Surveillance of Nipah virus in Pteropus medius of Kerala state, India, 2023

Introduction

Since 2018, the Indian state of Kerala has reported four Nipah virus (NiV) disease outbreaks, raising concerns about NiV spillover from bats to the human population. Considering this, a cross-sectional study was undertaken in the Pteropus medius bat population around the Nipah virus-affected regions of Kozhikode, Kerala, India, during February, July, and September 2023.

Methods

Throat swabs, rectal swabs, and organ samples were collected from bats to test for NiV using the real-time reverse transcriptase polymerase chain reaction (RT-PCR), while serum samples were screened for anti-Nipah IgG antibodies through ELISA.

Results

An overall seroprevalence of 20.9% was observed in 272 P. medius bats tested. The throat and rectal swab samples of 321 bats were negative for NiV RNA. However, 4 of 44 P. medius bats tested positive for NiV in their liver/spleen samples. The partial N gene retrieved showed more than 99% similarity with the earlier reported NiV genome from Kerala state, India.

Discussion

The findings of the study caution that there is a spillover risk in the region and necessary precautions should be taken.

Development and evaluation of a new immunohistochemistry-based test for the detection of rabies virus neutralizing antibodies

Rabies claims about 55,000 human lives and many hundreds of thousands of livestock every year, worldwide. Despite a heavy disease burden, laboratory facilities to diagnose the infection remain scarce in most countries of the developing world where the disease is endemic. Rapid Fluorescent Focus Inhibition Test (RFFIT) and Fluorescent Antibody Virus Neutralization Test (FAVN) are the common tests done in the rabies diagnostic laboratories to detect and quantitate Rabies Virus Neutralizing Antibodies (RVNA). RFFIT is most often employed in confirming seroconversion following prophylactic vaccination, and to aid ante-mortem diagnosis in suspected cases of rabies. Though this remains one of the most sought-after diagnostic services in rabies laboratories, the requirements for expensive anti-rabies fluorochrome antibody conjugate and a fluorescent microscope restrict its performance to only a few reference laboratories. Cost-effective laboratory diagnostic methods employing affordable technology are a need of the hour in the rabies-endemic countries. In this study we have developed a new immunohistochemistry-based neutralization test and extensively evaluated it along with RFFIT. One hundred and 20 human serum samples collected after post-exposure vaccination were subjected to both the tests for determining RVNA titers. The results obtained with the new test correlated significantly with those of RFFIT. Further validation of the inter- and intra- assay precision, lower limit of quantification (LLOQ) and specificity was also performed. The best correlation between the 2 methods, however, was observed only when the RVNA concentrations in the samples were>20 IU/mL. Overall, the immunohistrochemistry-based neutralization test yielded satisfactory results. We suggest that it might serve as a cost-effective alternative to RFFIT in low-resource settings in the developing countries.

Biochemical characterization and evaluation of cytotoxicity of antistaphylococcal chimeric protein P128

BACKGROUND

Antibiotic resistant S. aureus infection is a global threat. Newer approaches are required to control this organism in the current scenario. Cell wall degrading enzymes have been proposed as antibacterial agents for human therapy. P128 is a novel antistaphylococcal chimeric protein under development against S. aureus for human use which derives its bacterial cell wall degrading catalytic endopeptidase domain from ORF56, the Phage K tail-structure associated enzyme. Lead therapeutic entities have to be extensively characterized before they are assessed in animals for preclinical safety and toxicity. P128 is effective against antibiotic resistant strains as well as against a panel of isolates of global significance. Its efficacy against S. aureus in vivo has been established in our lab. Against this background, this study describes the characterization of this protein for its biochemical properties and other attributes.

RESULTS

We evaluated the requirement or effect of divalent cations and the metal ion chelator, EDTA upon biological activity of P128. As the protein is intended for therapeutic use, we tested its activity in presence of body fluids and antibodies specific to P128. For the same reason, we used standard human cell lines to evaluate cytotoxic effects, if any.The divalent cations, calcium and magnesium at upto 25 mM and Zinc upto 2.5 mM neither inhibited nor enhanced P128 activity. Incubation of this protein with EDTA, human serum, plasma and blood also did not alter the antibacterial properties of the molecule. No inhibitory effect was observed in presence of hyper-immune sera raised against the protein. Finally, P128 did not show any cytotoxic effect on HEp2 and Vero cells at the highest concentration (5 mg/mL) tested.

CONCLUSIONS

The results presented here throw light on several properties of protein P128. Taken together, these substantiate the potential of P128 for therapeutic use against S. aureus. Further development of the protein and conduct of preclinical safety studies in animals is warranted.