(1) Mechanical transmission:
In mechanical transmission infection, the responsible parasites undergo no morphological changes. Many bacterial, protozoal, helminthic and viral infections are thusmechaically transmitted to human host through the agency of a wide variety of insects. Thus the housefly (with its equal liking for human excretions, e.g. feaces, sputum, nasal secretions, pus and urine and human food supplies) may take up germs or parasite ova and convey directly either on its feet, or in its feaces and vomit to the human host.
(2) Cyclical Transmission of Disease
The term cyclical transmission implies on intermediate period during to the parasite is developing, but since it as not yet become inspective it cannot be successfully transmitted by the vector. Mosquitoes, black flies, chrysops, Glassine, Phlebotomies are able to develop specific parasites within their gut to infective stages and infect man during next meal.
(3) Myasis
This refers to invasion of tissues by maggots. The blow files (mango flies) are of medical importance because their larvae, known as maggot, invade the skin, mucous membrane or conjunctive causing secondary infection. The lava obtains the oxygen through small air pore known as spiracles.
After about one week or more, the larva leaves their host and pupates in the ground to continue their development.
INSECT CONTROL MECHANISM.
(1) Environmental control
Examples of environmental manipulations are: elimination of breeding places (source reduction); filling and drainage operation; carefully planned water management; provision of piped water supply; proper disposal of refuse and other waste; cleanliness in and around houses, house netting.
(2) Chemical control
It involves the use of repellants such citronella applied on skin, the application of oil to water is one of the oldest known mosquito control measures. The oil most widely used are diesel oil, fuel oil, kerosene, and various fractions of crude oil. Special oils (e.g mosquito larvicidal oil) are also available. A wide range of insecticides belonging to the organ chlorine, organ phosphorous and carbonate groups of compounds are available for vector control. It must be mentioned that vector control by insecticides alone is no longer fully effective because of insect coupled with danger of environmental pollution, it is now considered essential to replace gradually the highly persistent compounds such as DDT with compounds which are readily ‘’biogradable’’ and less toxic to man and animal such as methoxychlor abate and Durban, paints containing insecticides.
(3) Biological control
To minimize environment pollution with toxic chemical, great emphasis is now being placed on biological control. The use of carnivorous fish especially Gambusia is well known in mosquito control. Fungi of the genus coelomomyces are also known to be pathogenic to mosquito. But the fear exists that the introduction of biological agents for the control of arthropods may pose a direct hazard to the health of man himself.
Insect as pest control mechanism.
Various types of biological control methods have had some success fish such as guppies, which breed rapidly and eat mosquito larvae, may be valuable especially in water tanks and other enclosed water collections. Two bacteria is which produce toxins and kill larvae which eat them are Bacillus thuringiensis and Bacillus spherical. The toxin paralyses its germinate and the resulting bacilli infect the insect and kill it.
- Frogs which eat mosquito
(4) Genetic control
Much progress has taken place in recent years in the theoretical and applied aspects of genetic control of arthropods.
The WHO/ ICMR Research unit at New Delhi has contributed massively to the techniques of genetic control of mosquito.
Techniques such as sterile male techniques, chromosomal translocations have been found to be effective in small field trials
(5) Newer methods:
These are:-
(a) Insect growth regulators and
(b) Chemosterilants
Life cycle of anopheles mosquito
Night 1: feeding
The female anopheles has to forage (feed) and take blood meal.
If she fails to forage that night, she rest during the day and forages again the next night.
Day 2: Rest
During the day, anopheles mosquito rest in cool shaded humid places. A fed anopheles begins to digest the blood and her eggs starts to develop:
Night 2: Rest, half gravid: The insect rest, blood digestion and egg production continues, she may leave the house or change her rest side.
Day 3: Rest, gravid
Still in a cool shaded humid place, egg production is completed and the female is fully gravid.
Dusk 3: The gravid female flies to a suitable water collection and lays 50 – 150eggs. She will then forage for another blood meal to start the cycle again.
Larvae: The eggs hatch in 2-3days into the larvae form.
The larvae or wrigglers feed by filtering algae and other materials from the water. In favorable conditions, they grow rapidly passing there3 moults (shedding of its outer covering 3 times)
Pupa: After the 3rd moult, the larvae feed and grow then become a mobile pupa. There is no feeding at this stage.
The pupa breathes there 2 air trumpet while development of the adult proceeds internally.
Emergence: After 2-3days, the adult emerges: the pupa splits and the soft adult climbs out. It needs to dry and harden for sometime before it can fly.
Fertilization: Matting is the 1st activity of the young adult anopheles.
This takes place usually at twilight. After copulation, a mating plug is formed in the female’s genital passages probably from a secretion deposited by the male at the final act of copulation.
The female copulates once only string sperms for all subsequent egg production.
From egg to a new adult formation takes between 7-21days depending on the temperature.
Adult lives for 1month if condition is favorable
Development of plasmodium in mosquito takes 8- 10days.
International Health (cooperation)
International health (cooperation) is any health action which involves person, community and or institution in two or more countries
Origin (rationale or motives)
(1) Fear and suspicion
(2) Compassion
(3) Mutual benefits
Primordial interest in until health has its origin in the early ventures of until trade and travel and it predates the recent global events that only recently turn the world into a global village.
The original stimulates towards the early interest towards until health was that of fear and suspicion rather than international cooperation. Individual country were afraid of the spread of epidermis dx from foreign lands their region and thus tried to formulate health actions to prevent such dx transmission.
e.g. in the 14th century, a procedure called quarantine was introduced in Italy Europe to protect the importation of plague thus the health action formulated was to detain the sheep and the travelers suspected for harboring infection for a 40days orquaranta period during which time it was hoped that any dormant dx in any of the person will have manifested or be seen or otherwise die out for no dx to enter the country. Thus a quarantine practice is the origin of international health work with countries adopting difference measures and practices.
(2) Compassion – Apart from fear and suspicion, compassion for other also helps to stimulate international health actions in the past. Here medical missions, religions and humanitarian agencies, NGOS and private voluntary organizations respond to health crises not only in their community or countries but also in distant lands.
Finally in more recent times, international health cooperation is been fueled by the realization of mutual benefits obtainable by all cooperating countries.
Developments (History) of international health cooperation.
International health cooperation become necessary because through the practice of quarantine become widespread among countries, its objective of preventing international spread of communicable dx failed because of lack of scientific knowledge regarding the causation and mode of spread of dxes. It thus became necessary that international agreement and cooperation on quarantine matters be made to control communicable dxes. So, international conferences were held and organizations set up for discussion, agreement and cooperation on all matters of international health.
(1) The first international sanitary conference (1851)
These are the origin of international health cooperation. This was held in Paris attended by mainly European nation of states – Great Britain, Austria, France, Spain, Greece, Russian, Portugal and four sovereign states (Sardinia, the two sicilies, the Papal States and Tuscango)
These states join to form Italy. The objective was to introduce some order and uniformity into quarantine measures.
This conference lasted for 6monthw but there were no lasting results which had 137 articles but unfortunately only 3 of the countries ratify these codes. The countries are France, Sardinia and Portugal.
In 1865, Sardinia and Portugal withdrew again leaving only France between 1851 and 1902, other international conference followed held in rapid succession (about 10 conferences)
(2) International sanitary conference of 1892. In this conference, a convention concerning cholera was made/ adopted
(3) ISC (1897): Convention dealing with preventive measures against plague was adopted.
(4) International or pan American Bureau 1902.
This was the next important milestone in international health work. It was held in the Americans and 10ly intended alone. In 1924, they had the American sanitary code.
1947 – Reorganized and renamed PASO (pan America sanitary organization)
1947 – All agreed among themselves that PASO will be their WHO regional office for all the Americas.
