Review on Infectious Bovine Keratoconjunctivitis and its Economic Impacts in Cattle- Juniper Publishers
Journal of Dairy & Veterinary Sciences- Juniper Publishers
Abstract
Infectious bovine keratoconjunctivitis is one of the
most common eye diseases of cattle and is of major eco-nomic importance
in the world. It is a bacterial infection of the eye that causes
inflammation and in severe cases temporary or permanent blindness. In
cattle, the gram-negative bacterium Moraxella bovis is regarded as the
main cause of the disease that affects cattle of all ages and occurs
worldwide. Also, Moraxella bovoculi and a range of other bacteria,
viruses, and environmental conditions seem to be involved. Moraxella
bovis has several pathogenic mechanisms; however, only two, pili and the
secretion of a β-hemolytic cytotoxin, have been determined to cause
clinical disease. The pili allow the bacteria to attach to the dark
cells of the corneal epithelium. The hemolysin is a pore-forming toxin
that lyses corneal epithelial cells leading to ulceration and causes
lysis of bovine leukocytes. The virulence of Moraxella bovis is
influenced by both host and environmental factors. It is one of the
examples of the diseases that may cause production losses in both dairy
and beef farms in many countries.
The economic impact of the disease is significant
due to its high contagious nature. Most cattle producers are familiar
with this disease but may not know how to best treat it and minimize its
spread within the herd. The cost and time used in treating infected
cattle adds to the economic losses. The best strategies to prevention
and control of an outbreak are maximizing the herd’s immune status,
minimizing the concentration of the Moraxella bacteria, and maintaining
as irritant-free environment as possible. Treatment decisions are
influenced by numerous factors such as effectiveness of the drug
selected, cost, labor availability, withholding times, facilities, and
availability of veterinary support. Vaccines are partially protective
and cannot be completely relied upon to prevent the disease. Coming up
with one solution is difficult because of all the contribution factors.
Therefore, isolation and a swift reaction are keys in reducing the
spread of the disease.
Keywords: Cytotoxin; Economic; Hemolysin; Infectious bovine keratoconjunctivitis
Abbrevations:
IBK: Infectious bovine keratoconjunctivitis; BVD: Bovine Virus
Diarrhea; IBR: Infectious Bovine Rhinotracheitis; BHV1: Bovine Herpes
Virus 1; RTX: Repeats in-Toxin; FAT: Fluorescent Antibody Testing; PCR:
Polymerase Chain Reaction
Introduction
Infectious bovine keratoconjunctivitis (IBK), or
commonly known as pinkeye is a highly contagious and infectious ocular
disease of cattle characterized by conjunctivitis and ulcerative
keratitis, which occurs worldwide [1]. The disease also occurs in other
livestock [2] and wildlife [3] and is generally regarded as a
multifactorial disease. The most common causative agent of IBK is Moraxella bovis (M. bovis)
[4]. The pathogenesis of the disease is influenced by many factors,
such as season, mechanical irritation, host immune response, eyelid
pigmentation, and concurrent presence of pathogenic bacteria, and strain
of M. bovis [5]. Also, Moraxella bovoculi and a range of other bacteria, viruses, and environmental conditions seem to be involved [6].
At the present time, it is not known if Moraxella bovoculi (M. bovoculi) plays a primary or secondary role in the pathogene
sis of IBK [7]. For a long period of time it had been thought the bacterium M. bovis was the primary cause of IBK. However, M. bovoculi can be isolated with or without M. bovis
from eyes of cattle with IBK. Morever, several other infectious agents
such as Adenovirus, Mycoplasma, Branhamella (Neisseria), and Listeria
have been recovered from the eyes of cattle showing clinical signs like
those seen in Moraxella-induced IBK [8].
There are a lot of contributing factors involved
with the disease IBK. These include environmental factors like bright UV
sunlight, conditions in the paddock like long stalky grass, dust and
overhead hay feeders. Nutritional deficiencies also play a role with
vitamin A, and the minerals copper and selenium. A high concentration of
face flies, breeds of cattle lacking eye pigment and young cattle as
well as compromised immunity from other viruses such as Bovine Virus
Diarrhea (BVD) [9].
