Browsing by Author "Christison, Kevin W."

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    The development, optimisation and evaluation of molecular methods to diagnose abalone tubercle mycosis (ATM) caused by Halioticida Noduliformans in South African abalone, Haliotis Midae
    (University of the Western Cape, 2012) Greeff, Mariska R.; Christison, Kevin W.; Macey, Brett M.
    Land-based abalone aquaculture in South Africa started in the early 1990s and is based on the local species Haliotis midae. This industry expanded with great success over the last decade. In 2006 abalone exhibiting typical clinical signs of tubercle mycosis was discovered for the first time in South African abalone culture facilities,posing a significant threat to the industry. Halioticida noduliformans, a fungus belonging to the Peronosporomycetes (formerly Oomycetes), has been identified as the causative agent of abalone tubercle mycosis (ATM). While diagnoses of this disease are currently done by gross observation and histopathology, these methods fail to be sensitive enough to identify the causative agent accurately and reliably.Molecular confirmation could provide for quicker more accurate diagnostic information. The aim of this study was to develop a DNA based molecular diagnostic test. Polymerase chain reaction (PCR) has been used to rapidly detect, characterise and identify a variety of organisms. Nucleotide sequences of the smalland large-subunit ribosomal ribonucleic acid (rRNA) and mitochondrial cytochrome oxidase subunit II (cox2) genes of H. noduliformans were compared with closely related Peronosporomycete gene sequences to identify potential PCR primer sites. H. noduliformans specific real-time quantitative PCR (Q-PCR) primer sets were designed and optimised for each of the selected genes. Results indicate that, although all tested primers sets could amplify fungal DNA, only the LSU and cox2 primer sets - v -demonstrated no cross-amplification with the closely related Peronosporomycete and non-fungal DNA tested in the present study. The H. noduliformans specific LSU primer set was chosen for further analysis and used for all subsequent real-time PCR assays. The lowest detection limit for the LSU primer set was evaluated by running Q-PCR on serial dilutions of known quantities of extracted H. noduliformans DNA.Serial dilutions were made in PCR grade water as well as in an abalone tissue matrix.The sensitivity of the Q-PCR reaction was determined to be 266 pg of H.noduliformans DNA per 25 μL reaction volume. However, inclusion of a nested PCR step, utilising universal fungal outer primers, followed by Q-PCR with the H.noduliformans LSU specific primers improved sensitivity to 0.266 pg of H.noduliformans DNA per 25 μL reaction volume. This equates to approximately 2.4spores per 25 μL reaction volume. DNA extraction protocols were optimised to ensure efficient and repeatable extraction of high quality fungal DNA from pure fungus and tissue samples spiked with known quantities of fungal DNA. PCR amplification efficiency and potential inhibition were examined for each extraction method. Results suggest that real-time PCR has great potential in monitoring and quantifying H. noduliformans on abalone culture facilities in South Africa.
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    The evaluation and development of diagnostic tools for the detection of ichthyophonus hoferi in fish host tissue samples
    (University of the Western Cape, 2019) Wurdeman, Bret Mark; Christison, Kevin W.; Cole, Georgina; Gibbons, Mark
    Ichthyophonus hoferi is a highly pathogenic histozoic parasite that has low host specificity capable of producing mass mortalities of epizootic proportions in marine commercial fish populations. Currently in Southern Africa, I. hoferi has been reported from flathead mullet (Mugil cephalus) from the Kowie lagoon and from multiple species on exhibit at the Two Oceans Aquarium. Since epizootiologists rely on accurate assessments of prevalence to establish patterns of morbidity and mortality within populations, using the most accurate diagnostic techniques for accurate assessments of infection is imperative. Currently, several diagnostic techniques have been employed to detect I. hoferi in infected fish hosts. These include macroscopic examination of tissues, microscopic examinations of wet-mount squash preparations of tissue, histological examination of tissue sections, in vitro culture of tissue explants, the polymerase chain reaction (PCR) using I. hoferi-specific primers and real-time quantitative PCR (qPCR) using I. hoferi-specific primers and a hydrolysis probe.
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    Gyrodactylus molweni sp. n. (Monogenea: Gyrodactylidae) from Chelon richardsonii (Smith, 1846) (Mugilidae) from Table Bay, South Africa
    (Elsevier, 2021) Christison, Kevin W.; Vaughan, David B.; Shinn, Andrew P.
