Chain of infection

community

1. Chain of Infection By / Mahmoud Shaqria محمود محمد شقريه

2. Out lines - Agent - Infectively, - Pathogenicity, - Virulence - Antigenicity - Resistance - Reservoir of infection -Carriers Classification of carriers - Portal of exit - Period of communicability

3. - Mode of transmission. A) direct transmission B ) Indirect transmission : - Portal of entry - Incubation period -Host susceptibility and resistance Immunity - - Type of immune defense - Hazard of immunization - Herd immunity Out lines

4. Introduction Globally, millions of lives (and billions of dollars) are lost each year because of communicable diseases. WHO Millennium Development Goals continue to focus on communicable diseases as a main target. The basic component of every communicable disease transmission is the chain of infection. Breaking just one link in the chain of infection means that the communicable disease cannot be passed on to another individual.

5. Chain of Infection (Defined) The “Chain of Infection” describes the process of infection that begins when an infectious agent leaves its reservoir through a portal of exit, and is transmitted by a mode of transmission entering through a portal of entry to infect a susceptible hos t.

6. Chain of Infection

7. 1. Infectious Agent • Microorganisms that are responsible for causing disease production: • Viruses • Bacteria • Fungi • Protozoa and Helminthes • Parasites • Prions Agents are factors that affect disease transmission through infectivity, pathogenicity, virulence, antigenicity & resistance .

8. Infectively : the ability of an agent to invade and multiply ( produce infection ) in a susceptible host . high infectively : measles , polio Low infectively : leprosy How to measure the spread of infection ? Secondary attack rate : The proportion of exposed susceptible persons who become infected Secondary attack rate = __________________________ x 100 Number of secondary cases Number of susceptible

9. Virulence It refers the ability of organisms to produce sever pathological reaction . It can measure by : case fatality rate Pathogenicity : Is the ability of the organisms to produce specific clinical reaction after infection It refer to the proportion of infected persons who develop clinical disease It can measured by : Ratio of clinical to subclinical cases = Clinical cases sub clinical cases Case of fatality rate = Total number of deaths from a disease Total number of cases of disease x 100

10. Antigenicity ( immunogenicity ) : the ability of an organism to produce specific immunity ( antibodies , antitoxin ) it can be measure by : reinfection rate Second attacks are rare in measles , mumps and chicken pox Reinfection occurs as in case of common cold , syphilis and gonorrhea Resistance : the ability of an agent to survive adverse environmental condition Examples : Low environmental resistance as gonococci and influenza VIRUSES ARE typically fragile Moderate environmental resistance as salmonella High environmental resistance as mycobacterium tuberculosis

11. 2. Reservoirs of Infection The reservoir of an infectious agent is the habitat in which the infectious agent normally lives and multiplies. Types of reservoirs: • Humans • Animals • Environment

12.  Human reservoir : Two types of human reservoir exist : 1. cases : persons with symptomatic illness - typical : A case suffer from an infectious disease , discharges microorganisms , and is a source of microorganisms - Atypical : A case which can`t easily diagnosed or isolated. Subclinical cases : the person is infected but the disease is not clinically manifested. 2. Reservoirs of Infection ( cont )

13. 3. Carriers They are infected persons, apparently healthy with no symptoms, having the organisms in their bodies, excrete them with their discharges and disseminate infection to others Carriers are dangerous because: They don't show any clinical manifestations so they carry normal life. - -Carriers are not diagnosed and they are not know by others, it is difficult to discover them. -The carrier and his contacts aren't aware of their condition so they take no percussion. Large number of carriers and exceed very much the number of cases - -Carrier in some disease are dangerous because of nature of their work e.g. food handler and school personells -Carriers of some disease may remain infective for long period or sometimes for lifelong e.g. incubatory carrier of HIV and chronic carrier as hepatitis B and typhoid

14. Classification of carriers According to relation to case , carrier are to classified to : 1.Incubatory carrier : the case become infective before the onset of the disease During the incubation period e.g in the last few days ( cholera and typhoid ) In the last few weeks ( one weak before onset in viral A hepatitis ) 2. convalescent carriers : the recoverd cases continue to excrete the infective agents during the period of convalescence e.g typhoid , diphtheria and cholera 3. contact carriers :contact of cases having moderate immunity may be infected and get rid of infection within maximally two weeks eg typhoid 4. Healthy carriers : those infected persons from polluted environment such as contaminated food and water this occurs in endemic infectious disease and they are usually temporary carriers

