The dry-season malaria paradox, a bar to eradication, is solved | Hacker News Reader

The dry-season malaria paradox, a bar to eradication, is solved

economist.com

139 pointssohkamyung72 comments

TL; DR: they found that mosquitoes survived through the dry-season (previous theory was that they were migrating from a humid region). The researchers are making the supposition that the mosquitoes achieved this by entering "aestivation". Would be very interested to see what an aestivating mosquito would look like.

Edit: more reading about this.

The paper in question: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7449266/

A paper from 2010 by the same authors already demonstrating mosquito persistance through another marking method : https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2929058/

The 2010 paper goes into more details about evidence and counter-evidence for the aestivation theory.

>Would be very interested to see what an aestivating mosquito would look like.

Not very exciting, I would imagine. They probably just lay there. Jokes aside, this is a super interesting finding if that turns out to be what's going on.

In a related question, I've always wondered how Mosquitoes survive winters. Where I live the winters are very cold, with entire months deep in the negatives. All water freezes.

Would entering a state of torpor be a sufficient explanation for surviving winter? Would they need some other mechanism for surviving frost?

Doesn’t that question apply to pretty much all insects? I thought the answer is they are buried deep or preserved in small amounts of water that doesn’t freeze (water never freezes all the way through).

Certain amphibians (i.e. tree frogs) have a "natural anti-freeze" compound in their blood. This allows them to hibernate through 20°F freezes - without any cell walls rupturing due to ice spikes - and just thaw back out in the spring. Perhaps parent comment was wondering if a special subspecies of mosquito or mutation was capable of the same?

Who says they survive cold winter climates? They die out in colder climates and migrate back from temperate climates. Mosquitos may not be killed by frost, but frost is a layered phenomenon, a hard freeze definitely kills them.

I’m pretty sure that the mosquitos that show up almost instantly when things thaw in Alaska and Canada aren’t migrating from warmer climates. That would be pretty impressive, but no way do they move that fast.

Not impossible - things in Alaska and Canada thaw as the last, so the mosquitos could be already on their way long before the thawing there began.

However what I think is happening is that their eggs are what survives of them, and they hatch out quickly.

They can be very easy to miss as most of them piggyback on the great swarms of flying spiders, centipedes, and trees migrating north each year to repopulate the barren wastelands after the great freeze has killed all but the warm-blooded lifeforms.

I have to imagine a non-trivial number of them survive in areas with human settlements. Maybe they start getting more active when it warms up.

Probably not - they’re far worse where there aren’t humans for hundreds of miles.

Mosquitos in the tundra are insane [https://www.nationalgeographic.com/animals/article/150915-Ar...]

Interesting. I had heard caribou herds basically choose migration routes to avoid them so that makes sense.

> Who says they survive cold winter climates?

Anyone who put even a minute of effort into looking up the well-researched and publicly available information on the topic rather than defaulting to ignorance could have told you this.

Insects have numerous different strategies to make it through cold winters, either as eggs, larvae, or adults. Some can tolerate partial freezing, some lower the freezing temperature of their bodies in order not to freeze at subzero temperatures. These are combined with finding shelter inside tree stumps or bark, under leaves or rocks, or even underwater, granting them a layer of insulation and protection from the wind and the worst cold.

Here's a good starting point for those interested https://en.wikipedia.org/wiki/Insect_winter_ecology#Cold_tol...

I would expect the mosquitoes to die but their eggs to survive until warm enough

The latest Frozen Planet series shows a queen bee surviving winter in Siberian forest by digging down into earth and awakening in the spring thaw so other insects can do something like this or use eggs to do it.

A very common adaptation among insects is producing large amounts of polyhydroxy alcohols like glycerol in the hemolymph that acts as anti-freeze or cryoprotectant depending on the species.

I think eggs can survive below zero temperature, but not longer than 6 months.

In regions that are too cold, mosquitoes will just not thrive.

