Changes

'''Antibiotic responsive diarrhoea''' (ARD) describes a clinical syndrome which is associated with alterations in the population of enteric bacterial flora and in the response of the host immune system to these bacteria.  It may occur independently of any other apparent pathological process ('''idiopathic''') but it occurs commonly with a number of intestinal diseases ('''secondary''').  The term 'antibiotic responsive diarrhoea' has replaced the previous description of '''small intestinal bacterial overgrowth''' (SIBO) due to uncertainty over the level at which enteric bacteria could be said to be present in excessive numbers and because an increased number of bacteria is not always the cause of the clinical syndrome described.   

'''Antibiotic responsive diarrhoea''' (ARD) describes a clinical syndrome which is associated with alterations in the population of enteric bacterial flora and in the response of the host immune system to these bacteria.  It may occur independently of any other apparent pathological process ('''idiopathic''') but it occurs commonly with a number of intestinal diseases ('''secondary''').  The term 'antibiotic responsive diarrhoea' has replaced the previous description of '''small intestinal bacterial overgrowth''' (SIBO) due to uncertainty over the level at which enteric bacteria could be said to be present in excessive numbers and because an increased number of bacteria is not always the cause of the clinical syndrome described.   

The mucosal immune system of the host and the enteric bacterial flora interact constantly in the gastro-intestinal (GI) tract.  The host must remain tolerant of the enteric flora but must still be able to recognise and respond to potentially pathogenic organisms.  These apparently contradictory tasks are resolved by the ability of the immune system to 'tolerate' certain antigens if these are presented to macrophages and dendritic cells in an appropriate manner.  The evidence available so far suggests that ARD is partly due to an alteration in size and dynamics of the intestinal bacterial population and partly due to a failure of the normal tolerance mechanisms.

The mucosal immune system of the host and the enteric bacterial flora interact constantly in the gastro-intestinal (GI) tract.  The host must remain tolerant of the enteric flora but must still be able to recognise and respond to potentially pathogenic organisms.  These apparently contradictory tasks are resolved by the ability of the immune system to 'tolerate' certain antigens if these are presented to macrophages and dendritic cells in an appropriate manner.  A number of hypotheses have been advanced to explain idiopathic ARD that involve some alteration in this host-bacterial flora interaction.

 

Dogs with idiopathic ARD have higher levels of some cytokines and greater numbers of CD4 T-cells in their intestinal mucosa, suggesting that ARD might occur due to a breakdown in the normal host tolerance of the microflora.

In cases of idiopathic ARD, the only consistent clinical finding is responsiveness to antimicrobial therapy.  This is found commonly, but not exclusively, in young [[Canine Breeds - WikiNormals #Pastoral Group|German Shepherd dogs]] and it has been suggested that this is associated with a deficiency in [[IgA]] or with another form of immune dysregulation in this breed.  In cases of secondary ARD, there is usually an underlying intestinal disorder, of which the most common are:

In cases of idiopathic ARD, the only consistent clinical finding is responsiveness to antimicrobial therapy.  This is found commonly, but not exclusively, in young [[Canine Breeds - WikiNormals #Pastoral Group|German Shepherd dogs]] and it has been suggested that this is associated with a deficiency in [[IgA]] or with another form of immune dysregulation in this breed.  In cases of secondary ARD, there is usually an underlying intestinal disorder, of which the most common are: