{'fraction_non_alphanumeric': 0.027976686094920898, 'fraction_numerical': 0.0231473771856786, 'mean_word_length': 4.859512195121951, 'pattern_counts': {'":': 0, '<': 0, '<?xml version=': 0, '>': 0, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
Fasciolosis in horses: A neglected, re‐emerging disease

Fasciola hepatica (F. hepatica), the common liver fluke, is a trematode parasite that can infect many different mammalian hosts and is found throughout the world. In the UK, the fluke is most commonly associated with disease in sheep and cattle. It is a highly pathogenic parasite, heavy infections in the autumn lead to the death of sheep and subclinical infections are a major source of production losses in cattle, costing the livestock industry an estimated £300 million per year. Traditionally, liver fluke has been considered to be uncommon in horses; based on the failure to establish infection following experimental exposure, it was said that horses are resistant to infection and infections rarely reach patency (Nansen et al. 1975; Alves et al. 1988). However, fasciolosis has been previously described in horses: a report nearly half a century ago, following the very wet summer of 1968, found infections in horses grazed on pasture also used for sheep and cattle. A range of clinical signs was observed and fluke eggs detected in faeces. In total, 38 cases were described in one practice in south-west England in a 12month period; moreover, 4 out of 20 ponies bought at a Welsh market had mature flukes in their livers at post mortem examination (Owen 1977). Similarly, a study in the west of Ireland described fluke prevalence by faecal egg count in horses of 77% (Kearney 1974). However, since the mid-70s, fluke has become rather neglected as a potential cause of disease in horses, yet liver disease as a syndrome is common and often idiopathic (Pearson 1999). Outside the UK, fluke infections in horses have been fairly extensively described. In mainland Europe, prevalence based on faecal egg detection has been found to range from 0.07% in Poland to 60% in Northern Spain (Sadzikowski et al. 2009; Arias et al. 2012). Infections have been described in horses in Australia and a study in Western Australia found infection in 23 yearlings all previously treated with triclabendazole on 2 occasions. This indicates that horses are susceptible to infection and can carry fluke burdens which are triclabendazole resistant (Palmer et al. 2014). In contrast to horses, donkeys appear to be a much more permissive host and infection appears to be highly prevalent in working donkeys in Ethiopia, for example Getachew et al. (2010), and donkeys have been implicated as a reservoir of human infection in Bolivia and Egypt (Valero and Mas-Coma 2000; Haridy et al. 2002). A recent study in donkeys from the Donkey Sanctuary in the UK suggested that prevalence in donkeys admitted between 2011–2013 was 10.2% and was most commonly seen in donkeys coming from Northern Ireland (F. Burden, personal communication). Fasciola hepatica has an indirect life cycle involving an amphibious mud snail, Galba truncatula. The snail and free living stages of the parasite (egg, miracidium, cercaria and metacercaria) are all dependent on water and a temperature above 10°C for development. Hence, high summer rainfall is the leading risk factor for fluke (McCann et al. 2010) which is most prevalent in the wetter west of the UK with hot spots in South Wales, north-west England, southwest Scotland and Northern Ireland. There has been a rise in prevalence of F. hepatica in sheep and cattle over the past 15–20 years which has been attributed to changing weather patterns, with milder winters and wetter summers (Williams et al. 2014). Other factors which have contributed to this increase include changes to environmental/countryside stewardship schemes that encourage farmers to maintain wetlands and other wildlife habitats. In addition, stock are moved around the country more frequently and there is evidence that fluke has been introduced into parts of the country where it was previously rare or nonexistent (Pritchard et al. 2005). Climate change is likely to foster the life cycle of the parasite and changes in the epidemiology are predicted (Fox et al. 2011; Caminade et al. 2015). Whilst these factors will affect ruminant health and productivity most significantly, the knock-on effects on horses cannot be ignored. The summer of 2012 was the wettest since 1912 (Anon 2012b) and by the end of that year the level of flukeassociated disease, particularly in sheep, was huge (Anon 2012a). Associated with the increase in occurrence of fasciolosis, there appeared to be a much greater awareness of fluke amongst farmers and veterinarians. As a consequence, the diagnostic services of the University of Liverpool were approached by a number of veterinary practitioners requesting diagnostic tests for fluke infections in horses grazing pasture used for sheep or cattle. Diagnosis of F. hepatica infections in sheep and cattle is based on clinical signs, farm history, season and specific diagnostic tests. Faecal egg counts (FEC) using the sedimentation method are widely used to detect infection, particularly in cattle. Fluke FEC are time-consuming, only detect the presence of egg laying adults and have a low sensitivity of approximately 60% in cattle (Charlier et al. 2014). Eggs are shed by adult parasites in the bile ducts and in ruminants the eggs are often trapped in the gall bladder and released sporadically in faeces. Increasing the volume of faeces analysed up to 40 g can increase the sensitivity of a FEC (Charlier et al. 2008) but may also create difficulties in actually seeing the eggs because of the density of the faecal material in the dish. Antibody detection ELISAs are available using either serum or milk; they are highly sensitive, detect early infection but because antibodies persist for several weeks after treatment, antibody positive animals may not carry active infection (Salimi-Bejestani et al. 2005). More recently, an ELISA that detects fluke antigen in the faeces of infected animals has been evaluated for sheep, cattle and horses. A study in Australia showed that whilst the copro-antigen ELISA is over