Signs are somewhat non-specific which makes diagnosis a challenge. In healthy, older dogs no clinical signs may be obvious. In some dogs the virus may only cause only a transient fever and some mild depression. Other dogs may have more severe systemic illnesses including several, though usually not all, of the following signs (2):

 

Respiratory: - nasal and ocular discharges - coughing/ pneumonia - dyspnea	Source
Ocular (relatively uncommon): - anterior uveitis – inflammation in the front corner of the eye and cloudiness of the cornea - keratoconjunctivitis sicca (dry eye) - optic neuritis with concurrent sudden blindness - retinal degeneration/separation	Source
Gastrointestinal: - lack of appetite - vomiting - diarrhea	Source
Other: - callusing of the foodpads/nose (‘hard pad disease’)	Source

Often in the course of the disease, affection of the neurological system becomes apparent. These signs can develop at the same time as onset of the above clinical signs, or may occur up to a month after initial infection. Therefore sometimes the dog may recover from the initial signs, only to develop further neurological problems weeks later. Signs include:

Neurological Signs: - seizures - behavioural changes - walking in circles - rhythmic motions or ‘tics’ - steady continual contractions of head muscles (looks like dog is chewing gum)

Source