Marco Rozas Serri

Brazil is one of the world’s leading producers of Nile tilapia, Oreochromis niloticus. However, the industry faces a major challenge in terms of infectious diseases, as at least five new pathogens have been formally described in the last five years. Aeromonas species are Gram-negative anaerobic bacteria that are often described as fish pathogens causing Motile Aeromonas Septicemia (MAS). In late December 2022, an epidemic outbreak was reported in farmed Nile tilapia in the state of São Paulo, Brazil, characterized by clinical signs and gross pathology suggestive of MAS. The objective of this study was to isolate, identify, and characterize in vitro and in vivo the causative agent of this epidemic outbreak. The bacterial isolates were identified as Aeromonas veronii based on the homology of 16S rRNA (99.9%), gyrB (98.9%), and the rpoB gene (99.1%). A. veronii showed susceptibility only to florfenicol, while it was resistant to the other three antimicrobials tested, oxytetracycline, e...

The recent description of Amoebic Gill Disease (AGD) and Neoparamoeba perurans in Atlantic salmon (Salmo salar) farmed in Chile has necessitated the development of more reliable and sensitive diag- nostic tests. Final diagnosis of infection is normally confirmed by histology. However, the correla- tion between gross gill lesions and histological lesions is generally unclear. In the current study, moderate concordance level (k=0.5319) between gross pathology and histology was observed. The sensitivity and specificity of gross pathology was 77.91% and 71.05%, respectively. Neoparamoeba spp. are considered morphologically indistinguishable therefore by using histopathology limits the capacity to characterise the causative agent and it can be time consuming. We developed a PCR assay to amplify the N. perurans 18S rRNA gene from gill clinical samples of AGD-affected fish. High concordance level (k=0.95) between PCR and histological examination was observed. The sensitivity and specificit...

The mission of veterinary clinical pathology is to support the diagnostic process by using tests to measure different blood biomarkers to support decision making about farmed fish health and welfare. The objective of this study is to provide reference intervals (RIs) for 44 key hematological, blood biochemistry, blood gasometry and hormones biomarkers for the three most economically important farmed salmonid species in Chile (Atlantic salmon, coho salmon and rainbow trout) during the freshwater (presmolt and smolt age range) and seawater stages (post-smolt and adult age range). Our results confirmed that the concentration or activity of most blood biomarkers depend on the salmonid species, age range and/or the interaction between them, and they are often biologically related to each other. Erythogram and leukogram profiles revealed a similar distribution in rainbow trout and coho salmon, but those in Atlantic salmon were significantly different. While the activity of the most clinic...

Piscirickettsiosis (SRS) is the most prevalent bacterial disease in Chilean salmon aquaculture and is responsible for high economic losses. The aim of this study was to comparatively characterize the pathogenesis of SRS in post-smolt Atlantic salmon during the early and late stages of infection with Piscirickettsia salmonis LF-89-like (PS-LF-89) and EM-90-like (PS-EM-90) using a cohabitation challenge. The pathogenesis of cohabitant fish infected with the two isolates was relatively different due to cohabitant fish infected with PS-EM-90 showing higher cumulative mortality and shorter time until death compared with PS-LF-89 fish. PS-LF-89 caused an SRS infection characterized by kidney and liver lesions, whereas PS-EM-90 caused systemic and haemorrhagic disease characterized by kidney, liver, heart, brain, skeletal muscle and intestine lesions. Decreased serum concentration of total proteins and albumin as well as increased serum ALT, AST and creatinine levels in fish infected with both isolates confirmed that changes in liver and kidney function occurred during infection. Tissue damage, expressed as an SRS histoscore, showed a strong positive correlation with the bacterial load expressed as abundance of P. salmonis 16S rRNA transcripts in the livers and kidneys of fish affected with either isolate, but the correlation was significantly higher in fish infected with PS-EM-90. The results contribute to improving the understanding of the bacteria-host interaction.

