It’s possible, anonymous. As mammalian pokémon, a growlithe’s body temperature can indeed skyrocket if they’re feeling a bit under the weather. However, keep in mind that it’s also possible that your growlithe is reacting to the weather. For half of the world, it’s currently summer, and many fire-types “feed” on the heat, in a way. That is, they thrive in it and sometimes even feel more energetic and powerful on a particularly sunny day. For simplicity’s sake, this process (of “feeding” on heat) is often called “heat-boosting.”
Telling the difference between a fever and a heat-boosted growlithe is simple but requires quite a bit of observation on your part. Keep an eye out for these signs:
- Lethargy
- Faster or labored breathing; panting if it’s not particularly hot
- Dry nose and/or gums
- Lack of appetite or difficulty eating or drinking
- Runny nose
- Shivering
- If you’re particularly well-verse in your growlithe’s vitals: increased resting pulse
If you see any of these signs, then yes, your growlithe has a fever, and your next step should be taking him to the pokémon center immediately. If, conversely, your growlithe is displaying these signs:
- Disinclination to sit still for at least half a minute
- Fire displayed in his mouth, despite the fact that you haven’t ordered him to attack
- Increased appetite and thirst
- Increased energy and mood overall
…then your growlithe is actually heat-boosted, and it would be a good idea to take him out for exercise, a battle, and a period in cool water, in that order. These steps aren’t for his health, exactly. They’re more for you, as a heat-boosted growlithe will very likely continue to run about attempting to set everything it can see on fire until it releases its pent-up energy, and I highly doubt anyone short of someone paid rather handsomely by the League would have homeowner’s insurance good enough to cover fire damage from a rambunctious pokémon.
The Pokédex According to Bill 