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principle of infectious disease


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principle of infectious disease

  1. 1. Principles of infectious disease
  2. 2. IInnffeeccttiioouuss DDiisseeaasseess What is an infection?? Definition of infection a. Complex process of interaction between pathogen and human body b. Infection is composed of three factors: pathogen, host and environment
  3. 3. Microbiological Classification of Infectious Diseases Bacterial Gram-negative Gram-positive Viral DNA virus RNA virus Enveloped vs non-enveloped Fungal Disseminated Localized Parasitic Protozoa Helminths
  5. 5. PATTERNS OF INFECTION IN DEVELOPED COUNTRIES • During the last 100 years the incidence of communicable diseases in developed countries has fallen dramatically. • This has been due to improved nutrition, better sanitation and housing , immunizations and antimicrobial chemotherapy. • Infections such as diphtheria, poliomyelitis and tetanus have decreased and in some locations have almost disappeared. • Smallpox, has been eradicated from the world while another lethal infection, human immunodeficiency virus (HIV), has emerged in pandemic proportions.
  6. 6. INFLUENCES ON PATTERNS OF INFECTION IN DEVELOPED COUNTRIES The factors responsible for these changes are: Vaccines • Improved uptake of vaccines. • New vaccines, e.g. conjugate vaccines for Haemophilus influenzae type B, meningococcal type C disease, pneumococcal vaccine Animal husbandry and preparation of food • Salmonella and Campylobacter infections originating in poultry and eggs. • Escherichia coli type O157, causing haemorrhagic colitis and haemolytic uraemic syndrome, associated with beef. • Listeria infections from soft cheeses.
  7. 7. Microbial resistance • Staphylococcus aureus (meticillin-resistant, MRSA; glycopeptide-resistant, GRSA), • Gram-negative bacilli (extended spectrum β-lactamase resistance, ESBL), • Streptococcus pneumoniae (penicillin), • vancomycin-resistant enterococci (VRE) and • multidrug-resistant Mycobacterium tuberculosis (MDRTB) Sexual behaviour • Increase in HIV infection and other sexually transmitted diseases International travel • Importation of malaria • Legionnaires' disease from holiday hotels. • HIV infection.
  8. 8. Immunosuppression • Advances in the treatment of malignant disease and in organ transplantation, leading to infections with opportunistic organisms Resurgence of infections • Tuberculosis-world-wide, especially in association with HIV infection • Poliomyelitis in the Netherlands (in a religious sect refusing vaccines) • Streptococcal infections in the USA (including rheumatic fever) • Measles in the USA (mainly in immigrants in inner cities) • Diphtheria in the former Soviet Union • Hepatitis A and typhoid fever in the former Yugoslavia
  9. 9. Injection drug addiction 'New' and emerging infections 1. West Nile fever in the USA 2. Bioterrorism. 3. Avian/pandemic 'flu. 4. Swine flu
  10. 10. Killers of children, preventable but variably prevalent • Measles • Diphtheria • Pertussis • Poliomyelitis • Tetanus • Hepatitis B • Gastroenteritis • Malaria • Meningococcal disease • Acute diarrhoeal illness
  11. 11. Means of Transmission of Infectious Diseases Contact Requires direct or indirect contact (fomite, blood, or body fluid) Food or Water Ingestion of contaminated food or water Airborne Inhalation of contaminated air Vector-borne Dependent on biology of vector as well as infectivity of organism Perinatal Sexual Similar to contact infection, however, the contact may occur in utero or during delivery. transmission by sexual intercourse.
  12. 12. Factors Influencing Disease Transmission Agent Environment • Weather • Housing • Geography • Occupational setting • Air quality • Food Host• G Age • Sexe • Behaviour • Nutritional status •Health status • Infectivity • Pathogenicity • Virulence • Immunogenicity • Antigenic stability • Survival
  13. 13. IInnffeeccttiioouuss DDiisseeaasseess Barriers for Defense Against Infection: 1. Skin:  Prevents entry of infectious organisms, unless injured.  Severe burn patients who die are usually killed by infections. So much skin is damaged they are very vulnerable to infections. 2. Mucus membrane:  Mucous is usually rich in enzymes that will kill many pathogens 3. Cilia:  These are hair-like structures lining the respiratory tract. They work to sweep foreign particles out of the respiratory tract.  Damaged by smoking, leaving smokers more vulnerable to infections. 4. Coughing:  Helps remove foreign material from respiratory tract. 5. Personal Hygiene  Helps reduce the number of pathogenic organisms on the skin and other surfaces of the body.
  14. 14. IInnffeeccttiioouuss DDiisseeaasseess Infection and Immunity Manifestations of infectious process (Infection spectrum): 1) Clearance of pathogen (no infection) 2) Covert infection (subclinical infection) 3) Overt infection (Clinical infection or apparent infection) 4) Carrier states  Health carrier after covert infection.  Convalescent carrier after overt infection.  Incubatory carrier before onset of disease. According to carrier time : #acute (transient) carrier #chronic carrier 5) Latent infection.
  15. 15. MICROORGANISM-HOST INTERACTIONS Infection has many effects on the body, They may be • acute • chronic • allergic • toxigenic
  16. 16. CLINICAL EFFECTS OF INFECTION ON THE BODY - Acute : • Fever; anorexia, protein catabolism, acute-phase protein response, hypoalbuminaemia, low serum iron, sequestration of iron, anaemia, neutrophilia • Inflammation; pain, dysfunction, tissue damage • Convulsions; especially in children • Confusion; especially in the elderly • Shock. • Haemorrhage; haemolytic anaemia, intravascular coagulation • Organ failure.
