Parasitology


Research Article

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


R. J. QUINNELL a1 , O. COURTENAY a1 , L. GARCEZ a2 and C. DYE a1
a1 Department of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, Keppel Street, London WC1E 7HT
a2 Instituto Evandro Chagas, CP1128, Belém 66050, Pará, Brazil

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[minus sign]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.

(Received June 13 1996)
(Revised February 4 1997)
(Accepted February 7 1997)

Key Words: canine leishmaniasis; Leishmania infantum; serology; domestic dog; incidence rate; basic reproduction number.

Correspondence:

Corresponding author: Department of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, Keppel Street, London WC1E 7HT. Tel: +0171 927 2335. Fax: +0171 636 8739. E-mail: C.Dye@lshtm.ac.uk.



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