Bacterial Zoonoses
Many zoonotic diseases are bacterial in origin. Many of these bacteria are enteric organisms, as a result feces is a major
way to spread these infections. Others can be transmitted via bites or scratches such as Bartonella. Especially with enteric
bacteria it is important to remember that clinically healthy animals can still harbor pathogenic bacteria. Elimination of
these bacteria is often not possible so it is very important that measures are put into place in practices to minimize the
risk to other patients, staff and the general public. It is also very important to educate clients to the potential risks,
especially if the household has members that are not fully immunocompetent.
Salmonellosis
Salmonellosis has received public attention on occasion. Most cases of this disease are acquired as a result of ingestion
of contaminated food. Raw chicken and uncooked eggs are generally recognized as common sources of salmonella infections in
man. The risks of exotic pets, especially in regard to turtles have also been widely publicized. Another area that has received
some media attention is rawhide chews which can be contaminated with salmonella. Depending upon the source, a large percentage
of rawhides and pig ears can harbor salmonella. In one outbreak it was shown that contact with the treats or pets that consumed
them was responsible for human salmonellosis. Of 94 pig ear samples from retail outlets 51% were harboring Salmonella. Salmonella
was also found in other treats including beef hoof, braided chews and similar products. Of great concern were outbreaks of
multidrug resistant Salmonella typhimurium in small animal facilities including an animal shelter and 2 small animal clinics
in 1999. In one veterinary clinic the likely source of the infection was a kitten with diarrhea, 10 of 20 employees developed
clinical signs. In another instance one affected person was an employee and 2 were clients that had brought their cats to
the clinic for treatment. After discharge the cats developed diarrhea and the owners subsequently became ill. This obviously
raises the specter of liability for the pet and owner's illness.
It certainly is not surprising that dogs can also harbor Salmonella species. Most recent studies have shown a prevalence of
around 1 to 2 % in normal dogs and cats. Percentages may be higher in animals with diarrhea. Very high prevalence had been
found in racing sled dogs, where 69% of dogs without diarrhea were shedding salmonella. In Greyhounds with diarrhea 61% were
positive for Salmonella, in non-diarrheic dogs the percentage was 11%. The increased proportion of Salmonella positive animals
in these dogs may relate to the stress of athletic performance or to their diets.
Raw meat can be a source of salmonella infection in dogs. This has been shown in a variety of studies looking at athletic
dogs such as Greyhounds and sled dogs that routinely receive uncooked meat as part of their diet.
Recently there has been considerable interest in raw diets for pet dogs, the most popular called BARF (biologically appropriate
raw food). The internet is replete with sites that popularize this type of diet and it's supposed health benefits. It does
however mean that owners are routinely contaminating their environment with potentially infectious materials such as raw chicken.
Dogs are not known to be especially clean eaters and it is highly likely that infectious organisms are disseminated throughout
the home. In a recent study on a small number of dogs, 30% of dogs fed a BARF diet were shedding Salmonella, 80% of the food
samples were positive.7 This has also been my personal experience where dogs fed BARF diets are positive for Salmonella (2 of 3 tested) even without
clinical signs of diarrhea.
Campylobacter
The prevalence of campylobacter closely parallels that of Salmonella in cats, with approximately 1% harboring this infection.
The prevalence in dogs is considerably higher in some studies where up to 28% of dogs are infected. Other studies however
show the prevalence to also be around 1%. The majority of human cases are acquired by ingestion of contaminated food. The
percentage of poultry with campylobacter is higher than the percentage with salmonella. There is the possibility of spread
from dog or cat to man. The majority of dogs will not show clinical signs if infected.
Leptospirosis
Vaccination has decreased the importance of certain strains of leptospirosis, namely L. canicola and L. icterohaemorrhagiae.
Recently there has been an increasing frequency in which leptospirosis is diagnosed in dogs with renal failure. The causative
serovars are considered the atypical ones and include L. bratislava, L. grippotyphosa, L. pomona, and L. autumnalis. Clinical
signs are not specific enough to allow a clinical diagnosis without doing an MAT (microscopic agglutination test) to detect
antibodies against the organism. Clinical signs can vary from inapparent to terminal acute renal failure. The majority of
infections seem to occur in spring and fall, probably because of environmental conditions that favor the organism. Under the
right environmental conditions it is possible for the disease to become almost epidemic in it's spread. The reservoir species
include cattle, pigs, rodents, raccoons and skunks to name a few. Leptospirosis is also a major zoonotic organism in humans.
Although dog to man transmission is rare, it can occur and veterinary staff dealing with these patients are at risk. Transmission
is via urine, shedding can be prolonged if not terminated with antibiotics. Newer vaccines are available that protect against
some of the atypical strains. At this time there are no peer-reviewed articles that have looked at whether these vaccines
prevent inapparent renal shedding.
Prevention
Some very simple management techniques can prevent bacterial infections from being transmitted. Hand washing is vital; it
should be done between each patient and certainly before eating. Food should also remain out of the area where animals are
handled. In those cases with diarrhea or proven infections gloves should be worn when handling the patient and hands washed
after removing the gloves. Patients with diarrhea, confirmed or suspected zoonotic infections should also be isolated from
other animals, especially those that are very susceptible to infections such as those with major trauma, surgeries or on immune
suppressive therapy. Animals fed raw meat diets should be considered carriers of pathogens until proven otherwise. Antibiotics
should obviously be used wisely to limit the emergence of resistance strains. Dogs diagnosed with renal failure that do not
have an obvious cause, i.e. ethylene glycol intoxication, should be tested for leptospirosis. Even after exposure a short
course of antibiotics can prevent clinical disease in humans.
