Occurrence of equine coital exanthema in pastured draft horses and isolation of equine herpesvirus 3 from progenital lesions

Equine Coital Exanthema: New Insights on the Knowledge and Leading Perspectives for Treatment and Prevention

Equine coital exanthema (ECE) is a highly contagious, venereally-transmitted mucocutaneous disease, characterized by the formation of papules, vesicles, pustules and ulcers on the external genital organs of mares and stallions, and caused by equid alphaherpesvirus 3 (EHV-3). The infection is endemic worldwide and the virus is transmitted mainly through direct contact during sexual intercourse and by contaminated instruments during reproductive maneuvers in breeding facilities. The disease does not result in systemic illness, infertility or abortion, yet it does have a negative impact on the equine industry as it forces the temporary withdrawal of affected animals with the consequent disruption of mating activities in breeding facilities. The purpose of this review is to provide up-to-date relevant information on the knowledge of EHV-3 infection and to analyze new approaches on diagnostics, treatment and prevention in the interest of minimizing the negative consequences of ECE in light of the current situation of the equine industry.

Period of excretion of equine herpesvirus 3 (EHV-3) from a stallion before showing clinical signs of equine coital exanthema and the effect of acyclovir treatment on the duration of EHV-3 excretion

In 2017, two Thoroughbred stallions, A and B in Farms A and B, respectively, in Hokkaido in Japan showed clinical signs of equine coital exanthema (ECE). In 2020, stallion C in Farm B showed clinical signs of ECE. Eighteen mares were mated within five days before stallion A developed ECE. Ten mares that mated within 3 days before onset showed clinical signs of ECE on the external genitalia. Equine herpesvirus 3 (EHV-3) was isolated from vaginal swabs from three mares that mated within 2 days before onset. Swabs from 12 mares that mated within 4 days before onset were real-time PCR (rPCR)-positive and nine of those mares had an increased EHV-3 antibody titer. The three stallions were administered valaciclovir orally and topical acyclovir ointment was applied. Treatment started on the next day after onset in stallion A and on the day of onset in stallions B and C. EHV-3 was firstly isolated from penis swabs of stallions A and B before treatment and from penis swabs of stallion C 2 days after treatment. EHV-3 was not isolated after 8, 5 and 8 days from onset in stallions A, B and C, respectively. However, swabs were rPCR-positive for at least 12, 9 and 15 days after onset of stallions A, B and C, respectively. EHV-3 was excreted from the stallions at least within 4 days before the onset of ECE, and acyclovir treatment resulted in the termination of excretion within 8 days after onset.

Isolation of equine herpesvirus 3 (EHV-3) from equine coital exanthema of two stallions and sero-epidemiology of EHV-3 infection in Japan

In the spring of 2015, two stallions reared in Farms A and B in Hokkaido in Japan showed symptoms of equine coital exanthema. Equine herpesvirus 3 (EHV-3) was isolated from penis swab samples of both stallions, and the isolates from each stallion in Farms A and B were designated as SS-1 and YS-1 strains, respectively. BamHI restriction profiles of SS-1 and Japanese reference strain Iwate-1 were indistinguishable, but the BamHI-A fragment of YS-1 was larger than those of SS-1 and Iwate-1 by 1.9 kbp because of the lack of two BamHI sites. Nucleotide sequence analyses of glycoprotein G (gG), gB, gC and VP13/14 coding regions revealed that SS-1 and YS-1 had 99.77% to 100% identities to each other. These results suggested that the origins of SS-1 and YS-1 were different. For a sero-epidemiological survey, serum neutralizing tests using SS-1 against 319 sera of horses from eight farms in Hokkaido were conducted. Six of the eight farms were EHV-3 antibody-positive, and positive rates ranged from 2.6% to 17.6%. To determine the infection time of four EHV-3 antibody-positive horses, a retrospective study was conducted. Infection time of the four horses was in the breeding season, and re-infection or reactivation of latently infected EHV-3 might have occurred in one horse. However, these four horses had never shown any clinical symptoms. The results suggested that several EHV-3 strains are distributed in Japan and that infection is maintained widely in horses without clinical symptoms.

