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Aquatic snails are the intermediate hosts of the disease schistosomiasis. Irrigation schemes have often provided a favourable habitat for these snails, but rapidly flowing water will carry them away. The research established 23 stations in irrigation canals and monitored snail numbers and water velocity at these points. A maximum tolerable velocity for the snail Bulinus truncatus of 0.23 m/s was established, corresponding to 0.13 m/sat snail height. Aquatic weed did not invalidate this velocity, but the use of a single control velocity was found to be over-simplistic. The long-term mean velocity was found to be the best measure for snail control when velocity varied with time. Using specially designed filter-traps, snails being carried along by the flow were intercepted and counted. Attempts to relate these counts to velocity revealed daily and seasonal cycles of numbers of snails detaching. Snails in 130 syphon boxes were monitored and the number of snails compared with water velocity. The maximum velocity tolerated here was lower than in the canals. Turbulence theory was examined to explain the difference. The fieldwork was largely carried out in the Tessaout Amont Irrigation Scheme in Morocco. Recommendations are made for the design, operation and maintenance of irrigation schemes, if velocity is to be considered as a snail control.

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An understanding of characteristics of sheep and goat producers across the Southeast United States is crucial for the development and vitality of the small ruminant industry. The state of Mississippi (MS) is rich in animal agriculture, and sheep and goats display the potential to become an integral part of the state’s agricultural livelihood. However, sheep and goat producers are constantly combatting the negative effects gastrointestinal nematodes inflict upon their animals. With the anthelmintic resistance status rising across the globe, sustainable methods to control parasites in small ruminants are crucial. Therefore, small ruminant producers must develop an accurate targeted selective treatment (TST) for their herd or flock. The following studies sought to identify the demographic status of current small ruminant producers in the Southeast, as well as identify the most accurate parasitic indicators (FAMACHA© or body condition scoring, namely) that will contribute significantly to the development and use of TST in MS herds and flocks.

Feline hyperthyroidism is an important disorder in middle-aged and older cats. The cause and pathogenesis of the disease is still unknown and there are few published incidence rates or prevalence estimates. A descriptive cross-sectional study was conducted to determine the prevalence of and potential risk factors for feline hyperthyroidism in Hong Kong. Serum thyroxine (T4) was measured in 305 cats 10 years and older that presented at various veterinary clinics in Hong Kong between June 2006 and August 2007. The veterinarians taking the samples completed a questionnaire regarding the health of each cat. Each owner completed a questionnaire regarding vaccination history, internal and external parasite control, diet and the environment of their cat. Serum total T4 concentration was determined by use of a commercially available radioimmunoassay kit (Coat-a-count®, DPC®). For total T4 the feline reference interval was 12.8-50.0 nmol/L (1.0-3.9 ug/dL). All cats with a serum total T4 concentration of greater than 50.0 nmol/L were classified as hyperthyroid. Alanine aminotransferase (ALT) and alkaline phosphatase (ALP) activities were measured in all the samples. The prevalence of feline hyperthyroidism in Hong Kong was estimated at 3.93% (95% CI : 2.05-6.77) and there was no significant difference in prevalence between healthy (3.16%) and sick (4.37%) cats. This demonstrates that although this disease is present in Hong Kong, the prevalence is lower than the reported prevalence in other parts of the world. Risk factors that were examined included age, sex, breed, number of cats in household, vaccinations, parasite control, indoor environment, type of diet and type of water. Risk factors for hyperthyroidism identified by multivariate analysis were age and breed. Affected cats were more likely to be older (>15 years) and domestic shorthair cats were less likely to be diagnosed with hyperthyroidism than the other breeds combined. There was no statistically significant relationship between sex, vaccinations, parasite control or indoor environment and the development of hyperthyroidism. There was also no statistically significant relationship between the consumption of a canned food diet by the cats and hyperthyroidism. There were no characteristic clinical features amongst the cats that were hyperthyroid and only one cat exhibited the typical clinical syndrome of ravenous appetite with severe weight loss. The lack of distinctive clinical signs could be due to the presence of a mild or early form of the disease, but can also be due to an atypical form of the disease. This study showed that the disease needs to be considered if any of the following factors are present in an older cat : polyphagia, diarrhoea, and a significant raise in ALT and ALP activities. This study concluded that the prevalence of hyperthyroidism in cats in Hong Kong is less than in most other parts of the world, despite the presence of previously identified risk factors. Comparative epidemiological studies will be necessary to compare the presence of possible risk factors between feline populations in Hong Kong and elsewhere. / Dissertation (MSc)--University of Pretoria, 2008. / Companion Animal Clinical Studies / unrestricted

