Tsetse Flies & Trypanosomes

[Zirojtan]

Hello everyone! This is my first post in like a year and a half or so... I was once a member of this forum, but I wasn't really a frequent poster so it doesn't really matter.


I have a dilemma that I need a little bit of help with. I'm currently working on an alternate history timeline with a point of departure 176,000 years ago, and I'm currently 106,000 years into it in the Weichselian Glaciation. Since my point of departure was so long ago, there have been quite a few butterflies which allow for a number of possibilities, one of which I was hoping would be the end of human sleeping sickness in Africa.


Many other alternate history authors like to just say things like "for whatever reason", or perhaps give other extremely simplistic explanations for the events that shape their timelines. I strive to avoid this, because I view it as cheap writing, although what often ensues after these kinds of "cop outs" is usually very good work, it is very important for me in my own work to offer the most plausible explanation that I can get my hands on. In terms of the extinction of human sleeping sickness in Africa, I've found this to be extremely difficult to explain. For three weeks I've read pretty much anything I could kind on the web about tsetse flies and their relationship with the trypanosomes that cause this sickness in humans, and what I've learned is that this process is far from anything random, but one that has been carefully selected for over millions if not tens of millions of years.


Initially, my idea was to make the trypanosomes attack their invertebrate hosts. The obvious problem that this poses is that it poses no benefit of any kind to the trypanosome, and therefore is difficult to justify beyond writing it off as a random, freak mutation. Furthermore, the way the trypanosomes seem to be specialized to vertebrate blood makes this even more unlikely, as the very composition of our blood and insect blood is completely different.


The next idea was for the trypanosome to mutate to live out its entire life cycle within the blood of the fly. As insects have what is called an "open" circulatory system, this would allow infected blood to easily transmit the trypanosomes to other organs, including the sex organs, making them sexually transmittable. Besides the chemical composition of the fly's blood being an entirely different beast than that of vertebrate blood, there was a problem in justifying why this might be selected for amongst the parasite, as it could potentially kill flies and their offspring that are born with the trypanosomes. Some sort of change in the trypanosome life cycle would be required so as to delay its attack of the fly's blood cells long enough to not harm the fly's reproduction, as well as not harming the young that would be born infected. There of course was also the problem that an insect's blood does not receive enough oxygen to sustain populations of trypanosomes, which is why the parasite only spends a short beginning interval of its life cycle within the digestive system before being crapped out onto the skin of the animal/person that the fly is drawing its next meal from.


The third and final idea was for the trypanosomes to evolve to infect the skin cells of the insect rather than the blood cells, but preventing it from damaging the fly so that this would be selected for rather than against is a problem, and so is the fact that this would certainly require a number of fundamental changes in the trypanosome's life cycle and probably its morphology as well.


At this point in the game, I'm kind of out of ideas. I joined an entomologist forum at www.actias.de, but the trouble is, most of the people on that forum seem to not be proficient in English or any of the other languages that I speak, so there's a communication problem. I got one answer, which said basically that the person didn't really know much about the life cycle or morphology of the parasite in question and couldn't really answer without said knowledge.


There was another entomologist on the Speculative Evolution forums that I messaged with the question, but he never messaged back, so I don't really know what to think.


This development is really crucial for plausibly explaining something that was crucial for what I had planned for the timeline though, which would be human migration to the Americas between 68-62,000 years ago by fishermen on the West African coasts who were swept up in the ocean currents that would take them to the Caribbean Sea. This is important for the timeline for the following reasons:


A. Phenotypes will be very different in the timeline, and distributed very differently. I had wanted the Native Americans of South America to resemble Melanesian phenotypes of New Guinea and the Solomon Islands in the Amazon and Patagonia, while developing a more Australian Aboriginal appearance in the Andes. They would be descended from a phenotype that resembles Fijians in West Africa that would've once been very widely spread, but by the 20th century would be confined to areas like Namibia, South Africa, and Botswana. If I'm forced to go with migration via Beringia like our own timeline, then it is very unlikely that these kinds of dark skinned phenotypes will redevelop in the allotted time, or at all, and since I have planned for a number of North American phenotypes to very closely resemble different European phenotypes (although they will be as genetically distinct from Europeans as Australian Aborigines are from Africans), the closest phenotype I can see evolving in this time would be something like phenotypes present in modern day India.


