A.DESSOSAA MANOJ, Student of Veterinary College and Research Institute, Tirunelveli, Tamilnadu University of Veterinary and Animal Sciences, Tamilnadu
Guide: Dr.S. Dharmaceelan MVSc, PhD. Department of Veterinary Surgery and Radiology, Veterinary College and Research Institute, Tirunelveli, Tamilnadu University of Veterinary and Animal Sciences, Tamilnadu
Introduction:
India has the largest population of cattle accounting about 32% of world cattle population. Traditionally cows are raised as members of the family because of their economic importance. They play an important role in day to day life in rural areas. Hence cattle rearing is the backbone of many poor people. Vision is an important criteria for the survival of the animal. They aid in feeding, locomotion, nursing the young ones etc. Though cattle is nursed daily, eye problems are not properly treated due to lack of awareness. Physical examination of the eye during treatment is neglected until a major problem occurs. Proper eye care is not provided to the animal. Here we are going to discuss broadly about the eye diseases commonly occurring in cattle, treatment measures, prevention and control.
The fundamentals:
Vision is a complex phenomenon in which light from the object is captured by the eye, focused in the retina through lens. These electrical signals originated from the various receptors in retina reaches the central nervous system and process the image in visual cortex.
Congenital causes:
These eye defects occurs during the time of embryogenesis which are observed at the time of birth. It is usually due to exposed calves to some unknown teratogens at the critical time of active organogenesis and notochord formation. These affects the formation of eye and its associated structures causing impairment.
Some of the agents causing congenital anomalies in calves are Bovine viral diarrhea virus causing multiple ophthalmic defects such as cataract, persistent pupillary membrane, retinal degeneration, optic neuritis etc. Blue tongue virus causeshydrocephaly leading to corneal edema and blindness
Dermoid:
Dermoid is a benign tumours consisting of histological normal cells occurring in an abnormal location (eye). It consists of keratinized epithelium and adnexal structures such as hair follicle, sweat glands, sebaceous gland etc. These are common in calves which occurs during embryogenesis during closure of fetal sutures lines.
It is characterized by presence of hair tissue in the eye leading to impairment. Surgical excision of the tissue may be advised as the treatment of Dermoid. Prognosis is good during early surgical intervention
Keratoconjunctivitis:
Infectious bovine Keratoconjunctivitis commonly known as ‘pink eye, silage eye’ characterizedby inflammation of cornea and conjunctiva. It is very contagious and severe in young animals commonly occur during summer months. It is caused by various agents such as
Viral cause: Infectious Bovine Rhinotracheitis
Bacterial cause: Morexella bovis, Listeria monocytogenes
Fungal cause: Aspergillus, Fusarium
Parasitic cause: Thelazia sp,
Infectious bovine Rhinotracheitis:
It is caused by herpes virus which cause non ulcerative Keratoconjunctivitis. It is characterized by raised white plaques on conjunctival areas. It cause peripheral edema leading to chemosis resulting in blindness. Spontaneous recovery may occur in mild cases 3-5 days after clinical signs are first observed and complete in two weeks later. In severe cases ulceration may progress to corneal perforation.
Bacterial cause:
Moraxella bovis is the organism primarily responsible for the severe form of Keratoconjunctivitis. It is transmitted by direct contact with infected animals, fomites, mechanical vectors such as flies, insects. The vectors play an important role which occurs during onset of spring season. The indigenous breed is found to be more resistant than the exotic breeds
This bacteria causes haemolytic and cytotoxic reaction in the corneal epithelium which is found to be pathogenic. The clinical signs such as epiphora, Blepharospam, Photophobia, chemosis, corneal ulcer, hypopyon, panophthamitis are observed. The ulceration lead to iris prolapse leading to visual blindness
Another important cause is Listeria monocytogenes causing Keratoconjunctivitis during winter season. It is also known as silage eye. This disease occurs due to feeding of silage and haylage as the organism is found in silage. It is characterized by bluish white opacity of the eye with pus and whitish discoloration
Parasitic cause:
Thelazia spp:
Thelazia spp are small slender white nematode worms which are found inside the eye cavity. These worms primarily affects peritoneum but when occurring in different host it occurs in ocular region. Flies such as Musca spp act as a biological vectors and play an important role in transmitting a disease.The worms initially occur in the conjunctival sac and nasolacrimal duct, later they swim into the eye cavity.
