INFECTIOUS DISEASES

1. INFECTIOUS DISEASES

2. IMPACT OF INFECTIOUS DISEASES • 14th century - Europe - plague kills 20-45% of the world’s population • 1831 - Cairo - 13% of population succumbs to cholera • 1854-56 - Crimean war – deaths due to dysentery were 10 times higher than deaths due to casualties • 1899-1902 - Boer War – deaths due to dysentery were 5 times higher than deaths due to casualties

3. Infectious disease is one of the few genuine adventures left in the world. The dragons are all dead and the lance grows rusty in the chimney corner . . . About the only sporting proposition that remains unimpaired by the relentless domestication of a once free-living human species is the war against those ferocious little fellow creatures, which lurk in the dark corners and stalk us in the bodies of rats, mice and all kinds of domestic animals; which fly and crawl with the insects, and waylay us in our food and drink and even in our love. - (Hans Zinsser,1934 quoted in Murphy 1994)

4. “One can think of the middle of the 20th century as the end of one of the most important social revolutions in history, the virtual elimination of the infectious diseases as a significant factor in social life” Sir Macfarland Burnet

6. Epidemiology News Briefs - August 23, 2012 LA Times, 14 August 2012

7. LA Times, 13 August 2012

8. LA Times, Sept 2012

9. Direct economic impact of selected infectious disease outbreaks, 1990-2003 Heymann DL. Emerging and re-emerging infections. In Oxford Textbook of Public Health, 5th ed, 2009, p1267.

10. Factors in Promotion of Infectious Disease Agent Host  Environment Agent – virus, bacteria, parasite, prion, etc. Host – genetic profile, immune capacity, poverty, nutritional status Environment – biologic and chemical pollution, climate change, deforestation

12. DISEASE EMERGENCE ANDRE-EMERGENCE: CAUSES • GENETIC/BIOLOGIC FACTORS • Host and agent mutations • Increased survival of susceptibles • HUMAN BEHAVIOR • POLITICAL • SOCIAL • ECONOMIC • PHYSICAL ENVIRONMENTAL FACTORS • crowding • ECOLOGIC FACTORS • Climatic changes • Deforestation • Etc.

13. THE CHAIN OF INFECTION • Etiologic agent • Reservoir • Humans • Animals • Environment (e.g. soil) • Portal of exit • Mode of transmission • Direct • Indirect • Intermediate host • Portal of entry • Susceptible host

14. PORTALS OF ENTRY/EXIT* OF INFECTIOUS AGENTS • Respiratory – influenza, common cold agents, measels • Genitourinary – sexually transmitted agents • Alimentary track (gut) – Campylobacter, cholera, salmonella • Skin – streptococci, • Percutaneous (vector borne diseases e.g. arboviruses) • Eye – C. trachomatis • Transplacental – cytomegalovirus, HIV * Route of entry and exit not necessarily the same for a single agent e.g. HIV, schistosomaisis

15. MICROBIAL THREATS (1) • Newly recognized agents (SARS, acinetobacter) • Mutation of zoonotic agents that cause human disease (e.g., H5N1, H1N1) • Resurgence of endemic diseases (malaria, tuberculosis) • Persisting diseases (measles, polio)

16. MICROBIAL THREATS (2) • Development of drug-resistant agents (tuberculosis, gonorrhea) • Recognition of etiologic role in chronic diseases (Chlamydia causing respiratory and heart disease; HIV and heart disease) • Use of infectious agents for terrorism and warfare (anthrax)

17. Multidrug resistant National Academies Press http://www.nap.edu/books/0309071844/html/13.html

18. NEWLY IDENTIFIED INFECTIOUS DISEASES AND PATHOGENS (1) YearDisease or Pathogen 1993 Hantavirus pulmonary syndrome (Sin Nombre virus) 1992 Vibrio cholerae O139 1991 Guanarito virus 1989 Hepatitis C 1988 Hepatitis E; human herpesvirus 6 1983 HIV 1982 Escherichia coli O157:H7; Lyme borreliosis; human T-lymphotropic virus type 2 1980 Human T-lymphotropic virus Source: Workshop presentation by David Heymann, World Health Organization, 1999

19. NEWLY IDENTIFIED INFECTIOUS DISEASES AND PATHOGENS (2) YearDisease or Pathogen • MERS-CoV 2009 H1N1 2004 Avian influenza (human cases) 2003 SARS 1999 Nipah virus 1997 H5N1 (avian influenza A virus) 1996 New variant Creutzfelt-Jacob disease; Australian bat lyssavirus 1995 Human herpesvirus 8 (Kaposi’s sarcoma virus) 1994 Savia virus; Hendra virus Source: Workshop presentation by David Heymann, World Health Organization, 1999

20. Principles of Infectious Diseases

21. Microbiological Classification of Infectious Diseases • Disease is a disturbance in the state of health • Microbes cause disease in the course of stealing space, nutrients, and/or living tissue from their symbiotic hosts (e.g., us) • To do this, microbes do most of the following: • Gain access to the host (contamination) • Adhere to the host (adherence) • Replicate on the host (colonization) • Invade tissues (invasion) • Produce toxins or other agents that cause host harm (damage)

