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Biomedical subjects

D D Heath

Publications and source records attributed to D D Heath.

At least 73 records · Page 4Linked to original sources
PubMed1992

Echinococcus granulosus in sheep: transfer from ewe to lamb of 'Arc 5' antibodies and oncosphere-killing activity, but not protection.

Fourteen ewes were orally dosed with 2000 E. granulosus eggs at 2 weeks of age, were mated at 19 months, and produced lambs when the cysts were 2 years old. One week after parturition, all 14 ewes had 'Arc 5' antibodies in their serum, as did 11/14 of their lambs. Fourteen uninfected ewes were immunized three times before parturition with E. granulosus eggs injected intramuscularly. Cysts grew at the first, or first and second site, but not the third, indicating that the ewes were immune prior to parturition. Most sera from these ewes and their lambs, and from 14 control ewes and their lambs, produced precipitin arcs with hydatid cyst fluid, but no 'Arc 5'. All lambs were challenged with 500 eggs 2 weeks after birth. At necropsy, cyst numbers within groups ranged from 3 to > 200, but there was no significant difference between the three groups of lambs. The immunized ewes did not pass a protection to their lambs that was effective when the lambs were challenged. 'Arc 5' antibodies were induced by prolonged infection with cysts, and were not seen in the sera of ewes immunized with eggs, although the eggs developed into cysts at the injection sites. 'Arc 5' antibodies did not protect lambs against infection, and were not correlated with protection in ewes. Subcutaneous injection of oncospheres into four ewes from each group at the time of lamb challenge showed that the immunized ewes were immune to this method of challenge, but the infected and control ewes were not.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

Echinococcus granulosus: use of an intermediate host mouse model to evaluate sources of protective antigens and a role for antibody in the immune response.

A Balb/cJ mouse model was used to determine which stage of the E. granulosus life cycle possessed the most potent protective antigens. Mice were immunized with crude extracts of protoscoleces, brood capsules, cyst fluid, adult worm tissue, eggs or oncospheres and then challenged intraperitoneally with 600 activated oncospheres. Sonically disrupted oncospheres induced the highest levels of protection (greater than 90%) at doses greater than or equal to 10(3) oncosphere equivalents per mouse. High levels of protection were maintained when these preparations were solubilized in SDS. Immunization with Taenia ovis or T. hydatigena oncosphere preparations induced a maximum of 62 and 40% cross-protection, respectively. In passive transfer experiments, serum from triple-infected immune donors that were completely resistant to subsequent challenge induced 69% protection in naive recipients (P less than 0.01). Serum from mice that had been immunized with oncosphere sonicates that were shown to be highly immune, failed to induce statistically significant protection in recipients. A sheep trial confirmed the protective ability of prior infections. Immunization of sheep with a SDS solubilized oncosphere preparation produced 91% protection (P less than 0.01).

Animals↗
PubMed1992

Use of Echinococcus granulosus worm antigens for immunodiagnosis of E. granulosus infection in dogs.

Echinococcus granulosus worm excretory/secretory antigens (WES) were used in ELISA for diagnosis of E. granulosus infection in dogs and compared with protoscolex somatic antigens (PSM). Sera from 224 dogs were tested. There was no correlation between ELISA absorbance values and E. granulosus worm burdens using either antigen. There was a significant linear relationship between absorbance values of sera tested in the ELISA using WES (W-ELISA) and the ELISA using PSM (P-ELISA). However, there was a small but significant difference between the absorbance values of the sera tested against the two antigens. Western blot analysis of WES using sera from E. granulosus-infected and uninfected dogs revealed antigenic components of relative molecular mass (Mr) larger than 94,000, Mr 94,000-68,000 and Mr 43,000-39,000 in worms, and these were specific for E. granulosus and not identified in PSM; these antigenic differences may be responsible for differences in reactivity in ELISA. The sensitivities of W-ELISA and P-ELISA were 80.8% and 75.6%, respectively. The specificities of W-ELISA and P-ELISA were 93.7% and 97.9%, respectively. The reduced specificity in W-ELISA was mainly attributable to increased background reactivity of sera from Taenia hydatigena-infected dogs. Despite the reduction in specificity, both ELISAs are valuable epidemiological tools to determine the prevalence of antibody to E. granulosus in dog populations and to monitor the success of hydatid control campaigns.

Animals↗
PubMed1991

Echinococcus granulosus: development of an intermediate host mouse model for use in vaccination studies.

