phaidra.vetmeduni.ac.at o:4834 DOI 10.1080/03079457.2025.2497814 Long-term protection of turkeys with a live clonal monoxenic Histomonas meleagridis vaccine Histomonosis, caused by the protozoan parasite Histomonas meleagridis, is a major concern in turkey production due to the lack of licenced drugs and vaccines. Despite various studies on experimental vaccination, the duration of immunity of such a vaccine remains unclear. This study evaluated the long-term efficacy of an attenuated clonal monoxenic H. meleagridis culture in turkeys, focusing on its protective effects. Day-old turkeys were vaccinated orally using a frozen vaccine culture directly, without additional multiplication, and challenged 12 weeks later. The vaccine caused no adverse clinical signs, consistent with prior studies. Instead, vaccinated birds had an improved weight gain and higher body-weight at 42 days. Vaccine uptake was confirmed by the detection of histomonad DNA in faeces starting 14 days post-vaccination, coinciding with the first sampling time point, with 60–70% of birds testing positive by 49 days. Considering all sampling time-points before the challenge, every sampled vaccinated turkey secreted histomonads at least once. Following the challenge, analysed clinical scores showed a more than 20-fold reduction in disease severity in vaccinated birds compared to controls, and survival rates were remarkably higher in the vaccinated group (90%) than in non-vaccinated controls (16%). Overall, this study supports the long-term efficacy of the attenuated H. meleagridis vaccine, providing robust protection against histomonosis, reducing severity of clinical signs and a significant reduction of mortality, organ lesions as well as parasite burden. The vaccine’s effectiveness, when administered at day-old, highlights its potential to prevent histomonosis, though challenges remain for widespread use in commercial turkey farming. eng Duration of Immunity Histomonosis Histomonas Meleagridis Vaccine Oral Vaccination Long-term Efficacy Turkey 2026-01-29T12:51:06.058Z LOMv1.0 Author BEGIN:VCARD VERSION:3.0 N:Hatfaludi;Tamas; FN:Tamas Hatfaludi X-ORCID:https://orcid.org/0000-0001-6605-9556 END:VCARD BEGIN:VCARD VERSION:3.0 N:Rezaee;Mozhgan Sharokhyan; FN:Mozhgan Sharokhyan Rezaee END:VCARD BEGIN:VCARD VERSION:3.0 N:Vlerick;Lise; FN:Lise Vlerick END:VCARD BEGIN:VCARD VERSION:3.0 N:Sulejmanovic;Tarik; FN:Tarik Sulejmanovic END:VCARD BEGIN:VCARD VERSION:3.0 N:De Gussem;Maarten; FN:Maarten De Gussem END:VCARD BEGIN:VCARD VERSION:3.0 N:Vereecken;M.; FN:M. Vereecken END:VCARD BEGIN:VCARD VERSION:3.0 N:De Gussem;Koen; FN:Koen De Gussem END:VCARD BEGIN:VCARD VERSION:3.0 N:Liebhart;Dieter; FN:Dieter Liebhart X-ORCID:https://orcid.org/0000-0003-2412-1248 END:VCARD BEGIN:VCARD VERSION:3.0 N:Hess;Michael; FN:Michael Hess X-ORCID:https://orcid.org/0000-0002-6991-0120 END:VCARD https://w3id.org/kim/hcrt/scheme https://w3id.org/kim/hcrt/text Textdokument Text LOMv1.0 yes https://creativecommons.org/licenses/by-nc-nd/4.0 application/pdf 3561010 https://phaidra.vetmeduni.ac.at/o:4834 https://phaidra.vetmeduni.ac.at/api/object/o:4834/thumbnail LOMv1.0 discipline