Therefore, the objectives of this paper are
a. To give an overview on infectious bovine keratoconjunctivis
cause, occurrence, predisposing factors, method of spread
and treatment and as well as its control and prevention.
b. To highlight the economic impacts of the disease (IBK) in
cattle producers.
Overview on Infectious Bovine keratoconjunctivitis
Infectious bovine keratoconjunctivitis is a bacterial eye disease
of cattle. The disease is perceived to be of economic importance
due to poor thrift in affected animals. The financial loss is due
to decreased weight gain, increased treatment costs, and market
discounts due to eye disfigurement and blindness. Certain strains
of M. bovis can produce pit‐like depressions in conjunctival
and corneal epithelial cells causing impaired vision in affected
animals. This disease is the most common condition affecting beef
and dairy heifers, and the second most common disease of nursing
calves greater than three weeks old [10].
Etiology
The gram-negative rod bacterium M. bovis is the most primary
organism incriminated to cause IBK in cattle and the most frequently
isolated. The bacterium adheres to the cells via its fimbriae
and pili proteins and produces β–hemolysin toxins which lyse
the corneal epithelial cells [11]. Apart from the etiologic agent M.
bovis, many factors including exposure to UV light, accumulation
of dust and trauma at ocular region etc., predisposes the infection.
The ability of M. bovis to cause the disease is influenced by host
(the cattle) and environmental factors [10].
There are also several pathogens associated with IBK in cattle,
such as Bovine Herpes Virus 1 (BHV 1) which is the causative
agent of Infectious Bovine Rhinotracheitis (IBR). However, M. bovis
has thus far been the only organism demonstrated to cause IBK in
cattle [12]. There are other organisms which can result in severe
conjunctivitis and edema of the cornea but they are not known to
cause central corneal ulceration [13].
Moraxella bovoculi is a recently described bacterial species
that associates with outbreaks of IBK [14]. This new species of
Moraxella can be distinguished from two other Moraxella species,
M. bovis and M. bovis, since phenylalanine deaminizes activity, as
well as divergence at 6 housekeeping genes, and genetic variation
within a large ribosomal RNA (rRNA) encoding locus [15]. Moraxella
bovoculi has not been reported to cause IBK. However, M.
bovoculi isolates do contain known pathogenesis factors including
a Repeats in-Toxin (RTX) class operon which encodes a cytotoxin
that lyses and kills neutrophils and corneal epithelial cells [16],
and a pili (fimbriae) gene which is required for adherence to the
corneal epithelium by M. bovis [17]. The extent of host range, niche
specialization, and genetic diversity of M. bovoculi is unknown. In
addition to IBK cases, M. bovoculi has been detected in ocular secretions
from horse and reindeer conjunctivitis cases [18], IBK
asymptomatic cattle [19], as well as human respiratory tracts [20] and dog teeth [21]. Other causes like M. bovis, M. catarrhalis, Neisseria
ovis, and Aspergillus flavus were also isolated from IBK in cattle
and other ruminants [22].
Epidemiology
Infectious bovine keratoconjunctivitis is seen worldwide but
mainly in areas with high temperature climates and thus is widespread
in Asia, Africa and all-American continents. It is also seen
in parts of Europe and UK. In seasonal countries, this disease is
most prevalent in the summer months and it usually seen in young
animals. During the warmer months, fly numbers are higher and
intense sunlight and dust predispose the eye to infection [23].
