An observational study in Leptospirosis and Jarisch Herxheimer Reaction, sponsored by Institut Pasteur. Not yet recruiting. Open to participants aged 18 Years and older. Per ClinicalTrials.gov, last updated 2026-11-03.
Sponsored by Institut Pasteur · Observational
Leptospirosis is a neglected zoonosis caused by pathogenic spirochetes of the genus *Leptospira*, occurring mainly in humid tropical and subtropical regions. With over one million cases and \~60,000 deaths annually, it is among the most dangerous bacterial zoonoses worldwide. Its nonspecific onset-fever, headache, myalgia-mimics influenza, dengue, and other acute febrile illnesses, making diagnosis difficult. Delayed antibiotic treatment can lead to severe forms (in \~10% of cases) characterized by hemorrhage and multi-organ failure. In 2023, New Caledonia reported 152 cases, with 85% hospitalized and a 2.6% mortality rate.
This study aims to characterize the human host response and improve patient management. *Leptospira* evades innate immunity, triggering a strong anti-inflammatory IL-10 response and potentially ineffective phagocytosis. However, the WHO-recommended β-lactam antibiotics induce a Jarisch-Herxheimer reaction (JHR)-an acute inflammatory response occurring within hours of treatment-in over 50% of patients (LEPJAR study, PMID:40986630), the impact of which on phagocytosis is unknown.The NEUTROLEPTO study will be conducted in New Caledonia (NC) in patients with or without leptospirosis. Clinical and biological data will be collected at the time of suspected infection and 3 hours after antibiotic administration. Specifically, immune responses will be assessed through cytokine profiling and blood cell phenotyping, as well as by transcriptome analysis of infected patients before and after antibiotic treatment.
The aim of the study is to compare the immune cell responses in the blood of patients hospitalized for leptospirosis with those of patients with another infection, before and 3 hours after antibiotic therapy.
Individuals presenting to the emergency department of the Territorial Hospital Center of New Caledonia with signs and symptoms of leptospirosis will be recruited:
-with a confirmed diagnosis of leptospirosis (Group 1),-
-with an infectious diagnosis other than leptospirosis (Group 2)
Blood and clinical data will be collected from all the participants.
25 studies on the registry are indexed under Leptospirosis; 11 are open to participants now.
This study's planned enrollment of 70 is below the median of 175 across 11 observational studies indexed under Leptospirosis.
Browse Leptospirosis studies →Institut Pasteur is the lead sponsor of 99 studies on the registry; 41 are open to participants now.
Counted across the registry records on this site, refreshed daily.
Individuals presenting at the emergency department of the Territorial Hospital Center of New Caledonia with signs and symptoms of leptospirosis:
Go through the criteria one by one — yes, no or not sure — and take the list to your doctor or the study team. Kept in this browser only.
Exclusion Criteria:
Underlined terms in the criteria open these too. Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Before you join, the study team explains what taking part involves — its purpose, what happens, the risks and possible benefits — and answers your questions, so you can decide freely. Consent is usually recorded on a form (the informed consent form, ICF) signed by you or, where the law allows, by someone legally authorised to decide for you.
You can keep asking questions during the study, you are told of new information that matters, and you can choose to leave at any time.
Informed consent
Before you join, the study team explains what taking part involves — its purpose, what happens, the risks and possible benefits — and answers your questions, so you can decide freely. Consent is usually recorded on a form (the informed consent form, ICF) signed by you or, where the law allows, by someone legally authorised to decide for you.
You can keep asking questions during the study, you are told of new information that matters, and you can choose to leave at any time.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Other: 24 ml blood sample at H0 · Other: 16 ml blood sample at H3
Other: 24 ml blood sample at H0 · Other: 16 ml blood sample at H3
24 ml blood sample at H0
16 ml blood sample at H3
to compare the immune cell responses in the blood of patients hospitalized for leptospirosis with those of patients with another acute infection (MFA), both before and 3 hours after antibiotic treatment.
Flow cytometric phenotyping of different cell populations, as well as their activation markers and intracellular cytokines and measurement of cytokines using ELISA or LUMINEX in the blood (H0 at enrollment and H3, 3 hours after antibiotic administration) of individuals suspected of having leptospirosis
Time frame: 3 years
Test certain innovative host-based strategies aimed at restoring phagocytic responses against Leptospira in the blood of patients with leptospirosis.response.
Conduct ex vivo killing assays using patient blood in the presence of preparations based on so-called "natural" immunoglobulins to test a new host-targeted therapeutic strategy against leptospirosis.
Time frame: 3 years
Describe and characterise the Leptospira spp. strain
Measurement of bacterial load by PCR of the lipl32 gene, identification of the Leptospira spp. genogroup by bacterial DNA sequencing or other molecular biology methods (PCR) and/or of the serovar by MAT, sequencing of the bacterial mRNA.
Time frame: 3 years
No study locations are listed for this record.
Plan to share: No
No publications or documents are linked to this record.
Start is estimated for Dec 2026; primary completion for Dec 2029, 36 months later.
Since we started tracking on Sep 25, 2026, the dates moved once, on Nov 3, 2026: start Jul 2026 → Dec 2026, primary completion Jul 2029 → Dec 2029 and completion Jul 2029 → Dec 2029.
Earlier changes are on the record history on ClinicalTrials.gov ↗
How these figures are worked out, and which studies are left out of them.
From the registry record's own update history. This site started tracking changes on Sep 25, 2026; for anything earlier, see the record history on ClinicalTrials.gov ↗
This study is not yet recruiting, as verified in May 2026. You cannot join it, but the record below documents what was studied.
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