THE CANADIAN VETERINARY
LA REVUE VETERINAIRE
Contagious Equine Metritis:
A N D
S U M M A R Y
Contagious equine metritis is a highly contagious
genital infection of mares, spread venereally, and
contagious equine metritis outbreaks involved
Thoroughbreds, infection in other breeds has also
occurred. The disease has been reported in Europe,
Australia and the United
contagious equine metritis has been designated a
reportable disease under the Animal Disease and
Contagious equine metritis is characterized by
an endometritis and infertility and infected mares
show no signs of systemic infection. Clinical signs
have not been observed in stallions. An asympto-
matic carrier state exists
Infected mares respond clinically to the topical
parenteral administration of antibacterial
drugs. However, a proportion of mares remain
carriers of the contagious equine metritis or-
Haemophilus equigenitalis has been proposed as
the species name ofthe Gram-negative, microaero-
Sample collection and laboratory methods for
the diagnosis of contagious equine metritis are
in both mares and
Metrite contagieuse equine: Une revue
La metrite contagieuse equine represente une
infection genitale tres contagieuse des juments. I1
s'agit d'une maladie venerienne, decrite pour la
*Animal Pathology Directorate, Health of Animals Branch, Agriculture Canada,Animal Diseases Research Institute,
P.O. Box 11300, Station H, Nepean, Ontario, Canada
premiere fois en 1977. Meme si les eruptions les
plus graves de cette maladie ont affecte des sujets
Thoroughbred, ceux d'autres races en ont aussi
souffert. On a constate l'existence de cette maladie
en Europe, en Australie et aux Etats-Unis. Au
maladie nommee, aux termes de la loi sur les
La maladie se caracterise par une endometrite et
des problemes d'infertilite: lesjuments atteintes ne
manifestent pas de signes d'une infection systemi-
que. A date, les etalons n'ont pas manifeste de
signes cliniques. Des porteurs existent, tant chez
les juments que chez les etalons.
Les juments infectees repondent favorablement
a une antibiotherapie topique ou parenterale. Un
certain nombre d'entre elles demeurent cependant
porteuses de l'agent etiologique. Le traitement des
etalons s'avere aussi efficace. Haemophilus equi-
propose pour designer
negatif, responsable de
Les auteurs decrivent la fa,on de prelever les
echantillons, ainsi que les methodes de diagnostic
utilisees au laboratoire.
la metrite contagieuse equine est une
le nom specifique qu'on a
le coccobacille micro-
H I STO R I CA L AS PECTS
A previously und;cribed
spring of 1977. On one large breeding farm in the,
proportion of i'
jeteQrrW' to estrus aftdr'
service: their diestrous period was shortened an4i
some mares had a copious mucopurulent uterine
Further cases were reported on other farms in the
area and when the breeding season ended on 15th
July, approximately 200 mares had been infected
on 29 farms involving 23 stallions. The incidence of
disease on each farm varied from <5 to 30% of
mares and a proportion of mares on affected farms
were not bred (18).
Following intensive laboratory studies, a Gram-
negative coccobacillus which had been observed in
smears of cervical and vaginal pus was cultured
under microaerophilic conditions (17). On the
evidence of transmission experiments it was shown
1) and Ireland (41) during the
area, Englan, *-7e1usually large!.
Can. vet. J. 20: 201-206 (August 1979)
to be the causal organism of the genital infection
Contagious equine metritis (CEM) was con-
firmed officially in three countries in 1977: the
United Kingdom, Ireland and Australia. The
disease may have been present
population before 1977 as an outbreak of venereal
disease that had affected Thoroughbred horses in
Ireland during 1976 was similar to CEM on clinical
and epidemiological grounds (14).
In September, 1977 Canada and the United
States imposed a ban on the importation of horses
which could carry the disease from the United
Kingdom, Ireland and France. The disease was
confirmed in France in 1978 (19). Contagious
equine metritis was diagnosed in Kentucky in the
spring of 1978 and the transportation of breeding
mares within the state was prohibited (11, 29).
Restrictions on the importation into Canada of
Thoroughbred horses from Kentucky came into
effect in April 1978 and CEM was designated a
reportable disease in Canada under the Animal
Disease and Protection Act.
A consultative committee with representatives
the Health of Animals Branch of the
Department of Agriculture, various segments of
the horse industry and equine veterinary practi-
tioners convened in Canada. Recommendations
were made on measures to prevent the introduc-
tion of CEM into the country and an official code
of practice was prepared to deal with an outbreak
of disease should it occur. Restrictions were placed
on Thoroughbreds moving into Canada from
Kentucky which required that, as of January 1,
1978, 1) Thoroughbred breeding mares and stal-
lions a) had not been on premises where CEM was
diagnosed or suspected and b) had been negative
bacteriologically for CEM on three occasions at
weekly intervals, 2) Thoroughbred racing mares
and stallions had not been on a Thoroughbred
breeding farm or premises where Thoroughbred
mares were kept. Geldings, weanlings and year-
lings under two years of age were exempt from the
in the horse
Contagious equine metritis is characterized by an
endometritis associated with inflammation of the
cervix and vagina and infertility (6). A copious
mucopurulent uterine discharge is seen in acute
cases one to six days after service, but, in a few
cases, it may not be apparent for up to 80 days
following service (21). The discharge may persist
for up to two weeks.
discharge is seen, but a small volume of greyish
fluid may accumulate on the floor of the vagina.
Other cases may be detected only when mares
return to estrus, possibly after a shortened di-
estrous period. Mares show no signs of systemic
infection. The organism has not been recovered
from aborted fetuses, however,
In less severe cases no
it has been re-
covered from the placentae offour known positive
mares each of which had been covered by a stallion
which had transmitted the disease in 1977. The
foals born to these mares were healthy, but from
one of the foals, a colt, the organism was isolated
from the penile sheath on several occasions up to
three months of age (19).
An asymptomatic carrier state also exists in
mares and the organism has been isolated from
clitoral and urethral swabs from pregnant mares
(4) and nonpregnant mares (16, 26) and from
mares after the birth oflive, full-term foals (27,42).
Mares have also been identified as carriers of the
organism following clinical recovery.
Clinical signs have not been observed in stallions
and they are considered to be symptomless carriers
of the disease.
The disease is highly contagious. It is spread
primarily by venereal transmission but also by
personnel who have examined infected horses and
possibly by teaser stallions used to detect mares in
estrus (6). It is essential that aseptic techniques be
employed during the genital examination of mares
and stallions to prevent spread of the disease.
Initially CEM was diagnosed only in Thorough-
breds. In 1978 the disease was confirmed among
other breeds of horses in France (19).
A presumptive diagnosis based on clinical findings
is confirmed by culture of the CEM organism
(CEMO). In the nonpregnant mare, swabs for
bacteriological examination should be taken from
the uterus or cervical canal, the urethra and the
clitoral fossa and sinuses. The optimal time for
swabbing is during the early part ofestrus when the
cervix begins to relax and uterine exudate contain-
ing organisms can be collected from the cervical
canal. The clitoral fossa and the clitoral sinuses,
located on the dorsal aspect of the clitoral gland,
are favorable sites for CEMO which can persist in
these locations for prolonged periods (27). Only
urethral and clitoral swabs should be collected
from the pregnant mare.
Timoney et al (43) have shown that variations
can occur in the shedding of CEMO by carrier
clitoral swabs were taken daily for a period of 11
days from a known carrier mare. All the cervical
swabs were consistently positive, whereas, three
sets of clitoral swabs and nine urethral swabs failed
to yield the organism during the Il-day period.
The study emphasizes the advisability of taking
swabs from the uterus or cervix, the urethra and
clitoral area on more than one occasion to increase
the effectiveness of detecting the carrier mare.
In the stallion, swabs should be collected from
the fossa glandis and from the folds of the penile
During the collection of swabs careful attention
should be paid to hygiene. Disposable gloves, one
pair per animal, should be used and uterine swabs
should be guarded to avoid contamination. Swabs
charcoal for delivery to the laboratory.
Laboratories in Europe and the U.S. have been
involved in developing serological methods for
diagnostic purposes. Benson and co-workers (2)
obtained a reasonable correlation between serum
agglutination test (SAT), antiglobulin test (AGT)
and bacteriological findings. It was proposed that
animals showing positive SAT at a serum dilution
of 1/80 or above should be considered positive for
CEM (2). Dawson et al(7) carried out SAT, AGT
and complement fixation test (CFT) on sera taken
over a period of 98 days from two pony fillies
experimentally infected with CEMO. The three
tests showed positive titers confirming bacterio-
logical findings during the acute stage of the
observed between days 14 and 21. However, the
CFT reactions persisted at diagnostic levels longer
than those in the other two tests. Evidence was
cited from another work (5) that low titers in the
SAT/AGT and higher titers in the CFT persisted
indefinitely in cases of chronic infection, indicat-
ing that the CFT is potentially valuable for the
diagnosis of chronically
carrier cases. Fernie et al (9) have developed a
passive hemagglutination test for the detection of
antibodies to CEMO. They suggest that a titre of
1/256 or greater in a sample of serum may be
interpreted as a positive indication of infection.
They claim that the test provides a more rapid
means of detecting infection with CEMO than
other serological methods and is not affected by
the problem of anticomplementary activity as
reported with the CFT (5). Timoney et al (40)
reinfected mares with CEMO and found variable
serum antibody responses: the anamnestic
sponse was less than the primary antibody re-
sponse in virtually all cases. There was evidence of
local antibodies in the genital tract of the mares
after rechallenge with CEMO.
Problems associated with cross-reactivity, speci-
ficity and persistence of agglutinating antibody
remain to be answered. Indeed, the recent observa-
tion that agglutinins to the organism were present
in the serum of patients attending a genitomedical
clinic but were absent in the sera of four veterinary
surgeons who have been in close contact with
infected horses, further confirms problems of
specificity and cross-reactivity (31).
in Amies transport medium with
both ponies were
infected and healthy
Although Gram-negative coccobacilli were usually
seen scattered among neutrophils in stained smears
of cervical and vaginal pus, initial attempts to
recover CEMO using conventional aerobic culture
methods were unsuccessful (3, 17). Further tests
the presence of mycoplasmas,
chomonads and viruses (17). The agent was finally
isolated at a Public Health Laboratory that studied
human venereal diseases and was shown to grow
best in heated blood agar under microaerophilic
conditions (11, 17).
Morphological and colonial characteristics
CEMO is usually described as a Gram-negative
coccobacillus but it may appear also as mono-
morphic short rods with bipolar staining resembl-
ing members of the Brucella and Pasteurella
genera (17, 41). Pleomorphic forms may appear
with age. Under electron microscopy, the bacteri-
um exhibits the typical trilaminar structure of
Gram-negative cell walls and does not possess any
flagella. On tryptose chocolate blood agar (TBA),
the organism produces tiny, round, raised and grey
colonies about 0.3 mm to 0.5 mm in diameter after
48 h. On Eugons chocolate agar (EBA), colonies
appear earlier and somewhat larger than those on
TBA (10, 28). With further incubation at 37°C the
colonies may enlarge and turn whitish. A dis-
tinguishing feature of the colonies on EBA is that
they are slightly dry and granular and can be
pushed across the surface of the medium.
Cultural and biochemical characteristics
al (17) were the first to demonstrate the fastidious
requirements of CEMO. The organism was found
to grow best in heated blood (chocolate) agar in an
atmosphere of 5% to 10% CO2 in hydrogen. This
suggests a strict anaerobic condition although
subsequent reports refer to CEMO as microaero-
philic ( 18, 21). Gas-pak anaerobic system (Becton-
Dickinson) without the catalyst has been employed
to replace almost all the air with carbon dioxide
and hydrogen (10). More recent studies, however,
show that CEMO grows readily under 5% to 10%
CO, in air or with the use of candle jars (28. 29).
The bacterium is catalase, cytochrome oxidase
and phosphatase positive but unreactive to other
conventional tests for biochemical characteristics.
It is nonmotile and has a DNA base composition of
36.1% GC (32). The favourable growth supported
by chocolate agars may be associated with the
organism's apparent requirement for the X-growth
factor (porphyrins) or hemin (24). By contrast,
Taylor et al (32) did not observe any dependency
on X, V or XV factors although the X factor
stimulated growth ofCEMO. This nondependency
was further confirmed by a positive result with the
D-amino-laevulinic acid test of Kilian (12).
Thus far CEMO has not been shown to identify
with any known bacterium and certain workers
have proposed a new species name, Haemophilus
equigenitalis type strain NCTC 11184(61717 / 77)
for the organism (32).
An interesting feature of
CEM isolates from England and Ireland is their
minimum inhibitory concentrations for this anti-
biotic have been greater than 500 ,ug/lml (17).
Swerczek (29), however, reported the isolation of
level of resistance to streptomycin. The
sensitive strains in Kentucky. He suggested that
antibiotic sensitivity tests be carried out on field
isolates as the organism will adapt readily to
laboratory media and become resistant to anti-
biotics in these media.
The organism is sensitive to a number of drugs
including benzylpenicillin, ampicillin, the tetra-
cyclines, trimetophrim, sulphamethoxazole, clin-
damycin, erythromycin, gentamycin, tobramycin,
amikacin, neomycin, chloramphenicol, polymyxin
B, furazolidone and trivetrin (17, 41). Taylor et al
(32), however, showed that certain strains of
CEMO are resistant to trimetophrim, sulpha-
methoxazole and clindamycin. Gentamicin was
found to be superior to ampicillin or a combina-
tion of penicillin and polymyxin in eliminating
CEMO from extended stallion semen (38).
Transport media and isolation method
ofCEMO in swabs has been increased with the use
of transport media
medium (with charcoal) maintained the viability of
the bacterium for at least ten days at room
temperature and seemed
medium or Amies medium without charcoal (1). It
has been recommended that swabs in Amies
transport medium be shipped immediately to the
laboratory either frozen or at 4°C.
Isolation of the organism
streaking swabs directly to plates of EBA or TBA
and blood agar containing 200jig/ml to 400 ,ug/ ml
streptomycin. Eugons chocolate agar without anti-
biotics is needed to isolate streptomycin-sensitive
strains (29). Where fungal overgrowth presents a
problem, fungizone (Amphotericin B) may be
added at 5 ,ug/ml of medium (1, 29). Plum Island
Animal Disease Center, New York, recommends
isolation of CEMO (for streptomycin-resistant
strains) using a series of streptomycin-containing
media designed to discriminate between CEMO
and other organisms. These include EBA, TBA,
blood agar, MacConkey or eosin methylene blue
(EMB) agar, eugonbroth containing recrystallized
hemin, and cooked meat broth. Except for aerobic
blood agar and MacConkey plates, the inoculated
media are maintained in 5% to 10% CO2. All
inoculated and control media are incubated at
370 C. Tryptose chocolate blood agar appears
useful in distinguishing CEMO colonies which
appear much smaller and grow more slowly than
many contaminants. The CEMO does not grow on
aerobic blood agar and MacConkey plates. The
CEMO colonies usually appear after 48 halthough
in some cases it may take 15 days before they are
detected (29). Bacteriological techniques to iden-
tify the suspected colonies have been limited to
smears and catalase, oxidase, phosphatase and
antibiotic sensitivity tests. Hyperimmune serum in
slide agglutination test (16, 22) can be useful in
confirming identification of CEMO. Bulk cultiva-
streptomycin-resistant and streptomycin-
34). Amies transport
is carried out by
tion of CEMO for antigen production can be
facilitated by employing a recently developed
liquid medium (8).
Thus far, CEMO has been found to infect horses
and donkeys (37), and rabbits, guinea pigs and
albino Swiss mice (33). However, evidence that
cattle, sheep and pigs do not appear to be affected
suggests that the organism has a limited host-range
(39). After several passages on artificial media, the
organism may start to lose its virulence for the
horse. However, this characteristic may be re-
stored by in vivo passage. The presence of semen,
either alone or in an extender, appears to poten-
tiate the pathogenicity of the organism (36).
The main difference from other endometrial
infections of the mare caused by organisms such as
Klebsiella aerogenes (capsule type 1) and Pseudo-
CEMO and the rapidity with which the infection
spreads in a group of breeding horses.
