26 gennaio 2015

How we get infected with malaria: the plasmodium and the anopheles mosquito

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Plasmodium is a microorganism which causes malaria. Unlike other microorganisms (for example the bacteria in our gut) plasmodia don't seek permanent homes or stable jobs: they like vagrancy. That's why a plasmodium's life is so eventful; but also cyclically repetitive.

The story of malaria starts with a mosquito, a female anopheles mosquito. While male anopheles flutter insect-like from flower to flower in search of nectar, female ones go for warm human blood.
Just after biting, before sucking in the blood, they inject a spit of their saliva, which anaesthetizes the skin and keeps it from getting inflamed and painful. This helps mosquitoes stay unnoticed, and give them time enough to finish their meal and leave, without being smashed in a bloody pulp.
malaria anopheles mosquito cartoon comic
If a mosquito is infected from previously biting a person with malaria, she will inject with her saliva a number of plasmodia. From blood, they move to the liver, where they enjoy a period of acclimatization and training. At the end of this phase, plasmodia get back to the blood transformed in tiny, efficient, aggressive guerrilla fighters.

A few seconds (less than 2 minutes) after entering blood flow, each plasmodium has already identified and hooked his victim, chosen among the immense herds of stolid red blood cells populating the blood. Once a contact has been established, the plasmodium enters the cell, takes possession of it and literally starts eating it.

48 hours later, plasmodia have reproduced and are ready to leave red blood cells to get back to blood. Instead of coming out as they had entered, somewhat stealthily, plasmodia stage a most spectacular exit, causing the simultaneous breakup of all infected red blood cells.

Released plasmodia quickly disappear inside their next victims, while the abrupt materialization of large amounts of cellular debris irritates the immune system and activates it, leading to fever and flu-like symptoms. Debris are cleared quickly, and the fever is usually of short duration.
The invasion, reproduction and disruption cycle repeats with remarkable regularity, bringing about periodic outbreaks of fever, the most characteristic manifestations of malaria.

Infected red blood cells aren't definitely something you would want to show to your children. The poor things are stiff, swollen and energy-deprived. Ma, aderendo alle pareti dei vasi sanguigni, sfuggono al controllo del sistema immunitario e permettono al plasmodio di riprodursi con tranquillità.

Running normally in blood circulation, they would end up being caught in the spleen, a labyrinth of narrow alleys full of check-points, swarming with immune cells raging because of their inability to cope with the infection.
In the spleen of a malaria infected person, red blood cells are thoroughly searched, and killed upon the slightest suspicion: many cell never make it out of the spleen, but most of them are not infected. In fact, the infected ones are so exhausted that they lay down wherever they can, sticking to the walls of some distant blood vessel. By doing so, they avoid the spleen, escape control by the immune system, and allow plasmodia to reproduce, and to disseminate the infection.

The slaughter of (uninfected) red blood cells carried out by the immune system leads to severe anemia, a common complication of the disease, and a leading cause of death in people affected by malaria.

(you may want to read the second part of this article, about how quinine, tonic water and genetic mutations protect you from malaria)

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