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Notable Achievements
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| Research Interests |
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| Neurobiology of the Infective Process: focusing on gastrointestinal nematodes (roundworms) of sheep, swine, dogs, and humans. The worms involved include: the stomach worm of sheep (Haemonchus), the nodular worm of swine (Oesophagostomum), the hookworm of dogs (Ancylostoma) and the threadworm of dogs and humans (Strongyloides). These are important pathogens of domestic animals, and in one case, humans, all having considerable economic/medical impact. We are identifying individual sensory neurons using electron microscopy and computer-based reconstruction technology to create 3D images of the anterior sensory nervous system of these worms. Having identified the individual cells, we construct maps that permit us to locate these cells in living hatchling worms using a specialized optical technique, differential interference contrast microscopy (DIC). This combined with laser microsurgery permits us to kill individually recognized target neurons and, thereby, identify their functions by their failure to function normally in 1) positioning the infective larva in the environment, 2) establishing host contact, and 3) controlling aspects of development. To date, we have found and identified thermosensory and chemosensory neurons considered to be important in finding and penetrating warm-blooded mammalian hosts. In the case of S. stercoralis, we have also identified neurons that control the change in direction of larval development from that which normally leads to free-living adulthood to that which leads to an infective stage larva with a potential for development to parasitic adulthood. The same group of neurons apparently is associated with drug resistance. We have shown that, in ivermectin-resistant strains of the sheep stomach worm, Haemonchus, the amphidial neurons are foreshortened, whereas in an ivermectin-susceptible parental strain, the neurons are of normal length. We are also interested in adapting the Australian strongyloid nematode, Parastrongyloides trichosauri, to long-term in vivo and in vitro maintenance in the laboratory. We are in the process of establishing this parasite, which hopefully can be passaged indefinitely on agar plate cultures, in an in vitro culture system and have also succeeded in passaging it in Australian Sugar Gliders. To date, agar plate cultures have permitted us to passage this species for approximately 50 - 70 generations without a rejuvenating passage through a host. |
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| Selected Publications |
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| Li, J., Zhu, X., Boston, R., Ashton, F.T., Gamble, H.R., and G.A. SCHAD. 2000. Thermotaxis and thermosensory neurons in infective larvae of Haemonchus contortus a passively ingested nematode parasite. Journal of Comparative Neurology. 424: 58-73.
Lopez, M.P., Boston, R., Ashton, F.T., and SCHAD, G.A. 2000. The neurons of class ALD mediate thermotaxis in the parasitic nematode, Strongyloides stercoralis. International Journal for Parasitology. 30: 1115-1121. Bhopale, V.M., Kupprion, E.K., Ashton, F.T., Boston, R., SCHAD, G.A. 2000. Ancylostoma caninum The finger Cell Neurons Mediate Thermotactic Behavior by Infective Larvae of the Dog Hookworm. Experimental Parasitology.96: 70-76. Sciacca, J., Forbes, W.M., Ashton, F.T., Lombardini, E., Gamble, H.R., and SCHAD, G.A. 2002. Response to carbon dioxide by the infective larvae of three species of parasitic nematodes. Parasitology International. 51: 53-62. Herbert, D. R., Nolan, T.J., SCHAD, G.A., and Abraham, D. 2002. The role of B cells in immunity against larval Strongyloides stercoralis in mice. Parasite Immunology. 24:95-101 Herbert, D. R., Nolan, T.J., SCHAD, G.A., Lustigman, S., and Abraham, D. Immunoaffinity isolated antigens induce protective immunity against larval Strongyloides stercoralis in mice. Experimental Parasitology. 100:112-20 Sciacca, J., Ketschek, A., Forbes, W.M., Boston , R.A., Guerrero, J., Ashton, F.T., Gamble, H.R., and SCHAD, G.A. 2002. Vertical migration by the infective larvae of three species of parasitic nematodes: Is the behavior really a response to gravity? Parasitology. 125:553-560. Freeman, A.S., Nghiem, C., Li, J., Ashton, F.T., Guerrero, J., Shoop, W.L., and SCHAD,G.A. 2003. Amphidial structure of invermectin-resistant and susceptible laboratory and field strains of Haemonchus contortus. Veterinary Parasitology. 110: 217-226. Ligas, J.A., Kerepesi, L.A., Galioto, A.M., Lustigman, S., Nolan, T.J., SCHAD, G.A. and Abraham, D. 2003. Specificity and Mechanism of Immunoglobulin M (IgM)- and IgG-Dependent Protective Immunity to larval Strongyloides stercoralis in Mice. Infection and Immunity. 71: 6835-6843. Forbes, W.M., Ashton, F.T., Boston, R., Zhu, X., and SCHAD, G.A. 2004. Chemoattraction and chemorepulsion of Strongyloides stercoralis infective larvae on a sodium chloride gradient is mediated by amphidial neuron pairs ASE and ASH, respectively. Veterinary Parasitology, 120: 189-198. Kerepesi1, L.A. , Nolan, T.J., SCHAD, G.A., Lustigman, S., Herbert, D.R., Keiser, P.B., Nutman, T.B., Krolewiecki, A.J., and Abraham, D. 2004. Human Immunoglobulin G Mediates Protective Immunity and Identifies Protective Antigens against Larval Strongyloides stercoralis in Mice. JID 189: 1282. Nolan, T.J., Brenes, M., Ashton, F.T., Zhu,X., Forbes, W.M., Boston, R., and SCHAD, G.A. (2004). The amphidial neuron pair ALD controls the temperature sensitive choice of alternative developmental pathways in the parasitic nematode, Strongyloides stercoralis. Parasitology 129:753-759 Ketschek, A.R., Freeman, A.S., Boston, R., Habecker, P.L., Ashton, F.T., and SCHAD, G.A. (2004) Vertical Migratory Behavior of the Infective Third Stage Larval of Oesophagontomum dentatum. Veterinary Parasitology, 123:215-221 Artis, D., Wang, M.L., Keilbaugh, S.A., He, W., Brenes, M, Swain, G.P., Knight, P.A., Donaldson, D.D., Lazar, M.A., Miller, H.R.P., SCHAD, G.A., Scott, P., and Wu, G.D. (2004) RELMß/FIZZ2 is a goblet cell-specific immune-effector molecule in the gastrointestinal tract. PNAS early edition pgs.1-5 Ketschek, A.R., Joseph, R., Boston, R., Ashton, F.T., and SCHAD, G.A. (2004) Amphidial neurons ADL and ASH initiate sodium dodecyl sulphate avoidance responses in the infective larva of the dog hookworm Ancylostoma caninum. International Journal for Parasitology, 34:1333-1336 Ashton, F.T., Zhu, X., Boston, R., SCHAD, G.A. (2005) Neurobiology of the Nematode Infective Process: Resumption of development by infective Strongyloides stercoralis larvae is mediated by amphidial neurons ASJ. American Journal of Tropical Medicine (submitted) |
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| Graduate Groups |
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Biology Parasitology |
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| Postdocs and Fellowships |
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| Wayne M. Forbes |
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