Corneal ulceration associated with naturally occurring canine herpesvirus-1 infection in two adult dogs

A retrospective cohort study of canid herpesvirus-1 seroprevalence and epidemiology in kennel dogs in Croatia

Canid alphaherpesvirus-1 (CaHV-1) is an endemic pathogen of dogs worldwide. CaHV-1 is often related to abortions, neonatal mortality, and the death of puppies. Since the first description of the virus in 1965, there has been no generally accepted method for diagnosing CaHV-1. Many authors used the virus neutralisation test (VNT) as a 'reference standard' due to its high specificity. Nasal, vaginal, preputial swabs and serum samples for this study were collected in the population of kennel dogs in Croatia. To determine the optimal VNT protocol, three modifications of the VNT were compared. These modifications were: VNT using native serum samples, VNT using thermally inactivated serum samples, and VNT using thermally inactivated serum samples with the addition of the complement. The correlation between the results of the VNT methods was significant (P < 0.001). Of all three modifications of VNT, the one using native serum samples was the one that increased VNT sensitivity. The overall seroprevalence of CaHV-1 was 32.02%. The PCR did not confirm the CaHV-1 presence in collected swabs. According to analysed anamnestic data, significant risk factors for CaHV-1 infection were: kennel size, attendance at the dog shows, hunt trials, kennel disinfection protocols, and mating. The oestrus cycle had no significant effect on seropositivity. The study results indicate that CaHV-1 spreads horizontally between dams living in kennels and in males during mating. Although there was no correlation between seropositivity and a history of reproductive disorders, significantly more stillborn puppies were recorded in seronegative dames (P < 0.01).

In vivo confocal microscopic features of naturally acquired canine herpesvirus-1 and feline herpesvirus-1 dendritic and punctate ulcerative keratitis

OBJECTIVE

To describe the in vivo confocal microscopy (IVCM) features of the corneal epithelium and stroma in dogs and cats with herpetic dendritic ulcerative keratitis.

ANIMALS

6 client-owned dogs and 10 client-owned cats with herpetic dendritic ulcerative keratitis (affected group) and 10 dogs and 10 cats from specific-pathogen-free laboratory colonies (nonaffected group).

PROCEDURES

After complete ophthalmic examination, IVCM corneal examination was performed on the clinically diseased eyes of animals in the affected group and on both eyes of animals in the nonaffected group. Results by species were compared between groups.

RESULTS

In the affected group, all 6 dogs had unilateral ocular lesions (total, 6 eyes examined), whereas 7 cats had unilateral lesions and 3 cats had bilateral lesions (total, 13 eyes examined). For the nonaffected group, 20 cat eyes and 20 dog eyes were examined. Corneal epithelial morphological abnormalities were identified in all examined eyes of animals in the affected group and in no examined eyes of the nonaffected group. Hyperreflective punctate opacities and inflammatory cells were present in all epithelial layers in examined eyes of affected animals but were absent in nonaffected animals. Similarly, Langerhans cells and anterior stromal dendritic cells were identified in corneas of eyes examined for animals in the affected group but not in any eye of animals in the nonaffected group. Stromal changes were less consistent in the affected group, but absent in the nonaffected group.

CONCLUSIONS AND CLINICAL RELEVANCE

Results indicated that herpetic dendritic ulcerative keratitis in dogs and cats is associated with microanatomic corneal abnormalities that can be detected by IVCM.

Intensive ocular sampling for the detection of subclinical canine herpesvirus-1 shedding in dogs with experimentally-induced latent infection

Latent canine herpesvirus-1 (CaHV-1) infections are common in domestic dogs, but viral shedding patterns in dogs are poorly understood. Previous research failed to detect spontaneous subclinical ocular CaHV-1 shedding in dogs following ocular infection, a situation that is fundamentally distinct from many of the alphaherpesviruses closely related to CaHV-1. One possible explanation for this finding is that the sampling interval in the prior studies evaluating ocular shedding patterns was too infrequent to detect rapidly cleared, brief ocular viral shedding episodes. To evaluate for this potential viral shedding scenario, 10 laboratory beagles recovered from experimental primary ocular CaHV-1 infection and with latent CaHV-1infection were intensively monitored for viral reactivation and shedding for 28 days. Clinical ophthalmic examinations were performed daily. Ocular swab samples were collected for CaHV-1 polymerase chain reaction 3 times daily and CaHV-1 virus neutralizing antibody assays were evaluated at 2-week intervals. No abnormalities suggestive of recurrent CaHV-1 ocular disease were observed during clinical ophthalmic examination in the dogs during the study. Ocular CaHV-1 shedding was not detected by polymerase chain reaction and CaHV-1 virus neutralizing antibody titers remained stable in all dogs for the study duration. In the present study utilizing frequent multiple daily sample collections, no evidence of subclinical ocular CaHV-1 shedding was detected in mature dogs with experimentally-induced latent CaHV-1 infection.

