Lancet conference

The challenge of tuberculosis: statements on global control and prevention: Global control

A rapid serological test for tuberculosis (TB) infection was designed using antigens specific to Mycobacterium tuberculosis. Tuberculosis infection, TB vaccination and exposure to environmental Mycobacteria cannot be distinguished using skin tests based on tuberculin protein derivatives. The standard diagnostic techniques such as skin tests, X-rays and DNA techniques are time consuming, expensive, and not practical for screening large populations. We used the 38, 63, 64, 14, 59-kDa antigens of M. tuberculosis to develop a rapid immunochromatographic test kit. This study evaluates the diagnostic potential of the rapid test kit using TB positive and TB negative serum samples from various hospitals in India. The samples were obtained from patients infected with or exposed to bacteria and viral pathogens. The results demonstrated that the combination of antigens improved the diagnostic specificity and sensitivity. The specificity of the test was 99.42% with sensitivity of 98.52% (n=241). In case of multiple infections, the specificity was 93.15% with a low sensitivity of 73.52% (n=141). The test kit may offer an improved alternative to purified protein derivative (PPD). This rapid TB test kit may be a useful tool for first-line testing of suspected cases, epidemiological studies and in designing a quality health system to reduce health hazards in resource-poor countries.

Un test sérologique rapide pour le dépistage de l'infection tuberculeuse (TB) a été conçu en utilisant des antigènes spécifiques de mycobacterium Tuberculosis. Les animaux infectés ne peuvent être distingués des animaux vaccinés par les tests cutanés utilisant les tuberculines. Les techniques diagnostiques standard telles que des tests cutanés, les rayons X et les techniques utilisant l'ADN sont longues, chères, et pas pratiques à grande échelle. Nous avons utilisé les antigènes 38, 63, 64, 14, 59-kDa de M.tuberculosis pour développer un test immunochromatographique en coffret. Cette étude évalue les possibilités diagnostiques du test rapide en utilisant les échantillons négatifs de positif de sérum provenant de divers hôpitaux en Inde. Les échantillons ont été obtenus à partir des patients infectés ou exposés à des bactéries et à des virus. Les résultats ont démontré que la combinaison des antigènes améliore la spécificité et la sensibilité du diagnostic. La spécificité de l'essai était de 99,42% avec une sensibilité de 98,15% (n=241). En cas d'infections multiples, la spécificité était 93,15% avec une sensibilité de 73,52% (n=141). Ce test rapide peut être un outil utile pour le dépistage des cas suspects et les études épidémiologiques et peut être utilisé pour concevoir un système de santé pour réduire des risques sanitaires dans les pays pauvres.

Tuberculosis is an important cause of death, mainly in the less developed countries. Thus far the strategy for its control had relied on the diagnosis of sick individuals and provision of chemotherapy. However, this strategy is problematic for several reasons: poor education about the disease and the low income of people with tuberculosis are important barriers for them to have access to early diagnosis and to keep adherence to treatment; provision of `preventive therapy' to the enormous pool of people infected with tuberculosis is not feasible in less developed countries; and finally, long-term political commitment with the strategy is unlikely. Several facts indicate that tuberculosis patterns in different populations are shaped by biological, behavioral and socio-economic factors. This paper argues that a lasting control of tuberculosis requires a strategy based on a broader model of causality, which takes account of all these three causal factors.

BCG (bacille Calmette-Guérin) is an attenuated pathogen characterized by its capacity to induce cellular and humoral immune responses primarily against a nonpeptidic antigen, lipoarabinomannan. Immune responses against this substance contribute to the immunoprotection of the patient if the production of IL-2 and INF-γ is not impaired. The most adequate production of INF-γ and IL-2 is obtained by immunoreactivity against proteinic antigens. The formation of IgG-type antibodies and of cellular immunity against mycobacterial peptidic and proteinic antigens is an additional immunological response essential for a good protection. This is achieved by the BCG vaccine in only a small proportion of the vaccinees. A vaccine adjuvant that also finds application as an immunotherapeutic agent is composed of proteinic antigens such as sonicates ofMycobacterium vaccae and antigen 60 of Mycobacterium bovis. These enhance the beneficial Th₁-pole of the immune response. In addition, A60 induces the formation of antibodies against species-specific proteinic antigens.

Despite the questioning of its innocuousness and efficacy, the BCG vaccine was imposed worldwide in 1950 by medical and political organizations that showed no concern for these questions. The contemporary structures of research administration in this area make it unlikely that the efficacious means recently developed to complement the action of the vaccine and of chemotherapies to face the surge of tuberculosis (TB) will be readily adopted.