In cattle, C. pecorum and C. psittaci can generate subclinical infections or respiratory symptoms, encephalomyelitis or genital sexual-borne infections, affecting fertility, as well as miscarriages with great losses in production (Li et al., 2016; Barati et al., 2017). Although there are reports of Chlamydia pecorum in humans, its zoonotic potential is yet to be understood (Frutos et al., 2015). Some authors suggest that C. pecorum infection is endemic in livestock worldwide, but prevalence is yet unclear, since veterinary chlamydial diagnostics are limited to study genus only (Sachse et al., 2009; Walker et al., 2015).
Li et al., (2016) reported prevalences of several chlamydia species from both dairy and beef cattle production in China. Although in their research they did not test nasal swabs, they tested whole blood, vaginal swabs, feces and milk. In their study they reported high prevalence of C. pecorum in fecal samples, indicating C. pecorum as an endemic species optimally adapted to cattle, so it easily spreads throughout the intestinal tract. Our findings in nasal mucosa could indicate that C. pecorum it is not only present in intestinal tract; suggesting the aerial transmission, and support the idea of a prevalent pathogen in cattle worldwide. Moreover, several authors refer to the fact that C. pecorum may be asymptomatic in cattle, as our findings show (Reinhold et al., 2008; Poudel et al., 2012; Li et al., 2016).
In cattle, C. psittaci causes low milk productivity, respiratory disease, abortions, and its pathogenicity has been demonstrated experimentally (Borel et al., 2006; Ostermann et al., 2013; Van Loo et al., 2014). However, it is likely that C. psittaci infections in cattle occur in sporadic events, due to possible interactions with birds (Li et al., 2016). Li et al., (2016) reports a much lower prevalence (10%), comparing to C. pecorum (75%). In their study, sequenced strains had a genetic similarity close to pigeons. In that sense the circulation of C. psittaci is documented for several bird species in Argentina (Frutos et al., 2016). Although C. psittaci infection is mainly associated with birds, the findings of this work indicate that mammals are also a source of C. psittaci and may be carriers of strains associated with birds, as proposed by Frutos et al., (2014).
While our study was restricted to farm animals, it is important to highlight that the study site is located in the vicinity to an area of high wildlife conservation value, the Iguazu National Park in Argentina and the Iguaçu National Park in Brazil. To date we do not know which species of Chlamydia could affect the local fauna and what their relevance could be at the sanitary and conservation level. In the farms surveyed, many wild species frequent the area, and may have contact with domestic animals. This interaction (domestic/wild hosts) can result in the transmission of pathogens in both ways, by spillover from wildlife to domestic animals or vice versa. As an example, in Australia it has become a huge conservation issue for the koala (Phascolarctos cinereus) populations since the introduction of C. pecorum from infected livestock, causing in koalas ocular and reproductive disorders and thus, increasing mortality rates (Polkinghorne et al., 2013; Bachmann et al., 2014). Regarding C. psittaci, birds living in protected areas frequently visit farms, such as parrots and toucans, due to food availability (fruit trees, seeds and palms) and the scarce presence of predators. Cattle can be infected either by ingesting contaminated pastures by bird feces or seeds that they discard during the flight, making it difficult to control and eradicate the disease in the herds. In farming areas close to natural reserves, monitoring chlamydial species that affect wildlife can be an important tool to have a better understanding of the occurrence and potential of emergence of this pathogen in the area.
Regarding its zoonotic potential, it is necessary to analyze samples from farmers that may or may not have clinical manifestations of respiratory disease, being the infections under-diagnosed, and that are in close contact with the potential cattle reservoir of Chlamydia spp. In this study, the animals that tested positive and its owners did not show symptoms of respiratory disease, nor have they mentioned cases of recent abortions by the cattle.
This is the first study that detected the presence of two species of Chlamydia in the same study area in the triple border area of Argentina, Brazil and Paraguay: Chlamydia pecorum and C. psittaci, and the first report of C. pecorum in bovines for Argentina. The phylogenetic analysis of the strains detected in our study shows a genetic closeness to strains previously detected in central Argentina, which also indicates a regional clustering. Our study provides the basis to deepen the circulation of chlamydia in the area and to understand which animal species could be its hosts and amplifiers. The chlamydial species found are of zoonotic risk and therefore should be included as differential diagnoses in cases of respiratory symptoms in humans.
Monitoring birds and poultry in the proximity of the farms is strongly suggested to assess Chlamydial circulation. As in cattle, these diseases should be considered as differential diagnosis in spontaneous abortions or reproductive diseases. Therefore, it is necessary to extend surveillance and deepen studies on chlamydial species involved in animal pathology and their zoonotic potential, since information in the region is scarce.