INTH 301/401 Fundamental Concepts in Global Health
Ron BlantonCGHD, CWRU
Infectious Agents of Disease
• Viruses• Bacteria• Parasites
Viruses
• 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
protein coat(capsid)
DNA or RNA0.01-0.1 μm
Negative strand
RNA polymerase
Ribosomes
Classification
• Disease• Transmission• Nucleic Acid• Sequence
Classification
• Disease– 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
• 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 – Lassa, SAHF– Marburg, Ebola – Dengue, Yellow Fever
• Nucleic Acid– RNA
• Sequence– Bunyavirus – Arenavirus– Filovirus – Flavivirus
Life cycle
• Recognition - Receptor• Invasion• Transcription/translation or
translation/transcription• Packaging• Release
RNA
Invading virion New virions
Cell membrane
Cap
CapCap
CapCap
Cap
RNA
Flaviviral Replication
Proteases
Mature proteins
Viral particle = virion
Receptor
RNA
Invading virion New virions
Cell membrane
Filoviral ReplicationViral particle = virion
Cap CapCap CapCap CapCap Cap
RNA
Viral polymerase
Protein synthesis
Receptor
Implications
• Rapidly reproduced to high density• Mutation• Easily transported• Wide host range (sometimes)• Limited range of viral poisons • Many modes of transmission
Viral Tramission• 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
• Cytopathic effect• Inhibit DNA, RNA protein synthesis• Apotosis• Proliferation
Viral Prevention/Treatment
• Isolation (migration)• Host Response• Vaccination• Antivirals
Infectious Agents of Disease
• Viruses• Bacteria• Parasites
Bacteria
• Simple cells• Cell membrane and wall (and envelope)• Reproduction by division
Bacterial Structure
http://pathmicro.med.sc.edu/fox/protype.htm
LPS
Gram Staining Reveals Structure
E. coli S. aureus
http://www.buddycom.com/bacteria/gnc.html
“Bacterial Genetics”
• Bacteria & Archea• Eukaryotes
– Plant– Yeast– Parasites– Insects– People
Implications
• “Rapidly reproduce” in the right context• Resistance• Persistance• Mutation/Gene transfer• Toxin production
Bacterial Prevention/Treatment
• Contact• Host response• Vaccines• Antimicrobials/Antibiotics
Infectious Agents of Disease
• Viruses• Bacteria• Parasites
Parasites
• Single cell or multicellular eukaryotes living within a larger
• Complex developmental programs
Conceptual Basis of Parasitism
Commensalism Mutualism Parasitism
SYMBIOSIS
Host - Parasite Relationships
• Definitive host = Sexual reproduction– Echinococcosis - dogs– Schistosomiasis - humans– Pork tapeworm - humans– Malaria - mosquito
• Intermediate host = Asexual reproduction– Echinococcosis - humans– Schistosomiasis - snail– Pork tapeworm - humans– Malaria - humans
Parasitism in Human Biology and Medicine
• 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
• Helminths (Macroparasites)
• Chronic and persistent infections
• Disease related to intensity of infection
• Asymptomatic, chronic • Aggregated distribution
• Protozoa (Microparasites)
• Usually acute and transient infections
• Disease initiated by small inoculum
• Asymptomatic, acute• Distribution is random
Parasitic Protozoa
Single cell organismsMultiply in human host
Organelles analogous to tissues or organ systems
ApicomplexaInclude chloroplast-like structures
Malaria, toxoplasma
ArchezoaLack mitochondria, anaerobic
AmebaeGiardia lamblia
KinetoplastidaSingle large mitochondria
Trypanosomes Leishmania
Parasitic Helminths
TrematodesFlukes
CestodesTapeworms
MulticellularDoes not multiply in hostSpecialized organ systems
NematodesRound worms
PlatyhelminthesFlat worms
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• 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• 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