Increase the average temperature of one degrees and a lot of regions will welcome mosquitoes.

This can't be true. I lived on the Canadian Prairies, where it was normally below freezing for 6 months every single year, and below minus 40 for several weeks at a time, and yet there were tons of mosquitoes every summer.

Below freezing air, but it's not freezing just few centimeters underground or underwater.

You would have to go far more than a few cm underwater. We use ice bridges in the winter. A few cm of ice is not enough to support a giant truck.

frost line is like 6 feet underground in these places. There is permafrost in mosquito land!

this gives enough time for the eggs to hibernate and hatch.

for the eggs to die, there must be a lukewarm summer, and a long winter.

beyond that, it's also about averages.

I remember having snow on the ground every October, and it never leaving before April. I also remember having snow on the ground one year on my first day of school in August. They get hot summers though. Contrast that with the coast, when it's lukewarm summers, and barely a day with snow each year (lots of rain) but there are barely any mosquitoes.

> In regions that are too cold, mosquitoes will just not thrive.

Anyone who has visited canada's northern territories or alaska can assure you that mosquitos thrive in the far north.

Yeah there way fewer mosquitoes in Van than at the arctic circle.

It’s like the cold preserves them like a deep freeze.

And you can’t get much more standing water than in Vancouver.

Not only do they survive, it seems like the worst mosquitoes I experience are in areas with spring snowmelt in progress, even when there is no obvious standing water anywhere nearby.

Lots of bugs survive dry periods by basically becoming inactive. Ticks do it too

It's a bit odd that 'The Economist' doesn't mention that the persisitence of malaria in sub-Saharan Africa is fundamentally an economic problem. Malaria used to plague the American South and was eradicated through coordinated efforts led by the federal government, so we already know how to do it (DDT has been replaced by non-persistent insecticides, water drainage and cleanup of standing water reservoirs (i.e. old tires etc.) that form breeding sites, etc.):

https://www.cdc.gov/malaria/about/history/index.html

Compare that to say, Niger:

> "Malaria remains a major public health issue in Niger and is endemic throughout the country. Malaria accounts for 28 percent of all illnesses and 50 percent of all recorded deaths. Children under five years of age account for about 62 percent of the burden of malaria."

https://www.pmi.gov/where-we-work/niger/

Notably, France has pulled billions of dollars worth of uranium out of its mines in Niger, while doing almost nothing to improve the economy of the country (which would provide the resources to run a decent malaria eradication campaign), so it's really just another colonial exploitation disaster tale.

The price France is paying for Niger's uranium has been higher that world market price for a long time. The main reason France has an interest in it is to be independent from Russia and Kazakhstan production.

Niger is a desert with catastrophic demographics.

I think if we compare the history of the relationship between America and Saudi Arabia (also a desert with catastropic demographics, but a rather different economic outcome) vs. that between France and its African colonies (or Britain and its India colony), we can see that European colonialism was actually a bit worse in outcome for its partners than what's known as American imperialism (which still has major problems, but not as bad as what Europe got up to).

Your comparison is flawed and oversimplistic. You might as well consider the US as a former British colony and consider that British colonialism faired quite well.

Surely you realize that this is not their only article on Malaria?

https://www.economist.com/search?q=malaria

> It's a bit odd that 'The Economist' doesn't mention that the persisitence of malaria in sub-Saharan Africa is fundamentally an economic problem.

Is it really though? I'm always curious to understand how malaria eradication in the US was so successful, primarily because, at least now anyways, we have a shit ton of mosquitos in the South. Why doesn't malaria rise up in the US again? Is the geography and climate of Africa just much more conducive to malaria?

The CDC has a good page about the eradication of malaria in the US, https://www.cdc.gov/malaria/about/history/elimination_us.htm..., and I understand the measures that were taken. But again, many days if I go out without slathering myself in bug spray in the summer I'll be covered with mosquito bites, so I don't understand why malaria isn't more common. Are our mosquito species just different?