Veterinary clinical pathology is a specialization of veterinary medicine that is dedicated to diagnostic support using laboratory tests on the blood and other body fluids of animals, including fish, providing necessary tools for decision-making in the diagnostic plan, treatment, control and prognosis of the population of animals being farmed. In this way, clinical laboratory tests are a fundamental tool in aquatic animal medicine, since they support both the diagnosis and the prognosis of farmed fish and their treatment. The objective of this Manual is to contribute to the knowledge, identification and interpretation of the most widely used clinical laboratory tests in salmon farming and to support the clinical diagnosis of our colleagues who daily develop their profession in aquatic animal medicine. In addition to the theoretical and practical content, this Manual describes the reference intervals of indicators of hematology, clinical biochemistry, blood gasometry and hormones for ...

The function of the immune system of fish is equivalent to that of other vertebrates: resistance against diseases. However, the absence of bone marrow and lymph nodes is one of the main characteristics of the immune system in teleost fish. The cells and effector molecules of innate immunity go to the site of infection, producing an inflammatory response. The immune big bang, precisely from the lineage of teleost fish, consisted of the appearance of adaptive immunity.

Abstract Global production of farmed salmon is increasingly threatened by emerging infectious diseases. Piscirickettsiosis or Salmonid Rickettsial Septicemia (SRS), a disease caused by the bacterium Piscirickettsia salmonis, is the major responsible for the overall disease-specific mortalities in the Chilean salmon industry. In this study, we applied a structured expert elicitation process to identify risk and protective factors associated with severe outbreaks of SRS during a production cycle. We used a qualitative based-expert approach to calculate risk estimators for ten risk factors and seven protective factors. In the expert elicitation process, each participant independently estimated factors in two rounds. Between the first and second round, we facilitated a workshop among experts to discuss preliminary results. As a result, the inter-expert variation of the experts' estimates was systematically reduced. Our results are concordant with preliminary studies about risk factors for SRS. Importantly, we identified novel factors that may be associated to an increased risk for severe SRS outbreaks, such as fouling of cages, density of farms in neighborhoods, presence of sea lions and early mature salmonids. Novel factors that appear to reduce the risk of severe outbreaks of SRS were synchronized farm rest periods, opportune diagnosis and necropsy training. Using these results, we propose an intervention model to provide better information for strategic decision making.

Piscirickettsiosis is the main bacterial disease affecting the Chilean salmon farming industry and is responsible for high economic losses. The development of effective strategies to control piscirickettsiosis has been limited in part by insufficient knowledge of the host response. The aim of this study was to use RNA sequencing to describe the transcriptional profiles of the responses of post-smolt Atlantic salmon infected with LF-89-like or EM-90-like Piscirickettsia salmonis. Enrichment and pathway analyses of the differentially expressed genes revealed several central signatures following infection, including positive regulation of DC-SIGN and TLR5 signalling, which converged at the NF-κB level to modulate the pro-inflammatory cytokine response, particularly in the PS-EM-90-infected fish. P. salmonis induced an IFN-inducible response (e.g., IRF-1 and GBP-1) but inhibited the humoral and cell-mediated immune responses. P. salmonis induced significant cytoskeletal reorganization b...

The recent report of amoebic gill disease (AGD) and of Neoparamoeba perurans in Chile has made it necessary to develop practical tools that will be useful for carrying out epidemiological studies. N. perurans. The prevalence of AGD in At-lantic salmon was 55.7% (29/52 farms) and the epidemic curve was observed between May 2007 300 g reared in Los Lagos Region during summer and autumn season showed 3.7 (p=0.0004), 4.2 (p=0.0178) and 6.2 (p=0.0031) times greater risk to be AGD positive, respectively. The reduction of Atlantic salmon biomass reared in Chile closely related with ISA crisis could considerably have increased the infection pressure of N. perurans to rainbow trout (63.2%, 12/19 farms) and coho salmon (90.9%, 10/11 farms).

