Catching Schisto Early: How eDNA is Revolutionizing Disease Surveillance in Brazil

Hey there! Let me tell you about something pretty cool that could really shake things up in the fight against a nasty disease called schistosomiasis. You might know it as snail fever. It’s a big problem in places like Brazil and Africa, causing a lot of health issues and economic pain.

Now, this disease is tricky because its transmission is tied to water bodies, poor sanitation, and these specific snails that act as intermediate hosts for the parasite, *Schistosoma mansoni*. Finding out where the parasite is hiding has traditionally been a bit of a headache.

The Old Way: A Real Snail’s Pace

Think about it: to know if an area is risky, you usually have to go out and collect snails. Lots of them! And let me tell you, snail sampling isn’t always easy. Sometimes the snail populations are low, especially during dry seasons. Plus, even if you find snails, only a small percentage might be infected. Then you have to bring them back to the lab, check them individually (which takes forever!), and you need highly trained folks to do it. It’s time-consuming, labor-intensive, and honestly, you can miss things, especially in areas where the disease isn’t super common anymore. It’s like trying to find a needle in a haystack, but the haystack is a whole river and the needle is a tiny parasite in a snail!

This is a real challenge, particularly in Brazil, where many areas now have low levels of the disease. People might have very few parasites, meaning fewer eggs in the environment, making it harder to detect the parasite in humans *and* in snails. We really needed a better way to spot these transmission hotspots.

Enter eDNA: A Game Changer?

This is where environmental DNA, or eDNA, comes into the picture. It’s been totally transforming how we study ecosystems. Instead of trying to find the organism itself (like a snail or a parasite), you look for tiny traces of its DNA left behind in the environment – in water, soil, or even air. Pretty neat, right?

For parasites, this means we can potentially detect their DNA in water where infected snails or even infected people have been. It’s non-invasive and can be much more efficient. You just collect a water sample, filter it, extract the DNA, and use molecular techniques to see if the parasite’s genetic signature is there.

Scientists have already had success using eDNA to find parasites and their hosts in water samples elsewhere. Techniques like PCR, qPCR (quantitative PCR), and LAMP (loop-mediated isothermal amplification) are super useful for this. They can amplify even tiny amounts of DNA so you can detect it.

Using eDNA to monitor for *S. mansoni* has shown promise in Africa for identifying active transmission sites. But Africa has a different situation – often higher disease levels and different parasite/snail species. We needed to see if this eDNA approach could work effectively right here in Brazil, under our specific conditions.

Putting eDNA to the Test in Brazil

So, that’s exactly what we set out to do in this study. Our goal was to standardize and apply an eDNA-based method specifically for detecting *Schistosoma mansoni* in Brazil. We wanted to see if it could be a reliable tool for surveillance, helping us get closer to the WHO’s target of eliminating schistosomiasis by 2030.

Our approach had a few key steps:

• Standardizing the molecular test: We needed to make sure our main test (a qPCR assay) was super specific and would only detect *Schistosoma* DNA, not DNA from other similar parasites or the snails themselves that are found in Brazil.
• Standardizing the eDNA collection and extraction: We figured out the best way to filter water samples and get the parasite’s DNA out of those filters.
• Field validation: We took our standardized method out into the real world, sampling water in areas in Minas Gerais, Brazil, known to have schistosomiasis, and compared the results to traditional snail surveys done at the same spots.

We tested three different molecular techniques: a Low-Stringency PCR (LS-PCR), a LAMP assay, and a qPCR assay. We first tried these out using water from tanks containing *Biomphalaria glabrata* snails – some tanks had snails infected with *S. mansoni*, and others had non-infected snails or just clean water. This helped us check if the methods could actually detect the parasite’s DNA in water and if they produced false positives.

For the specificity test of the qPCR, we used DNA from a whole bunch of different *Schistosoma* species, other trematodes found in Brazil, and many different snail species, including various *Biomphalaria*. We wanted to be absolutely sure our test wasn’t picking up the wrong signals.

Turns out, the qPCR assay was pretty specific! It amplified *Schistosoma* DNA. It did show some amplification for *Schistosoma haematobium* and *Schistosoma intercalatum* as well, but those species aren’t found in Brazil, so for our purposes here, it worked perfectly. Importantly, it didn’t amplify DNA from any of the Brazilian snails or other trematodes we tested. Phew!

