|An Update On Bovine Pinkeye
Infectious bovine keratoconjunctivitis (IBK), commonly known
as pinkeye, is an economically important and often frustrating
disease of cattle. The disease is quite common and highly
contagious. A 1993 survey of Kansas cattle producers found
IBK to be the second most common disease. A Missouri study
found 45.4% of cattle herds to be affected by the disease.
Cattle affected by the disease are painful and often become
temporarily blind and, therefore, do not consume as much feed.
This leads to economic losses due to decreased daily gain
and lower weaning weights. The cost of treatment adds to
economic losses. A 1984 study estimated that $200 million
were lost due to IBK. This is a significant disease to the
cattle industry and prevention and control should be of utmost
importance. However, current treatment and prevention measures
can be unrewarding and often do not circumvent the economic
IBK is a multifactorial disease. The primary etiologic
agent is the bacterium Moraxella bovis. However, there
are many factors that add to the virulence of this microorganism.
In addition, other bacteria have been isolated from eyes with
clinical IBK in the absence of M. bovis, indicating
that other bacteria may be a primary pathogen in some cases
M. bovis possesses virulence factors that allow
it to colonize the eye and result in pathology. Cell membrane
pili are responsible for colonization of the cornea. Two
functionally distinct pili have been identified. The Q pilus
is responsible for attachment and the I pilus allows for local
persistence and maintenance of an established infection.
It is thought that bacteria possessing the Q pilus can convert
to the I pilus during the course of disease. Non-piliated
strains do not cause clinical IBK. M. bovis also
possesses hemolysins. The hemolysins damage neutrophils
that are recruited to the area of infection. It is the destruction
of neutrophils and release of collagenolytic enzymes that
ultimately lead to corneal liquefaction and ulceration. Non-hemolytic
strains of M. bovis are non-pathogenic. Seven serologically
distinct groups of M. bovis have been identified based
on antigenic differences in membrane pili. Of these serogroups,
groups 3 and 4 (strains Epp63 and Fla64, respectively) are
most common in the United States.
IBK is most often seen in summer and early fall. This
is most likely because ultraviolet light and face flies are
the two most important contributing factors. Ultraviolet
light causes nuclear fragmentation and corneal epithelial
loosening, which enhances the ability of M. bovis
to colonize the cornea. Flies are the primary vector for
M. bovis. Musca autumnalis is the important
specie of fly in transmission. Direct transmission of M.
bovis between cattle is rare. Therefore, face flies
are likely the most important factor in outbreaks of IBK.
Wind, dust, tall grasses, hay, and high ammonia levels in
the air contribute to eye irritation and initiation of IBK.
A relationship between vaccination with a modified live IBR
vaccine and the development of IBK has been found, suggesting
the ability of IBR virus to enhance M. bovis infection.
Several other bacteria have been implicated as a predisposing
factor and primary cause of IBK. Mycoplasma bovoculi and
Branhamella ovis have been cultured from normal eyes
and eyes displaying clinical signs of IBK. M. bovoculi
is known to enhance IBK caused by M. bovis by
extending its colonization. M. bovoculi alone can
cause a mild catarrhal conjunctivitis. B. ovis, alone,
has been shown to cause a keratoconjunctivitis similar to
M. bovis. However, like M. bovis, factors contributing
to ocular irritation are required for clinical disease.
B. ovis has also
been cultured concurrently from eyes with M. bovis
infection. This suggests that B. ovis plays
a role as a primary pathogen and a contributing factor in
Diagnosis of IBK is by clinical signs which include blepharospasm,
epiphora, photophobia, chemosis, corneal edema, corneal ulceration
and blindness. Culture and sensitivity is recommended in
outbreaks to determine the bacteria involved and the best
treatment options. Conjunctival swabs and lacrimal secretions
are the best samples to submit for culture. M. bovis
is extremely susceptible to dessication; therefore, the sample
should be transferred to appropriate growth media prior to
shipment to a diagnostic laboratory. For best results, the
sample should be transferred to 5% blood agar within 2 hours
of collection. It may be necessary to request Mycoplasma
culture in refractory cases or in outbreaks where predisposing
factors are unclear. M. bovis cultures may be serotyped
for pili through immunofluorescence or immunogold electron
microscopy. A fluorescent antibody test is available to demonstrate
M. bovis in lacrimal secretions. An ELISA for identifying
serum or lacrimal IgG is useful in determining the M. bovis
serogroup responsible for the outbreak; however, these
special tests for serotyping are not widely available.
