Signs:
Clinical signs in livestock appear abruptly, usually following some external stimulation. They include tremors, ataxia, adoption of a wide-based stance, stumbling and falling over, nystagmus, convulsions while recumbent and death (Allen, 2012). Animals may appear to recover between episodes of ataxia and convulsions. Sheep often exhibit a high stepping gait with their forelimbs, while the head is held high. When forced to run, some sheep have a stiff-legged or "rocking horse" gait. Some cattle appear disorientated and wander aimlessly between episodes of convulsions. Signs may appear as soon as four days after introduction to toxic pasture or feed. Animals may continue to exhibit neurological signs and die for up to 10 days after removal from toxic feed. Ewes may abort (Allen, 2012).
Symptoms:
Nematode-infected seeds are pointed, shorter than normal, and are black or yellow. A yellow coloration indicates that bacteria are present in the gall (Clarke and Nurse, 1999).
When introduced to a gall, Rathayibacter toxicus bacteria rapidly multiply soon after the gall is initiated, smother the nematode larvae, and colonize the structure to form a bacterial gall. If the bacteria are deposited outside the galls but within the developing inflorescence, under suitable environmental conditions they can multiply to form a yellow slime that will become apparent on the surface of the plant at the time of head emergence. With time, the slime hardens and turns orange and then brown. The slime does not always appear and may also be washed off by rain (Clarke and Nurse, 1999).
Rathayibacter toxicus can go undetected for long periods, making visual detection a serious challenge. Most of the infected plants do not show any visible symptoms. Thus, absence of visible slime (gummosis) does not necessarily mean that a pasture is free of R. toxicus. In many cases, bacteria and nematode infections go undetected or the disease is misidentified. The nematode vector and bacterium can survive in the dry state for many years (Murray et al., 2014).