A mouse model has been developed to evaluate potential protective antigens which could render intermediate hosts resistant to a challenge infection with Echinococcus granulosus eggs. DBA/2J, CBA/J, Balb/cJ, C57/B16J and CF-1 mice were initially infected orally and parenterally with eggs, hatched eggs or activated oncospheres. Generally less than 1% of the oral dose established as cysts. Mean cysts counts were increased when Balb/cJ mice were injected intraperitoneally or intravenously with activated oncospheres. A challenge regime using 600 activated oncospheres injected intraperitoneally into adult Balb/cJ mice was subsequently adopted yielding means of 15-51 cysts per mouse. When activated oncospheres were injected intraperitoneally into Balb/cJ, DBA/2J and CF-1 mice, cysts were restricted to the peritoneal cavity. Activated oncospheres injected intravenously, however, lodged almost exclusively in the lung and thoracic cavity, except in DBA/2J mice where 55% lodged in the liver. This anatomical localization enabled the outcome of prior infection and challenge to be monitored separately. Prior infection rendered Balb/cJ mice fully resistant to subsequent challenge.

Animals↗
PubMed1989

Vaccination against ovine cysticercosis using a defined recombinant antigen.

Cysticercosis caused by larval tapeworms is a major public health problem and a cause of substantial economic losses in the farm-animal industries. Taenia ovis in sheep is a particularly important example. Immunity to reinfection with the larvae has a central role in regulating natural transmission of the parasites, and vaccination with antigens from the early larval oncosphere stage can induce complete protection against infection. As it is impractical to obtain enough oncospheres for a commercial vaccine against these tapeworms, an alternative approach is to use recombinant DNA methods to generate a cheap and plentiful supply of antigens. We report here the expression in Escherichia coli of complementary DNA encoding T. ovis antigens as fusion proteins with the Schistosoma japonicum glutathione S-transferase. Vaccination of sheep with these fusion proteins gave significant, although not complete, immunity against challenge infection with T. ovis eggs. Commercial development of a vaccine is being pursued.

Amino Acid Sequence↗
PubMed1989

Echinococcus granulosus: ultrastructure of epithelial changes during the first 8 days of metacestode development in vitro.

The epithelium of artificially hatched and activated oncospheres of E. granulosus was studied ultrastructurally over the first 8 days of metacestode development in vitro. Within 4 h of activation, the epithelium was transformed from a thin cytoplasmic layer into a much wider layer packed with penetration gland granules and containing mitochondria and Golgi apparatus. Microvilli were extended from the outer plasma membrane and the basal lamina on the inner epithelial surface virtually disappeared. Microvilli increased in number and length over the first 24 h of development while granules in both the epithelium and penetration gland decreased in number. The granules appear to be involved in microvilli formation. After 3 days of development, the first lamination resolved ultrastructurally as shortened microvilli and some microtriches extending from the epithelium surrounded by an electron-dense microfibrillate material containing sloughed microvilli. By 6 days post-activation, no microvilli remained and only double-walled truncated microtriches extended from the epithelium. The microfibrillate material had become more electron-dense and was closer to the epithelium than at day 1. Within 8 days of metacestode development, a second lamination had developed. Both microfibrillate and particulate material of a greater electron density than the first lamination was added to the microthrix side of the first lamination.

Animals↗
PubMed1988

A blind test of the serological response of dogs to infection with Taenia ovis.

Fifty six dogs of mixed age and sex were acquired from farms in the Otago/Southland region, and maintained at the Hydatid Research Unit, Taieri, where 43 were each fed two Tueniu ovis cysts. All were bled fortnightly for six or 12 weeks. Coded sera were sent to Wallaceville Animal Research Centre for testing using ELISA, with antigen from T. ovis scoleces. Dog treatments were identified after all tests were complete. A discriminant level was derived from the mean absorbance value plus three standard deviations of 56 sera taken at time zero and 78 sera from serially bled uninfected dogs. None of these 134 sera registered as a false positive using this discriminant level. The data showed no significant deviation from normality, and the expected frequency of the occurrence of false positives is therefore less than 0.14%. Four weeks after infection 63% of dogs proved to be infected were serologically positive, rising to 78% after 6 weeks. When worms were removed by anthelmintic treatment, ELISA absorbance levels decreased. Four weeks after removal 70% of previously infected dogs remained positive, decreasing to 30% after 6 weeks. Six weeks after infection the sensitivity of the test was 78%, and the specificity 63%. However, if dogs with positive ELISA absorbance levels, but which did not purge worms, were regarded as having had worms, the respective figures would be 82% and 100%. The latter figures are similar to our previously published laboratory results. The test is of comparable efficiency to arecoline purgation for surveillance, and has the additional advantage of detecting infection in the majority of those dogs that have been infected for three weeks or more but fail to pass worms on purgation, and a substantial proportion of those infected dogs that were treated by their owners prior to presenting them for purgation in order to avoid detection of infection.

