Enteric Septicemia Resistance in Blue Catfish and Three Channel Catfish Strains

Abstract

Seven full-sib families in each of three strains of channel catfish Ictalurus punctatus (mean weight, 10.7 g; SD, 2.6 g) and one family of blue catfish I. furcatus (mean, 10.9 g; SD, 0.4 g) were challenged by immersion with the bacterium Edwardsiella ictaluri, the causative agent of enteric septicemia, to evaluate variation in disease resistance. Blue catfish were resistant to infection and had only 0.7% mortality. Significant (P < 0.001) variation in channel catfish resistance was found among strains, families, and body weights. Red River strain channel catfish were the most resistant (14.9% mortality), followed by Mississippi-select fish (67.1%) and Mississippi-normal fish (72.3%). Mean family mortality of channel catfish ranged from 1.3% in a Red River family to 95.3% in a Mississippi-select family. Although weight had a significant effect on survival, the regression slope of survival on weight was ?0.10 (SE, 0.02). Sources of variation in channel catfish mortality adjusted for weight were 67.3% from strains, 29.7% from families, and 3.0% from replicate tanks. The mechanism for differential resistance presently is unknown. Results indicate considerable potential for reducing disease losses by using E. ictaluri-resistant catfish strains in aquaculture and for genetic improvement in resistance via selective breeding programs.     

Lack of Hemocyte Chemiluminescence Stimulation by Perkinsus marinus in Eastern Oysters Crassostrea virginica with Dermo Disease

Abstract

Phagocytosis of zymosan A particles by hemocytes of eastern oyster Crassostrea virginica stimulates the production of reactive oxygen species (ROS), which are easily quantified by luminol-augmented chemiluminescence (CL). Antimicrobial defense mechanisms of hemocytes may involve the activity of cytotoxic ROS. The CL response to phagocytosis of zymosan by hemocytes from C. virginica with advanced Perkinsus marinus infections is more elevated than that produced by zymosan in cells from uninfected oysters. This effect is perhaps akin to macrophage activation. Phagocytosis of P. marinus cells by hemocytes withdrawn from uninfected oysters produced no detectable CL response. Hemocytes withdrawn from oysters with P. marinus infections ranging from light to heavy were evaluated for CL responses after phagocytosis of zymosan or P. marinus. Increases in CL stimulation by zymosan were seen as the intensity of infection increased. Despite avid phagocytosis of P. marinus, CL activity of the hemocytes was not seen, regardless of the level of infection of the host. Lack of hemocytic ROS stimulation by ingestion of P. marinus cells may contribute to in vivo survival of this parasite.     

An Investigation of the Pathology Associated with Mass Mortality Events in the Cultured Japanese Pearl Oyster Pinctada fucata martensii at Four Farms in Western Japan

Abstract

The epidemiological and histopathological characteristics of the mass mortality of cultured Japanese pearl oysters Pinctada fucata martensii were investigated. Rearing experiments with Japanese pearl oysters in farms revealed that the mass mortality occurs as a regular annual event in particular farms in western Japan. Diseased oysters had marked atrophy and red-brown discoloration of the soft parts of the body. Light microscopy revealed that the epithelia of the stomach, the ducts of the digestive diverticula (DD), and the DD themselves showed marked blebbing and necrosis to varying degrees during earlier stages of the disease. At advanced stages, muscle fibers of the adductor muscle, heart, mantle, and other parts of the body and the connective tissues of various organs involving the vascular system also exhibited considerable atrophy and necrosis. There were no remarkable changes in the branchial and pallial epithelia. No viral, bacterial, mycotic, or parasitic causative organisms were found in diseased oysters. The results of a case study of mass mortality at one farm suggested that there is some causal relationship between outbreaks of this disease and the existence of neighboring fish farms. These findings suggest that the mass mortality is not due to an infectious disease. We discuss pathological features and possible causes of this disease.     

