Erosions and ulcers
Equine
Trypanosoma equiperdum
Equine coital exanthema - equid herpesvirus 3
EHV-3 is present in all the major horse breeding countries and areas of the world. It is venereally transmitted, and also transmitted in semen and at artificial insemination.
It causes papules, vesicles, pustules and ulcers on the vagina and vestibule, and on the external skin of the vulva and perineum of mares.
Equine coital exanthema is caused by an Alphaherpesvirus named Equid Herpesvirus 3 (EHV-3). Officially it is from the family Herpesviridae, genus Varicellovirus. It is distinctly different from the other equine herpesviruses. It can be cultured in equine cell lines and it refers to grow at 34°C rather than 39°C. It induces a latent infection and recrudescence occurs. It can be seen in subsequent breeding periods.
The virus infects the stratified squamous epithelial cells of the mucocutaneous junction and adjacent regions vulva. It causes cell lysis of these epithelial cells that results in microscopic vesicles that become larger and macroscopic.Subsequent stimulation of the immune system results in lymphocytic exocytosis.Lesions heal with depigmentation.
It causes a self-limiting vesicular and ulcerative lesion but apparently does not cause infertility, failure of pregnancy or other untoward is systemic effect.
Barrandeguy M, Thiry E. (2012) Equine coital exanthema and its potential economic implications for the equine industry. Vet J. 2012; 191: 35-40
There is much written about squamous cell carcinoma in the male horse, but much less about squamous cell carcinoma in the mare.
Genital papilloma of the clitorus and vulva, and squamous cell carcinoma of these areas is known in equine theriogenology and the progression from one to the other is recognised. Papillomas are caused by Equus caballus Papillomavirus type 2 and there is evidence of its involvement in squamous cell carcinoma.
Sykora and Brandt (2017) reviewed the literature about the association of EcPV2 and squamous cell carcinoma.
Amando et al (2024) studied epithelial-mesenchymal transition in mares with lesions of the vulva. They found less cytokeratin positive cells in carcinomas - and more vimentin positivity.
Armando F, Porcellato I, de Paolis L, Mecocci S, Passeri B, Ciurkiewicz M, Mechelli L, Grazia De Ciucis C, Pezzolato M, Fruscione F, Brachelente C, Montemurro V, Cappelli K, Puff C, Baumgärtner W, Ghelardi A, Razzuoli E. Vulvo-vaginal epithelial tumors in mares: A preliminary investigation on epithelial-mesenchymal transition and tumor-immune microenvironment. Vet Pathol. 2024; 61: 366-381.Scase T, Brandt S, Kainzbauer C, Sykora S, Bijmholt S, Hughes K, Sharpe S, Foote A. Equus caballus papillomavirus-2 (EcPV-2): an infectious cause for equine genital cancer? Equine Vet J. 2010; 42: 738-745.
Sykora S, Brandt S. Papillomavirus infection and squamous cell carcinoma in horses. The Vet J. 2017; 223: 48-54.
Smooth muscle tumors
Husby et al (2017) reported on a mare with a vaginal smooth muscle tumor that was classified as a well differentiated leiomyosarcoma. It was described as invasive. A marginal excision was done and no reoccurrence was reported.
Husby KA, Huber MJ, Phillips I, Heidel R. Vestibulovaginal leiomyosarcoma in a mare. Equine Vet Edu 2019; 31: 126-129Myxoma/myxosarcoma
Venkataramanan et al (2018) reported on a single case of a myxoma in the lateral vaginal wall of a mare. The mass was 20cm diameter. Histologically it was very bland, as anticipated with a benign tumor.
Venkataramanan R, Sreekumar C, Krishnakumar S, Kumar RA, Selvaraj J. Vaginal myxoma in a Kathiawari horse. Equ Vet Educat 2018; 30: 356–359.
Schöniger S, Summers BA. Equine skin tumours in 20 horses resembling three variants of human melanocytic naevi. Vet Dermatol. 2009 Jun;20(3):165-73. doi: 10.1111/j.1365-3164.2009.00741.x. Epub 2009 Apr 3. PMID: 19374725.
Valentine BA. Equine melanocytic tumors: a retrospective study of 53 horses (1988 to 1991). J Vet Intern Med. 1995; 9: 291-297.