Costs of diagnostic testing including sample collection, sampling frequency and sample size are an important consideration in the evaluation of the economic feasibility of alternative surveillance strategies for detection of infectious diseases in aquatic animals. In Chile, Piscirickettsia salmonis is the primary reason for antibiotic treatments in farmed Atlantic salmon. In 2012, a surveillance and control programme for piscirickettsiosis was established with an overall goal of reducing antibiotic use. The present study estimated the cost-effectiveness of different sampling frequencies and sample sizes to achieve at least 95% confidence of early detection of P. salmonis at the netpen and farm levels using a validated qPCR test. We developed a stochastic model that incorporated variability in test accuracy, within-pen prevalence and sampling costs. Our findings indicated that the current piscirickettsiosis surveillance programme based on risk-based sampling of five moribund or dead ...

SUMMARY Neospora caninum is a protozoan parasite whose infection has been detected in canine, bovine and others species around the world. In Chile, the presence of the disease has been already demonstrated in cows of the IX Region of the country. In the present ...

Early detection of piscirickettsiosis is an important purpose of government- and industry-based surveillance for the disease in Atlantic salmon farms in Chile. Real-time qPCRs are currently used for surveillance because bacterial isolation is inadequately sensitive or rapid enough for routine use. Since no perfect tests exist, we used Bayesian latent class models to estimate diagnostic sensitivity (DSe) and specificity (DSp) of qPCR and culture using separate two-test, single-population models for three farms (n = 148, 151, 44). Informative priors were used for DSp (culture (beta(999,1); qPCR (beta(98,2)), and flat priors (beta 1,1) for DSe and prevalence. Models were run for liver and kidney tissues combined and separately, based on the presence of selected gross-pathological signs. Across all models, qPCR DSe was 5- to 30-fold greater than for culture. Combined-tissue qPCR median DSe was highest in Farm 3 (sampled during P. salmonis outbreak (DSe = 97.6%)) versus Farm 1 (DSe = 85....

Entre marzo y mayo de 2005 se analizaron mediante examen parasitologico un total de 829 muestras de peces salmonidos cultivados intensivamente en Chile. El laboratorio SGS Aquatic Health examino 619 muestras (74,67%), el Servicio Nacional de Pesca (Sernapesca) inspecciono 100 ejemplares (12,06%), el Instituto Tecnologico del Salmon (Intesal), analizo 80 muestras (9,65%) y la Universidad Federal Rural de Rio de Janeiro, Brasil (UFRRJ), examino 30 muestras (3,62%). Para la deteccion de Diphyllobothrium spp. en musculatura y visceras de salmonidos, se utilizo la plataforma de transparentado o Candling Table. Las especies salmonideas analizadas correspondieron a Trucha arco iris, Oncorhynchus mykiss, 100 procedentes de planta de proceso y 28 procedentes de centro de cultivo de diversas areas geograficas, y Salmon del Atlantico, Salmo salar, 457 procedentes de centros de cultivo y 214 procedentes de planta de proceso. Ademas, se chequearon muestras de grupos de peces enviados para certif...

Piscirickettsiosis (SRS), caused by Piscirickettsia salmonis, is the main infectious disease that affects farmed Atlantic salmon in Chile. Currently, the official surveillance and control plan for SRS in Chile is based only on the detection of P. salmonis, but neither of its genogroups (LF-89-like and EM-90-like) are included. Surveillance at the genogroup level is essential not only for defining and evaluating the vaccination strategy against SRS, but it is also of utmost importance for early diagnosis, clinical prognosis in the field, treatment, and control of the disease. The objectives of this study were to characterize the spatio-temporal distribution of P. salmonis genogroups using genogroup-specific real-time probe-based polymerase chain reaction (qPCR) to discriminate between LF-89-like and EM-90-like within and between seawater farms, individual fish, and tissues/organs during early infection in Atlantic salmon under field conditions. The spatio-temporal distribution of LF-...