Occurrence
Infectious bovine keratoconjunctivitis is a highly contagious
and infectious bacterial eye disease in cattle which occurs worldwide
[4]. It is mainly a disease of young cattle commonly occurring
in their first summer. Calves are more susceptible to infection than
adults but immunologically naïve cattle can be severely affected
when the herd has not been previously exposed [24,25]. Severe
outbreaks may occur in older cattle if they have never been exposed
to the disease. After infection, cattle develop a temporary
immunity which lasts up to a year. Exposure to the causative
agents in following years gives further immunity, usually without
eye changes being obvious [26]. Natural outbreaks usually peak in
the third or fourth week, when as much as 80% of a herd may be
infected [27]. Variations, among cattle in breeds, the susceptibility
to IBK have been demonstrated Hereford cattle were found to be
more susceptible compared with all other purebreds such as Angus
and Bos Indicus breeds [5].
Infection can occasionally persist in a few animals and these
are a source of infection in the following summer. The infection
rate increases to a peak about 3-4 weeks after the first cases appear,
and then gradually decreases. The prevalence of IBK in districts
and on individual farms varies from year to year, depending
on seasons and weather, the fly population and whether cattle are
grazing long grass. On some farms there may be only occasional
cases while on others 60-80% of cattle may be affected in very
severe outbreaks [26].
Predisposing (Risk) factors
The bacteria M. bovis reportedly causes IBK. However, numerous
physical factors have been shown to influence the appearance
of the ocular disease such as breed and age of the animal, UV light
exposure, wind and pollen conditions, and pasture conditions. The
presence of other infectious organisms in the tissues surrounding
the eye, as well as concurrent upper respiratory infections, can
cause the disease problem to be much more severe [28].
Like many diseases, IBK can be considered a complex of organisms
and predisposing factors, which result in ocular changes
that favor bacterial colonization of the eye. Predisposing factors
are a largely variable component in initiation of disease and may
be a more important component of the IBK ocular disease complex when dealing with less virulent strains of Moraxella. Other
gram-negative bacterial cocci related to M. bovis, Moraxella ovis
(formerly Branhamella ovis), and M. bovoculi have been isolated
from clinical cases of IBK. A newly isolated strain of bacteria
known as M. bovoculi may play an important role in IBK but research
has not confirmed this. Other problems such as physical
trauma or trauma due to squamous cell carcinoma may also predispose
the eye to secondary bacterial infection [29].
And, Mycoplasma, Chlamydia spp., bovine herpes virus-1 and
bovine adenovirus, are among the microbial agents suspected to
predispose cattle to Moraxella colonization [30] or to add to the
severity of IBK [31]. Mycoplasma bovis can cause eye infections resembling
those seen with Moraxella bovis as well [32].
Method of Spread (Transmission)
Infectious bovine keratoconjunctivitis is transmitted by direct
contact, aerosols and fomites. Flies may serve as mechanical
vectors of the bacteria M. bovis [5]. The face fly Musca autumnalis
is the important species in transmission of M. bovis. Moreover,
the ocular and nasal discharges of infected animals can carry the
pathogens, hence direct transmission from animal-to-animal contact,
contaminated equipment and animal handlers can also transmit
the disease [33]. Transmission occurs when a non- infected
animal meets secretions infected with M. bovis. Secretions from
the eye, nose, or vagina can be infected. Carrier animals can shed
the organism for long periods of time so they are an important
factor in the spread of the disease and its survival over winter.
When the eyes of a carrier animal are irritated, its tear production
increases and promoting the shedding of M. bovis [34]. And, eye
irritation from dust, bright sunlight, thistles and long grass can
cause lacrimation which attracts flies. The flies feed on the infected
secretions and move from animal to animal, this spreading the
bacteria within the herd of cattle [9].
Pathogenic Mechanisms of M. bovis
The pathogenic strains of M. bovis are piliated strains that initially
bind through their pili to receptors on the surfaces of corneal
epithelial cells [35]. The bacterium adheres to the cells via its fimbriae
and pili proteins and produces β-haemolysin toxins which
lyse the corneal epithelial cells [11]. Moraxella bovis also secretes
cytotoxic toxin and pathogenic fibrinolysis, phosphatase, hyaluronidase
and aminopeptidases. The bacterial membrane proteins
and lipopolysaccharide are also pathogenic [36]. Moraxella bovis
invades the lacrimal and tarsal glands of the eye, causing keratitis,
opacity, uveitis, aqueous flare and corneal ulcers. Non-pathogenic
strains of M. bovis exist, strains that do not produce pili or cytotoxins
are much less capable of producing clinical disease [30]. And,
the hemolytic and cytolytic activity from culture filtrates of M. bovis
isolated from cattle with IBK has been reported recently and
this suggests a possible role for gram-negative cocci in the pathogenesis
of IBK [37].
