Leishmania is a parasite that targets immune cells. Why is it less dangerous than HIV?

Submitted by robotisland t3_105aeln in askscience

Leishmania is a protozan parasite that attacks immune cells and causes leishmaniasis. Since it also damages the ability of the immune system to protect against infection, why is leishmania less dangerous than HIV?

Does it have something to do with the speed at which leishmania can reproduce?

Why is there an AIDS pandemic but not a leishmaniasis pandemic?

Since leishmania can infect vertebrates and be spread by insects (and HIV can only infect humans and can't be spread by insects), what makes leishmania less infectious than HIV?

What makes leishmaniasis an easier disease to treat than AIDS?

Does the immune system have any defenses against leishmania?

If left untreated, what are the chances that someone infected with leishmania will recover?

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provocative_bear t1_j3ak0un wrote

Leishmaniasis (called L- from here on out) prevalence largely depends on the prevalence of the sand flies that spread it. While technically it can be spread sexually [1], people with visceral L- are not generally in a condition to be having sex. Therefore, it doesn't spread too well as an STD. Meanwhile, HIV is an insidious disease where the host can survive for years and be active for much of it before succumbing. Additionally, there are often visible signs of L- sores and lesions- while HIV patients show no outward signs of the disease. In short, L- patients are generally clearly sick to both host and partners, while HIV patients are not.

In terms of treatment, you can wipe it out L- with antiparasitics. Treatment is unpleasant, but it is curable. In contrast, HIV is a very sneaky disease. It is a retrovirus, meaning that it can jam its genetic material into your cells' DNA and hide in that form. Even if every virus in the human body is wiped out, the HIV DNA in the host cells can activate, and then the patient is infected all over again. That's why HIV treatments are the way they are, where a patient can be basically normal, but not cured.

[1]: https://pubmed.ncbi.nlm.nih.gov/32943348/

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BigCommieMachine t1_j3gy0y6 wrote

Could you hypothetically engineer a virus that just injects the undamaged/unaltered DNA of a person back into infected cells?

I mean if if a harmful virus can inject itself in your cells DNA, could we just create virus with “normal” DNA that just boots it out? I mean this could even apply to other genetic diseases. Put a person on massive amounts of immunosuppressants and let the “helpful” virus go to town.

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provocative_bear t1_j3jfchy wrote

We have only recently figured out safe viral gene therapies (usually called lentiviral therapies)- the FDA approved the first two of them in 2022 [1]. I agree that to actually cure HIV, we'd need a system that can hunt down and correct the rogue DNA in our cells, but the technology is not yet there. First of all, to my knowledge, current lentiviral therapies aren't very good at targeting where in the genome they insert. That would be important to correct the implanted HIV sequence. However, our CRISPR DNA engineering systems are good at this. Understandably, there is work underway to combine the two [2], but academia tends to lead actual therapies by quite a bit. In the cases of both potential therapies, they wouldn't come close to screening / inserting into every potentially infected cell with our current technology. There's a lot of interest in improving this issue in pharma, though. Maybe it'll be possible some day, but not before a lot of work in the field.

I think about this specific question in the shower a lot, and am kind of stoked that somebody asked it.

[1]: https://asgct.org/publications/news/september-2022/eli-cel-second-lentiviral-vector-gene-therapy

[2]: https://pubmed.ncbi.nlm.nih.gov/34372494/

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NerdWithoutACause t1_j3airig wrote

HIV is a retrovirus, meaning it inserts its genetic code into the host cells. So not only do those cells make the virus, but all their descendants will, as well. This makes HIV almost impossible to eradicate from the host.

We have drug treatments for leishmaniasis which are extremely effective, and once it’s out of your body, it’s gone for good. With HIV, we have treatments that can inhibit the virus’s spread inside the body, but the infect cells and their progeny are still infected, and will remain so for decades. If the treatment is stopped, the infection will resume in full force.

So basically, leishmaniasis is easily curable in most cases, but HIV is not.

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isisisisufo t1_j3diut8 wrote

This! Virus infection is way more dangerous than a protozoa one, for example. The life cycle of a virus evolves basically entirely around infect host cells to reproduce. Protozoas are more complex, they have more particular needs to set the proper environment to reproduce successfully and also to transmite.

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whyyou- t1_j3ap4d0 wrote

Leishmania infects a type of cell known as phagocytes, they’re part of the innate immune system and “eat” bacteria, parasites and cellular detritus (very basic functions) meanwhile HIV infects T-CD4 cells wich are part of the acquired immune system and are vital because they act as regulators (akin to an administrator) without them you can have other defensive cells but they won’t do anything; that’s why an advanced HIV infection basically collapses the entire immune system.

As to sexual transmission; the parasite has 2 phases, one is the amastigote wich is replicative and lives within the phagocyte; when the sandfly drinks infected blood it also takes some of these infected cells and inside the insect these amastigotes turn into promastigotes wich are the infectious stage. As you see this bug needs an insect to complete it’s cycle and turn itself infectious so the human / human transmission is very rare, that’s why it’s not considered an STI.

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whyyou- t1_j3aqgeu wrote

Leishmania is endemic in some areas but it’s not pandemic due to its need of a vector (the sandfly) that cannot reproduce in some areas.

Why is it easier to treat than HIV?, well the HIV can insert itself into the DNA of its host cell making it extremely difficult to completely eradicate; we can only control the mature viruses but we cannot remove its genetic code from infected cells; as for leishmaniasis, it’s a parasite for wich we have several medications and can be completely eradicated (but it’s not easy, sometimes lengthy IV treatments are needed).

Does the immune system have defenses against Leishmania?? Yes, the infected cells can express some particles in its membrane wich makes them recognizable to the acquired immune system, the infected cells are surrounded by a bunch of other cells causing a “granulomatous inflammation” containing the infection in a single place (most of the times, not always effective) that we can see in the form of skin ulcers or lumps inside the organs (depends of the leishmania type).

Can it be contain by the immune system to a single place? Yes. Can it resolve without treatment? Most likely not.

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robotisland OP t1_j3fvj2o wrote

This is great info! Thanks so much!

So leishmania can only infect immune cells that are phagocytes, right?

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Thisisnotdelicious t1_j3dnv9x wrote

Cutaneous leishmaniasis will generally resolve without treatment in healthy individuals. Treatment of cutaneous ulcers in healthy patients is primarily preventing scarring. Most healthy people exposed to parasite species that cause visceral leishmaniasis don't develop symptoms, although more disease is seen in children and the elderly.

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robotisland OP t1_j3fwbwq wrote

I didn't know that most people exposed to leishmania never develop symptoms. Thanks for the info!

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bettinafairchild t1_j3eevy9 wrote

In addition to what others have said, keep in mind that from the time AIDS was first observed until about 1996, there was no treatment for AIDS and it was a death sentence. And during all that time, it’s not like people could say “soon we will have a treatment.” We simply didn’t know when I’d ever there would be a treatment. When if ever AIDS would stop being a death sentence. For those of us alive at that time, that’s a frightening feeling that is hard to let go of. It lingers even today. Adding to that was the stigma surrounding the disease which is a miasma surrounding feelings about it. But Leishmania has a cure. It never had all that emotion surrounding it .

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robotisland OP t1_j3fy935 wrote

Great point. Leishmania never had the fear and stigma surrounding it. Thanks for your reply!

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