9 bio265 viruses, fungi, protozoa, helminths instructor dr di bonaventura
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Introduction to viruses, fungi protozoa, and helminths
Introduction to viruses
Viruses cause infections and disease as pathogenic bacteria, fungi or protozoa do
Are obligate intracellular parasites Require living host cells to multiply
Viruses consist of a(n)
DNA or RNA genome Protein coat (capsid made of capsomers) Envelope: not always present (derived from the plasma
membrane of the host cell) Surface proteins/glycoproteins (spikes) that bind to receptors
of host cells
Host range of viruses
Viruses can infect bacteria (bacteriophages) fungi protozoa plants animals
Certain viruses can infect one species or even a particular
cell type within a given host HIV and T cells
Some others can infect a wider range of hosts
Flu virus, WNV (West Nile virus)
Host range of viruses
Eight segments of ssRNA
Antigenic shift
Size of viruses
Examples of shape of viruses
Polyhedral Complex
Common cold virus - ssRNA
Rabies virus - ssRNA
Smallpox virus - dsDNA
ssRNA virus
Helical
Viral envelopes
Envelopes are acquired from the membrane of the host cell
Viruses can attach to host cells using their spikes Influenza virus undergoes changes in its spikes (antigenic drift)
resulting in new strains!!!!
Influenza virus causes infection of the lower respiratory tract
Influenza virus budding from a host cell
Infects epithelial cells lining the lungs
Death of the cells eliminates the lung’s first line of defense against infection
Flu patients become susceptible to
secondary bacterial infections such as Haemophilus influenzae
Viruses are released by coughing or sneezing
Elderly, young children, people with chronic diseases are at risk of bronchitis, pneumonia, heart failure
A scene from the flu pandemic of 1918-19
Killed millions of people (influenza A virus - strain H1N1)
Replication of animal viruses
Replication can be summarized into five basic steps Attachment to the host cell
Entry of the virus or its genome Synthesis of viral DNA or RNA
and viral proteins
Assembly of virus Nucleus or cytoplasm
Release
Replication of animal viruses
Release of viruses from infected cells Enveloped viruses
Budding
Nonenveloped viruses Exocytosis
Or lysis and death
of the cells
AIDS (Acquired immunodeficiency syndrome)
Opportunistic infections associated with low CD4 T cells and infection by HIV
HIV is a retrovirus Structure
Two major types
HIV-1 HIV-2
Estimated to have emerged in the human population around 1930
HIV attachment
Active HIV infection
Latent HIV infection
HIV infection of CD4 T cells (Helper T cells)
Opportunistic infections associated with AIDS
HIV transmission
HIV is found in blood, semen, vaginal secretions, saliva, or breast milk
Must be injected into the body or contact a lesion in the skin or mucous membranes
Infected body fluids transmit HIV via Sexual contact Intravenous drug use Blood-contaminated needles Blood transfusion Organ transplants Placenta and breast milk
The global distribution of HIV/AIDS
Certain behaviors increase risk of infection: anal intercourse, sexual promiscuity, and intravenous drug use
HIV
Diagnosis
Detection of antibodies against HIV
Seroconversion may take up to 3
months
Plasma viral load (PVL) Detects viral nucleic acid (RNA)
Chemotherapy
HAART (Highly Active Antiretroviral
Therapy)
Cocktail of several antiviral drugs
Reduces viral replication, but
infection remains
Vaccine development has been
problematic
Mutations, subtypes
Antibody-binding sites “hidden”
Latency and reservoirs of the virus
Preventing AIDS
Use of condoms, reciprocal monogamy, use of sterile needles Health care workers use Universal Precautions (CDC)
Fungi
The study of fungi is called mycology
Fungi
Cell type Eukaryotic
Metabolism Chemoheterotrophs
Oxygen Aerobic or facultative anaerobes; few anaerobes
Cellular arrangement Unicellular; filamentous
Reproduction Budding; fission; Sexual and asexual spores
Fungi are beneficial: decomposers of plant and animal matter, symbiotic fungi (plants), used by human to produce foods and drugs
Out of thousands of species, few hundreds are pathogenic to humans and animals
Molds (filamentous fungi)
The fungal body is called thallus and consists of hyphae A mass of hyphae is called mycelium
Colony characteristics Opportunistic fungus
Yeasts are non-filamentous fungi
Unicellular fungi
Reproduce by fission or budding
Saccharomyces cerevisiae (not of clinical significance)
Candida albicans is an
opportunistic pathogen
Attaches to human epithelial cells as a yeast
Usually it requires pseudohyphae to invade deeper tissues In this form is resistant
to phagocytosis Buds form a short chain of cells
called a pseudohypha
Fungal Dimorphism
Histoplasma capsulatum is a pathogenic dimorphic fungus
Examples of pathogenic dimorphic fungi Blastomyces dermatitidis Coccidioides immitis Paracoccidioides brasilensis
Clinical identification Yeasts Biochemical analysis Filamentous fungi Colony Characteristics Microscopic analysis of asexual spores
Mycosis are usually chronic infections
Superficial Surface of epidermal cells
Cutaneous Epidermis, hair, nails
Subcutaneous Occur beneath the skin
Systemic From lungs spread to other body tissues
