In a small proportion of cases the primary complex progresses to produce more severe manifestations locally (e.g. gaseous pneumonia) or there may be hematogeneous dissemination to other parts of the body thus within a few years of the primary infection, especially during the first six months, there is the danger of haematogeneous spread either focal (e.g. bone and joint lesions) or disseminated (in the form of military tuberculosis and tuberculosis meningitis).
SECONDARY INFECTION OF TUBERCULOSIS
Apart from the primary complex and its early complications, the “adult” pulmonary form of tuberculosis may occur either as a result of the reactivation of an existing lesion or by exogenous re-infection. Destruction of the lung parenchyma, with fibrosis and cavitation are important features of this adult form. Clinically, it may present with cough, haemoptysis and chest pain, with general constitutional symptoms. Fever, loss of weight and malaise often it remains virtually asymptomatic especially in the early stages.
The incubation period is from 4 to 6 weeks.
The causative agent is mycobacterium tuberculosis, the tubercle bacillus. The human type produces most of the pulmonary lesions, also some extra pulmonary lesions; the bovine strain of the organism mainly accounts for extra-pulmonary lesions.
Tubercle bacilli survive for long periods in dried sputum and dust.