Recognising these events helps you understand how particular interventions at different stages could prevent or control the disease. You will learn about this in detail in Study Session 2. Events that occur in the natural history of a communicable disease are grouped into four stages: exposure, infection, infectious disease, and outcome see Figure 1. We will briefly discuss each of them in turn.
Here a contact refers to an association between a susceptible host and a reservoir of infection, which creates an opportunity for the infectious agents to enter the host. Examples of an exposed host include:. The entry and multiplication of an infectious agent inside the host is known as the stage of infection.
For instance, a person who has eaten food contaminated with Salmonella typhii the bacteria that cause typhoid fever is said to be exposed ; if the bacteria enter the cells lining the intestines and start multiplying, the person is said to be infected. At this stage there are no clinical manifestations of the disease, a term referring to the typical symptoms and signs of that illness. Symptoms are the complaints the patient can tell you about e.
Signs are the features that would only be detected by a trained health worker e. At this stage the clinical manifestations of the disease are present in the infected host. For example, a person infected with Plasmodium falciparum , who has fever, vomiting and headache, is in the stage of infectious disease — in this case, malaria. The time interval between the onset start of infection and the first appearance of clinical manifestations of a disease is called the incubation period. For malaria caused by Plasmodium falciparum the incubation period ranges from 7 to 14 days.
Remember that not all infected hosts may develop the disease, and among those who do, the severity of the illness may differ, depending on the level of immunity of the host and the type of infectious agent. Infected hosts who have clinical manifestations of the disease are called active cases.
Individuals who are infected, but who do not have clinical manifestations, are called carriers. Carriers and active cases can both transmit the infection to others. To which stage in the natural history of a communicable disease do a.
Depending on the time course of a disease and how long the clinical manifestations persist, communicable diseases can be classified as acute or chronic. Acute diseases are characterised by rapid onset and short duration of illness. For instance, diarrhoea that starts suddenly and lasts less than 14 days is an acute diarrhoeal disease. Chronic diseases are characterised by prolonged duration of illness; for example, a chronic diarrhoeal disease lasts more than 14 days.
At this stage the disease may result in recovery, disability or death of the patient. For example, a child who fully recovers from a diarrhoeal disease, or is paralyzed from poliomyelitis, or dies from malaria, is in the stage of outcome. In the next study session you will learn how communicable diseases are classified, and about the main types of prevention and control measures.
Now that you have completed this study session, you can assess how well you have achieved its Learning Outcomes by answering the questions below. You can check your answers with the Notes on the Self-Assessment Questions at the end of this Module. Consider a disease known as diabetes mellitus, which is characterised by an increase in the blood sugar level. Infectious agents may contribute to the development of the disease in early childhood, but are not the main cause of the disease.
Can it be classified as communicable? Explain your reasons. Giardiasis is an endemic communicable disease in Ethiopia. Its infectious agent Giardia intestinalis is a single-celled organism bigger than bacteria, but not visible with the naked eye.
To which class of infectious agents listed below is it likely to belong? C Protozoa is the correct answer. This group of infectious agents are single-celled organisms, which are bigger than bacteria but not visible with the naked eye. Hookworm infection is caused by parasites which are common in Ethiopia. The parasites live in the human intestine and lay eggs which are expelled from the body with the faeces into the soil.
The eggs grow into worms in the soil, which penetrate the skin of people walking barefooted. Identify each of the following in this example:. D The route of exit is through the anus with faeces, and the route of entry is through the skin. The risk factors for hookworm infection include walking barefooted and poor environmental hygiene due to expelling faeces into the soil. Typhoid fever is a disease that manifests clinically with high fever and headache. Suppose Abebe is infected with the infectious agent of typhoid fever, but he has no manifestations of the disease.
He works in a cafe and among 20 people he served in one day, five got infected, but only three of these developed the disease. Among the three who developed typhoid fever, two recovered and one died.
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Communicable Diseases Module: 1. Basic Concepts in the Transmission of Communicable Diseases Study Session 1 Basic Concepts in the Transmission of Communicable Diseases Introduction As you will recall from the Module on Health Education , Advocacy and Community Mobilisation, health is defined as a complete state of physical, mental and social well-being and not the mere absence of disease.
Learning Outcomes for Study Session 1 When you have studied this session, you should be able to: 1. Can you identify the communicable diseases in Table 1. The naming of infectious agents is discussed in Section 1.
Source as Table 1. A case refers to an individual who has a particular disease. Figure 1. Sizes and types of infectious agents Infectious agents can have varying sizes. The infectious agent is Mycobacterium bovis and the infected hosts are cattle and humans. Respiratory tract. Gastrointestinal tract Figure 1. Skin Some types of infectious agents can exit the body through breaks in the skin. Direct modes of transmission Direct transmission refers to the transfer of an infectious agent from an infected host to a new host, without the need for intermediates such as air, food, water or other animals.
A familiar example is the transmission of HIV from an infected person to others through sexual intercourse. Transplacental transmission : This refers to the transmission of an infectious agent from a pregnant woman to her fetus through the placenta. Indirect modes of transmission Indirect transmission is when infectious agents are transmitted to new hosts through intermediates such as air, food, water, objects or substances in the environment, or other animals.
Indirect transmission has three subtypes: Air borne transmission : The infectious agent may be transmitted in dried secretions from the respiratory tract, which can remain suspended in the air for some time. And sexually transmitted diseases STDs are spread through all types of sex — oral, anal, or vaginal. You can help protect yourself against contagious diseases by washing your hands well and often, staying away from those who are sick, making sure you're up to date on all vaccinations, and always using condoms during any type of sex.
What's the Difference Between Infectious and Contagious? Larger text size Large text size Regular text size. Wisconsin Childhood Communicable Diseases Chart. Topics A-Z. Responsive Menu. Communicable Diseases Communicable diseases, also known as infectious diseases or transmissible diseases, are illnesses that result from the infection, presence and growth of pathogenic capable of causing disease biologic agents in an individual human or other animal host.
Health Alert Network HAN The HAN enables public health staff, tribal governments, health care providers, emergency workers, and others to exchange reliable information as outbreaks evolve.
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