International Health, WHO Structure & Functions, and IHR 2005

INTERNATIONAL HEALTH - Definition and Origin

HISTORICAL EVOLUTION OF INTERNATIONAL HEALTH ORGANIZATIONS

1. First International Sanitary Conference (1851)

2. Pan American Sanitary Bureau (1902)

3. Office International D'Hygiene Publique (1907)

4. Birth of WHO

WORLD HEALTH ORGANIZATION (WHO)

Objective

"Health is a state of complete physical, mental and social well-being and not merely the absence of disease or infirmity."

• The enjoyment of the highest attainable standard of health is one of the fundamental rights of every human being without distinction of race, religion, political belief, economic and social condition.
• The health of all peoples is fundamental to the attainment of peace and security.
• Unequal development in different countries in the promotion of health and control of disease, especially communicable disease, is a common danger.
• Governments have a responsibility for the health of their peoples.

Membership

STRUCTURE OF WHO

(a) The World Health Assembly (WHA)

• Composed of delegates representing Member States, each with one vote
• Main functions:
  1. To determine international health policy and programmes
  2. To review the work of the past year
  3. To approve the budget for the following year
  4. To elect Member States to designate persons to serve on the Executive Board
  5. To appoint the Director General on the nomination of the Executive Board
• On the occasion of each Health Assembly, "technical discussions" on subjects of world interest are organized.

(b) The Executive Board

• Currently has 34 members, each designated by a Member State
• Members must be "technically qualified in the field of health" - they are designated by, but do not represent, their governments
• One-third of the membership is renewed every year
• Meets at least twice a year - generally in January and shortly after the WHA in May
• Main work: to give effect to the decisions and policies of the Assembly
• Also has power to take emergency action (epidemics, earthquakes, floods) where immediate action is needed

(c) The Secretariat

• Headed by the Director General, who is the chief technical and administrative officer
• Primary function: to provide Member States with technical and managerial support for national health development programmes
• By 2010, staffed by about 8,000 health and other experts and support staff
• At WHO headquarters in Geneva, there are 5 Assistant Director Generals

Secretariat Divisions (as listed):

1. Division of epidemiological surveillance and health situation and trend assessment
2. Division of communicable diseases
3. Division of vector biology and control
4. Division of environmental health
5. Division of public information and education for health
6. Division of mental health
7. Division of diagnostic, therapeutic and rehabilitative technology
8. Division of strengthening of health services
9. Division of family health
10. Division of non-communicable diseases
11. Division of health manpower development
12. Division of information systems support
13. Division of personnel and general services
14. Division of budget and finance

WHO REGIONAL ORGANIZATIONS

WORK (FUNCTIONS) OF WHO

1. Prevention and Control of Specific Diseases

• Communicable diseases form the core of WHO activities. The global eradication of smallpox is an outstanding example of international health cooperation.
• WHO now directs the global battle against poliomyelitis.
• Epidemiological surveillance of communicable diseases through the Weekly Epidemiological Record (WER) and the Automatic Telex Reply Service (ATRS).
• Non-communicable diseases: cancer, cardiovascular diseases, genetic disorders, diabetes, blindness, mental disorders, drug addiction and dental diseases.
• Vector biology and control, immunology, drug quality control, Expanded Programme on Immunization (EPI) as a priority programme.

2. Development of Comprehensive Health Services

• Promotes and supports national health policy development and comprehensive national health programmes.
• Activities include organizing health systems based on primary health care, development of health manpower, building of long-term national capability.
• Appropriate Technology for Health (ATH): a programme encouraging self-sufficiency in solving health problems.

3. Family Health

• A major programme activity since 1970.
• Broadly subdivided into maternal and child health care, human reproduction, nutrition and health education.
• Chief concern is improvement of the quality of life of the family as a unit.

4. Environmental Health

• WHO advises governments on basic sanitary services.
• Activities directed to protection of quality of air, water and food; health conditions of work; radiation protection; early identification of new hazards.
• WHO Environmental Health Criteria Programme; WHO Environmental Health Monitoring Programme.

