Introduction to Communicable Diseases


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Lecture given to Family and Community Medicine of the University of Saint La Salle. Due credit is given to the original sources of the concepts cited in this lecture.

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Introduction to Communicable Diseases

  1. 1. Communicable DiseasesCommunicable Diseases Understanding the Spread and Control of Infectious Diseases Lectured by Bien Nillos, MD Community Health and Environmental Sanitation
  2. 2. The Human Body’s Immune System a system of biological structures and processes within an organism that protects against disease by identifying and killing pathogens and tumor cells. It detects a wide variety of agents, from viruses to parasitic worms, and needs to distinguish them from the organism's own healthy cells and tissues in order to function properly. Detection is complicated as pathogens can evolve rapidly, and adapt to avoid the immune system and allow the pathogens to successfully infect their hosts.
  3. 3. The immune system protects organisms from infection with layered defenses of increasing specificity
  4. 4. A human infection happens when bacteria, fungi, parasites or viruses enter the human body and start to multiply. The growth of the organism (germ) may cause symptoms in the infected person.
  5. 5. Definitions Case - A person who has, or is suspected to have, an infection. Contagious - An organism (germ) that can be passed to another person. Syn. Infectious, communicable Disease - is an abnormal condition affecting the body of an organism. It is often construed to be a medical condition associated with specific symptoms and signs
  6. 6. Definitions • Direct Contact Transmission - Spread of infectious organisms (germs) from the skin of one person directly to another person. • Indirect Contact Transmission - Spread of infectious organisms (germs) by coming into contact with a contaminated object and then bringing the germ into your body
  7. 7. Definitions Airborne Transmission - Spread of infectious organisms (germs) through the air. These germs can survive in the air for long periods of time and travel far distances from the infected person. Blood-borne Transmission - Spread of infectious organisms (germs) through direct blood-to-blood contact
  8. 8. Definitions Droplet Transmission - Spread of infectious organisms (germs) from an infected person in tiny droplets of fluid that can travel small distances (less than one meter). Sexual Contact Transmission - Spread of infectious agents (germs) from an infected person to another person through sexual contact (e.g., vaginal, oral or anal sex)
  9. 9. Definitions Vector-Borne Transmission - Spread of infectious organisms (germs) by insects Common Vehicle Transmission - Spread of infectious organisms to multiple hosts (e.g., animals or people) from one common source (e.g., contaminated food or medication).
  10. 10. TRANSMISSION • Infectious organisms come in different sizes, shapes and types. There are many types of bacteria, fungi, parasites and viruses. Infections can be spread in many different ways. With such diversity, there is no perfect way of preventing infections
  11. 11. Single-celled microorganisms which can exist either as independent (free-living) organisms or as parasites (dependent upon another organism for life). What is a Bacterium?
  12. 12. What is a Virus? A microorganism smaller than a bacteria, which cannot grow or reproduce apart from a living cell. A virus invades living cells and uses their chemical machinery to keep itself alive and to replicate itself.
  13. 13. What is a Parasite? An organism that lives in or on and takes its nourishment from another organism. A parasite cannot live independently. Parasitic diseases include infections by protozoa, helminths, and arthropods
  14. 14. Reservoir of infection: Any person, animal, plant, soil or substance in which an infectious agent normally lives and multiplies. The reservoir typically harbors the infectious agent without injury to itself and serves as a source from which other individuals can be infected. The infectious agent primarily depends on the reservoir for its survival. It is from the reservoir that the infectious substance is transmitted to a human or another susceptible host.
  15. 15. Reservoir Mode of transmission Immune System Mode of transmission
  16. 16. Modes of Transmission Droplet Contact Diphtheria, Pneumococcal pneumonia, Influenza, Rubella, Pertussis, Tuberculosis, Mumps, Chickenpox (Varicella) droplets generally are large (greater than 10 micrometers) and do not stay suspended in the air
  17. 17. Fecal-oral Transmission Cholera, Hepatitis A, Polio, Rotavirus, Salmonella, Entameoba histolytica, roundworms Fecal material (or the germs present in the feces) can be ingested via contamination of water supplies, by poor handwashing between the bathroom and the kitchen, by eating food contaminated by houseflies, or by poor hygeine after handling baby diapers - a myriad of ways.
