Definition
Contagious
equine metritis (CEM) is a highly contagious venereal disease of horses that causes an
acute purulent metritis and a copious mucopurulent vaginal discharge 10 to 14 days
postbreeding to an infected stallion. The first exposure to the disease usually results in
temporary infertility in the mare. Mares may become chroni cally infected and remain
carriers of the causal organism for several months or longer. Stallions carry the
contagious equine metritis organism (CEMO) on their external genitalia, and the primary
site of localization is the urethral fossa. The stallions may carry the CEMO on their
external genitalia for years. Newborn foals may become infected at birth and remain
infected until they are mature.
Etiology
The
CEMO is a microaerophilic gram-negative coccobacillus (17). There are two important
strains of the CEMO, one being streptomycin sensitive and the other streptomycin resistant
(14). A suggested name, Taylorella equigenitalis, has recently been accepted by the
International Committee on Systemic Bacteriology.
The
organism is susceptible to most commonly used disinfectants such as sodium hypochlorite
(30 ml of household bleach in 1 gal of water), chlorhexidine, and ionic and nonionic
detergents.
Host Range
Only
the equine species appear to be natural hosts for the disease. Thoroughbred horses appear
to be more severely affected by the disease than other breeds (14).
Geographic Distribution
Although
the disease was first described as an entity in England in 1978 (4), the causal organism
was likely present in horse populations in different countries for several years before
that time.
The
CEMO has since been detected in several countries, including Australia, Czechoslovakia,
Ireland, France, Germany, Japan, Belgium, Denmark, Italy, Netherlands, Norway, Sweden,
Switzerland, and Luxembourg. The disease has been eradicated from the United States.
Transmission
The
disease is naturally transmitted by coitus. Also, the CEMO can be transmitted indirectly
to mares and stallions with contaminated instruments and equipment (3). Undetected carrier
mares and stallions are the source of infection for acute outbreaks of the disease. During
the breeding season, an infected stallion may infect several mares before the disease is
suspected and diagnosed. Also, the CEMO may be transmitted through the use of artificial
insemination.
Incubation Period
In
field cases, the disease does not become evident until 10 to 14 days postbreeding when the
mare short-cycles and shows signs of estrus. The inflammatory reaction starts 24 hours
after exposure to CEMO and reaches maximum intensity 10 days to 2 weeks postbreeding.
Clinical Signs
In
the mare, a copious mucopurulent vaginal discharge occurs 10 to 14 days postbreeding to an
infected stallion (Fig. 44). The first
indication of infection is short-cycling of infected mares and a return to estrus. At this
time, a mucopurulent vaginal discharge or a dried vaginal discharge can be found on the
tail and inside the thighs (Fig. 45).
The discharge subsides after a few days, but the mare may remain chronically infected for
several months. In experimental infections in ponies (9,18,19) and horses (1), there was
evidence of a mucopurulent vaginal discharge 24 to 48 hours postinfection, which lasted
for 2 to 3 weeks. Most mares will not conceive when infected at the time of breeding. If
infected mares do conceive, they may abort the fetus or carry an infected foal to term.
The newborn foal may then become a carrier of the causal organism.
Gross Lesions
The
lesions of contagious equine metritis are not pathognomonic for the disease. The most
severe lesions are present in the uterus, but salpingitis, cervicitis, and vaginitis also
occur (1,9). The most severe lesions occur at about day 14 postinfection. The changes
gradually decrease in severity over the next several weeks as the disease becomes chronic.
On the uterine mucosal surface, the endometrial folds may be edematous and swollen with a
mucopurulent exudate evident between the folds at the height of the infection (Fig. 46). The cervix is edematous and
hyperemic, and the surface is covered with a mucopurulent exudate (Fig. 47) (1).
Morbidity and Mortality
Morbidity
is high in animals exposed venereally to the organism. Death to CEM has not been observed.
Diagnosis
Field
Diagnosis
Mares
that have a copious mucopurulent vaginal discharge 10 to 14 days postbreeding are suspect
cases of CEM. Chronically infected mares and stallions do not have any clinical evidence
of the disease.
