Frequently Asked Questions
Consult the Network's list of frequently asked questions, with brief answers prepared by the clinical committee.
Go to FAQChagas in Argentina
Clinical care guide based on current protocols for the diagnosis, treatment and follow-up of Chagas disease.
Diagnosis
Summary
Acute phase
High parasitaemia, detectable by direct methods:
- Direct parasitological concentration methods.
- PCR.
- Seroconversion, between two samples 30–90 days apart.
Chronic phase
Parasitaemia undetectable by direct methods. Diagnosis is serological:
- At least two serological reactions based on different principles are required.
- Both tests must detect different antibodies on the same serum sample.
- Include at least one high-sensitivity technique (ELISA or IFA).
- The result is definitive when both tests agree.
- If they are discordant, perform a third test or refer to a reference centre.
Congenital
- Every pregnant woman must be tested with two simultaneous serological tests (Law 26.281).
Target-organ assessment in the chronic phase
To classify the patient by clinical form, the minimum test set includes:
- ECG in every patient (regardless of age or symptoms).
- Two-dimensional echocardiogram and chest X-ray in adolescents and adults.
- Symptom-directed tests when cardiac or digestive involvement is suspected.
Acute T. cruzi infection is a Notifiable Event to the SNVS within 24 h.
Diagnostic algorithm
Step 1 — Suspicion and route triage
With an epidemiological history (endemic area, infected mother, transfusion, transplant, laboratory accident) or a compatible clinical picture: determine the likely phase and route in order to choose the method.
Acute phase
High parasitaemia
Congenital Chagas
Newborn of a reactive mother
Chronic phase
Undetectable parasitaemia
Step 2A — Acute phase: direct parasitological diagnosis
Concentration methods, from least to most complex:
Fresh smear Microhaematocrit Microtube micromethod Strout
POSITIVE → confirms acute phase: TREAT + notify SNVS (24 h)
NEGATIVE with high suspicion: PCR (higher-complexity centres) · seroconversion (2 samples, 30–90 days) · CSF if neurological symptoms · biopsy of lesions.
Step 2B — Congenital Chagas
MOTHER WITH REACTIVE SEROLOGY (2 techniques)
↓
NEWBORN: microhaematocrit (perinatal; valid up to the 3rd–4th month)
Parasitaemia (+) → INFECTED → TREATMENT
Parasitaemia (–) → serology by 2 techniques from 10 months of age
Serology (+) → INFECTED → TREATMENT
Serology (–) → not infected: discharge from follow-up
Before 10 months of age serology is not valid, because maternal antibodies may persist.
Step 2C — Chronic phase: serological diagnosis
2 serological reactions based on different principles, on the same serum sample (≥1 of high sensitivity: ELISA or IFA; others: IHA, particle agglutination).
Both (+) → chronic infection confirmed
Discordant → third test or referral to a reference centre
Both (–) → infection ruled out
Step 3 — Target-organ assessment and clinical classification
History + physical examination + minimum test set: ECG (everyone) · 2D echocardiogram + chest X-ray (adolescents and adults).
No findings and no symptoms → chronic Chagas without demonstrated pathology
Cardiological findings → Holter, exercise test, tilt test, electrophysiological study
Digestive symptoms (dysphagia, megacolon…) → oesophageal series, barium enema
Chronic Chagas WITH demonstrated pathology (cardiac and/or digestive — they may coexist)
Additional stratification (chronic phase with pathology)
- Kuschnir stages (0 to III): based on ECG, chest X-ray and heart failure.
- Rassi score: risk of cardiac mortality (low / intermediate / high).
Cross-cutting considerations
- PCR may be positive in both acute and chronic infection → it does not distinguish the phase on its own.
- In immunosuppressed patients, serology may give false non-reactive results → support with parasitological methods/PCR.
- After treatment, serology may remain reactive for years without implying treatment failure.
Source: Guía para el diagnóstico y el tratamiento de la enfermedad de Chagas — clinical team guide, 3rd edition (2018). Ministerio de Salud y Desarrollo Social de la Nación, Argentina (figures 2 and 3; sections 3.1.3, 3.1.6 and 3.2.2).
Available diagnostic methods
Direct parasitological methods (acute phase / congenital)
They detect the parasite in blood; listed from least to most complex:
- Fresh smear
- Microhaematocrit (micromethod with capillaries)
- Microtube micromethod
- Strout
Molecular methods
- PCR (polymerase chain reaction) — available at higher-complexity centres. It may be positive in both the acute and the chronic phase.
Serological methods (chronic phase / screening)
They detect anti-T. cruzi antibodies (IgG)
- ELISA (enzyme immunoassay) — high sensitivity
- IFA (indirect immunofluorescence) — high sensitivity
- IHA (indirect haemagglutination)
- Particle agglutination
Treatment
Summary
Regimens and doses
- Benznidazole 5–10 mg/kg/day, maximum 300 mg/day.
- Nifurtimox 8–20 mg/kg/day according to weight.
- Standard duration: 60 days (30 days is the acceptable minimum in case of intolerance).
Who to treat
Clear indication to treat:
- Acute phase of any origin.
- Reactivation in immunocompromised patients.
- Chronic phase in people under 19 and women of childbearing age who are not pregnant.
Contraindications and precautions
Do not treat:
- Pregnancy.
- Severe renal or hepatic failure.