Prior to the isolation ofCEMO, O'Driscoll and
co-workers (13, 14) pointed out the interesting
regularity with which Bacillus proteus (Bacillus
proteus mirabilis) was isolated from CEM infected
animals. This organism, however, has not been
shown to reproduce CEM and, at best, may act as a
possible secondary invader in certain cases of
CEM and thereby exacerbate the severity of the
inflammatory reactions (35). Others (15, 17) have
discounted any role by Proteus because of its
affected horses. Simpson and Eaton-Evans (27)
reported the isolation ofboth CEMO and Klebsiel-
la from clitoral sinus material of mares as well as
from the sheath of a foal at 36 and 48 days of age.
is the highly contagious nature of
both healthy and
H I S TO P A T H O L O G Y
The histopathological changes ofthe endometrium
seen in CEM are unlike those ofthe morecommon
bacterial infections of the uterus (20, 21). Focal
luminal epithelial hyperplasia and degenerative
changes immediately below the luminal epithelium
are observed. Some epithelial cells show advanced
cytoplasmic and nuclear degenerative changes. A
supra-epithelial amorphous layer containing poly-
morphonuclear leucocytes is often present. The
predominant cellular infiltration in the stroma is
mononuclear (21). The presence of polymorpho-
considered an indication of infection. The CEMO
has been recovered from mares with no histo-
logical evidence of acute endometritis confirming
that a true carrier state can exist with this infection
Experience gained in the treatment of infected
mares during the outbreak in England (1977)
indicated that both topical and parenteral treat-
ment should be undertaken (6) although a single
course of treatment does not eliminate infection in
every case (26, 27). Intrauterine irrigation with
chlorhexidine, nitrofurazone, ampicillin or benzyl
penicillin daily for three to five days supported by
the daily parenteral administration ofampicillin or
penicillin is recommended (6). The clitoral fossa
sinuses and surrounding area should be
cleansed thoroughly to remove all smegma-like
material and other particles: a 4% chlorhexidine
gluconate solution is effective for this purpose.
Following mechanical cleansing and drying, the
fossa is dressed with an ointment such as 0.2%
nitrofurazone. The process is repeated at 24 or 48-
hour intervals on five occasions (4).
Treatment of the stallion consists of thorough
and careful washing of the erect penis, fossa
glandis and sheath with chlorhexidine gluconate
and the application of a nitrofurazone ointment.
Treatment is repeated at intervals of 24 or 48 h
for five to seven days and further treatments may
be necessary depending on the results of the
bacteriological tests. Nitrofurantoin administered
orally for a period of five days has been recom-
A proportion of infected mares have a rapid
clinical recovery without treatment and conceive,
but of these some will remain carriers. Reinfection
of mares with CEMO is possible after an interval of
two weeks (36). In an experimental investigation
the clinical response ofmares following reinfection
was appreciably less than that observed following
prior challenge with CEMO (40).
Treatment is associated in most cases with rapid
clinical recovery and may reduce the risk of
endometrial damage and susceptibility to other
However, a proportion of mares which respond
clinically to antibiotic treatment remain infected
(26, 27, 41). In the Kentucky outbreak the majority
of CEM infected mares remained carriers despite
different antibiotic treatment regimens (29). Swer-
czek (30) associates the prolongation of infection
after antibiotic treatment with the
destruction of the bacteria which constitute the
normal flora of the reproductive tract of the mare.
On chocolate agar antibiotic-free plates, strains of
these bacteria inhibit the growth of CEMO and
they may play a similar role in vivo in the mare.
Treatment of stallions is successful but it is not
known what effect the organism has on sperma-
togenesis. Data from Ireland indicate that the
fertility of mares and stallions which have been
cleared of infection returns to normal in the
following breeding season (14).
CONTROL AND PREVENTION
Outbreaks of disease in Thoroughbreds have been
controlled by 1) the cessation of breeding, 2) the
accurate detection of infected animals, 3) the
isolation of affected and in-contact mares and
stallions, 4) treatment and 5) careful attention to
Precautions to prevent the spread of this highly
contagious infection throughout the equine pop-
ulation are essential (25) and aseptic techniques
should be used during the genital examination of
mares and stallions. Artificial insemination offers
the best method of preventing the spread ofdisease
and "re-infection" of stallions (23).
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WARDS and D.G. POWELL. Serological response in
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