Spleen Index and Mannose-Binding Lectin Levels in Four Channel Catfish Families Exhibiting Different Susceptibilities to Flavobacterium columnare and Edwardsiella ictaluri

Abstract

Edwardsiella ictaluri and Flavobacterium columnare are two bacterial pathogens that affect channel catfish Ictalurus punctatus aquaculture. At the Catfish Genetics Research Unit (U.S. Department of Agriculture, Agricultural Research Service), some progress has been made in selectively breeding for resistance to E. ictaluri; however, the susceptibility of these families to F. columnare is not known. Our objectives were to obtain baseline information on the susceptibility of channel catfish families (maintained as part of the selective breeding program) to E. ictaluri and F. columnare and to determine whether the spleen index and plasma levels of mannose-binding lectin (MBL) are predictive indicators of susceptibility to these pathogens. Four channel catfish families were used: family A was randomly chosen from spawns of fish that were not selectively bred for resistance; families B, C, and D were obtained after selection for resistance to E. ictaluri. All four families were immersion challenged with both bacterial pathogens; the spleen index and plasma MBL levels of unchallenged fish from each family were determined. Mean cumulative percent mortality (CPM) after E. ictaluri challenge ranged from 4% to 33% among families. Families A and B were more susceptible to F. columnare (mean CPM of three independent challenges = 95% and 93%) than families C and D (45% and 48%), demonstrating that there is genetic variation in resistance to F. columnare. Spleen index values and MBL levels were not significantly different, indicating that these metrics are not predictive indicators of F. columnare or E. ictaluri susceptibility in the four tested families. Interestingly, the two families that exhibited the highest CPM after F. columnare challenges had the lowest CPM after E. ictaluri challenge. Further research on larger numbers of families is needed to determine whether there is any genetic correlation between resistance to E. ictaluri and resistance to F. columnare.

Received November 18, 2011; accepted February 23, 2012     

Summer Mortalities and Incidental Parasitisms of Cultured Pacific Oysters in Alaska

Abstract

During the summer of 1987, surface seawater temperatures in Alaska were unseasonably warm, periodically approaching 20°C with salinities of 29‰ in late July and early August. During this period at least one Alaskan oyster grow-out station sustained excessive mortalitygreater than 50%-within a group of 150,000 18-month-old Pacific oysters Crassostrea gigas. These oysters continued to die despite later reported declines in both seawater temperature and salinity. Histological examination of moribund oysters indicated mature or nearly mature gametes in both sexes and infiltration of tissues by opportunistic secondary invaders composed primarily of various bacterial types and the flagellate protozoan Hexamita sp. An incidental, but potentially pathogenic, rickettsia-like organism that formed cytoplasmic inclusions within vesicular connective tissues was also observed in some of the oysters. Circumstances associated with this oyster mortality were similar to those accompanying summer mortalities of raft-cultured Pacific oysters in Japan, where deaths were caused by physiological stress from rapid gonadal development or a prolonged prespawning condition.     

An Uncommon Presentation of Fungal Infection in Atlantic Salmon Fry

Abstract

Moribund fry from several families of Atlantic salmon Salmo salar had a conspicuous cranial defect that corresponded with 18.3% (SD, 4.5%) mortality of fry. The lesion was characterized by a domed, epithelium-covered swelling centered over the optic tectum. The swelling was an edematous reaction to the extension of a fulminating necrotizing mycotic stomatitis and bronchitis into the cranial tissues including the ventral meninges. An oomycete is believed to be the pathogen. The percentage mortality of fry in each separately reared family ranged from 1.0 to 63.3%. An analysis of variance revealed that the differences in mortality among families were significant (P < 0.0001), and that the difference between replicates of each family, reared apart, were not significant. A possible genetic basis for resistance to fungal infection is discussed.     

Susceptibility of Pacific Herring to Viral Hemorrhagic Septicemia Is Influenced by Diet

Abstract

Groups of specific-pathogen-free Pacific herring Clupea pallasii were highly susceptible to infection by viral hemorrhagic septicemia virus (VHSV); however, the level of mortality was influenced by diet during the 40–71 d before, during, and after the first exposure to the virus. Cumulative mortality was highest among the herring maintained on an experimental soy-based pellet, intermediate among those maintained on a commercially available fish-meal-based pellet, and lowest among those maintained on a second commercially available fish-meal-based pellet containing β-glucans. Additionally, the herring maintained on the experimental soy-based feed demonstrated less growth than those on the commercially available feeds. The results indicate the importance of standardizing diet during empirical determinations of disease susceptibility and provide insights into the risk factors affecting VHS susceptibility in wild populations.

