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Biomedical subjects

C H Courtney

Publications and source records attributed to C H Courtney.

At least 37 records · Page 2Linked to original sources
PubMed1994

Efficacy of injectable abamectin against gastrointestinal tract nematodes and lungworms of cattle.

Efficacy of abamectin against gastrointestinal tract nematodes and lungworms of cattle was determined in 4 experiments. The first 2 experiments were controlled trials in which efficacy was determined at necropsy in calves with either experimentally induced (n = 14) or naturally acquired (n = 16) infections. Half the calves in each experiment were treated with abamectin (200 micrograms/kg of body weight, SC), and half were left untreated as controls. Efficacy was > 99% against adult stages of Dictyocaulus viviparus, Haemonchus placei, Ostertagia ostertagi, Trichostrongylus axei, Cooperia punctata, Trichuris discolor, and C oncophora, and was 92.4% against Nematodirus helvetianus. The second 2 experiments were clinical trials in which efficacy was determined by fecal egg count reduction in naturally infected yearling heifers (n = 75) or 2-year-old heifers (n = 75). Within replicates of 5, 4 heifers were assigned at random to treatment with 200 micrograms of abamectin/kg and 1 was left untreated as a control. Abamectin was 100% effective in eliminating strongylate nematode eggs from the feces of these heifers. In all experiments, adverse reactions were limited to small, clinically unimportant injection site swellings in 29% of abamectin-treated calves. Abamectin was judged to be safe and effective in these trials.

Animals↗
PubMed1993

Genetic structure of populations of Ostertagia ostertagi.

Most genetic work to distinguish strains of parasitic helminths focuses on searching for genetic markers to correlate with phenotypes of interest, but in this study genetic diversity among individual Ostertagia ostertagi adults is partitioned into components within and between populations. Restriction fragment polymorphism data on mitochondrial DNA from ten individual worms from each of five different parasite populations are analyzed. Three of these populations are characterized by arrested larval development (hypobiosis) over the summer months, and the other two by hypobiosis over the winter months. Sequence divergence is scored by the presence or absence of 37 different restriction sites. Although the populations are genetically differentiated with respect to the timing of hypobiosis, greater than 98% of the total mitochondrial DNA sequence diversity is partitioned within a single population, and the geographic distribution of individual mitochondrial DNA haplotypes suggests high gene flow among populations. Further, estimates of within-population mitochondrial DNA diversity are five to ten times greater in O. ostertagi than typical estimates reported for species in other taxa.

Animals↗
PubMed1991

Cloning and characterization of the ribosomal RNA gene repeat from Ostertagia ostertagi.

Clones of the rRNA genes of Ostertagia ostertagi were selected from a library prepared from the genomic DNA of adult worms of strain LA-2. A 13.4-kb insert in a clone, lambda OOR78, is comprised of one complete 7.5-kb rDNA unit and portions of two adjacent units. The rDNA unit is directly repeated in a head-to-tail fashion and represents approximately 0.9% of the total genomic DNA. This repeating unit appears to be the only long tandemly repeated sequence in the genome. Restriction enzyme recognition sites in the rDNAs of four strains of O. ostertagi were fully conserved with the exception of one PstI site present in the large rRNA gene which was absent from a proportion of the genes of the LA-2 strain. The rDNA of O. ostertagi is more similar to that of Caenorhabditis elegans in unit length and arrangement than to parasitic helminths previously examined.

Animals↗
PubMed1990

Evaluation of heartworm immunodiagnostic tests.

In this report, the use of appropriate statistical methods for the evaluation of heartworm immunodiagnostic tests is discussed. The evaluation of these tests is complicated by factors causing variation in sensitivity, specificity, accuracy, and predictive values of positive and negative test results. The primary sources of inconsistency are variation in the prevalence of heartworm infection among populations of dogs and the sensitivity of immunodiagnostic tests to various categories of heartworm infections (ie, patent, immune-mediated occult, unisex occult, and immature occult). Sample size (ie, number of dogs tested) affects the confidence limit values of sensitivity and specificity. At least 100 dogs should be used in each testing group (infected and uninfected) to generate values of sensitivity or specificity within reasonably narrow confidence limits. Use of more than 200 dogs in each testing group contributes little to further narrowing of confidence limits. The selection of appropriate statistical tests for comparison of tests or comparison of the sensitivity or specificity of a single diagnostic test to various categories of heartworm infections is critical. The McNemar paired chi 2 test is appropriate for comparison of diagnostic tests, but it must be done by use of duplicate sera from each animal. A chi 2 test of independence, or, in the case of a small sample size, the Fisher exact test, is appropriate for comparing the sensitivity or specificity of a single diagnostic test to various categories of heartworm infection.

