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1、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/A
2、IDS 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 o
3、ils, 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, kanamy
4、cin, cycloserine, ethionamide, thiacetazone, ciprofloxacin/ofloxacin, rifapentine, amikacin, viomycin, capreomycin.,DOTS-The Best TB Therapy since 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. Co
5、ntinuation phase (3 times a week, 4 months) with 2 drugs: INH and RMP.,DOTS-Plus,DOTS + second-line TB drugs (PAS, ethionamide, cycloserine, 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 more tox
6、ic to patients- side effects) for up to two years DOTS-Plus works as a supplement to the DOTS, to address 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 367100,000 Prevalence of Sear pos
7、itive pulmonary diseases is 122100,000 130,000 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,Incidence of tuberculosis according to the report from China CDC,But incidence do not decrease!
8、,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?,HIV infected Tuberculosis Cases 1/100,000 population in China,Latency,TB bacilli can persist for long periods of time (decades) i
9、n 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
10、, 48-gene dormancy regulon, etc.,Dormant or Persistent Bacilli,Cornell 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
11、 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 “hi
12、dden 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 millio
13、n 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, 297311,TST positive in China, 2000,Shortage of TST,Poo
14、r 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
15、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
16、 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
17、 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 immun
18、osorbent 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
19、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 cel
20、ls: 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 tests excellent performance in immunosuppressed populations,The
21、strategic for treating latent infection of tuberculosis in China?,Lifetime Risk of Reactivation Tuberculosis,C. Robert Horsburgh. n engl j med 2004;350;20:2060-7,Latent infection of tuberculosis in China: Treat or not Treat?,BCG strategic or “find and treat” strategic? Conditionally treatment focusing high-risk groups: close house contacts and immunocompromised cases Chemotherapy or Immunotherapy?,