There are many things that can make one’s life uncomfortable, miserable or even threatening to their very existence. One of such things are mosquitoes, which ironically are relatively tiny little gnats of which the females bite people to suck blood for development of their eggs that eventually hatch into the next generation. Mosquitoes transmit agents of diseases such as malaria, elephantiasis as well as many viruses and bacteria that cause illness to people. In addition mosquitoes can be a nuisance, making it hard for one to sleep well because of the noise and bites. As a result, we cannot engage fully in our socio-economic activities due to being weak and unwell. It is, therefore, important to keep mosquitoes under control for our good health.
Mosquitoes need water to produce their next generation. To do this, the female mosquitoes lay their eggs in water and two days later, the eggs hatch into larvae which can swim and feed on the contents in the water. Within about seven days, the larvae turn into a non-feeding but swimming form called pupa. The adult winged mosquito emerges from the pupa in two days’ time. Over 90 per cent of the young forms of mosquitoes, that is, eggs, larvae and pupa, do not reach the adult mosquito stage due to a number of reasons, but just 10 per cent result in a multitude of adult mosquitoes we see flying about. A single mosquito can produce 1000 eggs in one week contributing relentlessly to an overwhelmingly high number of adult mosquitoes we have to contend with. In the case of “domestic” mosquitoes of which the breeding sites are relatively limited in number around our homes, it is feasible to deny them the water in which to lay eggs and multiply and therefore keep them under control.
In this article I am going to focus on one type of water collection that is normally found within our household compounds and that favours a particular type of mosquitoes called culex to develop. This is the water rich in decomposing matter found in septic-tank-cesspit system and pit latrines.
The latrines and septic-tank-cesspit system are designed to dispose of human excreta which on decomposing it produces gases that are attractive to the mosquito culex. Let me point out here that the mosquitoes that transmit malaria, anopheles, to humans are not attracted to such gases and therefore cannot be found developing in wet pit latrines and septic-tank-cesspit system in our homes.
Septic tank design usually includes a vent pipe to allow gases from the decomposing matter underneath to escape. Ironically, it is the same vent pipe to which mosquitoes get attracted to enter and lay eggs in the foul water below. When a septic tank is defective with cracks in it, the gases also escape through them, becoming entry points of mosquitoes seeking to lay eggs. To ensure that mosquitoes are denied access to water in the septic-tank-cess pit, the vent pipe should always be screened with a mosquito gauze, that can be replaced once corroded, and, cracks in the septic tank cesspit system should be sealed as soon as they appear.
Just like septic tanks-cesspit system, a pit latrine produces gases from decomposing matter inside, especially, when it contains some water due to either a high water table or water from other uses, thereby attracting mosquitoes to breed inside. In this case, a tight-fitting lid should be used to cover the drop hole when not in use. This will also reduce smells and keep not only the mosquitoes but other flies out of the pit. The slab and its edges should also be sealed properly to ensure that there is no inlet for mosquitoes.
The effect of the mosquito control efforts as explained here can be achieved much more quickly when it involves all the households in a neighbourhood. This is because mosquitoes have an ability to fly up to 2km away from the breeding site, thereby infesting already controlled areas. Planning and holding culex mosquito control activities as Umuganda community work can be such an educative and efficient way of promoting health among the members of the community. It would involve identifying unscreened vent pipes, latrines without tight fitting lids, cracked septic tanks and non-tightly sealed latrine slabs edges. Corrective measures can be collectively agreed upon with timelines for their implementation. The call is to have at our homes and institutions all septic tank vent pipes screened, and pit latrines drop holes covered when not in use. It can be done, only play your part.
The writer is a Professor of Medical Entomology and Parasitology, University of Rwanda.