Specimens
for Laboratory
In
both the acute and chronic stages of the disease, isolation of the bacterium is necessary
for a diagnosis of CEM (14). Mares suspected of being carriers of the CEMO should be
cultured during estrus, preferably during the first part of the heat cycle. Culture sites
in the mare are the uterus, clitoral fossa, and clitoral sinuses (11). In the stallion,
the culture sites are the urethra, urethral fossa and diverticulum, and the sheath (14).
Culture swabs should be placed immediately in Amies transport media and maintained at 4o C or lower to prevent the organism from dying and to prevent overgrowth by contaminating
bacteria. If the culture swabs are not cultured within a few hours, the specimens in the
transport media should be frozen. The organism appears to remain viable when frozen, for
it has remained viable in Amies transport media for 18 Years at -20o C (16).
Laboratory
Diagnosis
Smears
of the uterine exudate during the acute stages of the disease are helpful in making a
presumptive diagnosis of CEM (12). Examination of Gram- and Giemsa-stained smears of the
uterine exudate may reveal large numbers of inflammatory cells, mainly neutrophils.
Numerous gram-negative coccobacillary bacteria can be demonstrated in the mucus and in the
cytoplasm of the neutrophils. The organisms are usually seen individually or in pairs
arranged end to end.
In
both the acute and chronic stages of the disease, isolation of the bacterium is necessary
for a diagnosis of CEM (14).
Various
serologic tests may be used to detect antibodies to the CEMO (2,3,5,10). Evaluation of the
rapid plate agglutination (RPA), antiglobulin, enzyme-linked immunosorbent assay (ELISA),
passive hemagglutination (PHA), complement fixation (CF), and agar-gel diffuse tests in
ponies and Thoroughbreds provided varied results (10). Antibodies to CEMO were detected in
the sera of Thoroughbred mares by the ELISA, RPA, CF, and PHA tests. The CF test was
unreliable during the chronic stages of the disease owing to anticomplementary activity
and low or undetectable CF titers. Most acute and chronic CEM infections are detected with
the RPA, ELISA, and PHA tests. The rapid plate agglutination test (RPT) is very simple and
rapid. The RPT detected 100 percent of the culture positive mares in the 1978 outbreak of
the disease in Kentucky (14). The test also detected mares in the chronic stages of the
disease — in many cases over a year after exposure to the CEMO. The CF test is only
reliable between 15 and 45 days postinfection. A seropositive mare may or may not be
infected with the CEMO (14). Stallions do not develop detectable antibodies to the CEMO.
Differential
Diagnosis
Contagious
equine metritis is the most contagious bacterial venereal infection of horses and should
be suspected when several mares develop characteristic clinical signs after being covered
by the same stallion. Typically, an uncomplicated CEM-infected mare produces a mucoid,
gray purulent exudate from the uterus. However, mixed bacterial infections may occur, and
the discharge may vary from gray to yellow. Other bacterial venereal diseases in the mare
may produce a similar purulent, gray to yellow vaginal discharge, but they tend to be less
contagious. As with other bacterial infections, CEM infections may be very mild to
inapparent, or they may be severe. Although a tentative diagnosis of CEM may be suspected,
laboratory tests are necessary to confirm a case or outbreak of CEM.
Treatment
The
uterine infection can be treated with antibiotics, but it is questionable whether
treatment effectively eliminates or facilitates elimination of the CEMO. The mare cannot
be successfully treated until the CEMO clears from the uterus, which may take several
months. The external genitalia of the mare and stallion can be treated with disinfectants
and antibiotics. A standard treatment currently used is thorough washing of the external
genitalia with soap and water and then with chlorhexidine surgical scrub once a day for 5
days. After cleaning with chlorhexidine, the external genitalia are rinsed with warm water
to remove the chlorhexidine because it may irritate the sensitive mucous membranes. Then,
the external genitalia are coated with nitrofurazone-containing ointment. A disadvantage
of this treatment is the destruction of the normal flora and the potential overgrowth by
opportunistic pathogens such as pseudomonas and klebsiella (13). The clitoral sinuses are
common sites of persistence in carrier mares, and these sinuses are difficult to expose
for cleaning and treatment. Surgical excision of the clitoral sinuses will aid in the
treatment of the disease, and will usually rid the mare of infection (15).
