I did my undergraduate degree at Cardiff University initially working on fungi during a summer studentship 2007/08 investigating “The production of volatile organic compounds during interspecific fungal interactions” under the supervision of Lynne Boddy. I continued in this research field for my final year project, examining “Resource capture by foraging mycelial systems of Hypholoma fasciculare”. However, during a second year field course on Tropical Marine Ecology to Trinidad and Tobago I became interested in parasites after talking to my current PhD supervisors Jo Cable and Cock van Oosterhout. They introduced me to their collaborative research on the guppy-gyrodactylid host-parasite system and in the continuing months I followed the work of a close friend, who was supervised by Jo Cable, as she tested different herbal compounds using the model system Gyrodactylus turnbulli infecting the guppy. This turned out to be a preliminary study for my PhD project, funded by the BBSRC under a CASE studentship in collaboration with WALTHAM Centre for Pet Nutrition. I started this PhD in October 2009 entitled “Behavioural, environmental and transmission implications of botanical treatments on gyrodactylid infections”.
Location: School of Pharmacy, Cardiff University
I investigated the behavioural, environmental and transmission implications of botanical treatments on gyrodactylid infections. Gyrodactylids are ubiquitous on teleost fish and they represent a significant evolutionary force acting on their hosts in natural fish populations. In the aquarium industry gyrodactylids are also a major problem due to high fish densities and increased handling stress, both of which contributes to the spread of these directly transmitted pathogens. High parasite burdens commonly cause death in infected fish: this may be due to impaired physiological (e.g. low oxygen uptake if high parasite prevalence in gills) and physical (e.g. swimming due to fin clamping) abilities of the host or due to exposure to secondary infections of obligate and opportunistic microparasites through wounds left in the epidermis of the fish by the gyrodactylids’ attachment organs.
My work focused on gyrodactylid presence in artificially kept fish populations, particular those in the ornamental fish industry. Including non-exported products, retail sales, wages and associated materials this industry has been estimated to be worth around US$15 billion per year. Hence, there is strong demand for effective treatments against fish parasites some of which could potentially also be effective in the food fish industry. The current control methods employed in aquaculture against gyrodactylids include chemicals such as formaldehyde, rotenone and malachite green. All these compounds do not act against gyrodactylids specifically: (1) they are toxic to host, humans and environment; (2) due to their broad anti-parasitic properties they are low in efficacy; and (3) application of treatment is difficult since the treatment concentration for 100% efficacy often crosses the toxicity threshold for the host.
I investigated alternative methods to treat gyrodactylids using the model system Gyrodactylus turnbulli infecting ornamental and wild guppies (Poecilia reticulata). Alternative methods included:
1) Assessing the efficacy of various botanicals, traditional freshwater fish disease remedies and extreme environmental conditions against Gyrodactylus turnbulli in vitro and in vivo.
Due to the problems associated with many of the commonly used treatments against helminths infections in fish, there is strong interest in finding alternatives. I tested various plant extracts (e.g. garlic), assessed established traditional remedies (e.g. salt) and extreme environmental conditions (e.g. pitch) in vitro, but also in vivo successfully on individually maintained fish.
2) Assessing hybridisation rates and hybrid fitness of Gyrodactylus strains
Gyrodactylids are thought to reproduce asexually, parthenogenetically and sexually, but it is not known which of these reproductive modes prevails and whether external factors (such as the application of treatments) favours a particular reproductive mode. Assessing hybridisation rates between different strains of the same Gyrodactylus sp. has provided us further insights into the hyperviviparous reproduction of gyrodactylids confirming for the first time that sexual reproduction occurs in this specious genus. Furthermore, we have shown that interbreeding G. turnbulli strains show increased hybrid fitness which has important considerations for gyrodactylid population dynamics in infected fish populations.
In conclusion, my work aimed to support further knowledge on the controlled application of anti-helminthic compounds in the aquarium industry through an increased understanding of host-parasite interactions and parasite biology.
I am currently working on a project investigating the use of nematode worms, common soil organisms, to decontaminate anthrax contaminated soil. The project is a collaborative effort between Battelle (USA) and Les Baillie at the School of Pharmacy at Cardiff University and funded by the US Defence Threat Reduction Agency.
