mosquito is the vector § Host for sexual reproductive stages. q Humans: host for asexual reproductive stages. q Other forms of transmission § Transfusion; needles § Congenital Lippincott’s Illustrated Reviews  Parasite Life Cycle and Pathogenesis (cont.) Blood-stage parasites are responsible for the clinical disease (fevers, anemia, etc.): § The merozoites à RBCs and become trophozoites, which use hemoglobin as a nutrient; eventually, the infected red cells rupture. § Paroxysm (sudden onset) of fever correlates with simultaneous rupture of large numbers of RBCs. Malarial Parasites In RBCs Crescent  P. falciparum diagnostic Ring forms– lots of infected red cells (characteristic of P. falciparum) Crescent shaped gametocytes (characteristic of P. falciparum) Image source: CDC Public Health Image Library (PHIL), ID#5856  P. vivax in RBCs P. vivax infects reticulocytes– so not a lot of the red cells are going to be infected, and the red cells that are infected will be big Public health image library, ID # 3709  Prevention Of Malaria Control mosquitos and limit bites Prophylaxis: check with Infectious Diseases Vaccine development: Has been challenging 2 vaccines currently recommended for children in P. falciparum regions  MAJOR REFERENCES Lippincott’s Illustrated Reviews: Microbiology, Cornelissen, NA and Hobbs, MM (editors) 2019, 4th ed. Wolters Kluwer. Review of Medical Microbiology and Immunology by Warren Levinson, 18th Ed. 2024, McGraw Hill. UpToDate: Toxoplasmosis and pregnancy. Authors: Eskild Petersen, MD, DMSc, DTM & H Laurent Mandelbrot, MD. Updated: May 20, 2024. Malaria: Clinical manifestations and diagnosis in nonpregnant adults and children Laboratory tools for diagnosis of malaria Trichomoniasis: Clinical manifestations and diagnosis, Updated, July 17, 2023.