What is VOA, who is this Enterococcus species?
Imagine you are walking your barns, doing daily chores in a flock that is 28 days of age. Mortality and culling rates for the flock have been good, but on this particular day you start to notice that a number of birds appear lame and some have adopted a ‘dog sitting’ posture, sitting on their hind ends with their legs in front of them. After culling lame birds out for a couple of days, your level of concern starts to increase, as does the number of culls. What could be causing this? You have heard of some other producers describing similar symptoms and someone referred to this problem as ‘VOA’ or Enterococcus cecorum, but others calling it ‘kinky back’. Could this flock have VOA or is it kinky back?
While there are a number of potential causes for lameness in a flock of this age, in this article we hope to explain what VOA is, as well as to describe the organism that causes it.
What is Enterococcus cecorum and VOA?
Enterococcus cecorum is a bacterial species that is considered a normal part of the bacterial population in the chicken intestine. This bacteria can become a problem however if something allows it to exit the gut and enter into other locations within the bird via the blood stream. When this happens, Enterococcus cecorum prefers to set up in the bones, causing infection of the bone, generically referred to as osteomyelitis. One particular location that is at risk for infection in the chicken is a backbone (the free thoracic vertebrae). This is the only backbone in the chicken that is not fused to its neighbors which makes it a key location for problems in the spine. Infection here is referred to as Vertebral Osteoarthritis or ‘VOA’. Infection can however also occur in other bones as well.
Birds affected with VOA are particularly striking in appearance because they often adopt the ‘dog sitting’ posture described in the scenario above (shown in figure 1). The reason for this posture is because the infection in the backbone creates swelling, which pushes down on the spinal cord, interfering with the ability of the bird to control movement of the legs (figure 2). It is important to know that this presentation is similar to, but does not have the same underlying cause as the developmental condition referred to as kinky back. In cases of ‘kinky back’, there is no bacterial infection but rather the affected back bone is rotated out of proper position, causing similar compression of the spinal cord and interference with leg movement.
Also important to know is that Enterococcus cecorum is just one species of the Enterococcus genus of bacteria. There are other species of Enterococcus commonly found in chickens, however they have not yet been isolated from these VOA types of cases or lesions. Infection of a flock with Enterococcus species does not necessarily mean that the flock has or will develop VOA, and further testing is required to determine the species involved. In cases in Alberta we have seen changes in the strains of Enterococcus cecorum causing VOA that were misidentified as a related bacteria Aerococus viridans. The importance of this finding is that this bacteria like all pathogens can adapt over time and develop new biochemical and test profiles. Follow up and repeated culture can be required to get the right answer to the question of “what is wrong with my birds”.
Treatment of Enterococcus cecorum
Treatment of this bacterial infection, once clinical signs are evident (‘dog sitting’, lameness) has been difficult and often unsuccessful. The most likely reason for this is the nature of the infection causing the clinical signs; birds are too affected to be able to drink enough to receive and adequate dose, and the damage at the site of infection is too severe for the drug to be able to penetrate and fight off the infection. Field reports and lab sensitivity testing results indicate that Amoxicillin is the best choice for treatment, however Amoxicillin has only been mildly effective in some cases.
What should I do if I see lame birds in my flock?
Unfortunately there are numerous potential causes for lameness in poultry flocks. Some are nutritional, some developmental, some are disease related. If a flock starts showing signs of lameness and you have concerns, it is important to consult with your veterinarian. Not all causes of lameness can be treated, and not all treatments are harmless to a flock. For specific diagnosis and treatment advice it is best to contact your veterinarian.
A focus on prevention
On farms where this condition has occurred, research has shown that cleaning and disinfection plays an important role in preventing re-occurrence in subsequent flocks. This includes cleaning and disinfection of water lines, above flushing or super-chlorination. Occasionally if the condition continues to repeat, metaphylactic preventative treatment using amoxicillin and/or tylosin have been helpful. It is not yet well understood what factors predispose to this condition. The possibility of a link to broiler breeder flocks has been investigated and so far transmission of this pathogen from parent hens cannot be demonstrated. Some groups propose that intestinal health may play a role in allowing this normal bacterial species to invade other locations within the bird. Researchers have been able to show that by orally dosing this organism to chickens they can re-create the disease, suggesting that if this organism can grow to higher than usual numbers in the intestine, it may be able to overwhelm natural defense mechanisms. At any rate, taking steps to ensure good intestinal health and to monitor intestinal health programs is a good idea for flocks on a farm experiencing this disease.