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Do mosquitoes experience the same suffering caused by the malaria parasite?

Do mosquitoes experience the same suffering caused by the malaria parasite? & if not, why
Dave from Cumbria (Age 35-44)

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2 Responses

  1. No they don’t experience the same suffering. This is because 1) the malarial parasite (called a plasmodium) infects mosquitoes during a different stage of their life cycle than when they infect humans 2) mosquitoes obviously have a very different physiology to humans, so you can see that the way the plasmodium interacts with mozzies is going to be very different than the way it interacts with humans.

    But the disease spreading, biting, little pests do suffer from the infection (and I for one, feel no sympathy for them). Like any parasitic infection at the very least they deny the host food and cause some tissue damage. The amount of research on malaria in humans is pitifull when weighted up against its global effects (research money tends to be directed towards diseases that affect affluent westerners, tourism is changing this though) so its effects on mosquitoes is even less well known. But research has shown that the infection does cause an increase in mortality for the mosquitoes.

    However, we suffer much more than they do. This is typical for parasites that we get from animal vectors. The reason for this is that we haven’t been around as long as the mosquitoes have. Plasmodia have been infecting them for millions of years so the mosquitoes have evolved defense mechanisms against the plasmodium and the plasmodium have evolved to minimise the damage they do the insects that they depend on. If we survive for millions of years we may reach an understanding with the plasmodium as well, if we don’t wipe them out first (or vice versa).

    Interesting additional fact: only female mosquitoes drink blood, which they do to acquire protein they need before laying eggs. The males (and females the rest of the time) drink nectar and plant sap. So in this case the female of the species truly is more deadly than the male, being one of humanity’s greatest enemies.

  2. Dear Dave,

    That is an excellent question and one that has been looked into in some detail. The short is maybe – the story seems to become ever more complicated!

    When humans (and reptiles and birds and other mammals) are infected with malaria they become anaemic because the parasites live damage so many of our red blood cells. In some cases, malaria parasites become lodged in the capillaries of the brain and this can be fatal. However, when malaria parasites infect mosquitoes the live in different parts of the body but they do cause some damage.

    When a female mosquito bites someone with malaria, she takes up some of the person’s blood, including some parasites, and the blood meal is stored in her gut whist she digests it. As soon as malaria parasites find themselves in a mosquito they mate with each and the resulting offspring are able to infect their mosquito. To do this, malaria parasites travel through the wall of their mosquito’s midgut and attach to the outer wall, where they form a cyst. All mosquito cells that parasites pass through, on their way out of the gut, are destroyed – which is not ideal for the mosquito. Then, once parasites have formed their cysts they spend a couple of weeks replicating so each cyst ends up as a bag of a thousands of malaria parasites. These cysts eventually rupture and release the parasites, which then have to travel to the salivary glands of their mosquito. Once they get to the salivary glands, the parasites can be injected into the next person their mosquito bites.

    Parasites require energy and other resources to travel around their mosquito and replicate, which they take from their mosquitoes. Again, this is not idea for their mosquitoes as they wish to use their resources to make lots of eggs. However, parasites do have to strike a balance – if they cause a lot of damage to their mosquitoes there is a risk that their mosquito will die before the parasites have made it to the salivary glands and been transmitted to new people. So parasites have a vested interest in keeping their mosquito alive and well enough to bite people until the parasites have been transmitted. We think that parasites are able to manipulate their mosquitoes to do various things that are not necessarily in the mosquitoes best interests. For example, biting people to blood feed is risky (as mosquitoes are vulnerable to being killed by the person they are biting) so parasite seem to direct the mosquitoes to other sources of food until they are ready to be transmitted from the salivary glands. Also, every organism has to trade-off the resources it has available to maintaining its body and reproducing (much the same as we have to decide how much of our salaries to save and spend). Female mosquitoes should invest a large portion of their resources into producing eggs but this isn’t in the best interests of their malaria parasites. Malaria parasites need to use their mosquitoes resources, but also keep their mosquito alive. A sensible strategy would be to free up the resources that their mosquito was investing in reproduction. This is indeed what seems to be going on and by doing this, parasites have the resources they need and their mosquitoes can maintain themselves, but miss out on laying as many eggs as uninfected mosquitoes. It seems as if this mechanism id due to the parasites themselves, not simply the mosquitoes response to having a malaria infection.

    Finally, having their salivary glands full of malaria parasites makes it harder for mosquitoes to take blood meals. This means that mosquitoes must feed more often, which could mean biting more people. This is ideal to transmit the parasites to as many new hosts as possible. It is not yet clear whether this is a convenient by-product of parasite size / number / arrangement in the salivary glands or a parasite manipulation.

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