Clinical Signs
Infectious bovine keratoconjunctivitis is ocular disease of cattle,
which is clinically characterized by corneal ulceration, edema,
blepharospasm, photophobia, ocular pain, lacrimation, corneal
perforation and permanent blindness in severe cases [38,39].
Blepharospasm and photophobia suggest IBK is painful and pain
mitigation therapies may be useful adjuncts to antibiotic therapy
by improving animal welfare and reducing weight loss [40]. Since
blepharospasm, photophobia and ocular discharge are the earliest
indications of IBK, suggesting that detection occurs only once the
condition is quite advanced [25]. There are four stages of IBK. The
disease may resolve at any of these stages while, without treatment,
the most severe cases will progress through all four stages
[34].
a. Stage I: This stage is indicated when cattle’s have excessive
tearing and increased sensitivity to light. They will blink frequently
and there is redness along the eyelids. Cattle will often
seek shade, which will decrease their grazing time. Pain
associated with IBK also decreases their feed intake. Stage I
will progress to a small ulcer in the center of the cornea which
appears as a small white spot (Figure 1). The cornea develops
a slightly cloudy grey appearance due to inflammation [34].
b. Stage II: The clinical signs described in Stage I continue, but
this stage is indicated when the ulcer spreads across the cornea.
As more inflammation occurs, the cornea becomes increasingly
cloudy. At this point, some of the dark color of the
iris can still be seen. Blood vessels from the outside portion of
the cornea begin to grow across the cornea to help with healing
(Figure 2). These blood vessels make the cornea appear
pink, which is how the disease received its name [34].
c. Stage III: This is indicated when the ulcer covers most of the
cornea and the inflammation continues to spread into the inner
parts of the eye. When this occurs, the inside of the eye
fills with fibrin, which is a plus-like substance that gives the
eye a yellow appearance versus the typical brown appearance
(Figure 3) [34]. The hemolytic M. bovis strains produce a pore
forming cytotoxin [41] that promotes the development of corneal
ulcers by lysis (death) of corneal epithelial cells [42].
d. Stage IV: Some animals recover spontaneously in three to five
weeks, the ulcer heals and reduces, leaving a scar. In some
cases, the process becomes chronic, and the opacity takes 1–2
months to resolve. In other cases, depending on the severity
of the disease, a white scar may be present even after full resolution
of the disease. Occasionally, perforation of the corneal
ulcer results in iris prolapse, in which case, blindness may
result. This stage becomes obvious when the ulcer extends
completely through the cornea, and the iris may protrude
through the ulcer (Figure 4). The iris will become stuck in the
cornea even after healing [34].
Diagnosis
The clinical examination of IBK revealed mild to severe swelling
surrounding affected eyes, and profuse lacrimation. Lesions
typically affected either one or both of eyes, and involved the eyelid
skin, conjunctiva and corneal opacity [33]. And season and history
of infection and presence of flies will raise suspicion of IBK
before an animal is examined. Pathology remains confined to the
eye and does not reach the bloodstream [23]. On clinical examination,
early disease is detectable as a raised area of cloudiness in
the cornea indicating keratitis [43].
Ocular secretion specimens were collected by inserting a separate
sterile swab into the inferior conjunctival fornix, and then
directly inoculating the secretions on blood agar plates. And inoculated
plates were subsequently streaked for isolation and
incubated aerobically for 24 hrs. at 37°C and then examined for
bacterial colonies morphologically characteristic of M. bovis. The
colonies typical of M. bovis were subculture and identified, by using
described morphologic and biochemical criteria [44].
