Meta-analysis of age-prevalence patterns in lymphatic filariasis: no decline in microfilaraemia prevalence in older age groups as predicted by models with acquired immunity

• Published in: Parasitology 2004-11, Vol.129 (5), p.605-612
• Main Authors: STOLK, W. A., RAMAIAH, K. D., VAN OORTMARSSEN, G. J., DAS, P. K., HABBEMA, J. D. F., DE VLAS, S. J.
• Format: Article
• Language: English
• Subjects: acquired immunity; Adolescent; Adult; Africa South of the Sahara - epidemiology; Age; Age Distribution; Age groups; Animals; Biological and medical sciences; Elephantiasis, Filarial - epidemiology; Elephantiasis, Filarial - immunology; Elephantiasis, Filarial - parasitology; Epidemiology; Female; Filariasis; Fundamental and applied biological sciences. Psychology; General aspects; General aspects and techniques. Study of several systematic groups. Models; Humans; Immunity; Immunity, Active; Immunology; India - epidemiology; Indication; Infections; Infectious diseases; Invertebrates; Longitudinal Studies; lymphatic filariasis; Male; Mathematical models; Medical research; Meta-analysis; Middle Aged; Prevalence; Public health; Risk Factors; Studies; Tropical diseases; Vector-borne diseases; Wuchereria bancrofti; Wuchereria bancrofti - immunology
• ISSN: 0031-1820; 1469-8161
• DOI: 10.1017/S0031182004005980

The role of acquired immunity in lymphatic filariasis is uncertain. Assuming that immunity against new infections develops gradually with accumulated experience of infection, models predict a decline in prevalence after teenage or early adulthood. A strong indication for acquired immunity was found in longitudinal data from Pondicherry, India, where Mf prevalence was highest around the age of 20 and declined thereafter. We reviewed published studies from India and Subsaharan Africa to investigate whether their age-prevalence patterns support the models with acquired immunity. By comparing prevalence levels in 2 adult age groups we tested whether prevalence declined at older age. For India, comparison of age groups 20–39 and 40+ revealed a significant decline in only 6 out of 53 sites, whereas a significant increase occurred more often (10 sites). Comparison of older age groups provided no indication that a decline would start at a later age. Results from Africa were even more striking, with many more significant increases than declines, irrespective of the age groups compared. The occurrence of a decline was not related to the overall Mf prevalence and seems to be a chance finding. We conclude that there is no evidence of a general age-prevalence pattern that would correspond to the acquired immunity models. The Pondicherry study is an exceptional situation that may have guided us in the wrong direction.