Effect of Ascaris Lumbricoides specific IgE on tuberculin skin test responses in children in a high-burden setting: a cross-sectional community-based study
1 Desmond Tutu TB Centre, Department of Paediatrics and Child Health, Faculty of Health Sciences, Stellenbosch University, Tygerberg, South Africa
2 Section on Retrovirology and Global Health, Department of Pediatrics, Baylor College of Medicine, Houston, TX, USA
3 Center for Global Health, Texas Children’s Hospital, Houston, TX, USA
4 Division of Medicine, Geisinger Clinic, Danville, PA, USA
5 Immunology Research Group, Department of Biomedical Sciences, Stellenbosch University, Tygerberg, South Africa
6 Section of Microbiology and Immunology, The Gade Institute, University of Bergen and Department of Microbiology, Haukeland University Hospital, Bergen, Norway
7 Deptartment of General Pediatrics and Neonatology, University Childrens Hospital, Duesseldorf, 40225, Germany
BMC Infectious Diseases 2012, 12:211 doi:10.1186/1471-2334-12-211Published: 11 September 2012
M.tuberculosis (M.tb) is associated with enhanced T helper cell type 1 (Th1) immune responses while helminth infection is associated with T helper cell type 2 (Th2) immune responses. Our aim was to investigate whether helminth infection could influence the ability to generate an appropriate Th1 immune response that is characterized by a positive tuberculin skin test (TST), in M.tb exposed children.
We completed a community-based, cross sectional household contact tracing study, using matched enrolment of HIV negative children with and without documented household M.tb exposure. We documented demographics, clinical characteristics, HIV status, M.tb exposure (using a standard contact score) and M.tb infection status (TST > = 10 mm). Ascaris lumbricoides-specific IgE was used as proxy for Ascaris infection/exposure.
Of 271 children (median age 4 years (range: 4 months to 15 years)) enrolled, 65 participants (24%) were serum positive for Ascaris IgE. There were 168 (62%) children with a documented household tuberculosis contact and 107 (40%) were (TST) positive overall.
A positive TST was associated with increasing age (Odds Ratio (OR) =1.17, p < 0.001), increasing M.tb contact score (OR = 1.17, p < 0.001), previous tuberculosis treatment (OR = 4.8, p = 0.06) and previous isoniazid preventive treatment (OR = 3.16, p = 0.01). A visible bacillus Calmette-Guérin (BCG) scar was associated with reduced odds of being TST positive (OR = 0.42, p = 0.01).
Ascaris IgE was not associated with TST status in univariate analysis (OR = 0.9, p = 0.6), but multivariable logistic regression analysis suggested an inverse association between Ascaris IgE status and a positive TST (OR = 0.6, p = 0.08), when adjusted for age, and M.tb contact score. The addition of an age interaction term to the model suggested that the age effect was stronger among Ascaris IgE positive children; the effect of being Ascaris IgE positive significantly reduced the odds of being TST positive amongst younger children while this effect weakened with increasing age.
Our preliminary findings highlight a high prevalence of both Ascaris exposure/infection and M.tb infection in children in an urban setting. Helminth exposure/infection may reduce the immune response following M.tb exposure when controlling for epidemiological and clinical covariates. These findings might be relevant to the interpretation of immunological tests of M.tb infection in children.