A parasite best known for damaging the intestines, liver, and bladder has surfaced somewhere far less expected: the brain. Two physicians at Jose R. Reyes Memorial Medical Center in Manila, Mary-France G. Lebii and Bonifacio C. Pedregosa II, documented a case of cerebral schistosomiasis in a New England Journal of Medicine image report published in September.
Schistosomiasis is caused by parasitic flatworms picked up from contaminated freshwater. In most people, the damage centers on the gut, liver, or urinary tract. But the worms' eggs can travel through the bloodstream and lodge in the brain or spinal cord, where they trigger inflammation and form lesions that can resemble other brain diseases on a scan.
A Parasite That Gets In Through the Skin
The infection starts with water. According to the CDC, the parasite's infectious larvae leave freshwater snails and swim in the water, and people can become infected when their skin comes into contact with contaminated freshwater.
Some people develop a rash or itchy skin within the first few days. Within one to two months, symptoms may include fever, chills, cough, and muscle aches, the CDC says. Repeated infections in children can cause anemia, malnutrition, and learning difficulties.
Inside the body, the adult worms live in blood vessels and release eggs. The World Health Organization explains that some eggs become trapped in body tissues, "causing immune reactions and progressive damage to organs." Usually that means the intestines and liver, causing abdominal pain, diarrhea, and blood in the stool, or the urinary tract, where the classic sign is blood in the urine.
The brain is not the usual destination. When eggs do reach it, the body walls them off with clusters of inflammatory tissue called granulomas. On imaging, those clusters can look like other lesions, including tumors, which is why a patient's history matters so much.
The Philippines Has Its Own Species
The Philippines is one of the countries where the disease remains entrenched. The Department of Health's schistosomiasis control and elimination program puts the population at risk at approximately 12.4 million, with 2.7 million people directly exposed.
A 2025 review in Tropical Medicine and Infectious Disease reported that 28 of the country's 81 provinces are endemic, most of them in the Visayas and Mindanao. The species there is Schistosoma japonicum, carried by the snail Oncomelania hupensis quadrasi. Unlike some other schistosome species, S. japonicum also infects animals, and the review describes domestic animals, particularly bovines such as the carabao, the water buffalo used in rice farming, as persistently infected.
That animal link helps explain why the parasite has been hard to eliminate. Treating people alone does not remove the source when infected animals keep contaminating the same water. Village-level surveys conducted from 2014 to 2018 among people ages 5 to 65 found an overall prevalence of 4.8%, according to the review. The health department's program had set a target of eradicating transmission in all endemic barangays by 2025.
Seizures Topped the List of Warning Signs in a Manila Study
Brain involvement is a documented problem in the Philippines, not just a curiosity. A retrospective study from the Philippine General Hospital in Manila, published in Acta Medica Philippina in 2015, reviewed cerebral schistosomiasis cases seen from 2001 to 2011. Among the 29 patients whose records were available, the median age was 31, and men outnumbered women three to one.
Seizures were the most common symptom, affecting 76% of patients, followed by headache in 59%. About a third had numbness or weakness, 28% had cranial nerve palsies, and 24% had papilledema, a swelling of the optic nerve that signals raised pressure inside the skull. On imaging, 62% had multiple nodules, and the parietal lobe was the most frequently involved area. Most patients had traveled to or lived in endemic areas, with Samar and Leyte the leading sources.
The treatment picture was encouraging. Of 28 patients treated with the antiparasitic drug praziquantel, 24 improved, with steroids and anticonvulsants also used. No deaths were reported.
Why a Travel History Can Change the Diagnosis
Globally, the disease is far from rare. The WHO reports that at least 253.7 million people required preventive treatment for schistosomiasis in 2024, and more than 100.5 million were reported to have been treated. The agency also notes that tourists sometimes develop severe acute infection with unusual problems, including paralysis.
For readers in the United States, the risk is very low for anyone who has not had contact with freshwater in regions where the disease is common. But the Manila case is a reminder for clinicians that a travel or residence history can reframe a puzzling brain scan.
Because a parasitic lesion can mimic other brain diseases, an accurate diagnosis can lead to treatment that is inexpensive and widely available. The WHO describes praziquantel as "effective, safe and low-cost."
People who have waded, swum, or worked in freshwater where schistosomiasis is common, and who later develop seizures, persistent headaches, or other neurological symptoms, should share that history with a clinician.
Key Questions Answered
What is cerebral schistosomiasis?
It is a form of schistosomiasis in which the parasite's eggs reach the brain and trigger inflammatory lesions, instead of staying in the gut, liver or urinary tract.
How do people get schistosomiasis?
People become infected when their skin contacts freshwater contaminated with larvae released by infected snails.
What symptoms can brain involvement cause?
In a Philippine General Hospital study, seizures were the most common symptom, followed by headache, numbness or weakness, cranial nerve problems, and swelling of the optic nerve.
Is it treatable?
Yes. Praziquantel is the standard treatment. In the Manila hospital study, 24 of 28 treated patients improved, with steroids and anticonvulsants also used.
Who is at risk in the Philippines?
The health department estimates that about 12.4 million people are at risk, with 2.7 million directly exposed, mainly in endemic provinces in the Visayas and Mindanao.
Should Americans be concerned?
The risk is very low for people without freshwater exposure in endemic regions. Travelers who develop neurological symptoms after such exposure should tell their clinician.
Published by Medicaldaily.com
