Zoonotic bacteria and parasites found in raw meat-based diet for cats and dogs; a Critique
Critiqued paper: FPJ van Bree et al. Zoonotic bacteria and parasites found in raw meat-based diet for cats and dogs Vet Rec 182 (2), 50. 2018 Jan 13.
Critique by Nick Thompson BSc.(Hons) Path.Sci., BVM&S, VetMFHom, MRCVS.
Overall, this introduction is a catalogue of speculation and conjecture, suggesting the hypothesis of the entire paper is build on very shifting sands. One could interpret the introduction a case of ‘raw feeding may work in practice, but does it work in principle?’
- The authors state ‘It has been estimated that 51 per cent of dog owners in the Netherlands feed their dogs entirely or partially with raw meat-based products.1 Given that 36 per cent of households in the Netherlands own either a dog or a cat, it is possible that RMBDs are used in more than one million Dutch households.
Given this statistic, and the levels of zoonotic bacteria and parasites found in this one-off study, it is surprising that so few cases of animal (other than two cats 15 years ago, some historical cases of greyhounds in kennels and one report of some puppies, all with Salmonellosis) or human infection from raw food/raw fed pets are mentioned in the paper or any of the 59 references.
- Hyperthyroidism is quoted as a risk when feeding raw meat based diets (RMBD). A single case is quoted in the ‘Hyperthyroidism in a dog after raw meat feeding’ paper.
- Equally specious is the claim ‘and injuries such as gastrointestinal tract perforation’ are well recognised from raw bones in RMBD.
- This is not the case. They quote the Freeman et al, 2013 review paper, who themselves site four papers totalling 229 cats and dogs with foreign body obstructions. A word search of these four papers reveals the the word ‘raw’ was not mentioned at all.
- The authors continue in the next paragraph with ‘these diets are often deficient in several nutrients and may therefore lead to serious health problems, especially in young animals that are growing.’ They quote only one review, Schlesinger and Joffe, 2011 who say on the subject: Nutritional osteodystrophy was reported in 2 litters of 6-week-old large breed puppies fed a bones and raw food (BARF) diet from about 3 wk of age (from 2002). Nutritional secondary hyperparathyroidism has also been reported in a litter of German shepherd puppies fed a diet of 80% rice with 20% raw meat. The diet contained excessive amounts of phosphorus (from 1993). Not all puppies fed the diet experienced problems, suggesting individual or genetic susceptibility. I hardly think that three litters of puppies in 25 years constitutes an epidemic of nutritional disease caused by raw food feeding. Actually, given that some people feed raw food so badly, I’m surprised the reports are not more frequent.
- The following sentence is then offered: ‘The spread of such bacteria and parasites in the environment, either directly from contaminated RMBDs or by animals infected through consumption of RMBDs, represents a risk for the human population.’ Two papers are quoted. The first by Lejeune et al, 2001, mentions the word ‘risk’ 16 times. In none of these cases is the risk actually quantified or substantial evidence given for actual risk in the real world. It is a mostly speculative paper (if x, then surely y etc). The second paper by Jennifer Lenz et al in 2009 describes ‘Responses to a questionnaire probing practices and beliefs regarding raw meat feeding that was administered to dog owners demonstrated that dog owners may either not be aware or refuse to acknowledge the risks associated with raw meat-feeding; thus, they may neglect to conduct adequate intervention strategies to prevent zoonoses among themselves and their families.’ This is pure speculation without a shred of evidence to back it up.
- The authors continue,’Other bacteria that have a possible impact on human health and that have been isolated from RMBDs include enterohaemorrhagic Escherichia coli (including the serotype O157:H7, which may cause renal failure in human beings), Listeria monocytogenes18 and Brucella suis.’ And yet no clinical cases reported from RMBD.
- Anti-biotic resistant species of bacteria are mentioned and this is a worry in any medical context. I feel some of the blame should rest on the meat production industry and the overuse of antibiotics in farming. The raw feeding community cannot solely shoulder the responsibility here.
- It was heartening the see mentioned that Campylobacter spp were not found in any of the RMBD researched in the three papers cited in the Introduction to this paper. They rightly state that Campylobacter is labile at very low temperature storage conditions.
- Although only Sarcocystis spp and Toxoplasma gondii parasites were studied in this paper, the authors are at pains to mention a host of other parasites for some reason. Is this scare-mongering? I think this is inappropriate in a scientific paper, especially in the Introduction.
Materials and Methods
- Sample collection seems reasonable (choosing the most common in Utrecht). Storage, too, seems reasonable, but the time from purchase to storage is not noted, unfortunately. If this period was extended, and foods defrosted before storage, this would prejudice bacterial numbers.
- Most raw-feeders do not defrost frozen meat under the tap, in my experience. The most common methods are defrosting in the fridge overnight, or at room temperature. It is possible rapid defrosting influenced bacterial numbers. It is noted that ‘processing’ for analysis took place at 0-4 degreesC.
