Abstract
BackgroundIt has been documented that unplanned urbanization leads to the exposure of members of the Anopheles vectors to a range of water pollution in urban settings. Many surveys from African and Asian countries reported the presence of Anopheles larvae in polluted urban habitats. The present study documents an obvious tolerance of the melanic and normal forms of Anopheles arabiensis to urban polluted larval habitats accompanied by resistance to Temephos larvicide.MethodsA cross-sectional survey was carried out to inspect apparently polluted An. arabiensis larval habitats during the hot dry season of 2015. Larval specimens were collected from only apparently polluted habitats after visual inspection from 5 localities in Khartoum State. After morphological and molecular identification of random samples of larvae the magnitude of water pollution was determined using nine abiotic factors. The susceptibility status of An. arabiensis larval forms from normal and polluted habitats to Temephos was tested using the WHO standard diagnostic concentration doses.ResultsMorphological and PCR analysis of anopheline larvae revealed the presence of An. arabiensis, a member of the Anopheles gambiae complex. Seven out of 9 physiochemical parameters showed higher concentrations in polluted larval habitats in comparison to control site. Anopheles arabiensis larvae were found in water bodies characterized by high mean of conductivity (1857.8 ± 443.3 uS/cm), turbidity (189.4 ± 69.1 NTU) and nitrate (19.7 ± 16.7 mg/l). The range of mortality rates of An. arabiensis larvae collected from polluted habitats in comparison to An. arabiensis larvae collected from non-polluted habitats was 6.7–64% (LD50 = 1.682) and 67.6–96% (LD50 = 0.806), respectively.ConclusionsThe present study reveals that minor populations of An. arabiensis larval forms are adapted to breed in polluted urban habitats, which further influenced susceptibility to Temephos, especially for the melanic larval forms. This could have further implications on the biology of the malaria vector and on the transmission and epidemiology of urban malaria in Sudan.
Highlights
It has been documented that unplanned urbanization leads to the exposure of members of the Anopheles vectors to a range of water pollution in urban settings
All samples were identified as An. gambiae complex and all PCR products of the amplification of intergenic spacer region (IGS) of ribosomal DNA of larvae specimens showed the diagnostic fragments of 315 base pairs that identify An. arabiensis
Types of polluted larval habitats Anopheles arabiensis larvae were collected from 17 polluted larval habitats that were disproportionately divided between the 5 localities
Summary
It has been documented that unplanned urbanization leads to the exposure of members of the Anopheles vectors to a range of water pollution in urban settings. In Yaoundé, Cameroon, the presence of An. gambiae in organically polluted sites has been confirmed [3] Other studies such as in Pakistan and Sri Lanka indicated the adaptation of Anopheles gambiae sensu lato (s.l.) and Anopheles culicifacies to organically polluted water habitats [4, 5] and reported that rapid, unplanned urbanization is considered to favour adaptation of anophelines to various xenobiotics and the expansion of their niche to polluted habitats. Anopheles gambiae complex, which includes the major vectors in Africa, has the capacity to exploit different kinds of habitat that are created either directly or indirectly by humans This is evidenced by its wide geographical distribution and its occurrence in a variety of micro- and macro-environmental conditions throughout tropical Africa, and that larvae were found in habitats organically polluted by rotting vegetation, human faeces, or oil [2, 6, 7]
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