Veterinary Science Collected Works - Theses
Permanent URI for this collection
Search Results
1 - 2 of 2
-
ItemStudies on Intestinal Nematodes in Australian Thoroughbred Horses( 2023-10)Gastrointestinal nematodes (GINs) are the most important parasites of equines as they pose a significant threat to equine health and wellbeing, particularly in younger and geriatric horses. Strongylids (cyathostomins and strongylins) and ascarids (Parascaris spp.) are the significant GINs of horses, with the former constituting more than 75% of the total parasite fauna. Heavy burdens of these parasites such as Parascaris spp. in young horses, can cause impaction and rupture of the small intestine while cyathostomins can infect all age groups of horses, with variable severity of cyathostominosis, particularly when encysted larvae emerge synchronously from the intestinal wall. The literature review (Chapter 1) identified various research gaps related to the epidemiology, diagnosis, efficacy of commonly used anthelmintics and control of GINs in Australian horses. Over the last 50 years, only a few studies have investigated the epidemiology of GINs of equines in different states of Australia which were either restricted to some regions or involved only a small number of horses. To address some knowledge gaps on the GINs in Australian horses, this thesis aimed to (i) establish baseline epidemiological data on GINs in Australian Thoroughbred horses, (ii) develop and/or employ more sensitive and advanced molecular tools for the detection of GINs in horses in epidemiological and drug efficacy studies, (iii) ascertain the efficacy of commonly used anthelmintics against significant intestinal nematodes of horses, and (iv) assess worm control practices used by Thoroughbred farm managers and equine veterinarians. The longitudinal (Chapter 2) and cross-sectional (Chapter 3) epidemiological studies conducted using coprological methods showed high prevalence and egg-shedding patterns of GINs in various age groups of horses. Climatic zone and age had the highest impact on faecal egg shedding, particularly in the Mediterranean climate, the autumn season, and young horses (i.e., yearlings). The polymerase chain reaction-directed next-generation sequencing (PCR-NGS) method uncovered the diversity of strongylid nematodes as 31 species were detected in both epidemiological surveys and their occurrence varied across various climatic zones, seasons and age groups of horses. Traditionally, the faecal floatation method has been used to diagnose eggs of Strongyloides westeri – a free-living parasitic nematode of newborn foals. In Chapter 4, following the detection of S. westeri eggs in the faeces of foals using microscopy, a PCR-based diagnostic method was established for the first-time using DNA extracted from the parasite eggs. This method will help conduct future molecular epidemiological studies on S. westeri and assess the efficacy of commonly used anthelmintics in foals. Chapter 5 showed the extent of anthelmintic resistance (AR) in cyathostomins and Parascaris spp. prevalent in Australian Thoroughbred horses. An apparent failure of the efficacy of a combination of anthelmintic drugs (i.e., oxfendazole (OFZ) and pyrantel (PYR)) was observed for the first time against Triodontophorus brevicauda – a species of large strongyles. Cyathostomins were resistant to multiple anthelmintics, including abamectin (ABM), ivermectin (IVM), moxidectin (MOX) and OFZ, whether used individually or in combination with other classes of anthelmintics, i.e., OFZ+PYR. Furthermore, where anthelmintics were effective 2 weeks post-treatment, egg reappearance periods (ERPs) were reduced to four and/or five weeks. The major cyathostomin species identified 2 weeks post-treatment were from the two genera, Cylicocyclus and Cylicostephanus while those 5 weeks post-treatment with MLs were Cylicocyclus nassatus, Cylicostephanus longibursatus and Cylicocyclus ashworthi. Chapters 2 to 5 provided comprehensive information on the prevalence of GINs in Australian horses and resistance in ascarid and strongylid nematodes against commonly used anthelmintics. Subsequently, assessments of worm control practices surveys used by horse managers (Chapter 6) and veterinarians (Chapter 7) provided insights into their knowledge, aptitude and practices on GINs of horses, their diagnosis, treatment and control. Although both farm managers and veterinarians almost completely relied on anthelmintics to control GINs in horses, the latter seemed to use more targeted treatment strategies based on faecal egg count results. Multiple correspondence analyses used in Chapter 6 showed that the likelihood of suboptimal worm control practices on small farms (n = less than 50 horses) was greater than that of medium (n = 51-100) and large (n = above 100) farms. Furthermore, the findings highlighted a communication gap between veterinarians and horse managers. In conclusion, this thesis has contributed to addressing some key fundamental knowledge gaps on the GINs of Australian horses. Using conventional and advanced DNA-based diagnostic techniques, this thesis uncovered (i) the prevalence and egg-shedding patterns of GINs across various climatic zones during different seasons in various age groups of horses, (ii) the extent of AR against commonly used anthelmintics in ascarids and strongylid nematodes, and (iii) knowledge, aptitude and practices used by horse managers and veterinarians to control horse parasites. The novel findings of this thesis can pave the way for developing tailored guidelines for equine parasite control in Australia and globally.
