Discription of Yersinia ruckeri

	Yersinia ruckeri is the causative agent of enteric 
	
redmouth (ERM).  ERM most often infects rainbow trout, but it also

affects several other salmonids.  It has been found all over

the world in the US, Canada, Europe, and South Africa.

ERM gets its name from the distinctive reddening that occurs

in and around the mouth.  Sometimes, ERM is referred to as

Yersiniosis because the tale-tale redmouth is not always

present (Frerichs 1985).


Discovery of Yersinia ruckeri
		
	Yersinia ruckeri was first discovered by Rucker in the 1950's in  

Idaho.  It is now believed that it was probably in West Virginia 

and Australia in the 1950's, so it is impossible to determine where it 

originated (Bullock 1977).

				
Symptoms

	The symptoms of ERM are similar to many other fish diseases.  The fish 

stop eating and stay at the top of the water or they isolate 
	
themselves from the other fish.  The fish becomes darker and the fins become 	
	
inflamed.  The eyes become exophthalmic and if affected will burst (Busch 1983).  

The bacteria can be isolated from virtually every tissue of the affected fish.  

The bacteria prefer to colonize in well vascularized areas and this can lead to 
hemorrhaging (Bullock 1977). Internally, the organs, especially the spleen become red. This 
too is most likely due to hemorrhagic septicemia (Busch 1983).

				
Transmission
		
	ERM is most likely spread from direct contact with infected fish.

So far it seems that vertical transmission does not occur (Rucker 1966). 


				
Morphology

	Yersinia ruckeri is a gram negative rod without 

spores or capsules.  It often has a flagella which it uses for

movement, but this is not always present.  As of today, six different 

Yersinia serotypes have been discovered (Stevenson 1997).  This has caused some 
	
difficulty in the past when researchers were investigating how 

to make an effective vaccine.


Detection

	Accordint to Austin Yersinia ruckeri can be detected using fluorescent antibody 
tests and monoclonal ElISA assays (1986).  The diagnosis can be confirmed by isolating the 
bacteria and observing certain distinguishing characteristics:

	-Cytochrome oxidase negative
	-Produces acid, but not gas in glucose
	-Produces alkaline slant and acid butt in triple sugar iron agar
	-Reacts positively with ornithine and lysine decarboxylase

				
Suppliers of the Vaccine:

Alpharma
800/722-3840

Aqua Health
208/543-5369