1958 – Changed the name from PASO to PAHO (Pan America health organization) which had it’s headquarter in Washington BC.
PASB was the world’s first international health agency.
(5) Office international D’ Hygiene Publique (OIHP) 1907.
Decision was taken in 1903 I.S.C to have a permanent international health bureau established. So the Paris office was established in 1907 with a permanent secretariat and a permanent committee of senior public health of member govt.
Objectives.
Empower to disseminate information on communicable dxes and to supervise international quarantine measures.
Initially only European countries were involved but late with cooperation growing between PASB and OIHB, 60 other countries joined the OIHB giving the office an international xter.
OIHB existed until 1950 by which time WHO has fully taken over its responsibility
(6) The health organization of the league of Nations (1923)
After the 1st world war (1914 – 1918), the league nation was established in 1919 to help build a better world. It also included ‘a health organization to take steps in matters of international concern for the prevention and control of dx. It was established in 1923.
The health organization diversity into other matters such as nutrition, housing, rural hygiene, training of public health workers and the standardization of certain biological preparations.
The health organization also analyzed epidemiological information received from member nations and started the series of epidemiological report which the WHO also adopted.
They also laid down lines for technical studies including the use of expert committees also sustained by the WHO.
So the WHO as it stands and works today owes a lot to the found initiative and foresighted efforts to amalgamate PASB, OIHB and the health organization of League of Nation failed and all them co-existed between the years of the 2 world wars.
In 1939, the political League of Nations was dissolved but its health organization continued its work. The health organization of the League of Nations headquarter was in Gen3va.
(7) I.S.C 1926 – The international convention was revised to include provisions against typhus
(8) I.S.C 1935 – Convention for aerial navigation came into force4.
(9)Last I.S.C Paris 1938 – Sanitaria, maritime et Quarantine at Alexandria, Egypt which became a regional office of WHO for Easter Mediterranean region.
(10) United nations relief and rehabitation administration another international health programme began in 1943
Set up 1943 with the general purpose of organizing recovery from the effect of the 2nd world war. UNRRA had a health division to care for the health of the millions of displaced persons, to restore and help services and to revive the machinery for international interchange of information on epidemic dxes.
UNRRA worked to prevent the spread of typhus and other dxes so that there were no epidemics anywhere. It equally assisted in the control of other dxes e.g. malaria in Greece and Italy.
The world’s renowned campaign for the eradication of malaria was indeed begun as a joint effort of UNRAA, the Rockefeller foundation and the Italian govt.
By the end of 1947 UNRRA terminated its official activities and its health programmes and financial assets were taken over by the interim commission of the WHO.
The Birth of the WHO
(1) United nations conference on international organization April 1945 held in san Francisco USA. This conference unanimously approves the proposal made by the representatives of china and Brazil that a new autonomous, international organization be established and that a conference to frame the constitution should be convened.
(2) International health conference in New York 1946 – This conference approved the constitution of the proposal international health organization. This international health conference was attended by 51 nations. The constitution was drawn up by a technical preparatory committee. This same conference set up an interim commission of the WHO to prepare the ground for the new organization and to carry out urgent task until the WHO constitution had been accepted by the required no of UN member states.
In 1947, the interim commission has part of its effort helped to organize assistance to Egypt to combat cholera.
(3) The WHO constitution came into force on 7th April 1948 and this day is thus celebrated as the UN world health day. This happened following the required ratification of the WHO constitution by member nations when the 26th of the 61 member states who signed the constitution ratified its signature. Thus marking the establishment of the WHO as a specialized agency of the United Nations.
Later, the 1st world health was held in Geneva with delegations from 53 countries. Thus the formation of WHO represents the culmination of efforts to establish a single world wide intergovernmental health agency.
WHO
Definition: - This is a specialized nonpolitical health agency of the united nations with headquarter in Geneva
In 1946, the constitution was drafted by the technical preparation committee under the chairmanship of Mr. Rene Sand and was approved in the same 1946 by an international health conference of 51 nations in New york city of USA.
