Background Nipah virus (NiV) is 1 of 10 potential causes of imminent public health emergencies of international concern. We investigated the NiV outbreak that occurred in May 2018 in Kerala, India. Here we describe the longitudinal characteristics of cell-mediated and humoral immune responses to NiV infection during the acute and convalescent phases in 2 human survivors. Methods Serial blood samples were obtained from the only 2 survivors of the NiV outbreak in Kerala. We used flow cytometry to determine the absolute T-lymphocyte and B-lymphocyte counts and the phenotypes of both T and B cells. We also detected and quantitated the humoral immune response to NiV by virus-specific immunoglobulin M (IgM) and immunoglobulin G (IgG) enzyme-linked immunosorbent assay. Results Absolute numbers of T lymphocytes remained within normal limits throughout the period of illness studied in both survivors. However, a marked elevation of activated CD8 T cells was observed in both cases. More than 30% of total CD8 T cells expressed Ki67, indicating active proliferation. Proliferating (Ki-67+) CD8 T cells expressed high levels of granzyme B and PD-1, consistent with the profile of acute effector cells. Total B-lymphocyte, activated B-cell, and plasmablast counts were also elevated in NiV survivors. These individuals developed detectable NiV-specific IgM and IgG antibodies within a week of disease onset. Clearance of NiV RNA from blood preceded the appearance of virus-specific IgG and coincided with the peak of activated CD8 T cells. Conclusions We describe for the first time longitudinal kinetic data on the activation status of human B- and T-cell populations during acute NiV infection. While marked CD8 T-cell activation was observed with effector characteristics, activated CD4 T cells were less prominent.

Chikungunya is a mosquito-borne viral illness associated with chronic arthritic symptoms that persist for months. The IgM antibody appears within a week post any infection and declines at 2-3 months. The present study was aimed to demonstrate the presence of specific IgM antibody among chikungunya confirmed cases. Blood samples were collected from chikungunya PCR positive patients at the time of diagnosis, at 1-week, 1, 8, 10 and 12 months post infection. All acute and follow-up serum samples were evaluated for chikungunya virus-specific IgM antibodies using ELISA technique. Our findings indicate the persistence of anti-chikungunya IgM up to 10-months post-infection in a majority of chikungunya virus infected persons. Interpretation of results should be carefully done as only IgM ELISA is used to diagnose acute infection, especially post chikungunya outbreak. The presence of IgM antibody does not rule out the absence of any other diagnosis due to its persistence. Thus, we hypothesize that real-time PCR is more reliable for the detection of acute chikungunya cases in endemic areas while IgM detection may be useful in identifying exposure to this disease.

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