Vectors

A vector is something that transmits a pathogen but isn’t itself a pathogen. The classic example of a vector is the mosquito. Later we will look at vectors as things used to transmit genetic information from one organism to another in genetic engineering but when discussing disease a vector transmits a pathogen.

A mosquito itself is merely annoying. It buzzes in your ear just when you are on the point of sleep waking you and maybe, if you don’t notice, lands on you and draws some blood. Or rather, she does, leaving a small, itchy bump. It is the female mosquito that feeds on humans and other mammals as she needs the nutrients from blood to develop her eggs. Males and non-pregnant females are actually vegetarians! Generally, a mosquito is nothing other than irritating. Unless of course she happens to be a vector for a disease such as Malaria, or Ross River Fever, or Dengue Fever or Yellow Fever, or Japanese Encephalitis or... Mosquitoes are vectors for many, many diseases. Malaria is spread by the mosquito vector but is actually the protozoan, Plasmodium, that causes the disease. I’m not going to discuss the life cycle of plasmodium or what it does to the human body, this can be found in most textbooks. However, I will mention that according to WHO in 2008 there was almost a quarter of a billion (247 million) cases of malaria globally resulting in approximately a million deaths. Most of these deaths were in African children.

One of the most important ways to stop the spread of diseases such as malaria isn’t to target the plasmodium, instead it is to control the mosquito. Remove the vector and the disease’s spread is contained. This is the main focus of global anti-malarial programmes.

The mosquito is not the only vector though. There is a huge catalogue of animal vectors that include insect, mollusc and vertebrate. Bubonic plague is spread by fleas, bats are vectors for the Hendra virus, dogs, monkeys and other mammals can spread rabies but the example I would like to finish with is a case that occurred in Sydney last year (2010). I don’t know what the inspiration was, maybe alcohol, Jack Ass movies or a combination of both, but boys being boys one mate dared another to eat a slug. Unfortunately for the slug-eater, this slug was a vector of a rat lungworm, a nematode that causes a rare type of meningitis. It left him fighting for his life with doctors hoping his immune system would fight it off.
Malaria Life Cycle 1
Malaria Life Cycle 2