Schistosoma mansoni infections are associated with hepatosplenic organometry within the context of repeated praziquantel treatment and co-endemic infections of malaria, hepatitis B, and HIV: a population-based study in rural Uganda

In a population-based study in rural Uganda, current *Schistosoma mansoni* infection intensity was found to remain significantly associated with splenomegaly in children and hepatomegaly in adults, even after accounting for co-endemic malaria, HIV, hepatitis B, and repeated praziquantel treatment.

The Gist

Imagine your body as a bustling city. The liver is the city's main factory, filtering toxins and processing nutrients, while the spleen is the security guard, patrolling the streets to catch invaders like bacteria and parasites.

In many parts of rural Uganda, this city is under constant attack by invisible invaders. The main culprit is a parasite called Schistosoma mansoni (a type of flatworm), but the city is also dealing with Malaria, HIV, and Hepatitis B.

This study is like a massive city inspection. Researchers went into three districts in Uganda, checked the "buildings" (organs) of over 3,000 people using ultrasound machines, and tried to figure out: Who is damaging the city, and how much?

Here is the breakdown of their findings in simple terms:

1. The Big Question: Is the Worm Still the Problem?

For years, health officials have been spraying medicine (Praziquantel) to kill the worms. The big question was: Now that we are killing the worms, are the organs still getting damaged?

• The Answer: Yes, but it's complicated.
• The Metaphor: Imagine the worm is a vandal who scratches the factory walls. Even if you catch the vandal today, the scratches (damage) might still be there. But, in this city, there are other vandals too (Malaria, HIV, Hepatitis) who are also scratching the walls. The researchers had to figure out who did what.

2. The Children: A Battle Between Two Invaders

In children (ages 5–17), the Spleen (the security guard) was often swollen and enlarged. This is called splenomegaly.

• The Malaria Factor: Think of Malaria as a massive, chaotic riot. It was the biggest cause of the Spleen getting swollen. About 47% of the severe swelling in kids was directly because of Malaria.
• The Worm Factor: Even after accounting for the Malaria riots, the Worm (Schistosoma) was still a troublemaker. It was responsible for about 24% of the severe swelling.
• The Lesson: You can't just say, "Oh, the Spleen is big, it must be Malaria." In these areas, the Worm is still doing real damage, even if Malaria is the bigger bully.

3. The Adults: A Different Kind of Damage

In adults, the story changed. The Spleen was still swollen, but the Liver (the factory) started showing signs of serious trouble.

• The Viral Villains: In adults, HIV and Hepatitis B were the main drivers of severe liver damage.
  • HIV was linked to the liver shrinking and getting smaller (like a factory that has been abandoned and is collapsing).
  • Hepatitis B was also linked to the liver shrinking.
• The Worm's Role: The Worm was still causing some trouble, specifically making the left side of the liver slightly larger (early damage), but it wasn't the main cause of the severe shrinking seen in adults.
• The Takeaway: In adults, the liver problems are often a mix of the Worm's past damage and the current damage from viruses like HIV.

4. The Medicine Mystery (Praziquantel)

The researchers looked at people who had taken the anti-worm medicine in the last year.

• The Surprise: They expected to see that the medicine fixed the organs. Instead, they saw a confusing pattern. People who took the medicine sometimes had worse organ damage.
• The Explanation: This isn't because the medicine is bad. It's likely reverse causality. Think of it like this: People who are already very sick (with big livers or spleens) are the ones who go to the clinic to get the medicine. The medicine didn't cause the sickness; the sickness caused them to get the medicine.
• The Reality: The medicine kills the worms, but it doesn't instantly fix the "scratches" on the factory walls. The damage persists.

5. The Old Map vs. The New Map

For decades, doctors have used an "Old Map" (the WHO Niamey Protocol) to decide if an organ is too big or too small. This map was drawn based on data from Senegal years ago.

