cem6.pdf

~ Pergamon

Comp. Immun. Microbiol. infect. Dis. Vol. 19, No. 3, pp. 199-204, 1996

Printed in Great Britain. All fights reserved

0147-9571/96 $15.00 + 0.00

CONTAGIOUS EQUINE METRITIS

P. J. TIMONEY

Department of Veterinary Science, Gluck Equine Research Center, University of Kentucky,

Lexington, KY 40546-0099, U.S.A.

(Received for publication 23 January 1996)

Abstract---Contagious equine metritis (CEM) is a highly contagious venereal infection of equids

caused by Taylorella equigenitalis, a bacterium with fastidious growth requirements. A disease of

major international concern, CEM can be the cause of short-term infertility and, very rarely,

abortion in mares. Unlike the mare, stallions exposed to T. equigenitalis do not develop clinical

signs of disease. CEM is transmitted by direct or indirect venereal contact. The carrier state occurs

in the mare and the stallion and carrier animals are frequently the source of infection for new

outbreaks of the disease. There are streptomycin-sensitive and -resistant biotypes of T. equigenitalis,

and diagnosis is based primarily on culture of the bacterium from its predilection sites in the

reproductive tract of the mare and the stallion. Treatment modalities are available for elimination

of the carrier state. Prevention and control of CEM is achievable through a comprehensive

programme of breeding farm management that includes early detection and treatment of carrier

Key words: Contagious equine metritis, Taylorella equigenitalis, symptomatology, epidemiology,

diagnosis, treatment, control.

Rrsumr--La mrtrite contagieuse 6quine (MCE) est une infection vrnrrienne hautement contagieuse

des 6quidrs dont l'agent responsable, la Taylorella equigenitalis, est une bactrrie qui se propage

seulement dans des milieux particuliers. La MCE, source de beaucoup d'inqui&ude fi l'rchelle

internationale, peut provoquer l'infrcondit6 ~ court terme, et trrs rarement, l'avortement spontan6

chez les juments. A la diffrrence des juments, les 6talons porteurs de T. equigenitalis ne drveloppent

pas de manifestations cliniques de la maladie. La MCE se transmet par le contact vrnrrien direct

ou indirect. Les juments ainsi que les 6talons peuvent 6tre porteurs de germes, et il arrive souvent

que les animaux porteurs sont fr6quemment fi l'origine de nouvelles 6ruptions de la maladie. I1 y

a des biotypes de T. equigenitalis sensibles ~ la streptomycine ainsi que des biotypes rrsistants, et le

diagnostic s'effectue principalement par la culture de la bactrrie prrlevre sur les sites de prrdilection

dans les appareils grnitaux de la jument et de l'rtalon. I1 existe des modalitrs de traitment

permettant l'61imination de l'rtat de porteur de germes. Un programme complet de gestion des

haras, incluant le drpistage et le traitment prrcoces des juments et des 6talons porteurs, perment

Mots-clefs: Metrite contagieuse equine, Taylorella equigenitalis, symptomatologie, epidemiologie,

diagnostic, traitement, prophylaxie.

INTRODUCTION

Contagious equine metritis (CEM) is a highly contagious venereal infection of members

of the horse family that was first recognised as a previously undescribed disease of horses

in 1977, when it was reported in Thoroughbred breeding populations in the United

Kingdom and Ireland [1]. It is caused by Taylorella equigenitalis, a gram-negative

bacterium with fastidious growth requirements [1, 2]. Two biotypes of the organism have

been identified, those sensitive to and resistant to streptomycin [1].

199

PII: S0147-9571(96)00005-7

200

P.J. Tirnoney

While CEM has been reproduced in donkeys, similar attempts to achieve transmission

to cattle, swine, sheep and cats have been unsuccessful. Certain species of laboratory

rodents are susceptible to experimental infection with T. equigenitalis following exposure

by the intrauterine route [3]. Since the initial reports in 1977, CEM has been recorded in

various horse populations throughout the world, including those in many European

countries, Japan, Australia, and North and South America, in some of which the disease

has since been successfully eradicated. Contagious equine metritis continues to be the

focus of considerable international concern, not only because of its potential to cause

widespread, short-term infertility in brood mares, but also because of the ease with which

the carrier state can be established in stallions and mares [3].