Occurrence of equine coital exanthema (ECE) in stallions in Japan and effectiveness of treatment with valacyclovir for ECE

Equine coital exanthema (ECE) has been reported in many countries, but equine herpesvirus 3 (EHV-3) has been isolated only once in Japan. In 2015, symptoms of ECE were found, and EHV-3 was isolated in two stallions. Valacyclovir, an anti-herpesvirus agent, was administered orally. The stallions rested from mating for more than two weeks, causing enormous financial losses because of their high fees. This is the first study in which valacyclovir was administered for ECE. Though valacyclovir treatment did not shorten the duration of healing, the affected area did not expand after administration of valacyclovir. Valacyclovir therefore seems to be effective for suppression of EHV-3 infection. Further investigation about the administration protocol might be required.

Experimental reactivation of equine herpesvirus-3 following corticosteroid treatment

State of latency, well known for several herpesviruses, has been proposed for equine herpesvirus-3 (EHV-3) and supported by epidemiological observations. No detailed assessment about reactivation, patterns of excretion and reexcretion has been formally reported. An experimental reactivation study by corticosteroid treatment in previously naturally infected horses was therefore carried out. Two polo mares with clinical and virologically confirmed history of equine coital exanthema were injected with dexamethasone and prednisolone on 3 successive days. Clinical signs, body temperature and clinical samples for virological and serological studies were obtained daily. Mares did not show any systemic clinical signs or hyperthermia. EHV-3 shedding, seroconversion and the presence of a small lesion were observed in one of the mares under study 2 weeks after corticosteroid treatment. The results demonstrate that this virus exhibits a latency-reactivation behaviour similar to that of other alpha herpesviruses. Reactivation of latency may have an important bearing on the appearance of clinical signs in mares and/or stallions during the breeding season without the actual evidence of transfer from mare to stallion or vice versa.

ASSESSMENT OF VIRAL PRESENCE IN SEMEN AND REPRODUCTIVE FUNCTION OF FROZEN-THAWED SPERMATOZOA FROM PALLAS' CATS (OTOCOLOBUS MANUL) INFECTED WITH FELINE HERPESVIRUS

Although herpesviruses are known to contaminate the semen of several mammalian species, the occurrence of feline herpesvirus type 1 (FHV-1) in semen of infected cats has not been reported. Our objectives in this study were to investigate the presence of FHV-1 DNA in seminal fluid and frozen-thawed spermatozoa from FHV-1 infected Pallas' cats (Otocolobus manul) and assess the functionality of their frozen-thawed spermatozoa in vitro. Over a 3-yr period, semen (n = 33 ejaculates) was collected periodically via electroejaculation from four Pallas' cats chronically infected with FHV-1. Spermic ejaculates were frozen by pelleting on dry ice and stored in liquid nitrogen. After thawing, sperm motility and acrosome status were assessed over time during in vitro culture. For vitro fertilization (IVF), viable domestic cat (Felis silvestris catus) oocytes were inseminated with frozen-thawed Pallas' cat spermatozoa and evaluated for embryo cleavage. For FHV-1 polymerase chain reaction (PCR) analysis, DNA was extracted from seminal fluid, frozen-thawed spermatozoa, inseminated oocytes, heterologous IVF embryos, and conjunctival biopsies and analyzed for presence of a 322-base pair region of the FHV-1 thymidine kinase gene. Immediately post-thaw, sperm motility and percentage of intact acrosomes were decreased (P < 0.05) compared to fresh samples, and declined further (P < 0.05) during culture. However, all frozen-thawed IVF samples were capable of fertilizing domestic cat oocytes (overall, 46.1 +/- 6.0% cleavage). PCR analysis did not identify FHV-1 DNA in any reproductive sample despite the repeated detection of FHV-1 DNA in conjunctival biopsies. These results suggest that semen collected from Pallas' cats infected with FHV-1 does not contain cell-associated or non-cell-associated virus and that frozen-thawed spermatozoa exhibit adequate function for potential genetic rescue with minimal risk of FHV-1 transmission.

Disease transmission in horses

Bacterial, viral and protozoal infections may cause severe reproductive losses. The present paper reviews the risk factors, clinical signs and preventive measures for the most important venereal or potential sexually transmitted diseases in horses. The stallion and use of semen for artificial insemination represent major risk factors for the transmission of bacterial contaminants of the penis, including Streptococcus equi subspecies zooepidemicus, Pseudomonas aeruginosa and Klebsiella pneumoniae, known to cause endometritis and infertility in the mare. The role of the stallion in disease transmission is also due to the non-clinical manifestation of diseases such as contagious equine metritis and equine viral arteritis. Dourine has been eradicated from many countries, but continues to be a problem in other areas of the globe. Strategies for the prevention of introduction and transmission of diseases in breeding operation are discussed.