Novel bacterium identified in three joint infections affecting Thoroughbreds

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Hunter Valley, Australia
A panorama of the Hunter Valley. © Mfunnell at the English Wikipedia [CC BY-SA]
A previously unidentified species of bacterium appears to have caused joint-related infections in three Australian horses, researchers report.

They say the cause was identified as a gram negative cocco-bacillus.

Bernard Hudson and his colleagues have described what they know about the novel bacterium in the journal, Case Reports in Veterinary Medicine.

The farms where the three affected horses lived were at least 80km apart, and two were more than 300km apart. There was no known contact between any of the horses and farm personnel.

The first case involved a 15-month-old Thoroughbred filly in Hunter Valley, New South Wales.

The case, from late 2012, involved progressive lameness in the right foreleg which had continued for two weeks. On arrival for treatment, she had a fever and was severely lame in the affected leg. Otherwise, she had normal vital signs and no other identified focus of infection.

There was swelling and obvious pain on direct palpation of the right fore shoulder region.

The second case involved a 7-month-old Thoroughbred filly living in the Southern Highlands district of New South Wales. Her lameness developed in August 2013 and had continued to progress, despite treatment with doxycycline.

On arrival at hospital, the horse was bright and alert but severely lame, with the infection affecting a lower leg.

The third case involved an unweaned male Thoroughbred aged just three months, living in the Hunter Valley. He developed severe lameness late in 2016 with fluid buildup affecting the left hind digital flexor tendon sheath. Few other clinical details about the case are available, the study team said.

The tendon sheath was lavaged and a large amount of fibrin was removed arthroscopically under general anaesthesia. Synovial fluid was described as turbid, with protein and cell count being abnormal.

All appeared to make a full recovery with surgical intervention and antibiotic therapy.

“What effect the infection had on racetrack performance is difficult to determine as there are many variables involved in such performance.”

The researchers described their testing of samples, including the use of biochemical and gene profiling techniques, to identify the causative agent.

The evidence suggests the bacterium was related to Alysiella crassa and Kingella kingae, but were not close enough genetically to represent the same species.

They said they believed they had isolated a hitherto unknown bacterium, which most closely resembled the Kingella species, in particular, Kingella kingae.

Kingella kingae has been identified as the most common cause of septic arthritis in children aged between 6 months and 5 years of age.

In equines, despite efforts to improve the detection of bacterial pathogens, none is identified in almost 60% of cases.

The authors noted that little information is available in scientific literature around microbiology, clinical manifestations or management of Kingella infection in horses.

They say further analysis is required to determine the classification of this potentially new species.

The only antibiotics to which all three isolates were found to be susceptible were ceftiofur and tetracycline.

They say the epidemiological significance of infection with this organism remains to be determined.

“But its occurrence in young horses may suggest epidemiological similarities to Kingella kingae infections in humans.”

Osteoarticular Infection in Three Young Thoroughbred Horses Caused by a Novel Gram Negative Cocco-Bacillus
Bernard J. Hudson, Catherine Chicken, Anna Blishen, Kristen H. Todhunter, Angela P. Begg, Leonie Chan, Thomas Karagiannis, Benjamin Raymond, Daniel Bogema, Angus R. Adkins, Christopher B. O’Sullivan, Brendon A. O’Rourke, Piklu Roy Chowdhury, Steven P. Djordjevic, Ian G. Charles, Andrew Edgar, and Katerina Mitsakos.
Case Reports in Veterinary Medicine https://doi.org/10.1155/2020/9785861

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

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