Contagious agalactia (CA) is a disease of small ruminants associated with several clinical signs, including mastitis, arthritis, keratoconjunctivitis, pneumonia and septicaemia. CA is listed by the World Organization for Animal Health and is responsible for significant economic loss, with its severity and expression being dependent on several factors, including the host species, the aetiological agent, the production system and the environmental conditions [1–4]. In this context, defining the sanitary status of herds or regions with respect to CA is essential, but also very challenging. Three statuses are currently recognised: disease-free areas, areas with sporadic acute outbreaks and endemic areas, where infection is widespread although not always acute [1, 4]. In CA endemic regions animals typically have no to transitory clinical sign and there are many asymptomatic auricular carriers [5–8]. Preventive and therapeutic strategies remain very inefficient in the control of CA, most likely because of both pathogen-specific features and the lack of epidemiological data. Thus far management strategies have been the most satisfactory method for controlling this disease .
Mycoplasma species responsible for CA include Mycoplasma mycoides subspecies capri (Mmc), Mycoplasma capricolum subspecies capricolum (Mcc) and Mycoplasma putrefaciens, from the spiroplasma phylogenetic group, and Mycoplasma agalactiae (MA), from the hominis phylogenetic group, with this latter species being designated the stricto sensu aetiological agent of CA [1, 4]. Interestingly, CA in sheep is often associated only with MA, while the situation can be more complex in goats, in which CA is commonly associated with both MA and mycoplasmas of the “mycoides” cluster [1, 4, 8].
The complex clinical situation described above requires tools capable of exploring the dynamics of infection in order to set up management strategies. Thus far, several typing techniques have been used to characterize CA agents, including analysis of variable numbers of tandem repeats (VNTR) , multilocus sequence typing (MLST) , Southern blots using DNA probes , insertion sequence (IS) typing [8, 12] and pulsed field gel electrophoresis (PFGE) [8, 13, 14]. However, their capacity to answer epidemiological questions is variable. For instance, PFGE is very useful when comparing an asymptomatic goat herd infected with multiple polymorphic Mmc strains to an outbreak in which one unique clone was predominant . However, application of the same technique to MA isolates in another situation resulted in poor discrimination and was not informative about the strain circulation .
A number of studies has been conducted to characterize and compare isolates of MA from outbreaks of CA. These have generally focused on sets of isolates from various geographical origins [11, 12, 14], but the reports have provided few details about the status of the herds with respect to infection, the type of herds or the animals from which the isolates were collected [9, 10]. In addition, typing analyses that have been performed in well-documented epidemiological contexts have mainly examined CA in sheep [13, 15] leaving the situation in goats unexplored. This gap is surprising, as CA in goats can be of considerable economical importance, and also because the two currently available genomic sequences [16, 17] from which many typing tools were derived, are both from strains with a caprine origin.
The present study is, to our knowledge, the first to conduct a detailed characterization of potential molecular differences between caprine MA isolates collected in a geographically restricted area (Murcia, Spain). This area hosts a native goat breed, the Murciano Granadina, and uses a semi-intensive production system based around a single insemination centre. Although this limits the entry of animals from other regions, Murcia is known to have had endemic CA for many years [18, 19]. This has raised the question of the mode of dissemination and the origins of the agent responsible for CA in this area.
The purpose of the present study was to assess the relevance of typing approaches already validated on large and diverse strain collections (PFGE, VNTR, IS-typing) to discriminate a limited number of caprine isolates from a common geographical origin (Murcia) and to explore the discriminative power of new, more specific markers. This is an essential step before addressing more complex epidemiological questions that can be crucial in improving management of CA in goats in endemic areas.