Schistosomiasis is treated with a single day of an oral antiparasitic medication called praziquantel, which kills the adult worms responsible for the disease. The standard dose is 40 mg/kg of body weight, split into two doses taken the same day. Treatment is effective against all species that infect humans, and most people complete the entire course in just one day.
How Praziquantel Works
Praziquantel disrupts the way adult schistosome worms regulate calcium inside their cells. By interfering with calcium channels on the worm’s surface, the drug causes the worm’s muscles to contract uncontrollably and its outer protective layer to break down. This exposes the worm to the immune system, which finishes the job. The drug also reduces the worms’ ability to lay eggs, which is important because the eggs, not the worms themselves, cause most of the organ damage associated with schistosomiasis.
One key limitation: praziquantel works primarily against adult worms. Juvenile parasites (called schistosomula) that haven’t yet matured are largely unaffected. This is why a second round of treatment is sometimes needed a few weeks later, particularly if someone was recently exposed and may still be carrying immature parasites.
Dosing Differences by Species
The dose you receive depends on which species of schistosome is involved. For infections caused by S. mansoni, S. haematobium, or S. intercalatum, the standard regimen is 40 mg/kg split into two doses over a single day. For S. japonicum and S. mekongi, which tend to produce more eggs and cause heavier infections, the dose is higher: 60 mg/kg divided into three doses over one day.
Your doctor determines the species based on where you were exposed geographically and what type of testing was done. S. mansoni is found in Africa, South America, and the Caribbean. S. haematobium is concentrated in Africa and the Middle East. S. japonicum occurs in parts of China, the Philippines, and Indonesia.
What Side Effects to Expect
About 29% of people experience some kind of side effect within the first four hours after taking praziquantel. The most common is abdominal pain, followed by vomiting, dizziness, and diarrhea. These symptoms are generally mild and short-lived, resolving within the same day for most people.
Side effects tend to be worse in people with heavier infections. This makes sense: as the drug kills large numbers of worms simultaneously, the immune response to all that dying parasite material can be more intense. People who were anemic before treatment are more likely to experience vomiting specifically. Taking praziquantel with food can help reduce stomach-related side effects.
Treatment for Children Under Six
Standard praziquantel tablets are large and bitter, making them difficult for young children to swallow. For years, healthcare workers had to crush and mix them with food or juice, which made dosing unreliable. A new formulation called arpraziquantel has been developed specifically for children aged 3 months to 6 years. It’s an orodispersible tablet, meaning it dissolves on the tongue without needing water.
In a phase 3 trial involving 288 preschool-aged children in Côte d’Ivoire and Kenya, arpraziquantel at 50 mg/kg achieved cure rates of about 88%, comparable to the 81% seen with standard praziquantel in older children. The most common side effects were abdominal pain (14%), diarrhea (9%), drowsiness (7%), and vomiting (6%). No serious safety concerns were identified. This formulation represents a significant step forward, since the WHO has long identified the lack of a child-friendly treatment as a gap in schistosomiasis control.
Pregnant and Breastfeeding Women
Praziquantel is considered safe during pregnancy and breastfeeding. The WHO recommends that pregnant and lactating women be included in public health treatment programs rather than excluded, as untreated schistosomiasis poses its own serious risks to both mother and child, including anemia and impaired fetal development. Women and adolescent girls of childbearing age are specifically listed among the target populations for preventive treatment in areas where the disease is common.
When a Second Drug Is Needed
For infections caused specifically by S. mansoni, an older drug called oxamniquine can serve as an alternative. Oxamniquine works through a completely different mechanism: it gets activated by an enzyme inside the worm, and the activated form damages the parasite’s DNA. However, it only works against S. mansoni, not S. haematobium or S. japonicum, so its use is limited to certain regions and situations, typically when praziquantel isn’t available or isn’t effective.
There’s also growing interest in combining praziquantel with artemisinin-based compounds (the same family of drugs used to treat malaria). The logic is complementary: praziquantel kills adult worms, while artemisinins target the juvenile stages that praziquantel misses. In animal studies, combining both drugs produced significantly higher rates of worm elimination than praziquantel alone. This approach could be particularly useful in areas where people face constant reinfection and may be carrying parasites at multiple life stages simultaneously.
Treating Severe or Complicated Cases
Most schistosomiasis cases respond well to praziquantel alone. But when the disease has progressed to involve the spinal cord or brain, a condition called neuroschistosomiasis, treatment becomes more complex. Eggs that lodge in nervous tissue trigger intense inflammation, which can cause lower limb pain, weakness, numbness, bladder dysfunction, and even paralysis.
In these cases, praziquantel is given alongside corticosteroids to control the inflammatory response. In one study of 16 patients with spinal cord involvement, this combined approach was successful in all cases, with patients who received steroids for more than two months showing the best outcomes. The corticosteroids prevent the immune system’s reaction to dying parasites from causing additional damage to delicate nerve tissue.
Long-standing infections can also cause liver fibrosis, portal hypertension (increased pressure in the blood vessels around the liver), and kidney damage from chronic inflammation. Praziquantel kills the worms and stops new egg production, but it doesn’t reverse organ damage that has already occurred. Managing these complications often requires additional care focused on the affected organs.
Confirming the Infection Is Cleared
After treatment, follow-up testing is important to confirm that the parasites have been eliminated. This typically involves stool examination (for intestinal species) or urine testing (for S. haematobium) performed several weeks after treatment. The delay is necessary because eggs already deposited in tissue at the time of treatment will continue to appear in stool or urine for some time even after all adult worms are dead.
If eggs are still present on follow-up testing, a second course of praziquantel is given. True drug resistance remains rare. While some studies have reported lower cure rates in populations with very heavy infections or recent exposure, widespread clinical resistance to praziquantel has not been documented. It remains the drug of choice worldwide.