The constitutions come into force on 7th April 1948 which is celebrated every year as the world’s health day.
A world health day’s theme is chosen every year to focus attention on a specific aspect of public health.
Objectives of WHO.
(1) Attainment of all people of the highest level of health and this is set out in the preamble of its constitution.
(2) Current objective is the attainment of all people of the world by the year 2000 AD of a level of health that will permit them to lead a socially and economically productive life also known as the health for all by the year 2000 AD.
Membership of WHO.
- open to sill countries but with some difference e.g. Switzerland is a member of WHO but is not a member of united nation.
In 1948, they were 56 members
In 1996, 190 full members and 2 associate members
Now, 191 members.
All these members are entitled to aide’s services that the organization can provide.
Functions of WHO.
(1) WHO is the directing and coordinating authority on all international health work?
Specific responsibilities.
Establishing and promoting international standards in the difference fields of health.
These fields are:
(1) Prevention and control of specific dxes.
(2) Development of comprehensive health services
(3) Family health
(4) Environmental health
(5) Health statistics
(6) Biomedical research
(7) Health literature and information
(8) Cooperation with other oragnization.
Structure of WHO.
Consists of 3 principal organs.
(a) World health assembly
(b) The executive board
(c) Sectariat.
WHO is the supreme governing body of the WHO. The meet in every month of May in Geneva.
The executive board is made up representative members of member states who are technically qualified in health matters. Recently, there are 31 of them.
The sectariat is needed by a director General in Geneva and they provide support (technical and managerial support) for the national health programmes of the individual member states. There are also 5 assistance D.G in the Geneva office.
Regional offices.
In order to meet special health needs of difference areas or regions, WHO has regional headquarter or office.
African regional office – Harare Zimbabwe
East Mediterranean regional office – Cairo (Egypt)
Western pacific regional office – manila (Philippines)
The American regional office – Washington DC (USA).
Europe regional office – Copenhagen (Denmark)
South East Asia regional office – new- Delhi (India)
The Africa regional office was formally in Congo AFRO was temporarily evacuated from Congo to Harare.
Other united Nation organization Agencies.
(1) UNICEF – united nation children fund
(2) UNDP – united nation development program
(3) UNFPA – united nation fund for population activities
(4) FAO – food and Agricultural organization
(5) ILO – international organization
(6) World Bank.
MEDICAL STATISTICS
The concept of a 2x2 table:
A 2 x2 table is the table that consists of 2 columns (vertical) representing the presence or absence of a dxc and 2 rows (horizontal) that represent a tue or ve test result.
These tables may also be employed in risk factor studies.
The ffg 2 x2 table is a tool for the evaluation of standardized screening test which predict the presence or absence of dx.
Pr Abs
+ A B A+B
- C D C+D
Test
A representing true tves, B rep false tves, C rep false ves and D rep true – ves.
Validity is the extent to which a test measures what it was designed to measure.
Accuracy is the ability of a test to produce a true value for the measurement and true classification for the values under study.
Validity has 2 components.
(1) Sensitivity- Defined as the ability to correctly identify individual who have a specific dx or condition.
(2) Specificity is defined as the ability to correctly identify individual.
Who do not have a specific dx or condition?
Although the validity of a diagnostic test can be determined by sensitivity and specificity, 3 other measure are important.
(3) False true rate: defines as the proportion of false true B among non dxed B + D subjects.
(4) False – ve rate is defined as the proportion of false – ve C among dxed A+C subjects.
(5) The accuracy of a test is defined as the proportion of true results i.e. true tve A, + true – ve D among all test results
Sensitivity = A specificity = B
A + C B + D
False tve rate = B false – ve rate = C
B + D A + C
Accuracy = A + D
A +B+C +D.
The predictive value of a screening test measures the true presence or absence of a dx.
