Chapter 3 infectious diseases

1. Chapter 3 infectious diseases MED 1210 PATHOPHYSIOLOGY Human Diseases: A Systemic Approach, 7th Edition

2. Introduction • Infectious diseases are still a major caused of death, disability, and social and economic upheaval despite medical advances • 90% of deaths from infectious diseases worldwide are caused by a few diseases such as lower respiratory infections, HIV/AIDS, diarrheal disease and tuberculosis to name a few • In developed countries, infectious diseases count for 1 out of 10 deaths

3. Introduction Continued • In developing countries, infectious disease accounts for 6 out of 10 deaths • Factors that affect these deaths: • Poverty • Lack of access to health care • Antibiotic resistance • Evolving human migration patters • New infectious agents • Changing environmental and developmental activities

4. Principles of Infectious Disease • Pathogen – a disease-causing microorganism • Contagious or communicable – diseases transmitted by human contact • Measles and Influenza are examples • Noncommunicable – cannot be transmitted directly from person to person • Rabies and Cholera are examples. Rabies is transmitted by infected animals. Cholera by drinking fecal-contaminated water

5. Principles Continued • Epidemiology – the study of the transmission, occurrence, distribution and frequency of diseases • Incidence – the number of new cases of a disease in a population • Prevalence – the number of existing cases of a disease • Endemic – when a disease always occurs at low levels in a population

6. Principles Continued • Epidemic – when a disease occurs in unusually large numbers over a specific area • Pandemic – when an epidemic has spread to include several large areas worldwide • AIDS is now considered to be pandemic • Outbreak – when a disease suddenly occurs in unexpected numbers in a limited area and then subsides

7. Principles Continued • Notifiable diseases – diseases that are under constant surveillance in the U.S. • Physicians are required to report the occurrence of these disease to the Centers for Disease Control and Prevention • Notifiable Infectious Diseases include: • Chlamydia • Measles • Mumps • Polio • Tuberculosis • Legionnaires'’ disease • Tetanus

8. Principles Continued • Normal Flora – or microbiota – the 100 trillion microorganisms in and on our bodies • Do not harm us • Helps us by preventing overgrowth of harmful microorganisms • Helps us produce certain vitamins • Can become harmful if the opportunity arises to become opportunistic pathogens • Opportunists do not cause disease in the usual location in a healthy person • Can cause disease in a different location or if the host becomes weak or immunocompromised

9. Transmission of Infectious Diseases • Reservoir – source of an infectious agent • Humans • Animals • Insects • Soil • Water • Carriers – those who harbor an infectious agent but do not have signs or symptoms • Play an important role in the transmission of pathogens

10. Transmission Continued • Horizontal transmission – when infectious diseases are transmitted directly from an infected human to a susceptible human • Examples: Influenza and gonorrhea • Vertical transmission – when infectious diseases are transmitted from one generation to the next • Examples: Syphilis, HIV or opthalmia neonatorum is transmitted to newborns from infected mothers

11. Transmission Continued • Portals of entry – to cause disease microorganisms have to enter the human host • Respiratory tract – easiest and most frequently used portal of entry • Used by the common cold, influenza and tuberculosis • Parenteral route – punctures, injections, bites and surgery allow microorganisms to be deposited directly into the tissues below the skin • Used by HIV and hepatitis B • Direct contact – occurs when an individual is infected by contact with the reservoir • Ringworm, AIDS, rabies, malaria

12. Transmission Continued • Droplet transmission – inhaling the infectious agent in droplets emitted by sneezing, coughing or laughing is a form of direct contact • Example: Pneumonia and Influenza • Indirect contact – occurs when a pathogen can withstand the environment outside its host for a long period of time before infecting another individual • Airborne transmission – droplets are small enough to remain airborne for prolonged periods of time and travel more than 3 feet from the reservoir • Examples: tuberculosis and measles

13. Transmission Continued • Fomites – inanimate objects that are contaminated by direct contact with the reservoir and then become the indirect contact for a susceptible individual • Examples: tissues, syringes or utensils used by the reservoir

14. Control of Infectious Diseases • Isolation – keeping the infected person in a special hospital room away from other patients or having the infected person remain in their home with no visitors • Quarantine – the separation of persons who may or may not be infected from healthy people until the period of infectious risk is passed • Disinfection – removing potentially infectious materials from implements

15. Survey of Infectious Agents & Pathogenic Microorganisms: Prions • Prion – short for proteinaceous infectious particle • An infectious agent composed only of protein • Causes spongiform encephalopathies in humans and animals • Prion diseases all affect the structure of the brain or other neural tissue • Cause of Creutzfeldt-Jakob disease, familial CJD, and kuru

