Question

Study Questions (Quiz 3)
1. Discuss how infectious and noninfectious diseases relate to communicable and noncommunicable dis
eases and conditions.

2. List and explain the different general classifications of diseases.

3. Classifications were given of major infectious diseases.

List the five modes of transmission and provide examples.

4. List the three general sources of infectious diseases and provide examples,

5. How do incubation periods differ from latency periods?

6. Choose five infectious diseases and identify the typical incubation periods for these diseases.
7. Explain the concept of notifiable diseases.

8. Explain and discuss herd immunity.

9. What role does increasing life expectancy over the last century have on the types of diseases and
conditions affecting mankind?

10. Describe how the age-adjusted percent distribution of limitation due to one or more chronic
conditions is influenced by race/ethnicity and poverty in the United States, 2012 (see Figure 3-7).

11. Describe how the age-adjusted percent distribution of limitation in work activity due to health
problems among persons aged 18-69 is influenced by race/ ethnicity and poverty in the United States,
2012 (see Figure 3-8).

Answer 1

1.

Infectious diseases-
Infectious diseases are the diseases caused by micro-organisms like bacteria, virus, fungi and protozoa.
They are spread from one person to another through agents like contaminated air, food, water, vectors etc. are called as communicable diseases.
Non-infectious diseases-
Non-infectious diseases are the diseases caused by genetic abnormalities, malfunctioning of organs, environmental factors etc.
They do not spread from one person to another and are called as non-communicable diseases.

2.

The most widely used classifications of disease are (1) topographic, by bodily region or system, (2) anatomic, by organ or tissue, (3) physiological, by function or effect, (4) pathological, by the nature of the disease process, (5) etiologic (causal), (6) juristic, by speed of advent of death, (7) epidemiological, and (8) statistical. Any single disease may fall within several of these classifications.

In the topographic classification, diseases are subdivided into such categories as gastrointestinal disease, vascular disease, abdominal disease, and chest disease. Various specializations within medicine follow such topographic or systemic divisions, so that there are physicians who are essentially vascular surgeons, for example, or clinicians who are specialized in gastrointestinal disease. Similarly, some physicians have become specialized in chest disease and concentrate principally on diseases of the heart and lungs.

In the anatomic classification, disease is categorized by the specific organ or tissue affected; hence, heart disease, liver disease, and lung disease. Medical specialties such as cardiology are restricted to diseases of a single organ, in this case the heart. Such a classification has its greatest use in identifying the various kinds of disease that affect a particular organ. The heart is a good example to consider. By the segregation of cardiac disease it has been made apparent that heart disease is now the most important cause of death in the United States and in most other industrialized nations. Moreover, it has become apparent that disease caused by atherosclerosis of the coronary arteries is by far the most important form of heart disease. In making a diagnosis of cardiac disease in an elderly patient, the cardiologist must first determine whether this disease of the coronary arteries is responsible for the heart’s failure to function normally.

The physiological classification of disease is based on the underlying functional derangement produced by a specific disorder. Included in this classification are such designations as respiratory and metabolic disease. Respiratory diseases are those that interfere with the intake and expulsion of air and the exchange of oxygen for carbon dioxide in the lungs. Metabolic diseases are those in which disturbances of the body’s chemical processes are a basic feature. Diabetes and gout are examples.

The pathological classification of disease considers the nature of the disease process. Neoplastic and inflammatory disease are examples. Neoplastic disease includes the whole range of tumours, particularly cancers, and their effect on human beings.

The etiologic classification of disease is based on the cause, when known. This classification is particularly important and useful in the consideration of biotic disease. On this basis disease might be classified as staphylococcal or rickettsial or fungal, to cite only a few instances. It is important to know, for example, what kinds of disease staphylococci produce in human beings. It is well known that they cause skin infections and pneumonia, but it is also important to note how often they cause meningitis, abscesses in the liver, and kidney infections. The sexually transmitted diseases syphilis and gonorrhea are further examples of diseases classified by etiology.

The juristic basis of the classification of disease is concerned with the legal circumstances in which death occurs. It is principally involved with sudden death, the cause of which is not clearly evident. Thus, on a juristic basis some deaths and diseases are classified as medical-legal and fall within the jurisdiction of coroners and medical examiners. A person living alone is found dead in bed—dead of natural causes or killed? Had the person who dropped dead on the street been given some poison that took a short time to act? Much less dramatic, but perhaps more common, are disease and death caused by exposure of the individual to some unrecognized danger to health in working or living conditions. Could the illness or disease be attributable to fumes or dusts in a factory? These are examples of the many types of disease and death that fall properly in this classification.