Vaccination
Natural
infection does confer some immunity in the mare, for the first exposure to the CEMO causes
a very severe metritis, which usually results in temporary infertility. Subsequent
exposure to the CEMO is less severe, and the infection may not prevent conception.
However, the carrier state may result. Because of the nature of the disease and the
carrier state, artificial immunization is a not practical or recommended procedure for
preventing transmission of infection.
Control and Eradication
Preventive Measures
Inapparent
infections in carrier mares (19) and carrier stallions make the disease difficult to
control. To prevent the spread of the disease, it is necessary to detect and treat the
infection in mares and the stallion. Suspect carrier mares should be tested
bacteriologically to ensure they are not carrying the CEMO when bred to stallions because
one stallion may infect several mares. Stallions suspected of being carriers should be
cultured and bred to susceptible test mares free of the disease and the test mares
cultured for CEMO.
The
small-colony types are less virulent and may be responsible for the gradual decrease in
the number of naturally infected horses showing typical clinical signs of CEM in the field
(7). These variants present unique problems, both clinically and in laboratory testing,
for the small variants have no distinguishing cultural characteristics except that
colonies are transparent and small. In addition, the slow growth of these variants,
possible contaminating bacteria, and occurrence of streptomycin-sensitive strains of the
organism make bacteriologic testing for the disease rather difficult.
Because
of the difficulty of bacterial isolation of the streptomycin-sensitive strains, serologic
testing is a valuable aid in detecting mares that have previously been exposed to the
CEMO. Currently, the CF test is the only serologic test used to detect the disease in the
field, but it will only detect the infection during the acute phase when the organism is
easy to culture. Other serologic tests are available, and they will detect mares that have
previously been exposed to the CEMO. If other serologic tests were utilized, the disease
could easily be detected in carrier mares and steps taken for quarantine and treatment.
Such testing would also aid in the prevention of reintroducing the disease into the United
States from CEM-infected countries. Serologic testing is of no value in stallions because
the latter do not produce detectable antibodies to the CEMO.
Public Health
There
is no evidence that man is affected by the CEMO.
Contagious Equine Metritis Regulations
All
horses must have been in the country of export for 60 days immediately preceding
exportation. If not, the horse is to be accompanied by a health certificate issued by a
full-time salaried veterinary officer of the national government of each country in which
the horse has been during the 60 days immediately preceding shipment to the United States.
Preembarkation
Requirements in Country of Origin
Stallions
Collect
one set of specimens from the surface of the prepuce, urethral sinus, fossa glandis
(including the diverticulum of the fossa glandis) within 30 days of export but not less
than 21 days following treatment if treated.
Mares
The
importer has the options to have the clitoral sinusectomy performed on the mare in the
country of origin prior to export or performed in the United States after arrival.
Mares
(Option for Clitoral Sinusectomy in the United States)
Collect
one set of specimens from the clitoral sinuses within 30 days prior to export, but not
less than 21 days following treatment if treated.
Mares
(Option for Clitoral Sinusectomy in the Country of Origin)
Surgically
remove clitoral sinuses no less than 30 days prior to export. Two hours prior to surgery
collect a specimen from the clitoral sinuses and submit with removed clitoral sinuses to
approved laboratory.
After
surgery, collect a specimen from the clitoral fossa within 30 days prior to export but not
less than 21 days following treatment if treated.
U.S.
Entry Requirements
Horses
imported into the United States are required to be detained at the port of entry while
tests for dourine, glanders, equine piroplasmosis, and equine infectious anemia (EIA) are
conducted. Horses that are positive to tests for any of these diseases will be refused
entry.
Upon
completion of USDA import quarantine and testing requirements, the mare or stallion must
be consigned to a State approved to receive mares and stallions from CEM-affected
countries to undergo the prescribed CEM treatment and testing requirements.