• The Problem: When the researchers used this Old Map on the Ugandan population, it was wildly inaccurate.
  • It thought half the people had swollen spleens (when really, only about a quarter did). It was crying wolf!
  • It missed almost all cases of the liver shrinking. It was blind to the danger.
• The Solution: The researchers built a New Map using data from the actual Ugandan population. This new map is much more accurate and tells the true story of what is happening in these communities.

Summary: What Does This Mean for the Future?

1. Don't Ignore the Worm: Even in areas with lots of Malaria, the Worm is still hurting children's spleens. We need to keep treating it.
2. Watch the Viruses: In adults, we can't just look at the Worm. We have to check for HIV and Hepatitis B, because they are causing the liver to shrink and fail.
3. Update the Rules: The old rules for measuring organs are wrong for these specific communities. We need new, local rules to accurately diagnose who is sick.
4. Medicine isn't a Magic Wand: Taking the pill kills the worm, but it doesn't instantly heal the organ damage. We need better ways to manage the long-term scars left behind.

In a nutshell: The city is under attack from multiple sides. To save the factory (liver) and the security guard (spleen), we need to fight all the invaders (Worms, Malaria, HIV, Hepatitis) and use a better map to see who is really in trouble.

Technical Summary

1. Problem Statement

Schistosomiasis, caused by Schistosoma mansoni, is a leading cause of hepatosplenic disease in Sub-Saharan Africa (SSA), often resulting in periportal fibrosis (PPF) and organomegaly. However, the relationship between current S. mansoni infection intensity and hepatosplenic organometry remains unclear in the modern context of:

• Widespread Mass Drug Administration (MDA) using praziquantel.
• High rates of co-endemic infections (Malaria, HIV, Hepatitis B).
• Existing clinical guidelines (WHO Niamey Protocol) that recommend against assessing splenomegaly in malaria-endemic areas, assuming malaria is the sole cause.

There is a critical knowledge gap regarding whether current infection drives morbidity in adults (who bear the highest burden of fibrosis) and how co-infections with HIV and HBV influence liver and spleen pathology in the presence of schistosomiasis.

2. Methodology

Study Design & Population:

• Type: Community-based, cross-sectional study nested within the SchistoTrack prospective cohort.
• Location: Three rural districts in Uganda (Pakwach, Buliisa, Mayuge).
• Participants: 3,121 individuals (1,507 children aged 5–17; 1,614 adults aged 18+).
• Data Collection: Conducted Jan–Feb 2024.

Data Collection & Measurements:

• Organometry: Point-of-care B-mode ultrasound (Philips Lumify) was used to measure liver (left and right lobes) and spleen dimensions.
• Reference Standards: Instead of relying solely on external WHO Niamey standards, the authors constructed internal, height-standardized reference values derived from a "healthy" reference population (negative for S. mansoni, malaria, HIV, HBV; no alcohol use; no fibrosis).
  • Abnormalities were classified by Standard Deviations (SD) from the mean of the healthy reference population within specific height deciles.
  • Categories: Severely shrunken (≤−2 SD), Moderately shrunken, Normal, Moderately enlarged, Severely enlarged (≥+2 SD).
• Exposures:
  • S. mansoni: Kato-Katz microscopy (Eggs Per Gram - EPG).
  • Co-infections: Rapid Diagnostic Tests (RDT) for Malaria, HBV, and HIV.
  • Treatment History: Self-reported praziquantel use in the past year.
• Statistical Analysis:
  • Multinomial Logistic Regression: Used to estimate Relative Risk Ratios (RRR) for organ outcomes, stratified by age (children vs. adults).
  • Covariates: Controlled for sociodemographics, Water, Sanitation, and Hygiene (WASH), and behavioral factors.
  • Population Attributable Fractions (PAFs): Calculated using G-computation to estimate the proportion of abnormal organometry statistically attributable to specific infections.
  • Sensitivity Analysis: Compared internal reference standards against WHO Niamey Protocol fixed cut-offs.