Phylogenomic Analysis of Global Isolates of Canid Alphaherpesvirus 1

Canid alphaherpesvirus 1 (CHV-1) is a widespread pathogen of dogs with multiple associated clinical signs. There has been limited prior investigation into the genomics and phylogeny of this virus using whole viral genome analysis. Fifteen CHV-1 isolates were collected from animals with ocular disease based in the USA. Viral DNA was extracted for Illumina MiSeq full genome sequencing from each isolate. These data were combined with genomes of previously sequenced CHV-1 isolates obtained from hosts in the UK, Australia and Brazil. Genomic, recombinational and phylogenetic analysis were performed using multiple programs. Two isolates were separated into a clade apart from the remaining isolates and accounted for the majority of genomic distance (0.09%): one was obtained in 2019 from a USA-based host (ELAL-1) and the other in 2012 from a host in Brazil (BTU-1). ELAL-1 was found to contain variants previously reported in BTU-1 but also novel variants in the V57 gene region. Multiple non-synonymous variants were found in USA-based isolates in regions associated with antiviral resistance. Evidence of recombination was detected between ELAL-1 and BTU-1. Collectively, this represents evidence of trans-boundary transmission of a novel form of CHV-1, which highlights the importance of surveillance for this pathogen in domestic dog populations.

Case Reports for Topical Treatment of Corneal Ulcers with a New Matrix Therapy Agent or RGTA® in Dogs

Superficial corneal ulcers that fail to heal within a normal time period and are refractory to conventional therapy in dogs are common in veterinary practice. Different etiologies can lead to this result, including spontaneous chronic corneal epithelial defects (SCCEDs) and ulcerative keratitis associated with bullous keratopathy. Thus, there is an urgent need to find new therapeutic approaches such as matrix therapy replacement. To determine the efficacy of a new ophthalmic treatment (Clerapliq^®) for SCCEDs and ulcerative keratitis associated with bullous keratopathy, a total of 11 dogs referred to the clinic because of nonhealing erosive ulcers after a classic primary treatment were enrolled to get this new treatment. Dogs underwent ophthalmic exams and 7 dogs (10 eyes) were diagnosed with superficial ulceration and 4 dogs (5 eyes) with bullous keratopathy due to endothelial dystrophy/degeneration. They received eye drops of Clerapliq^® every 3 days until recovery. The results showed that the corneas with recurrences of the ulcers were resolved predominantly by using Clerapliq^® every 3 days in 83.3% of the cases during a period of treatment ranging between 6 to 35 days. Therefore, this new approach using matrix therapy regenerating technology in treating superficial ulcers and bullous keratopathy in dogs can be successfully considered as an adjunctive therapy.

Comparison of bacterial culture results collected via direct corneal ulcer vs conjunctival fornix sampling in canine eyes with presumed bacterial ulcerative keratitis

OBJECTIVE

To compare aerobic bacterial culture results between samples obtained from the corneal ulcer versus lower conjunctival fornix in eyes with presumed bacterial ulcerative keratitis.

ANIMALS STUDIED

Fifty five client-owned dogs diagnosed with ulcerative keratitis.

PROCEDURES

Ophthalmic examinations were performed on each dog including slit-lamp biomicroscopy and indirect ophthalmoscopy. Microbial swabs were collected by direct sampling of the infected corneal ulcer as well as the lower conjunctival fornix, of the same eye, using a sterile rayon-tipped swab. Samples were submitted to an outside reference laboratory for aerobic bacterial culture and sensitivity.

RESULTS

One hundred twelve samples were obtained from 56 eyes (55 dogs). Sixty-eight samples yielded bacterial growth. Positive growth from both sites was obtained in 31 eyes (55%). Six eyes yielded bacterial growth from the conjunctival fornix but not from the cornea. No bacterial growth was obtained from either sampling site in 19 eyes. Overall, 31/56 (55%) corneal samples were positive and 37/56 (66%) conjunctival fornix samples were positive. Comparison of organisms isolated from the two collection sites of the same eye revealed an exact correlation in 42/56 (75%) eyes and differed in 14/56 (25%) eyes. Twenty different bacterial isolates were obtained from 68 positive samples. Gram-positive (71%) organisms were more common than Gram-negative (29%). The most commonly isolated organisms were Staphylococcus pseudintermedius (25%), beta-hemolytic Streptococcus spp. (23%), and Pseudomonas aeruginosa (12%). Methicillin-resistant organisms were isolated in 9% of samples.

