Some common dog illnesses include parvovirus, distemper, kennel cough, adenovirus and leptospirosis. Parvovirus, colloquially called "parvo," is a contagious illness usually striking dogs ages 12 weeks to 3 years old, with symptoms that include a fever and eventually bloody diarrhea and vomiting that leads to dehydration and weakness. The virus is transmitted via canine bodily secretions; dogs can be vaccinated against parvo beginning at 6 weeks of age, notes PetMD.
Distemper is a type of illness in dogs that begins with symptoms of upper respiratory infection, including eye discharge and sneezing, and may lead to pneumonia or neurological issues. In its worst form, it can cause fatal brain damage. There is a vaccine for it, however, that's administered to puppies, notes PetMD.
Kennel cough, which is also contagious, causes lethargy, fever and decreased appetite. As the illness progresses, dogs develop a deep cough that may lead to pneumonia.
Adenovirus is canine hepatitis, although it is rarely seen in modern veterinary medicine. The symptoms of this illness are hard to detect, but often begins with vomiting and diarrhea and leads to jaundice.
Leptospirosis is a type of canine bacterial infection usually transmitted from infected urine or contaminated water. Symptoms include fever, lethargy and vomiting. A vaccine for this disease is also available, but not all clinics offer it.