16. Survey of Infectious Agents & Pathogenic Microorganisms: Viruses • Viruses – infectious particles made of a core of genetic material (either RNA or DNA) wrapped in a protein coat called a capsid • There are several types of viruses classified into morphological types • Not considered living organisms because they do not independently grow, metabolize or reproduce • Must “highjack” a host cell and use its energy, materials and organelles for these purposes • Can cause latent infection – where the virus inserts itself into a cell and then does not reproduce until a trigger reactivates the virus at a later time

17. Survey of Infectious Agents & Pathogenic Microorganisms: Bacteria • Bacteria – microscopic, single-celled organisms • Has no nucleus or membranous organelles and is very small • Have evolved complex strategies for infecting and surviving in the human body • Cell walls – rigid layer of organic material surrounding their delicate cell membranes which give the bacteria their characteristic shapes

18. Bacteria Continued • Cocci – spherical, round bacterial cells • Bacilli – rod –shaped bacterial cells • Spirilla – spiral-shaped bacterial cells • Spirochetes – corkscrew-shaped bacterial cells • Vibrios – comma-shaped bacterial cells • Penicillin – antibiotic which interferes with correct cell wall construction making the cells susceptible to bursting

19. Bacteria Continued • Gram stain – procedure used in the lab to stain the cell wall of bacteria in order to identify them • Thick walled cells will turn blue-purple • Thin walled cells will turn red • Identifying the bacteria is critical to obtain an accurate diagnosis and effective treatment of an infection • Other types of bacteria that do not fit into the shape and gram stain categories above include Chlamydias and Rickettsias

20. Bacteria Continued • Other properties of bacteria include: • Glycocalyx – sugar coat on the surface of the cell • Capsule – organized and firmly attached glycocalyx, can protect the bacteria from phagocytosis • Slime layer – unorganized and loosely attached glycocalyx, aid in attachment to surfaces • Flagella – whip-like tails that bacterial cells use for locomotion • Fimbrae – short, hairlike appendages on bacteria that enable them to attach to surfaces • Pili – longer, hairlike appendages on bacteria that help join bacteria in preparation for the transfer of DNA from one cell to another

21. Bacteria Continued • Other properties of bacteria includes: • Endospores – commonly called spores – contains the genetic material of the cell packaged in a tough outer coat that is resistant to outside conditions and allows the cell to germinate and form growing cells once conditions become favorable • Endotoxin – potent toxin that causes life-threatening shock, released by gram-negative cells when they die • Plasmids – small circular double-stranded DNA molecules which contain extra genetic material that replicates independently of the bacterial chromosome • Binary fission – way bacteria reproduce by splitting in half, can take under 30 minutes in correct conditions

22. Survey of Infectious Agents & Pathogenic Microorganisms: Protozoa • Protozoa – single-celled eukaryotic microorganisms, much larger than bacteria with complex internal structures • Classified as: • Amoeboids – move by means of cell membrane extensions called pseudopodia, cause amoebic dysentery which is an intestinal infection • Flagellates – swim by using whip-like appendages called flagella, Trichomonas vaginalis causes an STI • Ciliates – move by means of numerous short hair-like projections, this group has very few pathogens

23. Protozoa Continued • Sporozoans – not mobile, Plasmodium which causes malaria is one example

24. Survey of Infectious Agents & Pathogenic Microorganisms: Fungi • Fungi – single-celled or multicelled organisms with cell walls that contain chitin – a special polysaccaride • Mycelia – specialized filaments that absorb nutrients from the cell’s surroundings • Spores – reproductive structures which are known allergens • Mycoses – term denoting fungal infection • Candida (yeast infection), Pneumocystis (opportunistic pathogen associated with AIDS), and ringworm are all examples of Fungi

25. Survey of Infectious Agents & Pathogenic Microorganisms: Helminths • Helminths – parasitic worms • Infestation – infection with a helminth • Ascaris – type of helminth which infests humans when they ingest the eggs, the larvae hatch in the intestines and mature into adults, the eggs are then passed out with the feces • Hookworms – Necator americanus is one type – leading cause of anemia and protein malnutrition in the tropics. Enterobius vermicularis is the most common worm infection in the US, also known as pinworm.