Received August 26, 2011; accepted November 4, 2011     

Mortality of American Bullfrog Tadpoles Lithobates catesbeianus Infected by Gyrodactylus jennyae and Experimentally Exposed to Batrachochytrium dendrobatidis

Abstract

The fungal pathogen Batrachochytrium dendrobatidis (Bd), which causes the disease chytridiomycosis in postmetamorphic amphibians, has been linked to amphibian population declines. Different amphibian species, however, exhibit different susceptibility to Bd pathogenicity. At the same time, agricultural pesticides commonly found contaminating aquatic habitats have been reported to increase the susceptibility of amphibians to pathogens. To investigate whether certain pesticides are able to alter the pathogenicity of Bd to larval amphibians, we exposed larval American bullfrogs Lithobates catesbeianus to end-use formulations of the herbicides atrazine or glyphosate, and then exposed them to Bd. Following the experimental exposures, a preexisting infection of the tadpoles by the monogenean ectoparasite Gyrodactylus jennyae was detected in all experimental and control tadpoles. Gyrodactylus jennyae infection intensity varied, and individuals with heavy G. jennyae infections suffered more skin erosion due to grazing by the parasite. Tadpoles experimentally exposed to Bd, or to Bd and either herbicide, had significantly reduced survival rates compared with untreated tadpoles that were only infected by G. jennyae. Increased mortality was also correlated with degree of skin erosion; survival of tadpoles with severe skin erosion was significantly reduced compared with that of tadpoles with no, or mild, skin erosion. While infected with G. jennyae, the group of tadpoles with the lowest survival rate (exposed only to Bd) included significantly more individuals exhibiting severe skin erosion and significantly fewer individuals without skin erosion, compared with the control group. These results emphasize the potential pathogenicity of gyrodactylid infections in larval amphibian hosts and suggest that concomitant exposures to Bd may enhance infections and effects of G. jennyae in bullfrog tadpoles.

Received February 3, 2012; accepted August 10, 2012     

Survival and Antibody Response of Channel Catfish,Blue Catfish,and Channel Catfish Female × Blue Catfish Male Hybrids after Exposure to Edwardsiella ictaluri

Abstract

Juvenile Norris strain channel catfish Ictalurus punctatus, blue catfish I. furcatus, and Norris strain channel catfish female × blue catfish male hybrids were challenged with Edwardsiella ictaluri by bath immersion or intraperitoneal injection (high or low dose) in aquaria. Survival (%) after bath immersion was highest for blue catfish (89.5 ± 2.8), intermediate for hybrids (73.8 ± 6.7), and lowest for channel catfish (62.0 ± 4.2). Prechallenge antibody levels to E. ictaluri, measured by enzyme-linked immunosorbent assay, were negative (mean ± SE optical density [OD] = 0.010 ± 0.003). Postchallenge antibody response for blue catfish (OD = 0.132 ± 0.045) was significantly lower than that of channel catfish (OD = 0.350 ± 0.045), whereas the response of the channel × blue catfish F₁ hybrids (OD = 0.263 ± 0.051) was intermediate and not significantly different from either parental species. Intraperitoneal injections of E. ictaluri resulted in significant mortality only in channel catfish (88.3 ± 2.6% survival) and were sublethal to hybrid catfish and blue catfish with 100.0% and 99.3 ± 0.4% survival, respectively. Antibody responses after the injection challenge were significantly different among catfish groups and injection dose with no group × dose interaction. Antibody responses after the injection challenge were consistent with the immersion challenge, and means of high and low challenge doses were lowest in blue catfish (OD = 0.061 ± 0.014), intermediate in hybrids (OD = 0.187 ± 0.014), and highest in channel catfish (OD = 0.272 ± 0.014). For all fish groups combined, the high injection challenge dose resulted in higher antibody levels (OD = 0.206 ± 0.011) than low injection challenge dose (OD = 0.140 ± 0.012). Overall results indicate greater resistance to E. ictaluri and lower antibody response in blue catfish, and show the potential to identify molecular markers linked with disease resistance and introgression of resistance genes from blue catfish into channel catfish.     