Opportunistic
Debilitated/traumatized hosts, under treatment
with broad-spectrum antibiotics, immune system
suppressed by drugs, immune disorder (AIDS)
Any fungal infection is called mycosis
Examples
Superficial Black piedra - Piedra hortae - hair shafts
Cutaneous Tineas: ring worm and athlete’s foot
Pityriasis caused by Malassezia furfur*
Subcutaneous Sporotrix schenckii
Systemic
Blastomyces dermatitidis
Coccidioides immitis
Paracoccidioides brasiliensis
Histoplasma capsulatum
Cryptococcus neoformans (meningitis)
Opportunistic Mucor, Aspergillus, Candida*
Piedra hortae - hair shafts
Tineas: ring worm and athlete’s
foot
Protozoa are a large and diverse group
Protozoa inhabit water and soil
Relatively few cause human disease but with a significant impact: malaria is the fourth leading cause of death in the world
Protozoa
Cell type Eukaryotic
Cellular arrangement Unicellular
Metabolism Chemoeterotrophs
Oxygen Aerobic; anaerobic growth (intestinal protozoa)
Asexual reproduction Fission; budding; schizogony
Sexual reproduction Can produce gametocytes
Characteristic features Motility; cyst
Classification is currently based on rRNA sequences
Protozoa – Amoebozoa (amoebas)
Move by pseudopods
Acanthamoeba is a free-living amoeba found in water, including tap water Can infect the cornea and cause blindness
Protozoa – Amoebozoa (amoebas)
Pathogenic amoeba
Found in the human intestine, causes amebic dysentery
Transmitted through
ingestion of cysts excreted in the feces of infected person
Presence of ingested red blood cells is diagnostic of Entamoeba
Protozoa - Archaezoa
Giardia lamblia also called G. intestinalis or G. duodenalis
Found in the small intestine of humans and other mammals Trophozoite is the feeding and growing stage Cyst is the survival stage before being ingested by the next host
Diagnosis of giardiasis is based on the identification of cysts in feces
Protozoa – Apicomplexa Plasmodium species – The life cycle of P. vivax
Laboratory diagnosis: blood smear examined for the presence of Plasmodium
Plasmodium
Ring-stage - trophozoites within red blood cells
Protozoa – Euglenozoa
Hemoflagellates (blood parasites)
Transmitted by the bites of blood-feeding insects
Found in the circulatory system of the bitten host
Trypanosoma
Trypanosoma brucei gambiense (Sleeping sickness – Africa) Transmitted by the tsetse fly
Trypanosoma cruzei (Chagas’ disease - cardiovascular system) Transmitted by the kissing bug
Nucleus of Trypanosoma
Protozoa - Archaezoa Trichomonas vaginalis
Human parasite
Found in the vagina and in the male urinary tract
Transmitted by sexual intercourse
Multiple flagella (flagellate) No cyst stage – must be transferred from host to host quickly
before desiccation occurs
Parasitic helminths
Parasitic helminths
Cell type Multicellular eukaryotic animals
Nutrition Absorbs nutrient from their hosts
Cellular arrangement Tissues and organs Reduced digestive system or absent Reduced nervous system Reduced locomotion or absent
Reproductive system Complex
Trematodes (flukes) and Cestodes (tapeworms) Nematodes (round worms)
Parasitic helminths – Life cycle
The life cycle can involve Multiple intermediate hosts needed for the development of
the larval stages Definitive host for the adult parasite
Reproductive systems Separate male and female reproductive systems Hermaphroditic
Male and female reproductive systems in one animal
Egg larva(e) adult
Trematodes - flukes
Flukes are given names according to the tissue of the definitive host in which the adults lives
Lung fluke, liver fluke, blood fluke
Cause progressive damage to tissues and organs
The blood fluke Schistosoma will be discussed in a later lecture
Lung fluke Paragonimus westermani
Laboratory diagnosis: sputum and feces examined for fluke eggs
Cestodes (tape worms)
Cestodes are intestinal parasites
Absorb food through their cuticle
Diagnosis is based on the presence of mature proglottids and eggs in the feces
Cestodes (tape worms)
Common cestoda beef tapeworm, Taenia saginata pork tapeworm, Taenia solium
Cattle and pork are intermediate hosts
The larvae migrate to their muscles in which they encyst (cysticercus) Cysticerci can be seen macroscopically in meat (measly
meat) Human infection
Caused by ingestion of undercooked infected beef and pork (measly meat)
Cysticercosis in humans occurs when they ingest T. solium eggs cysticerci can form in muscle and brain
Nematodes (round worms)
Eggs infective for humans: Enterobius vermicularis (large intestine) and Ascaris lumbricoides (small intestine)
E. vermicularis: The female migrates to the anus to deposit her eggs on the perianal skin at night (Diagnosis: Graham sticky-tape method)
Nematodes (round worms)
Ascaris lumbricoides Infects over one billion people worldwide Small intestine: feeds on partially digested foods Eggs excreted with feces can survive for long periods
Nematodes (round worms)
Hookworms: Necator americanus and Ancylostoma duodenale Larvae infective for humans by penetrating the host’s skin Live in the small intestine of humans Feed on blood and tissue rather than on partially digested
foods, leading to anemia
Ancylostoma hookworm attached to intestinal mucosa
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