The column below was contributed by by Rasha Azrag & Guy Reeves.
I did not want to write anecdotes and in a search of scientific evidence from the field, I went to the office of my head department asking for our field car. Unfortunately it was being used by one of my colleagues. However, I managed to arrange to use the Botony department car. Next day I went on a field trip accompanied by two of my MSc. students to explore a repeated field observation: Anopheline breeding in dirty habitats.
Previously I had searched the internet looking for published papers about malaria vectors breeding in polluted habitats. I only found four. Two publications were from Ghana, West Africa (1985 and 2011) and both found an increase in the number of An. gambiae s.s. in organically polluted anthropogenic habitats. These habitats had developed as a result of urbanization in Accra. The third piublication was from urban Lagos, south western Nigeria (2007) and reports the breeding of An. gambiae s.s in polluted water bodies and the fourth publication was from Trincomalee district in Sri Lanka (2013) where An. culicifacies was found breeding in polluted water bodies.
On the field day, I woke up early in the morning anticipating what we would find during the day. After searching a couple of expected dirty habitats with high potentiality for propagating Anopheline larvae we reached an uncovered canal for drainage of rain water. It was clear that the canal was dirty with an unfavorable smell. Human practices from neighbouring houses makes this canal a foci for accumulation of different kinds of dirty water types such as waste water from traditional bathrooms and kitchens. Additionally kitchen garbage and plastic bags were covering the surface of canal. After careful examination of the water I found some anopheline mosquitoes. Later in the laboratory we found that these were An. arabiensis mosquitoes, the dominant malaria vector in northern Sudan (see video ).
When I returned from the field I questioned the extent of pollution tolerance in terms of the physical and chemical properties of the water. But there was no doubt that this was a dirty larval habitat. This is not an evidence of the tolerance of polluted habitats but it is an unexpected anopheline habitat to our field workers in Sudan. This makes me think: are we observing the first steps towards the tolerance reported in sibling mosquito species in neighboring African countries? Adaptation to new habitats can happen as a gradual shift in response to different water parameters.
Personally I consider that characterization of larval habitats of An. arabiensis in Sudan needs further verification. However, for all other malaria endemic areas with reported tolerance to polluted habitats many questions are in my mind; what are the reasons of such tolerance? Is it associated with specific genotypes? Its impact on malaria or other vector borne disease? And the most important question: what is the best control method for such polluted larval habitats?
Rasha is a medical entomologist working in the department of Zoology/ University of Khartoum, Sudan and used to teach basic entomology courses to undergraduate students and molecular entomology to master students in the Medical Entomology and Vector Control program. She has experience from working in different vector control programmes, from basic classic control methods to the use of genetic methods.
Guy is a research scientist at the Max Planck Institute for Evolutionary Biology in Plön, Germany. Part of his research involves the exploration of genetic methods to control vectored diseases.
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