Abstract
Fowl cholera (FC) caused by Pasteurella multocida is among the serious infectious diseases of poultry. Currently, formalin inactivated FC (FI-FC) vaccine is widely used in Ethiopia. However, reports of the disease complaint remain higher despite the use of the vaccine. The aim of this study was to develop and evaluate gamma-irradiated mucosal FC vaccines that can be used nationally. In a vaccination-challenge experiment, the performance of gamma-irradiated P. multocida (at 1 kGy) formulated with Montanide gel/01 PR adjuvant was evaluated at different dose rates (0.5 and 0.3 ml) and routes (intranasal, intraocular, and oral), in comparison with FI-FC vaccine in chicken. Chickens received three doses of the candidate vaccine at 3-week intervals. Sera, and trachea and crop lavage were collected to assess the antibody levels using indirect and sandwich ELISAs, respectively. Challenge exposure was conducted by inoculation at 3.5×109 CFU/ml of P. multocida biotype A intranasally 2 weeks after the last immunization. Repeated measures ANOVA test and Kaplan Meier curve analysis were used to examine for statistical significance of antibody titers and survival analysis, respectively. Sera IgG and secretory IgA titers were significantly raised after second immunization (p=0.0001). Chicken survival analysis showed that intranasal and intraocular administration of the candidate vaccine at the dose of 0.3 ml resulted in 100% protection as compared to intramuscular injection of FI-FC vaccine, which conferred 85% protection (p=0.002). In conclusion, the results of this study showed that gamma-irradiated FC mucosal vaccine is safe and protective, indicating its potential use for immunization of chicken against FC.
Highlights
Poultry production contributes significantly to the livelihoods of farmers and to the national economic system
After 48 h of culturing, avian P. multocida exposed to doses more than or equivalent to 1 kGy of irradiation had fully inhibited replication, and no growth was seen (Figure 2)
Chickens vaccinated with 0.9 kGy gamma-irradiated candidate vaccine had higher levels of antibodies as compared to the remaining groups (p=0.04)
Summary
Poultry production contributes significantly to the livelihoods of farmers and to the national economic system It is hampered by various factors, including poor husbandry practices and poultry diseases [1]. Despite the contribution by the locally produced formalin-killed FC vaccine in reducing the disease burden, FC remains to be a big challenge to the poultry sector in the country. This in part can be explained by the fact that the current used formalin-inactivated FC vaccine produced by the National Veterinary Institute (NVI) confers a short duration of protection [4]. Owing to its nature of being inactivated parenteral preparation, the vaccine is expected to be a poor inducer of mucosal immunity, which is the desired protective immunity against mucosal pathogens such as avian Pasteurella [5]
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