5. Health Statistics

• WHO has been concerned with dissemination of morbidity and mortality statistics since 1947.
• Data published in: (a) Weekly Epidemiological Record (b) World Health Statistics Quarterly (c) World Health Statistics Annual.
• Publishes the International Classification of Diseases (ICD), updated every 10th year. The Tenth Revision (ICD-10) came into effect from 1st January 1993.
• Provides assistance to countries in improvement of medical records and planning national health information systems.

6. Biomedical Research

• WHO does not itself do research, but stimulates and coordinates research work.
• Has established a worldwide network of WHO Collaborating Centres.
• Established Regional Advisory Committees on health research, plus a Global Advisory Committee.
• Six tropical diseases targeted by the WHO Special Programme for Research and Training in Tropical Diseases: malaria, schistosomiasis, trypanosomiasis, filariasis, leishmaniasis and leprosy.

7. Health Literature and Information

• WHO acts as a clearing house for information on health problems.
• Publications comprise hundreds of titles on health subjects.
• WHO library is one of the satellite centres of the Medical Literature Analysis and Retrieval System (MEDLARS) of the U.S. National Library of Medicine.
• MEDLARS is a fully computerised indexing system covering medicine on an international basis.
• A public information service is maintained at both headquarters and each of the six regional offices.

8. Cooperation with Other Organizations

• WHO collaborates with the UN and other specialized agencies, and maintains working relationships with various international governmental organizations (UNICEF, FAO, World Bank, ILO, etc.).

INTERNATIONAL HEALTH REGULATIONS (IHR) 2005

Background and Historical Context

• (a) Diseases subject to IHR (1969): cholera, plague and yellow fever
• (b) Diseases under WHO surveillance: louse-borne typhus fever, relapsing fever, paralytic polio, malaria, viral influenza-A, SARS, smallpox, etc.

IHR 2005

• Obligatory notification by Member States to WHO of events that may constitute a PHEIC
• Requirement for core public health capacities at national and local levels
• The use of a decision instrument (algorithm) to assess whether an event constitutes a PHEIC
• Measures applicable to travellers, ports of entry, conveyances, and goods

Diseases Subject to IHR (2005)

• Smallpox
• Poliomyelitis (due to wild-type poliovirus)
• Human influenza caused by a new subtype
• SARS (Severe Acute Respiratory Syndrome)

Amendment to IHR 2005 - Yellow Fever Vaccination (2014/2016)

"The period of protection afforded by yellow fever vaccination, and the term of validity of the certificate will change from 10 years to the duration of the life of the person vaccinated."

• On 11th July 2016, this amendment entered into force and is legally binding upon all IHR states.
• Lifetime validity applies automatically to all existing and new certificates, beginning 10 days after the date of vaccination.
• As of 11th July 2016, revaccination or a booster dose of yellow fever vaccine is not required for international travellers as a condition of entry into a State Party, regardless of when the original certificate was issued.
• In India, the lifetime validity of yellow fever vaccination applies automatically.

International Certificate of Vaccination

• India and most other countries require a valid certificate of vaccination against yellow fever from travellers coming from infected areas.
• A few countries (including India) require this even if the traveller has only been in transit.
• India requires vaccination of infants (≥ 9 months of age) coming from endemic areas.

IHR Implementation - India's Approach

1. Travellers: Valid international certificate of vaccination against yellow fever required before entry into receptive areas. Without certificate, quarantine in a mosquito-proof ward for 6 days.
2. Mosquitoes: Aircraft and ships from endemic areas subjected to aerosol spraying with prescribed insecticides; airports and seaports kept free from breeding of insect vectors over an area extending at least 400 metres; Aedes aegypti index kept below 1%.

Source: Park's Textbook of Preventive and Social Medicine (ISBN: 9789382219163), Chapter 25 (International Health and WHO), pp. 1020-1025; and relevant sections from chapters on Communicable Diseases and Yellow Fever.

Gene-Environment Interaction in Common Lifestyle Disorders

Conceptual Background

"As with other chronic diseases, cancer has a multifactorial aetiology."

"The aetiology of CHD is multifactorial."

"The aetiology of obesity is complex, and is one of multiple causation."

