Medically Important Fungi and Parasites PDF

Medically important fungi and parasites Dr Samson Wong Department of Microbiology BMSC3104 BMSN2603 • Describe the basic classification and morphology of medically important fungi and parasites. • List locally important examples fungi and parasites causing human infections. • Understand the types...

Medically important fungi and parasites Dr Samson Wong Department of Microbiology BMSC3104 BMSN2603 • Describe the basic classification and morphology of medically important fungi and parasites. • List locally important examples fungi and parasites causing human infections. • Understand the types of infection caused by fungi and parasites. Learning objectives • Describe the life cycle and vector for transmission of malaria parasites. • Bacteria • Fungi • Viruses • Parasites • Prions Pathogenic microorganisms • Eukaryotes. • Cells encased in a hard cell wall made up of chitin and glucan. • Reproduce by forming spores, budding, or fission. • No division of cells into organs or tissues. • Saprophytes, commensals, or parasites. What are fungi? • Independent single cells. • Hyphae (a chain of tubular, filament-like cells). Basic units of fungi Two ways to classify fungi that cause disease: by growth form and by type of infection. (A) Hyphae in skin scraping from ringworm lesion. (B) Spherical yeasts of Histoplasma. Goering RV, Dockrell HM, Zuckerman M, Chiodini PL. Mims’ Medical Microbiology and Immunology, 6th edition. Elsevier. 2019. Candida albicans: yeast. Long arrow points to a budding yeast. Candida albicans: pseudohyphae. Two arrows point to pseudohyphae of Candida albicans. • Yeasts • Moulds • Dimorphic fungi • Pneumocystis jirovecii (P. carinii) Classification of fungi (based on morphology) Candida albicans, a yeast. Example of a mould. Reiss E, Shadomy HJ, Lyon III GM. Fundamental Medical Mycology. Wiley‐Blackwell. 2012. • Body site of infection. • Superficial mycoses. • Subcutaneous mycoses. • Deep/systemic mycoses. Classification of fungal infections (mycoses) • Nature of patients. • Immunocompetent patients. • Immunocompromised patients. • Can occur in completely healthy individuals. Superficial mycoses Examples Pathogens Tinea (ringworm) Dermatophytes (Trichophyton, Microsporum, Epidermophyton) Candidiasis Candida, e.g. Candida albicans Pityriasis versicolor Malassezia furfur Tinea infection (ringworm) Candida albicans: diaper rash. Note extensive area of inflammation in perineal region. Deep mycoses Examples Pathogens Fungaemia Various fungi, usually yeasts such as Candida Systemic candidiasis Candida Cryptococcosis Cryptococcus neoformans Aspergillosis Aspergillus Talaromycosis (penicilliosis) Talaromyces (Penicillium) marneffei Fungi as hospitalacquired pathogens Infection Predisposing factors Fungaemia Secondary to catheter-related infections, intra-abdominal infections, etc. Other invasive fungal infections Often in compromised hosts • Cryptococcus neoformans. • Diseases. • Pulmonary infections (nodules, pneumonia). • Central nervous system infections (meningitis). • AIDS-defining illness. Cryptococcosis Cryptococcus neoformans. Indian ink preparation. Arrow points to a budding yeast of Cryptococcus neoformans. Note the thick, translucent polysaccharide capsule outlined by the dark Indian ink particles. • Aspergillus fumigatus, A. flavus, etc. • Commonest in lungs of immunocompromised patients (e.g. neutropenic patients, those on immunosuppressants). Aspergillosis Desoubeaux G, Bailly É, Chandenier J. Diagnosis of invasive pulmonary aspergillosis: updates and recommendations. Med Mal Infect 2014;44:89–101. Aspergillus fumigatus: septate hyphae. Long arrow points to the septate hyphae of Aspergillus. • Talaromyces (Penicillium) marneffei. • The only ‘Penicillium’ species that is: • Regularly pathogenic to humans. • Dimorphic. • Found only in southeast and south Asia. Talaromycosis (penicilliosis) • Association with AIDS patients and other immunocompromised patients. • AIDS-defining illness in Southeast Asia. SYN Wong, KF Wong. Penicillium marneffei Infection in AIDS. Pathology Research International 2011. Murray PR, Rosenthal KS, Pfaller MA. Medical Microbiology, 9th edition. Elsevier. 