Inherent Serum Inhibition of Influenza Virus Neuraminidases

Influenza virus vaccines have been designed for human and veterinary medicine. The development for broadly protective influenza virus vaccines has propelled the vaccine field to investigate and include neuraminidase (NA) components into new vaccine formulations. The antibody-mediated protection induced by NA vaccines is quantified by inhibition of sialic acid cleavage. Non-immune inhibitors against influenza viruses naturally occur in varying proportions in sera from different species. In this brief report, the inherent ability of raw animal sera to inhibit a panel of influenza virus NA was determined. Raw sera from the same species inhibited more than 50% of influenza viruses tested from four different subtypes, but the breadth of inhibiting NA activity depended on the source of sera. Furthermore, different influenza viruses were inhibited by different sources of sera. Overall, additional studies are needed to ensure that scientific methods are consistent across studies in order to compare NA inhibition results. Through future investigation into the differences between sera from different animal species and how they influence NA inhibition assays, there can be effective development of a broadly protective influenza virus vaccines for veterinary and human use.

A Case Report of Penicillin-Tolerant Streptococcus mitis Endocarditis Chang-Hua Chen, MD, MSc, PhD

There is no clear relationship between the serum inhibition test and clinical outcome for Streptococcus mitis (S. mitis) endocarditis. We report an 84-year-old male with endocarditis caused by penicillin-tolerant S. mitis. The results for the serum inhibitory test (SIT) and serum bactericidal test (SBT) showed a trough level of SIT = 1:256 and SBT = 1:4 and a peak level of SIT ≥ 1:1024 and SBT = 1:16. In addition, the SIT/SBT ratio was 64 at peak level and more than 64 at trough level, which is compatible with penicillin-tolerant S. mitis. Following a 42-day high-dose penicillin treatment (24 M IU/day, via a continuous drip), the patient made a good recovery. In vitro inhibitory and bactericidal test results were not a valid predictor of medical treatment failure. Physicians need to continue to evaluate the surgical indications when treating patients with S. mitis endocarditis.