Showing papers by "Agriculture and Agri-Food Canada published in 1992"

Competitive ELISA for serodiagnosis of bluetongue: evaluation of group-specific monoclonal antibodies and expressed VP7 antigen.

Abstract: The performance of 2 competitive enzyme-linked immunosorbent assays (C-ELISA) was compared with the reference C-ELISA I for the detection of antibodies to bluetongue virus (BTV). One of the assays (C-ELISA II) used a group-specific monoclonal antibody (MAb) to BTV, obtained from the American Type Culture Collection (8A3B-6) and tissue culture (TC)-derived BTV antigen (Ag), and the other assay (C-ELISA III) used BTV core protein VP7 (expressed in yeast) and the reference MAb (Pirbright Laboratory, 3-17-A3). Test sera were obtained by sequential blood samples from 22 calves, each inoculated with a different serotype (T) of BTV (South African [SA] T-1-T-16 and T-18-T-20 and USA T-11, T-13, and T-17). Sera were also obtained from 4 calves and 4 sheep inoculated with USA BTV T-10 and from several groups of calves exposed to single or multiple doses of epizootic hemorrhagic disease virus (EHDV) T-1-T-4 grown in TC (BHK-21) or suckling mouse brain (SMB). A total of 618 bovine and ovine field sera collected from BT-free and BT-endemic areas were also tested. The C-ELISA III was more sensitive than the C-ELISA II in the detection of anti-BTV antibody in sera from cattle and sheep early after infection with BTV. Seroconversion was demonstrated by the 3 C-ELISAs in all animals inoculated with BTV by 20 days postinfection (DPI), except in calves that received SA T-3 or USA T-13, which became positive at 40 DPI.(ABSTRACT TRUNCATED AT 250 WORDS)

Dynamics of Panonychus-Ulmi and Typhlodromus-Pyri - Factors Contributing to Persistence

Abstract: We addressed the question of persistence of predator and prey in a biological control system by examining temporal patterns ofPanonychus ulmi (Koch) and its predator,Typhlodromus pyri Scheuten at two geographic locations and at two spatial scales. At the scale of an orchard, bothP. ulmi andT. pyri were persistent over the time frame of 6 years. At the scale of an individual tree,T. pyri appeared to be more persistent than its prey,P. ulmi. We used a simulation model of single populations ofP. ulmi andT. pyri to determine which of several aspects of the biology of the two species could contribute to such a pattern. Spatial incongruity between predator and prey was essential for persistence of both species. The generalist food habit ofT. pyri probably contributes to the persistence ofT. pyri on individual trees, and may cause occasional extinction ofP. ulmi at this spatial scale. The presence of alternate food is likely an essential element for successful biological control in this system. Cannibalism byT. pyri results in higher prey densities, that is, it is detrimental to the biological control ofP. ulmi, but has no effect on the relative persistence of the two species.

Paratuberculosis in saiga antelope (Saiga tatarica) and experimental transmission to domestic sheep.

Abstract: Mycobacterium paratuberculosis was isolated in low numbers from the small intestine and associated mesenteric lymph nodes of a saiga antelope (Saiga tatarica) using routine culture techniques in spite of histologic evidence of high numbers of acid-fast bacteria in these tissues. Two newborn domestic sheep were fed the ground intestinal tissue containing acid-fast bacteria and the progression of the experimental disease was followed by fecal culture, immunodiffusion (AGID) and lymphocyte stimulation (LST) tests. One experimentally infected sheep developed progressive clinical illness 1 yr postinoculation. Few M. paratuberculosis were isolated from feces or tissues although an extensive granulomatous mycobacterial enteritis, lymphadenitis and lymphangitis were observed containing large numbers of typical acid-fast organisms. No clinical illness was observed in the second inoculated sheep after 18 mo of observation, although infection was demonstrated at necropsy. Both sheep developed AGID and LST reactions ...

The effect of nitrogen fertilizer and irrigation on black point incidence in soft white spring wheat

Abstract: Agronomic studies were conducted to examine the effect of fertilizer N on black point incidence in Fielder soft white spring wheat (Triticum aestivum L. em Thell.). Black point incidence rose with increases in the amount of N supplied either as fertilizer applied during the growing season in irrigation water or as soil N, specifically nitrate, from fertilizer N application in previous years. A comparison of four different irrigation regimes demonstrated that black point incidence was highest under frequent irrigation (irrigate to field capacity at 75% available moisture) and lowest under conventional irrigation (irrigate to field capacity at 50% available soil moisture). In each irrigation regime, disease incidence increased as N rates were raised from 0 to 120 kg ha-1. A residual fertilizer-N study demonstrated in 1985 and 1986 that black point incidence generally rose with increasing levels of nitrogen from either preplant applications in the spring or soil nitrate from the previous year. However, additions of fertilizer N were shown to slightly reduce black point incidence at soil nitrate levels above 150 kg ha-1. A two-year fertilizer N study demonstrated that in treatments receiving the same amount (90 kg ha-1) of fertilizer N, the amount broadcast as a preplant treatment versus the amount applied in irrigation water in a fertigation treatment had no effect on black point incidence, but all fertilized treatments had significantly higher levels of disease than the unfertilized check.

The larva and habitat ofParakiefferiella nigra Brundin (Diptera: Chironomidae)

Abstract: Collections of adults ofParakiefferiella nigra Brundin indicate that this chironomid occurs widely in arctic and subarctic zones. In addition, it has occasionally been collected in cool temperate and boreal forest lakes of both North America and Europe. Although widely distributed, the larva and its habitat have not previously been described. Identity of the larva ofP. nigra has been established by studying associated reared specimens. The distinctive larva, with reduced second lateral mental teeth, is stenotopic, and on the basis of modern collections appears to be most abundant in cold, oligotrophic lakes. More data is required to establish the range of thermal environments inhabited by the larva. Larval head capsule remains ofP. nigra are common in late-glacial sediments of southwestern British Columbia lakes and provide important evidence for oligotrophic conditions during late-glacial time.