I. CORONARY HEART DISEASE (CHD)

Risk Factors - Modifiable vs Non-Modifiable

Genetic Factors in CHD

"A family history of CHD is known to increase the risk of premature death. Genetic factors are probably the most important determinants of a given individual's TC and LDL levels. However, the importance of genetic factors in the majority of cases is largely unknown."

• Apolipoprotein genetics: Levels of plasma apolipoprotein-A-I (the major HDL protein) and apolipoprotein-B (the major LDL protein) are better predictors of CHD than HDL cholesterol or LDL cholesterol respectively. These apolipoprotein levels are substantially genetically determined.

Gene-Environment Interaction in CHD

"There is evidence that the influence of smoking is not only independent of, but also synergistic with other risk factors such as hypertension and elevated serum cholesterol. This means that the effects are more than additive."

• Hormonal interaction: The pronounced difference in CHD mortality between males and females suggests a hormonal basis - hyperestrogenemia may be the common underlying factor in atherosclerosis and its complications. This hormonal difference is in part genetically determined.
• Diabetes and CHD: The risk of CHD is 2-3 times higher in diabetics than non-diabetics (itself partly genetic); CHD is responsible for 30-50% of deaths in diabetics over 40 years in industrialized countries. Thus, genetic predisposition to diabetes amplifies CHD risk.

II. TYPE 2 DIABETES MELLITUS

Agent Factors - Genetic Mechanisms

• Genetic defects, e.g., mutation of insulin gene
• Decreased insulin sensitivity due to decreased numbers of adipocyte and monocyte insulin receptors
• Autoimmunity (in genetically susceptible individuals)

"Evidence is accumulating that the insulin response to glucose is genetically controlled."

Genetic Factors (Host)

"Twin studies showed that in identical twins who developed type 2 diabetes, concordance was approximately 90 per cent, thus demonstrating a strong genetic component. In type 1 diabetes, the concordance was only about 50 per cent indicating that type 1 diabetes is not totally a genetic entity."

• Type 1 diabetes is associated with HLA-B8 and B15, and more powerfully with HLA-DR3 and DR4. The highest risk of type 1 diabetes is carried by individuals with both DR3 and DR4.
• Type 2 diabetes is not HLA-associated.

"Some people appear to have defective immunological mechanisms, and under the influence of some environmental 'trigger', attack their own insulin producing cells." This is a direct description of gene-environment interaction: a genetic defect in immune regulation + an environmental trigger (viral infection) = type 1 diabetes.

Gene-Environment Interaction in Diabetes

"In obese patients with type 2 diabetes, the association of hyperglycaemia, hyperinsulinaemia, dyslipidaemia and hypertension ... may result from a genetic defect producing insulin resistance, with the latter being exaggerated by obesity."

• Genetic defect = insulin resistance
• Environmental factor = obesity (driven by sedentary lifestyle + diet)
• Interaction = full-blown metabolic syndrome / type 2 diabetes

"The population in India has an increased susceptibility to diabetes mellitus. This propensity was demonstrated by multiple surveys of migrant Indians residing in Fiji, Singapore, South Africa, U.K. and USA. The rates of diabetes in migrants from the Indian subcontinent have consistently shown to exceed those of the local population."

"Unfavourable modification of lifestyle and dietary habits that are associated with urbanization are believed to be the most important factors for the development of diabetes."

"Among the viruses that have been implicated are rubella, mumps, and human coxsackie virus B4. Viral infections may trigger in immunogenetically susceptible people a sequence of events resulting in β-cell destruction."

"Offsprings of diabetic pregnancies ... tend to develop obesity in childhood and are at high risk of developing type 2 diabetes at an early age." Maternal diabetes associated with intrauterine growth retardation and low birth weight, when associated with rapid catch-up growth later, further increases risk.

III. OBESITY

Genetic Factors

"There is a genetic component in the aetiology of obesity. Twin studies have shown a close correlation between the weights of identical twins even when they are reared in dissimilar environments. The profile of fat distribution is also characterized by a significant heritability level of the order of about 50 per cent of the total human variation. Recent studies have shown that the amount of abdominal fat was influenced by a genetic component accounting for 50-60 per cent of the individual differences."