Animals↗
PubMed1990

Seasonal transmission of Fasciola hepatica in north central Florida (U.S.A.).

To assess seasonal transmission of Fasciola hepatica 37 groups of fluke-free tracer sheep, one group of four sheep each month in succession, grazed an infected pasture in north central Florida (U.S.A.) from June 1984 to June 1987. At the end of each month, tracers were moved to a fluke-free barn for 2 months, then necropsied and flukes counted. Fluke transmission mostly occurred during the first half of the year, with peak transmission from February to April. No transmission occurred during the warm summer months, having ceased in either May or June of each year to begin again in late autumn or early winter (November-January).

Animals↗
PubMed1990

The development of an enzyme-linked immunosorbent assay for Trypanosoma vivax and its use in a seroepidemiological survey of the Eastern Caribbean Basin.

An enzyme-linked immunosorbent assay (ELISA) for IgG antibodies against a South American (New World) strain of Trypanosoma vivax was developed and used for mass screening of cattle from 20 islands in the Eastern Caribbean Basin. The sensitivity and specificity of antigens prepared from a bovine-derived field strain and a murine-adapted laboratory strain of T. vivax, both of New World origin, were compared using an indirect fluorescent antibody (IFA) test, and an antigen prepared from the murine-adapted strain was subsequently used to develop an ELISA test. The results of the ELISA test were then compared with the results of a concurrently run IFA test. There was no cross-reactivity with either test using serum from a Trypanosoma theileri-infected cow. Both tests were weakly cross-reactive with sera from a T. brucei-infected steer, and the IFA test was moderately cross-reactive with several serum samples from a T. evansi-infected steer. For bovine sera collected from herds on islands in the Eastern Caribbean region, only five of 640 tested positive with the ELISA test. Thirty five of 653 sera tested were positive by IFA although the fluorescence elicited was weak as compared to that elicited by sera from known infected animals. Sera collected from 27 cattle in a region known to be free of T. vivax (OH, U.S.A) were negative with the ELISA test, whereas seven of 30 sera from a herd in French Guiana known to be infected with T. vivax were positive.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1989

Distribution of Onchocerca spp. microfilariae in the dermis of cattle.

A grid was drawn on a lateral half of 10 hides, from cattle infected with both Onchocerca gutturosa and Onchocerca lienalis, which were obtained from an abattoir in central Florida. Paired 7-mm diameter skin cores were taken from 24 grid sites on each hide and microfilariae (mff) extracted to determine their distribution. The only consistent pattern distribution was that mff were recovered from all 10 hides at four sample sites along the ventral midline near the umbilicus. Microfilariae were also frequently found in large numbers along the dorsal cervical midline and in the region of the tarsal and carpal-metacarpal joints.

Abattoirs↗
PubMed1989

Onchocerca gutturosa and Onchocerca lienalis in cattle: variation in length of microfilariae by site of recovery.

Dermal microfilariae recovered from specimens obtained from umbilical and cervical sites of cattle infected with adult Onchocerca gutturosa alone or with adults of O gutturosa and O lienalis were measured and compared with uterine microfilariae obtained directly from gravid female worms of each species. Uterine microfilariae of O gutturosa were longer than dermal microfilariae obtained from cattle harboring only adults of O gutturosa. Dermal microfilariae were recovered from umbilical and cervical sites in these cattle. Those found at the cervical site had lengths equal to or greater than lengths of microfilariae recovered from the umbilical site. There was a significant (P less than 0.0001) shift in length across populations of microfilariae of O gutturosa from various sites in its bovine host, with a progressive decrease in length between microfilariae recovered from the worm's uterus, microfilariae from the cervical dermis, and microfilariae from the umbilical dermis, respectively. A similar direct comparison was not possible for microfilariae of O lienalis, because none of the cattle was infected with only adult worms of this species. In an indirect comparison, microfilariae of O lienalis were identified at the umbilicus, but their presence in the cervical region could not be determined unequivocally because of confounding of microfilariae length by concurrent infection with O gutturosa. Uterine microfilariae from O lienalis were longer than uterine microfilariae of O gutturosa, although a degree of overlap in the range of measurements existed between species.

