Mosquiiiiiiiiiiiiiiiiiiiiito’s Moving Malaria!

I think you will struggle to find someone in NZ who doesn’t shudder when they are curled up in bed at night and they hear that high pitched whining around their head. Mosquiiiiiiiiiiiiiiiiito! You know it is going to wait until you are sound asleep and then feast on your nutrient rich blood, and there is nothing you can do about it!

Although I have always been one of those people, I have always been thankful that as a New Zealander, I do not have to worry about being infected by such life threatening diseases as malaria. Having been to malaria infested countries, seen the damage and worry it causes people, I was naturally interested in how these wee critters work and cause so much damage. The article I have chosen to help me in my quest for knowledge is “Mosquito ecology and control of malaria” by H. Charles and J. Godfray.

A huge amount of the world’s most infectious diseases are transmitted by insects, and in particular mosquitos (Family: Culicidae). Although this article focuses on malaria, as does this blog post, mosquito are also vectors for other fatal and well known human pathogens such as Yellow fever, the West Nile virus, the Rift Valley fever,  the Ross River fever, as well as numerous animal diseases. The most widely known and damaging of these is malaria, which is vectored by the genus Anopheles and infects approximately 200 million people per year and causes between 06-1.2 million deaths per year.

Although there are 40 known genus of mosquito, the only one which transmits malaria is the Anopheles, and out of the 500 species of Anopheles, only 70 are known to transmit malaria competently between humans.  The basic mosquito biology is similar between all mosquito genus and species. Females merge from their larval life stage and mate immediately. They then need a blood meal in order for their eggs to mature, however they can obtain energy from nectar. The Anopheles genus of mosquito feed from several different host species, however the 70 species that do transmit competently between humans show a preference towards feeding on humans, hence the reason they are successful transmitters. Some species even seem to have evolved to hunt and feed around buildings or other likely locations where they will find people.

http://www.myhealthnewsdaily.com/2998-best-insect-repellents.html

After having a feed on human blood, the mosquitos are heavy and struggle to fly, so rest to aid with digestion. This is why you often see mosquitos resting on the walls of houses. Once digested and the eggs have matured, the mosquito flies to its aquatic breeding site where it will oviposit its eggs.

The actual malaria disease is caused by the genus Plasmodium which is a single celled eukaryote in the phylum of Apicomplexa. The species which is most prolific in causing the damage to humans is Plasmodium falciparum however Plasmodium vivax is also capable of such illness. The pathogen enters into the human body when the mosquito pierces into the bloodstream to feed. It then colonises the liver and divides, ruptures the cell it is in and enters the blood stream where it infects red blood cells. Once it is in a red blood cell, it then begins to multiply again and can infect other red blood cells. These red blood cells spread around the body and cause the disease symptoms.

Some of the Plasmodium which has entered the red blood cells takes on a different developmental approach. It undergoes meiosis and male and female gametes are produced, which can then be taken up by mosquitos when they feed on the blood of the infected victim. These male and female gametes can then ‘mate’ in the mosquitos gut, making that new mosquito a vector for malaria.

The malaria pathogen is well protected from the host’s immune system as it spends the majority of its lifetime inside the host’s cells. Malaria can be removed by the spleen of humans, so it has developed a defence against this. It produces proteins which bind the infected red blood cells to capillary walls, which is a major cause of the disease symptoms of malaria. Humans can however produce some immunity to malaria and adults in highly infected regions generally have some immunity to it.

http://novatravelclinic.com/wp-content/uploads/2010/12/malaria-map.png

After looking into how malaria occurs and the complex adaptations and relationships that surround it, it is hard to see how an effective vaccine will be developed. The relationship between the mosquito, the malaria pathogen and the human immune system is highly complex and the pathogen well evolved. With advances in technology and knowledge, and an increase in funding from uninfected western countries, hopefully we will see a vaccine in our lifetimes.

So next time you hear that high pitched whining around your head, be thankful that you don’t have to worry about a tiny protist infecting you, and let the wee mosquito enjoy its meal in peace!

LAND where you want to be,

Nick