Gasterophilosis in horses in Sardinia (Italy): effect of meteorological variables on adult egg-laying activity and presence of larvae in the digestive tract, and update of species.

Gasterophilus larvae are common obligate parasites of the digestive tract of the equids. Horses become infected with this parasite by ingesting the larvae hatched from eggs laid by the female flies. In this study carried out monthly, we (i) counted the Gasterophilus eggs deposited by female flies on the coat of 30 grazing horses, (ii) counted and identified the Gasterophilus larvae retrieved from the digestive tract of 128 slaughtered horses, and (iii) compared these results to meteorological data. Eggs were deposited on all monitored horses, and were present from October to January and from May to September, whereas they were absent from February to April. The number of laid eggs was significantly different between the months, body regions, genders, and age classes (p < 0.05). Larvae were recovered in 112 (87.5%) horses, and 6 species of Gasterophilus were identified. The prevailing species were Gasterophilus intestinalis (recovered in 110 horses; 85.9%) and Gasterophilus nasalis (69 horses; 53.9 %), recovered in all months. Gasterophilus inermis (5 horses; 3.9%), Gasterophilus pecorum (3 horses; 2.3%), Gasterophilus haemorrhoidalis (3 horses; 2.3%)¸ and Gasterophilus meridionalis (2 horses; 1.6%) larvae were also found. Significant differences were found among monthly larval burdens for both Gasterophilus spp. and G. intestinalis (p < 0.05), but not for G. nasalis (p > 0.05). Larval burdens and prevalences did not differed significantly between both genders and age classes (p > 0.05). Monthly eggs and larvae trends were not significantly correlated (p > 0.05). With regard to the meteorological variables, minimum air temperature was significantly correlated with the eggs trend (rho = 1.000; p < 0.001) and maximum air temperature with the Gasterophilus spp. (rho = 0.972; p < 0.001) and G. intestinalis (rho = 0.972; p < 0.001) larvae trends. In addition, the number of hours with a temperature below +10 °C was significantly correlated with G. intestinalis larvae trend (rho = 0.602; p < 0.05). Our findings confirmed that in Sardinia, Gasterophilosis is an important parasitosis in the horses, and it needs more attention and extensive and/or correct treatment to reduce its prevalence.