B. North and South America have already been populated by both neanderthals AND denisovans in this timeline who came over during the Saalian Glacial Period and the Eemian Interglacial, respectively. The smallpox virus is believed to have evolved between 69-65,000 years ago according to my research (which was minimal, addmitedly), which would be a fine justification for the marginalization of neanderthal and denisovan populations after the introduction of anatomically modern humans, who it bring it from its West African home. This would also be beneficial in the long run, as Native Americans would not be as susceptible to it as they were in our timeline, although I realize that I could also plausibly butterfly the virus away if I wanted to, since my point of departure was long before its hypothesized date of evolution...


C. Although I am a firm believer in the Second-Order Predation Hypothesis as applied to the North American Quaternary Extinction (I have been able to find very little reading material on how it might be applied to Eurasian extinctions of the period), and will be applying the reasoning of this hypothesis to this timeline, there are a number of new studies that have indicated that the introduction of tuberculosis may have been an important contributing factor in the extinction of mastodons. From what I have read, mastodons were an important keystone herbivore in creating the more open boreal forests that Bootherium (Harlan's Musk-Ox) specifically was able to thrive in, at least in the Eastern United States populations. As I had hoped to see this animal become a North American domesticate, butterflying tuberculosis out of the North American scene is important for the timeline. The virus, from what I have read, may have originated as early as 60-50,000 years ago, so getting humans to the Americas before this date is important. Although I realize that the moose is also a perfectly viable domesticate for the area as well if need be.


So yeah, that's it in a nutshell. Is there anyone on this forum with enough knowledge of trypanosome parasites, specifically those in the species Trypanosoma brucei that can help me out? I've been at this for about 3 weeks now, and I haven't been able to find a good answer, and I don't want to have to be cheap here.


If anyone can help me solve this problem, it would be great.

[Bedlam]

This is sort of my specialist subject as I did my doctorate studying the feeding behaviour of blood feeding flies specifically Tsetse flies (to start with I spread out into mosquitoes), although I didn't go that much into Trypanosomes

You could look at it from other directions.

How about wiping out tsetse flies, they're an unusual insect species they give birth to live offspring and in very small number, they give birth to one child every few weeks it wouldn't take much of an increase in mortality to wipe them out. After feeding they're very vulnerable as they can't fly well they normally sit in a nearby tree for half an hour or so excreting water. Both sexes only feed on blood as well and their bio chemistry makes a switch to another food source unlikely. Maybe a bird or insect species could prey on them more frequently leading to their numbers crashing which in turn takes the Trypanosomes with them.

Alternatively the vertebrate host become immune to Trypanosomes although that's less likely as Trypanosomes effect a wide range of hosts, you could make the local humans immune due to a chance mutation I suppose.

[Zirojtan]

Aaaahh...


You've made me very happy. I can hear a choir in my head right now...


I am FINALLY talking to someone who knows something about this! You must understand that I had to bask in the moment for a little bit before replying. You must understand, I've been EVERYWHERE I could think of going to ask about this. I even emailed a couple of university professors in the entomology department in WSU up in Seattle to no avail.


I did discuss an immunity with a friend of mine who is good with chemistry, but he said that that would be difficult to come by as the trypanosomes are very savvy at mutating before the human/other vertebrate immune system can take care of the problem. In all truth, I could simply justify it with a simple "people who were never born in our timeline are born in this one", but I kinda felt like that could be seen as cheap, so I wanted to explore other options before falling back on this.


Wipe the flies out by other means you say? I do realize that they are extremely specialized, and the specialization here goes further than just tsetse in general, as I'm sure your well aware. The problem I see with that is that the trypanosome species that causes human sleeping sickness, Trypanosoma brucei (and its subspecies gambiense and rhodesiense) can be found in at least 6 different varieties of the fly from what I've read (morsitans, palpalis, fuscipes, pallidipes, swynnertoni, and tachinoides). Now, at the time in question, Africa's rainforests were severely reduced because of the more arid climate of the Glacial Period, which I'm sure would've limited the range of many varieties and favored the morsitans type, which is known to inhabit drier habitats like savannas. So we have two subspecies of trypanosomes that can occur in in several varieties of tsetse fly. You say have a bird species alter its habits to feed on the flies more often, but the flies that are most important here, the morsitans type, roost when they're tired and vulnerable deep in the underbrush of bushes where most birds wouldn't go. Besides that, why would a predator eat its prey into extinction? To my knowledge this has only been observed in humans.