CONCLUSION

Sampling from the conjunctival fornix may be a suitable alternative to direct ulcer sampling in eyes with compromised corneal structural integrity.

Evaluation of topical ophthalmic ganciclovir gel for the treatment of dogs with experimentally induced ocular canine herpesvirus-1 infection

OBJECTIVE To determine the in vitro half maximal effective concentration (EC₅₀) of ganciclovir for canine herpesvirus-1 (CHV-1) and to evaluate the efficacy of ganciclovir ophthalmic gel in dogs with experimentally induced ocular CHV-1 infection. ANIMALS 10 specific pathogen-free adult Beagles. PROCEDURES Cytotoxicity and EC₅₀ of ganciclovir for CHV-1 were determined during in vitro experiments. During an in vivo experiment, dogs with experimentally induced ocular CHV-1 infections received 1 drop of 0.15% ganciclovir (ganciclovir group; n = 5) or artificial tear (control group; 5) ophthalmic gel in both eyes 5 times daily for 7 days, then 3 times daily for 7 days. For each dog, ophthalmic and confocal microscopic examinations were performed at predetermined times to determine severity of ocular disease and inflammation. Conjunctival swab specimens were collected at predetermined times for PCR assay analysis to determine CHV-1 shedding. RESULTS No in vitro cytotoxic effects were observed for ganciclovir concentrations ≤ 500μM. The EC₅₀ of ganciclovir for CHV-1 was 37.7μM. No adverse effects associated with ganciclovir were observed during the in vivo experiment. Mean ocular disease and inflammation scores for the ganciclovir group were significantly lower than those for the control group. Mean duration of CHV-1 shedding for the ganciclovir group (0.4 days) was significantly shorter than that for the control group (6.2 days). CONCLUSIONS AND CLINICAL RELEVANCE Topical administration of 0.15% ganciclovir ophthalmic gel was well tolerated and effective in decreasing clinical disease scores, ocular tissue inflammation, and duration of viral shedding in dogs with experimentally induced ocular CHV-1 infection.

Canine Diabetes Mellitus Associated Ocular Disease

Diabetes mellitus (DM) is a commonly encountered disease in companion animal veterinary practice. Ocular complications in dogs with DM are thought to be common but there are no reports of the overall incidence of DM-associated ocular disease. Some complications, such as cataracts and ocular surface disease, can lead to vision loss and significant morbidity among DM patients, therefore early recognition and intervention are essential for successful outcomes. The purpose of this article is to provide a review of several currently known or suspected ocular diseases associated with DM.

Clinical and immunological assessment of therapeutic immunization with a subunit vaccine for recurrent ocular canine herpesvirus-1 infection in dogs

Latent canine herpesvirus-1 (CHV-1) infections are common in domestic dogs and reactivation of latent virus may be associated with recurrent ocular disease. The objectives of the present study were to evaluate the ability of a subunit CHV-1 vaccine to stimulate peripheral CHV-1 specific immunity and prevent recurrent CHV-1 ocular disease and viral shedding. Mature dogs with experimentally-induced latent CHV-1 infection received a 2-dose CHV-1 vaccine series. Recurrent ocular CHV-1 infection was induced by corticosteroid administration in the prevaccinal, short-term postvaccinal (2 weeks post-vaccination), and long-term postvacccinal (34 weeks post-vaccination) periods. Immunological, virological, and clinical parameters were evaluated during each study period. Quantitative assessment of peripheral immunity included lymphocyte immunophenotyping, proliferation response, and interferon-γ production; and CHV-1 virus neutralizing antibody production. In the present study, vaccination did not prevent development of ocular disease and viral shedding; however, there was a significant decrease in clinical ocular disease scores in the short-term postvaccinal period. Significant alterations in peripheral immunity detected in the dogs during the short-term and long-term postvaccinal periods included increased T and B lymphocyte subpopulation percentage distributions, increased lymphocyte expression of major histocompatibility complex class I and II, increased CHV-1 virus neutralizing antibody titers, decreased lymphocyte proliferation, and decreased interferon-γ production. Vaccination of latently infected mature dogs with the selected subunit CHV-1 vaccine was not effective in preventing recurrent ocular CHV-1 infection and viral shedding induced by corticosteroid administration. The vaccine did induce long-term CHV-1 specific immunity and may decrease the severity of clinical ocular disease in the immediate postvaccinal period.