Mares
Mares
with an Incomplete Sinusectomy or Option for Surgery in the United States
Surgery
must be performed at The College of Veterinary Medicine, University of California, Davis,
California, or The School of Veterinary Medicine, Cornell University, Ithaca, New York.
Two
hours prior to surgery, collect a specimen from the clitoral sinuses and submit with
removed clitoral sinuses (or portion) to the National Veterinary Services Laboratories,
(NVSL), Ames, IA or to a laboratory approved by APHIS.
Within
2 hours prior to treatment, collect a specimen from the clitoral fossa and clitoral
sinuses if present and submit with the clitoral sinuses (or portion) to NVSL or a
laboratory approved by APHIS. For 5 consecutive days, clean, wash (2 percent
chlorhexidine) and coat the external genitalia and vaginal vestibule with not less than
0.20 percent nitrofurozone ointment. Wait 7 days after cleaning and washing. Collect three
separate sets of specimens not less than 7 days apart from the clitoral fossa. Collect one
additional specimen from the endometrium of the uterus during estrus.
Pregnant
mares are treated the same as above. except 7 days after foaling collect three specimens
from the endometrium of the uterus and one specimen from the foal. Collect specimens from
the vaginal vestibule of the female foal and the prepuce of the male foal.
Stallions
One
specimen each shall be taken from the prepuce, the fossa glandis, and urethral sinus of
the stallion and be cultured for CEM. After the specimens have been cultured for CEM, for
at least 5 consecutive days the prepuce, penis (including the fossa glandis) and urethral
sinus of the stallion shall be thoroughly cleaned and washed while in full erection with a
solution of not less than 0.2% nitrofurazone by an accredited veterinarian under the
monitoring of a State or Federal veterinarian.
The
stallions must be tested for CEM by being bred to two mares. The test breeding shall be
performed in not less than 7 days after treatment is completed. Mares selected for test
breeding must be permanently identified before the mares are used for testing with the
letter T (hot iron, freezemarking, or lip tatoo).
Before
breeding, the mares must be to qualified as free from CEM by negative culture of two sets
of specimens (bacteriological swabs) collected at intervals of not less than 7 days and a
negative complement fixation (CF) test.
The
two mares are to be bred by the stallion. The mares are then cultured for CEM by
collecting three sets of specimens from each of the mucosal surfaces of the cervix, the
clitoral fossa, and the clitoral sinuses on the second, forth, and seventh days after
being bred.
Another
set of specimens, the fourth set, must be collected from the endometrium of the uterus,
the clitoral sinuses, and clitoral fossa during the next estrus. If natural estrus does
not occur within 28 days of the date of the breeding, hormonal precipitation of estrus
shall be carried out. The test mares are required to have two negative CF tests after they
are bred. Serum samples are to be collected between the 15th and 40th days after breeding.
The intervals between collection of serum samples should not be less than 7 days.
NOTE:
The clitoral sinusectomy is not required for thoroughbred mares from England, France,
Ireland, and Germany.
Thoroughbred
mares and stallions from England, France, and Ireland shall be treated as follows:
Mares
Collect
one set of specimens during estrus from the endometrium and the mucosal surfaces of
urethra, clitoral fossa, and cervix. Collect two sets of specimens from the mucosal
surfaces of the urethra, clitoral fossa, and cervix. The samples should be collected at
intervals of not less than 7 days apart, and the last of the sets shall be collected
within 30 days of export.
Stallions
Collect
three 3 sets of specimens from the prepuce, urethral sinus, and fossa glandis (including
the diverticulum of the fossa glandis) at intervals of not less than 7 days and with the
last of the sets collected within 30 days of export.
Upon
completion of the USDA import quarantine in the United States, the horses are free to
compete without any further restrictions.
GUIDE TO THE LITERATURE
1.
ACLAND, H.M., and KENNEY, R.M. 1983. Lesions of contagious equine metritis in mares. Vet.
Pathol., 20:330-341.
2.
BENSON, J.A., DAWSON, F.L.M., DURRANT, D.S., EDWARDS, P.T., and POWELL, D.G. 1978.
Serological response in mares affected by contagious equine metritis. Vet. Rec.,
102:277-280.
