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bThe immunological mechanisms associated with protection of vaccinated rainbow trout, Oncorhynchus mykiss, against enteric redmouth disease (ERM), caused by Yersinia ruckeri, were previously elucidated by the use of gene expression methodology and immunochemical methods. That approach pointed indirectly to both humoral and cellular elements being involved in protection. The present study correlates the level of protection in rainbow trout to cellular reactions in spleen and head kidney and visualizes the processes by applying histopathological, immunohistochemical, and in situ hybridization techniques. It was shown that these cellular reactions, which were more prominent in spleen than in head kidney, were associated with the expression of immune-related genes, suggesting a Th2-like response. Y. ruckeri, as shown by in situ hybridization (ISH), was eliminated within a few days in vaccinated fish, whereas nonprotected fish still harbored bacteria for a week after infection. Vaccinated fish reestablished normal organ structure within a few days, whereas nonprotected fish showed abnormalities up to 1 month postinfection. Protection in the early phase of infection was mainly associated with the expression of genes encoding innate factors (complement factors, lysozyme, and acute phase proteins), but in the later phase of infection, increased expression of adaptive immune genes dominated. The histological approach used has shown that the cellular changes correlated with protection of vaccinated fish. They comprised transformation of resident cells into macrophage-like cells and increased occurrence of CD8␣ and IgM cells, suggesting these cells as main players in protection. Future studies should investigate the causality between these factors and protection.

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Avian Infectious coryza, a highly opportunistic respiratory tract infection caused by Avibacterium paragallinarum is now believed to be evolving as a re-emerging disease of poultry birds. Albeit adoption of strong precautionary/prophylactic measures i.e. vaccine/vaccination practice, the infection continues as complicated pattern of disease course worldwide that results in massive economic and production losses. India, being a major admirer of poultry products suffers tremendously with this insidious infectious insult every year, thus strives for some better optional measures to curtail this curse. This review article blazons some significant development(s) that took place over the period of last decade with regards to its epidemiologic spectrum, characterization of its etiologic agent and important improvement(s)/advancement(s) in its diagnostic as well as prophylactic approach (es). Although, the major achievements to identify and restrict this disease has been carried out in early 80s and 90s, however precarious nature of this organism has largely left scientific and farming community abstruse over its ambit on host specificity and geographic limitation(s). Following strong vaccinal/prophylactic measures, the causative organism(s) further acquired superlative advantages having bypassing host immune surveillance mechanisms acquired through existing vaccine components, besides violating constitutive immunity of host. The plausible reason behind such immunity exclusion is hitherto unknown, when it comes to host's response against pathogen. Resultantly, a detailed study to this effect is highly warranted to avoid further sinister in our poultry operation(s) due to Avibacterium paragallinarum infection. Most of the recent studies endeavoured to work on serovar B of Avibacterium paragallinarum organism which is quite prevalent at the moment at varied places across the globe. This warrants concerted/dedicated diagnostic techniques employing high end bio-molecular approaches for better comprehension of the disease, and to have a blue print with regard to adoption of newer therapeutic strategy towards containment of the infection for fruitful future.