This piece on treatment and follow up may give some credence to the official position,especially if he has been infected for a long period before diagnosis.
It does mention follow ups at 36 months and possible though not automatic retreatment.
http://www.snp.com.au/media/160501/schistosomiasis.pdf
TREATMENT
Praziquantel (Biltricide) 20 mg/kg bodyweight every 4 hours for
2 to 3 doses depending upon the species is recommended. In
travellers, this is likely to achieve cure rates in the order of 90%.
Tablets are scored and available as a 600 mg dose dispensed 6
per pack. In patients at risk of chronic disease, such as refugees
and migrants, it is important to be aware of complications that
may arise from chronic infection: liver fibrosis, portal hypertension
and its sequelae, and colorectal malignancy in the intestinal forms;
obstructive uropathy, superimposed bacterial infection, infertility
and possibly bladder cancer in the urinary form.
FOLLOW-UP
Follow-up Schistosomiasis serology is recommended in 12 to 36
months after treatment. Follow-up serology may differ between
immigrants and returned travellers. Travellers may show a more
rapid serological decline post-treatment due to a shorter duration of
infection and lower parasite burden. Immigrants may even show a
rise in titre within the first 6 to12 months post-treatment. Persisting
titres should not automatically justify retreatment, this should be
based on symptoms, parasite identification or eosinophilia. Viable
eggs may continue to be excreted for up to one month after
successful treatment. Non-viable and degenerate eggs can be
found in tissue biopsies for years after infection has occurred.