The sandfly vectors and epidemiology of cutaneous leishmaniasis in the Landazury Focus, Colombia
This thesis describes a comprehensive cohort study of cutaneous leishmaniasis (CL) in a population of 2,704 followed over a period of 19 months, in the Opon focus, Landazury, Santander, Colombia. Chapter 1 reviews the public health importance of CL at international, national (Colombia), and local (Santander) levels. Particular attention is given to the distribution of Leishmania parasites, sandfly vectors and reservoirs in Central and South America, according to the ecological regions defined by the Andes mountain range. Chapter 2 describes the materials and methods of the whole project, emphasising its clinical, epidemiological and entomological aspects, respectively. Each one of the following three chapters contains an introduction, results and discussion. Chapter 3 addresses the diagnosis, aetiology and clinical symptoms of leishmaniasis patients. The principal findings were as follows: (i) from three methods tested, PCR and the direct examination of slides are recommended as diagnostic tools in distant leishmaniasis foci; (ii) the main parasite circulating in Opon is L. panamensis; (iii) cutaneous lesions were larger if patients were infected at a younger age, and tended to be located on the face of children, on the legs of women, and on the torso of man; and (iv) about 10.2% of CL patients had mucosal lesions of low severity. Chapter 4 presents the results of the cross-sectional survey carried out between May-July 1995, and the results of the 19 months prospective survey. Results are divided into sections on the population structure; the population transmission rate for infection and disease; the personal, household and village risk factors for infection; seasonal variation in the incidence of leishmaniasis; the risk factors for developing clinical symptoms with infection; acquired immunity; and finally an analysis of the potential bias in the study. The main findings were as follows: (i) the cumulative prevalence of infection amongst the whole study population was 0.75; (ii) the average transmission rate in this focus is currently ca. 0.19/year; (iii) the risk of infection is equal for both genders and for all ages; and (iv) transmission was less likely in houses surrounded by secondary forest. In Chapter 5 the sandfly fauna in the focus are described, focusing on their seasonal and nocturnal activity patterns; the relationship between habitat type and indoor sandfly abundance; the spatial relationship between abundance and transmission rate; and the natural infection rate with Leishmania. The main findings were as follows: (i) the principal vectors in the Opon focus are Lu. trapidoi and Lu. gomezi; (ii) a significant proportion of transmission to humans takes place indoors and at night; and (iii) the widespread deforestation that characterises the Opon focus has not caused any reduction in the incidence of leishmaniasis, presumably because the sandfly vectors continue to breed successfully in the cacao plantations that have replaced much of the primary forest. Chapter 6 provides a discussion of the complete project, focusing on the significance for public health in Santander.