Coupling between annual and ENSO timescales in the malaria-climate association in Colombia.

We present evidence that the El Niño phenomenon intensifies the annual cycle of malaria cases for Plasmodium vivax and Plasmodium falciparum in endemic areas of Colombia as a consequence of concomitant anomalies in the normal annual cycle of temperature and precipitation. We used simultaneous analyses of both variables at both timescales, as well as correlation and power spectral analyses of detailed spatial (municipal) and temporal (monthly) records. During "normal years," endemic malaria in rural Colombia exhibits a clear-cut "normal" annual cycle, which is tightly associated with prevalent climatic conditions, mainly mean temperature, precipitation, dew point, and river discharges. During historical El Niño events (interannual time scale), the timing of malaria outbreaks does not change from the annual cycle, but the number of cases intensifies. Such anomalies are associated with a consistent pattern of hydrological and climatic anomalies: increase in mean temperature, decrease in precipitation, increase in dew point, and decrease in river discharges, all of which favor malaria transmission. Such coupling explains why the effect appears stronger and more persistent during the second half of El Niño's year (0), and during the first half of the year (+1). We illustrate this finding with data for diverse localities in Buenaventura (on the Pacific coast) and Caucasia (along the Cauca river floodplain), but conclusions have been found valid for multiple localities throughout endemic regions of Colombia. The identified coupling between annual and interannual timescales in the climate-malaria system shed new light toward understanding the exact linkages between environmental, entomological, and epidemiological factors conductive to malaria outbreaks, and also imposes the coupling of those timescales in public health intervention programs.

Phlebotomine sandflies and leishmaniasis risks in Colombian coffee plantations under two systems of cultivation.

The phlebotomine sandfly fauna of traditional (shaded) and intensified (unshaded) coffee plantations in Colombia was sampled by a variety of methods and the species composition and density under the two systems compared. Twenty species of Lutzomyia sandflies (Diptera: Psychodidae: Phlebotominae) were collected, of which eight were found only in the 'Coffee Axis' ('Eje Cafetero') of the departments of Caldas, Risaralda and Quindio, six were exclusive to the department of Norte de Santander and six occurred in both regions. Four species were collected only in traditional plantations and two exclusively in intensified ones. At least 13 species occurred in both plantation types. Fifteen species are opportunistic man-biters and eight are suspected vectors of leishmaniasis caused by Le. braziliensis, Le. panamensis or Le. mexicana. Seven species were collected inside houses and may be involved in intradomiciliary transmission of Leishmania. The dominant species in Norte de Santander was Lu. spinicrassa, which made up 93.8% of all the sandflies collected in this department. This species was absent from the Eje Cafetero and a number of others among the 15 recorded there might be responsible for Leishmania transmission in this region, including Lu. trapidoi, Lu. yuilli, Lu. gomezi, L. hartmanni and Lu. ovallesi. Sandfly population densities were significantly higher in traditional plantations than in intensified ones. Residents of traditional plantations were able to describe sandflies in significantly more detail than those of intensified plantations, based on seven basic characteristics related to the appearance and biting behaviour of the insects.

Indoor resting heights of some anophelines in Colombia.

The nocturnal, indoor resting behavior of female anophelines in Colombia was studied. Anopheles darlingi and An. marajoara had a tendency to rest close to the ground, but An. oswaldoi and An. rangeli rested higher up. This behavior was independent of bloodfed status (except for An. oswaldoi) and whether the surface had been sprayed with DDT. With this information it should be possible to modify insecticide applications to coincide with the resting preferences of these species.

First record of DDT resistance in Anopheles darlingi.

DDT susceptibility of Anopheles darlingi was compared from the southeastern and northwestern regions of Colombia. Mosquitoes from southeastern Colombia (Puerto Lleras) were fully susceptible to DDT but in the northwest (Quibdo) LT50s were 14.3 times higher. This resistance appeared to be restricted to the Quibdo area. This is the first time that the DDT resistance has been detected in this important malaria vector.

Irritability to DDT of natural populations of the primary malaria vectors in Colombia.

Natural populations of Anopheles albimanus, An. darlingi and An. nuneztovari were tested for their irritability to DDT in different regions of Colombia. Individual anophelines were exposed to filter papers impregnated with 2% DDT and irritability was determined based on the number of flights a mosquito made in 15 min. All three species showed variability in their irritability to DDT. Anopheles albimanus showed irritability only in Bolivar, but not in three other regions. Anopheles darlingi showed no irritability in neither the Atlantico nor Llanos regions, while An. nuneztovari showed irritability in the Oriente but not in Uraba. The irritability to DDT shown in some populations of An. albimanus and An. nuneztovari may reduce the effectiveness of residual applications of this insecticide by causing the mosquitoes to seek untreated surfaces and/or leave the house to rest outdoors and thus avoid a lethal dose.