CLINICAL SIGNS

Contagious equine metritis is a disease that is confined to the reproductive tract in the

mare. Stallions do not develop clinical signs of CEM, nor do they in fact become infected

following exposure to T. equigenitalis. They merely harbor the organism as a surface

contaminant on their external genitalia, where it stimulates neither a local tissue reaction

nor a detectable serum antibody response [1].

The clinical response of mares following natural or experimental exposure to

T. equigenitalis for the first time can vary significantly, from overt disease to subclinical

infection. Clinical signs are restricted to the reproductive tract and there is no evidence

of systemic illness in affected animals. After an incubation period of 2-12 days, typically

affected mares may develop an odorless, grayish-white mucopurulent vulvar discharge of

uterine origin, which is variable in amount and usually lasts for approximately 2 weeks,

and occasionally longer. The discharge is associated with periods of endometritis, cervicitis

and vaginitis and a return to oestrus after a shortened dioestrous period. In some mares,

the extent and severity of the inflammatory response is not readily assessable unless the

reproductive tract is examined with the aid of a speculum. Regardless of any clinical

indications of infection, most mares fail to conceive following primary infection with

T. equigenitalis. This infertility is short-term, however, lasting usually a few weeks. No

long-term adverse effects on fertility have been reported in the mare. Re-exposure of

mares previously infected with T. equigenitalis is associated with the development of

minimal or no clinical evidence of CEM [3]. Persistence of the organism in the reproductive

tract of the chronically infected mare will not, in the majority of cases, interfere with the

maintenance of a normal pregnancy. Abortion is a rare sequel to infection in the pregnant

mare [4]. In two reported cases of abortion ascribed to T. equigenitalis, the bacterium was

recovered not only from the placenta but also from several sites in the aborted foetus.

TRANSMISSION

The carrier mare or stallion has been found to be the most important source of infection

in outbreaks of CEM [1, 3]. Spread of T. equigenitalis occurs by the venereal route,

primarily through natural service or artificial insemination. The disease can also be

mechanically transmitted by indirect means through the inadvertent contamination of

equipment, e.g. vaginal specula, examination sleeves, insemination equipment, etc., or by

personnel failing to observe adequate hygienic precautions in handling mares and stallions

at time of breeding. Though not of proven significance, a carrier teaser stallion also has

the potential to serve as a means of transmitting CEM. Transplacental transmission of

Contagious equine metritis

201

T. equigenitalis can occur in pregnant mares. This may result in foals congenitally infected

or contaminated with the bacterium at birth [5] or rarely, in abortion [4]. There is no

evidence that T. equigenitalis is a free living organism or that it is especially resistant to

conventional disinfectants or various environmental factors.

EPIDEMIOLOGY

The single most significant factor in the dissemination and persistence of T. equigenitalis

in various horse populations throughout the world is occurrence of the carrier state in the

stallion and the mare [1, 3].

A clinically inapparent carrier state can be established in a high percentage of stallions

after exposure to T. equigenitalis. Preferential sites for sequestration of the organism are

the urethral fossa and associated sinus. It can also be found in the distal urethra, on the

external surface of the penis, prepuce, and less frequently, in the pre-ejaculatory fluid.

T. equigenitalis may persist on the external genitalia of untreated stallions for years and

can be effectively transmitted to susceptible mares either by natural service or by artificial

insemination. Carrier stallions continue to pose the greatest risk in relation to the national

and international spread of CEM.

An asymptomatic carrier state can develop in a variable percentage of mares after

recovery from the acute phase of T. equigenitalis infection [1, 3]. While two types of carriers

have been reported, uterine and clitoral, the vast majority of persistently infected mares

harbor T. equigenitalis on the mucous membrane surfaces in the clitoral sinuses and fossa.

