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Latent Infection of Tuberculosis in China
HUASHAN HOSPITAL,
FUDAN UNIVERSITY, Shanghai, China
Wenhong Zhang, M.D & PhD.
TB: A leading infectious killer- top 3 infectious killer
• TB kills about 2 million people each year
• 8 million people become sick with TB each year
• TB is the leading killer of HIV/AIDS patients
• 50 million people infected with drug-resistant TB
The New Tuberculosis
HIV and Drug-resistant TB – A lethal combination and a major threat to TB control
WHO declared TB a global emergency in 1993
TB Chemotherapy: THE Effective TB Control
• Pre-antibiotic era: before 1940s (e.g., cod liver oils, bed rest, fresh air)
• Drugs used to treat TB: Streptomycin first TB drug (1944), followed by PAS (1946), isoniazid (1952), pyrazinamide (1952), rifampin (1963)
• (a) Front-line Drugs: isoniazid (INH) rifampicin (RMP), pyrazinamide (PZA), streptomycin, ethambutol.
• (b) Second-line Drugs: PAS, kanamycin, cycloserine, ethionamide, thiacetazone, ciprofloxacin/ofloxacin, rifapentine, amikacin, viomycin, capreomycin.
DOTS-The Best TB Therapysince 1991
• DOTS: 6 month therapy - The best therapy against TB (78%-96% cure rate).
• Initial phase (daily, 2 months) with 4 drugs: INH, RMP, PZA, Ethambutol.
• Continuation phase (3 times a week, 4 months) with 2 drugs: INH and RMP.
DOTS-Plus• DOTS + second-line TB drugs (PAS, ethionamide, cy
closerine, kanamycin, amikacin etc.)• Too expensive (TB case: $11 to $100, cost of treating
an MDR-TB case: $150,000) • MDR-TB requires extensive chemotherapy (also mor
e toxic to patients- side effects) for up to two years • DOTS-Plus works as a supplement to the DOTS, to a
ddress both drug-susceptible and MDR-TB in areas with significant MDR-TB.
Disease Burden of Tuberculosis in China, 2000 data
• Prevalence of active pulmonary diseases is 367 / 100,000
• Prevalence of Sear positive pulmonary diseases is 122 / 100,000
• 130,000 patients die from tuberculosis every year
• No data of latent tuberculosis in China up to now
China CDC 2006
Prevalence of Smear Positive Tuberculosis in China
020406080
100120140160180200
prevalence (1/100,000)
1979 1990 2000
Incidence of tuberculosis according to the report from China CDC
But incidence do not decrease!
0
200000
400000
600000
800000
1000000
1200000
1400000
1600000
2003 2004 2005 2006
China CDC 2006
Factors contribute to tuberculosis reemerging in China
• MDR TB?
• HIV increasing?
• Latent infection?
• Diagnosis tools are more accurate to find more new cases?
Latency• TB bacilli can persist for long periods of ti
me (decades) in the host before reactivating and causing active disease
• Host factors: immunocompromised conditions, viral infections (e.g. HIV and measles), steroids, anti-TNF antibody (REMICADE® infliximab) as part of the treatment of rheumatoid arthritis
• Bacterial factors: e.g. isocitrate lyase, alpha-crystallin, 48-gene dormancy regulon, etc.
Dormant or Persistent BacilliCornell model: Mice infected with TB bacilli are treated for 3 months with INH and PZA --> No bacilli found in infected organs (spleens/lungs) by plating --> stop treatment --> 3 months later, 1/3 mice relapse with TB (drug susceptible) and all mice relapse with TB if treated with immonosuppressing steroids --> suggest existence of dormant bacilli or persisters (phenotypic resistance).
• New TB cases are driven by the reservoir of latently infected people.
• If we want to stop active TB cases, we need to eliminate this reservoir of infection.
• This “hidden epidemic” of people infected with latent TB is enormous.
• The growth in latent TB is becoming a clinical time bomb.
• We need to defuse this bomb by increasing our efforts to identify and treat latently infected people.
Latent tuberculosis is the reservoir of active tuberculosis
Active TB – 8 million new cases a year- Unfortunately just the tip of the iceberg
Latent TB - the “hidden epidemic”-2 billion people infected
Epidemiology of latent infection in the world
Frothingham R, et al.International Journal of Infectious Diseases (2005) 9, 297—311
Shortage of TST
• Poor specificity: antigenic
cross-reactivity of PPD with BCG
and environmental mycobacteria
• Poor sensitivity: 75-90% in
active disease (lower in disseminated
TB and HIV infection; unknown for
latent infection)
Factors leading to False-Positive TST Reactions
• Nontuberculous mycobacteria– Reactions caused by nontuberculous mycobacteria
are usually 10 mm of induration
• BCG vaccination– Reactivity in BCG vaccine recipients generally
wanes over time; positive TST result is likely due to TB infection if risk factors are present
T SPOTTM detect INF-r released by specific T cells
Collect white cells using BD CPT tube or Ficoll extraction. Add white cells and TB antigens to wells. T cells release interferon gamma.
Interferon gamma captured by antibodies.
Incubate, wash and add conjugated second antibody to interferon gamma.
Add substrate and count spots by eye or use reader. Each spot is an individual T cell that has released interferon gamma.
How does T-spot Technology Work
Patient Whole blood Sample
PBMC ESAT-6 CFP10
T cell secreting INF
Ab capture INF
Blue spot
2 commercial Kit available for detecting latent or active tuberculosis
• T cell-based assay for interferon gamma, the enzyme-linked immunosorbent spot test (ELISPOT), has promise in the diagnosis of Mycobacterium tuberculosis infection after exposure to a known tuberculosis (TB) patient.
• Commercialisation of two T cellbased tests for the diagnosis of M. tuberculosis infection (T Spot TB by Oxford Immunotec and Quantiferon-TB Gold by Cellestis)
T-cell based assay is recommended for detecting infection of M. Tb
• measures individual reacting T cells:– Even individual cells can be detected in a sample.– Therefore even those who are severely immunocompromised, if a
single cell reacts then it can be detected.
• measures all types of T cells:– Both CD4 and CD8 type T cells are detected.– Therefore if one type of T cells is depleted in a patient (e.g. CD4 T
cells in HIV infected patients) a response can still be detected from the CD8 T cells.
This sensitivity is key to the test’s excellent performance in immunosuppressed populations