Probably the fact that in the US any malaria patient would be quickly diagnosed, isolated and treated plays a big role? It makes it a lot less likely that they would transmit it to the next mosquito.

Also in poor countries most people also get bitten in their house at night, with not screend doors or quality windows. I would assume this is pretty rare in well developed countries in comparison.

This is probably the most likely case. Malaria is a purely human disease with no animal reservoirs other than mosquitos as a vector. No malaria in the humans, no malaria in the mosquitos.

Link on Internet Archive [1]

[1] https://web.archive.org/web/20221017015321/https://www.econo...

One thing the article doesn't clarify is how knowledge of these dry season hiding places could help with eradication, especially given that they go dormant and do not breed during this period. Apparently the researchers already know where the wet season hiding places are, so what makes the dry season sites more appealing targets?

There’s likely a lot less of them and they’re not moving around, making it easier to eradicate.

Have a team of people hit the 50 known hiding spots in your “county/district/diocese sized equivalent” every season is an achievable plan.

Knowing that they exist, and what they are, is surely a step in the direction of intervention.

The article says that knowing the hiding places could inform efforts to kill them in the dry season. I assume that it would be easier with more time to do that in the dry season, as soon as they start breeding again you're batteling an exponential increase. Maybe if one would know what kind of place they look for to spend the dry season, traps could be built?

It also says that knowing that they stay around is good evidence that spraying insecticide at the start of the wet season is a good strategy.

https://archive.ph/m850O

Only The Economist could write "The mosquitoes that transmit malaria in Africa have short and merry lives"

Plenty of English writers could do the same. I suspect that it is The Economist's Englishness rather than anything specific to the Economist. We anthropomorphize much more than people from elsewhere; we give names to our cars, we apologize to furniture when we bump into it. Saying that a mosquito had a short and merry life is not something that I would have reacted to at all, or to the use of a diminutive, mozzies, in the next paragraph.

Just to add a little to the English-language chat - "mozzies" feels more Australian English than British English to me. So it could even be that this was written by an Australian contributor. That or this is another Australianism which has entered the British lexicon (see also: "uni")

It's marked here [0] as "also common in other English dialects". I heard it plenty in South Africa.

[0] https://en.wikipedia.org/wiki/Diminutives_in_Australian_Engl...

Ahhhh I didn't even think to look for a list. That's actually amazing. And it gives me an excuse to drop a link to a song called "Smoko" (Smoko, a smoking break while at work. Since smoking has been banned in many workplaces, a smoko has come to mean any rest break at work) https://www.youtube.com/watch?v=j58V2vC9EPc

TIL from your list: "selfie" originated in Australia.

Mozzies (and mozs [sp?], pronounced "moz-is") is common in UK too, IME.

Never heard of it as Australian influenced. We used to call an unspecified wasp-or-bee a wobby/wo-bee (eg "look out there are a bunch of wobbies about today"). Which I mention for having a similar pattern.

Never really heard it growing up, but we had "midgies" which are similar but distinct

Where I grew up they were always just 'midges', AFAIK, it can vary at a family level too though.

I'm really curious to see where they find them hiding out. And top notch science!

Yes super happy to see this quality work being done in the stuff that kills hundreds of thousands annually and literally contributes to whole regions remaining poor.

I'd expect it can be literally anywhere to not be exposed to the elements, sun and predators, ie cracks in ground, rocks or wood (given they've seen most of the marked survive means its pretty efficient hiding)

I really like this study & feel like it reflects what grammar school instructs that science is supposed to look like. A hypothesis is proposed and tested, where the act of testing is not mere simple direct observation (which in this case, as in many famous historical scientific experiments like Thompson’s, Millikan’s, & Rutherford’s, was inaccessible using more commonly-understood contemporary observational technology), but requires unique, oblique intervention of uncertain efficacy (the application of deuterium for the mosquitoes to incorporate) to bring out the response from the system to be observed.

