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Biomedical subjects

J R Egerton

Publications and source records attributed to J R Egerton.

At least 19 recordsLinked to original sources
PubMed1996

Efficacy in sheep and pharmacokinetics in cattle that led to the selection of eprinomectin as a topical endectocide for cattle.

Eprinomectin (MK-397 or 4"-epi-acetylamino-4"-deoxy-avermectin B1) is a novel avermectin selected for development as a topical endectocide for all cattle, including lactating cows. The initial efficacy assessments were made in sheep to identify subclasses of the avermectin/milbemycins that possessed inherent activity against a spectrum of nematode parasites. This included examination of several hundred analogs each given orally to a single sheep experimentally infected with a range of parasitic nematodes. Representatives of several subclasses, most notably the 4"-epi-amino avermectin B1 subclass, were identified as possessing potent, broad-spectrum activity against the endoparasites, whereas subclasses such as those with a variety of synthetic substitutions at C-4a or oximes at C-5 were among the least potent. Eprinomectin, a member of the 4"-epi-amino subclass, possessed potent activity against the range of nematodes when tested at 0.025 mg kg-1 per os. Milk and plasma concentration profiles were also made for these and other selected avermectin/milbemycins following topical administration to lactating dairy cattle. The molecular structure of each compound had a significant effect on the milk to plasma ratio, but the ratio of each was constant over time, implying an equilibrium between the 2 compartments. Compounds that were saturated at the C-22,23 bond had milk to plasma ratios > or = 1.0, whereas those unsaturated at this bond were generally < or = 1.0. The milk to plasma ratio of eprinomectin was < or = 0.2. Therefore, not only is eprinomectin the most potent broad-spectrum avermectin/milbemycin identified to date, but it also possesses one of the lowest milk partitioning coefficients in this class of antiparasitics.

Administration, Topical↗
PubMed1996

Eprinomectin: a novel avermectin for use as a topical endectocide for cattle.

Eprinomectin (MK-397 or 4"-epi-acetylamino-4"-deoxy-avermectin B1) is a novel avermectin selected for development as a topical endectocide for all cattle, including lactating dairy cows. Herein, we show its anthelmintic, insecticidal and miticidal activity. To determine its anthelmintic capabilities, eprinomectin was tested topically on Jersey calves at 0.08, 0.2, or 0.5 mg kg-1 in a probe formulation against experimental infections of adult Haemonchus placei, ostertagia ostertagi, Trichostrongylus axei, T. colubriformis, Cooperia oncophora, C. punctata, Nematodirus helvetianus, Oesophagostomum radiatum and Dictyocaulus viviparus. Eprinomectin removed > or = 99% and > or = 98% of the adult stage of every species at the 0.5 and 0.2 mg kg-1 dosage levels, respectively. The lowest dosage (0.08 mg kg-1) produced maximal or near maximal efficacy against most of the adult endoparasites with the exception of T. colubriformis (87%) and C. oncophora (88%). In a separate test, eprinomectin was evaluated topically against the immature stages of species at the same dosages. Results showed > or = 99% and > or = 98% removal of the immature stages of each species at the 0.5 and 0.2 mg kg-1 dosage levels, respectively. The 0.08 mg kg-1 dosage maintained > or = 97% efficacy against 6 species with reduced activity against H. placei (42%) and N. helvetianus (66%). For ectoparasites, eprinomectin was tested topically at 0.16, 0.24, 0.32 or 0.5 mg kg-1 on mixed breed cattle naturally infested with the sucking louse, Linognathus vituli. Complete elimination of lice at all dosages was observed by day 14. Topical delivery of eprinomectin at 0.16, 0.24, 0.32 or 0.5 mg kg-1 to Holstein calves experimentally challenged with horn fly, Haematobia irritans, produced 100% efficacy to challenge by week 2 post-treatment in all dosages groups and 94% and 99% efficacy to challenge at the 0.32 and 0.5 mg kg-1 dosage groups, respectively, at week 4. Topical delivery of eprinomectin at 0.16, 0.24 or 0.5 mg kg-1 to Deutsches Fleckvieh cattle infested with mange mites, Chorioptes bovis, produced > or = 95% control at all dosages levels by day 14 post-treatment and was maintained at or near this efficacious level for the 6-week duration of the trial. No adverse reaction was observed in any animal in any of these tests. In summary, these experimental data indicate that eprinomectin is an excellent broad-spectrum endectocide for cattle and is suitable for topical delivery.

Administration, Topical↗
PubMed1995

The protective efficacy of cloned Moraxella bovis pili in monovalent and multivalent vaccine formulations against experimentally induced infectious bovine keratoconjunctivitis (IBK).