Anthelmintic resistance of parasites infecting livestock animals is a global problem resulting in decreased animal welfare and production losses. Horses are not exempt from this issue as wide-spread anthelmintic resistance exists among the equine cyathostomins and Parascaris spp. Of the three drug classes available for treating equine intestinal helminths anthelmintic resistance, defined as less than 90-95% drug efficacy, exist to all three. New pharmaceutical control regimens and the elucidation of parasite drug response mechanisms are needed. Two studies were carried out evaluating combination deworming regimens. A population of cyathostomins with known resistance to the benzimidazole (BZ) and pyrimidine drug classes maintained in a herd of Shetland ponies was used. Fecal egg counts were performed every two weeks and used to evaluate drug efficacy. The first study evaluated the combination of a BZ and pyrimidine drug for four consecutive treatments, and compared the individual drug efficacies before and after combination use. The first combination treatment exhibited an additive effect at 76.6%, but the subsequent three combination treatments decreased to approximately 40%. There was no significant difference between the initial and final efficacies of individual drugs (BZ, p=0.4421; pyrimidine, p=0.8361). It appears the combination treatment selected for double-drug resistant adult parasites. The timeframe of this study (1 year) and the one year lifespan of adult cyathostomins prevented observations of combination treatment on subsequent generations, however given the sustainability of resistance in this cyathostomin population, it seems unlikely efficacy would improve over time. The second study examined the combination of a BZ drug with a macrocyclic lactone (ML) drug. This parasite population was 100% naïve to the ML drug class. This study was carried out in a similar manner to the first, except only two combination treatments were given. ML exhibited 100% efficacy when it was used alone, or in combination. The initial and final BZ efficacy did not significantly differ (p=0.9890). In summary, the results described herein do not support the use of combination treatments where resistance is prevalent, but more long term studies are needed to fully understand the long-term effects on subsequent generations. The in vitro maintenance of Parascaris spp. provides opportunity for various molecular analyses. An objective motility scoring assessment allowed for continuous monitoring of worm viability. In this study, several saline solutions, nutrient supplements, environmental conditions, and Roswell-Park Memorial Institute medium 1640 (RPMI-1640) were evaluated for the longevity and viability of adult Parascaris spp. Overall, RPMI-1640 resulted in better longevity (168 hours) and significantly better viability (pParascaris spp. to in vitro drug exposure. Oxibendazole at 10 µg/mL for 24 hours and ivermectin at 1 µg/mL for three hours were employed, and worms were used for transcriptomic analyses to identify drug response mechanisms. The top four genes which were significantly different between drug treated and control groups were: cyp4504C1, sup-9, frmd4a, and klhdc10. It is hypothesized that cyp4504C1 and klhdc10 are drug detox mechanisms, while sup-9 and frmd4a may be indirect response related to the drug effects. Their expression was further evaluated using quantitative RT-PCR, however there was no significant difference in any gene expression between groups. It should be noted that there are several limitations associated with the qPCR method, and the lack of significance should not rule out the possible involvement of these genes and more research on drug response mechanisms is needed. In summary, there is very little research regarding combination deworming in horses, and their current use is largely due to some success for ruminant parasites, but the current work summarized herein does not support their use. Finally, until now the lack of in vitro methods for equine helminths has significantly delayed the elucidation of drug response mechanisms. This was the first whole-transcriptome approach for any ascarid parasite and uncovered proteins with possible involvement in drug metabolism or compensate for the toxic effects Overall, the research surrounding anthelmintic resistance in livestock helminths, particularly in horses, is lacking and the resistance crisis demands further investigation.