A novel Henneguya species from channel catfish described by morphological, histological, and molecular characterization

Channel catfish Ictalurus punctatus from a commercial farming operation in the Mississippi Delta were submitted for examination for the presence of infection by the trematode Bolbophorus damnificus. The fish were instead found to possess skin nodules suggestive of Henneguya pellis, a species previously described in the blue catfish I. furcatus. Despite the dermal location and distribution of lesions, morphological characteristics of the myxospores were inconsistent with H. pellis. Spores possessed a lanceolate spore body 15.4 +/- 1.5 microm (mean +/- SD; range = 12.2-19.3 microm) in length and 5.5 +/- 0.6 microm (range = 4.5-6.8 microm) in width in valvular view, and 4.7 +/- 0.2 microm (range = 4.2-5.0 microm) in width in sutural view. Polar capsules were pyriform and unequal in both length and width and contained polar filaments with six coils. Polar capsules measured 6.1 +/- 0.8 microm (range = 4.0-7.9 microm) long and 1.7 +/- 0.3 microm (range = 1.0-2.2 microm) wide. The caudal appendages were 50.5 +/- 8.3 microm (range = 34.8-71.4 micorm) long and the total length of the spore was 65.9 +/- 8.6 microm (range = 48.2-90.0 microm). The "blister like" plasmodia were round or ovoid, up to 2 mm in diameter, and randomly distributed throughout the epidermis of the fish. Histologically, plasmodia were confined to the dermis and elicited no inflammatory reaction from the fish. A blast search of the 18S small subunit rDNA sequence obtained by polymerase chain reaction amplification resulted in no identical sequence matches but indicated a close relationship to H. gurlei, H. ictaluri, and H. exilis. The unique host record, spore morphology, and novel genetic sequence derived from this isolate lead us to propose this isolate as a novel species, H. sutherlandi.

Morphologic, Pathologic, and Genetic Investigations of Bolbophorus Species Affecting Cultured Channel Catfish in the Mississippi Delta

Trematodes belonging to the genus Bolbophorus have recently been reported as the cause of substantial morbidity and mortality in cultured channel catfish Ictalurus punctatus in Mississippi and Louisiana. Previous investigators identified only a single species, B. confusus. In this investigation, genetic techniques were used to identify all stages of the parasite in all of its hosts. The 18s rRNA genes from specimens collected in Mississippi were sequenced and compared; this analysis revealed that there are two distinct species, B. damnificus (previously identified as B. confusus) and another, undescribed species. (Phylogenetic analysis indicated that a third species, B. levantinus, is also closely related to the Mississippi species.) Species-specific polymerase chain reaction assays capable of identifying and differentiating between these two parasites were developed. Both species were found to infect the first intermediate host (the ram's horn snail Planorbella trivolvis) in commercial channel catfish ponds, but only B. damnificus was recovered from the fish themselves. The new, unidentified Bolbophorus species was determined to be highly pathogenic to a number of fish species. The contribution of B. damnificus to disease in cultured channel catfish remains undetermined. Future investigations of these parasites must now take into account the presence of two distinct species.

Portals of entry and systemic localization of proliferative gill disease organisms in channel catfish Ictalurus punctatus

Immunized rabbit serum adsorbed in live catfish was used in indirect fluorescent antibody test (IFAT) to detect developmental life stages of Henneguya ictaluri n. sp. This myxozoan parasite is associated with proliferative gill disease in channel catfish Ictalurus punctatus (Rafinesque) in the USA. Specific pathogen free fingerlings were experimentally infected with the actinosporean stage of H. ictaluri and necropsied 24, 48, 72, and 96 h post-infection. At 24 h post-infection parasite stages were observed primarily in the gastric mucosa and submucosa but were also observed in the skin and buccal cavity. Ovoid organisms were detected in heart and blood vessels of the liver. From 48 to 72 h after exposure, fewer fluorescent organisms were located in all organs, with the exception of the gills, than were observed at 24 h. These organisms appeared to be degenerating except for those in the gills, which appeared to be multinucleated. By 96 h post-infection, the organisms could not be detected in fish tissues with the exception of the stages in the gills, which appeared to be a preferred site of development. Throughout the entire 96 h period of study, no stage of the organism was detected in the brain. Infected tissue sections treated with non-immune rabbit serum and non-infected tissue sections treated with immune rabbit sera all showed negative results by IFAT.

