Abundance, biting behaviour and parous rate of anopheline mosquito species in relation to malaria incidence in gold‐mining areas of southern Venezuela

Abstract

A longitudinal entomological and epidemiological study was conducted in five localities of southern Venezuela between January 1999 and April 2000 to determine the abundance, biting behaviour and parity of anopheline mosquitoes (Diptera: Culicidae) in relation to climate variables and malaria incidence. A total of 3685 female anopheline mosquitoes, representing six species, were collected. The most abundant species were Anopheles marajoara Galvão & Damasceno (60.7%) and Anopheles darlingi Root (35.1%), which together represented 95.8% of the total anophelines collected. Abundance and species distribution varied by locality. Malaria prevalence varied from 12.5 to 21.4 cases per 1000 population. Transmission occurred throughout the year; the annual parasite index (API) for the study period was 813.0 cases per 1000 population, with a range of 71.6-2492 per 1000 population, depending on locality. Plasmodium vivax (Grassi & Feletti) (Coccidia: Plasmodiidae) accounted for 78.6% of cases, Plasmodium falciparum (Welch) for 21.4% and mixed infections (Pv+Pf) for < 0.1%. Anopheles marajoara and An. darlingi were more abundant during the rainy season (April-September). There was no significant correlation (P > 0.05) between mosquito abundance and rainfall. Correlations between malaria incidence by parasite species and mosquito abundance were not significant (P > 0.05). Monthly parous rates were similar for An. marajoara and An. darlingi throughout the year, with two peaks that coincided with the dry-rainy transition period and the period of less rain. Peaks in the incidence of malaria cases were observed 1 month after major peaks in biting rates of parous anophelines. Anopheles darlingi engages in biting activity throughout the night, with two minor peaks at 23.00-00.00 hours and 03.00-04.00 hours. Anopheles marajoara has a different pattern, with a biting peak at 19.00-21.00 hours and 76.6% of biting occurring before midnight. Although both vectors bite indoors and outdoors, they showed a highly significant (P < 0.01) degree of exophagic behaviour. The present study constitutes the first effort to characterize the bionomics of anophelines in malaria endemic foci in different ecological situations in relation to malaria transmission in southern Venezuela and to provide relevant information to be considered when planning and implementing vector control programmes.

Malaria entomological inoculation rates in gold mining areas of Southern Venezuela

“…neomaculipalpus (n = 362), Anopheles braziliensis (n = 103), Anopheles triannulatus (n = 42), Anopheles oswaldoi (n = 12) and Anopheles apicimacula (n = 1). The number of mosquitoes collected in each locality by species and by catching method has been reported previously (Moreno et al 2002(Moreno et al , 2007.…”

“…Similar results have been reported for An. darlingi in state of Amazonas (AM), Venezuela (Magris et al 2007 (Moreno et al 2007) and AM (Magris et al 2007) and also provided information about the role of An. marajoara as an emerging malaria vector in the region.…”

“…The area and the villages have been previously described by Moreno et al (2002Moreno et al ( , 2007. Transmission occurs throughout the year; the annual parasite index (API) was 813 cases per 1,000 population.…”

“…Cross-sectional surveys conducted during the study showed that the prevalence varied from 12.5-21.4 cases per 1,000 population. More cases were diagnosed in the under-15 age group than in any other group (Moreno et al 2007). Vector control activities in this area includes house spraying with pyrethroids and space spraying with organophosphates in areas with active transmission, as well as selective treatment of larval habitats with Bacillus sphaericus.…”

“…Longitudinal studies conducted in this area during the past decade have characterised the anopheline larval habitats (Moreno et al 2000), species diversity (Moreno et al 2002, Moreno & Rubio-Palis 2003, anopheline bionomics in relation to malaria transmission (Moreno et al 2007) and vector incrimination (Moreno et al 2005). Moreno et al (2005) found Anopheles (Nyssorhynchus) darlingi Root, Anopheles (Nyssorhynchus) marajoara Galvão & Damasceno and Anopheles (Anopheles) neomaculipalpus Curry that were positive for Plasmodium falciparum (Welch) and Plasmodium vivax (Grassi & Feletti) variants 210 and 247 circumsporozoite (CS) protein.…”