In the tank experiments, all three molecular methods (LS-PCR, LAMP, and qPCR) successfully detected *S. mansoni* DNA in the water from tanks with infected snails. They didn’t pick up anything from the tanks with non-infected snails or clean water, which is exactly what we wanted to see – no false positives there.

Out in the Field: eDNA vs. Traditional

Then came the real test: taking it to the field. We collected water samples at the same points where traditional snail surveys were being conducted in two areas in Minas Gerais. The snail surveys involved collecting snails, identifying them, and checking if they were releasing parasite larvae (*cercariae*).

In one area, Giru district, snail surveys found *Biomphalaria glabrata* at several spots, and they confirmed *S. mansoni* infection (snails releasing cercariae) at two specific points across two surveys. Interestingly, at some points, the snails collected died before they could be fully examined, which is a common problem with traditional methods.

Simultaneously, we ran our eDNA tests (blindly, so we didn’t know the snail results yet) on the water samples from these same locations. Guess what? The eDNA approach, using both LAMP and qPCR, successfully detected *S. mansoni* DNA at the *exact* same points where infected snails were found. That’s great validation!

But here’s where it gets even more exciting: the eDNA method also detected the parasite’s DNA at *one additional site* that the traditional snail survey missed! This really highlights the sensitivity of the eDNA approach, showing it can pick up traces that might be missed by just looking for infected snails, especially if snail numbers are low or they die before examination. The LS-PCR method didn’t perform as well in the field samples compared to LAMP and qPCR, so we focused on those two.

In another area, Ribeirão das Neves, snail surveys found different *Biomphalaria* species (*B. straminea* and *B. tenagophila*), but none of the collected snails were found to be infected. Our eDNA tests in Ribeirão das Neves also came back negative for *S. mansoni* DNA, which matched the traditional findings there.

Environmental Clues

We also looked at environmental factors like water temperature, pH, calcium, conductivity, and the presence of fecal contamination indicators like *E. coli* and total coliforms. These factors are important because they influence where snails live and how well the parasite can survive and transmit.

All the water bodies we sampled showed signs of fecal contamination, with high levels of *E. coli* and total coliforms. This isn’t surprising given the sanitation challenges in many areas, but it’s a strong indicator that the water is being contaminated with feces, which is exactly how *Schistosoma* eggs get into the water in the first place. Monitoring these bacteria can help identify potentially risky sites.

Water temperature seemed particularly relevant. We found more snails at points with higher water temperatures, which makes sense as snails are sensitive to temperature and warmer water (within a certain range) is better for their reproduction and survival. Climate change is a big concern here, as rising temperatures could potentially shift where schistosomiasis transmission is possible.

Why This Matters for Public Health

So, why is all this important? Well, the WHO and local health programs like FioSchisto in Brazil are pushing hard to eliminate schistosomiasis. To do that, we need better tools to find where transmission is *still* happening, especially in those low-endemic areas where it’s hard to spot. We also need ways to verify that transmission has truly stopped in areas aiming for elimination.

Traditional methods have limitations, as we saw. They are time-consuming, require specialized skills, and can miss low levels of infection or struggle with snail transport and identification issues.

eDNA sampling offers a much simpler way to collect samples – just grab some water! This could allow health programs to sample more locations more easily and frequently. It could also be more cost-effective in the long run.

This study is a pioneering effort in Brazil to show that eDNA, combined with molecular techniques like LAMP and qPCR, is a valid and effective strategy for monitoring schistosomiasis. It successfully identified transmission foci, including one missed by traditional methods.

LAMP is great because it’s simpler and cheaper, potentially usable in field settings with less equipment. qPCR is the gold standard for accuracy and quantification in the lab. Both worked well with eDNA in this study.

Looking Ahead

This is a pilot study, meaning it’s an important first step. We need more studies like this in different areas of Brazil, with varying levels of disease, to really fine-tune the method and make sure it’s reliable everywhere. Combining eDNA analysis with traditional surveys and human health data will give us the most complete picture.

But the potential is huge! Imagine being able to quickly and easily test water bodies across a whole region to pinpoint exactly where the parasite is active. This information can guide public health interventions, like targeted snail control or improving sanitation, making our efforts much more efficient and effective in reaching that elimination goal.

So, yeah, using eDNA to find *Schistosoma mansoni* in water? It’s not just a cool science trick; it’s a promising new weapon in the fight against a neglected disease, helping us advance surveillance and protect communities in Brazil and beyond.

Source: Springer