Pathogenesis of West Nile virus in domestic geese in Germany Cora M. Holicki1 , Hannah Reemtsma1 , Christine Fast1 , Friederike Michel1,2 , Felicitas Bergmann1 , Martin Eiden1 , Martin H. Groschup1 , Ute Ziegler1 1) Institute of Novel and Emerging Infectious Diseases, Friedrich-Loeffler-Institut, Greifswald-Insel Riems, Germany 2) Landesuntersuchungsanstalt für das Gesundheits- und Veterinärwesen Sachsen, Dresden, Germany Corresponding author: cora.holicki@fli.de
The first two authors contributed equally. Since its introduction into Germany in 2018, West Nile virus (WNV) has become an endemic mosquitoborne flavivirus with annually reoccurring outbreaks throughout the avifauna. With its vast vector and host range, WNV can be transmitted by numerous mosquito species and equine as well as human infections are becoming increasingly frequent. On a global scale, domestic waterfowl has repeatedly been described as a possible amplifying host for WNV and outbreaks with high mortality rates have occurred in Israel, United States of America, Canada, and Hungary. The question, however, persists: What role does free-ranging domestic waterfowl, such as geese, play in the transmission of WNV throughout Germany? To investigate the pathogenesis in waterfowl, domestic geese (juvenile; 3-week-old) were infected via a subcutaneous needle injection either with a lineage 1 strain from Italy (GenBank accession no. HM991273/HM641225) or a lineage 2 strain isolated in Germany (GenBank accession no. MH924836). Subsequently, the birds were monitored daily for clinical signs and blood and swab samples as well as body weights were collected at set time points. Genome virus and antibody loads were quantified via RT-qPCR and ELISA and VNT, respectively. Depending on the experiment, the geese were either all euthanized 21 days post infection (dpi) or throughout the experiment at various time points (3, 6, 10, 14, and 21 dpi), followed by a subsequent pathological examination. Juvenile geese were susceptible to a WNV infection and viral loads in the blood, swabs, and tissues of the birds were similar independent of the virus strain. All geese developed viremia levels that peaked 2 or 3 dpi, shed virus from 2 to 7 or 8 dpi, and rapidly seroconverted. At 21 dpi, histological lesions were confined to the brain (encephalitis) and heart (myocarditis) and low genome loads were only isolated from brain tissues. The only observed difference in the pathogenesis between the two European strains was linked to the clinical signs; these were more frequent with an earlier onset after an infection with the German lineage 2 strain. Two geese, however, stood out: One goose developed a severe clinical manifestation after infection with the German WNV lineage 2 strain (i.e., was highly susceptible) and had to be euthanized. Another goose developed a delayed course of infection after inoculation with the Italian WNV lineage 1 strain with a later onset of viremia and viral shedding. In conclusion, geese are susceptible to WNV with only minor, if any, differences in pathogenesis between an Italian WNV Lineage 1 and a German WNV Lineage 2 strain. Even though high susceptibility could be observed in individual cases, geese in general are less susceptible than for example passerine species and do not succumb to an infection with European WNV strains. The majority of infected geese produce viremia levels that are too low to transmit the virus to mosquitoes and, therefore, probably do not constitute as primary amplifying hosts for WNV. Part of the experiments are already published: Holicki, C.M.; Michel, F.; Vasi?, A.; Fast, C.; Eiden, M.; R?ileanu, C.; Kampen, H.; Werner, D.; Groschup, M.H.; Ziegler, U. Pathogenicity of West Nile Virus Lineage 1 to German Poultry. Vaccines 2020, 8, 507. https://doi.org/10.3390/vaccines8030507
52