Tuberculosis is an acute and chronic infection caused by the Mycobacterium tuberculosis, an acid-fast microbe which involves primarily the lungs—the largest respiratory organ—but may also affect any organ of the body.
TB is endemic the world over, occurs in all ages frequently early in life and also affects middle-aged adults. There are two peaks in incidence of TB with the first occurring within the first three years of life; the second peak in women occurs in the third decade while in men, it occurs in the fifth decade of life.
Tuberculosis is a granulomatous infection, similar to leprosy, syphilis, tularemia, sarcoidosis, but differs in the creation of a amorphous pink lipid rich debris which is cheese-like, giving the disease its characteristic caseation necrosis. Although the microbe is composed of carbohydrates, proteins—which is responsible for its antigenicity—it is the lipid portion that makes it more virulent.
TB is an acquired disease; humans are susceptible only to the human strain (90%) with 10% being due to the bovine strain. The bacilli is resistant to drying and can survive for days in ordinary room temperatures and humidity.
Four possible portals of entry of the microbe are through the respiratory tract (inhalation of minute particles less than 15 microns in diameter), the lymphoid tissue of the oropharynx, gut, and the skin.
Natural resistance is varied; with black people being more susceptible than Caucasians. Malnutrition, fatigue, debilitation, intercurrent diseases (esp. diabetes mellitus), severity of exposure—these all materially influence susceptibility to the disease.
Testing techniques include intracutaneous inoculation of tuberculoprotein or PPD-purified protein derivative (aka Mantoux test). The patch test involves the exposure of a measured area of skin to a known dose of TB protein with hyperemia as a positive result.
Primary TB follows the first seeding of the tissues of the body by the TB microbe, usually in infants, young children but may also occur in adults when they have never been exposed to the microbe in early life.
Reinfection TB, also called adult TB or secondary TB is the phase of infection that follows the reactivation of primary TB or a repeat infection of a previously exposed individual. It is well known that viable TB microbes may persist in caseous, partially fibrotic and even calcified lesions for many years and sometimes for life.
TB in children is also called “primary complex.” The first exposure to the microbe in children means no previous sensitization to the TB protein so there is very little, if at all, scarring when the infection is healed.
In adults, however, there is a florid excessive reaction of lymphocytes and other macrophages resulting in massive lung tissue destruction which sadly leads to a fibrotic scarring which is present on x-rays even when the patient is well.
TB in children is not communicable while in adults it is more likely, especially if the lesion is close or connected to a bronchus, which enables the expulsion of microbes through coughing, sneezing, or even loud talking. The presence of lymph nodes on the posterior triangle of the neck—movable, non-tended, matted—is highly suggestive of TB in children with associated frequent upper respiratory tract infection.
Cough may be a late symptom in adults, with night sweats even in cold nights, late afternoon fever, and unexplained weight loss being more common presenting signs and symptoms in adults.
Common with primary complex and adult TB is the now recommended duration of treatment: a six-month regimen divided into two phases, two-months aggressive and 4-months maintenance treatment.
Rifampicin-gold standard in TB therapy-Isoniazid or isonicotinic acid hydrazide, and pyrazinamide are given in the first two months in children. For adults, Rifampicin, INH, PZA and Ethambutol—the last one not given to children because of its effect on their retina—comprise the aggressive phase of treatment, with PZA likewise eliminated in the last four months.
Traditionally, streptomycin, an aminoglycoside, was a routine drug for TB in adults (not in children) as it’s quite efficacious and cheap. However, it is given only parenterally, a gram per day for one or two months, with warnings about its ototoxicity.
Pulmonologists and infectious disease experts strongly recommend that the TB drugs be all together taken before breakfast daily for maximum efficacy. From experience, the strict isolation of a TB patient requires only 21 days, by then there would have been sterilization of the bacilli.
Extrapulmonary tuberculosis include military TB in which the whole lung fields are seeded with millet-seed like particles or like canary bird seeds, with the liver and spleen most commonly affected when the microbe erodes the pulmonary artery. The meninges could also be affected, so are the eyes, kidneys, bones.
In males, a possible cause of infertility is the involvement of the epididymis while in females, their fallopian tubes are common sites of TB. The Peyer’s patches on the distal part of the ileum could also be sites of GIT TB. Hemoptysis is a serious manifestation of a far-advanced TB infection and requires immediate hospitalization considering the respiratory difficulty it entails.
Fortunately, in general, with the improvement in socioeconomic conditions especially among developing nations, plus more active primary healthcare initiatives of health agencies, less than 10% of those affected die of the disease.
The Department of Health has an active program for helping TB patients with its free TB-DOTS-TB-Direct Observed Treatment Short Course, which should be availed of by our citizens.