Predictive values has 2 components
(6) Positive productive value – This is the proportion of true tves among all tves. A/ A+B
(7) Negative predictive value is the proportion of true –ve among all –ves D/ C+D
E.g. an investigator evaluated 100px suffering from major depression as confirmed by the attending pscyatrics, the results were as follows
Clinical depression.
Pres Abs
+ 12 18
- 28 42
Test
Evaluate all the 7 indices.
In a prospective study of the relationship between oral contraceptive use and the subsequent risk of developing endometrial cancer, a cohort. Of 1000 women were followed for 5years. The results were as follows.
Endometrial cancer.
Pr Abs
+ 245 75
- 50 630
Oral contraceptive.
(1) What was the incident rate (absolute risk) of endom? Cancer among women who used oral contraception.
(2) Asses fully the association between oral contraception and the presentation of endometrial cancer.
Sampling in health survey
A health is a planned study or investigation to obtain primary or additional information on the health of the people in the community. This is usually done on ad-hoc basis and it is another major source of health data.
The first step in the conduct of a health survey is a good definition of the health problem followed by a definition of the population. Once the objectives are well spelled out, one basic problem in the implementation process is the decision as to whether all individual.
In a defined population should be studies or some selected units’ init and if the decision is to study selected unit, how best to do this.
It is therefore imp define the concept of the world population in its statistical sense.
Procedures.
(1) Identify the problem
(2) Identify target population e.g. under 5
(3) Objectives of the study
(4) Study design e.g. case sense, cross sectional/ prevalence study, case control.
Population
This is the totality of all available units in a defined area falls within the scope of statistical investigator i.e. the totality of units that are of interest to the researcher. The unit may be individual, households, families, schools, the community, villages, insects etc.
In survey terminology, the aggregate of all the units about whom information is required is called target population and the results of the study will apply to those population. But the population from which is the data are actually collected is the survey or study population. more often than not practical problems makes it difficult for the investigator to cover all individual in the target population in particular when the target population is large and well dispersed and shortage of personally, money and time makes it difficult to have a complete coverage.
Sample
This is part of a population selected for study such that we may be able to infer the xtics of a population from those of the sample.
Sampling approach
(1) Total population- in this case, every individual in the defined population is included and studied.
Advantages:
(a) The estimate is accurate and without error since no unit is left out
(b) There is no need to worry about selection procedure
(c) There are no feelings of discrimination created in the population
Disadvantages
(a) It is expensive
(b) takes time to complete
(c) Demands a lot of personella
(d) It may not be feasible
(e) It may be less accurate
(2) Sample approach, - Here, a sample is selected from the population and studies. It has its own merits and Demerits.
Merits
(a) Less expensive
(b) Quick results guaranteed
(c) Demands on personella is less
(d) Possibility of obtaining more accurate data because of the small no of units involved
(e) Allows studies to take place at all situations.
Demerits
(a) Some units or people are left unstudied. Estimates obtained from the sample is likely to be different from that would have been obtained if the total population have been studies. This discrepancy is called sampling error and it is always present.
(b) It is sometimes difficult to select a good sample i.e. a representative sample.
(c) Sampling may create a feeling of discrimination in the population called bias
(d) In certain situation, information may be legally required from every person in the population (census)
(e) For rare events, sample sizes have to be large.
Principles of sampling
In most surveys, we are constrained to study a sample of the population therefore it is important to consider the various sampling methods that guarantee the assumptions underlying certain statistical methods employed in the analysis of the data collected.
In the selection procedure, 2 principles are often considered.
(1) Avoidance of bias
(2) Achievement of maximum precision for a given outlay of resources.
The ffg definitions are required in order to satisfies the conditions and select a good sample from the population.
(1)Sample size – No of units in the sample
(2) Sampling fraction – This is the proportion of the total population that is constituted by the sample. If the total population is 5000 units and the sample size is 200, sampling fraction = 200/500 = 1/25.