- Products containing only meat/by-products should not, in my opinion, be sold as ‘complete’ or ‘complete and balanced’ foods. This label should only apply to products having been analysed to comply with FEDIAF/AAFCO regulations, in my opinion. There are limitations with following these guidelines and I have reservations, but it establishes a benchmark, a minimum standard to which the raw food industry should aspire.
- Warnings were only found on one brand in the study. I believe all raw food, whether for human or animal use, raw or intended to be cooked, should have handling instructions for optimum hygiene for both owners and pets.
- Sarcocystis and Toxoplasma DNA were found in the products. The researchers confirmed (personal communication Feb 2018) that they did not believe these organisms to be viable. Both are killed by freezing at -18degreesC.
- It must be well noted that the authors state ‘The low sample size and no randomised selection in this study do not allow generalisation of infection rates or to perform a risk analysis’.
- Mention is made of pathogen contamination, quoting two studies. In the first: ‘This is in contrast with dry, semimoist and canned pet food, which is rarely contaminated with pathogens’. Both studies mention finding bacteria in raw (and processed) foods, but mention is not made of real-world risk. i.e. finding one E.coli in your food means it’s contaminated, but finding a billion is a completely different matter. Work needs to be done on real-world risk. The second study, the Strohmeyer paper in JAVMA is wholly and typically biased. 20 raw foods were compared to just two dried foods and two canned foods. Pathogens, interestingly and somewhat surprisingly, were found in the canned products. This is surprising because the heat processing should render all canned goods pathogen free. If pathogens were found in such a small sample of canned pet food, it could be induce that much of the canned pet food available in the USA could be potentially contaminated. I am surprised this has not been followed up by the AVMA who are otherwise keen to find fault with potential infectious disease derived from raw food feeding. Risk of raw food feeding to owner or pet was not quantified in either paper.
- It is noted that ‘The overall microbiological quality of the commercial RMBDs tested in this study was acceptable since none contained more than 5×106 cfu total aerobic bacteria/g meat, and only two contained more than 5×105 cfu/g’. However, spurious and unhelpful comparisons are made between raw food contamination levels and human food bacterial thresholds, where the food/meat is most likely to be cooked.
- The authors list direct and indirect means of contamination from raw pet food. These equally apply to all households, even vegetarian homes!
- Interestingly, the authors note ‘While most cases of E coli O157:H7 infections in human beings have been associated with raw or undercooked beef, cats and dogs are known to be short-term shedders of these bacteria’. They are unable to show any evidence for infection of animals or humans as a result of raw food feeding.
- In a similar vein, they are only able to note one paper where Salmonella has been implicated in infection of two cats. Many felines are fed raw in Europe, USA and the Antipodes.
- Three papers are quoted to demonstrate that ‘RMBD have also been identified as a source of gastroenteritis in greyhounds’. This is disingenuous as Salmonella is found in dogs fed many different foods (Arsevska E et al., Small animal disease surveillance: GI disease and salmonellosis. Vet Rec. 2017 Sep 2;181(9):228-232.). Salmonella is also referenced as causing diarrhoea in puppies. The paucity of reports for what they suggest is such a widespread infection problem in raw food (20% of food sampled) begs the question that finding bacteria in food and risk to pets and people may not be correlated.
- The authors imply a review paper has ‘shown that direct contact with pets plays a major role in human salmonellosis’. This is not the case. The abstract from the review says: ‘Reviewed results suggest that illnesses and outbreaks are most commonly attributed to exposure to contaminated food, and that eggs, broiler chickens, and pigs are among the top sources. Although most source attribution studies do not attribute salmonellosis to produce, outbreak data in several countries suggest that exposure to raw vegetables is also an important source. International travel was also a consistently important exposure in several studies’. Therefore banning vegetables and international travel might be a good idea before targeting raw food feeding in cats and dogs where actual risk to pets and owners is unknown.
- Dried pigs ears and chicken jerky pet treats are noted as having Salmonella contamination. Depending on how they are produced, they may not be raw, i.e. uncooked, therefore should not appear in this paper without explanation.
- Antibiotic resistance is of concern to humans and pets. The Schmidt et al paper (2015) is quoted where 73 healthy Labradors were tested for antibiotic resistance in stool bacteria. Raw meat feeding was considered to be a significant risk factor in this small study. We must remember that this is not a function of feeding raw meat as such, it is a side effect of the UK meat industry producing meat products high in bacteria with antibiotic resistance, which is a completely different discussion – one that needs to be had and needs further study.
- Parasite (Sarcocystis and Toxoplasma) DNA was found in the samples, but, as the authors note, this poses no risk to owner or pet if the food is frozen at -20degreesC for 48 hours, as would be the case with most commercial meats/diets. Emphasis should be made to owners that if fresh meat is bought from supermarkets or similar, that freezing for at least 2 days is essential before feeding.