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HLTB21H3 (204)


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University of Toronto Scarborough
Health Studies
Caroline Barakat

Tuberculosis - Most commonly associated with lungs but can affect almost any tissue or organ - Primary cause is acid-fast bacillus Mycobacterium tuberculosis. - Chronic disease lingers for months and sometimes years. - Acute forms that commonly strikes infants and children can be fatal in matter of weeks/days - Acute form – military tuberculosis has small grainlike tubercles that create simultaneously in almost every organ of body. - Ancient times tuberculosis had low prevalence rate. After industrialization, prevalence went up th th between 18 and 20 century. - Until 1944, no drug therapy. That year, researchers discovered streptomycin. Proved effective in inhibiting disease - 2 more drugs: para-aminosalicyclic acid (PAS), and isoniazid (INH) discovered in 1946 and 1952 - No longer epidemic, but still affect people worldwide from most industrialized countries b/c of higher risk of disease when malnourished or old Etiology and Epidemiology Species Classification - Tubercle bacillus is necessary but not only condition for causation - The host and environment contribute numerous other causes central to its pathogenesis - Mycobacteria can affect variety of animals. Of animal forms, only bovine can infect people o Some bacteriologists consider bovine separate from tubercle bacillus - Human bacillus divided into 2 types according to phage types o Type 1: found in India  Least virulent making Indians more susceptible to Type A and B o Type A: in Africa, China and Japan as well as in Europe and North America o Type B: exclusive to Europe and North America - M.tuberculosis show strong resistance to mutation. Unlikely increase virulence = disease become epidemic or decrease in virulence = decline mortality rates Transmission - Airborne, can transmit through talking, coughing, sneezing, spitting, singing, and other respiratory functions - People produce droplet nuclei and if emitted by tubercular individual, can contain 1-3 bacili - One bacilli is enough to establish infection when inhaled - Particles can disperse and some remain suspended like smoke - Large ones fall to floor (little threat) but dry bacilli can remain viable for months - Transmission in dust is rare but use to think that was main transmission - Countries forbade spitting in public - Bovine bacilli ingested through digestive tract by milk. Pasteurization eliminates source of infection Incubation Period - Indefinite and variable incubation period - Durable persistent. Remain viable through host’s lifetime - Dormant until resistance fails and cause active disease, even when it didn’t the first time Host-dependant factors - Whether disease will be active or not depends on host’s: o Age: infancy, puberty and old age = low resistance / high susceptibility  The younger, the more likely that primary infection will become active disease and result in death.  Infacts particularly susceptible to acute military tuberculosis  Exposure early in life leads to relatively high mortality rates o Gender: most females die than do males when disease just starts and more males die when disease declines  Not yet know why exactly  Young females higher mortality rate, after 30, male mortality rates surpass females  Onset of the mesnses brings on metabolic changes that increase body’s need for protein and when unavailable, o Genetics: some families experience more tuberculosis than others.  Long history of inhabiting urban environment made Jews more resistance  But populations previous lack of exposure cvan lead to acute epidemics of disease  Natural selection idea: susceptible are weeded out explains decline in mortality rate(other oppose theory)  Economic and social changes made most important contributions to decline in tuberculosis mortality rates until late 1940s when cures became available Primary environmental factors - Crowding: increases risk of infection when disease individuals constantly releases bacilli into air o Population density however has little impact on tuberculosis mortality rates - Nutrition: importance of protein - Working conditions: o workers in “dusty” trade inhale particulates that inflame lungs, increasing risk of development of disease o Physical exhaustion and stress magnifies individual’s risk as so does smoking o Lowest income = suffer the most from disease, rising income = reduces tuberculosis mortality - Other environmental factors: o Temperature, humidity or other climatic factors does not influence risk Clinical Manifestations - Frequently causes disease in the meninges, intestines, bones, lymph glands surrounding neck, skin, spine, kidneys and genitals - Most forms except tubercular meningitis are chronic. Months-years before recovery or death - Military tuberculosis concurrently affects almost every vital organ - Pulmonary tuberculosis most common form. o Symptoms: increasingly frequent and violent cough that produces purulent sputum and sometimes blood - Systematic symptoms of tuberculosis generally include: fatigue, lethargy, anorexia, weight loss, irregular menses, ill0definted anxiety, chills, muscular aches, sweating, low grade fevers. - Autopsies and xrays showed many people developed mild or asymptomatic cases of disease and recovered without knowing - Diagnosis hard because early stages have unalarming symptoms - Tuberculin test: preliminary diagnosis that indicates whether person has become infected with tubercle bacillus. Highly reliable but false-positives or not unknown - Tubercle bacillus itself not damaging; not toxic. Rather, it is allergic reaction in body / hypersensitivity that occurs in response to contact with bacillus - Immune system destroys invading tubercle bacilli, releasing proteins and fatty substances that i
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