The use of polymerase chain reaction assay to diagnose proliferative gill disease in channel catfish (Ictalurus punctatus)

To assess the potential of a polymerase chain reaction (PCR) assay as a diagnostic tool in the detection of proliferative gill disease (PGD) in channel catfish (Ictalurus punctatus), PCR assays were compared with the traditional diagnostic methods of gill wet mounts and histology. A PCR assay using primers for Aurantiactinomyxon ictaluri, the actinospore associated with PGD, was performed with tissues from fish from commercial ponds. Using histology as the "gold standard," the sensitivity, specificity, and accuracy of the PCR assay were all >90%. In comparison, the wet mount examinations had a lower sensitivity and specificity. Using the chi-square test and a test for strength of association, there was a significant, strong association between results obtained by PCR and those obtained by the other 2 methods. These results demonstrate that the PCR assay is a good diagnostic tool for the detection of PGD.

Small subunit ribosomal RNA sequence of Henneguya exilis (class Myxosporea) identifies the actinosporean stage from an oligochaete host

Several transmission studies, as well as recent molecular data, have indicated that the two classes Myxosporea and Actinosporea represent different life cycle stages of Myxozoa. To evaluate the life cycles of myxozoa in catfish aquaculture systems, the small subunit (18S) ribosomal RNA gene sequences of Henneguya exilis, a myxosporean from channel catfish Ictalurus punctatus, and an actinosporean (previously designated as Aurantiactinomyxon janiszewskai) from the aquatic oligochaete Dero digitata were determined. The sequences were identical, indicating that H. exilis and the actinosporean are alternate life stages of a single species. This is the first report identifying the actinosporean stage of the genus Henneguya.

Efficacy of doramectin for treatment of experimentally induced infection with gastrointestinal nematodes in calves

OBJECTIVE

To determine the efficacy of injectable doramectin against experimentally induced infections with adult and larval (L4) stages of gastrointestinal nematodes in calves.

PROCEDURES

In each experiment, between 20 (experiments 1 and 2) and 30 (experiment 3) parasite-free yearling calves were selected and allotted to groups of 10/group. All calves received oral inoculation of the following infective larval stages of these nematode species: Cooperia onchophora, C punctata, C zurnabada, Cooperia spp, Haemonchus placei, Nematodirus helvetianus, Oesophagostomum radiatum, Ostertagia ostertagi, Trichostrongylus axei, and T colubriformis. Infections or treatments were timed so that, by day of treatment, the population of each parasite species had matured to the stage to be tested (adult or L4). On day of treatment, calves received doramectin (200 micrograms/kg of body weight, SC), and infected nonmedicated control calves received saline solution SC at the same time. All calves were slaughtered at least 14 days after treatment.

RESULTS

Efficacy against the following adult and L4 species was > or = 99%: C onchophora, C punctata, C zurnabada, Cooperia spp, H placei, Oes radiatum, O ostertagi, and T colubriformis. Doramectin was also 100% efficacious against the L4 stage of T axei. Efficacy against the adult and L4 stages of N helvetianus was 9.6 and 77.4 to 83.3%, respectively.

CONCLUSIONS

Doramectin, at a dosage of 200 micrograms/kg, is effective in controlling the prevalent gastrointestinal nematodes (adult and L4 stages) found in naturally infected calves.

CLINICAL RELEVANCE

Doramectin, a new anthelmintic, was effective against recent field strains of the most prevalent gastrointestinal parasites found in cattle in the United States, and could provide another alternative for control of these parasites.

The effect of added complex carbohydrates or added dietary fiber on necrotic enteritis lesions in broiler chickens

Two trials utilizing two corn diets and four wheat diets were conducted. In Trial 2, all chicks were crop-infused at 9 d of age with Eimeria acervulina. In both trials, a broth culture of Clostridium perfringens was mixed with the diets for 3 consecutive d. Necrotic enteritis lesion scores were lowest in chickens consuming the corn diet with no C. perfringens and highest in chickens fed the wheat diets with C. perfringens. Chickens consuming a wheat diet with no added complex carbohydrates or added fiber exhibited the highest lesion score. Chickens on wheat diets with 4% new, ground, pine shavings had intestinal lesion scores intermediate to those of chickens that consumed the wheat or corn diets. Chickens consuming corn diets yielded the lowest lesion scores. Chickens provided diets containing either guar gum or pectin were not fully consumed and thus probably reduced the number of challenge organisms ingested.

A comparison of Eimeria oocysts isolated from litter and fecal samples from broiler houses at two farms with different management schemes during one growout

Eimeria oocyst populations were monitored in broiler houses on two farms during a growout and prior to the placement of new chicks on the same litter. Numbers of oocysts in litter were enumerated at Weeks 0, 5, 6, 7, and 9 and in feces at Weeks 5,6, and 7 in broiler houses with different management practices (both farms had identical coccidiostat programs but Farm A had a history of poor performance whereas Farm B had excellent performance records). On Farm A the number of oocysts in litter increased (P < .05) at the time of slaughter (Week 7) and placement of a subsequent flock (Week 9) when compared with Day 0. The number of oocysts in feces on Farm A also increased (P < .05) from Week 5 to 7. On Farm B there were no differences in numbers of oocysts in litter or feces over time. Farm B had (P < .05) lower numbers of oocysts in litter than Farm A at Week 7. The number of oocysts in feces from Farm B were consistently lower (P < .05) than Farm A at Weeks 5, 6, and 7. There were no differences in the species of Eimeria in litter between farms; however, there were differences in the species composition over time. Small (Eimeria mitis) and medium (primarily Eimeria acervulina) oocysts increased significantly over time, whereas the large oocysts (Eimeria tenella and Eimeria brunetti) and Eimeria maxima did not change over time. An increase (P < .05) in large oocysts was observed in fecal samples from Farm A over time.

