Ichthyophthiriasis (Ich / White Spot Disease) in Aquaculture Systems: Biology, Epidemiology, Pathogenesis, Economic Impacts and Control Strategies

One of the most important parasitic diseases in freshwater fish farming due to its clinical and economic importance, ichthyophthiriasis results from I. multifiliis (a ciliate obligate parasite) infection, also known as "white spot disease" or simply "Ich." This literature review is aimed at compiling the existing knowledge about the taxonomical position, biological features, and three-stage life cycle (consisting of the theront, trophont, and tomont) of the parasite under the influence of various environmental parameters such as temperature, salinity, and pH. In addition, the epidemiological features of the infection (host specificity, susceptibility factors, transmission methods, and seasonal prevalence) as well as host-parasite relationships (mechanisms of parasite entry, i-antigen-induced immune evasion, and host response) will be considered. Clinical features and histopathological changes for various cultured species are reviewed along with the diagnosis, which includes both traditional methods as well as molecular diagnostics like qPCR and ddPCR. It is emphasized that the disease creates significant financial loss, costing more than USD 1 billion annually on a worldwide basis. The effect of the disease is significant in aquacultures from Europe, China, and North America. Prevention and management of this disease include chemical treatment, salt treatment, biological control, immunostimulants, vaccine, and biosecurity. There is no method available which gives total protection. Latest innovations in the fields of genomics, transcriptomics, novel treatment methods and DNA vaccines are also mentioned. The conclusion made by the authors is that sustainable management of I. multifiliis calls for an integration of various measures such as decreased use of chemicals, increased biosecurity, biological control, genetic resistance and precision aquaculture, with vaccine efficacy, drug resistance and climate change adaptation highlighted as key research areas.