1.3.3  Stage of infectious disease

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. active cases and b. carriers belong?

    • a.Carriers are in the stage of infection, as they do not have clinical manifestations of the disease.
    • b.Active cases are in the stage of infectious disease, as they have the manifestations.

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.

1.3.2  Stage of infection

1.3.4  Stage of outcome