International transparency would help to curb contagious equine metritis, says scientist


International transparency around the presence of contagious equine metritis in countries and their efforts to control it would help breeders and the global horse trade, according to a scientist who investigated the first known cases of the disease in Portugal.

Contagious equine metritis (CEM) is a highly contagious bacterial venereal infection of horses caused by Taylorella equigenitalis. It is of major international concern and causes short-term infertility in mares.

Portugal’s first known outbreak occurred in 2008.

Teresa Rocha, of Portugal’s National Institute of Agrarian and Veterinary Research, noted that the country had been considered free of the disease until the outbreak that year.

Rocha, writing in the peer-reviewed Open Veterinary Journal, said T. equigenitalis was isolated in May of that year from a stallion and two mares from the same stud. The stallion had recently been imported from Germany and had entered Portugal with a negative certificate for T. equigenitalis.

The exact origin of the infection could not be confirmed with the information available to the institute, Roche said.

“Although two positive mares were detected on the same premises shortly after the stallion, it could not be confirmed whether the stallion was used for breeding prior to testing at our laboratory, thereby acquiring T. equigenitalis from those mares, or if the stallion was a carrier of T. equigenitalis despite his negative CEM certificate and had in fact transmitted the infection to the mares.”

The Portuguese Veterinary Authority went on to perform mandatory testing on the 30 remaining equines at the stud, resulting in a further four positive animals.

They were treated and subsequently tested negative for T. equigenitalis.

Since this outbreak, more then 2000 genital swabs from 736 Portuguese horses have been tested at the institute’s laboratory, with no further positive animals identified.

The available information suggested the outbreak was an isolated event, Roche said. However, a wider epidemiological study would be needed to better evaluate its incidence in the country.

Discussing her findings, Roche noted that the disease had attained worldwide distribution since being recognised as an emergent disease in equines in 1977.

This spread, she said, had resulted from the shipment of carrier stallions and mares both within and between countries.

Sporadic outbreaks have been confirmed in equine populations in more than 29 countries in Europe and North and South America, as well as in Japan and Australia.

Horse importing countries outside Europe, such as the United States, have considered all countries of the European Union, and a small number of other European countries outside the EU, to be affected with this disease, despite the fact that information on its occurrence in Europe was scarce.

“International transparency regarding the presence of contagious equine metritis in a country, as well as on the actions undertaken to prevent and control its spread would be very beneficial to individual horse breeders and to the international equine trade as a whole,” she said.

It would ultimately assist in preventing the spread of the disease and improve the general health status of equines worldwide, she added.

Commenting on the 2008 outbreak, Roche said: “The isolation of T. equigenitalis from a stallion believed to be negative for T. equigenitalis reinforces the insidious nature of this disease and reiterates the fact that effective prevention and control of CEM must include a comprehensive testing program to allow for early detection and treatment of carriers animals, particularly stallions.”

Contagious equine metritis in Portugal: A retrospective report of the first outbreak in the country and recent contagious equine metritis test results
T. RochaOpen Veterinary Journal, (2016), Vol. 6(3): 263-267 DOI:

The report, published in the Open Veterinary Journal under a Creative Commons License, can be read here

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