3.
BRYANS, J.T., and HENDRICKS, J.B. 1979. Epidemiologiocal observation on contagious equine
metritis in Kentucky, 1978. J. Reprod. Fertil. (Suppl.), 27:343-349.
4.
CROWHURST, R.C. 1977. Genital infection in mares. Vet. Rec., 100:476.
5.
CROXTON-SMITH, P., BENSON, J.A., DAWSON, F.L.M., and POWELL, D.G. 1978. A complement
fixation test for antibody to the contagious equine metritis organism. Vet. Rec.,
103:275-278.
6.
FALES, W. H., BLACKBURN, B.O., YOUNGQUIST, R.S. et al. 1979. Laboratory methodology for
the diagnosis of contagious equine metritis in Missouri. Am. Assoc. Vet. Lab. Diagn.,
22:187-197.
7
KANEMARU, T., KAMADA, M., ANZAI T., and KUMANOMIDO, T. 1978. Contagious Equine Metritis:
The Pathogenicity for Mares of Small and Large Colonies Variants of Taylorella
equigenitalis Isolated from a Laboratory Strain. Equine Infectious Diseases V.
Proceedings of the Fifth International Conference, Lexington, KY: The University Press
of Kentucky, pp 155-163.
8.
O'DRISCOLL, J.G., TROY, P.T., and GEOGHEGAN, F.J. 1977. An epidemic of venereal infection
in Thoroughbreds. Vet. Rec., 101:349-360.
9.
PLATT, H., ATHERTON, J.G., and SIMPSON, D.J. 1978. The experimental infection of ponies
with contagious equine metritis. Equine Vet. J., 10:153-159.
10.
SAHU, S.P., POMMEL, F.A., FALES, W.H., HAM DY, F.M., SWERCZEK, T.W., YOUNGQUIST, R.S., and
BRYANS, J.T. 1983. Evaluation of various serotests to detect antibodies in ponies and
horses infected with contagious equine metritis bacteria. A.J.V.R., 44:1405-1409.
11.
SIMPSON, D.J., and EATON-EVANS, W.E. 1978. Sites of CEM infection. Vet. Rec., 102:488.
12.
SWERCZEK, T.W. 1978. The first occurrence of contagious metritis in the United States. J.
Am. Vet. Med. Assoc., 173:405-407.
13.
SWERCZEK, T.W. 1978. Inhibition of the CEM organism by the normal flora of the
reproductive tract. Vet. Rec., 103:125.
14.
SWERCZEK, T.W. 1979. Contagious equine metritis - - outbreak of the disease in Kentucky
and laboratory methods for diagnosing the disease. J. Reprod. Fertil. (Suppl), 27:361-365.
15.
SWERCZEK, T.W. 1979. Elimination of CEM organism from mares by excision of clitoral
sinuses. Vet. Rec., 105:131-132.
16.
SWERCZEK, T.W. 1984. Unpublished data.
17.
TAYLOR, C.E.D., ROSENTHAL, R.O., BROWN, D.F.J., LAPAGE, S.P., HILL, L.R., and LEGROS, R.M.
1978. The causative organism of contagious equine metritis 1977: Proposal for a new
species be known as Haemophilus equigenitalis. Equine Vet. J., 10:136-144.
18.
TIMONEY, P.J., McARDLE, J.F., O'REILLY, P.J., and WARD, J. 1978. Experimental reproduction
of contagious equine metritis in pony mares. Vet. Rec., 102:63.
19.
TIMONEY, P.J., McARDLE, J.F., O'REILLY, P.J., and WARD, J. 1978. Infection patterns in
pony mares challenged with the agent of contagious equine metritis 1977. Equine Vet. J.,
10:148-152.
20.
TIMONEY, P.J., WARD, J.,and KELLY, P. 1977. A contagious genital infection of mares. Vet.
Rec., 101:103.
T.W.
Swerczek, D.V.M., University of Kentucky, Veterinary Science Department, Lexington, KY
40546
Agricultural
Experiment Station, Department of Microbiology and Immunology, Davis, CA.
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