Is there something else that the flies are vulnerable to? Perhaps some kind of disease that might break out amongst them? Do they even get sick from diseases the same way we do?

[Bedlam]

Its been about 15 years since I really worked on this so I'm probably behind the times. I was looking into the use of pour on insecticides to control sleeping sickness on ranches the idea was you can kill the flies by pouring persistent insecticides over the cattle to remove the hosts and thus the disease. That had been done for a few years but I was looking into what animals in a herd got bitten and why to see of you could do it more efficiently by just dosing a proportion of the herd. Turns out the top 20% largest animals get bitten 80% of the time, calves don't get bittern much at all mostly because they react more when bitten (possibly a defence to prevent infection as they are more vulnerable to Tryps). Some other scientists at the same institute were looking into the effect of the insecticide on dung beetles which luckily turned out to be negligible.

I've got to say sitting in a pit for several hours at midday near the equator recording how cows react to being bitten was not much fun.

Yes typs are quite immune resistant, they don't mutate per say but they change their surface proteins every week or so in much the same way as immune cells produce a wide range of antibodies which makes it hard for the body to fight them off although different species have different levels of resistance to them.

On the predators wiping out prey, well its not like predator's decide not to eat something if its going extinct, they're just less likely to encounter them as the number decrease so certainly locally its possible for a predator to exhaust its food supply and them die back itself. Its not likely by itself to totally exterminate a species but it can reduce its numbers so other factors, disease, environmental conditions, etc can finish them off. As I said Tsetse's slow reproductive rate make them vulnerable to this as a small increase in mortality will start them spiralling down to extinction. Other fly species less so but I think they are less efficient at spreading tryps though.

The flies can catch a disease and die just like anything else although Tsetse aren't very social so they don't transmit from each other very well. I suppose you could have a bacteria or fungus that sort of works like a reverse Tryp is harmless to the vertebrate and just sits on the coat or in the bloodstream until sucked up by a fly which it then kills after enough time to allow itself to be spread to more vertebrates.

Also back to how the tryps effect their invertebrate hosts I do remember that they sometimes partially block their hosts proboscis making feeding more difficult resulting in more frequent feeds and so more infection.

[Zirojtan]

Its been about 15 years since I really worked on this so I'm probably behind the times. I was looking into the use of pour on insecticides to control sleeping sickness on ranches the idea was you can kill the flies by pouring persistent insecticides over the cattle to remove the hosts and thus the disease. That had been done for a few years but I was looking into what animals in a herd got bitten and why to see of you could do it more efficiently by just dosing a proportion of the herd. Turns out the top 20% largest animals get bitten 80% of the time, calves don't get bittern much at all mostly because they react more when bitten (possibly a defence to prevent infection as they are more vulnerable to Tryps). Some other scientists at the same institute were looking into the effect of the insecticide on dung beetles which luckily turned out to be negligible.

Any kind of a pesticide option is out of the question for the timeline because of the fact that we're trying to place the extinction between 69-65,000 years ago. Modern humans at this point in the timeline make up majority populations in Eurasia and the Indian and Sundaland subcontinents, but they are still either completely nomadic, seasonally moving, or totally sedentary hunter-gatherers.

I've got to say sitting in a pit for several hours at midday near the equator recording how cows react to being bitten was not much fun.

Doesn't sound like much fun... lol.

On the predators wiping out prey, well its not like predator's decide not to eat something if its going extinct, they're just less likely to encounter them as the number decrease so certainly locally its possible for a predator to exhaust its food supply and them die back itself. Its not likely by itself to totally exterminate a species but it can reduce its numbers so other factors, disease, environmental conditions, etc can finish them off. As I said Tsetse's slow reproductive rate make them vulnerable to this as a small increase in mortality will start them spiralling down to extinction. Other fly species less so but I think they are less efficient at spreading tryps though.

