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

Cap

CapCap

CapCap

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