It would be really cool if scientific investigations could be regularly classified post-facto on this basis. But then a philosophical discussion: If the observation was trivially observable (by eye or by video camera), yet yielded the same finding, would it be any less an advancement of science as it is popularly understood? Would it be any less praiseworthy?

And what if there had not been a hypothesis in the first place? Just a dry (no pun intended) observation (using technology that we understand doesn’t exist in the real-world) & accompanying posted dataset that happened to reflect that mosquito eggs persisted on-site through the dry season. Would such a dataset (again yielding the same findings as the real-world study) be any less ‘scientific’ or praiseworthy?

I imagine there are philosophy-of-science papers on this topic -

The title graphic of Wikipedia’s article on the Scientific Method demonstrates “This diagram represents one variant, and there are many others.”

https://en.m.wikipedia.org/wiki/Scientific_method

Is the topic rigorously treated, e.g. not just whether a given study was observational vs experimental, but whether an experiment’s observational apparatus was novel & unproven vs contemporarily known? If a study employs hitherto novel & unproven apparatus, is it then more worthy of praise (and press articles) than a study of higher impact but that employs more mundane apparatus?

To make matters worse, there's evidence malaria can hide in the spleen.

https://www.nejm.org/doi/10.1056/NEJMc2023884

I'm curious why you think it's worse? P. falciparum infection can be hard to eradicate in general, as the paper states the blood can be an infection reservoir. It's certainly interesting that viable malaria parasites can be harbored in the spleen (where they were originally thought to accumulate, but destroyed in the end) but this discovery doesn't really change the prognosis?

The objective is eradication when it comes to malaria due to the high risk factors of outbreaks and endemicity. The last mile to eradication is hindered by malaria hiding in the spleen. It makes treatment harder, eradication harder. The more hurdles the more people die.

In May, the rains returned, and so did the mosquitoes. And, lo, a fifth of them were full of deuterium. They had, in other words, been aestivating.

The next step is therefore to find out just where the insects were holing up while the rains were gone. If these shelters can be identified, they can be attacked. Alternatively, special efforts might be made to ambush the aestivators as they wake up, by extensive insecticide-spraying campaigns at the beginning of the rainy season. Either or both of these could put a significant dent in local mosquito populations—which would, in turn, make malaria less of a problem.

Killing mozzies to rid us of their pathogens is worse than attacking the pathogens themselves, because: 1) let's not kill these little lives unnecessarily and 2) we risk upsetting the ecosystem that we can neither understand nor repair if we damage it.

Let's have vaccines for malaria, or "cure" mosquitos of malaria. Let's improve doxycycline so it doesn't stain your teeth but is still a good prophylaxis. Let's genetically modify humans (with a virus) so we have innate immunity to malaria, and the various "river fever" diseases that are mozzie-borne.

I just think attacking the pathogens is a much safer bet than attacking their vectors via ecosystem-engineering. Our ecosystems are getting hammered enough, we can't risk further upsetting their delicate balances. It's sort of like saying "Let's eradicate heavy metal poisoning by killing all fish stocks and draining the oceans", a sickening, hard-to-undo ridiculously mistaken strategy.

Unfortunately, Florida already targets mosquito populations with several techniques towards the goal of driving them to vastly reduced numbers.

A gene drive has been deployed in the Keys, as I understand it. I don't know if the objective was extinction or not.

Humans are going to impact their environment, and it's not productive to deny that this is going to happen. Smallpox was driven extinct, and many would like to do the same to dangerous mosquitos. I can't judge the morality, but it will likely happen all the same.

>A gene drive has been deployed in the Keys

The Oxitec mosquitoes aren't gene-drive, but genetically engineered to be sterile.

(This is different from a gene drive, for a true gene drive see https://www.nature.com/articles/s41467-021-24790-6 )

> Killing mozzies to rid us of their pathogens is worse than attacking the pathogens themselves, because: 1) let's not kill these little lives unnecessarily and 2) we risk upsetting the ecosystem that we can neither understand nor repair if we damage it.

