Occupational diseases.

 

Natural History of disease

 NATURAL HISTORY OF DISEASE :

Introduction -

 This concept signifies the way in which a disease evolves over time, from the earliest stage of its pre-pathogenesis phase to its termination as recovery, disability or death.

• Incubation period  : 

 The time interval between invasion by an infectious agent and appearance of the first sign or symptom of the disease in question 

• Latent period : 

It is used in non-infectious diseases as the equivalent of incubation period in infectious disease -”Period from disease initiation to disease detection” 

• Infectious period : 

 The time during which the host can infect another susceptible host. 

 • Non-infectious period : 

 The period when the host’s ability to transmit disease to other hosts ceases.

It has 02 phases : 

pre-pathogenesis phase  -It is the period preliminary to the onset of disease in man. The diseases agent has not yet entered the man but the factors which favor its interaction with the human host are already existing in the environment.

 pathogenesis phase -The phase known as the pathogenic period is when the patient's cells, tissues, or organs change but he or she is still devoid of any symptoms or disease-related signs. This subclinical stage can be divided into two additional stages

 1- NATURAL HISTORY OF TYPHOID :

Natural History of disease

     2- NATURAL HISTORY OF MALARIA :

The natural history of malaria involves cyclical infection of humans and female Anopheles mosquitoes.

 In humans, the parasites grow and multiply first in the liver cells and then in the red cells of the blood. 

The blood stage parasites are those that cause the symptoms of malaria. When certain forms of blood stage parasites (gametocytes, which occur in male and female forms) are ingested during blood feeding by a female Anopheles mosquito, they mate in the gut of the mosquito and begin a cycle of growth and multiplication in the mosquito. 

After 10-18 days, a form of the parasite called a sporozoite migrates to the mosquito’s salivary glands. When the Anopheles mosquito takes a blood meal on another human, anticoagulant saliva is injected together with the sporozoites, which migrate to the liver, thereby beginning a new cycle.

Natural History of disease

3- NATURAL HISTORY OF TUBERCULOSIS :

Tuberculosis infection occurs when a subject inhales the Mycobacterium tuberculosis bacilli (MTB). An active case of pulmonary or laryngeal tuberculosis generates infectious particles called droplet nuclei of <5 microns in diameter, when coughing, sneezing or through any other forceful expiratory maneuver. The infectiousness of a patient with TB is directly related to the form of the disease (laryngeal, pulmonary), the presence of cough, cavitary lung disease and the positivity of the sputum smear/culture.

Natural History of disease

       4- NATURAL HISTORY OF DENGUE :

     Dengue fever generally lasts about 6 to  7 days, with a smaller peak of fever at the trailing end of the fever (the so-called "biphasic pattern"). The platelet  count will drop until the patient's temperature is normal.

Natural History of disease

5- NATURAL HISTORY OF HIV :

   

The natural course of untreated HIV infection varies widely with some HIV-positive individuals able to maintain high CD4  cell counts and/or suppressed viral load in the absence of ART. 

Although similar, the underlying mechanistic processes leading to long-term non-progression and viral control are likely to differ.