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Microfilarial distribution of Loa loa in the human host: population dynamics and epidemiological implications

Published online by Cambridge University Press:  09 June 2006

S. D. S. PION ,
J. A. N. FILIPE ,
J. KAMGNO ,
J. GARDON ,
M.-G. BASÁÑEZ  and
M. BOUSSINESQ
S. D. S. PION
Affiliation:
Laboratoire mixte IRD (Institut de Recherche pour le Développement) – CPC (Centre Pasteur du Cameroun) d'Epidémiologie et de Santé publique, Centre Pasteur du Cameroun, BP 1274, Yaoundé, Cameroun Department of Infectious Disease Epidemiology, St Mary's Campus, Norfolk Place, London W2 1PG, UK
J. A. N. FILIPE
Affiliation:
Department of Infectious Disease Epidemiology, St Mary's Campus, Norfolk Place, London W2 1PG, UK
J. KAMGNO
Affiliation:
Laboratoire mixte IRD (Institut de Recherche pour le Développement) – CPC (Centre Pasteur du Cameroun) d'Epidémiologie et de Santé publique, Centre Pasteur du Cameroun, BP 1274, Yaoundé, Cameroun
J. GARDON
Affiliation:
Laboratoire mixte IRD (Institut de Recherche pour le Développement) – CPC (Centre Pasteur du Cameroun) d'Epidémiologie et de Santé publique, Centre Pasteur du Cameroun, BP 1274, Yaoundé, Cameroun Institut de Recherche pour le Développement, UR 24 Epidémiologie et Prévention, CP 9214 Obrajes, La Paz, Bolivia
M.-G. BASÁÑEZ
Affiliation:
Department of Infectious Disease Epidemiology, St Mary's Campus, Norfolk Place, London W2 1PG, UK
M. BOUSSINESQ
Affiliation:
Laboratoire mixte IRD (Institut de Recherche pour le Développement) – CPC (Centre Pasteur du Cameroun) d'Epidémiologie et de Santé publique, Centre Pasteur du Cameroun, BP 1274, Yaoundé, Cameroun Institut de Recherche pour le Développement, Département Sociétés et Santé, 213 rue La Fayette, 75480 Paris Cedex 10, France
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Abstract

Severe adverse events (SAEs) following ivermectin treatment may occur in people harbouring high Loa loa microfilarial (mf) densities. In the context of mass ivermectin distribution for onchocerciasis control in Africa, it is crucial to define precisely the geographical distribution of L. loa in relation to that of Onchocerca volvulus and predict the prevalence of heavy infections. To this end, we analysed the distribution of mf loads in 4183 individuals living in 36 villages of central Cameroon. Mf loads were assessed quantitatively by calibrated blood smears, collected prior to ivermectin distribution. We explored the pattern of L. loa mf aggregation by fitting the (zero-truncated) negative binomial distribution and estimating its overdispersion parameter k by maximum likelihood. The value of k varied around 0·3 independently of mf intensity, host age, village and endemicity level. Based on these results, we developed a semi-empirical model to predict the prevalence of heavy L. loa mf loads in a community given its overall mf prevalence. If validated at the continental scale and linked to predictive spatial models of loiasis distribution, this approach would be particularly useful for optimizing the identification of areas at risk of SAEs and providing estimates of populations at risk in localities where L. loa and O. volvulus are co-endemic.

Keywords

Loa loamicrofilarial aggregationivermectinCameroon
Type
Research Article
Information
Parasitology , Volume 133 , Issue 1 , July 2006 , pp. 101 - 109
Copyright
2006 Cambridge University Press

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