24. BIOLOGIC CHARACTERISTICS OF INFECTIOUS AGENTS Infectivity – the ability to infect a host Pathogenicity – the ability to cause disease in the host Virulence – the ability to cause severe disease in the host Immmunogenicity –the ability to induce an immune response in the host

25. Infectious Disease Terms Infectious dose – number of organisms needed to successfully infect Latent period - exposure to infectiousness interval Incubation period – interval from exposure to clinical symptoms Infectious period – interval during which host can transmit infection Reproductive rate – ability of an agent to spread in populations Virulence Pathogenicity Immunogenicity Outbreak – limited spread Endemic – usually present; steady prevalence Epidemic – rapid spread Pandemic – occurring across countries and in multiple populations

26. Important Terms Used for Infectious Diseases (1 of 2)

27. Important Terms Used for Infectious Diseases (2 of 2)

28. MODES OF TRANSMISSION • Direct • Droplet • Aerosol • Skin to skin • Indirect • Fomites (clothes, blankets, door handles etc) • Vectors (e.g. mosquitoes) • Food and water • Intermediate hosts (e.g. snails)

30. CLINICAL RESPONSES TO INFECTION BY AN AGENT • Inapparent infection – no clinical symptoms generated • Carrier state – usually no clinical symptoms but host can transmit infection for long periods • Clinical symptoms • Mild disease • Severe disease • Residual impairment • death

31. CLASSIFICATION OF INFECTIOUS AGENTS (1 of 2) • Bacteria – survive on appropriate media, stain gram-positive or -negative • Viruses – obbligate intracellular parasites which only replicate intracellularly (DNA, RNA) • Fungi – non-motile filamentous, branching strands of connected cells • Metazoa – multicellular animals (e.g.parasites) with complicated life cycles often involving several hosts

32. CLASSIFICATION OF INFECTIOUS AGENTS (2 of 2) • Protozoa – single cell organisms with a well-defined nucleus • Rickettsia – very small bacteria spread by ticks • Prions – unique proteins lacking genetic molecules • Chlamydia – bacteria lacking cell walls

33. Size Comparison of Microbes

34. Bacterial Cell Structure James D. Dick, PhD, Johns Hopkins University

35. Taxonomy of Bacteria Strain O157:H7

36. Microbiological Classification of Infectious Diseases • Bacteria are classified by their Gram stain characteristics. • Gram staining is the application of a crystal violet dye to a culture of bacteria. Bacteria that retain the color of the dye are called Gram positive; bacteria that don't are Gram negative. • The Gram stain attaches to peptidoglycan in the bacterial cell wall. • In Gram-negative bacteria, the peptidoglycan layer is protected by an outer membrane.

37. Microbiological Classification of Infectious Diseases

38. Microbiological Classification of Infectious Diseases

39. Microbiological Classification of Infectious Diseases • Viruses are acellular, obligate intracellular organisms. • The complete infectious virus is termed a virion. • The virion consists of the specific nucleic acid (DNA or RNA) surrounded by a protein coat (capsid). • Some viruses are enveloped which means that they possess a lipoprotein coat that surrounds the capsid and is acquired from infected host cell membrane. • Viruses that lack an envelope are “naked.”

40. Microbiological Classification of Infectious Diseases • Viruses are typically classified by: • Genetic material (DNA vs. RNA) • Strandedness (single vs. double) • Size and shape of the capsid and whether its enveloped or non-enveloped • Method of replication

41. Microbiological Classification of Infectious Diseases

42. Microbiological Classification of Infectious Diseases

43. Microbiological Classification of Infectious Diseases

44. VirusesEntry into the Host Cell with an Envelope

45. VirusesEntry into the Host Cell with an Envelope

46. Microbiological Classification of Infectious Diseases • All fungi are chemoheterotrophs • Pathogenic fungi have two forms: yeasts (unicellular) and molds (multicellular) • Some fungi are dimorphic (this is particularly true for the pathogenic fungi) • Molds grow as filamentous, branching strands of connected cells known as hyphae

47. Microbiological Classification of Infectious Diseases • Types of Parasites: • Protozoa: Single-celled, microscopic organisms that can perform all necessary functions of metabolism and reproduction. Some protozoa are free-living, while others parasitize other organisms for their nutrients and life cycle. • The morphology of protozoa varies widely and includes oval, spherical and elongated cells that can range in size from 5-10 to 1-2 mm. • Structurally, the protozoa resemble other eukaryotic cells and possess a cytoplasmic membrane that encloses cytoplasm containing membrane-bound nuclei, mitochondria, 80s ribosomes and a variety of organelles.

48. Microbiological Classification of Infectious Diseases • Types of Parasites: • Helminths: A large, multicellular organism (worm) that is generally visible to the naked eye in its adult stages. • Helminths can be free-living or parasitic. • Nematodes: Roundworms • Trematodes: Flukes • Cestodes: Tapeworms

49. Microbiological Classification of Infectious Diseases • Prions are abnormal, transmissible agents that are able to induce abnormal folding of normal cellular prion proteins in the brain, leading to brain damage and the characteristics signs and symptoms of the disease. • Prion diseases are usually rapidly progressive and always fatal.