The causative organism is identified based on cultural, morphological
and biochemical characteristics [45]. Characteristic hemolytic
colonies are observed on blood agar where it forms small,
round, shiny, friable colonies but no colonies were developed on
MacConkey agar plate. The pattern of hemolysis was very peculiar
1–2 mm diameter with corrosion of the agar at the edges of colony.
Further, some of the colonies were found to be surface spreading.
The organism is gram negative diplococci resembling tumbles,
non-motile, catalase and oxidase positive. Gelatin agar is liquefied
by the organism within in 24hrs of stab culture and able to auto
agglutinate normal saline in sugar tubes [23].
Bacteriological examination revealed the production of virulent
factors such as hemolysin and proteolytic enzyme production
which could have caused opacity or cloudiness of the affected eye
[46]. However, fimbriae also help in colonization of the organism
in cornea along with capsule, the main virulence factor of M. bovis
and the spreading nature of the hemolysis may be due to the
presence of fimbriae which is also responsible for the auto agglutination
of normal saline [47]. Further the laboratory results are
correlated with clinical evidence such as blepharospasm, epiphora,
photophobia, chemosis, corneal edema, corneal ulceration and
blindness.
Fluorescent antibody testing (FAT) is available for identification
and the bacterium may be visible on smears of lacrimal secretions.
Polymerase chain reaction (PCR) has become an important
tool for research and clinical diagnosis of infectious diseases. Multiplex
real-time PCR assay was developed for the detection and
differentiation of M. bovis, M. bovoculi and M. bovis [48,49].
Differential Diagnosis
Differential diagnosis includes traumatic conjunctivitis is usually
easily differentiated because of the presence of foreign matter
(e.g. grass awns) within conjunctival sac of the eye or evidence of a
physical injury [50]. Unlike IBK, cases of bovine iritis rarely develop
corneal ulceration or prulent ocular discharge, as the pathology
is limited to the uveal structures. And, IBR causes conjunctivitis
within rare blepharospasm and there is normally no corneal involvement
[51]. Mycoplasma bovis has been isolated from the eyes
of steers with an outbreak of severe conjunctivitis with corneal
opacity, ulceration, and involvement of the eyelids with marked
swelling was prominent. Conjunctivitis is prominent in other
mycoplasmal infections that produce keratoconjunctivitis [52].
Moreover, chlamydial keratoconjunctivitis presents with identical clinical findings but has a protracted course despite treatment and
a higher morbidity [53].
Treatment
Effective treatment of IBK can be done by use of a specific
antimicrobial therapy along with proper manage approach. Early
treatment of cattle with IBK is important, first for a successful
outcome for the affected individual animal and then to stop the
shedding of the bacteria, decreasing the risk of transmission to
other cattle [54]. Appropriate antimicrobial selection requires
knowledge of antimicrobial sensitivities and distribution in ocular
tissues and tears. While therapeutic efficacy is affected by the
frequency and mode of drug delivery, variations between intensive
and extensive enterprises dictate the practical method of antimicrobial
delivery. Specific recommendations for antimicrobial
therapies targeting Australian IBK outbreaks are dependent upon
antimicrobial pharmacokinetics, drug regulations and associated
costs [55]. Generally, effective treatment of IBK is very important,
as in untreated cases the corneal opacity may lead to corneal ulceration
and blindness in turn it finally leads to production loss
of animals. Drugs may be delivered to the eye in several ways:
subconjunctival injection, topical application and systemic administration
and in severe cases surgical treatment options are indicated.