Dose-titration to confirm the level of fenbendazole for control of Raillietina cesticillus in broiler chickens

A total of 452 broiler chickens, naturally infected with Raillietina cesticillus, were allotted into six treatment groups. One group was fed unmedicated broiler ration (Group 1), and the other five groups were fed broiler ration containing fenbendazole at 180 ppm for 3 days (38.5 mg/kg body weight [BW]), 240 ppm for 3 days (50.9 mg/kg BW), 120 ppm for 6 days (52.2 mg/kg BW), 180 ppm for 6 days (79.9 mg/kg BW), or 240 ppm for 6 days (104.3 mg/kg BW). Fenbendazole was 100.0% efficacious against R. cesticillus when administered in the diet at 240 ppm for 6 days; 99.9% at 240 ppm for 3 days and at 180 ppm for 6 days; 99.5% at 120 ppm for 6 days; and 96.9% at 180 ppm for 3 days. Fenbendazole treatment had no adverse effect on weight gain or feed intake.

Characterization of proteins in sporulated and unsporulated Eimeria maxima oocysts

Proteins in sporulated and unsporulated oocysts of Eimeria maxima were characterized, using monoclonal antibodies (MAB), ELISA, sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), and protein (western) immunoblotting techniques. Three MAB (EM1, EM2, and EM4) were produced against proteins of sporulated oocysts. The ELISA results indicated that EM1 was reactive with sporulated oocyst proteins, EM2 was reactive with sporulated and unsporulated oocyst proteins, and EM4 was reactive with unsporulated oocysts and proteins. Separation of proteins in E maxima sporulated and unsporulated oocysts by SDS-PAGE indicated that sporulated oocysts had proteins of approximately 200 kilodaltons (kD) and distinct protein bands at 21.5 and 45 kD. Using SDS-PAGE, unsporulated oocysts had less-distinct high molecular weight protein bands (greater than 200 kD), compared with sporulated oocysts, and a distinct protein band at 31 kD. Use of all 3 MAB yielded negative results in western blot analysis of fractions obtained by SDS-PAGE.

Critical test evaluations of oxfendazole and trichlorfon: effectiveness of a paste formulation in the horse

Critical tests were performed on 6 horses to evaluate the antiparasitic effectiveness of oxfendazole given in combination with trichlorfon in a paste formulation. Treatments were given orally as a single dose. The rates of active ingredient administration were 2.5 and 40 mg/kg of body weight for oxfendazole and trichlorfon, respectively. The combined activities of the 2 antiparasitic compounds proved 100% efficacious in the removal of adult Strongylus vulgaris, S edentatus, Oxyuris equi, and Parascaris equorum. Fourth stage O equi, and 2nd and 3rd instars of Gasterophilus nasalis also were completely removed. Second and 3rd stage instars of G intestinalis were removed at the rates of 98.1% and 98.8%, respectively. Nematodes of the "small strongyle" category were removed at the combined rate of 97.0%. Pronounced larvicidal effects of the test formulation were demonstrated via culturing fecal nematode eggs during the trial. Untoward effects of treatment were not seen in any of the trial animals.

Antiparasitic efficacy of ivermectin in naturally parasitized sheep

Sixteen sheep harboring naturally acquired parasitisms were allocated to 1 of 2 treatment groups: (i) sheep given ivermectin in an oral solution at the dosage rate of 200 micrograms/kg of body weight, and (ii) those given the vehicle at a dosage rate of 0.25 ml/kg. All animals were necropsied at 2 weeks after treatment. Parasites and percentages of parasitic reductions, as demonstrated in this trial, were: Dictyocaulus filaria (99.4%), Oestrus ovis first stage instars (100%), Trichuris ovis (98.9%), Strongyloides papillosus (99.8%), Nematodirus spathiger (100%), arrested 4th stage Nematodirus spp (96.2%), Trichostrongylus colubriformis (100%), T axei (100%), Oster tagia circumcincta (100%), Haemonchus contortus (100%), and arrested Haemonchus spp 4th stage larvae (99.9%). The sheep showed no adverse effects due to ivermectin or vehicle administration.