Elias Papadopoulos DVM, MSc, PhD, Dip. EVPC, Georgios Sioutas DVM
Laboratory of Parasitology and Parasitic Diseases, School of Veterinary Medicine, Aristotle University of Thessaloniki, Thessaloniki, Greece
Raw diet feeding, which is the feeding of dogs and cats with raw uncooked meat products, appears to have originated in the beginning of the 1990s, when the Australian veterinarian I. Billinghurst wrote a book on the subject promoting the advantages of a raw meat diet for dogs (Billinghurst 1993). At the same time, use of the abbreviation “BARF” started, meaning “Biologically Appropriate Raw Food” or “Bones and Raw Food”, which nowadays is synonymous with raw meat diets, also commonly referred to as Raw Meat Based Diet (RMBD).
Feeding BARF diets aims in awakening the instincts of hunter-prey in domestic dogs and cats, considering that these are diets composed of raw meat, with high content in bones and visceral organs. Furthermore, fruit and vegetables, nuts, oils and herbs complement these diets in limited amounts together with eggs, fish and dairy products. The addition of grains in such diets is usually avoided, even though potatoes and legumes are allowed.
Reasons for which owners often turn to BARF diets for their pets include the desire for a more natural and healthy diet (Morgan et al. 2017, Morelli et al. 2019). Other reasons are chronic illnesses (such as gastrointestinal disorders, allergies and skin diseases) which owners hope to improve with a new diet, and the common belief among participants in research enquiries that commercial diets contain chemical substances and other components dangerous to their pet and that these are responsible for various disorders. This insecurity and mistrust drive them to seek better and “healthier” alternate diets, such as BARF.
The majority of the information received by raw diet supporters, mainly originates from the internet and non-scientific books (Morgan et al. 2017, Morelli et al. 2019). However, such sources are usually written by non-experts on the subject of animal nutrition, containing potential inaccuracies and misguiding information presented with a supposedly scientific manner in order to be more easily believable. In general, raw diet supporters present various claims regarding their advantages, which are usually based on unreliable and contradictory scientific data. In particular, the most common reported advantages include that the animal owner knows the origin and components of the diet, chemicals or other additives are not included, grains are avoided, and it is also claimed that cooking the diet reduces its nutritional value. Also, they claim that their pets have a smaller amount of faeces with improved texture, improved oral hygiene due to chewing, shinier hair coat and improved behaviour (Freeman et al. 2013, BARF World 2020).
On the other hand, there are several questions on the selection of a raw diet, such as nutritional imbalance (for example in protein content, fat, micro- and macronutrients). If inspection of such diets is not thorough, the presence of harmful components is likely. Furthermore, bone ingestion may cause injuries (fractures) on teeth, buccal mucosae, oesophagus (perforation or rupture), and in general throughout the gastrointestinal tract (constipation, ileus etc.) Beyond the aforementioned, the health risk from ingestion of raw meat is added, considering that they can contain various pathogens, such as viruses (hepatitis Ε, rabies, calicivirus, Aujeszky’s disease etc.), several species of bacteria (Coliforms, Escherichia, Salmonella, Campylobacter, Yersinia, Brucella, Listeria, Staphylococcus, Enterococcus, Clostridia) and parasites (Freeman et al. 2013, van Bree et al. 2018, Davies et al. 2019). In particular for parasites, it is possible to identify several protozoans and helminths (such as Toxoplasma gondii, Neosporum caninum, Sarcocystis spp., Cryptosporidium parvum, Giardia spp., Echinococcus granulosus, E. multilocularis, Taenia hydatigena, T. ovis and Trichinella spp.) (Freeman et al. 2013, Silva & Machado 2016, van Bree et al. 2018, Davies et al. 2019), which can be risk factors for infection for companion animals fed with RMBDs but also for their owners or any farm animals they may be farming. Moreover, dogs can be infected with a multitude of parasites after ingesting raw fish, such as Diphyllobothrium latum (fish tapeworm), Opisthorchis tenuicollis (trematode of bile ducts, pancreatic ducts and the small intestine), Dioctophyma renale (the giant kidney worm) and Nanophyetus salmincola (vector for Neorickettsia helminthoeca, the parasite responsible for salmon poisoning in dogs) (LeJeune & Hancock 2001).
Even though research studies regarding the risk of infection by the above parasites from raw diets is still limited, it is known that there is risk of parasitic infection for humans and farm animals from dogs and cats shedding and spreading the parasites in the environment. The common practice of freezing raw meat prior to ingestion helps in destroying most of the aforementioned species of parasites, however the efficiency of purification from parasites highly depends on parasite species and conditions (temperature and duration) of freezing (Pet Food Manufacturer’s Association 2017).
