Rare tuberculosis case reported in horse in South Africa

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Mycobacterium bovis. Photo: CDC
Mycobacterium bovis. Photo: CDC

A rare case of tuberculosis in a horse caused by Mycobacterium bovis (M. bovis) has been described by researchers in South Africa.

Tuberculosis caused by M. bovis is very uncommon in horses worldwide.

M. bovis most commonly causes tuberculosis in cattle. The bacterium is capable of infecting a range of mammals, but horses are considered more resistant to mycobacterial infections than other livestock.

University of Pretoria researcher Tiny Motlatso Hlokwe and her colleagues described the infection in an eight-year-old thoroughbred in a case report published this month in the open-access peer-reviewed journal BMC Veterinary Research.

The horse, which had a good body condition and was said to be bright and alert, was admitted to the equine clinic at the Onderstepoort Veterinary Academic Hospital in 2005. It was bleeding from both nostrils and was coughing.

The bleeding was identified as coming from the trachea and a chest x-ray revealed a primary pulmonary mass. M. bovis was isolated from a fluid taken from the lungs.

The lung mass reduced in size three months later after an oral course of enrofloxacin.

Genetic analysis identified the M. bovis isolate as being the spoligotype SB0868 strain. This M. bovis strain type has never been described previously in South Africa, the researchers reported.

It was, they said, the first case of M. bovis infection in a horse in South Africa to be fully documented, including clinical findings, isolation and genetic characterisation of the causative pathogen.

“This report indicates that horses may contract and harbour M. bovis despite their lower susceptibility compared to other domestic animals,” they wrote.

Bleeding from the nostrils had not previously been reported as a clinical sign with tuberculosis in horses, the study team noted.

“Infection with M. bovis in horses appears to occur mostly by ingestion and the most common site of infection is the gastro-intestinal tract. This is considered unlikely in the reported case since the lesion was associated with the lungs, suggesting the respiratory route as the most probable mode of transmission.”

Their findings, they said, supported the conclusion that horses may contract and harbor M. bovis despite their reported lower susceptibility compared to other domestic animals.

“The source of this infection is unknown as the M. bovis strain has not previously been detected in domestic animals or wildlife in South Africa.”

The organism was isolated from a broncho-alveolar lavage sample, indicating that the horse could have been shedding the organism, presenting the risk of forward transmission at the time.

“Because of the contagious and zoonotic nature of the disease, it is of outmost importance to ensure that measures are taken to prevent transmission of M. bovis between potentially infected horses and in-contact persons,” they concluded.

Hlokwe was joined in the report by David Sutton, Patrick Page and Anita Luise Michel, all affiliated with the University of Pretoria.

Isolation and molecular characterization of Mycobacterium bovis causing pulmonary tuberculosis and epistaxis in a Thoroughbred horse
Tiny Motlatso Hlokwe, David Sutton, Patrick Page and Anita Luise Michel
BMC Veterinary Research 2016 12:179 DOI: 10.1186/s12917-016-0813-6

The study, published under a Creative Commons License, can be read here.  

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