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Volume 31, Number 6—June 2025

Research Letter

Usutu Virus Antibody Dynamics in Naturally Infected Blackbirds, the Netherlands, 2016–2018

Erwin de Bruin1, Jurrian van Irsel, Felicity Chandler, Robert Kohl2, Tess van de Voorde, Anne van der Linden, Fred de Boer, Marion Koopmans, Henk van der Jeugd3, and Chantal Reusken23Comments to Author 
Author affiliation: ErasmusMC, Rotterdam, the Netherlands (E. de Bruin, F. Chandler, R. Kohl, A. van der Linden, M. Koopmans, C. Reusken); Nederlands Instituut voor Ecologie, Dutch Centre for Avian Migration and Demography, Wageningen, the Netherlands (J. van Irsel, T. van de Voorde, H. van der Jeugd); Wildlife Ecology and Conservation Group, Wageningen University and Research, Wageningen (W.F. de Boer)

Main Article

Table

Summary of serologic results for USUV and WNV in a study of antibody dynamics naturally infected blackbirds, the Netherlands, 2016–2018*

Serologic result USUV
 WNV VNT No. samples
Protein microarray VNT 2016 2017 2018 Total
USUV negative <6,000 NT NT 59 249 192 500
USUV positive >6,000 >16† 4-fold <USUV VNT 3 21 26 50
WNVpositive <6,000 <16 >16 0 0 1 1
Subtotal
62
 270
 219
 551
Orthoflavivirus positive >6,000 >16 NT 0 7 9 16
>6,000 >16 equal to WNV VNT >16 equal to USUV VNT 0 0 3 3
<6,000 NT >16 0 0 2 2
Subtotal
0
 7
 14
 21
Possible orthoflavivirus >6,000 NT NT 1 3 4 8
Subtotal
1
 3
 4
 8
Total 63 280 237 580

*Serum samples were screened in a 2-tier system of protein microarray testing, followed by confirmation of positive IgG results based on VNT. Strains used for virus neutralization were WNV strain B956 and USUV isolate Africa-3 collected from a blackbird in the Netherlands in 2016. Serum was only considered confirmed for USUV antibodies when VNT USUV antibody titer was >4-fold the WNV antibody titer, and vice versa for WNV. Serum samples with a positive USUV microarray result but no conclusive confirmation by VNT were considered orthoflavivirus positive. Negative indicates absence of detectable level of specific antibodies, positive indicated presence of detectable level of specific antibodies. NT, not tested; USUV, Usutu virus; VNT, virus neutralization test; WNV, West Nile virus. †Reciprocal titers ranged from 1:16 to >1:1,024.

Main Article

1Current affiliation: Faculty of Veterinary Medicine, Utrecht University, Utrecht, the Netherlands.

2Current affiliation: Centre for Infectious Disease Control, National Institute for Public Health and the Environment, Bilthoven, the Netherlands.

3These authors contributed equally to this article.

Page created: May 08, 2025
Page updated: May 14, 2025
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