"Obesity frequently runs in families (obese parents frequently having obese children), but this is not necessarily explained solely by the influence of genes."

Gene-Environment Interaction in Obesity

• Genetic component: ~50% heritability for BMI; 50-60% for abdominal fat distribution
• Environmental modifiers (the other ~50%):
  • Physical inactivity: Convincing evidence that sedentary lifestyle promotes unhealthy weight gain; physical activity is a key modifier of morbidity and mortality related to overweight.
  • Diet: High energy-dense diets, fast foods, eating habits established early in life
  • Socioeconomic and psychosocial factors
  • Endocrine factors (Cushing's syndrome, growth hormone deficiency) in occasional cases

"The first adverse effects of obesity to emerge in a population in transition are hypertension, hyperlipidaemia and glucose intolerance, while coronary heart disease and the long-term complications of diabetes such as renal failure begin to emerge several years (or decades) later."

IV. CANCER

Environmental Factors (80-90% of all human cancers)

Genetic Factors

"Genetic influences have long been suspected. For example, retinoblastoma occurs in children of the same parent. Mongols are more likely to develop cancer (leukaemia) than normal children. However, genetic factors are less conspicuous and more difficult to identify."

"There is probably a complex interrelationship between hereditary susceptibility and environmental carcinogenic stimuli in the causation of a number of cancers."

• Occupational exposures + smoking: "The risk of occupational exposure is considerably increased if the individuals also smoke cigarettes." - a classic gene-environment-lifestyle interaction.
• HBV/HPV infection + genetic susceptibility in liver cancer and cervical cancer
• BRCA genes + lifestyle: Implied in the breast cancer-dietary fat relationship

V. HYPERTENSION

Risk factors (Non-modifiable):

• Age, sex, family history (genetic), race/ethnicity

• Age
• Family history / genetic predisposition

• Obesity/overweight
• Physical inactivity
• High sodium diet
• Excess alcohol
• Stress

Key Principles Summarized

1. Multifactorial causation: All common lifestyle disorders have multiple contributing factors - genetic and environmental - acting simultaneously.
2. Genetic susceptibility as a "background": Genes set the individual's susceptibility threshold. Environmental factors then determine whether disease actually occurs and at what severity.
3. Synergism: The combination of genetic susceptibility and environmental exposure produces a risk that is more than additive (as shown in the CHD risk factor combination diagram in Park's).
4. Population-level evidence: Migration studies (especially in South Asian populations) demonstrate gene-environment interaction at the population level - the same genetic background expressed differently in different environments.
5. Modifiability: Because the environmental component is modifiable, the emphasis in prevention is on lifestyle changes - diet, physical activity, avoidance of tobacco and alcohol - which can reduce risk even in genetically susceptible individuals.
6. Intergenerational dimension: Maternal diabetes, intrauterine growth retardation, and rapid postnatal catch-up growth represent gene-environment interactions that span generations.

Source: Park's Textbook of Preventive and Social Medicine (ISBN: 9789382219163) - Chapter on Coronary Heart Disease (p. 417-420), Diabetes Mellitus (p. 443-453), Obesity (p. 447-452), Cancer (p. 432-438), and Hypertension (within Block 6).

Genetic Counselling: Indications and Importance in Preventive Medicine

Definition

"The most immediate and practical service that genetics can render in medicine and surgery is genetic counselling."

• Park's Textbook of Preventive and Social Medicine

Background: Genetic Disorders - A Public Health Problem

Chromosomes and Genes

• Human beings have 46 chromosomes (23 pairs); one member of each pair from each parent
• Genes are units of heredity encoded in DNA, numbering approximately 50,000 from each parent (total ~100,000)
• Each gene occupies a specific locus on the chromosome
• Genes also occur in pairs; if alike (AA) - homozygous; if unlike (Aa) - heterozygous

Classification of Genetic Disorders

• Incidence: 5.6 per 1000 live births
  • Sex aneuploidies: 2 per 1000 live births
  • Autosomal aneuploidies: 1.7 per 1000 live births
  • Chromosomal translocations: 1.9 per 1000 live births

