The sparse data available for the longevity of specific serum IgM for diseases such as scrub typhus, murine typhus, leptospirosis, and Japanese encephalitis suggest that these immunoglobulins might be detectable for months or perhaps years.45, 46 Hence, assays based on detection of these IgM antibodies are at risk of being interpreted as mixed infection when they represent previous symptomatic or asymptomatic infection. Here, CD40LG is linked to leptospirosis.