  18. 18. Direct Physical Contact (Person to Person) Gonorrhea, Hepatitis B, HIV/AIDS, Syphillis, Herpes, Cytomegalovirus, Chlamydia, Impetigo, Athlete’s foot, Warts These diseases can also be transmitted by sharing a towel (where the towel is rubbed vigorously on both bodies) or items of clothing in close contact with the body (socks, for example) if they are not washed thoroughly between uses. This also includes any form of sexual contact
  19. 19. Airborne or Droplet nuclei Anthrax, Varicella, Measles, Influenza, Tuberculosis, Smallpox. occurs when bacteria or viruses travel on dust particles or on small respiratory droplets that may become aerosolized when people sneeze, cough, laugh, or exhale. They hang in the air much like invisible smoke. They can travel on air currents over considerable distances
  20. 20. Vector-borne Transmission Dengue, Malaria, Sleeping Sickness, Filariasis, Yellow Fever, Japanese Encephalitis, Cutaneous Leishmaniasis, Schistosomiasis, Leptospirosis A vector is an organism that does not cause disease itself but that transmits infection by conveying pathogens from one host to another
  21. 21. Soil Transmission (Direct Contact) Tetanus, Ascariasis, Trichuriasis, Soil-transmitted helminths common known as intestinal worms, are the most common infections worldwide affecting the most deprived communities (WHO)
  22. 22. Animal (Bite) Transmission Bubonic Plague, Anthrax, Avian Flu, Leptospirosis, Rabies, Loiasis (?), Cat- Scratch,
  23. 23. Vertical Transmission HIV, Hepatitis B, Syphilis, rubella, Candidiasis, Herpes, Gonorrhea, Toxoplasmosis (TORCH) the transmission of an infection or other disease from mother to child immediately before and after birth during the perinatal period
  24. 24. Objective in Infection Control Reservoir Mode of transmission Immune System Eliminate Disrupt Enhance Barriers
  25. 25. Controlling Spread of Infection: The Reactive Approach Diagnosis is importance – establish the occurrence of a disease based on the signs and symptoms Presumptive vs. Definitive Use of Clinical history, Physical Exam Lab tests CASE DEFINITION
  26. 26. Start treatment of sick person immediately according to protocol (Early Diagnosis and Prompt Treatment)
  27. 27. Identify the Source of Infection – Where did the sick person get the infection? Identify the mode of transmission – How did the sick person get infected?
  28. 28. Controlling Spread of Infection: Proactive Approach Identify Risk Groups – who are people in the population that are susceptible to acquiring specific communicable diseases Is the community at risk of exposure to various communicable diseases?
  29. 29. Preventive Measures to address: 1. Identified Reservoir of Infectious Diseases 2. Community’s Defense Against Infection (Herd Immunity, Barriers on Routes of transmission) 3. Screening of presumed healthy population
  30. 30. Examples of Common Communicable Diseases in the Philippines
  31. 31. Community Acquired Pneumonia Causative Agent: Streptococcus Pneumonia • Case Definition: Tachypnea and/or cough and/or difficulty breathing Tachypnea >50 breaths/minute if 2 months to < 12 months >40 breaths/minute if child 12 months to < 5 years CXR confirmed - Chest radiograph performed and read to have an infiltrate consistent with pneumonia (using WHO standardized definition for primary end point pneumonia “A dense fluffy consolidation (alveolar infiltrate) of a portion of a lobe or entire lung. This often contains air bronchograms, and may be associated with a pleural effusion.”)
  32. 32. Pulmonary Tuberculosis Causative Agent: Mycobacterium Tuberculosis Definition: chronic infection of the lungs. Patients exhibit chronic coughing for more than 2 weeks accompanied with weight loss, night sweats, unexplained fever, with or without blood-stained sputum. Direct sputum smear microscopy with AFB can visualize the mycobacterium
  33. 33. Malaria • Malaria is caused by a parasite called Plasmodium, which is transmitted via the bites of infected mosquitoes. In the human body, the parasites multiply in the liver, and then infect red blood cells. • Symptoms of malaria include fever, headache, and vomiting, and usually appear between 10 and 15 days after the mosquito bite. If not treated, malaria can quickly become life-threatening by disrupting the blood supply to vital organs. In many parts of the world, the parasites have developed resistance to a number of malaria medicines.
  34. 34. Dengue Fever • Dengue is a mosquito-borne infection that causes a severe flu-like illness, and sometimes a potentially lethal complication called dengue haemorrhagic fever. • Global incidence of dengue has grown dramatically in recent decades. • About two fifths of the world's population are now at risk.
  35. 35. Leptospirosis (Weil’s Disease) • Leptospirosis is caused by exposure to several types of the Leptospira bacteria, which can be found in fresh water that has been contaminated by animal urine. It occurs in warmer climates. • Symptoms can take 2 - 26 days (average 10 days) to develop
  36. 36. Preventive Measures Immunization - is the process whereby a person is made immune or resistant to an infectious disease, typically by the administration of a vaccine. Vaccines stimulate the body’s own immune system to protect the person against subsequent infection or disease.
  37. 37. Expanded Program of Immunization • The Expanded Program on Immunization (EPI) in the Philippines began in July 1979. And, in 1986, made a response to the Universal Child Immunization goal. The four major strategies include: – Sustaining high routine Full Immunized Child (FIC) coverage of at least 90% in all provinces and cities, – Sustaining the polio-free country for global certification – Eliminating measles by 2008, – Eliminating neonatal tetanus by 2008.