Anthrax is caused by Bacillus anthracis, one of the many bacteria that naturally occur in soil. The pathogen is associated with regular outbreaks of the infectious disease during hot summer months in mammals of economic (e.g. livestock) and conservation (e.g. wood bison in Canada; herbivores in the Kruger National Park, South Africa) importance. Human anthrax infections are commonly resulting from handling of infected animals or after terrorist attacks such as the ‘anthrax letters’ sent in 2001. Soil decontamination efforts in areas where anthrax is endemic aim to prevent the disease in livestock, which is essential to the impoverished local communities, and transmission of the disease from infected animals to humans.
Anthrax contaminated areas are currently treated with chemicals that are toxic to humans, mammals and the environment. On Gruinard Island, which in the 2nd World War has been extensively bombed with anthrax spores, the decontamination required 280 tonnes of formaldehyde to ensure the island was safe for humans and animals to enter in the late 1980s. In areas in which anthrax is commonly found in soil or after terrorist attacks, an ideal decontamination agent is environmentally friendly and safe to use.
Nematodes are tiny (up to 1 mm) worms that are essential in the soil food web feeding on amongst others bacteria. We are investigating whether we can use nematode worms to clean up B. anthracis bacteria in areas where anthrax is present, ideally using locally isolated nematode worms to take advantage of local co-adaptation and prevent the introduction of invasive species into new geographical areas. Hence, the project aims to ascertain the detailed interactions of the predator prey relationships between nematode worms and Bacillus anthracis, both in its spore form and during the vegetative growth phase. Further, the application of germinants during decontamination efforts may increase the efficacy of the nematode treatment as bacterial spores will germinate, so being more digestible to the nematodes. At the end of this project, we are hoping to have found an effective, environmentally friendly decontamination system of anthrax contaminated soil.
Schelkle B., Snellgrove D., Cable J. (2013) In vitro and in vivo efficacy of garlic compounds against Gyrodactylus turnbulli infecting the guppy (Poecilia reticulata). Veterinary Parasitology 196: 96-101 http://dx.doi.org/10.1016/j.vetpar.2013.08.027
Williams C.F., Vacca A.R., Lloyd D., Schelkle B., Cable J. (2013). Non-invasive investigation of Spironucleus vortens transmission in freshwater angelfish Pterophyllum scalare. Diseases of Aquatic Organisms 105: 211-223 http://dx.doi.org/10.3354/dao02618
Schelkle B., McMullan M., Mohammed R.S., Coogan M.P., Gillingham E.L., van Oosterhout C., Cable J. (2012). Parasites pitched against nature: Pitch Lake water protects guppies (Poecilia reticulata) from microbial and gyrodactylid infections. Parasitology 139: 1-8 http://dx.doi.org/10.1017/S0031182012001059
Schelkle B., Faria P., Johnson M., van Oosterhout C., Cable J. (2012). Mixed infections and hybridisation in monogenean parasites. PLOS One 7: e39506 http://dx.doi.org/10.1371/journal.pone.0039506.t001
Mohammed R.S., van Oosterhout C., Schelkle B., Cable J., McMullan M. (2012). Upstream guppies go against the flow. Biota Neotropica 12: 68-72 http://dx.doi.org/10.1590/S1676-06032012000300006
Schelkle B., Paladini G., Shinn A.P., King S., Johnson M., van Oosterhout C., Mohammed R.S., Cable J. (2011). Ieredactylus rivuli n. gen. et sp. (Monogenea: Gyrodactylidae) from Rivulus hartii (Cyprinodontiformes: Rivulidae) in Trinidad. Acta Parasitologica 56: 360–370 http://dx.doi.org/10.2478/s11686-011-0081-3
Mohammed R.S., McMullan M.J., Schelkle B., van Oosterhout C. (2010). Colour variation of an individual of Hart’s Rivulus (Rivulus hartii) found in a habitat rich in polycylic aromatic hydrocarbons in the Pitch Lake of Trinidad. Ecologia Balkanica 2: 61-63
Schelkle B., Doetjes R., Cable J. (2010) The salt myth revealed: treatment of gyrodactylid infections on ornamental guppies, Poecilia reticulata. Aquaculture 311: 74-79 http://dx.doi.org/10.1016/j.aquaculture.2010.11.036
Schelkle B., Shinn A.P., Peeler E., Cable J. (2009) Treatment of gyrodactylid infections in fish. Diseases of Aquatic Organisms 86: 65-75 http://dx.doi.org/10.3354/dao02087