On Mosquitoes

More words than necessary about mosquitoes

I was recently pleased to pick up an English-language issue of the Guardian. I don’t think there is any relation to the UK newspaper as there are a number of differences in style and content – for example the puzzle page includes a join-the-dots and a picture to colour in. Mostly there is news of domestic affairs but there is an international section which included the important story, and large and pixelated picture, of people enjoying the weather at a beach in southern England, which I enviously read from monsoonesque Machame.

The front page story was more immediately relevant to me, reporting on a recent outbreak of Dengue fever in Dar es Salaam, a viral disease (also known as breakbone fever due to characteristic joint and muscle pain) that is mostly found around the equator and is spread by mosquitoes. The species of mosquito that carries the bug is endemic to Tanzania but the virus itself is not, so the outbreak is a fairly new problem for Tanzanians. As of 20^th May there were 400 confirmed cases of the disease in Dar, and 3 deaths.

The majority of infections are mild or asymptomatic, so good odds for the individual but this also means that the disease can spread swiftly and silently from unwitting carriers. The outbreak has caused an uneasy atmosphere about the hospital as there have now been a number of cases reported nearby. Most of the staff have no experience with the virus and so it became the topic of a heated discussion in church on Wednesday – bizarrely I was asked to stand up and report what I knew about the disease to the assembly as if I was some wise foreign visiting professor, rather than a bewildered foreign visiting hindrance. I managed to articulate the basics that I could remember – that the disease usually causes a rash and high fever but in severe cases can cause haemorrhage, shock, and (rarely) death, and that since there is no vaccine or effective anti-viral drug treatment is supportive.

I learnt afterwards that my exceedingly English public speaking accent is nearly incomprehensible for the local people so my platitudes largely went unheard. I did manage to communicate that dengue is not present in England and I that I didn’t know how it is diagnosed in English laboratories. I get the feeling that I did nothing to assuage the worry of the congregation, and actually I merely scaremongered with a notion of an unknown and sometimes fatal disease with neither a simple diagnostic test nor a definitive treatment.  Dengue sharply contrasts with that other, commoner, mosquito-borne scourge that the hospital is so familiar and comfortable with - patients with almost any presentation are often labelled “clinical malaria” and started on anti-malarials. The doctors like diagnosing malaria because they know how to treat it, and the placebo effect is pretty effective too.

So now, in addition to trypanosomiasis from abundant tsetse flies, I have another reason to keep my blood safe from vicious hungry little arthropods; a task that I have never been able to accomplish with any degree of success. I’m a fraction too big for my bunk in the guest house so either my feet stick out of the end of mosquito net or I inadvertently collapse it onto myself with my somnolent kicking. This isn’t the main problem (the net is full of holes anyway), as in the daytime I rarely remember to use sufficient insect repellent and I am apparently oblivious to the presence of mosquitoes even when they are enjoying feeding on me,  I am usually surprised later to discover a large red itchy swelling.  So the combination of my ineptitude and my delicious delicious blood means that I am getting quite a number of bites and good size dose of mosquito saliva; right now I have a fairly large swelling on my left tricep (making me look uncommonly muscular, though in an asymmetrical unnatural and inflamed manner) and a troublesome lesion on my left little finger – it hurts a bit to bend or use so the alert reader will notice that due to the discomfort of typing I have used the letter Q significantly less frekwently than usual. Fittingly, as I write these last words I have been bitten, again.

Aedes aegypti - as stolen from the internet

Cool ways to prevent dengue – memories from an essay I wrote during my undergrad
No vaccine yet, so we need to control the disease vector:  for dengue these are Aedes aegypti mosquitoes.

Obvious/don’t get bit:

-          Wear long sleeves and long trousers (an advantage of wearing a burkha.) Bonus: no sunburn.

-          Use insect repellent (unpleasant, expensive, health risks)

-          Sleep under an insecticide treated net (But mosquitoes still bite in the day)

Common/low tech:

-          Spray urban areas with insecticide, fairly ineffective but makes a government look proactive.

-          Tanzania are fumigating buses to avoid transmission of mosquitoes around the country – but asymptomatic humans can easily travel and spread the disease

-          Drain pools that are mosquito habitat – often impractical

-          Add larvacide to mosquito habitat – might involve poisoning water supplies

Biological control:

-          Introduce fishes that eat mosquito larvae – disruption of ecosystem

-          Introduce bacteria that infect mosquitoes, reducing their lifespan and viral transmissibility

Add more mosquitoes/cool high tech science fiction stuff:

-          Release sterilised male mosquitoes, causing a population crash

-          Release self-destructing mosquitoes, males which carry a lethal gene, causing a population crash

-          Release female-incapacitating male mosquitoes, modified genes when expressed in female offspring cause development without wings, and so these mosquitoes rubbish at living or transmitting disease

-          Add genetically modified virus-resistant mosquitoes to outcompete and replace the existing harmful population