  38. 38. BCG is a vaccine against tuberculosis that is prepared from a strain of the attenuated (weakened) live bovine tuberculosis bacillus, Mycobacterium bovis, that has lost its virulence in humans by being specially subcultured (230 passages) in an artificial medium for 13 years. The bacilli have retained enough strong antigenicity to become a somewhat effective vaccine for the prevention of human tuberculosis. At best, the BCG vaccine is 80% effective in preventing tuberculosis for a duration of 15 years; however, its protective effect appears to vary according to geography BCG is given as a single intradermal injection at the insertion of the deltoid
  39. 39. DPT • refers to a class of combination vaccines against three infectious diseases in humans: diphtheria, pertussis (whooping cough) and tetanus. The vaccine components include diphtheria and tetanus toxoids, and killed whole cells of the organism that causes pertussis (wP). • DTaP (also known as Tdap,DTPa, and TDaP) refers to similar combination vaccines in which the pertussis component is acellular.
  40. 40. OPV • Two polio vaccines are used throughout the world to combat poliomyelitis (or polio). The first was developed by Jonas Salk and first tested in 1952. Announced to the world by Salk on April 12, 1955, it consists of an injected dose of inactivated (dead) poliovirus. An oral vaccine was developed by Albert Sabin using attenuated poliovirus
  41. 41. Hepatitis B Hepatitis B virus is a member of the Hepadnavirus family It consists of: HBsAg, HBcAg (HBeAg is a splice variant), Hepatitis B virus DNA polymerase, HBx The vaccine contains one of the viral envelope proteins, hepatitis B surface antigen (HBsAg). It is produced by yeast cells, into which the genetic code for HBsAg has been inserted. The first vaccine became available in 1981.
  42. 42. Measles • Dr. John Enders was able to use the cultivated virus to develop a measles vaccine in 1963 based on the material isolated by Dr. Thomas Peebles. The vaccine Enders developed was based on the Edmonston strain of attenuated live measles virus, which was named for the student from which Peebles had taken the culture that led to the virus' cultivation
  43. 43. Measles, also known as rubeola or morbilli, is an infection of the respiratory system caused by a virus, specifically a paramyxovirus of the genus Morbillivirus. Morbilliviruses, like other paramyxoviruses, are enveloped, single- stranded, negative-sense RNA viruses. Symptoms include fever, cough, runny nose, red eyes and a generalized, maculopapular, erythematous rash.
  44. 44. Cold Chain To ensure the optimal potency of vaccines,a careful attention is needed in handling practices at the country level. These include storage and transport of vaccines from the primary vaccine store down to the end-user at the health facility, and further down at the outreach sites. Inappropriate storage, handling and transport of vaccines won’t protect patients and may lead to needless vaccine wastage
  45. 45. A "first expiry and first out" (FEFO) vaccine system is practiced to assure that all vaccines are utilized before its expiry date. Proper arrangement of vaccines and/or labeling of expiry dates are done to identify those close to expiring. Vaccine temperature is monitored twice a day (early in the morning and in the afternoon) in all health facilities and plotted to monitor break in the cold chain. Each level of health facilities has cold chain equipment for use in the storage vaccines which included cold room, freezer, refrigerator, transport box, vaccine carriers, thermometers, cold chain monitors, ice packs, temperature monitoring chart and safety collector boxes
  46. 46. EPI Schedule: Wednesday
  47. 47. Preventive Measure Health Promotion - is the process of enabling people to increase control over, and to improve, their health. It moves beyond a focus on individual behaviour towards a wide range of social and environmental interventions. (WHO, Bangkok Charter for Health Promotion in a Globalized World 1995)
  48. 48. It is the science and art of helping people change their lifestyle to move toward a state of optimal health. This definition was derived from the 1974 Lalonde report from the Government of Canada Health promotion can be performed in various locations. Among the settings that have received special attention are the community, health care facilities, schools, and worksite
  49. 49. Preventive Measure Environmental Sanitation - involves controlling the aspects of waste management that may lead to the transmission of disease. Included in the term waste management are water, solid waste, and industrial waste
  50. 50. Integrity of Water Supply Proper Waste Disposal Food and Food Handlers Control of Vectors
  51. 51. Preventive Measure Accessibility to Drugs/Health Care - Increasing access to affordable drugs in developing countries requires better government intervention, not less of it. (David Dickson, SciDev.Net Director)
  52. 52. Outbreak - an occurrence of disease greater than would otherwise be expected at a particular time and place Epidemic - occurs when new cases of a certain disease, in a given human population, and during a given period, substantially exceed what is expected based on recent experience
  53. 53. Endemic - that infection is maintained in the population without the need for external inputs Pandemic - an epidemic of infectious disease that is spreading through human populations across a large region; for instance multiple continents, or even worldwide
  54. 54. Notifiable Diseases - any disease that is required by law to be reported to government authorities. The collation of information allows the authorities to monitor the disease, and provides early warning of possible outbreaks Republic Act No. 3573 – Law of Reporting Communicable Diseases a.k.a. Revised List of Notifiable Diseases, Syndromes, Health-related events and conditions
  55. 55. “Thought is an infection. In the case of certain thoughts, it becomes an epidemic.” Wallace Stevens