In Vitro and In Vivo Evaluation of Cidofovir as a Topical Ophthalmic Antiviral for Ocular Canine Herpesvirus-1 Infections in Dogs

PURPOSE

The effects of cidofovir were investigated against canine herpesvirus-1 (CHV-1) in vitro and in dogs with experimentally induced recurrent ocular CHV-1 infection, a host-adapted pathogen animal model of ocular herpes simplex virus-1 (HSV-1) infection.

METHODS

The cidofovir EC50 was determined for CHV-1 and HSV-1. A randomized, masked vehicle-controlled trial was performed using beagles with experimentally induced recurrent ocular CHV-1 infection. Dogs received 1 drop of 0.5% cidofovir solution or 0.9% sodium chloride solution (vehicle) in both eyes 2 times daily for 14 days. Dogs were monitored at intervals for 30 days by a clinical ophthalmic examination, in vivo confocal microscopy of the cornea and conjunctiva, ocular sample CHV-1 polymerase chain reaction assay, hemogram, and serum biochemistry panel. Clinical ocular disease scores were calculated and infiltrating leukocytes detected by in vivo confocal microscopy quantified.

RESULTS

Cidofovir displayed similar in vitro antiviral activity against CHV-1 and HSV-1. Clinical ocular disease scores were significantly higher in the cidofovir group compared to the vehicle group. Marked conjunctival pigmentation and blepharitis were also detected in the cidofovir group, but not the vehicle group. Conjunctival and corneal leukocyte infiltration scores determined by in vivo confocal microscopy were significantly higher in the cidofovir group. Dogs administered cidofovir had significantly reduced durations of ocular viral shedding compared to the vehicle group. Hemogram and serum biochemistry panel values were unremarkable.

CONCLUSIONS

Twice-daily application of topical 0.5% cidofovir ophthalmic solution reduced the duration of ocular viral shedding in dogs with experimentally induced recurrent ocular CHV-1 infection, but was associated with local ocular toxicity.

Detection of equine herpesvirus in horses with idiopathic keratoconjunctivitis and comparison of three sampling techniques

OBJECTIVES

To determine the role of equine herpesvirus (EHV) in idiopathic keratoconjunctivitis in horses and to determine whether sample collection method affects detection of EHV DNA by quantitative polymerase chain reaction (qPCR).

ANIMALS STUDIED

Twelve horses with idiopathic keratoconjunctivitis and six horses without signs of ophthalmic disease.

PROCEDURES

Conjunctival swabs, corneal scrapings, and conjunctival biopsies were collected from 18 horses: 12 clinical cases with idiopathic keratoconjunctivitis and six euthanized controls. In horses with both eyes involved, the samples were taken from the eye judged to be more severely affected. Samples were tested with qPCR for EHV-1, EHV-2, EHV-4, and EHV-5 DNA. Quantity of EHV DNA and viral replicative activity were compared between the two populations and among the different sampling techniques; relative sensitivities of the sampling techniques were determined.

RESULTS

Prevalence of EHV DNA as assessed by qPCR did not differ significantly between control horses and those with idiopathic keratoconjunctivitis. Sampling by conjunctival swab was more likely to yield viral DNA as assessed by qPCR than was conjunctival biopsy. EHV-1 and EHV-4 DNA were not detected in either normal or IKC-affected horses; EHV-2 DNA was detected in two of 12 affected horses but not in normal horses. EHV-5 DNA was commonly found in ophthalmically normal horses and horses with idiopathic keratoconjunctivitis.

CONCLUSIONS

Because EHV-5 DNA was commonly found in control horses and in horses with idiopathic keratoconjunctivitis, qPCR was not useful for the etiological diagnosis of equine keratoconjunctivitis. Conjunctival swabs were significantly better at obtaining viral DNA samples than conjunctival biopsy in horses in which EHV-5 DNA was found.

Establishment and characterization of an air-liquid canine corneal organ culture model to study acute herpes keratitis

Despite the clinical importance of herpes simplex virus (HSV)-induced ocular disease, the underlying pathophysiology of the disease remains poorly understood, in part due to the lack of adequate virus-natural-host models in which to study the cellular and viral factors involved in acute corneal infection. We developed an air-liquid canine corneal organ culture model and evaluated its susceptibility to canine herpesvirus type 1 (CHV-1) in order to study ocular herpes in a physiologically relevant natural host model. Canine corneas were maintained in culture at an air-liquid interface for up to 25 days, and no degenerative changes were observed in the corneal epithelium during cultivation using histology for morphometric analyses, terminal deoxynucleotidyltransferase-mediated dUTP-biotin nick end labeling (TUNEL) assays, and transmission electron microscopy (TEM). Next, canine corneas were inoculated with CHV-1 for 48 h, and at that time point postinfection, viral plaques could be visualized in the corneal epithelium and viral DNA copies were detected in both the infected corneas and culture supernatants. In addition, we found that canine corneas produced proinflammatory cytokines in response to CHV-1 infection similarly to what has been described for HSV-1. This emphasizes the value of our model as a virus-natural-host model to study ocular herpesvirus infections.