-
ItemThe Likely Effect of Varroa destructor on Australian Honey Bee Populations( 2021)Varroa destructor, an invasive ectoparasitic mite of honey bees, is believed to be responsible for a large proportion of reported honey bee deaths globally. Australia remains the only Varroa-free country in the world with a beekeeping industry and horticulture sector reliant on Apis mellifera, the European honey bee. This thesis addresses issues essential to prevent the introduction of Varroa into Australia and better manage Varroa if an incursion (and then establishment) were to occur. The managed honey bee population in Australia is unusual, compared with other livestock industries, because a large sector of the industry (hobby beekeepers) are concentrated in locations where incursions of exotic diseases are likely to occur — urban areas adjacent to sea and international airports. For this reason, hobby beekeepers play an important role in early detection of honey bee diseases and limiting the spread of these diseases once an incursion has occurred. Hobby beekeeper networks need to be documented and appropriate communication and biosecurity resources developed for this sector of the industry to ensure roles and responsibilities are clearly defined (Chapter 3). A quantitative assessment of the Sugar Shake Team surveillance program for Varroa surveillance using scenario tree methods was made in Chapter 4 showing that if one of the 23,300 feral and managed apiariesin the Melbourne Metropolitan area were infested with Varroa there was only a 0.40% chance that it would be detected using the Sugar Shake Team surveillance program during one of the three or four surveillance events held each year. Reasons for low surveillance system sensitivity include poor sensitivity of the sugar shake method as a diagnostic test for the presence of Varroa in a colony and the relatively low frequency of testing of high-risk colonies in the greater Melbourne area. If the Sugar Shake Team program is to be used as a credible means for Varroa incursion detection the frequency of testing and the number of participants in the program needs to be increased. Research effort should be directed towards identifying more sensitive diagnostic tests to detect the presence of Varroa in honey bee colonies. If Varroa were to be introduced into Australia and there was a need to control the parasite using miticides, the cost per hive per year, if recommended controls were applied, would be in the order of AUD 51 (Q1 40; Q3 65) per hive per year (Chapter 5). In 2020 this represents a 17% reduction in net hive profitability. Assuming colony annual mortality rates attributable to Varroa ranging from 30% to 50% the percentage of apiary-year simulations where the cost of recommended Varroa controls was less than a suboptimal Varroa control strategy ranged from 32% to 43% (assuming a 30% Varroa attributable mortality rate) and 40% to 57% (assuming a 50% Varroa attributable mortality rate). While the use of suboptimal controls may be a pragmatic and rational economic choice for a beekeeper this represents a classic ‘tragedy of the commons’ situation whereby individual users, acting independently according to their own self interest, behave contrary to the common good of the industry. On the basis of these analyses, thought should be given to what changes can be made to the industry to make application of recommended Varroa controls cost effective for beekeepers. The first is to consider ways by which Varroa inspection and treatment times might be reduced. The second is to ensure that the cost of colony replacement is kept relatively high. A model was developed to simulate the introduction and spread of resistant Varroa Sensitive Hygienic (VSH) genetics into the managed honey bee population as a means for enhancing resistance of the feral population (Chapter 6). Introduction of VSH queens into the managed honeybee population had relatively little effect on the development of resistance in the feral population because the spread of Varroa resistance from the managed population to the feral population is slow compared with the rapid collapse of the feral population following Varroa the introduction of the mite. The only exception to this is that if the size of the resistant, managed population is large relative to the size of the feral population. This being the case there is scope for managed honey bee colonies in high risk areas to be seeded with Varroa-resistant queens to form a ‘barrier’ to limit the spread of the mite away from its point of entry into the country. If VSH genetics are to be used in this way as a means for either promoting Varroa resistance in the feral colony population or for iideveloping a Varroa resistance barrier around likely incursion sites (i.e., ports and international airports) it is essential that programs are established well in advance of a Varroa introduction.