Bacteria are a normal part of an animal's healthy status. "Good" bacteria are present within 24 hours after birth - both from the environment and from the dam. Obviously the "bad" or pathogenic bacteria are readily available as well.
Puppies who nurse start off life with a big boost. The first milk a dam produces is called colostrum and for about 24 hours this milk is very rich in antibodies to help protect the newborn pups. Working in concert with this flow of antibodies is the fact that the intestinal tract is more open to absorbing these large molecules. So the puppy absorbs these antibodies and for 6 to 8 weeks they are protected against many pathogens (see glossary). At about this time, the levels start to decrease while hopefully the puppy's own immune system will start to function and produce its own antibodies. Puppy immune systems develop from about 4 to 20 weeks of age. Milk itself provides some local immunity by coating the oropharynx (see glossary) and the intestinal tract with some antibodies. So young pups that are well cared for, born of healthy mothers with good immune systems have the best chance of survival.
When a pathogenic bacterium does take hold in a young pup, the signs are not usually specific for any particular bacterial strain. Puppies may be found dead with no warning signs or they may show the general "sick puppy" symptoms - restlessness, crying, low temperatures, diarrhea, breathing difficulty, and even blood in the urine. Laboratory tests will often indicate anemia and possibly low blood glucose. Puppies who have not been kept warm, who have other virus or parasitic infections or who have immune system deficiencies will be the most ill and have the least chances for survival.
Treatment for bacterial infections in young puppies starts off with good nursing care and symptomatic treatments. The puppies need to be kept warm and once warmed up, can be given fluids and glucose if needed. Oxygen via a nasal tube or through use of an oxygen cage can make a sick puppy much more comfortable. Antibiotics are usually required, but there are some caveats with young puppies. Puppies have lower body fat than adult dogs as well as lower levels of albumin (a blood protein). The kidneys may not be fully developed yet and the blood/brain barrier is poorly developed. Often the dosage must be adjusted - both in amount and frequency. It should also be noted that the pups receive some medications via the milk if they are nursing and the dam is on medication.
The most commonly used antibiotics in young puppies are the penicillin and the cephalosporin classes of antibiotics. These both provide coverage for a variety of bacteria, and have minimal side effects. It may be necessary to give these by injection (as opposed to orally) for best effect.
Aminoglycosides can be very effective drugs, but care must be taken due to the immature renal function in pups. The potentiated sulfonamides are quite safe and have a wide spectrum of efficacy, but the immature liver and kidney functions may affect dose.
The tetracyclines come with broad spectrum effects, but some problems. The use of tetracyclines in young animals may cause discoloration or pitting of the enamel on the teeth. The tetracyclines should not be given at the same time as anything with calcium or magnesium that could interfere with absorption of the drugs. This means pups may have to be kept from nursing for a while after administration of the drug orally.
The fluorquinones, such as enrofloxacillin, are excellent antibiotics for older dogs, but do potentially cause cartilage defects in young dogs.
Your veterinarian will consider all of the above factors, plus try to determine the exact bacteria and its susceptibilities while planning a treatment regimen for your sick pup. The nursing care and administration of the medications will be up to you unless your pup requires
Author: Debra M. Eldredge, DVM
Editor: Johnny D. Hoskins, DVM, PhD, Dipl. ACVIM