IMPORTANCE

This study is the first to describe the establishment of an air-liquid canine corneal organ culture model as a useful model to study ocular herpesvirus infections. The advantages of this physiologically relevant model include the fact that (i) it provides a system in which ocular herpes can be studied in a virus-natural-host setting and (ii) it reduces the number of experimental animals needed. In addition, this long-term explant culture model may also facilitate research in other fields where noninfectious and infectious ocular diseases of dogs and humans are being studied.

A serological study of canine herpesvirus-1 infection in a population of breeding bitches in Norway

Background

Canine herpesvirus-1 (CHV1) causes a fatal hemorrhagic disease in neonatal puppies and is associated with infertility in female dogs. This study was conducted to assess the status of CHV1 infection in bitches in proestrus or estrus and to investigate possible risk factors by a detailed questionnaire. Blood samples were collected from healthy bitches (n = 193) not vaccinated against CHV1, aged one year or older and admitted for estrus control to the Canine Reproductive Clinical Unit, Norwegian School of Veterinary Science. The serum samples were analysed by immunoperoxidase monolayer assay and serum titers were recorded as the reciprocal value of the highest dilution producing specific cell staining.

Results

Altogether, 85.5% of the dogs had CHV1 titers ≥ 80 and were classified as positive. Mean age for dogs included in the study was 4.2 years (95% CI 4.0-4.5), and there was no difference in age between seronegative dogs vs seropositive dogs. When grouping the seropositive dogs into three categories according to the magnitude of the titer, a total of 38.8% of the bitches displayed a weakly positive titer of 80, 44.8% had moderately positive titers of 160 or 320 and 16.4% of the dogs fell into the strongly positive category with titer of ≥640. No association was demonstrated when comparing CHV1 antibody titers to fertility parameters such as previous matings, pregnancies, whelpings, puppies born or condition of puppies. Further, there was no difference in seroprevalence between bitches that had been abroad for a period of time and dogs only living within a Norwegian environment. Samples from dogs collected in summer and fall displayed moderate to high antibody titers indicating recent infection with CHV1. Season, previous birth, and participation in competitions/shows explained 67-78% of the variation in antibody titer.

Conclusions

This study demonstrates that CHV1 infection is common in breeding bitches in the eastern part of Norway. Associations with putative risk factors were not identified. However, season, previous whelping, and participation in competitions/shows explained 67-78% of the variation in antibody titer.

Canine herpesvirus-1 ocular diseases of mature dogs

Canine herpesvirus-1 (CHV-1) is an alphaherpesvirus with a host range restricted to canids. Latent CHV-1 infection is endemic in domestic dog populations worldwide. The role of CHV-1 in severe systemic neonatal infections and as an aetiology of infectious infertility and abortion has been appreciated for decades; however, ocular diseases of mature dogs conclusively associated with CHV-1 infection were only recently described. Clinically, CHV-1 infection may produce a diverse range of adnexal and ocular surface lesions in mature dogs, including blepharitis, conjunctivitis, ulcerative keratitis, and nonulcerative keratitis. These conditions can develop during primary or recurrent ocular CHV-1 infection. Recurrent CHV-1 infections associated with reactivation of latent virus may be observed during a variety of situations and in association with numerous different viral reactivation stimuli, including the administration of immunosuppressive pharmaceuticals. The understanding of CHV-1 pathophysiology and ocular infections in mature dogs has expanded rapidly during the past few years, but much remains to be elucidated. As the number of dogs living with chronic immunomodulatory systemic diseases and receiving immunosuppressive therapeutics continues to grow, the clinical importance of CHV-1 ocular infections is also likely to increase.

