Upper respiratory infections are the leading cause of death in pet guinea pigs — bacterial pathogens spread easily between animals and cause rapid deterioration without prompt veterinary care.
Guinea pigs with respiratory infections experience dyspnea — difficulty breathing that is profoundly distressing for an obligate nasal breather. As infection progresses, the animal must work harder and harder to breathe, spending energy on respiration that should go to thermoregulation and normal behavior. The rapid deterioration possible in untreated respiratory disease means welfare harm escalates quickly — what appears as mild sneezing can progress to fatal pneumonia within days in untreated animals.