Subconjunctival injection: Subconjunctival administration
of antimicrobials [56] aims to reduce treatment costs and total
dosages of drug while achieving higher ocular drug concentrations
[57]. This probably led to some direct diffusion across the sclera
and choroid; alternatively, the drug may gradually leak from the
injection site, entering the tear film and eventually the eye via the
cornea as if it were applied topically [58]. It also provides pharmacological
advantages over deep muscle administration. Most
importantly, lower dosages may be used which yield higher ocular
concentrations. Difficulty of subconjunctival administration is a
drawback which must be considered. Penicillin and aminoglycosides
are the most commonly used subconjunctival preparations
[59]. Although these drugs result in high ocular concentration,
healing rates are not markedly different from deep muscle parenteral
oxytetracycline [57].
Topical application: Topical administration of antimicrobial
formulations has been recommended as a potentially cost-effective
and less labor-intensive method for treatment of IBK [57].
Showing much promise for topical administration is oil- based
formulations of benzathine cloxacillin which reduces the shedding
of M. bovis and hasten the resolution of corneal ulcers [60].
Topical instillation of silver nitrate (1%) and zinc sulphate (0.4%)
eye drops along with oxytetracycline parenterally, twice daily for
7–15 days to all the infected animals, which also exhibited corneal
opacity were found to be more effective and led to cure within
fortnight. Zinc sulphate is antiseptic, immunostimulant and astringent.
It is reported that in catarrhal conditions of conjunctiva,
application of zinc sulphate lotion had a proven recovery in later
stage of acute infection [61]. It is also reported that zinc sulphate
act as integral part of several enzymes important for wound healing
and ophthalmic solution is used as mild astringent for relief of
eye irritation [62].
Systemic administration: Systemic antimicrobial therapy
has been recommended as to target M. bovis located within lacrimal
glands and nasal passages. Drugs administered systemically
may enter the eye via the tear film or through the perilimbal or
intraocular circulation. Generally, lipophilic drugs achieve higher
intracorneal and intraocular concentrations and are more effective
at penetrating the blood-tear barrier than hydrophilic drugs.
Elimination of M. bovis in calves with IBK has been demonstrated
following parenteral treatment with oxytetracycline [63] or florfenicol
[64].
Surgical treatment options: Surgical treatment options that
have been used in treating cattle with IBK include third eyelid
flaps and tarsorrhaphy. In cases where globe rupture has occurred
or where severe scar formation and globe protrusion represents
a potential liability to the animal, exenteration may be indicated.
Controls and Prevention
Management practices that reduce the risk factors associated
with IBK are the most effective tools in decreasing the incidence
of the disease. Topping pastures can be a good way to reduce
seed heads, and thistles which can irritate the eye. Good quality
nutrition and minerals available always, will improve the overall
condition of the cattle and decrease the incidence of this disease.
The pre-corneal tear film is essential in eye defense mechanisms
as tears wash away pathogens and tear proteins are an important
part of protecting the eye. With a lower incidence rate of the disease,
the overall concentration of the bacteria on the farm will be
lowered, reducing the risk of a large outbreak. Shaded areas need
to be provided to so cattle can get out of bright UV light when it is
most intense.
Prevention of IBK is difficult because of the different types of
M. bovis, its ability to change from one type to another, and the predisposing
environmental conditions. Fly control is one of the most
important factors. Insecticide impregnated ear tags in both ears
has been shown to decrease the spread of disease. Alternatively, or
additionally, insecticide sprays, pour-on, dusters, and back oilers
can be used.
Vaccination can be done using bacterin such as pilli
from the
organism M. bovis. Cellular vaccine comprises of vaccines developed
to prevent IBK include live, killed, whole cell or subunit vaccines
[65]. Efforts to develop an efficacious vaccine have primarily
focused upon the use of surface pili or cytolysin to stimulate host
immunity; however, M. bovis possesses other virulence determinants
that include proteases, fibrinolysins, phospholipases and
other cell surface components such as outer membrane proteins.
These potentially conserved antigens provide additional possibilities
for vaccine development. Examination of appropriate antigen
presentation is necessary to attain an adequate immune response.
Further, the potential for antigenic diversity as well as epitope
conversion requires continuous epidemiological surveillance of isolates
recovered from outbreaks. Current work targeting conserved
immunogens provides hope for efficacious vaccines that
when used in tandem with proper management may control, if not
prevent, IBK.
