The raw end of the deal: the risks of bacteria in raw pet food

A raw meat-based diet (RMBD) has become increasingly popular for household pets, and has been posited as a “more natural” alternative to mass-produced processed feeds in wide use today. While RMBDs can serve as a nutritious option for our pets, owners should be aware of the health risks posed to pets and owners alike if raw feeding is undertaken irresponsibly.

Chief among the risks associated with RMBDs is the propensity of raw meat to carry pathogenic and parasitic microorganisms, not eliminated or inactivated by a cooking process, which can pose a risk not only to the pet, but also to their owners and others around them. One of the most prevalent pathogens carried by raw meat are bacteria. While these present a risk of transmission from pets to humans, much of the risk can be minimised by implementing good hygiene practices at home. Although a RMBD can be a divisive matter for those for and against it, it is important to remember the common goal of all concerned is ensuring that our pets, and the people around them, are kept as safe as possible.

What are the benefits of a raw meat diet?

RMBDs include uncooked animal meat, by-products and/or bone, and can be prepped at home or acquired commercially. Having accelerated in popularity in recent years, RMBDs have been endorsed as a more natural alternative for household pets. Claimed benefits of adopting a RMBD over conventional pet food include improved dental and skin/coat health, improved organ health and behavioural improvements – but what evidence is available to support this?

There have been various reported benefits of a RMBD and one of the more robustly proven benefits is improvements to digestion, stool quality and gut microbe diversity. In one study, raw-fed dogs displayed greater bacterial diversity in their stool compared to those fed upon conventional processed food (Kim et al., 2017). This has been demonstrated in cats too: kittens raised on a RMBD showed better stool quality, assessed with a visual grading system, than their contemporaries fed a commercially prepared diet (Glasgow et al., 2002).

Beyond improved stool and microbial diversity, much of the evidence surrounding other health benefits of RMBDs are largely anecdotal

How does a better gut microbe diversity improve pet health? The advantages gained are not fully understood, but research into its effects in veterinary and human physiology is growing exponentially, and gut microbes are showing to have a profound influence upon various body systems. Testament to the benefits of gut biome diversity in pets are studies showing dogs with chronic enteropathies benefitting from faecal transplantation.

Beyond improved stool and microbial diversity, much of the evidence surrounding other health benefits of RMBDs are largely anecdotal. Notwithstanding, there are several plausible claims including that RMBDs can reduce inflammatory markers and benefit dogs suffering from atopic skin disease, and dental advantages owing to demonstrated benefits in zoo animal studies. We know that there are proven benefits of RMBDs, but more peer-reviewed studies are required to back up many of the claimed benefits.

Do pets need a raw meat diet?

Meat and animal products can be a great source of nutrition for household pets. Dogs are omnivorous and can absorb all of their essential amino acids through meat or plant-based food; however, cats are obligate carnivores – meaning that meat is an essential part of their diet – but what about raw meat?

Home-prepped RMBDs can be particularly susceptible to nutritional imbalances, as recipes are not always formulated with optimum nutrition in mind

The raw meat diet of wild species related to household pets has been a common rationale for those who choose a RMBD for their pet. Wolves, for example, have a limited capacity to absorb carbohydrates, one of the main foodstuffs found in conventional dog foods. This may be an unhelpful parallel, though, as modern domesticated dogs and cats have altered genetically from their wild ancestors, and their lifestyle has changed significantly, meaning that they require a different, more relevant range of nutrients in their diet.

Studies into the nutritional content of some commercial and home-prepared RMBDs have identified potential problems including calcium/phosphorus imbalances and vitamin deficiencies (Freeman et al., 2013). Home-prepped RMBDs can be particularly susceptible to nutritional imbalances, as recipes are not always formulated with optimum nutrition in mind. Commercial raw pet food isn’t perfect either – some have been formulated without the benefit of feeding studies. Great care should be taken, therefore, to ensure that when choosing any diet, and especially when adopting a RMBD, all of a pet’s nutritional needs are met. Particular attention should be paid to life-stage and any additional health considerations, which may include the addition of supplements into the diet.

The bacterial risks of raw meat diets

The bacteriological quality of raw commercial pet foods doesn’t match up to the high standards required for products for human consumption, and measures such as total bacterial or coliform counts regularly exceed quality thresholds. This, coupled with the presence of pathogens and increased likelihood of antibiotic resistance, can pose a risk to the pet and owner alike. Some of the most prevalent bacterial pathogens associated with RMBDs are set out below.

Salmonella

Of any bacteria found in raw meat, Salmonella spp. (Figure 1) present the greatest risk of transmission from pets to humans. The proportion of Salmonella-containing raw meat pet products has been reported as high as 20 percent, and where pet food is contaminated, humans can pick up Salmonella via handling the contaminated food, direct contact with the pet (eg licking) and contact with Salmonella shed in faeces. Where Salmonella is shed in this way, vulnerable people in the household, such as children, the aged or the immunocompromised, carry a risk of developing severe effects from Salmonella infection.

