November 25, 2018

An Outbreak of Tuberculosis Due to Mycobacterium bovis infection in a pack of English Foxhounds (2016-2017)

By Photograph by Mike Peel (www.mikepeel.net)., CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=35028554

Mycobacterium bovis is a bacteria commonly found in cattle that is known to cause tuberculosis in social mammals (humans, lions, cattle, etc.) however an outbreak in canines is extremely uncommon. In the UK, tuberculosis is considered rare, and most canine cases are found in individuals or in small groups. Thus, when a tuberculosis outbreak in ~180 foxhounds occurred in 2016-17 in a ‘edge area’ (an area on the edge of a high risk area), a study was promptly conducted to determine the cause.

 

Similar to many kennels, and previous outbreaks in English Foxhounds, the infected hounds had been fed raw meat, and allowed to eat offal and bones from dead livestock. Additionally, the hounds worked in a many counties, most of which being in the ‘edge area,’ with the rest being in a low risk area (for tuberculosis.)

 

Due to the danger a tuberculosis outbreak, researchers adopted a ‘test and cull’ policy with the infected hounds. A test was conducted on the hounds to determine if they had Mycobacterium bovis. If so, they were immediately removed from the pack and euthanized, and a post mortem examination of each euthanized hound was conducted.

 

Out of the 164 hounds tested, 57% of the hounds tested positive in at least one test for M. bovis, 52% were deemed infected and potentially infectious, but only 3% had visible lesions post mortem.

 

A epidemiological assessment was then conducted to attempt to determine the cause of the outbreak.

 

First, they looked at 16 female hounds who had been brought to other kennels from breeding, to see if they contracted M. bovis there. However, only one of these females tested positive for M. bovis, but did not have visible lesions at post mortem examination. Thus, it was concluded the movement of these female hounds was not likely to be the cause of the outbreak.

 

Researchers then looked at possibility of having fed the hounds M. bovis infected livestock. They traced back hound feed to to an approved finishing unit, from which there have been no tuberculosis positive cattle for three years, which thus discounted this theory.

 

Additionally, it was concluded that the hounds had not contracted M. bovis from local livestock or while on a hunt, as about 85% of the area the hounds were ever exposed to was low risk. The other 15% had seen previous tuberculosis outbreaks in cattle, reportedly caused by wildlife. Despite this, due to the rarity of a M. bovis outbreak in dogs, this 15% was not regarded as a significant factor in the potential cause of the outbreak.

 

Thus, researchers concluded that despite the uncertainty in the source of M. bovis, it was determined that the hounds feed was responsible. In all the hounds that tested positive for M. bovis, the bacterium contained shared an isolated genome, one that was not commonly seen in the area the foxhounds were being kept. This finding suggests they all got the infection from one source. Thus it was concluded a large dose of infected material was given as food, and then spread horizontally.

 

Since this outbreak, standards for feed and living conditions for foxhounds have been raised significantly. Feeding hounds raw offal from fallen livestock was banned, along with increased health surveillance requirements for hounds.

 

O'Halloran C, Hope JC, Dobromylskyj M, et al. An outbreak of tuberculosis due to Mycobacterium bovis infection in a pack of English Foxhounds (2016–2017). Transbound Emerg Dis. 2018;00:1–13.

 

https://doi.org/10.1111/tbed.12969

 

Reviewed by Calvin Isley | Nov 28 2018