The reasons Chihuahuas shiver is because they are cold and they don't have much of thermal mass. It is the smallest dog that is affected by the cold weather. The virus can cause distemper in Chihuahua puppies if they are not vaccinated.
Sometimes Chihuahuas shake because they are in pain, fear, anxiety or nerves. Chihuahuas will burrow under blankets. You can dress them to go outside. They also like heated bedding.
Anxiety is when they need to get into a car, go to the vet or groomer and having to take medicine.
Excitement of getting a treat. The message goes from the taste buds to the brain and then to the body and they will shake.
Nausea is very unpleasant and can cause shivering from discomfort.
Professional Pet Sitting Services offered in the Upper to Mid-Pinellas County Area