The stages of an infection Incubation period: no symptoms, but organism is growing and spreading Prodrome period: non-specific symptoms, fever, weakness; disease is communicable. Specific Illness: rash, cough, etc. Convalescence: Increasing levels of antibodies, specific immune response Recovery: sometimes with a persistent carrier state.

Mycobacteriae Mycobacterium tuberculosis Mycobacterium leprae - agent of tuberculosis (TB; Hansen’s Disease) Mycobacterium leprae - agent of leprosy Nontuberculosis mycobacteria (NTM): - opportunistic, rare (in otherwise healthy individuals) “Not so ‘typical’ bacteria” Bacteria that have special shapes, sizes or staining properties Acid-fast bacteria

Tuberculosis is an old disease. DNA tests on mummy show TB killed ancient Egyptians (600 BC).

Tuberculosis has been a major disease for a long time. During the Industrial Revolution, nearly 100% of Europeans were infected and 25% died. White Death or White plague Consumption Vampirism

Tuberculosis remains a major disease. Leading cause of bacterially related death Kills more than HIV, malaria & other tropical diseases One-third of the global population is infected 8 million develop active TB every year 2 million die/year HIV infection sharply increases risk for TB (25% of deaths from TB are in patients also infected with HIV). About 90% of those infected have asymptomatic, latent TB infection. 10% have a lifetime chance active TB disease. If untreated, the death rate for these active TB cases is more than 50%.

Predisposing factors Immunosuppressed Immunocompromised (HIV/AIDS) Reduced general health close contact (homeless shelter, nursing homes, dormitories, schools, prisons)

Mycobacterium tuberculosis Acid-fast bacillus (non-motile slender rod) Obligate aerobe; replicates in oxygenated tissues Doubling time of 15-20h Increased resistance to chemical agents (acidic or alkaline), antibiotics, reactive oxygen species, osmotic lysis via complement deposition and dehydration Grows readily inside macrophages, hiding from the host's immune system

Waxy coat – nearly water proof The Mycobacterial cell wall Proteins and fatty acids Lipoarabinomannan Mycolic acids Arabino galactan om PG PG PG im im im Gram + Gram - Acid fast

Ziehl-Neelsen stain Stain with fuchsin (red dye) in detergent Wash with acid (3% HCl) to remove dye from all but “acid-fast” bacteria. Counterstain with dimethylene blue A.  Non acid-fast bacteria B.  Acid-fast bacteria Everything else (other bacteria and white blood cells) – stained with counter stain only

Mycobacterium tuberculosis Obligate aerobe; replicates in oxygenated tissues Mycolic acid modifies murein cell wall (waxy fatty acid, low permeability, interferes with Gram-stain; resistant to drying, chemicals, disinfectants, phagocyte killing)

Transmission Transmission can only occur from people with active — not latent — TB

Transmission Air-borne droplets are inhaled. Bacteria are ingested by alveolar macrophages. However, the macrophages are not activated and are unable to destroy the intracellular organisms.

Respiratory System

Virulence mechanism The probability of transmission depends on: number of infectious droplets expelled by a carrier effectiveness of ventilation duration of exposure

Phagosomes containing Mtb evade fusion with lysosomes Alveolar macrophage Intracellular pathogens: protected from serum, antibody, complement and antibiotics

Virulence factors No classic bacterial virulence factors such as toxins, capsules and fimbriae, but… Mycobacteria can grow intracellularly. Slow generation time. High lipid concentration in cell wall.

The course of TB infection 1- 3 weeks post infection. Bacteria multiply within unactivated macrophages until the macrophages burst. Other macrophages move in and also phagocytose Mycobacteria. Repeated cycles of phagocytosis and cell lysis. 3- 8 weeks: Lymphocytes begin to infiltrate. T-cell activation. Liberation of lymphokines. Activation of macrophages. Increased ability to kill Mycobacteria and Mycobacterium-infected cells. Containment of infection: The immune response results in the formation of granulomas – walling off the bacteria. The center of the granuloma - "caseous necrosis", semi-solid or "cheesy" consistency. Latent infection: Mycobacteria cannot multiply within these granulomas (low pH and anoxic environment). Mycobacteria can persist within these granulomas for extended periods. Latency; most people remain in this state (positive PPD test).

