Application of different laboratory techniques to monitor the behaviour of a Mycoplasma synoviae vaccine (MS-H) in broiler breeders

Background

Mycoplasma synoviae (MS) is a major poultry pathogen which causes severe economic losses in all the productive sectors. The prevalence of MS in European countries has increased in the last few years, leading to greater attention to the available methods to prevent its spread. The main strategy currently applied for its containment is the development and maintenance of MS-free breeder flocks. A live MS vaccine (MS-H) obtained by mutagenizing an Australian field strain has recently been introduced in Italy. The aim of the present study was to evaluate the vaccine behaviour in broiler breeder groups at different production stages and the effectiveness of the available laboratory tests in discriminating the MS-H from a field strain.

Results

The vaccine diffused extensively through the population, shown by the wide serological response (over 80% of positive samples in RSA and 85% in ELISA), the high serological titres, the positivity of all the tracheal samples collected during the production phase by MS PCR and the positivity by cultivation from tracheal swabs at the end-point (55 weeks after vaccination). In contrast, only one swab from a sternal bursa was positive in MS PCR, while all the joint and oviduct samples were negative. There was no evidence of vertical transmission. Different genotyping techniques were used to achieve a clear classification of the MS positive samples. The vlhA and the obg gene analysis showed that most of the strains were homologous with the vaccine, but some ambiguous samples were further investigated with the multi locus sequence typing (MLST) scheme which confirmed the homology.

Conclusions

The development of a multi-technique approach to monitor vaccinated avian flocks, based both on serological and biomolecular methods, is advised as well as the use of effective genotyping techniques to analyse the MS strains circulating in high densely populated poultry areas.

Electronic supplementary material

The online version of this article (10.1186/s12917-018-1669-8) contains supplementary material, which is available to authorized users.

Viral encephalopathy and retinopathy outbreak in freshwater fish farmed in Italy

Viral encephalopathy and retinopathy (VER), otherwise known as viral nervous necrosis (VNN), is a neuropathological condition affecting > 40 species of fish. Although VER affects mainly marine fish, the disease has also been detected in certain species reared in freshwater environments. There are relatively few reports concerning the disease in freshwater species, and there is not much information on clinical signs. Nevertheless, the most common clinical findings reported from affected freshwater species are consistent with the typical signs observed in marine species. In this paper we describe the main clinical signs and the laboratory results associated with the detection of a betanodavirus in hybrid striped bass x white bass (Morone saxatilis x Morone chrysops) and largemouth bass Micropterus salmoides, reared in a freshwater environment. We also detected the virus by real-time PCR and isolated it in cell culture from a batch of pike-perch Sander lucioperca farmed in the same system.

Investigation of ornamental fish entering the EU for the presence of ranaviruses

A survey was performed on ornamental fish imported into the EU to detect viral agents belonging to the genus Ranavirus. The objective was to gain knowledge of the potential for these systemic iridoviruses to gain entry into the EU via international trade in ornamental fish. A total of 208 pooled samples, representing 753 individual fish, were tested. The samples included 13 orders and 37 families, originating from different countries and continents. Tissues from fish that died during or just after transport were collected and examined by standard virological techniques in epithelioma papulosum cyprini cells, by transmission electron microscopy and by PCR for the detection of the major capsid protein and DNA polymerase gene sequences of ranaviruses. Virus was isolated from nine fish species but ranavirus was not identified in those samples. The results suggest that ranaviruses are not highly prevalent in ornamental fish imported into the EU.

Susceptibility of black bullhead Ameiurus melas to a panel of ranavirus isolates

Ranaviruses are considered a serious threat to lower vertebrates, including fish, amphibians and reptiles. However, epidemiological data on these agents are lacking, and further investigations are needed to understand the role of carriers and to update the list of susceptible hosts. We carried out various experimental infections under controlled conditions to contribute to the current knowledge on the susceptibility of black bullhead Ameiurus melas to European catfish virus (ECV) and other ranaviruses. A panel of 7 ranavirus isolates was used to challenge duplicate groups of A. melas juveniles maintained in aquaria supplied with running dechlorinated tap water. The experiments were performed at 15 and 25 degrees C. The results confirmed the high susceptibility of A. melas to ECV infection. Furthermore, a significant mortality associated with the typical signs of systemic viral infections was observed in groups challenged with Epizootic haematopoietic necrosis virus (EHNV) at 25 degrees C, and to a lesser extent, at 15 degrees C. No significant mortality was recorded in fish challenged with European sheatfish virus (ESV), Frog virus 3 (FV3), Rana esculenta virus-like (REV-like), Bohle iridovirus (BIV) or short-finned eel virus (SERV).