Severely Asthmatic Horses Residing in a Mediterranean Climate Shed a Significantly Lower Number of Parasite Eggs Compared to Healthy Farm Mates

SIMPLE SUMMARY: Severe equine asthma is an allergic disease and commonly affects adult horses, resulting in increased respiratory effort, nasal discharge and cough. Human patients affected by allergic diseases tend to present a lower gastrointestinal parasitic burden, when compared to healthy individuals. The present study intended to ascertain if this tendency would also be observed in a group of non-related severely asthmatic horses living in a Mediterranean climate. Thus, the number of gastrointestinal parasites shed by severely asthmatic and non-asthmatic horses from the same farms subjected to a similar management and deworming program were compared. The horses diagnosed with severe equine asthma shed a lower number of parasitic eggs and infective larvae in comparison to their healthy mates. This being a brief report, there is still the need to ascertain if this occurs in a larger population of horses; in addition, further research is necessary to understand the mechanisms behind this process. ABSTRACT: The relationship between helminth infection and allergic diseases has long intrigued the scientific community. This interaction was previously studied in a horse family with high incidence of severe equine asthma and in non-related severely asthmatic horses from equine hospital referrals in Switzerland. Our aim was to determine if this interaction would also be observed in a group of non-related client-owned severely asthmatic horses living in a Mediterranean climate and recruited through a first-opinion veterinarian group. Fecal samples from severe equine asthma-affected and healthy horses living in the same farms and subjected to identical environmental and deworming management were evaluated qualitatively and quantitatively. Strongyle-type eggs and Cyathostomum sensu latum larvae were the most abundant parasites in the studied population of horses; no significant differences between the groups were observed regarding the types of egg and infective larvae. However, we observed significant differences in the number of eggs and infective larvae per gram of feces shed, as this number was significantly lower in the SEA group than in the healthy horses. This may indicate that severely asthmatic horses have an intrinsic resistance to gastrointestinal helminths. Further studies in a larger population of horses are required to ascertain the immunological mechanisms responsible for these findings.