Haplosporidium nelsoni (MSX) in Eastern Oyster Populations of North Carolina

Abstract

Populations of the eastern oyster Crassostrea virginica from 36 locations off the coast of North Carolina were examined cytologically in the fall of 1989 for Haplosporidium nelsoni (MSX). The pathogen was found in oysters from 11 (31%) of the sites. Systemic Perkinsus marinus infections were noted in oysters from 26 (72%) of the locations.     

Sero‐epidemiological screening of pig sera collected at the slaughterhouse to detect herds infected with Aujeszky's disease virus,porcine influenza virus and Actinobacillus (Haemophilus) pleuropneumoniae in the framework of an Integrated Quality Control (IQC) system

Summary

Over a period of six months, approximately 4700 blood samples were collected from 97 pig‐finishing farms in the provinces of Noord‐Brabant and Gelderland and screened for antibodies with respect to Aujeszky's disease virus (ADV), porcine influenza virus (PI) and Actinobacillus (Haemophilus) pleuropneumoniae (App). There were significant differences in the percentages of seropositive pigs between the two provinces, which may be related to the difference in the density of the pig population in the two provinces.

In practice, it was possible to perform a reliable sera collecting procedure at the slaughterhouse. No farms remained seronegative with respect to most of the disease agents during the sampling period. There was a high degree of variation in the percentages of seropositive pigs per farm as to most of the disease agents. Evidence was found that animals that were seropositive with respect to ADV were significantly more susceptible to becoming seropositive with respect to App. serotype 2, and vice versa. The same connection was observed for PI serotype H₁N₁ and PI serotype H₃N₂. Furthermore, evidence was found that pigs seropositive with respect to PI serotype H₁N_i only, or to PI serotype H₁N₁ and ADV or PI serotype H₃N₂ show a significant decrease in average daily weight gain compared to pigs that were seronegative.     

Grass defoliation affecting survival and growth of seedlings of Acacia karroo,an encroaching species in southwestern Zimbabwe

Abstract

Two experiments were conducted, one in the field and the other in the greenhouse, to investigate the effects of the intensity and frequency of grass defoliation on the survival and growth of Acacia karroo seedlings. In the greenhouse, seedlings growing with heavily clipped grasses had higher biomass production than those competing with moderately clipped grasses. Root/shoot ratios were higher in treatments with undipped grasses. There was a negative relationship between grass root production and A. karroo biomass production. The field experiment was carried out in two paddocks, one previously heavily‐grazed and the other lightly‐grazed. Grazing in both paddocks was simulated by artificial defoliation. Generally more A. karroo seedlings emerged under lightly defoliated treatments. Clipping frequency had a strong effect (P=0.066) on the survival of emerged seedlings during the wet season. There were no differences in survival rate at the end of the dry season. Though grass defoliation was shown to enhance seedling growth under controlled conditions, no evidence was found to suggest that seedling establishment during the first year is influenced by the intensity of grass defoliation.     

Experimentally Induced Whirling Disease I. Dose Response of Fry and Adults of Rainbow Trout Exposed to the Triactinomyxon Stage of Myxobolus cerebralis

Abstract

The intensity and prevalence of whirling disease was tested by exposure of 2-monthold fry and 1-, 2-, and 3.5-year-old adults of rainbow trout Oncorhynchus mykiss to a known number of laboratory-produced Myxobolus cerebralis at the actinosporean triactinomyxon stage. Fry exposed to graded concentrations of infectivity (triactinomyxons) for 3 h were individually examined for spores of Myxobolus cerebralis 5 and 6 months later. Exposure of fish to the lowest doses, 1 and 10 triactinomyxons per fish, did not result in detectable myxosporean spores. Fish that became lightly infected by a dose of 100 triactinomyxons per fish experienced a decrease in the incidence of infection between 5 and 6 months after exposure. A linear relationship was found between the numbers of recovered myxosporean spores and doses of 100–10,000 triactinomyxons per fish, and the spore burden appeared to plateau at doses of 10,000–100,000 triactinomyxons per fish. Adult fish continuously exposed to the highest dose of triactinomyxons for 3.5 months were infected and asymptomatic, however, the severity of myxosporean infection decreased with increased age of fish. This information may help in controlling whirling disease in salmonids.     