• Klinefelter's syndrome (XXY): ~1 in 1000 males; eunuchoid males with non-functional testes, gynaecomastia, mental retardation
• XYY syndrome: ~1 in 1000 males; exceptional height, personality disorder
• Turner's syndrome (XO): ~1 in 7,500 live-born girls; short stature, primary amenorrhoea, infertility, cardiac and renal defects
• Down's syndrome (Trisomy 21 / Mongolism): Incidence at maternal age 20 is 1:3000; by age 40, it is 1:40

• Estimated combined incidence: ~1% of all live-born individuals
• 793 autosomal dominant phenotypes, 629 autosomal recessive traits and 123 sex-linked diseases have been catalogued
• Modes of inheritance:
  • Dominant: One abnormal gene is sufficient; trait appears in every generation
  • Recessive: Both genes must be abnormal; carriers (heterozygotes) appear normal
  • X-linked: Gene carried on X chromosome (e.g., haemophilia, muscular dystrophy, G6PD deficiency)

• Most common category - frequency higher than Mendelian and chromosomal disorders
• Include: essential hypertension, schizophrenia, mental retardation, duodenal ulcer, ischaemic heart disease (early onset), diabetes, congenital heart malformations

• "The mode of inheritance of multifactorial disorders is complex because environmental factors are also involved, as for instance, the influence of smoking, diet, obesity and lack of exercise on ischaemic heart disease. Campbell (1965) stressed that environmental agents and genetic constitutions usually interact closely in producing abnormalities."

• The relative contributions of genetic predisposition and environmental factors will vary greatly from patient to patient

Types of Genetic Counselling

(i) Prospective Genetic Counselling

"This allows for the true prevention of disease."

• Requires identifying heterozygous individuals (carriers) for a particular defect by screening procedures
• Explains to them the risk of having affected children if they marry another heterozygote for the same gene
• If heterozygous marriage can be prevented or reduced, the prospects of giving birth to affected children diminish
• Examples: sickle cell anaemia and thalassaemia
• Represents primary prevention in the truest sense

(ii) Retrospective Genetic Counselling

"Most genetic counselling is at present retrospective, i.e., the hereditary disorder has already occurred within the family."

• A WHO survey showed genetic advice was chiefly sought for:
  • Congenital abnormalities
  • Mental retardation
  • Psychiatric illness
  • Inborn errors of metabolism
  • Only a few sought premarital advice
• Methods suggested under retrospective counselling:
  1. Contraception
  2. Pregnancy termination
  3. Sterilization - depending on the attitudes and cultural environment of the couples involved

"The WHO recommends the establishment of genetic counselling centres in sufficient numbers in regions where infectious disease and nutritional disorders have been brought under control and in areas where genetic disorders have always constituted a serious public health problem (e.g., sickle cell anaemia and thalassaemia)."

Indications for Genetic Counselling

1. Indications for Prenatal Diagnosis (Table 3, Park's)

2. Specific Indications for Amniocentesis

1. Mother aged 35 years or more (high risk of Down's syndrome)
2. Previous child with Down's syndrome or other chromosomal anomalies
3. Parents known to have chromosomal translocation
4. Parents who have had a child with a metabolic defect detectable by amniocentesis (e.g., Tay-Sach's disease, galactosaemia, Maple syrup urine disease, alpha-thalassaemia, neural tube defects)
5. Family history of a sex-linked genetic disease (e.g., certain muscular dystrophies)

3. Sickle Cell Anaemia

• Prenatal diagnosis is available for couples at risk
• DNA from foetal cells can be directly examined
• Presence of the sickle cell mutation can be accurately diagnosed

• "Genetic counselling should be made available to such couples."

4. Thalassaemia

• Identified prospectively by carrier screening (haemoglobin electrophoresis)

• "Genetic counselling can have the greatest impact when individuals or couples at genetic risk are identified prospectively, i.e., before they have developed symptoms themselves or produced their first affected child."

