Experimental infection by Yersinia ruckeri O1 biotype 2 induces brain lesions and neurological signs in rainbow trout (Oncorhynchus mykiss)

Abstract

Pathological manifestations in rainbow trout (Oncorhynchus mykiss) following experimental waterborne infection with Yersinia ruckeri serotype O1 biotype 2 (strain 07111224) were investigated. Rainbow trout were exposed to 8 × 10 CFU/ml of Y. ruckeri by bath for 6 hr, and mortality was then monitored for 22 days post-infection (dpi). Organs were sampled at 3 dpi and also from moribund fish showing signs of severe systemic infection such as bleeding, exophthalmia or erratic swimming behaviour. Y. ruckeri was observed in the meninges and diencephalon of the brain, and lamina propria of olfactory organ at 3 dpi. At 12 dpi, Y. ruckeri had spread throughout the brain including cranial connective tissues and ventricles and the infection was associated with haemorrhages and an infiltration with leucocytes. Y. ruckeri infection and associated with leucocyte infiltration were observed at 13 dpi. In conclusion, Y. ruckeri strain 07111224 causes encephalitis in the acute phase of infection, which could explain why Y. ruckeri-affected fish show exophthalmia and erratic swimming known as signs of ERM.

Evaluation of the efficacy of enrofloxacin in rainbow trout (Oncorhynchus mykiss) following experimental challenge with Yersinia ruckeri

“…Indeed, significantly greater virulence was demonstrated between different isolates of Y. ruckeri in trout following challenge by injection compared to a more natural exposure route (bath challenge) 7 . However, only the injection route ensures high inter‐individual reproducibility of the disease, which is essential to compare different dosing regimens 8 . Therefore, it is likely that mortality would have been lower with natural infection.…”

“…7 However, only the injection route ensures high inter-individual reproducibility of the disease, which is essential to compare different dosing regimens. 8 Therefore, it is likely that mortality would have been lower with natural infection.…”

The Nasal Epithelium as a Route of Infection and Clinical Signs Changes, in Rainbow Trout (Oncorhynchus mykiss) Fingerlings Infected with Aeromonas spp

“…On the other hand, the medulla oblongata participates in progressive hearing loss, in balance disorders and in the feeding role of fish [33]. Strom et al [16] demonstrated that experimental infection with Yersinia ruckeri O1 biotype 2 causes lesions in the nasal epithelium and nervous system of fish infected via an immersion bath; this shows that bacterial pathogenesis begins with direct contact of the pathogen and the nasal epithelium close to the nervous system, causing problems in coordination and abnormal behavior. In the control group, the presence of congestion in the nasal epithelium was observed in two small fingerlings, because the hierarchy behavior of trout at feeding or the social status in the aquarium cause injuries in some subordinated rainbow trout; this induces stress by the biogenesis of cortisol [34].…”

“…Currently, the immunization of fish against Aeromonas is carried out by intraperitoneal injection or by immersion bath [6]. Recently, the nasal route of Yersinia ruckeri was demonstrated as an entry point for bacteria to establish, infect and spread through the nervous system, which in turn causes erratic swimming and exophthalmia [16]. This suggests that pathogenic and virulent bacteria can cause nervous problems that affect behavior.…”