Prevalence of Renibacterium salmoninarum among DownstreamMigrating Salmonids in the Columbia River

Abstract

Bacterial kidney disease (BKD) is an important contributor to mortality of salmonids in hatcheries in the Columbia River basin. However, the impact of BKD on the survival of downstream migrants is difficult to determine because there is little information on the disease-related mortality among these fish. In this study, the impact of BKD on juvenile salmonids was examined by determining the percentage of downriver migrants infected with Renibacterium salmoninarum (the causative agent of BKD) and evaluating the effects of salt water on the progress of the disease. During the 2 years of this study, approximately 20% of the three species of migrating hatchery and wild salmonids (Oncorhynchus spp.) collected were infected with R. salmoninarum. Mortality caused by BKD increased when fish were held in salt water.     

Abundance of the Parasitic Copepod Caligus elongatus on Wild Pollock near Commercial Salmonid Net-Pens

Abstract

Between July and December 1993, wild pollock Pollachius virens collected near salmonid net-pens on the Atlantic coast of Maine in the United States were examined for parasitic copepods of the family Caligidae to determine the role of pollock as host reservoirs. Only Caligus elongatus was detected on 1,456 pollock sampled. Most pollock (97.39%) had two or fewer sea lice per fish. A maximum prevalence (percent of fish infested) of 50%, an abundance (average number per fish) of 0.9, and an intensity (average number per infested fish) of L79 were recorded. Only one larval C. elongatus was found. No seasonal or geographic trends in infestation statistics were observed.     

Clinical characteristics of elephant endotheliotropic herpesvirus (EEHV) cases in Asian elephants (Elephas maximus) in Thailand during 2006–2019

BackgroundElephant endotheliotropic herpesvirus causes a hemorrhagic disease (EEHV-HD) that is a major cause of death in juvenile Asian elephants with EEHV1 and EEHV4 being the most prevalent.AimTo perform a retrospective clinical data analysis.MethodsRecords of a total of 103 cases in Thailand confirmed by polymerase chain reaction (PCR) on blood and/or tissue samples.ResultsThe severity of clinical signs varied among EEHV subtypes. EEHV1A was the most prevalent with 58%, followed by EEHV4 with 34%, EEHV1B with 5.8% and EEHV1&4 co-infection with 1.9%. Overall case fatality rate was 66%. When compared among subtypes, 100% case fatality rate was associated with EEHV1&4 co-infection, 83% with EEHV1B, 75% with EEHV1A, and the lowest at 40% for EEHV4. Calves 2- to 4-year old were in the highest age risk group and exhibited more severe clinical signs with the highest mortality. Majority of cases were found in weaned or trained claves and higher number of cases were observed in rainy season. A gender predilection could not be demonstrated. Severely affected elephants presented with thrombocytopenia, depletion of monocytes, lymphocytes and heterophils, a monocyte:heterophil (M:H) ratio lower than 2.37, hypoproteinemia (both albumin and globulin), severe grade of heterophil toxicity, and low red blood cell counts and pack cell volumes. Survival was not affected by antiviral drug treatment in the severely compromised animals.ConclusionEarly detection by laboratory testing and aggressive application of therapies comprising of supportive and anti-viral treatment can improve survival outcomes of this disease.     

Pathogenesis of Enteric Septicemia of Channel Catfish,Caused by Edwardsiella ictaluri: Bacteriologic and Light and Electron Microscopic Findings