Lifecycle: The fly ingests the larvae and becomes infective in 2-4 weeks. The worms are deposited mechanically in the host eye during feeding. The worms develop and mature in 1-2 weeks. The worm has a rough cuticle which enters the eye causing irritation and inflammation
The clinical signs include excess production of tears, cloudiness of the cornea, lack of response to the antibiotics. The close physical examination of the eye reveals small worms inside the eye cavity and conjunctival fluid.
Ectoparasites:
Sarcoptic mange caused by Sarcoptes scabeiicharacterized by intense pruritus, papules and general erythema around the face and eyelids. These lesions are wide spread causing inflammatory response in the eye
Demodex bovis is a host specific burial mite which invades the eye causing irritation and inflammation. It causes pruritus and pustule formation leading to secondary bacterial infection
Ocular myasis:
It is the parasitic infection of fly larvae (maggots) in the ocular region. The fly deposits its egg in the margin of the eye canthus. Later it develops into larvae and invades the ocular tissue. It buries deeply into the ocular tissue causing serious injury and complete blindness
Keratomycosis:
Fungal infection is quite uncommon in cattle though Aspergillus and Fusarium species are found to infect eye. They produce periorbital swelling, full thickness corneal infiltrate, hypopyon, diffuse corneal edema. Mycotic culture, histopathology and tape impression smear aid in diagnosis
Treatment:
For Infectious Bovine Rhinotracheitis, vaccine is available as modified live virus vaccine and inactivated/ killed virus vaccine. The calves are vaccinated at 4-6 months of age
In case of bacterial infection Oxytetracycline is drug of choice for systemic treatment as it is concentrated in corneal tissue. Two injection of long acting oxytetracycline at 72 hrs interval is found to be effective. Antibiotics such as ampicillin, gentamicin, and penicillin is also used to reduce severity. Corticosteroid such as dexamethasone is given in intraconjunctival route to reduce inflammation
For parasitic infection, systemic dewormers such as levamisoleat 5mg/kg and Ivermectin, Doramectin at dose of 0.2 mg/kg given as subcutaneous are found to be effective. Ocular paracentesis at the limbal region of the eye is used to remove the mature worms found inside the eye. Complete temporary tarsorapphyand nictitating membrane flaps are used in deep and perforated corneal ulcer.
Photosensitization:
It is the abnormal reaction to the body through sunlight due to photodynamic substances released from the plants ingested by the animal. When the photodynamic substances are not excreted by the body it gets accumulated in the body surface and extremities. It also gets accumulated in the ocular region which reacts with the sunlight and cause corneal edema and other tumour condition. Plants causing photosensitization are Lantana camera, Hypericum esculantum etc
Phenothiazine is used as prophylactic and anti-helminthic to control worms. It is also found to cause photosensitization. Phenothiazine absorbed in rumen as phenothiazine sulfoxide which is detoxified in liver and excreted in urine and bile. When animal fail to detoxify, phenothiazine sulfoxide enters the blood stream reaches the eye and causes keratitis and conjunctivitis
Treatment includes complete withdrawal of the source followed by administration of anti-histamines such as chlorpheneramine at 2mg/kg intramuscularly. Avoid grazing in sunlight and complete rest is necessary
Neoplasia:
Ocular squamous cell carcinoma and ocular papilloma are the two most common tumour condition occurring in cattle. Among these squamous cell carcinoma is the severe form of tumour in cattle leading to death of animal. It leads to economic loss and shorten the productive life of cattle
Ocular squamous cell carcinoma:
Several factors play a major role in causing this tumour including exposure to sunlight, eyelid pigmentation, genetic predisposition, nutrition etc. Exposure to UV radiation in the sunlight and high plane of nutrition are important factors for causing this tumour
It is characterized by cauliflower growth which is growing from the eyeball surfaces. It initially starts as non-cancerous, smooth projections, later it grows and invades the globe and orbit making it severe. Sometimes oozing of blood is seen leading to complete blindness. It also causes systemic metastasis through parotid lymph node to the regional lymph node. It gains access to thoracic duct and enterinto venous circulation. Metastasis can affect lungs, heart, pleura, liver,kidney.
Diagnosis is done through fine needle aspiration biopsy of the tumour mass which reveals polygonal pleomorphic cells occurring in clusters. The malignancy is determined by the cell morphology however histopathology of tumour biopsy is used for confirmatory diagnosis.