Calves were vaccinated with cloned Moraxella bovis pili of serogroup C (experiment 1) or B (experiment 2) either as a monovalent formulation or as part of a multivalent preparation with pili of six other serogroups. Within 4 weeks of the second vaccine dose vaccinated calves and non-vaccinated controls were challenged via the ocular route with either virulent M. bovis strain Dal2d (serogroup C) or M. bovis strain 3WO7 (serogroup B) in experiments 1 and 2, respectively. Calves vaccinated with multivalent vaccines had significantly lower antibody titres than those vaccinated with monovalent preparations. Nevertheless, the levels of protection against infectious bovine keratoconjunctivitis (IBK) achieved with multivalent vaccines were 72% and 83% for the groups challenged with M. bovis strains of serogroups B and C, respectively. The serogroup C monovalent vaccine gave 100% protection against experimentally induced IBK and M. bovis isolates cultured from the eyes 6 days post-challenge were identified as belonging solely to serogroup C. Unexpectedly, only 25% protection was achieved against homologous strain challenge of calves that received the monovalent serogroup B vaccine. Furthermore, the majority of M. bovis isolates recovered from calves in this group belonged to serogroup C, as did half of those isolates cultured from the multivalent vaccinates. The remaining bacterial isolates from the latter group, together with all isolates from the non-vaccinated controls, belonged to serogroup B. Results are consistent with the hypothesis that derivatives of the serogroup B challenge inoculum had expressed serogroup C pilus antigen within 6 days of the challenge, possibly as a result of pilus gene inversion occurring in response to the presence of specific antibody in eye tissues and tears.

Animals↗
PubMed1994

A haemolytic cell-free preparation of Moraxella bovis confers protection against infectious bovine keratoconjunctivitis.

Protection conferred by a cell-free preparation from a haemolytic Moraxella bovis isolate, UQV 148NF, was compared to an equivalent fraction from a non-haemolytic M. bovis isolate, Gordon 26L3, and to a recombinant DNA-derived pili vaccine. Three groups of ten calves were vaccinated twice with one of the three preparations and, together with ten non-vaccinated calves, challenged with virulent M. bovis isolate Dal 2d. Compared to the control group, significant protection was observed in the group receiving the pili vaccine and the group receiving the preparation from haemolytic isolate, UQV 148NF.

Animals↗
PubMed1994

Protective antibody titres and antigenic competition in multivalent Dichelobacter nodosus fimbrial vaccines using characterised rDNA antigens.

The relationship between K-agglutination antibody titres and protection against experimental challenge with Dichelobacter nodosus, the effect of increasing the number of D. nodosus fimbrial antigens, and the importance of the nature of additional antigens in multivalent vaccines on antibody response and protection against experimental challenge with D. nodosus were examined in Merino sheep. A total of 204 Merino sheep were allocated to one of 12 groups, and vaccinated with preparations containing a variable number of rDNA D. nodosus fimbrial antigens. The most complex vaccine contained ten fimbrial antigens from all major D. nodosus serogroups, while the least complex contained a single fimbrial antigen. In addition to D. nodosus fimbrial antigens, other bacterial rDNA fimbrial antigens (Moraxella bovis Da12d and Escherichia coli K99), and bovine serum albumin (BSA) were used in some vaccines. Antibody titres to fimbrial antigens and BSA were measured by agglutination and ELISA tests, respectively. Antibody titres were determined on five occasions (Weeks 0, 3, 6, 8, and 11 after primary vaccination). All sheep were exposed to an experimental challenge with virulent isolates of D. nodosus from either serogroup A or B, 8 weeks after primary vaccination. For D. nodosus K-agglutinating antibody titres, a strong negative correlation between antibody titre and footrot lesion score was observed. This relationship was influenced by the virulence of the challenge strain. Increasing the number of fimbrial antigens in experimental rDNA D. nodosus fimbrial vaccines resulted in a linear decrease in K-agglutinating antibody titres to individual D. nodosus serogroups. Similarly, a linear decrease in protection to challenge with homologous serogroups was observed as the number of D. nodosus fimbrial antigens represented in the vaccine increased. The reduction in antibody titres in multicomponent vaccines is thought to be due to antigenic competition. The level of competition between individual antigens is not constant and appears to be related to the immunodominance (nature) of the competing antigens. Both BSA ELISA, and M. bovis K-agglutinating antibody titres were adversely affected by the presence of two D. nodosus fimbrial preparations, whereas the antigenicity of E. coli K99 was unchanged by the presence of two additional D. nodosus antigens. Further studies are required to determine the step(s) in the immune response which are influenced by antigenic competition. Our results suggest that antigen presentation, particularly following primary vaccination, is the step most strongly influenced by antigenic competition.