- Pre-existing severe neurological disorders.
Where to treat
- Management preferably at the first level of care, with periodic supervision.
Benznidazole treatment regimen
Presentation
Scored tablets of 12.5 / 50 / 100 mg.
Dose
- All ages: 5–10 mg/kg/day
- Divided into 2 daily doses (every 12 h), after meals
- Maximum dose: 300 mg/day
Duration
- 60 days (acceptable minimum: 30 days in case of intolerance)
Monitoring during treatment
- Clinical: 7 days after starting, then fortnightly until the end
- Laboratory (full blood count, urea/creatinine, liver panel): before treatment, during treatment (day 15–20) and if adverse events occur
Characteristic adverse events
- Skin rash (hypersensitivity dermatopathy, the main effect)
- Stevens-Johnson syndrome (severe, uncommon)
- Peripheral polyneuropathy (late, dose-dependent)
- Raised transaminases, eosinophilia, bone marrow suppression
Special considerations
- Breastfeeding: not contraindicated (milk concentrations pose no risk to the infant)
- Low-fat, hypoallergenic diet; complete abstinence from alcohol; avoid prolonged sun exposure
Nifurtimox treatment regimen
Presentation
Scored tablets of 120 mg.
Dose (by weight) — 3 daily doses (every 8 h), after meals
- < 40 kg; treatment: 10–20 mg/kg/day
- 40–60 kg; treatment: 12.5–15 mg/kg/day
- > 60 kg; treatment: 8–10 mg/kg/day (max. 720 mg/day)
- Adults < 60 kg: calculate using the adult dose, not the adolescent dose.
- Infants who cannot swallow tablets: crush and mix with a small portion of food.
Duration
- 60 days (acceptable minimum: 30 days in case of intolerance)
Monitoring during treatment
- Clinical: weekly during the first month, then fortnightly until the end
- Laboratory (full blood count, urea/creatinine, liver panel): before treatment, during treatment (day 15–20) and if adverse events occur
Characteristic adverse events
- Digestive disorders (nausea, vomiting, diarrhoea — more frequent than with benznidazole)
- CNS neurotoxicity (irritability, dizziness, anorexia, weight loss)
- In the first year of life it may cause stagnation of weight gain (does not require discontinuation)
Special considerations
- Do not drive or operate precision machinery during treatment
- Low-fat, hypoallergenic diet; complete abstinence from alcohol; avoid prolonged sun exposure
Follow-up
Summary
Acute phase
- Direct parasitological monitoring on days 15–20 (it should become negative).
- Serology (IgG) at the end and at 6, 12, 24 and 48 months.
Chronic phase
- Annual clinical and serological follow-up.
- Response criterion: sustained fall in titres and serological negativisation (earlier the shorter the time since infection).
- Treatment failure is demonstrated only by detection of the parasite.
- Quantitative serology with an ELISA reader (not visual reading).
Pregnancy and Congenital Chagas
Summary
Pregnant woman
- Mandatory screening with 2 simultaneous serological tests (Law 26.281).
- Do not treat during pregnancy.
- Do not perform radiological studies.
- Breastfeeding is not contraindicated.
Newborn
- Parasitological micromethod in the perinatal period, in the newborn of a reactive mother (valid up to the 3rd–4th month).
- If negative → serology by 2 techniques from 10 months.
- If confirmed → treatment (cure >90 % in the first year of life).
Pediatrics
Summary
Who to treat
- Indication to treat in every child or adolescent <19 years with chronic infection.
Treatment
- Treat as early as possible: better tolerance, fewer adverse effects and a higher response rate (high rate of negative seroconversion).
- In endemic areas, coordinate with vector control.
- Additional benefit: reduction of future congenital transmission.
Adverse Reactions
Summary
Frequency and presentation
They appear mostly between days 15 and 30; frequency and intensity increase with age.
- Frequent (mild to moderate): skin rash (benznidazole), digestive disorders (more with nifurtimox), general symptoms (fever, arthromyalgia), neurotoxicity (headache, irritability, paraesthesias), raised transaminases, eosinophilia.
- Serious (uncommon): leucopenia/neutropenia <2500/mm³, thrombocytopenia, Stevens-Johnson syndrome (benznidazole).
Management
- Mild: symptomatic treatment and, if needed, transient dose reduction.
- Severe or recurrent: discontinuation.
- Notify every adverse event to the National Pharmacovigilance System (ANMAT).
Surveillance
Summary
Notification
- The legal framework includes Law 15.465 (notifiable events), Law 26.281, Law 26.279 and Law 22.990 (p. 44).
- Vector-borne acute Chagas disease: compulsory individual notification within 24 h through SNVS 2.0 (pp. 44-45).
- Acute Chagas disease by other transmission routes and congenital Chagas disease: compulsory individual notification (pp. 44-45).
- Chagas disease in pregnant women: individual and aggregated notification (p. 45).
- Chronic Chagas disease in people under 19: individual notification (p. 45).
- Chronic Chagas disease in blood banks and population studies: individual and aggregated notification (p. 45).
- Notification is considered complete when the case is registered in SNVS 2.0 (p. 44).
- Registering treatment follow-up in SNVS 2.0 does not make it a notifiable event (p. 45).
Pharmacovigilance
- Notify every pregnant woman who has received trypanocidal medication to the Línea Salud Fetal (0800 444 2111) (p. 46).
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