    Gyrodactylus molweni sp. n. is described from the body surface and fins of the South African mullet, Chelon richardsonii (Smith, 1846) collected from Table Bay Harbour, Cape Town and is compared to five other Gyrodactylus species described from grey mullets globally namely G. zhukovi Ling, 1963 and G. mugili Zhukov, 1970 from Planiliza haematocheila (Temminck and Schlegel, 1845); G. mugelus Rawson, 1973 from Mugil cephalus L.; G. curemae Conroy and Conroy, 1985 from Mugil curema Valenciennes, 1836 and G. xiamenensis Zang,Yang and Liu, 2001 from Planiliza macrolepis (Smith, 1846). Morphologically, G. molweni sp. n. has prominent ventral bar processes that near cover the hamulus roots, marginal sickles with large rhomboid heels, slender shafts and fine points that extend beyond the sickle toes. Gyrodactylus molweni sp. n. can, however, be readily differentiated: G. mugili and G. xiamenensis have ventral bars with small ventral processes; G. zhukovi has marginal hooks sickles with slender shafts and proportionately short points and open-faced blades; G. mugelus possesses marginal hook sickles with deep, rounded heels, forward slanting shafts and an angular, square line to the inner face of the blades. Although the length of the marginal hooks of G. curemae are similar to G. molweni sp. n., their hamuli are double the size. A GenBank BlastN search with the 931 bp sequence covering ITS1, 5.8S and ITS2 gave no close hits; the nearest species for which sequences are available is G. nipponensis Ogawa and Egusa, 1978 (identity 96.56%, 899/931 bp). The proposal of G. molweni sp. n. as a new species, therefore, is well supported by both the molecular and morphological analyses presented herein. This Gyrodactylus species is the first to be described from C. richardsonii and only the second Gyrodactylus species to be described from the marine environment off the African continent.
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    Managing ichthyophonus in multi-species exhibits at the two oceans aquarium
    (University of the Western Cape, 2020) Nicolle, Nicholas; Christison, Kevin W.; Cole, Georgina; Gibbons, Mark
    Ichthyophonus hoferi has been diagnosed in multiple species at the Two Oceans Aquarium, this study focuses on Rhabdosargus globiceps (White stumpnose). I. hoferi is a mesomycetozoan parasite that multiplies in blood rich organs in the fish hosts causing a wide range of clinical signs resulting in organ dysfunction. I. hoferi can be diagnosed from microscopic examination of tissue squash preparations, culture, polymerase chain reaction (PCR) and histopathology. In the literature only lethal methods of diagnosis are described. The development of a non-lethal diagnostic tool for disease monitoring is vital for collections where euthanasia of specimens is not possible.
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    Review of South African genera of the family hexabothriidae price, 1942, parasites of chondrichthyan fishes
    (2009) Vaughan, David Brendan; Christison, Kevin W.
    The oligonchoinean monogenean family Hexabothriidae Price, 1942 currently consists of approximately 60 valid species, representing 15 genera. Hexabothriids are gill parasites of chondrichthyan fishes (sharks, rays and chimaeras). Some hexabothriid species have been reported as problematic in public aquaria, directly responsible for host pathology and subsequent host mortalities. However, without information on specific hexabothriid species and their host associations, accurate captive management of hexabothriids in public aquaria is hindered. Hexabothriid taxonomy is in a state of confusion. The historic taxonomic restoration of the priority of Hexabothrium sees the beginning of the taxonomic uncertainty of the hexabothriids, and is continued into the present literature particularly among lower-level taxa in Hexabothriidae. In addition, there is currently no consensus for a single accepted morphometric protocol for the discrimination of hexabothriid taxa, which leads to unnecessary ambiguity of character variable nomenclature, measurement and interpretation. A call for stability in the nomenclature and morphometric discrimination of species is therefore proposed. A novel morphometric protocol is tested for the sclerotised haptoral armature, supported by the proteolytic digestion of structures for optimal representation. Character variables, subjected to univariate and multivariate analyses were systematically accepted or rejected based on their potential to discriminating species of Callorhynchocotyle Suriano and Incorvaia, 1986. The hexabothriid genera Callorhynchocotyle and Branchotenthes, represented by South African taxa, are reviewed, using these variables. Four Callorhynchocotyle species and 2 Branchotenthes species are redescribed with the inclusion of some new voucher specimens.