  17. 17. CLINICAL EFFECTS OF INFECTION ON THE BODY-Chronic : • Weight loss and muscle-wasting • Malnutrition; especially associated with diarrhoea • Retardation of growth and intellect in children • Anaemia; iron sequestration, maturation arrest in marrow, folate deficiency • Tissue destruction; e.g. lung in pneumonia or tuberculosis, nerves in leprosy, liver in hepatitis B • Post-infective syndromes; e.g. lactose intolerance, malabsorption, irritable colon, depression, post-viral fatigue syndrome
  18. 18. CLINICAL EFFECTS OF INFECTION ON THE BODY-Allergic (immune-mediated) • Rash; e.g. urticaria with helminths, maculo-papular in typhoid and endocarditis, erythema nodosum in tuberculosis • Arthritis; e.g. in rheumatic fever, Reiter's syndrome • Pericarditis; e.g. in meningococcal infection • Encephalitis; e.g. in measles or following vaccines • Peripheral neuropathy; e.g. in post-infective polyneuritis • Haemolytic anaemia; e.g. in infectious mononucleosis • Nephritis; e.g. in streptococcal infection
  19. 19. Clinical effect of infection on the body-toxic or toxin mediated • Erythematous rash in streptococcal infection • Multisystem disturbance in staphylococcal or streptococcal toxic shock syndrome • Diarrhea; e.g. staphylococcal enterotoxin, Bacillus cereus • Organ disturbance; e.g. diphtheria • Neurological; e.g. tetanus, botulinum, diphtheria
  20. 20. • The incubation period is the period between the invasion of the tissues by pathogens and the appearance of clinical features of infection. • The period of infectivity is the time that the patient is infectious to others.
  21. 21. INCUBATION PERIODS OF IMPORTANT INFECTIONS Short incubation periods (< 7 days): • Bacillary dysentery 1-7 days • Cholera Hours-5 days ( 2-3 hours) • Diphtheria 2-5 days • Gonorrhoea 2-5 days • Scarlet fever 1-3 days
  22. 22. Intermediate incubation periods (7-21 days) • Chickenpox 14-21 days • Measles 7-14 days • Mumps 12-21 days • Poliomyelitis 3-21 days • Rubella 14-21 days
  23. 23. Long incubation periods (> 21 days) • Brucellosis Days-months • Hepatitis B 6 weeks-6 months • Rabies Variable • Tuberculosis Months-years
  24. 24. PERIODS OF INFECTIVITY IN CHILDHOOD INFECTIOUS DISEASES Disease Infectious period • Chickenpox 5 days before rash to 6 days after last crop • Measles From onset of prodromal symptoms to 4 days after onset of rash • Mumps 3 days before salivary swelling to 7 days after • Rubella 7 days before onset of rash to 4 days after
  25. 25. Prevention of infection Any reduction in the reservoirs of infection will naturally reduce the incidence of disease produced by these organisms. Endogenous reservoirs may be reduced by • chemoprophylaxis • physical isolation of cases whilst infective • physical separation of animal sources from human hosts and • their rapid treatment will reduce zoonoses. Blockage of transmission by source isolation, vector control careful infection control will also halt the spread of infection. Public health measures control spread of infection and • vaccination may improve 'herd immunity' in communities. • Prophylactic immunoglobulin may help some individuals at high risk of infection
  26. 26. INDICATIONS FOR CHEMOPROPHYLAXIS IN CONTACTS OF PATIENTS WITH INFECTIOUS DISEASE Infection Antimicrobiol agent Adult dose • Diphtheria Erythromycin 500 mg 6-hourly for 5 days • Meningococcal Rifampicin 600 mg 12 hrly 2 days or Ciprofloxacin 500 mg single dose • Whooping cough Erythromycin 500 mg 6-hourly for 7 days • Tuberculosis Isoniazid 300 mg daily for 6 months
  27. 27. INDICATIONS FOR PROPHYLACTIC IMMUNOGLOBULINS Human specific immunoglobulin • Virus B hepatitis (needle stick injuries, sexual partner) • Tetanus (susceptible injured patients) • Rabies (post-exposure protection) • Chickenpox (immunosuppressed children, adults and pregnant women) • Respiratory syncytial virus infection (high-risk infants, e.g. premature-investigational use)
  29. 29. CHARACTERISTICS OF EFFECTIVE VACCINES • Safety • Protection • Long-lasting effects • Cost Inexpensive to produce and deliver • Administration Easy to deliver with no side-effects
  30. 30. GUIDELINES FOR IMMUNISATION AGAINST INFECTIOUS DISEASE • The principal contraindication to inactivated vaccines is a significant reaction to a previous dose • Live vaccines should not be given to pregnant women or to the immunosuppressed, or in the presence of an acute infection • If two live vaccines are required, they should be given either simultaneously in opposite arms or 3 weeks apart • Live vaccines should not be given for 3 months after an injection of human normal immunoglobulin (HNI) • HNI should not be given for 2 weeks after a live vaccine • Hay fever, asthma, eczema, sickle-cell disease, topical corticosteroid therapy, antibiotic therapy, prematurity and chronic heart and lung diseases, including tuberculosis, are not contraindications to immunisation
  31. 31. IMMUNISATION SCHEDULE FOR INFANTS RECOMMENDED BY THE WHO EXPANDED PROGRAMME ON IMMUNISATION Vaccine Birth 6 weeks 10 weeks 14 weeks 9months  BCG *  Oral polio * * * *  Diphtheria, * * * pertussis, tetanus  Hepatitis B * * *  Measles *