Association between fungal detection and other infectious agents
To our knowledge, this is the first study to record detection of multiple types of infectious agents (bacterial, viral, fungal andMycoplasma spp) in both TW and BALF, and to examine their associations with equine asthma. Isolation of bacteria in TW has previously been associated with lower airway inflammation.33–36 However, due to a very low prevalence of positive bacterial samples in the present study, it was not possible to confirm this association with moderate or severe equine asthma. Alternatively, frequent co-detection of fungal elements and other infectious agents such as viruses or mycoplasms has been highlighted in this study. Mycoplasma spp were recently found to be detected in 19.4% of TW samples from horses with respiratory diseases,37 although their detection in TW was not significantly different between groups (CTL, MA, SA) in the current study. The potential implication of mycoplasms in equine asthma remains to be determined, especially by quantitative investigation as per other bacteria in TW.
Our results indicated a significant positive association between fungal detection by culture in BALF and detection of EHV-2 in BALF. So far, the evidence of a potential role of respiratory viruses is controversial; some studies report an association between MA and genome detection by PCR for EHV-2, EHV-5 and ERBV,18,38 while others do not.39,40 There has been speculation that these viruses may act as immunosuppressive agents, predisposing to other infections,41 or may be involved in persistent, chronic fatigue syndromes.42 Larger multicentric studies would be required to determine the possible synergy between viruses, bacteria, fungi, particles etc. (interactome) in the pathophysiology of equine asthma.