Why are Mosquitoes Found in Some Parts of Nairobi?

Machakos People's Park circa 2014. Let me assure you, that's neither a Marina nor a Jetty. Such stagnant water bodies around Nairobi form breeding grounds for mosquitoes if there are no control measures. 

Ever wondered why some places in Nairobi are mosquito prone, while others are not?

There's popular folk-lore that Nairobi was established a settlement because it's altitude, or height above sea level, is above that preferred by mosquitoes. But this proposition quickly runs into headwinds as much of Eastlands, including JKIA, the country's main airport (long pun coming) are frequented by mosquitoes. 

So, I got an expert from the International Centre of Insect Physiology and Ecology (ICIPE) to clear some air on this buzzy issue. 

Here is what Professor Clifford Mutero of ICIPE had to say:

"Nairobi has always had mosquitoes. No part of the city is too high for mosquitoes to breed and survive. However, it is important to note that there are many different species of mosquitoes, and some of them are not present or common in Nairobi.

The presence of stagnant water, which provides mosquitoes with suitable breeding habitat, is what is likely to determine whether a section of the city has mosquito infestation or not. Another factor would be mosquito control operations e.g. spraying with insecticides. However, mosquito control is not carried out on a routine or coordinated fashion in Nairobi and, therefore, has no bearing on whether a certain part of the city has mosquitoes or not.

Suitable mosquito breeding habitats may be in the form of:

• surface water pools and puddles due recent rain;
• puddles of water at building and road construction sites;
• collections of dirty water in blocked drains;
• poorly covered septic tanks;
• poorly covered water storage tanks;
• small dams/ reservoirs;
• Foot prints and hoof prints at the edges of slow moving streams or dams;
• Small water collections in discarded tyres, pots, plastic and metal containers.

Fortunately, the majority of mosquitoes found in Nairobi belong to species which do not transmit malaria. They are mainly mosquitoes that cause biting/noise nuisance at night (mainly Culex mosquitoes) or itchy bites during the day (mainly Aedes mosquitoes). Anopheles mosquitoes which transmit malaria are presently not common in Nairobi."

That clears the air on why mosquitoes are common in Nairobi, but Malaria is not endemic. 

As to why some parts of Nairobi have more mosquitoes than others - the response on breeding habitats gives some clarification. Eastlands may be a mosquito favourite because it is flater, hence more water pools, and also because of, surprise, open water tanks as a response to water shortage in the city. 

The Western bits of the city are sloppy hence have better drainage of stagnant water. This is stretching it, but the volcanic soil in the Western bits of Nairobi are better daining than the black cotton of Eastlands which is swampy. 

Lastly, if you live in an area that relies on boreholes for water supply, you may have fewer mosquitoes due to a closed water supply since tanks don't need to be outside or open. 

Bizarre, right?