Treatment:
Before therapeutic intervention the extent of lesion should be evaluated. The treatment method involves
Surgical removal:
The surgical procedure followed are enucleation and exenteration. Enucleation involves removal of globe and nictitating membrane of the eye. Exenteration involves removal of globe, nictitating membrane, orbital contents along with lid margins. These are determined based on the invasion of tumour growth
Cryotherapy:
It is a popular treatment followed for the regression of tumour growth. Liquid nitrogen and nitrous oxide is commonly used. The cryoagents are sprayed over the tumorous growth for regression. The extent of freezing is important factor during surgery. Polystyrene is used to protect the surrounding tissues.
Hyperthermia/ electro thermaltherapy
It involves selective destruction of the neoplastic cells with hyperthermia. This technique involves passage of radio frequencies electric current 2 MHz between two electrodes which is placed directly on the tumour. The resistance of the tissue to the flow of current causes heat generation in the tissue which cause regression of the tumour. The treatment is not recommended when the tumour is 3mm deep or 4cm large in diameter. Surgical debulking is used to reduce the size of the tumour
Immunotherapy
Serum obtained from the animal infected plague, papilloma, keratitisreacts to the tumour cells and cause regression to certain extent. The immune cells accumulate in precancerous and neoplastic tissues and cause spontaneous regression eg: IgG and peritumoural Interleukin-2. Nonspecificimmunotherapy involves usage of BCG vaccine
Radiation
Ionizing radiation has been extensively used in the treatment of squamous cell carcinoma but is very expensive and requires some legal procedures. In this therapy beta, gamma and roentgen rays are used. These radiation are passed through the tumour that causes regression. The desired tumour dose is 5000 rads. Beta radiation such as strontium 90 is used in superficial keratectomy. This technique is also known as interstitial brachytherapy.
Cataract.
Cataract is the opacity of the lens. It occurs either congenital or acquired .Congenitally it occurs due to the inherited autosomal recessive gene which occurs mostly in exotic animals. The cataract is usually nuclear type and mature at 4-11 months. Secondary cataract occurs due to inflammatory response to severe infection leading to pigment deposition to lens. Several infections such as vasculitis, suppurative keratitis, chronic retinitis causes cataract. Mimosine a toxic component present in Mimosa pudica is responsible for the formation of insoluble protein aggregates leading to cataract
Condition related to eye infection:
Epiphora– excess production of tear
Hypopyon– pus accumulation in the eye ball
Plaque– small area of hyperplastic epithelium occurring in conjunctiva
Hyphema– blood accumulation in eye ball
Chemosis– edema of third eyelid
Keratitis– inflammation of cornea
Blepharitis- inflammation of eyelids
Conjunctivitis– inflammation of conjunctiva
Economic importance:
Impairment of eye causes reduction in the vision and the animal faces difficulty in grazing, feeding, locomotion etc. It leads to financial losses such as decreased feeding, decreased milk production, decreased weight, reduced growth, poor productivity, carcass condemnation at slaughter, high treatment cost, loss of value of breeding stock etc
First aid in eye infection:
- Slowly remove the particles or substances present in the eye
- Clean the eye with warm water and wipe with clean towel.
- Apply topical antiseptic ointment and eye drops if any infection is present
- Close the eye region with clean towel to avoid contamination
- With the help of veterinarian inject corticosteroidsintraconjunctival to reduce inflammation
- Temporary tarsorrhaphy is advised to prevent contamination of the eye
Prevention and control:
- Apply tick grease or fly repellants around the eyes
- Manually remove the ticks
- Vaccinate the animal
- Do not herd the animal in the thorny areas
- Use shrubs and leafs for fencing the shed and pen
- Segregate the infected animals from the herd
- Avoid over crowding
- Allow free access to shade with planting of trees
- Keep the sheds and yards clean and hygiene
- Use insecticides and pour on to remove ectoparasites
- Practice selective breeding to prevent congenital diseases and tumours
- Avoid silage feeding during winter season
Conclusion:
As said vision is an important and complex phenomenon which is essential for the survival of the animal but most of the farmers remain unaware of it until it turns out to be a serious issue. The main motto of cattle rearing is the production of milk hence for achieving it, proper care of animal is necessary. Eye care of the animal remains neglected even though a problem is detected because of lack of awareness and a thought that the treatment is expensive. Hence for better production and welfare of the animal eye care should also take as an important criteria in the treatment of animal.
