Assignment 2

Review of "Onchocerca lupi causing 
ocular disease in two cats"

by Amber L. Labelle, Joshua B. Daniels, Michael Dix and Philippe Labelle

To find this paper please click here.

 
NOTE*: Due to the fact that this paper illustrates the first findings of Onchocerca lupi causing ocular disease in cats, there are a lack of photos specific to cats. Therefore photos mainly from dogs or humans will be used in this post.

     

Summary of the Paper's Content

        This paper's finding claim to have discovered the first cases of ocular disease in cats cause by Onchocerca lupi. Onchocerca lupi is a nematode parasite that is commonly associated with eye-disease in dogs and even humans (Onchocerca volvulus). This parasite is thought to be transmitted through an intermediate arthopod host (i.e. insects). The intermediate host is then either engulfed or bites the dog and transmits the parasite. Dogs are the most common definitive hosts of Onchocerca lupi. However, the findings of this paper reveal two cases within the United States where cat eyes have been diagnosed with Onchocerca lupi. These are the first reported cases of such infections in cats. 

        Figure 1: A visual of an Onchocerca species within the top left corner of a human iris (white substance) Source

           The first case described (Case 1) was of a young male feline who was ill with Feline Leukemia Virus (FeLV). The male began showing signs of ocular problems such as: conjunctivitis, chemosis (swelling of the conjunctiva) and opacity. After enucleation (removal of the eye) and histological analysis using H&E staining it was found that Onchocerca lupi species were inhabiting the eye globes of this cat. All parasites sectioned were females that contained many uteri.

Figure 2: Histological section of the ocular globe of Cat 1 stained with H&E. Large arrow points to fibrosis (connective tissue aggregated to repair tissue). The small arrow points to the cuticle of the parasite (cross-sectional view).

        Case 2 involved a female cat that was also suffering from Feline Leukemia Virus. This cat, as in Case 1, also suffered from serious ocular illness such as conjunctivitis, partial nerve paralysis and ulcers of the cornea. Histological sectioning revealed an the diseases were caused by invasion of the Onchocerca lupi nematode.

Figure 3: The arrows indicate the cuticle of Onchocerca lupi within the cat eye globe. The uteri are the dark purple spots under the cuticle.

Both cats were treated with Anti-Helminthic (antibiotics against round-worms) medications such as Praziquantal along with select surgeries. Both cats became healthy many months after treatment.

The nematodes found in the eyes of these cats were identified via molecular methods such as Polymerase Chain Reaction (PCR). After the DNA from each nematode sample was sequenced, the DNA was amplified and compared to each other using websites such as Clustal W (used to align and compare multiple DNA sequences) and BLAST (used to sequence DNA and Amino Acid sequences). Results indicated that each sample was > 99% the same. This confirms that both species were the same species; Onchocerca lupi.

Conclusions:
     The FeLV suppressed the immune systems of both cats leading to increased probability of contracting infections. Onchocerca lupi infected the eyes of both cats leading to glaucomas, conjunctivitis and other eye diseases. The immunosuppression of these cats may be an explanation why Onchocerca lupi has infected a new, uncommon species (although reasons are not clear). Ocular Onchocerciasis in felines should now be considered as a possible diagnosis when symptoms such as conjunctivitis and other ocular diseases.

Opinions of the Paper

Q: Did you like the paper?
I did enjoy this paper because my interests are tailored to infectious diseases and internal medicine (whether it involves humans or animals). However, I wished the paper would contain more photos of the histological sections of the eyes. I also would have enjoyed to see photos of the cats eyes to observe the degree of disease occurring in each cat. I did not enjoy the section of the paper outlining the evolutionary phylogeny of Onchocerca lupi because I felt it was not relevant to the paper's main thesis and ideas. It was interesting that Onchocerca lupi was able to infect a brand new species due to the genetic similarity.

Q: Did the results support the author's claim?
Yes, the results do support the authors' claim. The authors' claimed that these two cases involved the first ocular diseases caused by Onchocerca lupi in cats discovered. It was shown by molecular analysis that both feline eyes contained Onchocerca lupi and that certain symptoms and diseases were caused by this parasite.

Q: Were the experiments well conducted?
The paper did not involve "true" experiments but rather real veternarian cases with actually ill patients. Therefore the diagnostic methods and treatments used for the patients were nothing less than professional. Patients were carefully examined and diseases were diagnosed with care. After diagnosis, the Veterinarians decided on the best possible treatments for the cats. Histological sectioning and staining was also done professionally. Therefore all "experiments" were very well conducted.

Q: Are the methods appropriate?
The methods of diagnosis were very appropriate. The molecular methods used to identify the nematode species were some of the most specific methods which indicates that they were successful and useful. All methods used for diagnosis and treatment were appropriate for the well being of the patient. The methods used for determining the phylogenetic analysis of Onchocerca seemed irrelevant to the main focus of the paper.

References

Labelle, A.L., Daniels, J.B., Dix, M.,and Labelle, P. (2011). Onchocerca lupi causing ocular disease in two cats. Ohio State University, Ohio: Vet Opthalmol, Volume 1, 101-110.

