HELMINTH OF LEPUS EUROPAEUS: PARASITE ECOLOGY IN A DECLINING POPULATION

Since the Seventies, a reduction of the European brown hare population (Lepus europaeus) has been observed in most European Countries, including Italy. This reduction suddenly accelerated, at least in some italian areas areas, from 2008 and is still continuing. The studied hares come from the eastern hunting-management district of the Province of Bologna (Emilia-Romagna Region) known as ATCBO2. In ATCBO2, both the hares hunted in the hunting areas and the hares captured in the protected areas severely dropped from 2008-09. For example, about six thousands hares were hunted in 2009-10 while about four thousands were hunted in 2015-16; consistently, captured hares were more than 2 thousands in 2008-09 and about seven hundred in 2015-16. However, the same data suggest a reduced speed of hare decline from 2013-14, when the hare population seems to stabilize at low densities. 54 and 61 hares legally hunted in 2013-14 and 2015-16 hunting season, respectively, were examinded for helminth parasites. Sex and full weight was recordered by hunters; age was estimated observing Stroh’s tubercle. No significant difference in the sampled hare population was found between the two hunting seasons: sex-ratio, age-ratio and full weigh was similar in both years. In both hunting seasons, the intestinal nematode Trichostrongylus retortaeformis and the visceral larval form of the tapeworm Taenia pisiformis (cysticercus) were collected; moreover, lesions ascribed to lung nematode infection were observed in 3+3 hares collected in each hunting season. In the second hunting season only, the nematode Trichuris sp. and the filarial nematode Micipsella numidica were also collected from the intestine and the sierosae, respectively. Parasite biodiversity was, therefore, particularly low in both seasons, but improved in the second one. Significant differences between the two hunting seasons were observed for both T. pisiformis and T. retortaeformis. T. pisiformis infection was less frequent in 2015-16 (3.28%) than in 2013-14 (14.81%); on the contrary, T. retortaeformis abundance was significantly higher in the second hunting season. While T. pisiformis abundance appeared to be negatively related with the weight of the hares in the first hunting season, T. retortaeformis abundance was higher in heavier hosts in both seasons. Both parasites are typical of adult hosts: T. retortaeformis was significantly more abundant in adults and T. pisiformis cysticerci were never isolated in animals younger than 7 month. From 2007-08 hunters (and mass-media) reported a sudden increase of hares infected by T.pisiformis cysticerci, seldom or even never found before in the same area. Previous reports about hare parasites showed quite composite helminth communities, with different helmith species parasitising the gastro-intestinal tract of the hares. The results of the present study reveal an atypical parasite situation, with the strong dominance of one gastro-intestinal helminth species only and the appearance of heavy infections due to cysticerci of T. pisiformis. The difference in parasite infections suggest a modification of the host-parasite relationship over time. The hares examined in the first hunting season show a very critical parasite situation, with T. pisiformis possibly affecting host condition and a strongly depauperated intestinal helminth community dominated by T. retortaeformis alone. The reduction of T. pisiformis infection two years later and the appearance of other helminth species suggest improved host-parasite relationship and could indicate that the period of hare population decline is going to end up. It is impossible to know if parasites played any role in promoting hare population decline, but it is very difficult that T. pisiformis alone could have induced such a dramatic host decline. Hosts and parasites appears, rather, to be tied by a common ecological destiny.