What kind of a bird might we be talking about here? Because if this were to happen, we're looking for a bird on the savanna to severely reduce the populations of the morsitans type enough for human population to experience a temporary boom along the costs of Southwest Africa that would promote the kind of fishing that would get them swept up in the currents headed for the Caribbean. I can see a bird's sudden preference for tsetse driving the extinction if at least the savanna type around the last glacial maximum when global aridity would've been at an all time high.

The flies can catch a disease and die just like anything else although Tsetse aren't very social so they don't transmit from each other very well. I suppose you could have a bacteria or fungus that sort of works like a reverse Tryp is harmless to the vertebrate and just sits on the coat or in the bloodstream until sucked up by a fly which it then kills after enough time to allow itself to be spread to more vertebrates.

Unfortunately I don't know enough about bacteria or fungi to even know where to begin searching for such a bacterium or fungus. Do you have any suggestions?

Also back to how the tryps effect their invertebrate hosts I do remember that they sometimes partially block their hosts proboscis making feeding more difficult resulting in more frequent feeds and so more infection.

See, this is why I wanted to talk to a person. WHY is that not in ANYTHING that I read? It seems kind of important... I would think that this could be hugely detrimental as the population is decreased.

[Bedlam]

On the predators wiping out prey, well its not like predator's decide not to eat something if its going extinct, they're just less likely to encounter them as the number decrease so certainly locally its possible for a predator to exhaust its food supply and them die back itself. Its not likely by itself to totally exterminate a species but it can reduce its numbers so other factors, disease, environmental conditions, etc can finish them off. As I said Tsetse's slow reproductive rate make them vulnerable to this as a small increase in mortality will start them spiralling down to extinction. Other fly species less so but I think they are less efficient at spreading tryps though.

What kind of a bird might we be talking about here? Because if this were to happen, we're looking for a bird on the savanna to severely reduce the populations of the morsitans type enough for human population to experience a temporary boom along the costs of Southwest Africa that would promote the kind of fishing that would get them swept up in the currents headed for the Caribbean. I can see a bird's sudden preference for tsetse driving the extinction if at least the savanna type around the last glacial maximum when global aridity would've been at an all time high.

Well the tsetse I dealt with were more bush than open savannah but I saw several cases of birds picking off the resting flies, however, I'm not a good enough ornithologist to say what species they were small to mid sized birds would be my best description.

The flies can catch a disease and die just like anything else although Tsetse aren't very social so they don't transmit from each other very well. I suppose you could have a bacteria or fungus that sort of works like a reverse Tryp is harmless to the vertebrate and just sits on the coat or in the bloodstream until sucked up by a fly which it then kills after enough time to allow itself to be spread to more vertebrates.


Unfortunately I don't know enough about bacteria or fungi to even know where to begin searching for such a bacterium or fungus. Do you have any suggestions?

Not really although I don't know if you need to go into that level of depth, no one in universe is going to know what it is just what its effects were / are.

Also back to how the tryps effect their invertebrate hosts I do remember that they sometimes partially block their hosts proboscis making feeding more difficult resulting in more frequent feeds and so more infection.

See, this is why I wanted to talk to a person. WHY is that not in ANYTHING that I read? It seems kind of important... I would think that this could be hugely detrimental as the population is decreased.[/quote]

I can only remember a few references and I think it was mostly hypothetical. I think there was some evidence they part blocked the proboscis but it wasn't clear if it lead to increased feeding or not. It's a shame we didn't look into it at the time as the technique I was using wasn't bad at detecting multiple feeds (we were genetic fingerprinting the blood from the Tsetse guts) and they didn't seem that common but there can be a lot of reasons for that. From what I remember the blocking would effect older flies (they would mostly be the ones spreading the infection anyway) so they would probably have reproduced a few times before their is any effect, but as I said Tsetse are slow reproducers.

[Zirojtan]

Hmmm... how would I explain the development of a human immunity?

[Bedlam]

Hmmm... how would I explain the development of a human immunity?

Why explain at all? Someone is immune or resistant its a survival advantage and its passed on x generations later most of the population is immune, the people don't need to know how it happened.