Animals↗
PubMed1994

Application of ELISA to the serological diagnosis of virulent ovine footrot.

The sensitivity and specificity of an ELISA that detects antibody in the serum of sheep against Dichelobacter nodosus was investigated. The sensitivity of the assay was determined in two trials in which sheep free of virulent footrot were exposed to a virulent strain of D. nodosus. In the first trial up to 96.6% of sheep that developed severe foot lesions were seropositive 2 weeks later. The proportion of seropositive sheep depended on the interval between exposure to D. nodosus and collection of blood samples and reached a maximum 6 weeks after exposure in the first trial and plateaued from 8 weeks after exposure in the second trial. Of sheep with severe lesions present for only 1 week, 40.0% became seropositive, while 98.3% of sheep with severe lesions present for 3 or more weeks became seropositive in Trial 1. Of the unexposed control sheep from the same flock, 93.3% remained seronegative. At least 75% of sheep that were vaccinated with commercial footrot vaccines remained seropositive for at least 24 months after last vaccination and 58.5% remained seropositive for at least 36 months. The specificity of the assay in flocks of sheep from different geographical regions was determined also. Overall, 95.2% of 2978 sheep free of virulent footrot were seronegative. However the rate of false positive serological reactions ranged from 1.6% to 11.3% between flocks and was higher in older sheep (7.0%) compared with sheep less than 1.5 years old (2.7%). Passively acquired colostral antibodies against D. nodosus were measured in 22 lambs and did not persist beyond 55 days mean age. Non-specific reactions with cross reactive antigens were proposed to explain age related changes in serological results. Applications of this ELISA in footrot control programmes are discussed.

Animals↗
PubMed1993

Detection of Dichelobacter nodosus using species-specific oligonucleotides as PCR primers.

Dichelobacter nodosus is an essential causative agent of ovine footrot, a disease of major economic significance. Four oligonucleotides complementary to variable regions of the 16S rRNA of D. nodosus were identified, synthesized and tested for their specificity and sensitivity as probes for the detection of D. nodosus. In hybridization reactions using total RNA as the target nucleic acid, three probes were found to be both sensitive and species-specific. When these probes were used as primers in PCR reactions, on both purified D. nodosus DNA and whole cells, the sensitivity of detection was increased by several orders of magnitude. Using PCR, it was possible to detect the presence of D. nodosus by direct examination of lesion material from footrot infected sheep.

Animals↗
PubMed1993

A Moraxella bovis pili vaccine produced by recombinant DNA technology for the prevention of infectious bovine keratoconjunctivitis.

Pili (fimbriae) were prepared from Moraxella bovis strain Dalton 2d (Dal2d) and from a derivative of Pseudomonas aeruginosa K/2PfS that contained a plasmid-borne Dal2d pilin gene and produced pili having serogroup-specific identity to Dal2d. Nine calves were vaccinated with two doses each of 30 micrograms authentic M. bovis Dal2d pili in oil adjuvant and 10 calves were vaccinated with a similar dose of P. aeruginosa-derived Dal2d pili in the same formulation. All 19 calves and 10 non-vaccinated controls were challenged by instillation of 1 x 10(9) virulent M. bovis Dal2d cells into both conjunctival sacs 19 days after the second vaccine dose. The serological response to vaccination and the degree of protection against experimentally induced infectious bovine keratoconjunctivitis (IBK) were assessed. None of the nine calves vaccinated with authentic M. bovis Dal2d pili developed IBK while two of those vaccinated with P. aeruginosa-derived Dal2d pili developed lesions which accounted for a mean group lesion score of 0.3. In contrast, 9 of the 10 non-vaccinated calves developed IBK lesions, the majority of which were progressive, required early treatment and accounted for a mean group lesion score of 1.5. These results demonstrate the potential of a relatively low dose of pili produced by recombinant DNA technology for development of an effective vaccine against IBK.

Animals↗
PubMed1993

Recombinant vaccines against ovine footrot.