5. Detection of Genetic Carriers

• Duchenne muscular dystrophy (X-linked): Female carriers detected by elevated serum creatine kinase (80% of carriers)
• Haemophilia, PKU, galactosaemia: Carriers detectable in a proportion of cases
• Acatalasia: Carriers recognized with high certainty
• Alkaptonuria: No detection method yet

6. Screening of Newborn Infants

• Sex chromosome abnormalities
• Congenital dislocation of hip
• Phenylketonuria (PKU) - Guthrie card, heel-prick blood at 5-10 days
• Congenital hypothyroidism
• Sickle-cell disease (haemoglobin electrophoresis using Guthrie blood spots)
• Cystic fibrosis (immunoreactive trypsin in Guthrie blood spots)
• Duchenne muscular dystrophy
• Congenital adrenal hyperplasia
• G6PD deficiency

7. Recognizing Pre-clinical Cases (Relevant to Counselling)

• Heterozygotes for PKU: Detected by phenylalanine tolerance test
• Diabetes: Glucose tolerance test in siblings and close relatives of diabetics
• Sickle cell trait: Red cells subjected to reduced oxygen tension
• Thalassaemia minor: Detected by studying the blood picture
• Gout: Raised serum uric acid

Importance in Preventive Medicine

Framework: Levels of Prevention Applied to Genetic Disorders

1. Health Promotional Measures (Primordial / Primary Prevention)

• Negative eugenics: Reducing frequency of hereditary disease through measures against reproduction of affected individuals. However, eugenic sterilization alone cannot eliminate genetic defects because new cases arise from fresh mutations and from hidden heterozygous carriers.
• Positive eugenics: Encouraging carriers of desirable genotypes to reproduce. Has very limited practical application due to complexity of multifactorial traits.

"Mere improvement of the genotype is of no use unless the improved genotype is given access to a suitable environment... Thus the solution of improving the human race does not lie in contrasting heredity and environment, but rather in the mutual interaction of heredity and environmental factors."

• Consanguineous marriages: First-cousin offspring showed death rate of 116 per 1,000 in first 8 years vs 55 among controls. Discouraging such marriages reduces recessive disorders (albinism, alkaptonuria, PKU)
• Late marriages (advanced maternal age): Risk of mongolism at age 20 is 1:3000; at age 40, it is 1:40. Early marriage of females prevents mongolism.

2. Specific Protection

• Protection against mutagens - X-rays, ionizing radiations, chemical mutagens
• X-ray examination of pregnant uterus must be strongly deprecated
• Rh haemolytic disease of newborn: preventable by anti-D globulin immunization
• Protection of gonads from unnecessary radiation exposure

3. Early Diagnosis and Treatment

• Detection of genetic carriers: Prospective counselling is technically possible only when carriers can be accurately identified
• Prenatal diagnosis (amniocentesis, chorionic villus sampling) for chromosomal anomalies and metabolic defects
• Neonatal screening (Guthrie card) for PKU, congenital hypothyroidism, sickle-cell disease, cystic fibrosis

4. Treatment of Established Disease (Disability Limitation)

• PKU: Low phenylalanine diet prevents mental retardation
• Haemophilia: Administration of antihaemolytic globulin promotes clotting
• Spina bifida: Modern surgical techniques have brought improvements
• Cystic fibrosis: Gene therapy expected within lifetime of current patients

5. Rehabilitation

"With many genetic or partially genetic conditions causing physical or mental disability, much can be done for the patient and for his family in helping him to lead a better and more useful life."

Role of Genetic Predisposition in Common Disorders (Importance of Counselling)

"Now, with increased control of the environment, genetic make-up is becoming an ever-more important determinant of individual health. Genetic predisposition may lead to the premature onset of common diseases of adult life such as cancer, coronary heart disease, diabetes, hypertension and mental disorders."

• Cancer: Genetic predisposition involved in 10-25% of breast/colon cancer cases. DNA screening tests being developed. Chemoprevention advice can be tailored to families.
• Coronary heart disease: Family histories often uncover genetic risks. High blood pressure and high cholesterol are genetically influenced. Risk detection + lifestyle counselling + drug treatment could dramatically cut heart attack incidence.
• Diabetes: Higher concordance in identical twins (25-30%) than non-identical (5-10%); strong familial tendency in type 2 diabetes. Candidate for gene therapy.
• Mental disorders: Alzheimer's disease caused by at least four different genes; genetic counselling and drug prevention possible.

