It's A Dog's Breakfast - Some Answers

Several readers of my five-part series have raised substantive issues in their comments, some of which required additional research of the scientific literature in order to answer accurately. Here is the first installment of answers to readers' questions and comments.


Salmonella in kibble and pet treats
Anonymous (who posted on March 15, 2008 10:32 AM) is correct in pointing out that there have been recalls of kibble and pet treats due to Salmonella contamination. The following products were recalled because of Salmonella in 2007.

• Eight-in-One, Inc. recalled chicken jerky treats for dogs, cats and ferrets. There was one confirmed case of salmonellosis in a dog that was traced to these treats.
• Doane Pet Care recalled a single lot of 55 lb. bags of kibble after FDA found Salmonella in the product.
• Mars Petcare US, Inc. recalled a single lot consisting of 1620 5-lb. bags of kibble and three 50-lb. bags after FDA found Salmonella in the product. The recalled product was distributed in five states.
• Bravo recalled 18,000 pounds of its raw, frozen dog food due to Salmonella contamination.

In 2003, approximately $5.4 billion dollars of dry dog food were sold in the US. Even assuming a premium price of $1.75/lb., this translates to more than 3 billion pounds of kibble. The total amount of kibble recalled in 2007 for Salmonella was 72,930 pounds (based on the information contained in the recall announcements and in the FDA enforcement reports dated August 1st and October 31st). Therefore, the recalled kibble represents less than 0.002% of the annual US sales of dry dog food.


Diet and Dental Disease
More than one reader stated that 80% of dogs develop periodontal disease by age 3. The only source for that statistic that I was able to find is the web site of Merial, a manufacturer of veterinary plaque-preventative gel.

I've identified several articles in scientific journals that address diet and its effect on the development of periodontal disease. I have quoted the main conclusions of these articles. The findings in these research studies show that a hard diet is better at preventing gingivitis and periodontal diseases than a soft diet, and that the most effective preventative of periodontal disease is regular brushing of the teeth and gums. Just as in humans, the mechanical brushing action stimulates and strengthens the gums.

Gorrel, C. 1998. Periodontal Disease and Diet in Domestic Pets. The Journal of Nutrition Vol. 128 No. 12, pp. 2712S-2714S.
"Daily toothbrushing remains the single most effective way of maintaining clinically healthy gingivae."

Gawor, J.P., et al. 2006. Influence of Diet on Oral Health in Cats and Dogs. The Journal of Nutrition Vol. 136, pp. 2021S-2023S.
"These results indicate that feeding a dry food diet has a positive influence on oral health, decreasing the occurrence of mandibular lymphadenopathy, dental deposits, and periodontal disease in cats and dogs."

Clarke, D.E. and A. Cameron. 1998. Relationship between diet, dental calculus and periodontal disease in domestic and feral cats in Australia. Australian Veterinary Journal. Vol. 76 No. 10, pp. 690-693.
The following is the complete Abstract of the journal article. I do not have access to the full article:
"OBJECTIVE: To compare the dental calculus scores and prevalence of periodontal disease in domestic cats eating commercially available canned and dry foods with those in feral cats consuming a diet consisting of small mammals, birds, reptiles and insects. ANIMALS: Twenty-nine feral cats and 20 domestic cats were included in the study. PROCEDURE: A dental chart and dental calculus scores were recorded using the maxillary canine, maxillary third and fourth premolar, mandibular canine, mandibular fourth premolar and first molar teeth on both sides. Periodontal disease was recorded using gingival recession, increased periodontal pocket formation, radiographic alveolar bone loss, osteomyelitis, furcation and root exposure, and the presence of calculus as indicators. RESULTS: Dental calculus scores were significantly higher in domestic cats than in feral cats. There was no statistical difference in the prevalence of periodontal disease between the two groups. CONCLUSIONS: It can be inferred that diet may play a role in the accumulation of calculus, but a diet based on live prey does not protect cats against periodontal disease."

Giardia
One commenter, referencing a 1995 article, questioned whether humans and animals shared the same species of Giardia. I have responded to this already, but will repeat my reply here for the convenience of those who might have missed it.

The 1995 reference has been superseded by more recent research. Please see the following direct quotations from the article Abstracts:

Eligio-García L., et al. 2005. Genotype of Giardia intestinalis isolates from children and dogs and its relationship to host. Parasitology Research, Vol. 97, No. 1, pp. 1-6.
"In this study, genotype A was associated with samples from children and dogs, and, therefore, we could infer zoonotic transmission as a way of getting the disease."

Lalle, M., et al. 2005. Genotyping of Giardia duodenalis from humans and dogs from Mexico using a beta-giardin nested polymerase chain reaction assay. Journal of Parasitology Vol.91, No. 1, pp. 203-205.
"The presence of cysts of the A1 and A3 genotypes in isolates from pet dogs is consistent with their role as reservoirs for human infection, although further studies are needed to confirm the occurrence of zoonotic transmission."

Thompson, R.C. 2004. The zoonotic significance and molecular epidemiology of Giardia and giardiasis. Veterinary Parasitology Vol. 126, No. 1-2, pp.15-35.
"The greatest risk of zoonotic transmission appears to be from companion animals such as dogs and cats, although further studies are required in different endemic foci in order to determine the frequency of such transmission."

Traub, R.J., et al. 2003. Humans, dogs and parasitic zoonoses – unravelling the relationships in a remote endemic community in northeast India using molecular tools. Parasitology Research, Vol. 90, Suppl. 3, pp. S156-7.
"The zoonotic potential of canine Giardia was also investigated by characterising Giardia duodenalis recovered from humans and dogs living in the same locality and households, at three different loci. Phylogenetic and epidemiological analysis provided compelling evidence to support the zoonotic transmission of canine Giardia."

These references make it clear that humans and dogs can and do share some of the same species of Giardia. Furthermore, the articles provide strong epidemiological evidence that dogs and cats can transmit Giardia to humans. The main outstanding question appears to be the frequency of such transmission.

Prevalence of bacterial pathogens in the human food supply
Several "Anonymous" comments mentioned – without providing any supporting evidence – that 80% of food for human consumption is contaminated with Salmonella. That number is grossly overstated. Except for raw poultry, no food products – not even other raw foods – come even close to that incidence of contamination.

It might sometimes seem, as a result of the all too frequent occurrence of pathogen-related food recalls, that our food supply is highly contaminated with Salmonella, Campylobacter, Listeria monocytogenes and E. coli O157:H7. But this is a false impression. Here are some examples of data from research reports. Please click on the live links to access the reports directly.

Consumer Reports published the results of a survey of raw poultry for bacterial pathogens. They found that 83% of fresh, whole broiler chickens purchased at retail stores in the United States were contaminated with Salmonella or Campylobacter, the two leading causes of food poisoning.

The incidence of Salmonella in US shell eggs is estimated at one in 20,000 eggs, or 0.005%, according to a research report published in the International Journal of Food Microbiology in 2000.

A survey of raw domestic and imported seafood published in 2000 in the Journal of Food Protection found that 10% of imported raw seafood contained Salmonella; the incidence in domestic raw seafood was 2.8%.

Several more questions and comments posted by readers remain to be answered. I am working on those answers and will post more information in the next few days.