For the past 20 years footrot vaccines have evolved from simple bacterins to highly specific recombinant DNA (rDNA) fimbrial vaccines. The development of these vaccines has left a trail of discoveries, challenges and solutions; these processes continue as we move closer to understanding the requirements of a footrot vaccine. The initial whole cell vaccines were unsuccessful due to the short duration of immunity and incorporation of limited serotypes. A multistrain vaccine eliminated the problem of serotype inclusion, although the duration of immunity in many cases is still inadequate. The proteases of Dichelobacter nodosus appear to be cross protective; however, little is known of their ability to protect sheep against footrot. The major protective immunogen is the bacterial fimbriae, which also forms the basis for the K-agglutination serotyping system. K-agglutinin titre correlates directly with resistance to challenge. The protective fimbrial epitope is conformationally dependent, suggesting little advantage in the development of synthetic peptide vaccines. To enhance the efficiency of vaccine production D. nodosus fimbrial genes were eventually cloned and successfully expressed in Ps. aeruginosa. Monovalent vaccines based on recombinant fimbriae are omnipotent, inducing high levels of agglutinins and long lasting immunity. In multivalent vaccines, on the other hand, incorporation of each additional serogroup into the vaccine results in reduced efficacy both in terms of reduced K-agglutinin titres and reduced protection following challenge. The least effective are multivalent formulations representing all major serogroups. In addition, considerable genetic variation has been observed in the ability of sheep to respond optimally to each serogroup in a multivalent vaccine. Results show that the limitation of the sheep to mount an effective immune response, rather than the quality or quantity of the immunogen, limits the efficacy of current footrot vaccines. Studies are being undertaken to examine in detail the immune response of sheep to potentially highly effective footrot vaccines.

Animals↗
PubMed1993

The effects of antigenic competition on the efficacy of multivalent footrot vaccines.

A multivalent footrot vaccine has been developed, containing pilus antigens produced in recombinant Pseudomonas aeruginosa and representing all nine serogroups of Dichelobacter (Bacteroides) nodosus commonly recognised in the field. The responses of sheep to the multivalent vaccine have been compared with those to monovalent vaccines representing only a single serogroup. Antigenic competition between serogroups occurred in sheep immunised with the multivalent formation, but high levels of protection were still achieved. The study showed that in multivalent footrot vaccines, antigenic competition is predominantly due to the presence of a family of immunologically-related pilus antigens rather than to interference by extraneous proteins.

Agglutination Tests↗
PubMed1992

Humoral responses to a multivalent vaccine in age-matched lambs of different bodyweight and nutrition.

K-agglutination, pilus-enzyme-linked immunosorbent assay (ELISA) and outer membrane protein-ELISAs were used to assess humoral responses after vaccination with a commercial, multivalent, ovine foot rot vaccine (Dichelobacter nodosus whole cells) in three groups of nine-month-old lambs of markedly different bodyweight, nutritional history and dietary protein supply. Mean bodyweights of lambs in low (L), medium (M) and high (H) bodyweight/nutrition groups were 22, 32 and 48 kg, respectively, at the time of vaccination. Few significant differences in humoral responses to vaccine antigens were found between groups. However, lambs in group H tended to have lower levels of antibody to a greater number of component antigens than did lambs in the other groups. These results suggest that low bodyweight due to poor nutrition is unlikely to affect the response of sheep to multivalent foot rot vaccines.

Agglutination Tests↗
PubMed1991

Gene sequences and comparison of the fimbrial subunits representative of Bacteroides nodosus serotypes A to I: class I and class II strains.

We have determined the nucleotide sequences of the genes encoding the fimbrial subunits representative of the known Bacteroides nodosus serogroups. All of the genes are preceded by a highly conserved region which includes the likely promoter and transcriptional regulator sites as well as the ribosome-biding site, and are followed within a short but variable distance by a sequence with the characteristics of a transcription termination or attenuation signal. Based on sequence and organization, the subunits can be divided into two major classes called I (serogroups A, B, C, E, F, G, and I) and II (serogroups D and H). All contain the same seven-amino-acid positively charged leader sequence and conserved hydrophobic amino-terminal sequence typical of type 4 fibriae. Beyond this point the class II subunits are quite different from class I and share features more in common with those from other type 4 fimbriate bacteria, such as Moraxella bovis and Pseudomonas aeruginosa. The larger class I may be further subdivided into two subsets: (i) [A, E, F)(B, I)) and (ii) (C, G). These proteins exhibit three major clusters of variation, at either end of the presumptive disulphide loop which spans the central third of the protein, and near the carboxy-terimus, with dispersed changes in between. The length of the mature subunits varies from 152-156 amino acids, and the variation includes small insertions or deletions in the variable clusters between more conserved domains. The class II subunits are 149 amino acids in length and contain two pairs of cysteine residues: one is at the end of the amino-terminal conserved region, and the other is at the end of the protein. The major variation occurs in the central region of the molecule, and again small insertions or deletions are required to align adjacent conserved domains. There is also a striking absence of silent codon changes in the 5' coding region of all of these genes, indicating that these sequences have a secondary genetic function, probably in recombinational exchange.