There are probably some mutations which alter the immune system to allow it to attack less variable parts of the parasite or which make part of the blood toxic to the parasite although they probably have negative consequences or they would spread through populations at risk. In real life its not impossible that their are resistant individuals who have not been identified. Other defences could be behavioural, self treatment via herbs may be possible or just staying out of risky areas, as I said in my studies host reactions drove off a lot of flies.

An interesting behavioural reaction we saw in Ethiopia when looking into Malaria was that high land farmers traditionally slept on raised platforms over their cattle when migrating to the lowlands and didn't tend to get malaria. We found two things, the platforms were higher than most mosquitoes flew and that the local species of mosquito when given the choice bit cattle rather than humans thus the majority of flies would bite the cattle and the few that tried to bite the farmers generally wouldn't fly that high. Of course the locals had tended to stop that behaviour leading to an increase in malaria incidents.

[Jub]

Could the flies perhaps be put on the path to extinction via some sort of weather pattern that not only hurts the flies but als drives their prey away from the area for a while? Say a drought or a long period of colder weather than normal?

[Zirojtan]

Could the flies perhaps be put on the path to extinction via some sort of weather pattern that not only hurts the flies but als drives their prey away from the area for a while? Say a drought or a long period of colder weather than normal?

I think that might actually require a second PoD (Point of Departure), since humans can't affect the weather and everything that has happened differently in this timeline is attributable to a point of divergence between two animals (a fox and a ptarmigan, hence the name of the timeline) during the final stages of the Saalian Glacial Period that had a direct effect on humans. More PoDs are a possibility for this timeline, but so far I've been able to do enough with just the one and would prefer to keep it that way.


However, I just read that human sleeping sickness actually wasn't an epidemic until at least the 14th century, when the slave trade caused an increased amount of contact between previously isolated regions of Africa where it was a problem (Eastern Africa and the Gambia River). So, in reference to how we get humans on the Congo Coast into South America between 69,000 and 65,000 years BP, that kind of renders the whole discussion irrelevant. However, the discussion is still relevant if I'm going to take a stab at more widespread complex civilizations in Africa with endemic domesticates like the Common Eland, which is also affected by the trypanosomes, just of a different subspecies: Trypanosoma brucei brucei.


It kind of leaves me wondering how on Earth I'm going to justify this though. I mean, I have talked about fishing and aquaculture having been practiced during the Eemian along the Nile, but I never went into any detail about how this spread in Africa during the Weichselian. Perhaps I could say that the severely increased aridity in the area of the Congo pushed many communities to the river and the coasts for survival, but then, simple coastal fishing and sailing out to see far enough to get picked up by the Caribbean bound currents are two different beasts...

[Jub]

I don't know that we don't effect the weather more than we're given credit for. Different human behavior could mean a different forest or section of grassland burns down, the smoke causes a local change in weather, and the change in vegetation causes light to reflect differently. Thus over years and years weather is effected.

I don't know how much it's effected or what effects it could cause though.

[LadyTevar]

Since I know nothing of insects, I will instead ask a question relating to the idea of a different culture/genetic makeup of South America. We have seen that humans sailed the South Pacific island hopping. Could the lowered oceans of the most recent Ice Age have allowed them to hop all the way to South America?

[Zirojtan]

I am unsure about the factors regarding the Melanesian migration into places like the Loyalty Islands, the New Hebrides, and New Caledonia, but I do know that the Austronesian Migrations are though to have been kick started by an agricultural revolution in Southeast Asia.


Besides that, much of Indonesia was actually above sea level at the time, creating a subcontinent called Sundaland. Australian, New Guinea, and Tasmania were also joined in a continent called Sahul. So the island-hopping incentives were slightly lowered. My friend suggested that I just have fishermen off the coast of Mauritania get swept up in Caribbean-bound currents, so I'm thinking that's what I might do.


Also, there would be a problem with that idea anyways with how I've already distributed the phenotypes. What's known as the Weichselian Rift Phenotype actually migrated out of Africa around 85,000 years ago and has been pushing into Southeast Asia and Sundaland ever since. This phenotype has a severely reduced brow-ridge, and by the time of the Holocene, they will be distributed in Melanesia, Polynesia, and Australia, and will have completely lost their brow-ridges. OTL Australian Aborigines have the most prominent brow-ridges on the planet as a group, so if I want the South Americans to look Melanesian, they're going to have to come from West Africa the way I've already written things.