(3) Sampling frame – This is the list containing all the units in the population.
It may be a register, a map or a telephone directory or the records in the 10 health centre. To select a probability sample, there must be a proper sampling frame.
(4) Sampling units- This is the smallest unit involved in the selection procedure. In the survey of the use of contraceptive in a community, each selected household may be sampling unit. In some cases, it may be a woman of 15yrs and above. However the sampling unit should be well defined.
(5) Unit of Enquiry – this is the unit about which information is required.
The sampling unit may be a household and the units of enquiry the female of that household say in the survey of the use of oral contraceptives in a community.
(6) Sampling error – This is an index for measuring the precision of the estimate obtained from a sample. A clear measure of how well a sample estimate is near to the population parameter.
The price paid for not studying the entire population. High precision implies small sampling error while low precision implies large sampling error.
(7) Good or representative sample:
This reflects properly some identified xtics of the population and an unrepresentative sample is based; the case where volunteers or those easily seen or haphazard sample are selected to draw reliable conclusions from the result of our sample, it is always recommended to pick a probability sample.
Non probability sample method.
(1) Quota sample
(2) Convenience sample
(3) Purposive sample
(4) Haphazard sample
(5) Volunteer sample
Each units in the population is given the same Ghana of been selected.
In general, when we select a sample, the selection must be scientific i.e. every unit in the population must posses a known chance of been selected.
A scientific sample is called a probability sample and efforts are made to ensure the selection of prob. Sample to allow the calculate of the precision of the estimates of the population parameter.
Types of probability sample.
(1) Simple random sampling – this is a sampling procedure in which each unit in the population has the same chance of being selected. However the population must be finite and a sampling frame must exist. Each unit must have an assigned no in the sampling frame. Without a proper sampling frame, it is impossible to take a simple random sample.
Selection procedure -3 ways:
(i) Lottery method
(ii) Table of random number
(iii) Computer facilities to generate sample by simple random sampling technique.
Advantage of simple random sampling
(1) It is an equitable method of selection
(2) The precision of the estimate is the highest of all methods of pro sample
Disadvantages
(1) The construction of the frame may be very laborious and expensive
(2) The same does not ensure that subgrps of interest will be adequately represented
(3) Advantage of the xture of the population is not utilized.
(2) Stratified Random sampling – Population is divided into homogenous strata according to some relevant xtics of the population and a simple random sample is selected from each stratum. The sample size may be divided in proportion to the population size in each stratum. This is called a proportional allocation. E.g. To select 200units from a population of 6000 units of which 2000units are females and 4000units male. The no chosen in each sex stratum will be 67 and 133 respectively. If there is a proportional allocation of the sample members in the strata.
Female = 2000/6000 x 200
Advantages.
(1) Increase in representative ness of the sample
(2) Provision of reasonably accurate estimates for subgrps of interest
(3) Increase in precision of estimates
(4) Most useful in heterogeneous population
Disadvantages
(1) Labour in preparation of the frame is still substantial
(3) Systematic random sampling – This is sometimes called quasi random units are selected in any one sample occupying related position to each order in the sampling frame and the 1st unit to be selected is selected at random and thereafter every kth unit is selected given that the sampling fraction is 1/k.
E.g. suppose a sample of 50px is required from the register 1000px available in the record section of the teaching hospital. The sample fraction here be 50/1000 = 1/20.
The 1st member in the proposed sample is selected randomly between 1 and 20; therefore, every 20th member is subsequently selected as sample members.
Advantages
(1) It is easy to select
(2) In some situations, the preparation of a frame is unnecessary
(3) The sample is spread evenly over the entire population
Useful in situation where arrival at a service point is at random and every arrival at known interval is selected.
Disadvantages
(1)Precision of the estimates is not easy to measure
(2) Where population unit has a periodic type of variation and interval between successive selected units happens to coincide with a particular xtics, the systematic sample will be based error of periodicity.
End
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