Amino Acid Sequence↗
PubMed1990

Antigenic stability of fimbriae of Bacteroides nodosus.

Successful vaccination of sheep against footrot and attempts to eradicate the disease depend on there being a limit to the antigenic diversity of the causative bacterium, Bacteroides nodosus. Fimbrial antigenic variation was therefore investigated in vivo, both under conditions of chronic infection and under the pressure of a vaccine-induced immune response, to ascertain whether this represented an obstacle to such goals. Material was available from 5 experiments and although B. nodosus appeared to have undergone changes in its fimbrial antigens in one of these, the possibility that superinfection was responsible for the variation detected could not be ruled out because all sheep in this case were maintained at pasture. Overall, the results provided no evidence of fimbrial antigenic shift in B. nodosus in vivo and in conclusion, the survival of the organism in the sheep's foot, both in long-term natural infection and following vaccination, must therefore be related to factors other than the ability to undergo antigenic variation in order to evade the host's immune response.

Animals↗
PubMed1990

Treatment of virulent footrot with lincomycin and spectinomycin.

A mixture of lincomycin and spectinomycin was investigated as a treatment for footrot in sheep. In a controlled clinical trial 92.5% of acute and chronic cases of virulent footrot were cured following a single intramuscular injection of a mixture containing 50 mg lincomycin and 100 mg spectinomycin/ml at a dose rate of 1 ml/10 kg bodyweight. No improvement in clinical response was observed in groups of sheep treated on 3 successive days with this dose rate nor in another group treated once at a dose rate 1 ml/3.3 kg bodyweight. Cure effectiveness of each of the 3 treatment groups relative to untreated controls was 89%, 95% and 95%. Efficacy of lincomycin/spectinomycin was compared with that of penicillin/streptomycin in the treatment of footrot on 2 farms in south western New South Wales. Assessments made 14 to 17 d after treatment showed that on one farm all 122 ewes treated with lincomycin/spectinomycin had recovered while 170 of 175 ewes treated with penicillin/streptomycin recovered in the same period. On the second farm 87 of 90 ewes treated with lincomycin/spectinomycin recovered, compared with 184 of 190 sheep in the same flock treated with penicillin/streptomycin. Supportive footbathing did not seem to improve the clinical response in either treatment group and the paring done was sufficient only to establish diagnosis and to remove grossly overgrown horn.

Animals↗
PubMed1990

Morphogenetic expression of Moraxella bovis fimbriae (pili) in Pseudomonas aeruginosa.

Type 4 fimbriae (pili) are found in a wide variety of gram-negative bacteria and are composed of small structural subunits which share significant sequence homology among different species, especially at their amino-terminal ends. Previous studies demonstrating morphogenetic expression of Bacteroides nodosus fimbriae from cloned subunit genes in Pseudomonas aeruginosa suggested that there is a common mechanism for type 4 fimbriae assembly and that the structural subunits are interchangeable (J. S. Mattick et al., J. Bacteriol. 169:33-41, 1987). Here we have examined the expression of Moraxella bovis fimbrial subunits in P. aeruginosa. M. bovis subunits were assembled into extracellular fimbriae in this host, in some cases as a homopolymer but in others as a mosaic with the indigenous subunit, indicating structural equivalence. This result contrasts with other studies in which recombinant P. aeruginosa expressing different subunits produced fimbriae composed almost exclusively of one subunit or the other (T. C. Elleman and J. E. Peterson, Mol. Microbiol. 1:377-380, 1987). Both observations can be explained by reversibility of subunit-subunit interactions at the site of assembly, with the forward equilibrium favoring chain extension between compatible subunits.

DNA, Recombinant↗
PubMed1990

Anthelmintic activity of the macrocyclic lactone F28249-alpha in sheep.

The macrolytic lactone F28249-alpha was titrated in experimentally infected sheep and found to be highly effective against most of the common gastrointestinal nematodes as a single oral dose, given at a rate of 0.025, 0.05, or 0.1 mg/kg. Specifically, maximal activity was evident at even the lowest dosage against adult Haemonchus contortus, Ostertagia circumcinta, Trichostrongylus axei, and T colubriformis and L4 O circumcinta. Activity against Oesophagostomum columbianum was also high at all dosages, with a calculated ED95 of 0.029 mg/kg. Cooperia curticei was eliminated at 0.1 mg/kg, but control was erratic at the lower dosages. The greatest weakness of this compound was its activity against C oncophora. The activity against this parasite was weak (less than or equal to 85%) at all dosages, and the dosage-response curve was flat, suggesting dosages substantially higher than those given would be necessary for high-order control of this species.

Administration, Oral↗