Infectious Diseases. Lecture 3. Pathology and Clinical Science 1 (BIOC211) Department of Bioscience. endeavour.edu.au

Transcription

1 Infectious Diseases Lecture 3 Pathology and Clinical Science 1 (BIOC211) Department of Bioscience Text Reference: Grossman, S.C. & Porth, C.M. (2014). Porth s Pathophysiology: concepts of altered health states, (9th ed.). Philadelphia, U.S.A. Walters Kluwer Health - Lippincott, Williams & Wilkins. endeavour.edu.au

2 Session Learning Outcomes This session aims are to understand: o Common causes of infection o Common pathways by which the human body can acquire an infection o Normal course of infection and the clinical features present during an infection o Complications of infections o Some common infections and their treatments Endeavour College of Natural Health endeavour.edu.au 2

3 Definition of Infection o The invasion of the body by pathogenic microorganisms that reproduce and multiply causing disease OR o A disease caused by invasion of the body by pathogenic organisms Endeavour College of Natural Health endeavour.edu.au 3

4 Normal Flora & Opportunistic Infections o Resident flora have a role in preventing the growth of invading pathogens. o These microbes exist in various locations and are site specific o The balance of these resident microbes must be maintained for health and wellbeing o If microbes are transferred from one location to another, if the body s normal defences are impaired or if the balance of organisms is lost, disease can result o Such infections are known as opportunistic Endeavour College of Natural Health endeavour.edu.au 4

5 Organisms causing Infections n2.gif o Prions- unusual infectious agents which appear to consist only of protein without any genetic material o Viruses- very small intracellular parasites that require a living host for replication s jpg 5/06/16/bacteria/ o Bacteria- unicellular organisms that do not require living tissue to survive o Fungi- single to multi-cellular, diverse range of yeasts and moulds Endeavour College of Natural Health endeavour.edu.au 5

6 Organisms causing Infections Parasites Protozoa- unicellular organisms with no cell wall /11/worms-in-gut.jpg?w=584 Helminths- multi-cellular organisms (worms) Arthropods- insects cards/ /jpg/tick-1477ef48d376c6257f2.jpg Endeavour College of Natural Health endeavour.edu.au 6

7 Relative Size of Micro-organisms Organisms Size Visibility Viruses m electron microscope Bacteria 1-10 m light microscope RBC 8 m light microscope Fungi 3-20 m light microscope Protozoa m light microscope Human hair 75 m human eye (limit) Arthropod 100 m human eye Endeavour College of Natural Health endeavour.edu.au 7

8 Principles of Infection o In order to acquire an infectious disease an individual must be exposed to a reservoir or source of the potential pathogen and a situation must exist whereby the pathogen can be transmitted to the human body and gain entry in sufficient numbers to cause an infection. From (2013). Microbiology and Infection Control for Health Professionals (5th ed.) by Lee, G. & Bishop, P. Frenchs Forest, NSW. Pearson Education. Endeavour College of Natural Health endeavour.edu.au 8

9 Principles of Infection o Susceptibility to infection relies on a number of factors Source of infection/disease reservoir Infection can come from animals and birds, insects, food, soil, water, inanimate objects, people o Method of transmission Contact: Direct, Indirect, Droplet transmission Vehicle: Air-Borne, Water-Borne, Food-Borne Vector: Mechanical, Biological o Host resistance (both innate and acquired) o Circumstances of infection o Virulence of the pathogen Endeavour College of Natural Health endeavour.edu.au 9

10 Transmission of Microbes Contact - Direct o No intermediate, must have close or intimate contact with the source of the infection Self to self (children - faecal / oral route) Person to person Animal to person (tinea, anthrax) Soil or water to person Contact - Indirect o Left behind by others Use of Fomites (inanimate objects) as intermediates Contact - Droplet transmission o Coughing, sneezing Endeavour College of Natural Health endeavour.edu.au 10

11 Transmission of Microbes Airborne Contracted by inhalation, microbes carried on air currents over distances of more than 1m Water-borne Transmitted via ingestion/bathing Food borne Food spoilage due to microbial growth Vector - transmission by a carrier Mechanical: Passive transport on the outside of an insects body to a susceptible host i.e. the house fly, from the garbage tip Biological: Infected insect bites susceptible host and passes on infection Endeavour College of Natural Health endeavour.edu.au 11

