Ocular Problems In Felines And Canines
A Two Year Analysis of DNA Testing

The field of diagnostic veterinary medicine has witnessed remarkable advancements in the last decade. These advancements have been mediated by the introduction of the polymerase chain reaction (PCR) to the field of molecular diagnostics. PCR is a method of detecting minute quantities of DNA or RNA sequences specific to an organism by logarithmically replicating the sequences, thus amplifying the organisms DNA signal and allowing for easy visual interpretation and pathogenic detection in the laboratory. Nucleic acid based testing with PCR amplification has allowed for a significant increase in the sensitivity and specificity of organism detection. This technique makes it possible to detect pathogens at any stage during the course of their infection, even if no clinical signs of disease are present. Nearly any biological sample that may possibly contain pathogens can be analyzed including blood, urine, feces, exudates, ocular fluids and nasal secretions to name a few.

HealthGene works closely with many internationally renowned ophthalmologists, helping to facilitate the exchange of knowledge and monitor the incidence of animal diseases as well as disease transmission to humans. Graphs 1 - 4 present some of HealthGene’s preliminary research on an associated ophthalmology clinic over a two-year period. This data illustrates the results of numerous diagnostic tests on blood and ocular swabs or fluid for infectious organisms known to cause ocular and systemic disease in canines and felines. It should be noted however that these results are representative of animals already displaying clinical symptoms and are not intended to reflect the general population.

HealthGene Laboratory offers three DNA profiles specifically designed to target infectious organisms that are commonly associated with ocular infections in both felines and canines. For example, the Feline Extraocular Infection profile (Test Code: FP14) precisely targets pathogens that are frequently linked to conjunctivitis and keratitis in cats. This is significant as conjunctivitis is likely the most common clinical ophthalmic disorder in felines. This profile screens for Feline herpesvirus, Chlamydia psittaci and Mycoplasma spp..

Feline herpesvirus 1 (FHV 1) is often a cause of ocular disease. Young cats that are infected commonly display respiratory tract disease and generally exhibit conjunctivitis with marked conjunctival hyperemia, chemosis, and serous to purulent ocular discharge. Once infected, cats become latent carriers of the herpesvirus and may have recurrences of ocular disease, including conjunctivitis and corneal ulcers. Graphs 1 & 2 clearly illustrate the prevalence of felines testing positive for herpesvirus infection after displaying signs of ocular infection.

Chlamydia psittaci and Mycoplasma spp. are common feline conjunctival pathogens that may also contribute to conjunctivitis along with FHV 1. The clinical presentation of conjunctivitis caused by Chlamydia psittaci is indistinguishable from that caused by FHV 1, and the two organisms may be present simultaneously. Mycoplasma may require a stressor to cause the disease such as another conjunctival pathogen or injury. Some studies have recovered Mycoplasma as normal flora from feline conjunctiva, whereas others have not. Once again,graphs 1 & 2 provide an indication of the number of felines testing positive for Chlamydia psittaci and Mycoplasma spp. after displaying symptoms of ocular infection. Keratitis in cats has been most frequently associated with invasion of the corneal epithelium by FHV 1. Some classic hallmarks of herpetic keratitis include stromal scarring, deep vascularization, inflammatory cell infiltrates and ultimately collagen damage and opacification.

In addition to the two previous ocular profiles discussed, HealthGene also offers a Feline Intraocular Infection Profile (Test Code: FP4) that screens for Feline Immunodeficiency virus (FIV), Feline Leukemia virus (FeLV), Feline herpesvirus. Unfortunately, canines are also prone to herpesvirus and Chlamydia infection. Graphs 3 & 4 illustrate the number of positive infections observed in canines displaying ocular disease. HealthGene Laboratory offers a Canine Ocular Infection Profile (Test Code: CP8) that detects both Chlamydia spp. and Canine herpesvirus. In addition, this profile screens for Ehrlichia canis and Toxoplasma gondii, which are also potential sources of ocular diseases. Toxoplasma gondii can be of particular concern since this single-celled parasite is able to infect both cats and dogs and is also transmittable to humans. Clinical infection by Toxoplasma is known as toxoplasmosis, which is often characterized by weight loss, fever, neurological or respiratory problems and ocular problems. Toxoplasmosis-mediated ocular problems in cats and dogs typically include uveitis, glaucoma, retinal detachment and blindness.

Although these profiles are designed to screen for the major causative agents of ocular infections, they are not exhaustive. In addition to the infectious organisms previously discussed, studies have implicated several other pathogens in instigating ocular disease. For example, research has indicated that other sources of canine conjunctivitis can include canine distemper virus and canine adenovirus. Additionally, symptoms of canine uveitis can be instigated by Ehrlichia canis, Brucella canis, and Borrelia burgdorferi (Lyme Disease) infection. HealthGene Laboratory offers testing for all of the above pathogens as well as a range of other diagnostic tests.

Although infectious diseases are a common source of ocular problems in canines, genetic disorders such as Progressive Retinal Atrophy (PRA) can also cause significant ocular problems. PRA can be described as the slow death of the retinal tissue. Progressive retinal degeneration may affect the rods alone, the cones alone, or both the rods and the cones. PRA often leads to total blindness in most breeds. The progression of the disorder is also breed dependent, occurring at different rates in different breeds. HealthGene Laboratory conducts canine genetic screening tests for PRA as well as an array of other breed specific genetic disorders. Currently, HealthGene is only offering PRA testing for Irish Setter and Cardigan Welsh Corgi breeds.

Veterinarians interested in conducting infectious or genetic tests should submit blood and ocular swabs or fluid samples in EDTA/lavender top tubes. HealthGene Laboratory recommends submitting multiple samples, which significantly increases the effectiveness of the DNA diagnostic test. Please note that there is no extra charge for additional samples from the same animal. Results for infectious testing are typically provided within 2-3 business days following their arrival, while genetic tests usually require 5-7 business days. HealthGene recommends that certain positive results for infectious agents be resubmitted two weeks following treatment to ensure that treatment was successful.

For additional information regarding the various tests and services HealthGene offers, please call 1-877-371-1551