The epidemiological classification of disease deals with the incidence, distribution, and control of disorders in a population. To use the example of typhoid, a disease spread through contaminated food and water, it first becomes important to establish that the disease observed is truly caused by Salmonella typhi, the typhoid organism. Once the diagnosis is established, it is obviously important to know the number of cases, whether the cases were scattered over the course of a year or occurred within a short period, and what the geographic distribution is. It is critically important that the precise address and activities of the patients be established. Two widely separated locations within the same city might be found to have clusters of cases of typhoid all arising virtually simultaneously. It might be found that each of these clusters revolved about a family unit including cousins, grandparents, aunts and uncles, and friends, suggesting that in some way personal relationships might be important. Further investigation might disclose that all the infected persons had dined at one time or at short intervals in a specific home. It might further be found that the person who had prepared the meal had recently visited some rural area and had suffered a mild attack of the disease and was now spreading it to family and friends by unknowing contamination of food. This hypothetical case suggests the importance of the etiologic, as well as the epidemiological, classification of disease.

Epidemiology is one of the important sciences in the study of nutritional and biotic diseases around the world. The United Nations supports, in part, the World Health Organization, whose chief function is the worldwide investigation of the distribution of disease. In the course of this investigation, many observations have been made that help to explain the cause and provide approaches to the control of many diseases.

The statistical basis of classification of disease employs analysis of the incidence (the numbers of new cases of a specific disease that occur during a certain period) and the prevalence rate (number of cases of a disease in existence at a certain time) of diseases. If, for example, a disease has an incidence rate of 100 cases per year in a given locale and, on the average, the affected persons live three years with the disease, it is obvious that the prevalence of the disease is 300. Statistical classification is an additional important tool in the study of possible causes of disease. These studies, as well as epidemiological, nutritional, and pathological analyses, have made it clear, for example, that diet is an important consideration in the possible causation of atherosclerosis. The statistical analyses drew attention to the role of high levels of fats and carbohydrates in the diet in the possible causation of atherosclerosis. The analyses further drew attention to the fact that certain populations that do not eat large quantities of animal fats and subsist largely on vegetable oils and fish have a much lower incidence of atherosclerosis. Thus, statistical surveys are of great importance in the study of human disease.

3.

Modes of Transmission of Infectious Diseases :-
Direct contact :-
An easy way to catch most infectious diseases is by coming in contact with a person or animal who has the infection. Three ways infectious diseases can be spread through direct contact are:

• Person to person. A common way for infectious diseases to spread is through the direct transfer of bacteria, viruses or other germs from one person to another. This can occur when an individual with the bacterium or virus touches, kisses, or coughs or sneezes on someone who isn't infected.

These germs can also spread through the exchange of body fluids from sexual contact. The person who passes the germ may have no symptoms of the disease, but may simply be a carrier.

• Animal to person. Being bitten or scratched by an infected animal — even a pet — can make you sick and, in extreme circumstances, can be fatal. Handling animal waste can be hazardous, too. For example, you can acquire a toxoplasmosis infection by scooping your cat's litter box.
• Mother to unborn child. A pregnant woman may pass germs that cause infectious diseases to her unborn baby. Some germs can pass through the placenta. Germs in the female reproductive system can be transmitted to the baby during birth.

Indirect contact :-
Disease-causing organisms also can be passed by indirect contact. Many germs can linger on an inanimate object, such as a tabletop, doorknob or faucet handle.When you touch a doorknob handled by someone ill with the flu or a cold, for example, you can pick up the germs he or she left behind. If you then touch your eyes, mouth or nose before washing your hands, you may become infected.

Insect bites :-
Some germs rely on insect carriers — such as mosquitoes, fleas, lice or ticks — to move from host to host. These carriers are known as vectors. Mosquitoes can carry the malaria parasite or West Nile virus, and deer ticks may carry the bacterium that causes Lyme disease.

Food Contamination :-

Another way disease-causing germs can infect you is through contaminated food and water. This mechanism of transmission allows germs to be spread to many people through a single source. E. coli, for example, is a bacterium present in or on certain foods — such as undercooked hamburger or unpasteurized fruit juice.

4.

Infectious diseases can be caused by:

Bacteria:- These one-cell organisms are responsible for illnesses such as strep throat, urinary tract infections and tuberculosis.

Viruses:-Even smaller than bacteria, viruses cause a multitude of diseases ranging from the common cold to AIDS.

Fungi:-Many skin diseases, such as ringworm and athlete's foot, are caused by fungi. Other types of fungi can infect your lungs or nervous system.

5.

The period between exposure and infection is called 'latent period', since the pathogen is present in a 'latent' stage, without clinical symptoms or signes of infection in the host. The period between exposure and onset of clinical symptoms is called 'incubation period'.

6.

Incubation period of chicken pox:-14 -16 days

incubation period of common cold :-1-3 days

incubation period of diphtheria :- 2-5 days

incubation period of malaria :- 7-30 days

Incubation period of polio :- 3-20 days

7.

A notifiable disease is any disease that is required by law to be reported to government authorities. The collation of information allows the authorities to monitor the disease, and provides early warning of possible outbreaks. In the case of livestock diseases, there may also be the legal requirement to destroy the infected livestock upon notification. Many governments have enacted regulations for reporting of both human and animal (generally livestock) diseases.

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