12 Host Resistance The ability of the host (person) to fight off an infection Factors that decrease host resistance include: Age (infants and the elderly) Genetics (eg. cystic fibrosis) Immunodeficiency or immunosuppression (of any type) Malnutrition (low protein intake) Chronic disease (cancer, CAD, Diabetes) Severe stress (physical or emotional) Damaged primary defense mechanisms (burns, cuts) Poor inflammatory response Endeavour College of Natural Health endeavour.edu.au 12

13 Sources of Infection o Socioeconomic factors (eg hygiene) o Nosocomial o Iatrogenic o Zoonotic (exposure to animals) Endeavour College of Natural Health endeavour.edu.au 13

14 Virulence o The degree of Pathogenicity of an organism o The potential of the organism to establish and cause disease o Factors influencing virulence Invasive qualities Viruses (small size) Adherence Factors Pili Fimbriae Production of toxins Production of destructive enzymes Immune evasion Resistance to treatment super bugs Endeavour College of Natural Health endeavour.edu.au 14

15 Pathogenicity To be a successful pathogen a micro-organism must: o Gain entry into the host o Attach to the host tissues and multiply o Evade the host defence mechanisms o Damage tissue and produce disease symptoms o Pathogenic effect of infection is influenced by Rate of replication Infectious dose Endeavour College of Natural Health endeavour.edu.au 15

16 Portals of Entry Skin o Mucosal surfaces o Ears o Conjunctiva, lacrimal glands o Puncture wounds, needle sticks o Burrowing parasites and insect derived infections o Splits or tears from dehydration or oedema, o Hair follicles and sebaceous glands o Scratching itching bites or rashes o Burns or damage to skin integrity o Contact with blood products if skin is broken Endeavour College of Natural Health endeavour.edu.au 16

17 MRSA Infection of the Hand MRSA_Hand_Infection-SPL.jpg IMPETIGO M Impetigo_skin_infection-SPL.jpg Endeavour College of Natural Health endeavour.edu.au 17

18 Acute Otitis Media Endeavour College of Natural Health endeavour.edu.au 18

19 Conjunctivitis R&pq=conjunctivitis+infection+images&sc=0-0&sp=-1&sk=#x0y285 Endeavour College of Natural Health endeavour.edu.au 19

20 Puncture wounds Endeavour College of Natural Health endeavour.edu.au 20

21 Scabies Endeavour College of Natural Health endeavour.edu.au 21

22 Portals of Entry Respiratory Tract o Inhaled aerosols o Inhaled spores or respiratory droplets o Air currents from air conditioning especially in hospitals o Common use of ventilators, humidifiers, nebulisers Endeavour College of Natural Health endeavour.edu.au 22

23 Portals of Entry Gastrointestinal Tract o Contaminated food and /or water o Must be resistant to acid so commonly the spores of the bacteria or the eggs or the cysts of Helminths and protozoa (like Giardia) are ingested in contaminated food or water and later hatch in the GIT o Many GIT pathogens have a very low infective dose so the few that survive the stomach acid are adequate to cause infection o Can also ingest the toxin rather than the bug such as in botulism and still get disease 012/02/17/ e-coli-outbreak-2012-rawsprouts-perfect-vehicle-for-pathogens.jpg Protozoa ogy/microbiology_image/vibrio.jpg an_eats/seasoning_raw_bbq_chicken.jp G Endeavour College of Natural Health endeavour.edu.au 23

24 Portals of Entry Genitourinary system o Urethra- contamination from faecal route o Catheters o Urinary retention o Sexually transmitted diseases o Blood borne viruses in semen and vaginal secretions E-Coli hia-coli--e--coli--bacteria l.jpg mages/medline007/dynd11552.jpg Endeavour College of Natural Health endeavour.edu.au 24

25 Affects on the Body o Dependent on pathogen o All cause tissue damage and therefore activate the immune response o The role of the immune system is to try to clear the infection from the body through elimination from the body or destruction of the pathogen o Therefore the bugs have to get out or find somewhere to hide if they want to survive o Some bugs can evade the immune system by leaving the body and finding a new home Endeavour College of Natural Health endeavour.edu.au 25

