Viruses, Bacterial, and Fungal Infections
Viruses are another bugaboo for small dogs. These microscopic disease agents multiply inside their hosts and cause such illnesses as distemper, parvovirus, hepatitis, rabies, bordetella (kennel cough), adenovirus, and parainfluenza. A rabies vaccination is required in most states, and dogs may be vaccinated against the other viruses according to their risk factor.
Bacteria are a mixed bag. Not all bacteria are bad. Others cause diseases, the most common in dogs being leptospirosis, campylobacteriosis, and thrombocytopenia, as well as streptococcal and staphylococcal (strep and staph) infections, tetanus, brucellosis, and such tickborne infections as Lyme disease, ehrlichiosis, and Rocky Mountain spotted fever. Some are preventable through vaccination.
Fungi, plants that propagate by releasing spores, also cause disease. When inhaled by dogs, these spores can cause a wide array of infections, including blastomycosis, ringworm, and others. Some are indigenous to certain regions, thriving along riverbanks. Some propagate in areas where bird or bat feces have accumulated, inside animal dens, or in rotting vegetation where dogs like to dig. They cause a wide variety of maladies, from respiratory to central nervous system problems to skin sores. Fungal infections are hard to diagnose and resistant to cures. They are best prevented by being careful about where you take your dog, not letting it run free in places where they may thrive.