University of Arkansas, Division of Agriculture, Poultry Science Department, Fayetteville, AR 72701, USA.
Department of Poultry Science, University of Georgia, Athens, GA 30602, USA.
Poult Sci. 2022 Mar;101(3):101656. doi: 10.1016/j.psj.2021.101656. Epub 2021 Dec 9.
Repeated serial in vitro passage of Histomonas meleagridis, the etiological agent of histomoniasis (blackhead) of turkeys, was demonstrated to markedly achieve attenuation and reduction of virulence as compared to the original wild-type isolate. Four experiments were performed to evaluate the route (oral vs. intracloacal) and age (day-of-hatch vs. d 14) for administration of attenuated H. meleagridis isolates as vaccine candidates against homologous or heterologous wild-type challenge. Attenuated H. meleagridis were developed from 2 different strains (Buford strain originating in Georgia; PHL2017 strain originating in Northwest Arkansas). Buford P80a (passage 80, assigned as isolate lineage "a" following repeated passage) was selected as the primary vaccine candidate and was evaluated in Experiments 1-3. Experiment 4 evaluated selected candidates of attenuated PHL2017 (P67, P129) and Buford (P80a, P200a, P138b, P198c) strains against Buford wild-type challenge. As has been demonstrated previously, wild-type H. meleagridis cultures administered orally after 1 day of age were not infective in the current studies, but infection with wild-type cultures could be induced orally at day-of-hatch. Infection was effectively achieved via the intracloacal route at day-of-hatch and in older turkeys (d 21, d 28-29, d 35). Intracloacal inoculation of turkeys with the attenuated passaged isolates as vaccine candidates at d 14 was shown to produce significant (P < 0.05) protection from mortality, reduction in body weight gain, as well as reduction in hepatic and cecal lesions in these experiments following challenge with either the homologous wild-type isolate or from a wild-type strain obtained years later from a geographically disparate area of the United States. Inoculation with the attenuated H. meleagridis isolates at day-of-hatch, either orally or cloacally, did not produce significant protection against subsequent wild-type challenge. While offering significant protection with minimal vaccine-related negative effects, the protection from cloacal vaccine administration was neither significantly robust nor encouraging for industry application using the methods evaluated in the present manuscript since mortalities and lesions were not completely reduced which could thereby potentially allow transmission from residual infection and shedding within a flock.
经反复多次体外传代，火鸡组织滴虫（黑头病）的病原体Histomonas meleagridis 的毒力明显减弱，与原始野生型分离株相比，其毒力显著降低。进行了四项实验，以评估减毒 H. meleagridis 分离株作为同源或异源野生型攻毒疫苗候选物的给药途径（口服 vs. 泄殖腔）和年龄（出壳日 vs. 14 日龄）。从 2 个不同的菌株（起源于佐治亚州的 Buford 株；起源于阿肯色州西北部的 PHL2017 株）中开发了减毒 H. meleagridis。Buford P80a（第 80 代传代，重复传代后指定为分离株谱系“a”）被选为主要疫苗候选物，并在实验 1-3 中进行了评估。实验 4 评估了减毒 PHL2017（P67、P129）和 Buford（P80a、P200a、P138b、P198c）菌株的候选株对 Buford 野生型攻毒的抗性。如先前所示，在当前研究中，1 日龄后口服给予野生型 H. meleagridis 培养物不具有感染性，但可在出壳日经口服诱导感染。通过泄殖腔途径在出壳日和年龄较大的火鸡（21 日龄、28-29 日龄、35 日龄）中可有效实现感染。在这些实验中，在 14 日龄时通过泄殖腔接种减毒传代分离株作为疫苗候选物，可显著（P <0.05）减轻死亡率、体重增加减少以及肝脏和盲肠病变，这些实验中使用的同源野生型分离株或来自美国地理上不同地区的多年后的野生型菌株进行攻毒。在出壳日经口或泄殖腔接种减毒 H. meleagridis 分离株，不能对随后的野生型攻毒产生显著的保护作用。虽然通过最小的疫苗相关负作用提供了显著的保护，但从泄殖腔接种疫苗的保护作用既不显著也不令人鼓舞，无法在本研究中评估的方法下用于行业应用，因为死亡率和病变并未完全减少，这可能会导致感染在鸡群内残留并继续传播。