Fatal Canid herpesvirus 1 infection in an adult dog

Canid herpesvirus 1 (CaHV-1) is a well-known cause of fatal hepatic and renal necrosis in neonatal puppies. In adult dogs infected with CaHV-1, papulovesicular genital lesions may be observed. CaHV-1 infection during pregnancy can lead to embryonic resorption, abortion, and stillbirth. In high-density dog populations, CaHV-1 can also contribute to kennel cough. Furthermore, recent literature has clearly documented that CaHV-1 can induce ocular disease in immature and adult dogs. The current study describes a case of fatal CaHV-1 infection in a 9-year-old spayed female Bichon Frise dog. Following a history of vomiting and diarrhea, the dog deteriorated and subsequently died. The main lesions were multifocal areas of necrosis with intranuclear inclusion bodies in the liver, adrenal gland, and small intestine, similar to the lesions observed in CaHV-1-infected puppies. Infection with CaHV-1 was confirmed on samples of liver by polymerase chain reaction, immunohistochemistry, and in situ hybridization. There was no indication of immunosuppression in this dog. Based on the results presented herein, CaHV-1 should be included in the list of differential diagnoses of hepatic necrosis in adult dogs.

Effects of cyclophosphamide myelosuppression in adult dogs with latent canine herpesvirus-1 infection

Latent canine herpesvirus-1 (CHV-1) infection is common in domestic dogs, but triggers for viral reactivation and recrudescent CHV-1 disease are poorly understood. Cyclophosphamide is a potent immunosuppressive and myelosuppressive agent used for the therapy of a variety of neoplastic and immune-mediated canine disorders. Cyclophosphamide (200mg/m(2)) was administered to mature dogs latently infected with CHV-1 to determine its potential to induce recurrent CHV-1 disease and viral shedding. Non-infected dogs and dogs recovered from experimental primary ocular CHV-1 infection with experimentally confirmed latent CHV-1 infection were divided into groups and administered cyclophosphamide or placebo. Dogs were monitored for myelosuppression and viral reactivation for 28days using clinical and virological outcome measures. Clinical ophthalmic and in vivo ocular confocal microscopic examinations were performed at intervals. Samples were collected for CHV-1 polymerase chain reaction (PCR), CHV-1 virus neutralizing (VN) antibody, and hemogram assays. Myelosuppression (i.e., decreased total leukocyte, segmented neutrophil, and erythrocyte counts) was detected on study day 7 in dogs administered cyclophosphamide, but not dogs administered placebo. There were no abnormalities suggestive of recurrent CHV-1 ocular disease during clinical ophthalmic or in vivo confocal microscopic examination in any dogs during the study. Ocular CHV-1 shedding was not detected by PCR and CHV-1 VN titers remained stable in all dogs. Following study conclusion, the presence of reactivatable latency was reconfirmed in the infected dogs by administering systemic prednisolone. Myelosuppression elicited by a single dose of cyclophosphamide does not result in detectable recurrent ocular CHV-1 infection in adult dogs with experimentally induced latent CHV-1 infection.

Canine reproductive, respiratory, and ocular diseases due to canine herpesvirus

This review documents how clinical inquiry expands as our knowledge base about canine herpesvirus (CHV) increases. We must understand the various forms of CHV infection that may occur in the dog population. This has prompted the veterinary community to develop more sensitive diagnostic assays. CHV is more common than we considered a decade ago. Up to 70% of some high-risk dog populations have been infected with and are latent carriers of CHV. Recognition of the various forms of CHV-induced disease, availability of diagnostic assays with increased sensitivity, and the formation of reliable biosecurity measures will allow for better control steps.

Acute primary canine herpesvirus-1 dendritic ulcerative keratitis in an adult dog

We present a report of dendritic ulcerative keratitis in a 4-year old locally immunosuppressed dog suspected to result from acute primary canine herpesvirus-1 (CHV-1) infection. The dog was presented for evaluation of mild blepharospasm and conjunctival hyperemia in the right eye (OD) shortly after attending a public boarding facility. For approximately 3 months, the dog had been receiving topical prednisolone acetate 1.0% and tacrolimus 0.02% in both eyes (OU) q12h for treatment of follicular conjunctivitis. Ophthalmic examination revealed three regions of corneal fluorescein retention OD. The lesions had a dendritic pattern, were approximately 2-3 mm in length, and were located at the dorsomedial, lateral, and ventromedial aspects of the cornea. No additional abnormalities were noted on complete ophthalmic and physical examinations. CHV-1 was identified in conjunctival samples OD by polymerase chain reaction, and paired CHV-1 serum virus neutralization antibody titers were positive and consistent with acute infection. Topical prednisolone acetate and tacrolimus were discontinued. The dog was treated with cidofovir 0.5% OU q12h for a period of 4 weeks, with resolution of corneal disease noted within 1 week of treatment. In conjunction with previous studies, this case report supports a central role for alterations in host immune status in the pathogenesis and clinical manifestations of CHV-1 ocular disease in dogs.