26. Nosocomial Infections • Also known as hospital-acquired infections, can occur in any healthcare facility • 32% of cases are urinary tract infections, 22% are surgical site infections, 15% are lung infections like pneumonia, and 14% are infections of the bloodstream (septicemia) • Principle routes of transmission are direct contact transmission from healthcare staff to the patient and indirect contact transmission through fomites and the hospital’s ventilation system

27. Nosocomial Infections Continued • Handwashing is the single most important means of preventing the spread of infections!!! • Occupational Exposure to Blood: • Blood-borne pathogens which healthcare works and related occupations may be exposed to include HIV, hepatitis B virus (HBV), and hepatitis C virus (HCV) • Most often occurs as a needlestick or percutaneous injury • HBV infection can be prevented by pre-exposure vaccination, there is no vaccine for HCV or HIV. However, the use of antiretroviral drugs after exposure to HIV can reduce the chance of transmission

28. Treatment of Infectious Disease • Depends on the type of causative pathogen • Antibiotics – used to treat bacterial infections. They can target the bacterial cell wall, the cell membrane, the protein synthesis machinery, bacterial metabolism, or DNA/RNA synthesis. • Antibiotic resistance – arises when bacteria adapt to antibiotics and that adaptation becomes common in the bacterial population. This is why it is important to use antibiotics only for bacterial infections and also to complete any course of antibiotics you are given

29. Treatment of Infectious Disease Continued • Viruses – are not susceptible to antibiotics • Nucleic acid analogues – antiviral drugs that interfere with the viruses use of human cells o reproduce and decode their genetic material • Substances that mimic the correct DNA/RNA bases • Used to manufacture viral genetic material but do not function as normal DNA/RNA would which causes the viruses to be reduced in number or eliminated

30. Treatment of Infectious Disease Continued • Antifungals – target fungal walls and membranes, can affect human cells as well • Causes serious toxic side effects • Topical agents are used for skin infections and pose fewer adverse effects • Systemic infection requires systemic treatment and entails the risk of serious side effects • Protozoa – treated with drugs that interfere with protein synthesis and metabolism, some antibiotics are effective on protozoa

31. Treatment of Infectious Disease Continued • Helminths – susceptible to drugs that paralyze their muscles or interfere with their carbohydrate metabolism • Complications: • Resistant microorganisms can evolve rendering existing treatments useless • Some treatments are accompanied by unacceptable toxic side effects or allergies • Preventive measures are the best choice for long-term control of certain diseases

32. Emerging and Re-Emerging Infectious Diseases • Emerging infectious diseases include outbreaks of previously unknown diseases or known diseases whose incidence in humans has significantly increased in the past 20 years. These include: • Rotavirus • Ebola virus • Legionnaires’ disease • T-cell lymphoma • Toxic Shock Syndrome • Lyme Disease

33. Emerging and Re-Emerging Infectious Diseases Continued • Re-emerging infectious diseases are known diseases that have reappeared after a significant decline in incidence. These include: • Mumps • Prion • Group A Strep • Staph aureus • Clostridium difficile • Hand, foot, mouth disease • Tuberculosis • Malaria • Dengue hemorrhagic fever

34. Emerging and Re-Emerging Infectious Diseases Continued • Factors which play a role in emergence/re-emergence of infectious disease are: • Human demographics and behaviors such as failing to vaccinate (measles and other childhood illnesses) • Technology and industry • Economic development and land use (Lyme disease) • International travel and commerce (SARS) • Microbial adaptation and change (drug resistant Staph aureus and tuberculosis) • Breakdown of public health measures • Climate change (affects the breeding of vectors)

35. Common Childhood Vaccine-Preventable Infectious Diseases • Vaccine-preventable childhood infectious disease levels are at or near record lows in the US • Measles is caused by the rubeola virus and is part of the MMR vaccine • Mumps, another part of the MMR vaccine, is caused by the paramyxovirus • Rubella is also known as German measles and is the last part of the MMR vaccine. It is caused by the rubella virus • Whooping cough or Pertussis is part of the DTP vaccine and is a highly contagious bacterial infection • Diphtheria is part of the DTP vaccine and is another highly contagious bacterial infection • Tetanus is part of the DTP vaccine, it is a bacterial infection that causes “Lockjaw”

36. Common Childhood Vaccine-Preventable Infectious Diseases Continued • Chickenpox now has a vaccine, it is a highly contagious viral illness caused by the varicella zoster virus • Hib – Haemophilus influenzae type b now has a vaccine available. It is a bacterial disease that causes meningitis and pneumonia • Poliomyelitis is caused by the polio virus which causes paralytic and nonparalytic forms of polio • Streptococcus pneumoniae causes meningitis and upper and lower respiratory diseases, there is now a vaccine available for this bacterial disease as well