Browsing by Subject "Parasite"
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Item The early life history and reproductive biology of Cymothoa excisa, a marine isopod parasitizing Atlantic croaker, (Micropogonias undulatus), along the Texas coast(2012-08) Cook, Colt William; Munguia, Pablo; Buskey, Ed; Walther, BenjaminParasite population dynamics and the evolution of life history characteristics are strongly correlated with the processes of host infection, survival within a host and reproduction, with each process posing a challenge to the parasitic lifestyle. Macroparasites living in marine environments have evolved extreme changes in physiology, morphology and life history traits to overcome these challenges. This study focused on the infective and reproductive stage of the parasitic isopod, Cymothoa excisa, a common parasite on Atlantic croaker, (Micropogonias undulatus), along the Texas coast. A two year survey identified infection rates and the relationship between fish density and size and parasite load, size and fecundity. Isopod morphology was quantified for each life stage, identifying shape transitions through ontogeny and sex change. Sex change in C. excisa was found to be driven by the absence of conspecific parasites within a host, where sex change only occurred in the first individual to arrive. To understand the infective stage of C. excisa parasite energetics and host detection mechanisms were tested. Parasites with free-living life stages have a narrow window to infect a host and have evolved a number of mechanisms to detect and locate a host. I used a series of energetic experiments to determine an infection window for free-swimming larvae (mancae) and behavioral response experiments testing both visual and chemical cues associated with host detection. Mancae were found to have a narrow infection window, where mancae began searching for a host as soon as they are born, but quickly switch to an ambush strategy to conserve energy. Mancae were also found to be responsive to both visual and chemical cues from its common fish host, as well as a non-host fish, indicating that chemical cues are used in host detection, but chemical specificity is not a mechanism that C. excisa uses to find its common host. The results from this study have implications to parasitic species and their hosts, as well as to other areas of study, including population and ecosystem dynamics.Item Endohelminths from six rare species of turtles (Bataguridae) from Southeast Asia confiscated by international authorities in Hong Kong, China(Texas A&M University, 2004-09-30) Murray, Rebecca AnnSpecimens of 6 species of threatened, vulnerable, and endangered turtles (Cuora amboinensis, Cyclemys dentata, Heosemys grandis, Orlitia borneensis, Pyxidea mouhotii, and Siebenrockiella crassicollis) belonging to family Bataguridae, were confiscated in Hong Kong, China on 11 December 2001 by international authorities. Endohelminth studies on these turtle species are scarce, and this study provided a rare opportunity to examine a limited number of specimens for endohelminths. Ten different parasite species were collected and there were 16 new host records. This is the first record of a parasite from P. mouhotii. The parasite prevalences found in this study provide a basis for a better understanding of the phylogenetic relationships of the family Bataguridae to other families, especially Testudinidae. Based on known life cycles, parasites found provided an indication of food preferences of these 6 turtle species that support previous studies of the turtles' feeding habits. However, the results of the parasite survey from O. borneensis provided additional feeding habit information. The list of endohelminths herein is intended to provide a foundation for future parasite studies of the 6 species of Asian turtles.Item Investigation of Anthelmintic Resistance and De-Worming Regimens in Horses(Texas Tech University, 2005-08) Blanek, Meghan; Brady, Heidi A.; Pond, Kevin R.; Wester, David B.; Jackson, Samuel P.Parasite resistance has emerged as a health dilemma in the livestock industry as many classes of parasites are becoming resistant to dewormers. Parasitism is very costly to the equine industry as it affects the performance and health of horses. Resistance has been documented for every type of equine anthelmintic class. A series of three studies was conducted to determine the efficacy of different deworming regimens. In Study 1, three fenbendazole deworming regimens were given to assess efficacy as determined by fecal egg reduction and to test for possible anthelmintic resistance in a herd that was administered only fenbendazole for 18 months prior. Resistance to fenbendazole was documented in this population based on fecal egg count reduction (FECR) tests and DrenchRite assays. Significant differences in FECR were observed between the larvicidal treatment and 5 mg/kg treatment on both day 42 versus 28 (P < 0.05) and day 72 versus 56 (P = 0.10). When analyzed by age of young horses (< 2 years of age) versus mature mares (> 2 years of age), there was a significant difference on both day 42 versus 28 and day 72 versus 56 (P < 0.05). In Study two, the efficacy of moxidectin, ivermectrin, and the larvicidial dose of fenbendazole were studied in this herd of known resistance. Mean FECR tested on day 14 post treatment was 99.91%, 98.73%, and 89.07% respectively, for the three treatment groups. Moxidectin and ivermectin groups were significantly different from the fenbendazole group (P < 0.05). When analyzed by age however, there were no differences between treatment groups in the mature mares (> 2 years of age). However, the moxidectin and ivermectin were significantly different from the fenbendazole group in the young horses (< 2 years of age) (P < 0.05). Study three determined the efficacy of a year-long rotation on breaking fenbendazole resistance in a field setting. A farm wide study showed a quarterly rotation of pyrantel pamoate (June), ivermectin (September), a larvicidal dose of fenbendazole (December), and moxidectin (March) broke resistance based on fecal egg count reduction tests. The mean fecal egg count reductions for the treatments, tested on day 7 post treatment, were 95.86%, 100%, 97.84%, and 100% respectively.