Development and validation of a real-time PCR assay for specific and sensitive detection of canid herpesvirus 1

A TaqMan-based real-time PCR assay targeting the glycoprotein B-encoding gene was developed for diagnosis of canid herpesvirus 1 (CHV-1) infection. The established assay was highly specific, since no cross-reactions were observed with other canine DNA viruses, including canine parvovirus type 2, canine minute virus, or canine adenovirus types 1 and 2. The detection limit was 10¹ and 1.20 × 10¹ DNA copies per 10 μl⁻¹ of template for standard DNA and a CHV-1-positive kidney sample, respectively: about 1-log higher than a gel-based PCR assay targeting the thymidine kinase gene. The assay was also reproducible, as shown by satisfactory low intra-assay and inter-assay coefficients of variation. CHV-1 isolates of different geographical origins were recognised by the TaqMan assay. Tissues and clinical samples collected from three pups which died of CHV-1 neonatal infection were also tested, displaying a wide distribution of CHV-l DNA in their organs. Unlike other CHV-1-specific diagnostic methods, this quantitative assay permits simultaneous detection and quantitation of CHV-1 DNA in a wide range of canine tissues and body fluids, thus providing a useful tool for confirmation of a clinical diagnosis, for the study of viral pathogenesis and for evaluation of the efficacy of vaccines and antiviral drugs.

The effect of topical ocular corticosteroid administration in dogs with experimentally induced latent canine herpesvirus-1 infection

Recurrent herpes simplex virus-1 (HSV-1) ocular infection is a frequent cause of morbidity and blindness. Factors that trigger viral reactivation are poorly understood and the role of topical ocular corticosteroid administration in the development of recurrent HSV-1 ocular disease is not clear. Clinical reports and epidemiological studies suggested topical corticosteroids may reactivate latent HSV-1 and result in recrudescent ocular disease; however, experimental studies to establish this causal relationship produced inconsistent results. The previous experimental studies were performed by infecting unnatural host species with HSV-1 and aspects of viral behavior and reactivation within these animals may differ from the host for which the virus is adapted. The purpose of the study reported here was to determine if topical ocular corticosteroid administration results in viral reactivation and recrudescent ocular disease in a host-adapted pathogen animal model of HSV-1 recurrent ocular disease. Canine herpesvirus-1 (CHV-1) is a corticosteroid-sensitive alphaherpesvirus that is biologically related to HSV-1 and induces similar ocular lesions in canids during recurrent infection. A randomized, masked, placebo-controlled, crossover study was performed. Primary ocular CHV-1 infection was experimentally induced in mature specific pathogen-free beagles by topical ocular inoculation and the presence of reactivatable latency was later confirmed by administration of an immunosuppressive dosage of systemic corticosteroid to the dogs. Twelve months following experimental CHV-1 reactivation, dogs were administered either topical ocular prednisolone acetate (1.0% ophthalmic suspension, one drop in both eyes, four times daily) or placebo (artificial tear solution, one drop in both eyes, four times daily) for 28 days. After a 14 day washout period, the treatment groups were reversed and study agents administered for an additional 28 days. Ophthalmic examinations, in vivo ocular confocal microscopy, real-time quantitative CHV-1 polymerase chain reaction assays, and CHV-1 serum neutralization antibody titers were performed at regular intervals throughout the study. Viral reactivation was not detected in dogs administered topical ocular prednisolone or placebo as determined by clinical ocular disease recrudescence, in vivo ocular confocal microscopic findings, ocular viral shedding, and serologic response. Similar to other animal models of recurrent HSV-1 ocular infection, the behavior of latent CHV-1 in dogs may differ from HSV-1 in humans; however, results of the present study suggest administration of topical ocular prednisolone at the evaluated drug concentration, dosing frequency, and treatment duration is not likely to result in detectable reactivation of latent CHV-1 in experimentally infected dogs. This may be attributed to insufficient systemic absorption of locally administered corticosteroid to reactivate latent virus and produce recurrent disease. Crystalline corneal opacities that were apparently not associated with viral reactivation were detected by clinical examination and in vivo confocal microscopy in two dogs during topical ocular prednisolone administration. The crystalline keratopathy may have resulted from corneal degeneration associated with metaherpetic disease, corticosteroid administration, or a combination of both factors.

Outbreak of ocular disease associated with naturally-acquired canine herpesvirus-1 infection in a closed domestic dog colony

OBJECTIVE

To describe clinical and virological findings of an outbreak of ocular disease attributed to naturally-acquired primary canine herpesvirus-1 (CHV-1) infection in a closed domestic dog colony.

ANIMALS STUDIED

Twenty-seven 10- to 16-week-old laboratory Beagles.

PROCEDURE

Complete ophthalmic examinations were performed and ocular samples collected for CHV-1 polymerase chain reaction and virus isolation.