3. Key Contributions

1. Internal Reference Tables: The study generated novel, height-decile-based reference tables for liver and spleen dimensions specific to the Ugandan context, accounting for co-endemic viral and parasitic infections. This challenges the applicability of the WHO Niamey Protocol (based on a Senegalese pre-MDA population) for current SSA contexts.
2. Disentangling Co-infections: It is one of the first studies to simultaneously model the independent and combined effects of S. mansoni, Malaria, HIV, and HBV on hepatosplenic organometry in both children and adults.
3. Re-evaluating MDA Impact: The study assesses whether repeated praziquantel treatment correlates with improved organometry in a high-transmission setting.
4. Age-Stratified Analysis: Distinctly separates pediatric and adult risk profiles, addressing the gap in adult-focused morbidity studies.

4. Key Results

Prevalence of Abnormalities:

• Children: Moderate-to-severe splenomegaly observed in 29.1%. Moderate liver abnormalities affected ~10–13%; severe pathology was rare (<5%).
• Adults: Splenomegaly (moderate/severe) in 23.3%. Liver abnormalities were more frequent, with significant rates of both enlargement and shrinkage (e.g., 20.9% had left lobe enlargement; 18.8% had right lobe shrinkage).

Determinants of Organometry:

• Children:
  • Spleen: Severe splenomegaly was strongly attributable to Malaria (PAF 46.7%) and S. mansoni intensity (PAF 23.6%). Even after controlling for malaria, higher S. mansoni egg counts significantly increased the risk of splenic enlargement.
  • Liver: Malaria was the primary driver of liver enlargement. S. mansoni intensity showed a negative association with moderate left lobe shrinkage (protective or confounded).
• Adults:
  • Spleen: HIV was a major driver of severe splenomegaly (RRR 3.62).
  • Liver:
    • S. mansoni: Intensity was associated with moderate left lobe enlargement (PAF 12.4%), suggesting early-stage morbidity.
    • HIV: Strongly associated with severe liver shrinkage (left lobe RRR 4.50; right lobe RRR 4.42) and severe enlargement.
    • HBV: Associated with severe left lobe shrinkage (RRR 2.54).
  • Praziquantel: Treatment in the past year showed inconsistent associations and no clear protective pattern. In some models, recent treatment was associated with increased risk of severe liver shrinkage (likely due to reverse causality: symptomatic individuals seeking treatment).

Comparison with WHO Niamey Protocol:

• The external Niamey standards systematically overestimated splenomegaly (classifying ~49% of the population as enlarged vs. 26% using internal standards).
• They systematically underestimated severe liver shrinkage and enlargement (e.g., identified only 0.1% of severe right lobe enlargement vs. 1.6% internally).

5. Significance and Implications

• Clinical Guidelines: The findings challenge the WHO Niamey Protocol's recommendation to exclude splenomegaly assessment in malaria-endemic areas. The study demonstrates that S. mansoni contributes significantly to splenomegaly in children even in the presence of malaria.
• Morbidity Monitoring: Current MDA strategies focusing solely on S. mansoni may be insufficient. The study highlights that HIV and HBV are critical drivers of severe liver pathology (shrinkage/cirrhosis-like outcomes) in adults, potentially interacting with past schistosome infections to accelerate fibrosis.
• Diagnostic Standards: The study provides evidence that external reference standards (Niamey) are inadequate for modern, co-endemic SSA populations. It advocates for the development of updated, context-specific reference tables (or global standards similar to WHO child growth standards) to accurately diagnose hepatosplenic morbidity.
• Future Research: The lack of a clear protective effect from praziquantel on organometry suggests that existing morbidity may be irreversible or that treatment coverage/intensity is insufficient to reverse established fibrosis. Prospective studies are needed to track the sequence of infections and organ changes over time.

Conclusion:
Current S. mansoni infection intensity remains a significant predictor of hepatosplenic abnormalities, particularly splenomegaly in children and early liver enlargement in adults. However, in adults, viral co-infections (HIV, HBV) are dominant drivers of severe liver pathology, including shrinkage. Accurate morbidity surveillance in SSA requires updated reference standards and integrated management strategies that address these co-endemic viral and parasitic interactions.