The COVID-19 pandemic and the fast global spread of the disease resulted in unprecedented decline in world trade and travel. A critical priority is, therefore, to quickly develop serological diagnostic capacity and identify individuals with past exposure to SARS-CoV-2. In this study serum samples obtained from 309 persons infected by SARS-CoV-2 and 324 of healthy, uninfected individuals as well as serum from 7 COVID-19 patients with 4–7 samples each ranging between 1–92 days post first positive PCR were tested by an “in house” ELISA which detects IgM, IgA and IgG antibodies against the receptor binding domain (RBD) of SARS-CoV-2. Sensitivity of 47%, 80% and 88% and specificity of 100%, 98% and 98% in detection of IgM, IgA and IgG antibodies, respectively, were observed. IgG antibody levels against the RBD were demonstrated to be up regulated between 1–7 days after COVID-19 detection, earlier than both IgM and IgA antibodies. Study of the antibody kinetics of seven COVID 19 patients revealed that while IgG levels are high and maintained for at least 3 months, IgM and IgA levels decline after a 35–50 days following infection. Altogether, these results highlight the usefulness of the RBD based ELISA, which is both easy and cheap to prepare, to identify COVID-19 patients even at the acute phase. Most importantly our results demonstrate that measuring IgG levels alone is both sufficient and necessary to diagnose past exposure to SARS-CoV-2.

West Nile Virus (WNV) is endemic in Israel and has been the cause of several outbreaks in recent years. In 2000, a countrywide mosquito survey was established to monitor WNV activity and characterize viral genotypes in Israel. We analyzed data from 7135 pools containing 277 186 mosquitoes collected over the past 15 years and, here, report partial sequences of WNV genomes obtained from 102 of the 336 positive mosquito pools. Phylogenetic analysis demonstrated that cluster 4 and the Mediterranean and Eastern European subtypes of cluster 2 within WNV lineage 1 circulated in Israel, as did WNV lineage 2, highlighting a high genetic diversity of WNV genotypes in our region. As a major crossroads for bird migration between Africa and Eurasia and with a long history of human infection, Israel serves as a resource hub for WNV in Africa and Eurasia and provides valuable information on WNV circulation in these regions.

Serological diagnosis of Zika virus is challenging due to high crossreactivity of Zika virus with other flavivirus antibodies. Recently, a Zika NS1-based enzyme-linked immunosorbent assay (ELISA) was developed and shown to be highly specific for Zika antibody detection; however, sensitivity was evaluated for only a small number of confirmed Zika-infected patients. In this study, we measured the sensitivity and kinetics of Zika IgM and IgG antibodies using the Zika NS1-based ELISA in 105 samples from 63 returning travelers infected with Zika virus (proven by PCR or neutralization assay) from Israel, Czech Republic, Italy, Belgium, Germany, and Chile. Zika virus IgM was detected from 2 to 42 days post-symptom onset (PSO) with an overall sensitivity of 79% in the first month and 68% until 2 months PSO, while IgG antibodies were detected from 5 days to 3 years PSO with 79% sensitivity. Interestingly, significant differences in IgM sensitivity and IgM detection period were observed between Israeli and European/Chilean Zika-infected travelers, adding to the complexity of Zika infection diagnosis and suggesting that other diagnostic methods should be complemented to reduce false-negative results.

bThe current diagnosis of West Nile virus (WNV) infection is primarily based on serology, since molecular identification of WNV RNA is unreliable due to the short viremia and absence of detectable virus in cerebrospinal fluid (CSF). Recent studies have shown that WNV RNA can be detected in urine for a longer period and at higher concentrations than in plasma. In this study, we examined the presence of WNV RNA in serum, plasma, whole-blood, CSF, and urine samples obtained from patients diagnosed with acute WNV infection during an outbreak which occurred in Israel in 2015. Our results demonstrate that 33 of 38 WNV patients had detectable WNV RNA in whole blood at the time of diagnosis, a higher rate than in any of the other sample types tested. Overall, whole blood was superior to all other samples, with 86.8% sensitivity, 100% specificity, 100% positive predictive value, and 83.9% negative predictive value. Interestingly, WNV viral load in urine was higher than in whole blood, CSF, serum, and plasma despite the lower sensitivity than that of whole blood. This study establishes the utility of whole blood in the routine diagnosis of acute WNV infection and suggests that it may provide the highest sensitivity for WNV RNA detection in suspected cases.