Granuloma formation Granuloma: alveolar macrophages release TNFa and other pro-inflammatory cytokines, which recruit more lymphocytes. The granuloma contains the infection but does not clear it.

Granuloma formation is a hallmark of tuberculosis Chest X-ray (radiograph)

Granuloma rupture releases infectious bacteria Months, years later - reactivation. The caseous centers of the granulomas liquefy. The liquid is conducive to Mycobacteria growth, and the organism begins to rapidly multiply extracellularly. Rupture of the surrounding bronchus - “cavitation”. Rapid spread of Mycobacteria to other parts of the lung.

Granuloma rupture releases infectious bacteria

Granuloma rupture releases infectious bacteria Weakened immunity leads to granuloma rupture and release of infectious bacteria. Disseminated (miliary) TB: spread throughout body, small tubercles form (infants and debilitated) Active TB is highly infectious and fatal if untreated (slow progression of tubercles and erosion of air passages and blood vessels).

A Person with Latent TB Infection A Person with TB Disease • No symptoms • Symptoms that may include: - a bad cough that lasts 3 weeks or longer - pain in the chest - coughing up blood or sputum - weakness or fatigue - weight loss - no appetite - chills - fever - sweating at night • Does not feel sick • Usually feels sick • Cannot spread TB bacteria to others • May spread TB bacteria to others • Usually has a test result indicating TB infection • Needs treatment for latent TB infection to prevent active TB disease • Needs treatment to treat active TB disease

The slow growth complicates TB diagnosis, therapy and research. 4-8 weeks for clinical isolation Months required for antibiotic susceptibility tests Antibiotics must be taken for months. Research is slowed by time required for bacterial growth.

Diagnosis Tuberculin skin test Stain sputum samples with Ziehl-Neelsen stain Chest X-ray or scans

Tuberculin skin test Injection of tuberculosis antigens intradermally (PPD = purified protein derivative) A hypersensitivity response is seen 2 days later in people infected with M. tuberculosis (= delayed-type hypersensitivity response, a.k.a. DTH response). A positive response is a firm, red, raised bump (filled with macrophages and neutrophils). Test does not distinguish between latent and active infection.

Therapy 4 different antimicrobial agents 6-9 months

Complications of TB therapy Problems emerge with the appearance of extreme multiple drug-resistant (MDR) bacteria. MDR Mtb are isolates with accumulated mutations in multiple target genes. MDR acquired by step-wise accumulation of mutations in response to selective pressure of antibiotic treatment. (NB: antibiotics are not mutagens!)

Vaccines No successful vaccine has been developed. Mycobacterium bovis causes tuberculosis in cattle. Bacillus Calmette-Guerin (BCG) is an attenuated strain of M.bovis which is used as a live vaccine. BCG provides incomplete protection, but reduces severity of disease. BCG vaccination compromises the tuberculin skin test (PPD).

Vaccines TB infection is controlled by cell-mediated immunity (not antibodies) Treatment and vaccine development for intracellular pathogens is difficult. Vaccine antigens must be delivered to MHC I pathway.

Mycobacterium leprae Obligate intracellular pathogen. Grows best at lower temperatures. Transmission inefficient, person-to-person via secretions, aerosols, close contact. Infection of skin and nerves (chronic granulomatous disease of peripheral nerves and nasal mucosa).

Mycobacterium leprae Disfiguring skin sores and nerve damage. Progressive debilitation: loss of sensation in the hands and feet, facial deformities and loss of sight. People affected by the disease and untreated can become severely disabled and unable to care for themselves. Historically more feared than tuberculosis. More social stigmatization.

Mycobacterium leprae M. leprae is difficult to study: Slow growing Cannot be cultivated

Therapy Complicated treatment 3 antibiotics for 1-2 years Once a person is treated, within a few weeks he is no longer contagious but physical deformities persist. 12 million cured

How do you know if a patient is sick with an infectious disease? Fever (but also present in autoimmune diseases and cancer) Inflammation (red, hot, tender, swollen) Inflammo = “I set alight; I ignite” Dolor = “pain” + Calor = “heat” + Rubor = “redness” + Tumor = “swelling” Functio laesa = “loss of function” Exudate (pus, discharge) Leukocytosis (increased white blood cell count in the blood)

Disfigurement associated with leprosy