15. B) According to period of carrier's state: 1. Transient carriers : they are infective only for days e.g. last few days of incubation period e.g. cholera 2. Temporary carriers : they are infective for few weeks up to few months e.g. viral A hepatitis last week of I.P and viral B hepatitis 3 weeks : 3 months 3. Chronic carriers : who are still infective for years e.g. chronic carriers in typhoid and hepatitis B C) According to the foci of infection: 1 . Respiratory system : who carry the microorganisms in the respiratory tract Throat e.g. diphtheria , streptococcus haemolyticus & staphylococcus aureus nose : diphtheria staphylococci nasopharynx : meningococci , pneumococcal 2. Gastro-intestinal tract : Gall bladder : e.g. salmonella typhi and para typhi Small intestine : salmonella typhi and para typhi 3. urinary tract : s.typhi and paratyphi 4. skin lesion or under the nails : as staphylococcus aureus in food poisoning

16. D) according to discharge that carry organisms outside the body 1. Respiratory discharge : from the nose and throat through coghing sneezing spitting etc , staph , stept , influenza ,meningitis . 2. faecal carriers in intestinal infections e.g. typhoid , paratyphoid , amaebiasis 3. urinary carrier as in typhoid and paratyphoid 4. skin discharge , organisms may be present in skin leasion as in skin disease . E) according to flow of the organisms outside the body . Continuous or intermittent N.B : the following disease have no carriers : - influenza -whooping cough -TB - measles -herpes zoster

17. B) animal reservoirs : Zoonoses : infectious disease that transmitted under normal conditions from vertebrate animals to humans ( with humans as incidental host ) Role of animal in zoonoses : 1. Animal are only reservoirs of infection ( strictly zoonotic diseases ) no man to man infection as in plague , brucellosis and q fever 2. both animals and man are reservoirs of infection and may be animal to man or man to man as: - yellow fever : monkeys and man are the reservoirs - salmonellosis and salmonella food poisoning : man and some animal species ( cattle , swine , poultry , rats ) are the reservoirs of non typhoidal salmonellae 3. animal may be intermediated host of parasitic disease and man is the definitive host e.g. hydatid disease 4. animal may be the definitive host man is affected by intermediate stage of the parasite as taenia saginata

18. C) Environmental reservoirs Plants soil and water Soil : agent live and multiply in the soil example : tetanus and anthrax spores and fungal agent causing histoplasmosis. Pools of water : the primary reservoir of legionnaires bacillus.

19. 4 – portal of exit Is the path by which an agent leave the source host. The organisms leave the body of the reservoir through : 1. Respiratory orifices: during forced expiratory acts such as sneezing , coughing as influenza , streptococci and measles. 2. Gastro intestinal tract: the organisms may found in vomitus e.g. cholera or fecal discharge as gonorrhea and syphilis 3. Genitourinary tract: urine as enterica and urinary tract infection and genital discharge as gonorrhea and syphilis. 4. Discharge of skin and mucous membrane : as in infected wounds , skin eruption , small pox and chicken pox eye discharge as in infective conjunctivitis 5. inutero transmission , from pregnant mother to her fetus e.g. German measles , cytomegalovirus and toxoplasma 6. blood: organisms & parasites in blood can find exit through contaminated syringes and during blood transfusion e.g. HIV , viral hepatitis and also exit through bites of insects 7. others : Milk as HIV , HCV cytomegalovirus and tears as HIV

20. 5- period of communicability Infectively may be terminated by clinical cure as in small pox , chicken pox , and measles In disease having carrier state , infectivity may star the last few days or weeks of incubation period ( temporary carriers ) as viral hepatitis and may extend during during the convalescent stages as in viral B hepatitis and typhoid ( chronic carrier )

21. 6. Modes of Transmission Direct A. direct transmission : there is essentially immediate transfer at the agent from a reservoir to a susceptible host There are five methods of direct transmission 1. direct transmission due to the agent being within a reasonably close distance of host as occurs in ( direct droplet infect on ) 2.contact of host skin or mucous membrane with infectious agent in a living tissue e.g. sexually transmitted disease 3.contact of skin or mucous membrane with the infectious form of the agent contained in inanimate environment e.g. hookworm (infective form in soil ) 4.inoculation of the agent , directly from the reservoir into the skin or mucous membrane as rabies 5. vertical transmission from mother to child or through the placenta e.g. HIV , syphilis , torch , toxoplasma , rubella , cytomegalovirus etc.

22. B) Indirect transmission: An agent is carried from a reservoir to a susceptible host by an intermediary agency : There are four methods of indirect transmission Airborne transmission : suspended air particles Vehicle borne : inanimate vehicle Finger ( hand to mouth ) Vector borne : animate vector

23. A).Airborne transmission : occurs by particles that suspended in air (two types) 1.Dust : result from re suspension of particles that have settled on floor or bedding as well as infectious particles blown from the soil by the wind . example fungal spores , legionnaires disease , Q fever , TB , nosocomial infection. 2.droplet nuclei : they represent the dried residue of droplets that have been coughed or sneezed into the air They are very tiny particles less than 5 microns in size and may remain suspended in the air for long periods. Examples: TB is transmitted more often indirectly through droplet nuclie than directly through direct droplet spread.

24. B). VEHICLE –BORNE : An infectious agent is carried from a reservoir to a susceptible host by an inanimate intermediary . vehicles included : 1) contaminated food and drink. 2) injectable biologic products (blood , blood products , drugs , vaccine , diluents ) e.g. HIV , viral hepatitis , syphilis and malaria 3) fomites ( inanimate objects of general use such as utensils , toys, tooth brushes , handkerchiefs , bedding , or surgical instruments ) . 3. fingers ( hand to mouth ) : finger from a very important mode of indirect transmission 4. vector borne indirect transmission. .

25. - A vector is aliving invertebrate which transfers the infection agent from the source of infection to another susceptible host. - mechanical transmission : the agent does not multiply or undergo physiologic changes in the vector - Biologic transmission : - propagative : when the agent undergoes multiplication within the vector before it is transmitted - developmental : when the agent undergoes changes within the vector before it transmitted . - cyclo -developmental : when the agent undergoes changes and multiplication within the vector before it is transmitted

26. Arthropod borne infection Some insects of medical importance : Mosquitoes : which include different species. Anopheles : ( pharaensis , sergenti , multicolor and Gambia ) transmit malaria Culex pipiens : transmit filariasis , rift valley fever , encephalitis Aedes Aegypti : transmit yellow fever and dengue fever.

27. 7- portal of entry An agent enters a susceptible host through a portal of entry . The portal of entry must provide access to tissue in which the agent can multiply or a toxin can act. Often , organisms use the same portal to enter a new host that they use to exit the source host.

28. 8 incubation period The period from the entry of infectious agent (or its toxin ) into the human body until the earliest clinical manifestations of the disease are apparent . it depends on : -the portal of entry -the rate of growth of the organism in the host -the dose of the infectious agent -the host resistance 2:6 hrs Staph .food poisoning The shortest I.P. 6 :12 hrs Salmonella food poison 12 :36 hrs Botulism 10d up to 1 year Rabies The longest I.P. 3 :5 years AIDS Up to 10 years. Leprosy

29. 9. Susceptible Host The host is a person or other living organism that can be infected by an infectious agent under normal conditions. Susceptibility of a host depends on: • General factors ( age , sex , education …etc. ) • Genetic factors • Specific acquired immunity A susceptible host is the final link in the chain of infection.

30. Treating high risk patients (immunosuppressed, old, young, surgery, burns, diabetics, CVD) Treating underlying diseases Employee health nvironmental sanitation Disinfection Reservoir management ( eg . culling) Rapid accurate organism identification Use of PPE  Hand washing  Control of secretions-skin droplets  Waste sample disposal  Personal etiquette (sneezing) Wound-Catheter care  Sanitation  Aseptic techniques  Hand washing  Use of PPE  Hand washing  Proper food handling  Sterilization-disinfection  Social distancing Public Health Actions to Break the Chain of Infection

31. Public Health Actions to Break the Chain of Infection at the Portal of Exit Breaking the Link Portal of Exit Wear a mask Do not talk directly into patient’s face Stay home if sick Practice cough etiquette Use hand hygiene Respiratory Tract. Agents leave by droplets or sprays (coughing, sneezing, talking, singing or breathing. Handle body secretions properly Use PPE Perform good housekeeping Use hand hygiene Gastrointestinal Tract. Agents leave by body secretions (e.g. stool and vomit). Dispose of wound dressings properly Use personal protective equipment Use hand hygiene Skin . Agents leave by wound drainage or through skin lesions. Safe handling of sharps Use PPE during risk of exposure to blood Diligence when processing specimens Use hand hygiene Blood. Transmission may occur by transfusion or use of contaminated sharps.

32. Public Health Actions to Break the Chain of Infection at the Portal of Entry Breaking the Link Portal of Entry Wear a mask/respirator • Maintain good ventilation • Isolate those with respiratory symptoms • Good respiratory hygiene/etiquette practices • Use hand hygiene Respiratory Tract. Agents can be inhaled (droplet nuclei) Dispose of body excretions carefully • Vigilant food handling • Perform good housekeeping • Wear appropriate personal protective equipment • Use hand hygiene Gastrointestinal Tract. Agents can enter a new host when food or water contaminated by feces is ingested (fecal/oral route). Use face shield during high risk procedures • Carry out good housekeeping • Use hand hygiene Mucous membranes. Agents absorbed through exposed eyes, nose and mouth. Dispose of wound dressings carefully and properly • Wear personal protective equipment • Maintain healthy intact skin • Use hand hygiene Skin. Agents enter by wound drainage or skin secretion contact.

33. Public Health Actions to Break the Chain of Infection Will depend on the infectious agent. General actions include: • Hand washing and Hand Hygiene Programs • Covering nose when coughing or sneezing • Social distancing strategies • Infectious disease hazard communication • Immunization – yearly flu shot • Personal Protective Equipment ( eg . gloves, gowns, visors, N95 masks). Use, fit, maintenance and replacement • Hand washing and Hand Hygeine Programs • Environmental controls ( eg . isolation, negative pressure rooms) • Surface cleaning and disinfection ( eg . sanitizing, UV light) • Ongoing updates, education and training for infectious disease • Targeting vectors ( eg . larvacides for WNV, trail brush cutting) • Reservoir management (culling programs) Individual Institutional- Organizational Municipal- Provincial

34. Immunity Immunity is the defense mechanism tat protect the body from micro organisms and potentially harmful agent Immune response Secondary immune response Primary immune response Re exposure to same Ag Characters -short latent period due to early Abs production -large amount of Abs -Abs last for long duration Abs have high binding capacity with Ag Importance Used in immunization programmer every few weeks to prolonged duration of immunization Exposure to the Ag for the 1 st time Characters -Long latent period : lasts for 10 days due to delayed AB production -small amount of Abs -Abs last for short duration ( disappear rapidly) -Abs have low binding capacity with Ag Importance Stimulate reticuloendothelial system to produce memory cells

35. Type of immune defense : 1)general non specific (innate) defense mechanism of the body. 1-mechanical barrier and surface secretion of the body Healthy and intact skin and mucous membrane prevent invasion of most of micro organism Sticky mucous that cover the mucous membranes trap any foreign material And microorganism Eye : blink reflex and tear can prevent infection . GIT : saliva, mucous secretion (lysozyme) and gastric acidity and diarrhea prevent infection Respiratory system :cilia, coughing , and sneezing reflex sweep out any foreign material and micro organism Genitourinary secretion : acidic ph of vagina inhabits growth of micro organisms

36. 2.normal bacterial flora Produce bacteriocins and acids that destroy micro organisms They complete with pathogens for essential nutrients 3. humoral defense mechanism such as Lysozyme lead to lysis of Bactria Interferon which is non specific defense mechanism against viral infection Complement which is considered a natural innate immunity Plasma can also dilute toxins 4.Cellular defense mechanism : as phagocytosis which engulf particles entering the blood 5.inflammatory reaction : vasodilatation , increase vascular permeability and cellular infiltration can resist invading agents .

37. Acquire immunity Artificially acquire Naturally acquire active passive active passive By administrate by Vaccine Live or killed Human immunoglobulins Disease attack Mother through placenta toxoid Animal anti sera Anti toxins Subclinical infection Mother through milk A)naturally acquire immunity 1- passive A) transplacenal B) mothers milk :

38. 2-Active A)subclinical infection : Exposure to subclinical infection gives immunity against endemic infection disease of community as : poliomyelitis and diphtheria B) clinical infection : Some disease have no sub clinical manifestation but represent clinically only as : measles , chicken pox , syphilis and gonorrhea . attack of infection disease are followed by variable degrees of immunity which may be: absolute (no second attack) after yellow fever only Solid (high degree , long lasting) as after measles , German measles , chicken pox and small pox Moderate : as after enteric fever weak ( short lasting ) as after influenza as multiplicity of strains of the virus , continuous mutation and change in antigenicity so there is repeated attack of influenza

39. B) artificial acquired immunity : 1- passive immunization ( seroprophylaxis ) It is the inoculation of the immune serum that contain already manufactured , immunoglobulins or lymphocytes to induce or cellular immunity . Types : animals or human preparation type disadvantages Advantage Anti toxic sera e.g. diphtheria & tetanus Anti snake sera Antiviral sera as antirabies serum Given in large doses Give short protection 1:2 week May lead to server hypersensitivity reaction Relatively cheap Usually available

40. Human immunogloblobulin ( homologous ) : prepared from human sources Disadvantage : relatively expensive and not constantly available. Advantage : used in small dose . gives immediate immunity for longer period 30 : 50 days safe as it dose not lead to hypersensitivity reactions Type : Specific human immunoglobulin Normal human immunoglobulin (NHI) Prepared from the donner who vaccinated against communicable disease or carrier of specific infections Uses : in prevention of viral disease HBIG .06ml/kg Prevention of varicella zoster infection Prevention of rabies 20iu /kg Prevention of tetanus 250 unite for prophylaxis and 3000: 6000 unit for therapy Prepared from plasma of hepatitis B and C and HIV free donors in endemic area Uses : effective in prophylaxis of measles , rubella , poliomyelitis & viral A hepatitis Sero prevention In early exposure & proper dose Sero attenuation In late exposure or small dose

41. Artificial acquire immunity ( active vaccination ) This type of immunity is induced after vaccination by different type of vaccines 1-Live vaccine : small pox vaccine prepared from cow pox virus 2-Live attenuated vaccine : vaccine prepared from attenuated organisms They should not be given to person with immunodeficiency It is more potent than killed vaccine It usually given as one dose Examples : BCG , measles , rubella , mumps , sabin oral polio vaccine and yellow fever vaccine 3-Killed or inactive vaccine : organisms is killed by heat or chemicals & injected to stimulate active immunization Generally , killed vaccine are less effective than live vaccine

42. 4) cellular fraction vaccine : prepared from extra cellular fraction vaccine : prepared from extra cellular fraction e.g. meningococcal vaccine Artificial acquire immunity ( active vaccination ) cont 5) surface antigen vaccine for viral B hepatitis of two type : Derived from the ( HBsAg ) from plasma of chronic carriers. 6)Poly valent vaccine : which contain the difference strain of the same organisms as in polio virus type 1 ,2 ,3 7)Combination of vaccine ( mixed or combined ) : more than one immunizing agent in the vaccine are combined to simplify administration of different immunization agent at one time and to reduce cost e.g. DPT : diphtheria , pertussis , tetanus DPT Salk : quadriple vaccine diphtheria , pertussis , tetanus and salk polio vaccine DT : Diphtheria , tetanus. MMR : measles , mumps , rubella

43. Hazard of immunization - General reaction : fever , malaise , headache and other constitutional manifestation. -General infection : contaminated needles and syringes as HIV , HBV , HCV CMV & pyogenic infection -Local reaction : e.g. pain swelling , redness tenderness and abscess at the site of infection -Hypersensitivity reaction : in case of anti sera or viral vaccine prepared from embrynated egg , e.g. influenza and mumps , in the form of serum sickness or anaphylactic shock - Neurological involvement : as post vicinal encephalitis or neuroparalytic accidents after rabies vaccine , encephalopathy as in pertussis vaccine

44. Contraindications to child immunization . There are almost no contra indication to vaccination It is safe to immunize children even if they are moderately ill If you delay vaccination due to mild illness many children will contract the target disease Children with mild illness should be immunized as usual Children with malnutrition can develop good immunity so they are immunized as usual Absolute contraindication are : Very sever ill children who who need to hospitalized or children who have very high fever : vaccination should be delayed If a child has had sever reaction from D.P.T ( convulsion or shock ) do not give the child any more doses of D.P.T and give him D .T B.C.G is only vaccine which shouldn't be given to children with clinically apparent AIDS or immune deficiency disease .

45. Herd immunity It is state of immunity of a group or community Also it is the resistance of the a group to invasion and spread of an infectious agent Based on immunity of a high proportion of individual members of the group Characteristics of herd immunity If a large percent of population is immune the entire population is likely to be protected Once a high proportion of all people in the community are immune the likelihood is small that an infected person will encounter a susceptible person Herd immunity operate optimally when there is random mixing of the population ( no clustering of susceptible persons)