Equine testicular lesions related to invasion of nematode larvae

Larvae of Strongyloidae nematodes have been reported to be able to erratically migrate to the vaginal cavity of the equine testis and to provoke characteristic inflammatory lesions. In a 20-year experience of equine genital organs collected from slaughters or castrations, we found 12 cases of atypical inflammatory lesions in scrotal testes, which are herein described. In one case, these lesions were associated to the presence of three viable nematodes of the species Setaria equina in the vaginal cavity of the testis. In the vaginal cavity of the affected testes, hydrocele was constantly observed. The tunicae vaginales were generally thickened and numerous adhesions could be present. Furthermore, large elongated bloody to yellowish areas could be seen on the surface of testis and epididymis, especially at the cranial pole. The appendix testis was often included in these lesions or appeared enlarged, prominent and inflammated. Only in one case, at section, haemorrhagic tracts could be observed in the different areas of the testicular parenchyma. Histologically, they were considered haemorrhagic tracts in a developing granulation tissue. Frequent vasculitis and perivasculitis were observed along with infiltrates of lymphocytes, macrophages filled with haemosiderin, mast cells and eosinophils. Squamous metaplasia could be observed focally in the appendix epithelium and diffusely on the surface of the elderly granulomatous lesions. The testicular parenchyma could display mild to severe degeneration, peritubular oedema and focal interstitial lymphocytic infiltrates. Only in one case, at section, haemorrhagic tracts could be observed in the different areas of the testicular parenchyma. The epididymis showed enlargement of head or tail, oedema, interstitial inflammatory infiltrates, sperm granulomas and hyperplasia/squamous metaplasia of ductal epithelium. In agreement with literature, these lesions have to be considered as resulting from invasion of nematode larvae, but the finding of the parasites in scrotal equine testis is extremely rare. It has been hypothesized that worms could penetrate the appendix testis and reach the testicular parenchyma, but generally only their tracks could be seen, identified as elongated and atypical haemorrhagic or already organized lesions with frequent foci of squamous metaplasia. Different grades of orchitis and epididymitis may occur in relation to intensity and time of worm invasion.