[madd0ct0r]

possible scenario.

Local humans use resin/sap traps to keep the number of insects in their house down (flypaper, sort of stuff)
Local humans domesticate some species of bird for eating, find the trapped insects make good bird food.
Insect trapping starts being done on large scale.
Local insect eating wild birds competing for scarcer food, tetse fly population goes down, unable to stand the pressure.

[Zirojtan]

possible scenario.

Local humans use resin/sap traps to keep the number of insects in their house down (flypaper, sort of stuff)
Local humans domesticate some species of bird for eating, find the trapped insects make good bird food.
Insect trapping starts being done on large scale.
Local insect eating wild birds competing for scarcer food, tetse fly population goes down, unable to stand the pressure.

The extinction of the extinction of the fly was supposed to boost the human population in Sub-Saharan Africa enough to allow for the kinds of fishing communities that would carry a fisherman from West Africa to the Caribbean/North Coast of South America, and to possibly allow for the domestication of endemic livestock, specifically the Common Eland, which is an antelope and as such affected by Trypanosoma brucei brucei. Now that I know that it is malaria, and not trypanosomiasis that has acted as the major population checkpoint over the years for humans, getting rid of the flies for the sake of human sleeping sickness is kind of irrelevant to the timeline, but in terms of animal sleeping sickness it would be. Although, the problem I see with your scenario is that in our timeline, no animal endemic to Africa was ever domesticated, and that probably has to do with three major factors:


1. The African ecosystem was so rich that domestication of livestock was not exactly necessary in the minds of hunter-gatherers, who made up the majority of the continent until about 5,000 years ago when the Bantu Expansion took place, fueled by the domestication of endemic crops that was probably made possible by introduced domestic animals (dogs especially, and cattle and goats as a food source).
2. The human population of Sub-Saharan Africa did not experience the population surpluses necessary for these kinds of expansions because surpluses were checked by malaria (and sleeping sickness in Eastern and Western Africa). Without these surpluses of humans to upset the balance of the ecosystem, the environment remained rich, and so domestication of a single animal, even a bird, would've been a lot of unnecessary work.
3. Endemic fauna were just as susceptible to local diseases as Eurasian domesticates, such as trypanosomiasis from Trypanosoma brucei brucei and others that effect local pigs that once the Eurasian domesticates were introduced, it didn't make much sense pursuing domestication in animals like zebras and Common Elands.


History has also shown us that microlivestock tends to come after macrolivestock, and that probably the domestication of another predator is either necessary or helps to facilitate in the domestication of prey animals. The dog was the first human domesticate, with studies indicating that they may have been domesticate as much as 90-100,000 years ago, which was followed by sheep and goats probably at the end of the Pleistocene, cows, and then horses, camels, and donkeys. Your microlivestock, like rabbits, chickens, ducks, and geese, came much later, probably around 5,000 years ago tops (I don't quite remember). The only example I can think of where microlivestock were domesticated before macrolivestock would be in North America, where the near absence of large domesticable animals (moose and caribou are domesticable, but oh well...) which was facilitated by an upset of the ecosystem that coincided with an extreme change caused the extinction of much of the endemic fauna and potential macrolivestock animals, such as Camelops, Hemiauchenia, and the North American equines, to name a few. So I think that in order for your scenario to work for complete extinction of the tsetse via using them as bird feed, you'd need to either get rid of malaria, or possibly get different species of antelope to develop a resistance to trypanosomiasis, making endemic fauna preferable to introduced fauna. Then later, when we have the microlivestock, it could work.


What sayeth our tsetse expert on that last part? Is that too big of a stretch?

[Bedlam]

I'd say getting rid of Malaria might be trickier than Trips although we do already know of mutations giving resistance (and sickle cell).

I doubt you could get rid of all Tsetse via your method but you could put enough of a dent in the population to make them non viable hosts for trips.

A species of antelope becoming immune seems reasonable, human selective breeding could probably speed up the spread of any mutation.

[Zirojtan]

Yeah I think if I wanted no malaria we'd have to go WAY BACK. And the butterflies of that would be pretty difficult to manage.