The organism may remain in these sites for months or years after it has been eliminated

from the rest of the reproductive tract. The shedding pattern of T. equigenitalis by carrier

mares can vary, with significant fluctuations in the number of detectable organisms being

observed in certain animals over time [3, 6].

As previously indicated, T. equigenitalis can persist in the uterus during pregnancy and

may be cultured from the placenta at time of foaling and infrequently from the external

genitalia of the newborn foal, especially colt foals. The organism may continue to colonise

on the external genitalia of these animals for a variable period of years even after they reach

sexual maturity [5]. Such foals constitute a reservoir of T. equigenitalis and a potential

source of infection for future outbreaks of CEM.

DIAGNOSIS

Diagnosis of CEM cannot be based on clinical grounds alone because of similarity of

this disease to certain other, more frequently encountered, bacterial infections of the

reproductive tract in the mare, e.g. Streptococcus zooepidemicus, Klebsiella pneumoniae and

Pseudomonas aeruginosa [7]. While isolation of T. equigenitalis in culture has long been

regarded as the only definitive means of establishing a diagnosis of CEM in the mare or

confirmation of the carrier state in the stallion [1, 3, 8], a recently developed polymerase

chain reaction assay for this organism may provide an equally sensitive and more rapid

means of confirming the infection [9]. The latter would be especially useful in instances

where major difficulties are encountered in culturing T. equigenitalis from sites heavily

contaminated with other gram-negative or gram-positive bacteria.

202

P.J. Timoney

The presence of organisms morphologically similar to T. equigenitalis, together with

numerous neutrophils in stained smears of vaginal exudate from putative cases of CEM

in mares, though suggestive, is not confirmatory of a diagnosis of the disease [1].

The most appropriate sites to culture for T. equigenitalis in the maiden, barren or

post-parturient mare include the uterus or cervix, clitoral sinuses and fossa, care being

taken to use swabs that are small enough to effectively sample the clitoral sinuses [1, 3].

Endometrial/cervical swabs should be taken during early oestrus. Swabbing of pregnant

mares is restricted to sampling the clitoral sinuses and fossa. Vaginal exudate, if present,

should also be cultured.

In the case of putative carrier stallions, it is important to swab the sites of persistence

of T. equigenitalis, namely the urethral fossa and sinus, distal urethra, external surface of

the penis and the prepuce, and perhaps also culture a sample of pre-ejaculatory fluid [1, 3].

The penis should be fully extruded and erect to ensure effective sampling of these sites.

Aside from culture, stallions can also be screened for presence of the carrier state by test

breeding to two mares, bacteriologically negative and serologically negative for antibodies

to T. equigenitalis. Confirmation of the carrier state in a stallion is based on demonstration

of T. equigenitalis in the reproductive tract of the test mares and/or development of

antibodies to the organism within 15-40 days after breeding.

In swabbing mares or stallions for the presence of T. equigenitalis, it is important that

the specimens be collected by a veterinarian to ensure that the appropriate sites are reliably

sampled. To optimise the chances of culturing the organism from carrier stallions or mares,

three sets of swabs should be taken at intervals of not less than 7 days [8]. Where individual

animals have been treated with antibiotics, it is important that the initial swabbing should

not occur within seven days after the completion of treatment.

T. equigenitalis is a fastidious organism requiring specific conditions for growth in the

laboratory [1, 8]. All swabs for culture of the organism must therefore be placed in an

antibiotic-free transport medium, e.g. Amie's medium, immediately after collection, and

transported, preferably under conditions of refrigeration, to a laboratory that is qualified

to test for CEM. Optimally, swabs should be cultured within 24 h of being taken, to

maximise the likelihood of isolating T. equigenitalis.

