BASIC PRINCIPLES IN THE FIGHTAGAINST INFECTIOUS DISEASES. PROPHYLACTIC AND ANTIEPIDEMIC MEASURES Prof. Dr. N. Ribarova, MD
STRUCTURE OF THEEPIDEMIOLOGICAL PROCESS Source of infection Mechanism of transmission Susceptibility of the Population
Changes in these factors caused by thesocial and natural environment reflecton the intensity of the epidemic process.
Thus the efficacious prophylactics and effective fight against infectious diseases are possible only when the antiepidemic measures are directed in three ways: measures eliminating or decontaminating the source of infection; measures stopping the mechanism of transmission of infection; measures stimulating insusceptibility of the population to a certain disease.
I. MEASURES ELIMINATING OR DECONTAMINATING THE SOURCE OF INFECTION It is the main trend in the fight against infectious diseases.* measures for extermination - elimination of the sick animals (carriers of infection). The method is the best one in case of infected wild animals as well as domestic animals;* measures for derattization - used at rodents, reservoirs of infections;* sanitary measures - concerning domestic and farm animals (for example, carriers of brusellosis). In this way animals are used for the purposes of the farms simultaneously with the measures for their recovery.
Measures for extermination are not applicable atanthroponosus infectious diseases where the sourceof infection is the man - a sick person or a carrier ofinfection. In this case the aim is to decontaminate thesource of infection putting it in such conditions inwhich the possibilities for transmission of infectionare cut off. *isolation of the sick persons - in an infectiousward or at home. Complete influencing of the sourceof infection is impeded also by the characteristics ofthe clinical course of the disease - inapparent, mildclinical forms, chronic forms, etc.
Localization and decontamination of the source ofinfection depend on:* living conditions - conditions facilitatingtransmission of infection to other persons should beeliminated;* attitudes of the population - whether peopleseek doctors help immediately, refusal of hospitali-zation, etc. as well as degree of health knowledgeand responsibility for the economic costs.* possibilities for specific, etiologic treatment ofthe sick persons and carriers of infection.
Urgent prevention is also one of the measuresfor influencing the source of infection. Urgentprevention - it is the use of prophylactic andcurative means to prevent development of thedisease from the carriers of infection in incubation.For this purpose immune serums, vaccines,bioproducts, chemotherapeutic agents –sulfonamides, antibiotics, etc. are applied.
II. MEASURES STOPPING THE MECHANISM OF TRANS-MISSION OF INFECTION These measures are various ones. They are mainly related to the specific characteristics of the mechanism of transmission of the different infectious diseases. Generally, it is very difficult to carry out such measures.
1. Diseases belonging to the group of entericinfections. The measures require the agents of infectionin the faeces of the sick persons not to getthrough food, water, etc. into thegastrointestinal tract of the healthy people.
Sanitary measures eliminating the faecal-oral way of infection are of crucial importance: development and urbanization of the built-up areas; water supply, sewerage; decontamination of the sewerage waters; collection and decontamination of the hard wastes; sanitary measures in public catering; following the regulations of sanitation; school hygiene; health knowledge of the population.
2. Diseases belonging to the group of respiratory infections: Gauze masks, aeration and ventilation, bactericidical lamps, disinfection.
3. Diseases belonging to the group of blood infections: Character, access and effectiveness of the measures applied depend on the biological carrier: agromeliorative measures; hydrotechnical measures; disinsection and derattization; means of individual prevention; stimulating accumulation of health knowledge.
4. Diseases belonging to the group of covering infections: They are transmitted through the personal belongings, household goods, etc.* disinfection;* hygienic measures for decontamination;* stimulating the accumulation of health knowledge of the population.
III. MEASURES STIMULATING INSUSCEPTIBILITY OF THE POPULATION A perspective for prevention and fight against infectious diseases is development of specific insusceptibility of the population to infectious diseases.
IMMUNITY represents a complex ofpreventive physiologic responses of thewhole organism, i.e. it is a way ofprevention of the organism from proteinbodies carrying themselves foreign geneinformation.
Immune system recognizes the relevantantigens through its immunocompetentcells and reacts against them producingIMMUNE RESPONSE as well asdeveloping immune memory and immunetolerability.
IMMUNE RESPONSE is a complexreaction of the organism induced by theantigen penetrated in it, whichmorphologic base is proliferation anddifferentiation of the immunocompetentcells.
Recognition of the antigen is made with the help of two types of lymphocytes:* T-lymphocytes - they have developed their immunologic competence through thymus and that is why they are called "thymus-dependent";* B-lymphocytes - they have developed their immunologic competence through the Fabricius bursa" (for the birds) or through its equivalent for the mammals, probably bone marrow or part of the lymph tissue of the intestines - Payers plaques, appendix and tonsils.
In the course of the evolution the followingtypes of immunity have been developed:1. Hereditary (species) immunity:It is formed during the philogeneticdevelopment of the individual. It represents astate of insusceptibility of the organismrelated to the species to which the man or theanimal belong. It is inherited (for example,people do not suffer from hen cholera,animals - from measles).
2. Acquired (individual) immunity. It is formed during the ontogenetic development of theindividual. The ability of the organism to developontogenetic mechanisms is a result from its philogenesis.Individual immunity is divided as follows:A. Naturally acquired immunity, which, on its part, is divided to: * passive - due to antibodies, inherited from the mother; * active – postinfectious, domestic immunity.B. Non-naturally acquired (pos-timmunization) immunity, divided to: *active - developed after application of vaccines and toxoids; *passive - after administration of readymade antibodies through serums and immunoglobulins.
The difference between these two typesof development of immunity is related tothe way of development as well as thelevel of its intensity and duration.
According to the mechanism of development of the immune response immunity is divided as follows:• humoral immunity - it acts thro-ugh B-lymphocytes as well as antibo-dies circulating freely as immunoglobulins in the blood and the other body liquids. The antibodies react directly to the antigens forming a type of response "antigen-antibody" - precipitation, neutralization, accumulation,etc. depending on its conditions.• cell immunity - it acts through the circulating T- lymphocytes together with the non-immunoglobulin mediators of the lymph function (activated macrophages). Local immunity is an antigen (mainly IgA) and is cell mediated - in the immunosecretory system of the mucous of the gastrointestinal tract and respiratory ways (the entrance of infection).
Collective immunity - it is the ability of thehuman collective to resist to the activity of theagents of the infectious diseases and toprevalence of the endemic process. It isdetermined by the specific immune structureof the population as well as the possibility forrealization of the mechanism of transmissionof infection in the real circumstances.
Immune structure is a concept reflecting thedistribution of the members of the groupdepending on the degree of their susceptibilityto infectious diseases.
Non-specific immunologic structure - it characterizes the degree of insusceptibility of the population to all infectious diseases. It is measured by different immunologic, physiologic, and other methods.
Specific immunologic structure - it characterizes insusceptibility of the population to a certain infectious disease. It is measured by the percentage of the individuals possessing immunity.
Collective immunity is not a simple sum of the individual immunity of the separate members of the group. Different individuals may belong to the group as follows: with highly intensive immunity; with partial immunity; with out developed immunity.
There are many different contingents of susceptible individuals: newborns and toddlers (due to undeveloped immune system); recovered individuals with short-term and slightly intensive immunity; individuals immigrating to regions, which are endemic for certain diseases; old-aged individuals (with reduced resistance of the organism); individuals suffering from innate and acquired impairments of the immune system, ofimmunogenesis, etc.
Characteristics of the three directions ofprevention and fight against infectious diseasesprovide the possibility for achieving the necessarypractical results at many infectious diseases if themeasures influencing the preventive directions aresimultaneously carried out – decontamination of thesource of infection, stopping the mechanism oftransmission of infection and stimulating thespecific insusceptibility of the population. This isthe basic principle of the antiepidemic fight.
One of these three ways of activity is thebasic one as the other two arecomplementary depending on the natureof the infectious disease and the situation.
ANTIEPIDEMIC MEASURES IN THE EPIDEMIC CENTRE I. Measures to the patient1. Early finding and recognition of the disease.2. Putting proper diagnosis. clinical methods; laboratory methods; epidemiological methods.3. Registration and informing for the infectious disease. quick informing - form N 58; Registration book of infectious diseases - form N 60; Registration book of hospital infections - form N 11.
4. Isolation of the patient in an infectious ward or at home: transportation of the patient - in a suitable way for him/ her; safe for the other persons; sanitary manipulation - bathing, decontamination of the clothes and underwear, eliminating parasites; specific etiologic therapy; dehospitalization of the patient: * after full clinical recovery * elimination of the pathogenic agent (the infect) * sanitary manipulation; * disinfection of the clothes, underwear, etc. Chronically sick patients are under dispensary observation.
II. Measures to the other persons (contacting ones as well as carriers of infection)1. Measures to contacting persons: epidemiological investigation for finding of all contacting persons; registration - "Book for persons in contacts with acutely infected patients" - form N 61; medical observation - a maximal incubation period, thermometring, clinical examination;
sanitary manipulation - when necessary; quarantine of the contacting persons - highly infected ones in isolation - serologic, microbiological, virusologic analyses; active or passive immunization; urgent prevention with antibiotics and chemotherapeutical agents.
2. Measures to the carriers of infection: finding - epidemiological investigation; - microbiological investigation; sanation of the carriers of infection - directed to elimination and cleaning of the pathogenic micro- organisms; isolation.
SPECIFIC PREVENTIONDefinition: An approach for development ofnon-natural specific insusceptibility to theetiologic agent of a certain infectious disease.
Vaccination process: An interaction between the vaccine agent and the human organism with its individual characteristics. It is a complex reaction, which includes as follows: specific immune reorganization resulting in development of immunity (the aim of the immunization); concomitant processes of non-specific reorganization (directed to restoration of the homeostasis) as well as allergization, clinically manifested or asymptomatic.
Different preparations are used fordevelopment of immunity - vaccines, toxoids,serums, immunoglobulins.
Live vaccines: Immune preparations, containingbacteria and viruses that have lost theirpathogenic properties but preserved theirimmunologic properties. Such types of vaccinesare as follows: against tuberculosis,polyomielitis, measles, mumps, influenza,smallpox, tularemia, brucellosis, anthrax, plaque,yellow fever, etc. These vaccines developintensive and longterm immunity.
Inactivated vaccines: They are prepared fromthe cultures of different infects, inactivatedphysically (heating up) or chemically (formalin,phenol, alcohol, etc.) - abdominal typhus,paratyphus, cholera, who-oping-cough,leptospyroses, etc. as their immunogenicproperties are preserved.Recombinant vaccines: They are made with thehelp of gene engineering with hybridomatechnic, etc.
Chemical vaccines: They are full antigen vaccines,derived chemically from bacterial cultures. They are maximally lacking ballast substances, sideprotein components and cause relatively lowallergization of the organism. They are stable.(Against enteric infections – abdominal typhus,paratyphus A and B, together with a tetanicus toxoid). Toxoids: They are derived from the products of themicroorganisms, mainly their toxins, through theirinactivation (by formalin or heating up) - againstdiphtheria, tetanus, staphylococcus infection, etc.
Protective antigens: Immunization substancesrelated to the pathogenic factors of bacterialand virus cells. Such antigens are discoveredlately in plaque and whooping-cough bacteria,streptococcus, staphylococcus, anthrax bacilli,Ricketsias, etc.
Serums: Immune preparations proving passiveimmunologic prevention for a short time (2 to 4weeks). They are ready-made antibodies (anthrax,whooping-cough, epidemic meningitis, tetanus,diphtheria, botulism, staphylococcus infection).Bacteriophages: live agents, which are parasitesin the bacterial cell - abdominal typhus,shigelloses, salmonelloses, cholera. They havelimited application.
Interferon: a protein synthesized from the cells inresponse to a virus infection making the other cellsresistant to infection. It inhibits virus proliferationthrough non-immunologic mechanisms (virusinterference) - application at influenza,parainfluenza, coxsackie B3, ECHO-13,adenoviruses, enteric infections, etc. Immunoglobulins: simple, hyperimmune.
Application of vaccines: * subcutaneous, intracutaneous, oncutaneous, peroral, intranasal, aerosol method.Application of serums and inimunoglobulins: * subcutaneous, intracutaneous (strictly according to the method of Bezredka).
Postimmunization reactions of the organism: general - changes in the body temperature and state of the organism; local - hyperemia and edema.Postimmunization complications: serum disease, anaphylactic shock, postvaccination encephalitis, etc.
Contraindications: severe states of the organism: acute infectious diseases, active form of tuberculosis, decompensated valvular disease, hypertension, renal diseases (nephritis), diabetes, broncl asthma, anemia, cachexia, the second half of pregnancy, etc. specific for the disease.
The effect of immunizations depends on: compatibility of the immunizations; the scheme and dosage of the vaccines; reactivity of the organism; size of the immune layer.
Organization of application of immunizations: bioproducts supply; quality of the bioproducts; storage conditions and transportation of the bioproducts.
Immunization calendar: importance.Inspection of the results of the immuniztions.Registrations, reporting, collective immunity.
Possibilities for application of the vaccines: according to the aims of prevention; according to epidemiological indications.Immune prevention with serums: when necessary.
DISINFECTION1. Generally, disinfection (decontamination) is a complex of methods and means directed to elimination of the source of infection in the environment. The concept includes the following stages: disinfection itself together with sterilization and antiseptic method, disinsection and derattization.
DISINFECTION (itself) means the eliminationof the pathogenic microorganisms in theenvironment
Types of disinfection according to its goals and tasks are as follows: Prophylactic (preventive) disinfection: It is carried out where a centre of infection does not exist but there are facilitating conditions of its development. It is performed systemically under plans for certain periods of time - in nursery schools, schools, hospitals, cinemas, theatres, railway stations, catering establishments, of drinking water, milk, food, etc.
Disinfection of the centre of infection. It is carried out in the centre of infection. Its aim is the elimination of the pathogenic mechanisms in the environment of the patient producing the microorganisms and contaminating the environment. Disinfection performed during the course of the disease is called current disinfection. After recovery of the patient, its hospitalization or after a lethal outcome the final (ending) disinfection is performed. The quality of the current disinfection determines the complex of tasks, methods and means for the final disinfection.
STERILIZATION. A method for elimination ofall microorganisms (pathogenic and saprophyte,viruses, bacteria, mould) in their different forms -vegetative and spores
SANITATION. A method for the rapidreduction of the microbial flora in an object inthe environment (for example, after washing). Itis widely applied in everyday life as a preventivemeasure.
ANTISEPTIC METHOD. A method forprevention of development of microorganismson the human skin and mucous.
DISINSECTION: elimination of the arthropods, carriers of infectious diseases. DERATTIZATION: elimination of the rodents, natural reservoirs of infections.
Methods of disinfection: Biologic method: biological filters for decontamination of the water (on the base of the microbial antagonism). Mechanical method: cleaning, wash ect. Physical method: sun shining, ultra-violet rays, ionizing radiation, supersound, dry heat for sterilization by dry air, wet heat – sterilization and vapour under pressure. Chemical method: use of chemical compounds- disinfectants.
Methods of disinsection: Biological method: use of the natural enemies of the harm arthropods - predatory animals (the fish gambusia), parasites, pathogenic microorganisms (Bacillus thuringiensis), genetically changed, sexually sterile populations. Mechanical method: cleaning, wash, etc. Physical method: high temperature - hot dry and wet air for vapouring, sterilization, burning out, etc.
5. Chemical method: insecticides: larvacides - for elimination of larvae; acaricides - for elimination of Acars; ovocides - for elimination of their eggs; pesticides - for elimination of weeds; * attractants - attracting insects; * repellents - repelling insects.
Insecticides for arthropods depending on their way of penetration in the organism are as follows: fumigants - gas insecticides - they act through the respiratory system; intestinal insecticides - through the digestive tract; contact insecticides - act at contact to outer parts of the insects: a) with residual effect; b) without residual effect.
Methods of derattization:1.Preventive (prophylactic) derattization: a) sanitary and technical means – lack of access of the rodents to the buildings – openings of drainage, doorstills, etc. b) sanitary and hygienic measures – lack of access to food.Exterminatory derattization: a) biologic method – natural killers of the rodents. b) mechanical method – use of traps; c) chemical method – use of chemical compounds – rodenticides.