Discussione

I risultati di questo studio evidenziano come il virus HEV sia presente, anche nel nostro paese, nella popolazione di conigli selvatici. Precedenti indagini hanno evidenziato la presenza di HEV nelle popolazioni di conigli selvatici in Francia (Izopet et al., 2012) e in Germania (Hammerschmidt et al., 2017). La sieroprevalenza di HEV osservata nel nostro studio è stata del 46,7%, più alta, anche se analoga, a quella rilevata da Hammerschmidt et al., 2017 (37,3%). La prevalenza di RNA virale è stata invece dell’11,4% contro il 23% riportato da Izopet et al., 2012 e il 17,1% di Hammerschmidt et al., 2017. Dei campioni positivi alla PCR solo due sono risultati anche sierologicamente positivi. Diversi autori suggeriscono come soggetti sierologicamente negativi, ma positivi mediante PCR su fegato possano essere interpretabili come soggetti immunocompromessi, cioè non in grado di sviluppare un’adeguata risposta immunitaria (Risalde et al., 2017; Geng et al., 2014; Tamura et al., 2007). Tuttavia si ritiene più probabile che il risultato negativo della sierologia sia attribuibile a un’infezione acuta, in accordo con quanto osservato nel cinghiale da Nardini et al., 2014. Il fatto che la maggior parte dei soggetti sieropositivi siano adulti virologicamente negativi, testimonia come nel coniglio l’infezione possa essere autolimitante, come accade anche nel cinghiale (Martelli et al., 2008; Nardini et al., 2014).

Attraverso l’analisi filogenetica è stato possibile evidenziare come i ceppi riscontrati in questo studio nei conigli # 1 e 5 siano geneticamente correlati ai ceppi HEV-3 di cinghiale (KJ427814 e KJ427815) isolati in Italia nel 2012, mentre quelli presenti nei conigli # 16 e 17 siano geneticamente correlati ai ceppi rHEV isolati in Cina nel 2005, 2012 e 2013, al ceppo rHEV isolato negli Stati Uniti nel 2010 e ai ceppi umani isolati in Francia nel 2015. Ciò conferma come l’infezione da HEV abbia un importante potenziale zoonotico e facilità di trasmissione cross-specie. Questo è un fenomeno già noto: un ceppo di HEV umano è risultato infatti essere in grado di infettare i suini (Halbur et al., 2001), un ceppo suino di infettare i primati non umani (Meng et al., 1998) e due ceppi di coniglio di trasmettersi ai suini (Cossaboom et al., 2012). Un recente lavoro ha dimostrato inoltre come il genotipo 3 circolante nella popolazione di

60 cinghiali europei possa essere trasmissibile ai suini domestici (Schlosser et al., 2014) e anche al coniglio, come evidenziato da Hammerschimdt et al nel 2017 e confermato anche dai nostri studi.

A livello istologico, la presenza di infiltrato infiammatorio, la fibrosi portale e la necrosi degli epatociti sono lesioni riscontrate nei soggetti infetti con entrambi i sottotipi di HEV, sebbene la presenza di un sottotipo piuttosto che un altro pare abbia influenzato la gravità e di conseguenza la distribuzione delle lesioni.

Nei conigli infettati con rHEV le lesioni risultavano analoghe a quelle descritte in questa specie da Han et al., 2014 e Ma et al., 2010 e in cinghiali e suini infetti rispettivamente con WBHEV-3 (Nardini et al., 2014) e SWHEV-3 (Schlosser et al., 2014). Nei conigli da noi esaminati infetti con ceppi di HEV-3 correlati geneticamente con WBHEV-3 le lesioni epatiche risultavano essere meno gravi e localizzate prevalentemente agli spazi portali. In entrambi i casi queste lesioni epatiche non presentavano una gravità tale da indurre un’evidente sintomatologia clinica. L’immunoistochimica ha evidenziato la presenza dell’antigene virale nelle aree coinvolte dai processi degenerativo-necrotici a carico degli epatociti e dalla risposta infiammatoria, confermando la correlazione tra queste alterazioni e l’infezione virale. I linfociti T sono risultati essere la popolazione di cellule principale negli infiltrati infiammatori (in accordo con quanto riscontrato da Schlosser et al., 2014) insieme ad una percentuale ridotta di macrofagi, mentre i linfociti B erano rari e talvolta assenti. Ciò testimonia come la risposta immunitaria messa in atto dall’ospite per la difesa nei confronti del patogeno sia prevalentemente di tipo cellulo-mediato e per questo potrebbe partecipare alla genesi delle alterazioni rilevate.

In conclusione le nostre indagini confermano la presenza e circolazione di HEV nella popolazione di conigli selvatici viventi in Italia e come questa specie possa essere infettata sia da rHEV sia da ceppi geneticamente correlati a quelli di altre specie (WBHEV-3), confermando la capacità del virus di essere in grado di infettare specie diverse (Spahr et al., 2018). Inoltre questo studio ha consentito di descrivere le lesioni indotte sia da rHEV che dai ceppi HEV-3 correlati al cinghiale. Considerando che HEV ha un importante potenziale zoonotico, esiste pertanto la possibilità che l’infezione possa trasmettersi all’uomo attraverso il consumo di carni contaminate o di fegato poco cotto proveniente da animali che non presentano viremia, ma che albergano il virus a livello epatico. Di fondamentale importanza sarebbe, quindi, studiare una metodica

61 diagnostica che consenta di testare in maniera rapida ed efficace gli animali destinati al consumo umano, nell’ottica di ridurre il rischio di zoonosi. Ulteriori studi sono sicuramente necessari per verificare quali siano le vie di trasmissione del virus e la patogenesi dell’infezione, particolarmente nelle specie selvatiche.

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