Histology of the Feline Eye: My Favourite Tissue

                          

Main Function: The cat eye is the main visual sensory organ of the cat. The feline eye's function is to detect light and convert it to chemical signals that can be interpreted by the feline brain. Cat eye's contain most characteristics associated with human eyes except for the well-known reflective layer located behind the retina called the tapetum lucidum (Wrycha, 2004). 

Main Anatomy of the Feline Eye:

Figure 1: Basic anatomy of the feline eye globe. (Wrycha, 2004)

Anterior Chamber: This chamber is covered by the cornea. The cornea receives light signals and directs them towards the lens. The cornea serves as a window to the eye and has great refracting power. The stroma makes up the majority of the cornea and is mainly composed of lamellae with sparse collagen fibres. The Anterior Chamber is filled with aqueous fluid (Wrycha, 2004).

Figure 1: Feline cornea showing the outer epithelium (stratified squamous), stroma and the endothelium (simple cuboidal) (Wrycha, 2004).

Posterior Chamber: This chamber contains the lens, and it is separated from the anterior chamber via the iris'. The iris and retina are very sensitive to light and may close around the pupil in a "slit-like" manner when exposed to bright light intensities (Wrycha, 2004).

The Lens: This convex structure serves to receive refracted light from the cornea and to refract and focus the light towards the retina.

The Iris: This structure accounts for the vibrant colours observed in the variety of feline eyes (as well as human eyes). The iris also contains a layer of muscle so that it can contract and dilate over the pupil in response to bright and low light intensities.

Figure 2: Histological section of a Feline Iris. "M" designates the melanocytes that give the iris colour while "U" designates the dilator muscle of the iris (Wrycha, 2004).

The Retina: This structure lines the inside of the feline eye and is the site of the conversion of light signals to chemical signals. Chemical signals are then transferred into electrical signals via nerve impulses sent from the Optic Nerve. The important cells within the Retina are the "Rods" and "Cones". Rods specialize in detecting light in low light intensities while cones specialize in detecting light in bright light intensities. Cones are also responsible for colour vision.

Figure 3: Histological section of the Feline Retina. "A" and "B" designate the thick layer of rod and cone cells. "T" designates the Tapetum (Wrycha, 2004).

INTERESTING FACT!

The layer of "rod" cells in cats are thicker than the rod cells in dogs. This extra thickness accounts for the reason why cats see much better in the dark than humans or dogs!

Figure 4: Cats being creepy in the dark. (Those are their tapetums shining!) (Rodo, 2010)

Sclera: The white area of the eye that contains collagen and elastic fibres. In cats, the sclera is not visible unless the eye-lid is pulled back (the iris takes up the visible area of the eye (unlike humans) (Sclera, 2012)

Pathology of the Feline Eye (The sad section)

This section will outline the most common problems and diseases that occur in the eye's of cats. Grab some tissues.

1. Conjunctivitis: This is the most common pathology observed in cats. It is similar to pink eye that we see in humans. It involves the swelling and irritation of the inner lining of the eye-lid or cornea. Conjunctivitis in cats is almost always indicative of another infection (i.e. herpes virus or chlamydophila). Without treatment, conjunctivitis can lead to serious vision problems. Most treatments entail the application of a topical, antibiotic cream to the eyes. (Carlson & Giffin, 2008)                                                                             

                                         

Figure 5: Kitten showing conjunctivitis in the eyes. (From "M's" blog, 2011)



2. Cataracts: This problem is associated with an opacity on the lens of the cat's eye. The opacity prevents light from passing through the lens and ultimately renders the cat partially blind (Cataracts in Cats, 2011)

                                                           

                                              Figure 6: Cat showing cataract in one eye (Don's Blog, 2010).

3. Feline Glaucomas: Glaucomas are diseases that are characteristically neuro-degenerative and result in the degeneration of the retinal and optic nerves. This degeneration results in the lost of vision for the cat. Glaucomas typically arise through elevated levels of intra-ocular pressure. Therefore the most common treatment used it the administration of hypo-tensive drugs (McLellan & Miller, 2012).

Figure 7: Cat eye displaying typical features of glaucoma. (Ferreira, 2010)

References:

Cataracts in Cats (2011, October 22). Retrieved from:
              http://www.pethealthnetwork.com/cat-health/cataracts-cats

Carlson, D., and J.M. Giffin. (2008). Conjunctivitis (Pinkeye) in Cats: Types, Symptoms, Causes and

             Treatments. Retrieved from: http://pets.webmd.com/cats/conjunctivitis-pinkeye-cats-types-symptoms-causes-treatments?page=2

McLellan, G.J., and P.E. Miller. (2012). Feline Glaucoma- A Comprehensive View. Retrieved From:

            http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3348181/

Sclera (2012). Retrieved from: http://www.stlukeseye.com/anatomy/sclera.html

 Wrycha (2004). Anatomy and Histology of the Canine and Feline Eye. Madison: University of Wisconsin