Abstract

To clarify early events in the pathogenesis of enteric septicemia of catfish, 140 channel catfish Ictalurus punctatus (8–10 months old) were each infected with approximately 1.0 × 10⁹ colony-forming units of Edwardsiella ictaluri by intragastric intubation. Fish were sacrificed at 0, 0.25, 0.5, 1, 3, 6, 12, 24, 48, 72, 96, and 120 h postinfection (PI). Multiple tissue samples at all scheduled sampling times were evaluated by gross observation, light and electron microscopy, and immunohistochemical methods. In addition, at each sampling time, stomach, intestine, trunk kidney, and liver were cultured to quantitate bacteria. Trunk kidney cultures were positive by 0.25 h PI, indicating rapid transmucosal passage. In the intestine, E. ictaluri was seen in contact with the brush border at 0.5 h PI. Also at 0.5 h PI, dilated basilar cells with large intracytoplasmic inclusions were observed adjacent to the basement membrane. From 1 to 3 h PI, occasional necrotic enterocytes were seen on tips of intestinal folds. Proprial leukocytes were rare before 24 h PI but common thereafter. Immunoelectron microscopy showed E. ictaluri in vacuoles within phagocytes as early as 24 h PI in the intestinal mucosa. In other tissues, earliest observed microscopic lesions (48 h PI) consisted of bacteria within vacuoles of phagocytic cells contained within blood vessels. Bacteria were also seen within degenerate vacuoles in enterocytes and hepatocytes at 72, 96, and 120 h PI. This study confirms that E. ictaluri can invade channel catfish within 0.25 h PI by crossing the intestinal mucosa and suggests that the bacterium may have invasion and survival strategies similar to those of other enteroinvasive members of the Enterobacteriaceae.     

Factors affecting egg production and layer bird mortality in private poultry farms in the subhumid zone of Nigeria

Egg production and layer bird mortality data obtained from five different private farms in Zaria within the subhumid zone of Nigeria, over a 6‐year period (1994–1999) were subjected to least squares analysis to determine the effects of age, season and year. It was demonstrated that age had a highly significant influence (P < 0.01) on egg production in that birds falling within the age group 30–39 weeks produced the highest number of eggs (3255 ± 109), while birds over 100 weeks of age produced the lowest number of eggs (1206 ± 412). Similarly, seasonal variation in egg production was also significant (P < 0.05); the highest egg production (2926 ± 90) was obtained during the early dry season, and the lowest (2423 ± 95) during the late wet season. Mortality was generally low (0.0–0.9%) and not significantly different from 20 to 49 weeks of age (P > 0.05). However, from 50 to 100 weeks of age, highly significant differences (P < 0.01) in mortality were observed, with the 90–100 weeks age group recording the highest mortality of 15.7 ± 1.3%. Furthermore, yearly variations in egg production and mortality were highly significant (P < 0.01) with 1999 producing the most eggs (4410 ± 102) and recording the lowest mortality (1.4%). It was concluded that due to the significant seasonal, age and yearly variations, data on egg production and mortality need to be adjusted for these effects to enable unbiased comparison between and within farms. Furthermore, farmers can make adequate feeding preparations commensurate with each season for optimal egg production.     

Protection of Chinook Salmon Smolts with Oral Doses of Erythromycin against Acute Challenges of Renibacterium salmoninarum

Abstract

We challenged duplicate groups of yearling smolts of chinook salmon Oncorhynchus tshawytscha held in seawater with an intraperitoneal inoculation of the kidney disease bacterium Renibacterium salmoninarum 1 d before and at intervals of 1, 11, and 29 d after a 21-d oral administration of erythromycin thiocyanate at 0.1 g/kg body weight per day. Most mortality attributable to bacterial kidney disease (BKD) in fish challenged with R. salmoninarum but not administered erythromycin occurred 2–3 weeks after challenge; the average survival 35 d after challenge was only 9%. Nearly 70% of the fish challenged 1 d before the erythromycin feeding were alive 35 d after the 21-d treatment, and more than 98% of the fish challenged the day after the 21-d erythromycin treatment survived a further 35 d. Fish challenged 29 d after the erythromycin treatment were not significantly protected against BKD. Chinook salmon that were not challenged with the bacterium but were injected with sterile phosphate-buffered saline and then fed a ration with erythromycin survived at a significantly higher rate than unchallenged fish injected with saline but not fed erythromycin. Fish that were not injected with saline or R. salmoninarum survived at a significantly higher rate than fish handled and injected with saline or pathogen. Because erythromycin protected fish challenged just before and immediately after treatment, the antibiotic should be useful early in an outbreak of BKD and as a prophylactic when stresses are expected.