Carriers

Definition:

       A carrier is defined as “an infected person or animal that harbours a specific infectious agent in the absence of discernible clinical disease and serves as a potential source of infection for others”.

Element: The elements in a carrier state are:

(a) The presence in the body of the disease agent

(b) The absence of recognizable symptoms and signs of disease, and

(c) The shedding of the disease agent in the discharges or excretions, thus acting as a source of infection for other persons.

Classification of Carriers: Carriers may be classified as below-

A. Type

            a. Incubatory

            b. Convalescent

            c. Healthy

B. Duration

            a. Temporary

            b. Chronic

C. Portal of Exit

            a. Urinary

            b. Intestinal

            c. Respiratory

            d. Others

Modes of Communicable diseases transmission

Communicable diseases may be transmitted from the reservoir or source of infection to a susceptible individual in many different ways, depending upon the infectious agent, portal of entry and the local ecological conditions.

Direct transmission

o   Direct contact

o   Droplet in faction

o   Contact with soil

o   Inoculation into skin or mucosa

o   Tran placental (vertical)

Indirect transmission

o   Vehicle-borne

o   Vector-borne

o   Mechanical

o   Biological

o   Air-borne

o   Droplet nuclei

o   Dust

o   Fomite-borne

o   Unclean hands and fingers

Epidemic and Endemic

Epidemic (Epi=Upon; Demos = people):

            The occurrence of cases of a disease or other health related events clearly in excess of normal expectation in a particular place in a given period of time is called on epidemic.

            The usual epidemic diseases are: measles, chickenpox and cholera.

Endemic (En-in; Demos = People):

            The occurrence of a disease or infectious agent regularly in an area either throughout the year, or in particular seasons on an yearly basis without importation from outside is called endemic.

            Example: Cholera in post monsoon period in rural Bangladesh, malaria and leprosy in some parts, goitre at Rangpur and Jamalpur regions.  

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• Hyperendemic and Holoendemic

Hyperendemic and Holoendemic

Hyperendemic : 

         It expresses that the disease is constantly present at high incidence and/ or prevalence rate and effects all age groups equally.

Holoendemic : 

        It expresses a high level of infection beginning early in life and effecting most of the child population, leading to a state of equilibrium such that the adult population shows evidence of the disease much less commonly than do the children.




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Pandemic

When an epidemic disease affects a large proportion of the population and occurs over a wide geographic area such as a section of a nation, the entire nation, a continent or the world, is called pandemic.

Pandemic diseases: Influenza, acute hemorrhagic conjunctivitis, syphilis, gonorrhoea, AIDS etc.







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• Hyperendemic and Holoendemic
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Zoonosis

An infection or infectious disease that usually and primarily develops in vertebrate animals and transmissible to man under natural conditions.

Zoonotic diseases: rabies, plague, bovine, tuberculosis, anthrax, brucellosis, salmonellosis, endemic typhus, hydatidosis etc.

Incidence rate

It is the number of new cases of a specific disease reported during a given time interval divided by the estimated mid interval population at risk. It is given by the formula.

                        Number of new cases of specific diseases      during a given time period

            =                                                                             x1000

                                    Population of risk

Uses of incidence rate:

            (i) To control disease, and

            (ii) For research into aetiology and pathogenesis, distribution of diseases, and efficacy of preventive and therapeutic measures.

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Prevalence rate

It is the number of current cases (old and new) of a specified disease during a specified time period divided by the estimated midinterval population at risk.

            The prevalence rate of a disease is calculated as follows :

                        Number of current cases (old and new) of a specified disease during a        specified time period

=---------------------------------------------------------------------------------x100

                                    Estimated midinterval population at risk

Uses of prevalence rate:

1. To measure the amount of illness.

2. To determine the health care need of the community.

3. Useful for administrative and planning purposes.

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Infectious disease

• A clinically manifested disease of a host resulting from an infection is called infectious disease.

• A communicable disease which can very easily and very rapidly attack a susceptible host from a primary or index case (one who comes to the notice of the health service at first) is an infectious disease e.g. measles.

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Communicable disease

A disease which can get transmitted from one host or reservoir to another through transference of a sufficient quantity of the causative agent is called a communicable disease, such as measles, tetanus, scabies etc.

An illness due to a specific infectious agent or its toxic products capable of being directly or indirectly transmitted from man to man, animal to animal, or from the environment (through air, dust, soil, water, food etc.) to man or animal.

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Incubation period

Incubation period

In infectious disorders (due to bacteria, viruses etc.) the period between exposure and the development of disease is called incubation period.

 It is often measured in days or weeks, and each infectious agent is usually associated with a characteristic incubation period.

             

Median incubation period: Time required for 50 percent of the cases to occur following exposure.

             

Latent period: In non-infectious disorders, the period from disease initiation to disease detection.

             

Intrinsic incubation period: Time period between the entrance of pathogenic organism into a host and the appearance of first symptom of the specific disease.

             

Intrinsic period helps to estimate the probable date of infection and thereby directs enquiries towards the source of infection.

             

Extrinsic incubation period: Time period between the entrance of pathogenic organism into a vector or an intermediate host and the maturity of the organism to cause infection in definitive or secondary host.

Infection

The entry and development or multiplication of an infectious agent in the body of man or animals (2,100). It also implies that the body responds in some way to defend itself against the invader, either in the form of an immune response (evidence of this may not be readily available) or disease. An infection does not always cause illness.

There are several levels of infection: Colonization (e.g., S. aureus in skin and normal nasopharynx); subclinical or inapparent infection (e.g. polio); latent infection (e.g. virus of herpes simplex); and manifest or clinical infection.

Mortality rate

Mortality rate

Measure the rate of death.

Types of mortality rate:

1. Crude death rate (CDR)
2. Cause specific death rate
3. Case fatality rate
4. Maternal mortality rate
5. Proportionate mortality rate
6. Life expectancy

Crude death rate (CDR):

It is defined as, the number of death (from all causes) per 1000 estimated midyear population in one year, in a given place.              

No of deaths during the year

---------------------------------------------------------1000

                        Mid year population

Maternal mortality rate (MMR);

It is defined as the number of death relate to pregnancy during a given time interval divided by the number of live birth reported during the same time interval

Number of death related to pregnancy during given time in A given area

----------------------------------------------------------------------------------------*1000

Number of live birth reported during the same time interval in the same area

Crude birth rate (CBR):

It is the number live births reported during a given time interval divided by the estimated mid interval population

It is expressed per 1000 population.