Algorithms↗
PubMed1988

Efficacy of febantel paste against naturally acquired gastrointestinal nematodes of cattle.

Twenty calves with naturally acquired gastrointestinal nematode infections were assigned to 10 replicates of 2 calves each and were treated with febantel paste (5 mg/kg of body weight, PO) or an equivalent volume of paste vehicle (control calves). Adverse reactions were not observed after febantel treatment. At necropsy, gastrointestinal nematode counts in febantel-treated calves, compared with control calves, were reduced by over 99% for all major species except Trichuris discolor, counts of which were reduced by only 69%. Counts of gastrointestinal nematode eggs in feces of febantel-treated calves were reduced by 100% after treatment.

Animals↗
PubMed1988

Possible association between Dirofilaria tenuis infections in humans and its prevalence in raccoons in Florida.

A study was undertaken to determine the prevalence of Dirofilaria tenuis in raccoons from subtropical southern Florida as compared to the northern part of the state. The results indicate that D. tenuis is more prevalent in southern Florida and suggest that this might be why humans suffer from more D. tenuis infections in southern Florida than in other parts of the state.

Animals↗
PubMed1986

Heterologous resistance to Fasciola hepatica conferred upon rats by passive transfer of serum from different breeds of sheep.

Two experiments compared the protection against oral challenge with 20 metacercariae of Fasciola hepatica conferred on rats by intraperitoneal injection of serum from three breeds of sheep infected with F. hepatica (Barbados Blackbelly, St. Croix, Florida Native). Experiment 1 used serum from sheep 5-6 months of age following two infections of 250 metacercariae each, while Experiment 2 utilized serum collected from the same sheep at 10-11 months of age following either a primary (first exposure) or challenge (after two previous exposures of 250 metacercariae each) infection with 500 metacercariae. Similar numbers of flukes were recovered from rats given either immune or nonimmune (control) serum from each breed of sheep in Experiment 1. In Experiment 2, rats given serum from infected St. Croix sheep had significantly fewer flukes than rats given either control or immune serum from Barbados Blackbelly or Florida Native sheep. There was no significant correlation of fluke counts between individual serum donors (sheep) and serum recipients (rats).

Analysis of Variance↗
PubMed1986

Epidemiology and control of parasites in warm climates.

The kind of parasites a horse acquires depends upon its environment. Because patterns of transmission vary greatly with climate and management, no one worming program has universal applications. This article discusses epidemiology and control of equine parasites in the southern United States, where climates vary from warm temperate to subtropical and from humid in the southeast to arid in the southwest.

Animals↗
PubMed1986

Onchocerca gutturosa and Onchocerca lienalis in cattle: effect of age, sex, and origin on prevalence of onchocerciasis in subtropical and temperate regions of Florida and Georgia.

Evaluation of 845 cattle from Florida and Georgia for onchocerciasis indicated a significantly higher prevalence of infection with Onchocerca gutturosa and a significantly lower prevalence of infection with Onchocerca lienalis in the southern portion of Florida (subtropical region) than in the northern portion of Florida or in Georgia (temperature region). In all regions, prevalence of infection with O gutturosa was significantly higher than infection with O lienalis. In the temperate region, bulls were infected more often with O lienalis than were cows. Other sex-related differences in infection with either filariid was not found. Prevalence of infection with O lienalis was similar between age groups in all regions. Rates of infection with O gutturosa differed between age groups within and between subtropical and temperate regions. Examination of cervical and umbilical skin specimens for microfilariae detected an additional 6.6% of infected animals that had not been found by examination for adult worms. However, microfilariae were not found in 21.4% of animals that were positive for adult worms.

Age Factors↗