E. coli

E. coli species from livestock are a common source of antimicrobial‐resistance genes, some of which can be readily transmissible to pets and their owners

Like Salmonella, viable Escherichia coli (Figure 2) is also highly prevalent in raw meat pet products. E. coli is universally present in source animal species and plant matter can also easily become contaminated from wildlife sources. There are a number of E. coli subtypes that are pathogenic to humans and can pass from pet to human via the same direct and indirect routes as Salmonella.

Of particular concern, though, is the presence of antibiotic-resistant E. coli strains. Heat treatment is a critical control step in the elimination of bacteria from livestock sources, and this is not available to producers of raw food. E. coli species from livestock are a common source of antimicrobial‐resistance genes, some of which can be readily transmissible to pets and their owners.

Campylobacter and Listeria

Unlike the above, Campylobacter and Listeria can be killed by freezing; however, Listeria will thrive at fridge temperatures. While the risk of transmission is low, it should be noted that infection in humans can have profound effects. It is especially dangerous in pregnancy, as infection can induce abortion and birth abnormalities.

Diagnostic support

An in-house veterinary PCR analyser can help veterinarians rapidly diagnose infections of the main pathogens associated with raw feed diets that can cause issues. HORIBA’s POCKIT Central benchtop PCR system automates the PCR testing process for up to eight pathogens simultaneously and can support veterinary practices in rapid diagnosis. The system offers over 190 simple cartridge-based PCR assays, including for raw feed diet-associated pathogens such as E. coli and Salmonella.

Minimising the risk of infection

Despite the evident risk of bacterial transmission from pets to humans where a RMBD is adopted, the incidence of disease is sporadic. That said, while bacteria pose a low risk to healthy adults, the consequences of infection to vulnerable individuals can be severe – including miscarriage in pregnancy, or hospitalisation and death in the immunosuppressed, as highlighted above. It is imperative, then, for owners to be made aware of the risks involved and how to negate them.

Good hygienic practice

The most effective way of reducing transmission of bacterial pathogens from raw-meat-fed pets to humans is to implement good hygienic practice at home. It is recommended that owners adhere to strict routines, including:

• Rigorous hand washing – hand washing with hot water and soap should be undertaken following handling raw meat (and packaging), petting your companion animal and picking up faeces. Also, handwashing should be undertaken more frequently throughout the day generally
• Appropriate storage and handling – it is best to keep raw food frozen and to defrost it at the bottom of the fridge in a leak-proof container. Food should never be refrozen; any uneaten raw meat should be removed and carefully disposed of as soon as the pet has finished eating
• Regular disinfecting of surfaces – this should be carried out immediately after each feed and separate wash bowls and utensils are also recommended for raw pet food

Education and clear information

Many raw pet foods from commercial outlets often lack package warnings about preparation and hygienic handling, and as such, owners can be unaware of the inherent risks. Veterinary staff should inform pet owners of the importance of good hygienic practice, and empower those opting for a RMBD with reliable, up-to-date information and resources, such as those provided by UK Pet Food (formerly the Pet Food Manufacturers’ Association (PFMA)) and PDSA. When conversing with owners considering a RMBD, it is important to have a calm, informative conversation, as opposed to an argument – this is never helpful, and unlikely to be convincing.

Veterinary staff should inform pet owners of the importance of good hygienic practice, and empower those opting for a RMBD with reliable, up-to-date information and resources

One thing that is also worth remembering is the fact that while a parasite may be isolated in a raw food product, and even destroyed during the physical preparation steps, the production processes for pet food manufacture including mincing and mixing may mean that bacteria can be spread throughout a whole batch of food. This can apply to all products, whether raw or mass-produced processed feeds.

Check for vulnerable household members

Where owners are considering adopting a RMBD, veterinary staff should always check whether there are any pregnant or vulnerable individuals living in the same household. Where this is the case, owners should be made aware of the increased risk of bacterial infection and the consequences this could bring. Providing good-quality resources as suggested can enable owners to make well-informed choices about feeding.

Dietary advice: a prescribing decision?

For veterinarians, dietary advice can indeed be viewed as a prescribing decision and should be treated as such – all advice given should be both objective and evidence-based. However, one of the main issues remaining regarding a RMBD is the current lack of scientific data or longitudinal feeding studies to back up the claims made by raw pet food manufacturers. In any case, pet food manufacturers and veterinarians alike should strive to provide as much information as possible regarding the bacterial risks posed by raw meat products, and how these can be negated by implementing good hygienic practice at home.