Journal Article↗
PubMed1986

Axon and neuron numbers after forelimb amputation in neonatal rats.

It seems a paradox that more primary sensory neurons are lost but recovery is better after peripheral nerve injury in neonates as compared to adult mammals. A possible explanation is that surviving neurons sprout in the neonate. To test this, forelimbs in neonatal rats were amputated, which caused the death of many primary sensory neurons. The number of neurons in the dorsal root ganglia, and the number of myelinated and unmyelinated fibers in the dorsal and ventral roots were determined on the amputated and contralateral normal sides. On the amputated side, soma loss in the ganglia was 30%, and the fiber numbers were decreased by 16% in the dorsal root and increased by 20% in the ventral root. These data are compatible with the hypothesis that there is axonal branching or sprouting from surviving sensory neurons. In addition, morphometric analyses showed a changed myelin-axon relationship for central processes of sensory cells whose distal processes have been cut.

Amputation, Surgical↗
PubMed1985

The use of excretory and secretory antigens of the scolex of Taenia ovis for the serodiagnosis of infection in dogs.

The excretory and secretory antigens from the evaginated scoleces of Taenia ovis were collected for 3 days in vitro, and used in an ELISA test to detect antibodies to T. ovis in the serum of dogs. When tested on sequentially collected sera, diagnostic ELISA values could be detected in many dogs 4 wk after infection, and remained for an average of a further 4 wk after worms were removed from dogs with an anthelmintic. Using an ELISA discriminant value that eliminated all false positives from 70 uninfected laboratory dog sera and from 57 uninfected farm dog sera, 54/62 true positives were found in sera from dogs infected with various numbers of T. ovis for various intervals. Sera from dogs infected with T. hydatigena gave 11/15 false positive reactions, whereas sera from 15 dogs infected with Echinococcus granulosus or 7 dogs infected with T. pisiformis were all negative. For T. ovis the test had a high repeatability, was not greatly influenced by the number of worms carried by the dog and higher titres were correlated with long-standing infections. Approximately 1,000 scoleces could be recovered from each experimentally infected sheep. Using the ELISA test with undiluted antigen and serum diluted 1:40, approximately 10 sera could be tested in duplicate with the excretions and secretions from each T. ovis scolex.

Animals↗
PubMed1984

Comparison of cestode antigens in an enzyme-linked immunosorbent assay for the diagnosis of Echinococcus granulosus, Taenia hydatigena and T ovis infections in sheep.

Nine antigens, prepared from somatic tissue, cyst fluids or produced during in vitro culture of Echinococcus granulosus, Taenia hydatigena, T ovis or T crassiceps were tested for their suitability for the diagnosis of larval cestode infections in sheep by the enzyme-linked immunosorbent assay (ELISA). The sensitivity and specificity of each of these antigens were assessed using sera from sheep experimentally infected with graded monospecific infections of E granulosus, T hydatigena or T ovis eggs and sera from naturally infected aged sheep. The ability of eight of the antigens to detect the antibody response to larval cestode infection was also compared over 12 months using sera from serial bleedings. Using the ELISA, all of the antigens were able to detect the presence of larval cestodes, even in sheep with only one or two cysts. Over 12 months, the antibody responses were not generally statistically related to the total number of cysts present in the animals. None of the antigens was able to detect specific infections only. The antigen with least non-specific background activity, which consistently detected the highest antibody titres in the sera of all infected animals was the secretion from T ovis worms cultured in vitro, and is, therefore, the antigen of choice for the detection of non-specific infections with larval cestodes in sheep.

Animals↗
PubMed1982

Vaccination of sheep against Taenia ovis. The response to various dose rates of antigens obtained by incubation of oncospheres in vitro.

Activated oncospheres of Taenia ovis were incubated in vitro for 14 days and the antigens produced were collected and concentrated. Tenfold serial dilutions of the antigens were emulsified with Freund's incomplete adjuvant and injected intramuscularly into sheep. When subsequently challenged with T ovis eggs, these sheep displayed a level of immunity that was related to the amount of antigen injected. The calculated dose-response curve indicated that for the vaccine to be 90 per cent effective, the secretion from approximately 4600 T ovis oncospheres need to be injected into each sheep.

Animals↗