COMPETITIVE ENZYME IMMUNOASSAY FOR the DETECTION of SALMONELLA LIPOPOLYSACCHARIDE1

Abstract: A competitive enzyme immunoassay for detection of Salmonella sp. was developed in order to provide a sensitive assay for same-day identification of Salmonella sp. the assay could be performed in about 90 min and consisted of the following steps. Lipopolysaccharide derived from Salmonella typhimurium was used to passively coat polystyrene 96-well plates and tubes. A titrated amount of monoclonal antibody specific for an outer lipopolysaccharide core epitope commonly found in Salmoneila sp. was mixed with the prepared test sample prior to adding the mixture to the antigen coated matrix. Antibody bound to the immobilized antigen was detected with horseradish peroxidase labelled goat antimouse IgG (H&L chain). The analytical sensitivity of the assay was 3.1 ng and 5.6 ng of lipopolysac-charide per ml for the plate and tube formats, respectively, if 25% inhibition or less was considered negative. This cutoff level was based on reactivity of unrelated monoclonal antibodies with S. typhimurium lipopolysaccharide and lipopolysac-charide from E. coli with the Salmonella specific monoclonal antibody in the assay.

Evaluation of an immunoassay kit for the detection of certain organochlorine (cyclodiene) pesticide residues in apple, tomato, and lettuce.

Abstract: Currently, the conventional multiresidue methods (MRMs) (Anderson et al. 1986, Krause 1980) are used in this laboratory for the residue determinations of organochlorine (OC), organophosphate, (OP) and carbamate pesticides. MRMs are time and solvent consuming and also require the use of expensive analytical instruments, such as gas and liquid chromatographs which have to be operated by highly-trained analysts.

A Simple and Inexpensive Glucose Oxidase Substrate System for Enzyme Immunoassay

Abstract: A simple and inexpensive glucose oxidase substrate system was developed for enzyme immunoassay. This system is based on the formation of a coloured complex between polyvinyl alcohol or starch and iodine produced from iodide in the presence of hydrogen peroxide generated by the glucose oxidase reaction. The rate of iodine production was enhanced by the supplementation of molybdate. In an enzyme immunoassay for anti-Salmonella antibodies using glucose oxidase as the indicator enzyme, the molybdate-enhanced polyvinyl alcohol- and starch-glucose-iodide substrate systems were as sensitive as a conventional glucose oxidase assay system employing horseradish peroxidase as a secondary enzyme and a suitable hydrogen-donating chromogen.

Endogenous leukosis viral antigen in eggs from meat-type chickens on an avian leukosis virus eradication programme.

Abstract: Summary In an effort to eliminate exogenous avian leukosis virus (ALV) from a susceptible population, albumen of one egg per hen from each of four generations was tested by ELISA for group‐specific antigen (gsa) of leukosis/sarcoma viruses. From 1510 to 2099 hens were tested in each generation. Hens were not used as breeders if optical density readings for gsa were 0.4 or greater. Despite this procedure, there was no appeciable change in the occurrence of gsa in eggs from one generation to the next and in the sire population the percentage of hens with levels of 0.4 or greater was 7.1 and 8.7 in the first and fourth generations tested, respectively. There were no consistent differences in antigen levels in any of the eight strains that comprised the two populations. For the most part, antigen detected in eggs resulted from expression of endogenous viral genes since there was a low incidence of exogenous infection. Six of 234 hens of the second generation tested from the sire population were positive for A...

COMPARISON of ANALYTICAL SENSITIVITIES of THREE ENZYME IMMUNOASSAY PROCEDURES FOR the DETECTION of SALMONELLA LIPOPOLYSACCHARIDE

Abstract: The analytical sensitivities of three different enzyme linked immunoassays (ELISA), two competitive and a capture format were assessed. the assay systems employed monoclonal antibodies to Salmonella lipopolysaccharide (LPS) outer core epitopes to detect crude LPS antigens from Salmonella typhimurium. the most sensitive ELISA was the capture procedure, being capable of detection 1.3 ng/ml of LPS. This technique, however also gave the greatest between-test variation and as a result, the lowest amount that could be detected with a 95% confidence limit was actually 12.8 ng/ml and it took the longest time to perform (3 h, 30 min). A competitive ELISA using limiting monoclonal antibody to compete between solid phase antigen and soluble antigen in the sample, ranked second in sensitivity, and can detect 2.8 and 3.8 ng/ml of LPS when tested with two different monoclonal antibodies. However, because of the slight between test variation, the actual sensitivities that could be detected with a 95% confidence limit were 3.1 and 4.6 ng/ml, respectively. This test takes approximately 1 h and 30 min to perform. The classical type of competitive assay, employing a labelled antigen, was the least sensitive being capable of detecting 5.8 ng/ml if the LPS was conjugated with horseradish peroxidase and 16.0 ng/ml if alkaline phosphatase was used as a label. to account for the between-test variation, the sensitivities with a 95% confidence limit were 8.6 and 18.7 ng/ml for the respective assays, which take 2 h and 15 min to perform. These sensitivities compare favorably with those published for similar assays, but all of the procedures were judged insufficiently sensitive for direct use on food samples to be tested for the presence of Salmonella species. However, the assays would be quite suitable for demonstration of Salmonella sp. after an enrichment procedure.