Evaluation of the immunogenicity of the P97R1 adhesin of Mycoplasma hyopneumoniae as a mucosal vaccine in mice.

The immunogenicity of P97 adhesin repeat region R1 (P97R1) of Mycoplasma hyopneumoniae, an important pathogenesis-associated region of P97, was evaluated in mice as a mucosal vaccine. Mice were immunized orally with attenuated Salmonella typhimurium aroA strain CS332 harbouring a eukaryotic or prokaryotic expression vector encoding IP97R1. Local and systemic immune responses were analysed by ELISA on mouse sera, lung washes and splenocyte supernatants following splenocyte stimulation with specific antigens in vitro. Although no P97R1-specific antibody responses were detected in serum and lung washes, significant gamma interferon was produced by P97R1-stimulated splenocytes from mice immunized orally with S. typhimurium aroA harbouring either expression system, indicating induction of a cell-mediated immune response. These results suggested that live bacterial vectors carrying DNA vaccines or expressing heterologous antigens preferentially induce a Th1 response. Surprisingly, however, mice immunized with the vaccine carrier S. typhimurium aroA CS332 induced serum IgG, but not mucosal IgA, against P97R1 or S. typhimurium aroA CS332 whole-cell lysate, emphasizing the importance of assessing the suitability of attenuated S. typhimurium antigen-carrier delivery vectors in the mouse model prior to their evaluation as potential vaccines in the target species, which in this instance was pigs.

Using immunology and resistant sheep to beat the fly

New methods for controlling blowfly strike will be needed when mulesing is phased out and the availability or efficacy of insecticides for control of fly strike decreases. The Australian Sheep Industry CRC has pursued two approaches for the development of new methods to help control blowfly strike. In the first, genetic resistance of sheep to survival and growth of blowfly larvae was examined. Resistance to growth of larvae was heritable (0.29 ± 0.22). The trait was not associated with resistance to internal parasites, nor was it influenced by wool characteristics such as fibre diameter or coefficient of variation of fibre diameter. This new trait differs from resistance to fly strike associated with resistance to fleece rot. Because measurement of the trait is labour intensive, gene markers or correlated measures are needed before it will be suitable for industry adoption. The second approach examined the impact of larval products on the immmune system of the sheep. Larvae suppress the sheep immune system and thereby limit the ability of the sheep to reject the larvae. The immunosuppresive agent is being purified and strategies to abolish its activity are being explored. Abolition of immunosuppression would create opportunities for the development of new vaccines againts blowfly strike.

Resistance to insect growth regulator insecticides in populations of sheep lice as assessed by a moulting disruption assay

Low-volume, backline applications with the benzoylphenyl urea insecticides triflumuron and diflubenzuron represent in excess of 70% of treatments for the control of sheep lice, Bovicola ovis (Schrank) (Phthiraptera: Trichodectidae), in Australia. Reports of reduced effectiveness from 2003 and subsequent controlled treatment trials suggested the emergence of resistance to these compounds in B. ovis populations. A laboratory assay based on the measurement of moulting success in nymphs was developed and used to assess susceptibility to diflubenzuron and triflumuron in louse populations collected from sheep where a control failure had occurred. These tests confirmed the development of resistance to triflumuron and diflubenzuron in at least two instances, with estimated resistance ratios of 67-94X at LC50.