Pneumonia is one of the top ten reasons guinea pigs need to see a vet. Guinea pigs often get potentially lethal upper respiratory infections from living in dirty cages or damp rooms. Because guinea pigs are so small, pneumonia can kill them in days, so they need to see a vet as soon as symptoms appear.
Runny Nose and Eyes
Guinea pig noses and eyes are normally dry and clear. Any crusting or even a continual stream of clear discharge can indicate pneumonia.
Loss of Appetite
Refusing to eat even the most favoured treat should always be treated as an emergency. According to the guinea pig expert Peter Gurney, a guinea pig will die if it does not eat within 2 days (see Resources).
Guinea pigs normally sneeze after they groom themselves. But a guinea pig with pneumonia will sneeze at times other than grooming.
The guinea pig will make uncharacteristically strange noises while breathing because of congestion. These noises can sound like wheezing, crackling or rasping.
Treatment of pneumonia in guinea pigs requires an immediate round of antibiotics. But keep in mind that guinea pigs are allergic to penicillin.