Abstract
BackgroundFilarial (and other helminth) infections are known to modulate mycobacteria-specific pro-inflammatory cytokine responses necessary for maintaining latency in tuberculosis (TB). We sought to address whether helminth co-infection alters progression to active pulmonary TB in a co-endemic area of South India.Methods/Principal FindingsIncidence of active pulmonary TB was assessed in 5096 subjects from five villages among helminth-infected (hel+) and –uninfected (hel−) groups. Baseline stool examinations, circulating filarial antigen, and tuberculin skin testing (PPD) were performed along with chest radiographs, sputum microscopy, and culture. During three follow-up visits each 2.5 years, patients were assessed using PPD tests and questionnaires and—for those with potential symptoms of TB—sputum microscopy and culture. Of the 5096 subjects, 1923 were found to be hel+ and 3173 were hel−. Follow up interval stool examination could not be performed. In each group, 21 developed active TB over the course of the study. After adjusting for sex, age, BCG vaccination status, and PPD positivity, no difference was seen in active TB incidence between hel+ and hel− groups either at baseline (relative risk (RR) 1.60; 95% confidence interval (CI): 0.69, 3.71, P = 0·27), or when followed prospectively (RR 1.24; 95% CI: 0.48, 3.18, P = 0·66).Conclusions/SignificanceOur findings suggest that, despite the immunomodulatory effects of helminth infection, baseline co-morbid infection with these parasites had little effect on the clinical progression from latent to active pulmonary TB.
Highlights
Mycobacterium tuberculosis (Mtb) infection remains a disease of significant public health importance, in resourcelimited parts of the world
When we tested for the effect of helminth infection on active TB at baseline by fitting a binary generalized linear models (GLMs) (Table 3), there was no significant association of helminth infection at baseline with the presence of active TB (RR: 1.60; 95% confidence interval (CI) 0.69, 3.71; P = 0?27) even after controlling for age, gender, bacillus CalmetteGuerin (BCG) vaccination status, and skin test reactivity
There were significant associations with gender and age, and there was a borderline significant association with tuberculin skin test positivity (RR = 6.84, P = 0?06)
Summary
Mycobacterium tuberculosis (Mtb) infection remains a disease of significant public health importance, in resourcelimited parts of the world. Intestinal and tissue-invasive helminth infections geographically overlap with Mycobacterium tuberculosis (Mtb) and, because of their chronic nature, induce significant immunemediated modulation. It is well known that bacillus CalmetteGuerin (BCG) vaccination has been ineffective in preventing adult-onset TB in many parts of the world where helminths are commonplace [3,4]. Filarial (and other helminth) infections are known to modulate mycobacteria-specific pro-inflammatory cytokine responses necessary for maintaining latency in tuberculosis (TB).
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