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The epidemiology of canine leishmaniasis: transmission rates estimated from a cohort study in Amazonian Brazil

Published online by Cambridge University Press:  01 August 1997

R. J. QUINNELL ,
O. COURTENAY ,
L. GARCEZ  and
C. DYE
R. J. QUINNELL
Affiliation:
Department of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, Keppel Street, London WC1E 7HT
O. COURTENAY
Affiliation:
Department of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, Keppel Street, London WC1E 7HT
L. GARCEZ
Affiliation:
Instituto Evandro Chagas, CP1128, Belém 66050, Pará, Brazil
C. DYE
Affiliation:
Department of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, Keppel Street, London WC1E 7HT
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Abstract

We estimate the incidence rate, serological conversion rate and basic case reproduction number (R0) of Leishmania infantum from a cohort study of 126 domestic dogs exposed to natural infection rates over 2 years on Marajó Island, Pará State, Brazil. The analysis includes new methods for (1) determining the number of seropositives in cross-sectional serological data, (2) identifying seroconversions in longitudinal studies, based on both the number of antibody units and their rate of change through time, (3) estimating incidence and serological pre-patent periods and (4) calculating R0 for a potentially fatal, vector-borne disease under seasonal transmission. Longitudinal and cross-sectional serological (ELISA) analyses gave similar estimates of the proportion of dogs positive. However, longitudinal analysis allowed the calculation of pre-patent periods, and hence the more accurate estimation of incidence: an infection–conversion model fitted by maximum likelihood to serological data yielded seasonally varying per capita incidence rates with a mean of 8·66×10−3/day (mean time to infection 115 days, 95% C.L. 107–126 days), and a median pre-patent period of 94 (95% C.L. 82–111) days. These results were used in conjunction with theory and dog demographic data to estimate the basic reproduction number, R0, as 5·9 (95% C.L. 4·4–7·4). R0 is a determinant of the scale of the leishmaniasis control problem, and we comment on the options for control.

Keywords

canine leishmaniasisLeishmania infantumserologydomestic dogincidence ratebasic reproduction number
Type
Research Article
Information
Parasitology , Volume 115 , Issue 2 , August 1997 , pp. 143 - 156
Copyright
1997 Cambridge University Press

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