INTH 301/401 Fundamental
Concepts in Global Health
Ron Blanton
CGHD, CWRU
Infectious Agents of Disease
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Viruses
Bacteria
Parasites
Viruses
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Acellular organisms
Nucleic Acids
Origins
Employ host cellular machinery to make
proteins, nucleic acid and new virus
• Do not divide
• Do not generate/manipulate energy
• Miniscule
Viral Structure
envelope
0.01-0.1 μm
protein coat
(capsid)
Negative strand
RNA polymerase
Ribosomes
DNA or RNA
Classification
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Disease
Transmission
Nucleic Acid
Sequence
Classification
• Disease
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Cold
Hepatitis
Encephalitis
Hemorrhagic fever
Oncogenic
• Transmission
• Nucleic Acid
• Sequence
Classification
• Disease
• Transmission
– Respiratory
– Enterovirus
– Arbovirus
• Nucleic Acid
• Sequence
Classification
• Disease
• Transmission
• Nucleic Acid
– DNA
– RNA
• Sequence
Nucleic Acid Classification
Classification
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Disease
Transmission
Nucleic Acid
Sequence
– International Committee on
Taxonomy of Viruses
– 7 Genera DNA viruses
– 15 Genera RNA viruses
Classification
Hemorrhagic Fever Viruses
• Disease
– Rift Valley Fever
– Marburg, Ebola
– Lassa, SAHF
– Dengue, Yellow Fever
• Nucleic Acid
– RNA
• Sequence
– Bunyavirus
– Filovirus
– Arenavirus
– Flavivirus
Life cycle
• Recognition - Receptor
• Invasion
• Transcription/translation or
translation/transcription
• Packaging
• Release
Flaviviral Replication
Viral particle = virion
Invading virion
New virions
RNA
RNA
Cell membrane
Receptor
Cap
Proteases
Mature proteins
Cap
Cap
Cap
Cap
Cap
Filoviral Replication
Viral particle = virion
Invading virion
New virions
RNA
RNA
Cell membrane
Viral polymerase
Cap Cap Cap CapCapCap CapCap
Protein synthesis
Receptor
Implications
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Rapidly reproduced to high density
Mutation
Easily transported
Wide host range (sometimes)
Limited range of viral poisons
Many modes of transmission
Viral Tramission
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Respiratory
Measles
Respiratory-oral Colds
Urine-Respiratory
Hanta pulmonary syndrome
Fecal-oral
Rotavirus diarrhea
Direct contact
Chickenpox
Veneral
HIV
Congenital
Rubella
Zoonoses
Congo-Crimean Hemorrhagic
Vector borne
Dengue
Transfusion
Cytomegalovirus
Virus and Disease
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Cytopathic effect
Inhibit DNA, RNA protein synthesis
Apotosis
Proliferation
Viral Prevention/Treatment
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Isolation (migration)
Host Response
Vaccination
Antivirals
Infectious Agents of Disease
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Viruses
Bacteria
Parasites
Bacteria
• Simple cells
• Cell membrane and wall (and envelope)
• Reproduction by division
Bacterial Structure
LPS
http://pathmicro.med.sc.edu/fox/protype.htm
Gram Staining Reveals Structure
E. coli
http://www.buddycom.com/bacteria/gnc.html
S. aureus
“Bacterial Genetics”
• Bacteria & Archea
• Eukaryotes
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Plant
Yeast
Parasites
Insects
People
Implications
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“Rapidly reproduce” in the right context
Resistance
Persistance
Mutation/Gene transfer
Toxin production
Bacterial Prevention/Treatment
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Contact
Host response
Vaccines
Antimicrobials/Antibiotics
Infectious Agents of Disease
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Viruses
Bacteria
Parasites
Parasites
• Single cell or multicellular eukaryotes living
within a larger
• Complex developmental programs
Conceptual Basis of Parasitism
SYMBIOSIS
Commensalism
Mutualism
Parasitism
Host - Parasite Relationships
• Definitive host
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Echinococcosis
Schistosomiasis
Pork tapeworm
Malaria
= Sexual reproduction
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dogs
humans
humans
mosquito
• Intermediate host =
reproduction
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Echinococcosis
Schistosomiasis
Pork tapeworm
Malaria
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humans
snail
humans
humans
Asexual
Parasitism in Human Biology and
Medicine
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Parasite – usually refers to protozoa and helminths
Distinction from other classes of infectious agents (bacteria and viruses) – historical
significance more than biological distinction
A ‘re-emerging’ cause of illness in industrialized nations.
Health impact greatest in developing nations and among impoverished people
Classification
• Eukayrotes – membrane-bound organelles
• Complex developmental programs
Epidemiology and Clinical
Characteristics
• Protozoa
(Microparasites)
• Usually acute and
transient infections
• Disease initiated by small
inoculum
• Asymptomatic, acute
• Distribution is random
• Helminths
(Macroparasites)
• Chronic and persistent
infections
• Disease related to
intensity of infection
• Asymptomatic, chronic
• Aggregated distribution
Parasitic Protozoa
Single cell organisms
Multiply in human host
Organelles analogous to tissues or organ systems
Apicomplexa
Include chloroplast-like structures
Malaria, toxoplasma
Archezoa
Lack mitochondria, anaerobic
Amebae
Giardia lamblia
Kinetoplastida
Single large mitochondria
Trypanosomes
Leishmania
Parasitic Helminths
Multicellular
Does not multiply in host
Specialized organ systems
Nematodes
Round worms
Platyhelminthes
Flat worms
Trematodes
Flukes
Cestodes
Tapeworms
Transmission of Parasitic Diseases
• Fecal-oral route – common for food-borne pathogens,
including Giardia lamblia and Entameba histolytica
(protozoa), many geohelminths including Ascaris, Trichuris,
Taenia (tapeworm) and Enterobius (pinworm)
• Vector-borne – includes mollusks (snails) and multiple
arthropods (mosquitoes, black flies). Examples are
schistosomes, lung flukes, filarial worms, leishmaniasis,
trypanosomiasis, malaria
• Note: Vectors are required for completion of parasite life
cycles. Not simply a vehicle for transfer to mammalian host.
Parasite Disease Mechanisms
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Physical damage – invasion, attachment to tissues, tissue consumption,
obstructions, parasite proteases and other products
Innate immune responses – TNF-a, other cytokine production
Immunopathology – host immune response leads to parasite containment
coincidental with secondary tissue damage
Spectrum of disease modified by transmission (i.e. intensity/chronicity of
exposure), parasite burden and innate factors (genetic, immunologic,
developmental)
Additional Courses
Medicine
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INTH 484: Geographic Medicine and Epidemiology
INTH 494: Infectious Disease Epidemiology
INTH 5001: Orientation to International Health
FAMD 5023: International Health Practice
IMMU 3002 Tuberculosis and AIDS
IMMU 3003: Tuberculosis and History
EPBI 592: Geographic Information Systems and Statistical
Analysis of Spatial Data