Among the protozoans transmitted through meat, the protozoan Toxoplasma gondii, is a common cause of zoonosis. Infection of humans and animals occurs through ingestion of raw or undercooked meat (with parasitic cysts), but also through infected wild-growing fruit and vegetables contaminated with oocysts from cat faeces. Furthermore, there is research evidence proving that cats fed with BARF diets have higher seropositivity rates and shed a higher number of oocysts of T. gondii in their faeces (Lopes et al. 2008, Coelho et al. 2011, Jokelainen et al. 2012, Freeman et al. 2013), whereas there is also the possibility of direct owner infection due to handling raw meat (Macpherson 2005). Therefore, owners also face a high risk of infection by T. gondii with raw diets. In a research study made in Denmark, in which the presence of the parasite in raw meat was detected by PCR, 6% of frozen commercial BARF diets were positive for T. gondii (van Bree et al. 2018). In the USA, the parasitic load of commercially sold meat is generally low, however it is sufficient for causing active toxoplasmosis in cats fed with RMBDs (Dubey et al. 2005). It has been experimentally proven that freezing in -20°C for at least three days is necessary in order to neutralise toxoplasma cysts in meat tissues, so as to reduce the parasitic load and the meat can be assumed as non-contaminated (Mirza Alizadeh et al. 2018). The main prevention method from T. gondii infection of food origin is cooking meat at least 67°C even for a few seconds, because in this way cysts are destroyed. Furthermore, measures must be undertaken in order to avoid contact between cooked and raw meat (Mirza Alizadeh et al. 2018).
Rarely, the protozoan Neospora caninum can be an infectious risk for dogs, which are the definitive hosts for the parasite when they consume raw meat. When its life cycle is completed, dogs shed the parasite to the environment and these infect farm animals (mostly cattle resulting in abortion) (Stoker 2013, Silva & Machado 2016). In a study conducted in Germany, 37.5% of Neospora seropositive dogs had been fed a diet with fresh raw meat which had undergone no thermal processing (Villagra-Blanco et al. 2018). Even though there are no specific research studies, the way of preventing infecting domestic dogs is the same as for Toxoplasma, meaning freezing in -20°C for at least three days and then cooking meat at least 67°C, even for a brief time.
Another protozoan which may cause zoonosis and infect dogs and cats fed RMBDs as definitive hosts, is Sarcocystis spp.Dogs consistently fed with raw meat are frequently infected by the particular protozoan (LeJeune & Hancock 2001) and can shed oocysts of the parasite in their faeces for several months, infecting the environment and therefore increasing the risk of infection for farm animals living in the same space. When cattle, goats and sheep or pigs that are the intermediate hosts, swallow the parasite that can be found in the environment, clinical disease can develop leading to severe financial losses (Hornok et al. 2015, Mirzaei & Rezaei 2016). Even though humans can be infected by certain species of the genus Sarcocystis, it rarely manifests as clinical disease. In a research study conducted in the United Kingdom, PCR was performed in 35 commercial frozen RMBDs, S. cruzi was detected in 11% of diets based on bovine meat, and S. tenella was detected in another 11% of diets based on bovine or sheep meat (van Bree et al. 2018). Freezing or cooking in temperatures and duration that were previously mentioned for Toxoplasma and Neospora seem to be the best methods for preventing food-borne companion animal infection (Gestrich & Heydorn 1974).
Cryptosporidium spp.is a protozoan that can be detected in RMBDs and can infect dogs and cats. Clinical disease varies from asymptomatic to chronic diarrhoea. Even though it can potentially result in zoonosis, most species of the parasite are host-specific, therefore when inappropriate hosts (such as humans) are exposed to C. canis and C. felis that are species-specific to dogs and cats, respectively, infection is unlikely, with the exception of immunosuppressed individuals. Humans are usually infected by C. hominis which occurs only in humans and C. parvum which also infects other animals, but not dogs or cats (Lucio-Forster 2010). In a research study conducted in the USA, in commercial BARF diets, genetic material of Cryptosporidium spp.was identified in 2.11% of samples obtained that had raw bovine meat or raw turkey meat as a basic component in canned food form (Strohmeyer et al. 2006). The elimination of C. parvum was experimentally obtained by freezing in -20°C for one hour or by cooking in 70°C for one minute (Rose & Slifko 1999).
Regarding the risk of infections with metazoan parasites, such as helminths, Echinococcus granulosus is a common cestode in our country that can infect dogs after ingestion of RMBDs and is a considerable threat to public health. It has an indirect life cycle with dogs (or other carnivores) as definitive hosts and sheep (or other farm animals such as goats, cattle, pigs) as intermediate hosts. Definitive hosts that are infected with the adult form of the parasite in the small intestine, shed proglottids or eggs through their faeces in the environment, which are ingested by the intermediate hosts where hydatid cysts are developed. Dogs and cats therefore become infected when they ingest these cysts in contaminated raw meat or visceral organs. Dogs and cats that are infected with Echinococcus spp. usually do not show clinical signs and remain asymptomatic (Companion Animal Parasite Council 2020). However, they increase the risk of zoonosis, because humans are intermediate hosts and eggs shed in the faeces survive for months in the environment under the appropriate conditions and can easily infect humans and evolve to hydatid cysts in the liver and lungs. Even though there are no safe guidelines to destroy hydatid cysts in raw meat, in a research study that evaluated their elimination by freezing or heating, it was noted that freezing in -18°C for three hours was ineffective (87.28%) in killing the scolex found inside the cysts. In contrast, freezing in -18°C for 6 and 9 hours was highly effective (Koutsoumanis et al. 2018, Mokhtaria & Ammar 2019).
Finally, other significant parasites, such as species of the genera Trichinella and Taenia, are usually not identified in commercial raw diets, because of the mandatory European Legislation for meat inspection and elimination of Trichinella- infected carcasses these do not enter in our food chain (EC Regulation No 854/2004 and No 2015/1375).
In conclusion, pathogenic microorganisms that can endanger animal and human health can be identified in RMBD diets. Specifically, for parasites, they can be found when raw diets with tissues of animal origin are inappropriately frozen.
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