Most of these vaccines require a booster dose to be effective
during the first year of use, then require a yearly booster thereafter.
It is important to note that there are several different strains of
M. bovis, many of which are not covered by vaccines. The disease
symptoms can also be linked to another bacterium known as M.
bovoculi, which is related to M. bovis. Incidentally, M. bovoculi is
not included in any commercial IBK vaccine. Moraxella bovoculi
appears to be associated with more severe IBK symptoms as well
as cases that occur sporadically or outside the normal IBK season.
In general, vaccination will help limit the number of outbreaks in
a herd but may not eliminate the occurrence of disease. However,
vaccination combined with careful management for the predisposing
factors provides the best chance for preventing disease [66].
The Economic Impacts of the Disease in Cattle
Infectious bovine keratoconjunctivitis cause a significant economic
loss throughout the world, due to a very painful condition
affecting beef and dairy cattle worldwide. In Ethiopia, the disease
causes economic losses arising from decreased weight gain
in beef breeds, loss of milk production, short-term disruption of
breeding programs, and treatment costs [67]. The bacterium, M.
bovis is known to be responsible for this condition. It has been estimated
that annual losses associated with only decreased weight
gain from infected cattle exceeds 150 million dollars [68]. Major
economic losses are the result of in appetence and poor weight
gain in affected animals suffering from ocular pain and visual impairment.
Although IBK is rarely fatal, the associated impaired vision results
in adverse economic impact of decreased weight gain, low
calf growth rate, increased treatment costs, and market discounts
due to eye disfigurement and blindness. It has been estimated that
IBK costs cattle producers 150 million US$ in the United States
and 22million AUD$ in Australia per annum as a result of in appetence
and poor weight gain in affected animals suffering from ocular
pain and visual impairment [69]. The largest economic loss is
incurred through decreased growth as affected calves are on average
35-40 pounds lighter at weaning compared to healthy calves.
Lower performance in post-weaning cattle also has also been documented
with reduced average daily gain, 365th day weight, and
final weight. Additionally, the drug cost for treatment, decreased
market value due to corneal scarring, the loss of value of show and
breeding stock, and reduced milk production from dairy animals
also make this disease a significant economic consideration [29].
Conclusion and Recommendations
Infectious bovine keratoconjunctivitis (IBK) is infectious and
a highly contagious eye disease of cattle, causes a great economic
impact in both beef and dairy cattle farms worldwide. In cattle, the
gram-negative bacterium Moraxella bovis is regarded as the main
cause of the disease. This bacterium has several pathogenic mechanisms;
however, only two, pili and the secretion of a β-hemolytic
cytotoxin, have been determined to cause clinical disease. Environmental
factors include UV light exposure, face fly populations,
climate and pasture conditions and host factors include genetics,
breed, age, nutrition, immune status and current infections influence
the virulence of M. bovis. Carrier animals are asymptomatic
but they shed the organism. M. bovis may be harbored in the nasal,
ocular, and vaginal secretions; and it may be transmitted by direct
contact, aerosol, or fomites. Cattles are the primary natural reservoir
for M. bovis and there is a high nasal carrier state. The face
fly, Musca autumnal is, is a primary mechanical vector for IBK and
serves as an irritant. Though IBK is rarely fatal, it causes considerable
economic losses to the cattle and dairy industries because
of decreased weight gain, decreased milk production, devaluation
because of eye disfigurement, and because of the high cost
of treatment.
Based on the above conclusions, the following recommendations
are forwarded:
a. Any cattle herd producer who has experienced IBK outbreak
aware of the discomfort and loss of performance that can occur.
b. Early detection, segregation and treatment of infected stock.
c. Reduce the incidence of flies and subsequent spreading of
bacteria with the application of pesticide self-application devices
or ear tags and pour-on treatments.
d. Development of a breeding program that selects for pigmented
eyelids and hair surrounding the eye.
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