26 Portals of Exit o Sputum and mucosal secretions o Saliva o Semen and vaginal secretions o Urine o Faeces o Blood Endeavour College of Natural Health endeavour.edu.au 26

27 Number of pathogens present The Course of the Infection Acute or Invasive phase Fatal outcome If infection not checked Prodromal Illness Decline Immune response or Treatment Incubation Convalescence No signs or symptoms Mild Signs or symptoms Acute identifiable Disease syndrome Time Recovery Endeavour College of Natural Health endeavour.edu.au 27

28 Incubation Period o The time interval between exposure of to the infectious agent and the onset of symptoms of infection o Factors vary dependent on: Properties of the pathogen (virulence) The infectious dose Route of entry relative to target organ Host resistance Endeavour College of Natural Health endeavour.edu.au 28

29 Incubation Period Examples Food Poisoning Tuberculosis Chickenpox Mumps Influenza Hepatitis A Hepatitis B Glandular fever HIV hours 4-12 weeks 2-3 weeks days 2-3 days 3-5 weeks 2-6 months 4-6 weeks min 3 weeks to months or years Endeavour College of Natural Health endeavour.edu.au 29

30 Prodromal Period o The onset of disease symptoms, signals the beginning of the disease o As the pathogen multiplies non-specific disease symptoms emerge such as Headache Nausea General malaise o If the host defences overcome the pathogen symptoms may disappear before a recognisable disease pattern occurs which may or may not result in acquired immunity to the infection Endeavour College of Natural Health endeavour.edu.au 30

31 Acute or Invasive Stage o Period of acute disease (specific signs and symptoms relative to the disease are observed) o Pathogen invades and damages host tissue o Often characterised by fever and chills caused by the release of pyrogens o Some invasive phases reach a crisis or peak over a short time period after which symptoms subside o Other infections have a longer invasive phase in which further signs and symptoms emerge such as cough, diarrhoea, jaundice, swelling, pain, discharge etc Endeavour College of Natural Health endeavour.edu.au 31

32 The Outcome of the Infection o The ability of the host to overcome the invasive phase determines the outcome of the disease. Decline Phase Recovery OR Death o The effect of the onset of protective immunity o The immune system overcomes the effects of the pathogen o Symptoms subside and patient begins to recover o In some cases host defences are inadequate to completely eradicate the pathogen and may result in a latent or chronic state Endeavour College of Natural Health endeavour.edu.au 32

33 Convalescence Outcome of Infection o The time when the body repairs itself and regains strength o Energy used to activate and support the immune system is directed back into the processes of cell regeneration and tissue repair o If insufficient time is allowed for the body to recover exposure to a subsequent pathogen may result in a second more serious infection as the immune system and body are already weakened and cannot protect the body effectively Endeavour College of Natural Health endeavour.edu.au 33

34 Variations of the Infection Course o Acute characteristic symptoms appear and the disease runs its course quickly o Fulminating symptoms appear suddenly and the disease runs its course rapidly, often to a fatal outcome o Chronic disease progresses slowly and persists for long periods with continuous shedding of the pathogen o Latent the pathogen is dormant in the host and may be reactivated at a later stage o Subclinical the infection produces an immune response without recognisable symptoms Endeavour College of Natural Health endeavour.edu.au 34

35 Types of Infections o Localised confined to one area of the body o Systemic pathogen affects more than one organ o Mixed disease is due to the effect of more than one pathogen o Primary the first sign of an infection in a healthy host o Secondary develops when the defences are lowered by the primary infection o Super-infection results from the overgrowth of opportunistic organisms following the destruction of normal flora Endeavour College of Natural Health endeavour.edu.au 35

36 Signs and Symptoms of Infection o Inflammation o Pain or tenderness o Swelling o Redness o Warmth o Purulent exudatebacterial o Serous exudate- viral o Fever o Fatigue o Weakness o Headache o Nausea o Skin rashes- can be both specific and non-specific Endeavour College of Natural Health endeavour.edu.au 36

