Evaluation of live-attenuated Histomonas meleagridis isolates as vaccine candidates against wild-type challenge.

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.

Research Note: Fate and dissemination of Salmonella enterica serovar reading in turkeys at processing using an oral gavage challenge model.

This study aimed to evaluate the fate and dissemination of Salmonella Reading (SR) in turkeys using an oral gavage challenge model. One hundred twenty-eight-week-old commercial turkey hens were moved from commercial production to research facilities. Upon arrival, a combination of enrofloxacin, 10 mg/kg, and florfenicol, 20 mg/kg, were orally administered sequentially before comingled placement on fresh pine shavings. Turkeys were challenged with 108 cfu SR by oral gavage on d 4 and 7 postplacement. Subsets were subjected to simulated commercial processing on d 14 (n = 40), 21 (n = 40) and 28 (n = 32) postplacement (corresponding to 10, 11, and 12 wk of age). Stifle joint, skin, trachea, crop, lung, liver + spleen (LS), and ceca were aseptically sampled and cultured for Salmonella recovery and serotyping. SR could not be recovered from stifle joint 14 d post inoculation (PI). However, at 14 d PI, recovery of SR were: Skin 80%; crop 75%; LS 67.5%; lungs 60%; and ceca 57.5%. (P < 0.01). Interestingly, the lowest recovery of SR was observed from trachea (40%). At 21 d PI, the highest rate of positive samples to SR were observed in ceca (87.5%) and crop (67.5%). By 28 d PI, SR was only recovered from ceca (75%); crop (43.8%); lung (34.4%); and LS (21.9%). The results of this study confirms that SR is an emerging problem for the turkey industry and immediate measurements to reduce foodborne pathogens such as Salmonella should target all parts of the supply chain and consumer education about food safety.