Parasitology



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


W. A. STOLK a1c1, K. D. RAMAIAH a2, G. J. VAN OORTMARSSEN a1, P. K. DAS a2, J. D. F. HABBEMA a1 and S. J. DE VLAS a1
a1 Department of Public Health, Erasmus MC, University Medical Center Rotterdam, P.O. Box 1738, 3000 DR Rotterdam, The Netherlands
a2 Vector Control Research Centre (Indian Council of Medical Research), Indira Nagar, Medical Complex, Pondicherry, 605 006, India

Article author query
stolk wa   [PubMed][Google Scholar] 
ramaiah kd   [PubMed][Google Scholar] 
van oortmarssen gj   [PubMed][Google Scholar] 
das pk   [PubMed][Google Scholar] 
habbema jd   [PubMed][Google Scholar] 
de vlas sj   [PubMed][Google Scholar] 

Abstract

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.

(Received January 24 2004)
(Revised April 9 2004)
(Accepted April 14 2004)


Key Words: lymphatic filariasis; Wuchereria bancrofti; prevalence; acquired immunity.

Correspondence:
c1 Department of Public Health, Erasmus MC, University Medical Center Rotterdam, P.O. Box 1738, 3000 DR Rotterdam, The Netherlands. Tel: +31 10 4087730/7714. Fax: +31 10 4089449. E-mail: w.stolk@erasmusmc.nl


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