RESULTS

The prevalence of ocular morbidity was 100% in examined dogs. Lesions were restricted to the ocular surface and included bilateral conjunctivitis (100% of dogs); punctate, dendritic, or geographic ulcerative keratitis (26% of dogs); and non-ulcerative keratitis (19% of dogs). Conjunctival petechiae were detected in 22% of dogs. Punctate and dendritic corneal ulcers were frequently organized into discrete groups or linear arrangements. Non-ulcerative keratitis appeared clinically as a perilimbal ring of superficial corneal vascularization and leukocyte infiltration. CHV-1 was detected in ocular samples by polymerase chain reaction or virus isolation in all dogs sampled.

CONCLUSIONS

In susceptible populations of domestic dogs, CHV-1 may be associated with outbreaks of highly contagious ocular infection in the absence of concurrent overt systemic disease. This naturally-acquired outbreak of CHV-1 infection provides an opportunity to report the spectrum and prevalence of ocular lesions associated with primary ocular CHV-1 infection in dogs. Conjunctivitis was the most frequent ocular lesion detected. Ulcerative and non-ulcerative keratitis were less prevalent and of variable clinical appearance. Dendritic ulcerative keratitis, a classic and relatively specific ocular lesion associated with alphaherpesvirus infection, was detected in < 20% of dogs.

Experimental reactivation of latent canine herpesvirus-1 and induction of recurrent ocular disease in adult dogs

Latent canine herpesvirus-1 (CHV-1) infection is common in domestic dogs, but recrudescent CHV-1 diseases are poorly characterized. To determine if administration of an immunosuppressive dosage of prednisolone to adult dogs latently infected with CHV-1 results in recurrent ocular disease, adult beagles with and without experimentally induced CHV-1 latent infection were divided into groups: group 1 latently infected and administered prednisolone, group 2 latently infected and administered placebo, and group 3 not latently infected and administered prednisolone. Prednisolone (3.0 mg/kg/day) was administered to dogs in groups 1 and 3 for seven consecutive days beginning on study day 1. Samples for CHV-1 polymerase chain reaction and serum neutralization (SN) assays were collected, and physical, ophthalmologic, and in vivo ocular confocal microscopic examinations were performed at intervals for 42 days. Bilateral ocular disease (i.e., conjunctivitis or keratitis) was detected in 83% of group 1 dogs between study days 3 and 18. In vivo confocal microscopic abnormalities included conjunctival leukocyte infiltration and corneal leukocyte infiltration, abnormal epithelial cell morphology, and Langerhans cell infiltration. Ocular viral shedding was detected in 50% of group 1 dogs on study days 10 and 13. Fourfold elevations in CHV-1 SN titers were detected in 100% of group 1 dogs by study day 14. Dogs in control groups did not develop clinical ocular disease (P<0.05), CHV-1 titer elevations (P<0.005), or viral shedding. Administration of an immunosuppressive dosage of systemic prednisolone to adult dogs latently infected with CHV-1 may result in viral reactivation and ocular disease recrudescence.

Canine adenoviruses and herpesvirus

Canine adenoviruses (CAVs) and canine herpesvirus (CHV) are pathogens of dogs that have been known for several decades. The two distinct types of CAVs, type 1 and type 2, are responsible for infectious canine hepatitis and infectious tracheobronchitis, respectively. In the present article, the currently available literature on CAVs and CHV is reviewed, providing a meaningful update on the epidemiologic, pathogenetic, clinical, diagnostic, and prophylactic aspects of the infections caused by these important pathogens.

Histopathologic evidence of capecitabine corneal toxicity in dogs

In an experimental model of transplant rejection, renal transplants were performed on 6 mixed-breed dogs. Capecitabine (CPC) was administered as an oral immunosuppressive agent. All recipients received systemic CPC, cyclosporine (CSA), prednisolone, and famotidine throughout the study. Two dogs developed superficial keratitis, which was characterized by multifocal geographic erosions, superficial corneal epithelial pigmentation, and corneal neovascularization. These clinical signs correlated with the dose of CPC given, whereas other drug doses remained unchanged. After euthanasia, routine histologic sections were stained with hematoxylin and eosin and with alcian blue periodic acid-Schiff for light microscopic evaluation. Ocular histopathologic abnormalities were limited to neovascularization and inflammatory infiltrate of the anterior corneal stroma and abnormal basal cell morphology, disorganization, thinning, and pigmentation of the corneal epithelium. The purpose of this communication is to describe the clinical and histopathologic evidence of CPC corneal toxicity in dogs.