As a diagnostic procedure, serological testing for CEM is of limited value in that it can

only be used for detecting infection in the acutely infected mare [1, 3, 8]. Antibodies are

detectable around seven days, reach maximal titres around three weeks and usually decline

between 6 and 10 weeks after primary infection with T. equigenitalis. Stallions do not

develop a demonstrable serum antibody response after single or multiple exposures to the

organism, and carrier mares may or may not carry a positive titre using one of a range

of serological tests that have been developed for CEM.

TREATMENT

While T. equigenitalis is sensitive to a wide range of antimicrobial drugs in vitro,

currently no one treatment will guarantee both rapid resolution of clinical signs of CEM

and clearance of the organism from the sites of persistence in the carrier mare [1].

Moreover, it remains to be established whether it is even beneficial to treat the acutely

affected mare, since there is some evidence that treatment may enhance the likelihood of

persistence of T. equigenitalis in the clitoral region after it has been cleared from the

Contagious equine metritis

203

proximal reproductive tract [3]. If it is decided to proceed with treatment, however, then

it is advisable to seek the advice of a veterinarian concerning the drug(s) of choice and

the optimal route(s) and period of administration.

Treatment of mares that are clitoral carriers of T. equigenitalis requires prior removal

of any smegma-type material from the clitoral sinuses [1]. The sinuses and fossa are then

thoroughly irrigated with a 4% solution of chlorhexidine following which they are packed

with 0.2% nitrofurazone ointment or equivalent. This regimen is repeated for 5 consecutive

days. In the case of some mares, several courses of treatment may be required before the

organism is successfully eliminated. In the event that repeated treatments prove unsuccess-

ful, it may be necessary to resort to surgical ablation of the clitoral sinuses.

In contrast to the mare, treatment of colts or stallions for elimination of T. equigenitalis

from the external genitalia is straightforward and frequently successful [1, 3]. With the

penis fully extruded, all smegma type material is removed and the urethral fossa and sinus,

prepuce and penis thoroughly cleansed with a 2% solution of chlorhexidine. After drying,

0.2% nitrofurazone ointment or equivalent is liberally applied to the external genitalia.

Treatment is repeated daily for 5 days. One course of treatment is usually adequate to

eliminate the organism from the reproductive tract of the stallion.

PREVENTION AND CONTROL

Integral to the success of any national program for the prevention and control of CEM

is the need to make the disease notifiable or a non-notifiable but reportable condition [1, 3].

The ultimate effectiveness of such programs is also predicated on the availability of

laboratories with the capability of providing a reliable and rapid diagnostic service for

T. equigenitalis. As yet, no effective vaccine has been developed against CEM [3].

In the case of countries in which CEM does not occur, it is critical to require screening

of all stallions imported from countries in which CEM is known or suspected to exist

[3, 8, 10]. Such screening should involve both bacteriological examination of the stallion

together with test breeding the stallion to two susceptible mares, which should be

monitored for evidence of transmission of T. equigenitalis infection. All mares imported

into CEM-free countries should be rigorously screened both bacteriologically and serolog-

ically for evidence of infection with T. equigenitalis before release from post import

quarantine.

Codes of practice have been developed by certain countries, which provide guidelines

for veterinarians, horse owners and breeders alike for the prevention and control of CEM

in horse breeding populations [1, 3 8]. These are based on comprehensive bacteriologic

screening of stallion and mare populations to identify clinical cases of the disease and

asymptomatic carrier animals. The codes emphasise the need for improved standards of

hygiene on breeding farms and more widespread use of disposable and sterile materials

and equipment in order to minimise the risk of indirect spread of CEM and other equine

venereal infections. Artificial insemination, in breeds in which it is allowed, provides a

means of further reducing the risk of transmission of T. equigenitalis. Any mares or

stallions cultured positive for T. equigenitalis must be isolated and not bred until treated

and confirmed free of the organism. Where rigorously implemented over a period of years,

well formulated programs for the control of CEM have been successful in preventing and

in some cases eradicating this disease from certain countries.

Plik z chomika:

Inne pliki z tego folderu:

Inne foldery tego chomika: