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BOVINE besnoitiosis is a chronic, debilitating disease characterised by both cutaneous and systemic manifestations with the possibility of severely affected animals dying (Fig 1). Economic losses are associated with sterility in bulls, the reduced value of the hides of affected animals, poor body condition, decreased milk production and occasionally abortions and deaths (Alvarez-García and others 2014b, Cortes and others 2014). It has been suggested that transmission mainly occurs through direct contact between cattle (Alvarez-Garcia and others 2013). Moreover, mechanical transmission of the causative agent, Besnoitia besnoiti, probably occurs through blood-sucking insects or from reusing syringes (Bigalke 1968).
This cattle disease gained the attention of veterinary health officials in Europe in 2010, and was considered as a re-emergent disease due to an increased number of cases as well as the geographical expansion of the disease (EFSA 2010, Alvarez-García and others 2013). From the initial foci in the Pyrenees and Alentejo in Portugal at the beginning of the 20th century (Besnoit and Robin 1912, Franco and Borges 1915) the disease has spread almost all over Spain, France and Portugal over the past two decades (Alzieu and others 2007, Fernandez-Garcia and others 2010, Gentile and others 2012, Waap and others 2014). Since then the disease has propagated from the Mediterranean region and is now emerging in central eastern Europe (Germany, Switzerland, Hungary and Croatia) (Rostaher and others 2010, Lesser and others 2012, Beck and others 2013, Hornok and others 2014). More recently, the disease has showed a northward spread to Belgium and Ireland (Vanhoudtand others 2015, Ryan and others 2016). In a paper summarised on p 608 of this issue of Veterinary Record, the recent outbreak in Ireland is discussed by Ryan and others (2016). This study offers novel data and highlights some issues around this transboundary disease in animal health such as:
▪ Bovine besnoitiosis is not restricted to mainland Europe, as previously thought. Hence the report highlights concerns about the risk of further disease outbreaks in the British Isles. However, there are questions about where the disease came from and how it spreads.
▪ Although exotic to Ireland, the serological results and clinical findings support the hypothesis that the disease may have been endemic in the herd studied. This finding raises the question of whether other herds may be infected since cattle are grazed outside, there are contiguous herds and farm biosecurity plans revealed weaknesses that could favour disease spread.
▪ Data are given on the impact of the disease in dairy milking cows. This issue is relevant since bovine besnoitiosis has been reported mainly in beef cattle raised under extensive husbandry systems (Alvarez-García and others 2014b, Gutiérrez-Expósito and others 2014).
Most recent outbreaks of the disease seem to be linked to the trade of animals with unknown health statuses. On the one hand, beef bulls are the primary focus of national and international animal trade in Europe. Indeed, several outbreaks reported in the south of Portugal (Cortes and others 2006) were mostly related to the purchase of breeding males. On the other hand, the introduction of cattle imported from France could explain several cases of the disease in Italy (Agosti and others 1994, Mutinelli and others 2011, Basso and others 2013), Switzerland (Lesser and others 2012), Hungary (Hornok and others 2014) and Belgium (Vanhoudt and others 2015). Despite the fact that several cases were originally isolated, autochthonous cases were also recorded and now endemic foci of the disease have been declared in Italy (Gentile and others 2010, Gazzonis and others 2014), and may occur elsewhere in the near future. In other reports in Spain (Fernández-García and others 2010) and Germany (Rostaher and others 2010), the origin of the infection could not be established although it is suspected that the disease was probably introduced by the entry of subclinically infected cattle in these herds.
Recent studies carried out in areas or herds where the disease is endemic, have shown that the absence of a herd health scheme under a stable endemic situation is conducive to constant high prevalence and incidence rates, with over 50 per cent of animals being infected (Alvarez-García and others 2014a, Gutiérrez-Expósito and others 2014, 2015). Similarly, in the outbreak reported by Ryan and others (2016) the pathognomonic scleral conjunctival tissue cysts were detected in 51 per cent of cattle, with a 68 per cent intra-herd seroprevalence rate.
Another typical feature of an endemic situation, also described by Ryan and others (2016), is the detection of mild clinical signs that mainly consisted of the presence of tissue cysts in the sclera conjunctiva and/or vestibulum vaginae. Clinical signs are more severe in recent outbreaks of the disease, where oedema occurs in the jowls and limbs, and scleroderma and hyperkeratosis, alopecia, crusting on the feet and udders, limping, weight loss and orchitis are observed (Fernández-García and others 2010, Gollnick and others 2015). In addition, Ryan and others detected seronegative animals with tissue cysts. This finding has already been reported and the percentage was shown to be higher in herds where the disease is endemic (Schares and others 2010, Fernández-García and others 2010, Gutiérrez-Expóstito and other 2015). However, the major concern about the impact of the disease was the initial milk-drop syndrome observed in animals showing pyrexia and limb/joint swelling. The decrease of milk yield together with scars in teats and udders may negatively influence the weight gain of beef cattle offspring. Therefore, quantification of economic losses in infected dairy and beef cattle is an issue that must still be addressed. Bigalke (1968) reported that clinical besnoitiosis is rare in animals under one year of age; however, Ryan and others observed scleral tissue cysts in calves and Hornok and others (2014) reported respiratory clinical signs in seropositive calves less than six months old. Unfortunately, a thorough description of clinical cases in young calves has not yet been provided and this warrants further investigation.
With this in mind, bovine besnoitiosis needs urgent attention by governments and the animal health industry considering the lack of efficient treatments and vaccines against the disease. In the absence of health schemes at a local, national and international level, animal trade has the potential to spread this parasitic disease. Therefore, any region or country free of besnoitiosis that is at risk of disease entry and establishment may be protected by effective management practices. Active surveillance based on a commonly adopted procedure combining an exhaustive clinical inspection of both the sclera conjunctiva and vestibulum vaginae with a specific and sensitive serological test should be adopted in valuable animals (before selective culling and new trade entries) (García-Lunar and others 2013, Gutiérrez-Expósito and others 2015).