Neglected infectious diseases, such as schistosomiasis and leptospirosis, represent a challenge to public health, especially in rural communities with poor sanitation and contact with contaminated water. Schistosomiasis, caused by trematodes of the genus Schistosoma, and leptospirosis, a systemic bacterial zoonosis caused by Leptospira spp., are transmitted through contact with contaminated water: the former via freshwater snails, the latter via the urine of infected mammals. Both are mandatorily notifiable, and although coinfections are rare, there is a risk of endemic outbreaks when there is an environmental focus.

Five patients, three men and two women (30 to 61 years), had contact with a lagoon in a rural area, a site with previous cases of schistosomiasis and leptospirosis among relatives. Three presented nonspecific symptoms: fever, headache, skin rash, night sweats, fatigue, cervical lymphadenopathy, and plantar pain. Two were asymptomatic but were investigated due to epidemiological linkage. Tests revealed eosinophilia between 780 and 4,505/mm³, and elevated ESR and CRP. Serologies showed reactive IgM for leptospirosis in four patients and IgG in two; schistosomiasis titers were 1:64 in three cases, with progression to 1:256 in one of them. One patient presented ground-glass lesions on chest CT. Treatment included doxycycline 100 mg twice daily for 7 days in cases of leptospirosis, and praziquantel 600 mg three times daily for 2 days for schistosomiasis. One patient used amoxicillin with clavulanate. All evolved with clinical and laboratory improvement and were reported.

This report highlights the importance of epidemiological history-taking in infectious diseases. The shared exposure to the lagoon was decisive for early diagnosis, including in asymptomatic individuals. Clinical similarity between the infections requires attention to context to guide the investigation. Eosinophilia was more marked in schistosomiasis cases, while serology was essential for confirmation. Mandatory notification enabled epidemiological tracing and control measures. The positive response to treatment confirms the effectiveness of management based on well-defined clinical and epidemiological criteria.