"Enough is already known about the genetics of common diseases to introduce a family-oriented approach into basic as well as specialist medical practice."

Advances in Molecular Genetics Supporting Counselling

1. DNA probes - identify specific complementary DNA sequences for genetic diagnosis
2. DNA sequencing - rapid analysis and identification of disease-causing mutations
3. Restriction enzymes - cut DNA at specific sequences for diagnosis
4. Polymerase Chain Reaction (PCR) - amplifies known DNA sequences from very small tissue samples (even a single cell)
5. Fluorescence In Situ Hybridization (FISH) - direct visualization of genes in living cells
6. Gene therapy - insertion of missing DNA sequences into cells with genetically determined disorders

Genetic Counselling in the Scope of Preventive Medicine

"Preventive medicine has branched into newer areas such as screening for disease, population control, environmental control, genetic counselling and prevention of chronic diseases."

"Genetic counselling is another aspect of the population problem that is receiving attention."

• Screening for pathological conditions related to the reproductive system
• Genetic counselling
• Premarital consultation and examination
• Marriage counselling

Source: Park's Textbook of Preventive and Social Medicine (ISBN: 9789382219163), Chapter on Human Genetics in Health and Disease (Block 11, pp. 924-935).

Concurrent Disinfection and Properties of an Ideal Disinfectant

Key Definitions (Park's)

• Disinfectant: Usually a chemical agent (but sometimes a physical agent) that destroys disease-causing pathogens or other harmful microorganisms, but might not kill bacterial spores. It refers to substances applied to inanimate objects.
• Disinfection: Thermal or chemical destruction of pathogens and other types of microorganisms. Disinfection is less lethal than sterilization because it destroys most recognized pathogenic microorganisms but not necessarily all microbial forms (e.g., bacterial spores).
• Sterilization: Validated process used to render a product free of all forms of viable microorganisms including bacterial spores.
• Antiseptic: Substance that prevents or arrests the growth or action of micro-organisms - used especially for preparations applied topically to living tissue.
• Germicide: Agent that destroys micro-organisms, especially pathogenic organisms.
• Hospital disinfectant: Disinfectant registered for use in hospitals, clinics, dental offices or any other medical-related facility. Efficacy demonstrated against Salmonella choleraesuis, Staphylococcus aureus, and Pseudomonas aeruginosa.

Types of Disinfection

(a) Concurrent Disinfection

"It is the application of disinfective measures as soon as possible after the discharge of infectious material from the body of an infected person, or after the soiling of articles with such infectious discharges."

• The disease agent is destroyed as soon as it is released from the body, and in this way further spread of the agent is stopped
• It is carried out throughout the course of the illness (i.e., while the patient is still sick and still a source of infection)

• Urine
• Faeces
• Vomit
• Contaminated linen and clothes
• Hands
• Dressings
• Aprons
• Gloves
• ...throughout the entire course of the illness

(b) Terminal Disinfection

"It is the application of disinfective measures after the patient has been removed by death or to a hospital or has ceased to be a source of infection or after other hospital isolation practices have been discontinued."

• Applied after the patient is no longer a source of infection
• Terminal disinfection is now scarcely practised
• Terminal cleaning is considered adequate, along with airing and sunning of rooms, furniture, and bedding

(c) Precurrent (Prophylactic) Disinfection

• Disinfection of water by chlorination
• Pasteurization of milk
• Handwashing

Natural Agents Used in Disinfection

1. Sunlight: Direct and continuous exposure is destructive to many disease-producing organisms. The ultraviolet rays (which do not penetrate through glass) are particularly lethal to bacteria and some viruses. Articles such as linen, bedding, and furniture may be disinfected by exposure to direct sunlight for several hours.
2. Air: Exposure to open air (airing) acts by drying or evaporation of moisture, which is lethal to most bacteria. However, natural agents like sunlight and air cannot be totally depended upon due to their vagaries.

Properties of an Ideal Disinfectant

Summary

Source: Park's Textbook of Preventive and Social Medicine (ISBN: 9789382219163), Chapter on Communicable Disease Control - Disinfection section, Block 2, pp. 144-145.