2021. • Commonest form of infection: pneumonitis. • Mainly seen in immunocompromised hosts: • AIDS patients. • Transplant recipients. • Patients on corticosteroids. Pneumocystis jirovecii (P. carinii) • The commonest AIDS-defining illness in Hong Kong. • Laboratory diagnosis. • Cannot be cultured in the laboratory using routine methods. • Diagnosis confirmed by microscopy using special stains (e.g. methenamine silver stain). https://www.msdmanuals.com/professional/pulmonary-disorders/pneumonia/pneumocystis-jirovecii-pneumonia https://webpath.med.utah.edu/HISTHTML/STAINS/STAIN022.html • Clinical suspicion. • Radiological suspicion. • Microscopy. • Fungal culture. • Antigens of fungi in blood or body fluids. Diagnosing fungal infections • e.g. cryptococcal antigen (polysaccharide capsular component of Cryptococccus neoformans). • Histopathology. • Nucleic acid amplification. Mucor species: non-septate hyphae. Arrow points to irregular-shaped, non-septate hyphae of Mucor. • Protozoa and helminths. • Protozoa. • Nematodes. • Trematodes. • Cestodes. Classification of parasites • Ectoparasites. • Infection • Invasion by endoparasites. • Infestation • External parasitism by ectoparasites. • Unicellular organisms. • Lumen-dwelling protozoa Protozoa • Blood and tissue protozoa • Plasmodium spp. • Entamoeba histolytica • Trypanosoma spp. • Giardia lamblia • Leishmania spp. • Trichomonas vaginalis • Toxoplasma gondii • Cryptosporidium parvum • Babesia spp. • Cystoisospora belli • Cyclospora cayatanensis • Microsporidia … • Naegleria fowleri • Acanthamoeba spp. … Trophozoites Cysts Peterson KM, Singh U, Petri WA, Jr. Enteric amebiasis. In: Guerrant RL, Walker DH, Weller PF (ed). Tropical infectious diseases: principles, pathogens and practice. 3rd edition. 2011. Elsevier. https://www.cdc.gov/dpdx/amebiasis/index.html Giardiasis https://www.cdc.gov/dpdx/amebiasis/index.html https://www.cdc.gov/dpdx/giardiasis/index.html https://www.cdc.gov/dpdx/giardiasis/index.html • Round worms. • Intestinal nematodes Nematodes • Blood and tissue nematodes • Ascaris lumbricoides • Wuchereria bancrofti • Enterobius vermicularis • Brugia malayi • Trichinella spiralis • Trichuris trichiura • Onchocerca volvulus • Strongyloides stercoralis • Loa loa … • Dracunculus medinensis … https://www.cdc.gov/dpdx/ascariasis/index.html https://www.cdc.gov/dpdx/ascariasis/index.html https://www.cdc.gov/dpdx/enterobiasis/index.html https://www.cdc.gov/dpdx/enterobiasis/index.html https://www.cdc.gov/dpdx/lymphaticfilariasis/index.html https://www.cdc.gov/dpdx/lymphaticfilariasis/index.html Lymphatic filariasis Peters W, Gilles HM. 1989. • Flukes. • Liver flukes. • Clonorchis sinensis. • Opisthorchis spp. • Fasciola hepatica. • Intestinal flukes. Trematodes • Fasciolopsis buski. • Blood flukes. • Schistosoma mansoni. • S. japonicum. • S. haematobium. • Lung flukes. • Paragonimus westermani … https://www.cdc.gov/dpdx/clonorchiasis/index.html https://www.cdc.gov/dpdx/clonorchiasis/index.html • Tapeworms. • Intestinal tapeworms. • Taenia solium • Taenia saginata • Diphyllobothrium latum • Hymenolepis nana Cestodes … • Tissue tapeworms. • Cysticercosis • Hydatid disease (Echinococcus) … https://www.cdc.gov/dpdx/diphyllobothriasis/index.html https://www.cdc.gov/dpdx/diphyllobothriasis/index.html Taeniasis https://www.cdc.gov/dpdx/taeniasis/index.html https://www.cdc.gov/dpdx/cysticercosis/index.html https://www.cdc.gov/dpdx/taeniasis/index.html Garcia HH, Nash TE, del Brutto OH. Clinical symptoms, diagnosis, and treatment of neurocysticercosis. Lancet Neurol 2014;13:1202–1215. • Insects Arthropods of medical importance • Arachnids • Mosquitoes • Ticks • Blackflies • Mites • Sandflies • Spiders • Tsetse flies • Scorpions • Flies • Fleas • Lice • Bedbugs • Triatomine bugs Head and body lice https://www.cdc.gov/dpdx/pediculosis/index.html https://www.cdc.gov/dpdx/fleas/index.html Bedbug https://www.cdc.gov/dpdx/bedbugs/index.html Scabies Vasanwala FF, Ong CY, Aw CWD, How CH. Management of scabies. Singapore Med J 2019;60:281–285. • Plasmodium spp. • P. vivax. • P. falciparum. • P. malariae. • P. ovale. • P. knowlesi. Malaria • 95% cases are due to P. vivax and P. falciparum. • Most fatalities due to falciparum malaria. • Vector • Female Anopheles mosquitoes. https://ourworldindata.org/malaria • Mosquitoes • Blood transfusion, organ transplantation • Contaminated needles, drugs, instruments • Congenital Transmission of malaria Greenwood B, Bojang K, Whitty CJM, Targett GAT. Malaria. Lancet 2005;365:1487–1498. Blood films are commonly used for the diagnosis of malaria. Individual Plasmodium species are distinguished by their microscopic morphology. (Figure is for illustration only. Students are not required to remember the detailed morphological features of the parasites.) Poostchi M, Silamut K, Maude RJ, Jaeger S, Thoma G. Image analysis and machine learning for detecting malaria. Transl Res 2018;194:36–55.