Evaluation of serum prevalence of salmonella typhimurium in backyard chickens flocks, in Italy: a pilot study

Poultry are well recognized as possible carriers of different Salmonella species and Salmonellosis is a significant zoonotic disease which has a considerable economic impact for the poultry industry. The Italian Salmonellosis Control Plan (SCP) excluded ornamental and self-consumption poultry farms. A scientific EFSA report of 2018, reported that in chicken flocks the percentage of positivity S. typhimurium (S.T.) and S. typhimurium monophasic variant (S.T. mv) is 0.2%, while in laying hens is 0.3% [1]. Overall, according to EFSA reports 2019, the prevalence of Salmonella in poultry remains <1% [2]. However, considering the epidemiological situation for S.T. and S.T. mv in industrial poultry farming, the aim of this study was to verify the only serum prevalence for S.T. in backyard chickens, considering that these farms are not subject to official controls and exposure to zoonotic pathogens could be more frequent. Between December 2018 and February 2019, 24 rural farms of backyard chickens, numbered from "A" to "Z", located in 8 different regions of Italy, were examined. On a total of 971 backyard hens, 240 samples were taken (expected prevalence <5%). From each farm, blood samples from 10 laying hens, aged between 5 months and 5 years, asymptomatic and unvaccinated against Salmonella, were taken to verify the presence of specific antibodies against S.T. Serum analysis was performed in according with the O.I.E. Manual of Diagnostic Tests and Vaccines for Terrestrial Animals [3], and using a commercial Antibody ELISA Kit X-Ovoflockscreen™ kit, to confirm the slow serum agglutination in micro-method (SAL) for positive or not conclusive results. Out of 240 blood samples 231 were analyzed. Nine serum were excluded for scarcity of serum, insufficient to perform the analysis. The results shows that the positive farms for S.T. were 4/24 (A,D,P,T) (16.66%). In these farms, the percentages of positive samples were 2/10 (20%), 2/8 (25%), 1/10 (10%) and 2/8 (25%) respectively. On "A" and "T" farm, 2 serum for each were not conclusive in ELISA test. The global serum prevalence was 3.03% (7/231). Our preliminary study shows the circulation of S.T. The serological prevalence obtained is >1%, not surprising aspect in consideration of the type of poultry farms. The circulation of S.T. in these farms must be an aspect not to be overlooked, whereas some amateur farmer often consider these animals as pets and consume their eggs. Further studies, including the isolation and characterization of isolates, are necessary to obtain a more precise picture of the presence and prevalence of zoonotic Salmonella species in this exclusively hobbyist breeding sector.