Chagas in Japan

Diagnosis is based on parasitological, molecular and serological tests, selected according to the phase of the infection.

Acute phase

• It includes congenital infection and reactivation; parasitaemia is high.
• Use direct parasitological methods and molecular tests (PCR).

Chronic phase

• Parasitaemia is low or undetectable; diagnosis is serological (detection of anti-T. cruzi antibodies).
• Combine two serological techniques with different principles; in non-endemic countries ELISA is usually used (ARCHITECT Chagas or a locally validated in-house ELISA in Japan).

Specific barriers in Japan

• Most patients are asymptomatic, with little contact with the health system.
• Low awareness means clinicians do not include the disease in the differential diagnosis.
• Chagas tests are not covered by the national insurance (no保険適応).

Centralised diagnosis

• The Central Analysis Department of Saitama Medical University accepts requests from doctors.
• The doctor must be treating a patient and consider the test clinically necessary.
• The test is free of charge and requests from private individuals are not accepted.

Sources: Saitama Medical University (中央検査部); Imai K. et al., Parasitol Int 2021 (ARCHITECT/ELISA validation in Japan); Guía de tratamiento farmacológico de parasitosis, JSP 2020 v10.2.

Treatment does not reverse established organ damage; the key is to diagnose and treat as early as possible.

Available drugs

• Two drugs are available: benznidazole and nifurtimox; benznidazole is the first-choice treatment.
• The drugs are not approved or marketed in Japan and are not stocked in the country.
• They can be requested individually from WHO through the responsible hospital.

Treatment duration

• The standard duration is 60 days, in line with the WHO/PAHO standard.

Who to treat

• Patients with acute or congenital infection.
• Asymptomatic patients aged ≤50 years.

Not routinely indicated

• Patients with established cardiac complications: the benefit/risk balance does not favour treatment.

Sources: Saitama Medical University; Guía de tratamiento farmacológico de parasitosis, JSP 2020 v10.2; JSTM (Yoshioka K., 2024).

Clinical follow-up

• The disease becomes chronic and may remain asymptomatic for decades before complications appear.
• Because of the risk of lethal arrhythmias and sudden death, careful and sustained outpatient follow-up is essential, with regular clinical and cardiological checks.

Response criteria

• Response criterion: serological negativisation (marker of an adequate therapeutic response).

Special populations

• In immunocompromised patients (HIV, transplant recipients, immunosuppression), watch for reactivation.

Sources: Saitama Medical University; JSTM.

Vertical transmission

• Vertical (congenital) transmission is one of the main routes of new cases in Japan, along with transfusion and transplantation.
• Japan already has documented cases of mother-to-child transmission (Imai K. et al., Emerg Infect Dis, 2014).

Screening in pregnancy

• Screen pregnant women from endemic areas (recommendation to monitor carriers).

Treatment

• Treatment is not given during pregnancy.

Newborn

• In a newborn of a reactive mother, perform direct parasitological diagnosis in the perinatal period and later serological follow-up.
• Treatment in the first year of life achieves high cure rates.

Sources: Imai K. et al., Emerg Infect Dis 2014; Saitama Medical University (future line: seroprevalence study in pregnant women).

Benefits of early treatment

• Treat as early as possible: better tolerance, fewer adverse effects and a higher chance of serological negativisation.

Who to treat

• Children and adolescents with chronic infection who meet the ≤50 years and asymptomatic criteria.
• Additional benefit in girls: reduced future congenital transmission.

Sources: Guía de tratamiento farmacológico de parasitosis, JSP 2020 v10.2; WHO/PAHO principles applied in the Japanese context.

Onset and profile by drug

• They appear mostly between 15 and 30 days after starting treatment, more frequently and intensely with older age.
• Benznidazole: mainly skin and neurological reactions.
• Nifurtimox: weight loss and digestive or psychiatric adverse effects.

Common and serious effects

• Common (mild to moderate): skin rash, digestive disorders, general symptoms (fever, arthromyalgia), headache, paraesthesias, raised transaminases, eosinophilia.
• Serious (uncommon): leukopenia/neutropenia, thrombocytopenia, Stevens-Johnson syndrome.

Management

• Symptomatic management in mild cases; discontinuation in serious cases.
• The withdrawal rate due to adverse effects is low, especially in children.

Sources: Guía de tratamiento farmacológico de parasitosis, JSP 2020 v10.2; PAHO 2018 (pharmacological reference).

Population at risk and case estimates

• Around 250,000 residents of Latin American origin, many nikkei (Japanese descendants) and their families.
• Historically ~3,000 cases, but recent data suggest much lower figures.
• Japanese Red Cross (2019): 0.016–0.02 % seropositivity in ~18,000 at-risk donations.
• Field study (Nagasaki Univ.): 1.6 % in Latin American migrants and 5.3 % in Bolivians.

Prevention of transmission

• Screening in blood banks and organ donation.

Challenges and priority lines of work

• Lack of insurance coverage for diagnostic tests.
• Low awareness among health staff.
• Language, cultural and socioeconomic barriers for migrants; information in their mother tongue and social/psychological support are recommended.
• Expansion of centres with diagnostic capacity and a seroprevalence study in pregnant women.

Sources: Iglesias Rodríguez IM. et al., Lancet Reg Health West Pac 2023; Japanese Red Cross 2019; Saitama Medical University; JSTM.