37 Specimens Used for Diagnosis Swabs Blood Urine CSF Faeces Sputum Saliva (rarer) Wound Swabs gy/portals/0/images/microbiology_images/ho w2sample_page/sample_containers/swabs.j pg Urine sample /530wm/M Urine_samples-SPL.jpg Blood samples WI/223/4128/PreviewComp/SuperS tock_4128r-2328.jpg Endeavour College of Natural Health endeavour.edu.au 37

38 Treatment of Infection o Self limiting nature of infection o Use of antibiotics o Use of anti-viral agents o Treatment of parasites- i.e. anti-malarialsd o Immunosuppressive agents o Symptom relief- i.e. anti-pyretics Endeavour College of Natural Health endeavour.edu.au 38

39 How does the Immune System Respond to Infection? Non-specific immune defences Fever Inflammation Complement Macrophages and NK cells Specific immune defences Antibody production Cytotoxic T- cells Endeavour College of Natural Health endeavour.edu.au 39

40 Clearance Mechanisms o The immune system is activated to produce immune molecules and immune cells to remove or clear the pathogen from the body o There are a number of ways in which clearance of the pathogen is achieved o In many cases more than one type of clearance mechanism is required to be able to remove the pathogen entirely Endeavour College of Natural Health endeavour.edu.au 40

41 Clearance Mechanisms o Complement Activated in two ways o Mechanisms of clearance inflammation opsonisation membrane attack complex o Phagocytosis o Interferon anti-viral agents activate NK cells Endeavour College of Natural Health endeavour.edu.au 41

42 Common symptoms Many diseases present with very similar symptoms Look at the following symptoms: Sore throat, fever, fatigue, malaise, pharyngeal inflammation, vomiting, petechia, loss of appetite These symptoms might indicate the following diseases: Common colds, influenza, Acute HIV, Leukaemia, Tonsillitis, Diphtheria, Epstein Barr virus (glandular fever) Treatment and prognosis varies depending on which disease is responsible Endeavour College of Natural Health endeavour.edu.au 42

43 Differential Diagnosis o The process of differential diagnosis allows us to determine which disease is responsible for the symptoms. o Listing all the possible diagnoses, and then attempting to remove some until only one remains Through further observation and diagnostic tests Rule look for the simplest diagnosis that makes sense Not every case will be straight off House Endeavour College of Natural Health endeavour.edu.au 43

44 Readings and Resources Resources: o o Set Textbooks: Colledge, N.R., Walker, B.R. & Ralston S.H. (2014). Davidson s Principles and Practice of Medicine, (22nd ed.). Edinburgh. Churchill Livingstone. Grossman, S.C. & Porth, C.M. (2014). Porth s Pathophysiology: concepts of altered health states, (9th ed.). Philadelphia, U.S.A. Walters Kluwer Health - Lippincott, Williams & Wilkins. Additional textbooks: Jamison, J.R. (2006) Differential Diagnosis for Primary Care: a handbook for health care practitioners. (2 nd ed.). Edinburgh. Churchill Livingstone. McCance, K.L. & Huether, S.E. (2014). Pathophysiology: the biological basis for disease in adults and children, (7 th ed.). St. Louis, MO. Elsevier. Murphy, K. (2011). Janeway s immunobiology, (8 th ed.). New York. Garland Science. Pagana, K.D. & Pagana, T.J. (2013). Mosby s diagnostic and laboratory test reference, (11 th ed.). St. Louis, MO. Elsevier. Smith, M.E. & Morton, D.G. (2010). The digestive system: basic science and clinical conditions, (2 nd ed.). Edinburgh. Churchill, Livingstone, Elsevier. VanMeter, K.C. & Hubert, R. (2014). Gould s pathophysiology for health professions, (5 th ed.). St. Louis, MO. Elsevier. Endeavour College of Natural Health endeavour.edu.au 44

45 COMMONWEALTH OF AUSTRALIA Copyright Regulations 1969 WARNING This material has been reproduced and communicated to you by or on behalf of the Endeavour College of Natural Health pursuant to Part VB of the Copyright Act 1968 (the Act). The material in this communication may be subject to copyright under the Act. Any further reproduction or communication of this material by you may be the subject of copyright protection under the Act. Do not remove this notice. Endeavour College of Natural Health endeavour.edu.au 45