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INTRODUCTIONS:
Tuberculosis is chronic granulomatous disease of human and other mammals caused by a group of closely related obligate pathogens, the mycobacterium tuberculosis complex, comprising M. tuberculosis. The human tubercle bacillus - M. bovis - the bovine tubercle bacillus, -agricanum - a heterogeneous type found principally in effuational Africa with properties intermediate between the former two species and M-microti-a rare cause of disease involves and other small mammals but attenuated for humans. Humans are the usual, but not unique, host of M. tuberculosis. M. bovis causes disease in cattle and also in badgers, deer, and other mammals. Humans are incidental hosts, usually acquiring infection by drinking contaminated milk although infection of farm workers may occur by aerogenous route. Human may transmit M. bovis to cattle but human to human is rarely reported (PDO D awis et al, 2003).
The annual tuberculosis infection rate or annual risk of infection is the best single indicator of the status and trend of tuberculosis in both developed and developing countries. It indicates the proportion of the population that will primarily infected or reinfected in the course of one year and is usually expressed as a percentage.
The risk of tuberculosis infection in developed countries is now very low, being less than 0.5% per annum in the majority, 0.1-0 % in most and less than 0.1% in a few countries. The risk of tuberculosis in these countries is declined by about 10% per year.
In developing countries much higher rates are found. The annual risk of infection for the richest and poorest countries is shown in following table. In most industrialized countries the annual rate of infection is now below 0.1% and continues decline by 10% per annum. In Africa, the annual risk of infection may be much as 2.5% or more, and in the present context of increasing tuberculosis, notification due to HIB epidemic is increasing rather than decreasing.