Treatment of IBK relies on the use of antibiotics and the
prevention of further ocular irritation. Oxytetracycline
is the only antibiotic labeled for the treatment of IBK.
Two doses of long-acting oxytetracycline given 72 hours apart
is usually effective in accelerating healing time. Parenteral
florfenicol can also shorten healing time. Daily subconjunctival
injections of penicillin have also been used in cases of IBK.
This treatment is economical but requires more handling and
labor. Two doses of benzathine cloxacillin at 375 mg given
topically 72 hours apart has been shown to be effective.
However, commercial mastitis preparations currently available
are not concentrated enough for use in IBK. Topical gentamicin
and betamethasone spray preparations have also been used topically.
Corticosteroids, such as dexamethasones, are often used to
reduce the inflammation and pain associated with IBK although
classically contraindicated in cases of corneal ulceration.
The use of 3rd eyelid flaps, tarsorrhaphy and eye
patches can aid in reducing irritation due to environmental
factors. Although treatment reduces healing time, research
has not proven the ability of treatment to improve weight
gain in affected animals.
Several commercial vaccines are available, including whole
cell monovalent and multivalent M. bovis bacterins.
Vaccination for M. bovis has met with mixed results.
It has been shown that lacrimal secretory IgA is required
for resistance to reinfection. The available bacterins produce
adequate serum IgG titers which have little correlation with
resistance to infection; therefore, currently available bacterins
may offer little protection. A mucosal vaccine would be much
more effective, but none are currently available. In addition,
there is little cross-protection among serotypes. Monovalent
vaccines do not protect against heterologous serotypes. Studies
using multivalent vaccines have reduced the incidence of IBK,
but not the severity of disease. Currently, multivalent bacterins,
including the Fla64 and Epp63 strains of M. bovis are
available. While providing cross-protection for other strains
within their serogroups, this bacterin cannot protect against
strains in the other five serogroups. These serogroups are
less commonly encountered in the United States, but can still
cause outbreaks. Recombinant multivalent vaccines will allow
for more serotype inclusion but are not currently available.
Autogenous vaccines may be considered where uncommon serotypes
are isolated from a herd.
Prevention of IBK centers on reducing the predisposing
factors of the disease. Since face flies are the major vector
of IBK, prevention should focus on fly control. The use of
insecticide ear tags, back rubs and feed-through insect growth
regulators can significantly reduce the incidence of IBK.
In the case of ear tags, both ears must be tagged to effectively
reduce the number of face flies. Affected cattle should be
isolated from other cattle if possible. New additions should
be isolated for 30-60 days prior to introduction to the herd.
Mowing tall grasses and noxious weeds from pasture and ensuring
adequate head space at the bale feeder can aid in reducing
ocular irritation. In case of an outbreak, mass treatment
with parenteral oxytetracycline may be beneficial. The use
of oxytetracycline in the feed may also be considered. Vaccination
with a modified live IBR vaccine should be avoided during
an outbreak. Vaccination with an M. bovis bacterin
should be considered in herds with recurring problems with
IBK. A multivalent pili vaccine is recommended. In addition,
culture, serotyping and sensitivity should be performed to
determine the bacterial pathogens and serotypes involved in
the outbreak. This information can aid in tailoring treatment
and vaccination programs.
-by Jill Franks, Class of 2003
-edited by Dr. Duane Murphy, ADDL Pathologist