Class 8- TB and HIV Flashcards
TB’s History
- Tuberculosis is an ancient disease
- Thought to have first appeared more than 1 million years ago in soil
- TB’s many aliases include
- Consumption
- King’s evil
- Scorfula
- Potts disease
- Respiratory infection by the gram positive bacteria Mycobacterium tuberculosis
TB history (1950-1990’s)
- In the 1950s and 60s new Tx were discovered
- Leading many in medical communities to assume TB was on the path towards eradication
- Caused a lag in anti-mycobacterial drug research
- What happened in the early 1980s?
- HIV started appearing
- WHO declared TB a global emergency in 1993
- Primary strategy relies heavily on DOTS (Directly observed therapy, short course)
TB Epidemiology
- Over 2.2 billion people, roughly 1/3 of the world’s total population, are infected with M. tuberculosis
- ¨Every second someone is newly infected with TB
- 1.4 million people died in 2010 of TB
The difference between active TB infections and Latent TB infections (LTBI)
- Only 5-10% of the 1/3 will ever activate.
- You are at your greatest risk of TB activation within the first 2 years after exposure
- HIV increases your risk of activation due to a compromised immune system
- Ninety-five percent of all tuberculosis cases in the world occur in developing countries.
- Tuberculosis is highly prevalent in Russia, India, Southeast Asia, sub-Saharan Africa, and parts of Latin America.
- Countries with a high prevalence of HIV infection have the greatest tuberculosis burden.
- Tuberculosis is highly prevalent in Russia, India, Southeast Asia, sub-Saharan Africa, and parts of Latin America.
TB Route of Exposure/Site of Infection
- Tuberculosis always begins as a latent infection
- Route of exposure is almost always inhalation
- Why does this matter?
- TB first infects the lungs and airway.
- TB can spread to other organs, which is known as extrapulmonary or disseminated tuberculosis
- Extrapulmonary - rarely infectious, but still deadly
- Why does this matter?
- Why does the site of infection matter?
- If you have a pulmonary infection then you are much more contagious because you are spreading the infection with every exhalation
Extrapulmonary TB
- More commonly found in children and HIV infected individuals
- Causes fatigue and weight loss, but symptoms are usually specific to the affected organ system
- Most frequent sides include
- pleura, pericardium, larynx, lymph nodes, skeleton (primarily the spine), genitourinary tract, eyes, meninges, gastrointestinal tract, adrenal glands, and skin. Can results in Systemic infection in essentially every organ
- Infections have occurred after autopsies of infected tissue
Active TB transmission and symptoms
- Infected Droplet nuclei are released into the air.
- Smaller the particles can penetrate your lungs deeper
- However incredibly small particles are of minimal risk because your will expel them quickly
- Smaller the particles can penetrate your lungs deeper
- Symptoms include
- Fatigue
- Extreme weight loss
- Sputum producing cough
- Fever
TB Stages
Step 1: 90-95 % of primary infections remain in the LTBI phase
Step 2: Several years later, members from the LTBI group may reactivate – creating a new set of infected TB cases (step 3)
Step 3: 5 – 10 % of the primary infections may progress to active infection (Step 4) within the first two years of exposure, the rest will enlarge the pool of latent infections (Step 1)
Step 4: Active TB infections will infect an average of 10 contacts (Step 3) of which a subset will progress to Step 4, the rest will enlarge latent pool
Tests used to diagnose Active TB
- Signs and symptoms overlap with a number of other pulmonary and systemic diseases
- Chest radiographs are critically important in diagnosing pulmonary TB
- Cavitation (shown in picture) commonly occurs in HIV infected
- Causes holes in lungs
- Rarely occurs with primary infection, commonly found in reactivation of infection years later
- Diagnosis involves a synthesis of both
- Clinical – symptoms and x-rays
- Laboratory findings – afb smears
- Laryngeal TB is particularly infectious
- All exhalations are forced through infected tissue
Issues with TB vaccine/surveillance
- Complications of the Bacille Calmette–Guérin, (BCG) vaccine, roughly 60% affective in preventing TB
- BCG vaccinated individuals will often come up positive because they have antibodies.
- Influences surveillance/screening
- BCG vaccinated individuals will often come up positive because they have antibodies.
Risk Factors Associated with TB
- Time since infection
- Most likely to activate within first 2 years
- Age
- Men at a higher risk at young and old ages
- Women at a higher risk in middle age
- Gender
- Risk by gender changes over life time
- Genetics
- Nutrition
- Occupation
- Silicosis in miners
- Smoking
- Diabetes
- HIV
TB in Eskimos
Study of active TB in Alaskan Eskimos, found individuals with AB and B blood types were three times more likely to have moderate to severe tuberculosis compared to blood types O and A
TB in Prisons
- Lack of access to care
- HIV co-infection
- Spread of multi drug resistance strains of TB (MDR)
- Overcrowding
- Increased risk of transmission
- Less serious prisoners are more likely to be released
- Results in infected prisoners bringing TB home
WHO DOTS program
Key strategy to reduce morbidity, mortality, and drug resistance
Downside- expensive and relies on countries ability to detect cases
TB Treatment
- TB drugs can be very hard on the liver
- All of the drugs create liver toxicity
- In the study we conducted we found elderly with LTBI were more likely to have a hepatic event than elderly with Active TB, why do you think that’s the case?
- Don’t have someone checking on them every day like with DOTS
Viral “set point”
The higher the level during the latent period, the sooner you will die. A lower viral “set point” during latency means you will live longer before infection becomes fatal.
