[pstinard]

I read the research article. The type of paralysis studied, acute polyradiculoneuritis (APN), is the most commonly diagnosed generalized peripheral neuropathy in dogs worldwide, and is considered to be the canine equivalent of Guillain-Barre Syndrome (GBS) in humans. (One of my work colleagues has GBS, so I know it's not that uncommon in humans.) It's an autoimmune disease where the body's own immune system attacks the nerve cells.

APN was originally called coonhound paralysis because it was first identified in the US in hunting dogs exposed to raccoons and raccoon saliva, but it has since been found in many other dogs and in many other countries that don't have raccoons. Other than a definite association with hunting dogs exposed to raccoon saliva, little else was known about the cause of the disease, but the similarity to GBS led veterinarians to suspect similar causes in dogs, including bacterial or viral infection. Campylobacter bacterial infection is associated with 40% of the cases of GBS in humans, so the authors of this study wanted to see if there was a link between Campylobacter infection and APN in dogs.

Most Campylobacter infections in humans come from the consumption of raw or undercooked poultry. Chickens are a natural reservoir for Campylobacter, and many Australians feed their dogs raw chicken as part of their diet or as a treat, so the authors of this study included a study of the dog's diet to see if feeding raw chicken was associated with APN. BUT, they studied other factors as well, including other raw meats, vaccination, contact with birds, contact with outdoor water sources, contact with pesticides, whether the dogs scavenged for food outdoors, whether they ate poop (seriously), and demographic factors such as sex, breed size, and whether they were spayed or neutered. The results are breathtaking, but we'll get to that in a minute.

The authors conducted a study of dogs with APN coming in to their clinics, and the study was conducted at the University of Melbourne Veterinary Teaching Hospital, which is a world class institution. For each sick dog studied, they studied two healthy dogs that were matched for body size for comparison purposes. A total of 27 dogs with APN were studied, along with a control group of 47 healthy dogs. Many small breed dogs were represented, including silky terriers, but no Yorkies.

I'll present the results with odds ratios. For instance, if the odds ratio is 2, that means that a dog with APN is twice as likely to be associated with the listed factor as a healthy dog. If the odds ratio is 70, that means that a dog with APN is 70 times as likely to be associated with the listed factor as a healthy dog. (I include the example of 70, because that's one of the shocking results.) If the odds ratio is 1, that means there is no association of the listed factor with APN. If the odds ratio is less than one (0.5 for example), that means that the factor is considered protective, because the dog with APN is half as likely to be associated with the listed factor as the healthy dog.

Results:

Campylobacter infection detected within 4 days of diagnosis: 12.4

Raw chicken in diet: 70.7 (!!!)

Raw meat in diet: 40.0 (!!!)

Contact with birds: 0.98 (no significant difference)

Vaccination within the past 6 weeks: 1.98

Access to outdoor water sources: 0.51

Use of pesticides: 1.83

Tendency to scavenge food: 0.75

Tendency to scavenge feces: 0.88

Outdoor access: 0.37

Rural: 2.44
Suburban: 1.65
Urban: 1.00

Female: 1.22

Neutered: 0.50

Large breed: 2.3
Medium breed: 1.0
Small breed: 6.2

weight > 20 kg: 1.0
11 to 20 kg: 3.38
7 to 10 kg: 5.03
< 7 kg: 7.31

I'll quote some of the conclusions verbatim:

We investigated a potential association between Campylobacter infection and APN in dogs. Other potential risk factors also were investigated, and a significant association was detected between dogs affected by APN and the consumption of raw chicken (with owners of 96% of APN cases reporting raw chicken consumption, compared to 26% of owners of control dogs). Thus, raw chicken in the diet is highly likely to increase the risk of developing APN in dogs in Australia. In addition, 48% of the dogs with APN were positive for Campylobacter infection compared with 23% in the control group. When a stringent case definition was applied (considering only cases in which the fecal sample was collected within 7 days from onset of the clinical signs), APN cases were 9.4 times more likely to have had a recent laboratory-confirmed episode of campylobacteriosis compared to control dogs (P < 0.001).

Previous studies have shown that exposure to racoons was the most common risk factor for dogs to develop APN in North America. However, it is unclear what triggers the immune response in dogs with no history of exposure to racoon saliva. Association with protozoal infections previously has been suspected. In a retrospective study investigating potential infectious origins, it was suggested that infection with T. gondii may trigger APN in dogs, as previously reported in humans. However, in a more recent study, only 1 of 14 APN dogs was positive for T. gondii Abs. In our study, APN cases tested for N. caninum and T. gondii all were found to be negative. Moreover, CK activity was within normal limits in most dogs (18/23). The other 5 dogs had mildly increased CK activity, which was interpreted to be a consequence of prolonged recumbency rather than neuro-myopathy. Studies in people have recognized the development of GBS after vaccinations against several pathogens within 6 weeks of receiving the injection. Recent vaccination also has been reported as a potential cause of APN in a dog. Only 1 of our APN cases had a history of vaccination within 6 weeks of hospital presentation. Overall, previous vaccination was not found to be a significant risk factor of APN in our study.

In our study, consumption of raw chicken meat was strongly associated with the occurrence of APN. Poultry is the most common source of C. jejuni infection in industrialized countries and, in retail surveys, C. jejuni is isolated relatively commonly from commercial poultry products. Therefore, contact with or consumption of raw or undercooked poultry products is an important source of exposure to Campylobacter strains associated with neurological diseases. Results from a study in New Zealand showed that food safety measures to decrease contamination of fresh poultry meat with Campylobacter spp. not only decreased incidence of campylobacteriosis but also were associated with decreased incidence of GBS. Transmission of Campylobacter may be prevented by improving sanitation, well-cooked poultry products and public health warnings about the hazards of raw chicken consumption. The presence of C. upsaliensis in commercial poultry has been reported to range from 1 to 9.7%, suggesting that chickens may be a source of emerging Campylobacter species.

A significant association was found between small breeds and APN. Based on our clinical experience, small dogs are more likely to be fed raw chicken because of the presence of small bones in the chicken which are easily eaten by these dogs rather than larger meat bones that may be fed to medium and large breed dogs. The association between breed size and APN may be explained by the hypothesis that small dogs are fed chicken necks and wings more frequently than are larger breed dogs. Genetic factors, as suggested in humans with GBS, also may be a factor in any breed differences in the incidence of APN.

Our study clearly demonstrates that consumption of raw chicken is a risk factor for dogs in the development of APN, and we suspect that Campylobacter infection is most likely to be an immunologic trigger as described in humans with GBS.

For me, the takeaway lesson is that feeding raw chicken (odds ratio of 70) and other raw meats (odds ratio of 40) is a high risk factor for the development of APN. The risk is likely to be reduced by cooking, good sanitation, and high quality control. Small breed dogs like Yorkies are at greater risk, probably because small dogs are more likely to be fed raw chicken necks rather than larger livestock bones, but they haven't ruled out a genetic component.