1) Mosquitoes carry more than just malaria, and trying to cure them of every pathogen is a crazy game of whack-a-mole. Even disease-free they are a major pest.

2) Research has been performed to determine if mosquitoes are a keystone species and has found that they are not.

We have the tools at our disposal to eliminate the species that has killed more people than all the wars in human history combined. It's mind-boggling to me that anyone would hem and haw about the consequences of this non-keystone species when plenty of other species are driven to extinction every year without any fanfare.

Keystone species...I don't know. But what if they are vital in ways we can't measure right now? Our blindspots. Pest is not enough to go f**ing with it. Mosquitos help humans develop and transfer immunity to each other against many things, I think and I have a really strong sense we shouldn't be wiping them out.

> Keystone species...I don't know. But what if they are vital in ways we can't measure right now? Our blindspots.

What number of deaths are you okay with causing while we delay the eradication of the species to assuage this general bad feeling you have about it?

Many, it seems. But not as many as may be saved by doing something different

My impression is that mosquitoes seem to thrive best in degraded ecosystems where there aren't enough birds and fish and other small insects to snack on them and keep the population low. But even then, they're so small that I don't think they provide enough calories to larger animals. As far as I know the only insects for whom mosquitoes are actually a worthwhile food source are other mosquitoes (the non-annoying ones that drink nectar like to eat the kinds that suck blood). So there may be a consequence in terms of being able to pollinate certain plants. But it's also likely the niche would be filled by other insects, though maybe that wouldn't be any less desirable.

Didn't we see this in Stargate Atlantis?

I’m glad this galaxy ended up with mosquitoes instead of the wraith.

Do we want to eradicate mosquitoes? What happens to the fish, reptiles, and mammals that depend on them as a primary food source? I believe mosquitoes also play a role in some pollination. I get that malaria is bad for humans, but eradicating mosquitoes could be much worse in the long term, right?

So far, no known species is known to be solely dependent on them. Seems like they are able to make up the difference with other bugs.

Considering even today somewhere around 700k people a year die from Mosquito born disease, with many more crippled from lifelong malaria infections, and the total number of deaths is though to be somewhere around a billion through history?

[https://www.who.int/news-room/fact-sheets/detail/vector-born...]

Nuke ‘em

The Asian Tiger Mosquito is the common one you see in most of the US and is an invasive species from Southeast Asia. It’s not as common up North and I think the ones up there aren’t the invasive ones.

> Do we want to eradicate mosquitoes?

Yes; fuck them.

We (intentionally or no, mostly not) cause the extinction of hundreds to thousands of species every year for much more mundane reasons: deforestation is the big one, climate change another. And that buys us arguably nothing but enriching people that benefit from the process of deforestation and climate change--folks that're economically desperate enough to log illegally, and energy barons. These extinctions are mostly tragic, and the net benefit to human societies is likely negative.

Mosquitoes are fucking evil. They kill more humans every year than any other animal. Malaria is only the most well-known disease they spread; see also dengue ("breakbone fever", named for what it feels like), West Nile virus, and more. Those that malaria doesn't kill are frequently left with a low-level chronic infection that makes them less effective as people. Malaria and mosquitoes kill children, disable the working population, and economically cripple entire nations.

As best we can tell, things that eat mosquitoes also eat other things. But I'd vote for nuking the mozzies from orbit even if that weren't the case. They're such an unmitigated cause of human suffering and hardship.

In the 20th century alone, malaria claimed between 150 million and 300 million lives, accounting for 2 to 5 percent of all deaths (Carter and Mendis, 2002). How do you imagine eradicating a mosquito species could be worse? Meanwhile, between 200 and 2,000 extinctions occur every year.

Only a small subset of mosquito species bite humans/carry malaria.

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