Raw pet food as emerging source of human infection

In August 2017, four people were infected with related strains of Shiga toxin-producing E. coli (STEC) O157:H7* in the United Kingdom. One person died after developing the kidney complication known as hemolytic uremic syndrome (HUS).

Three people of the four had been exposed to dogs fed on a raw meat-based diet (RMBD), specifically tripe. In two cases, tripe was bought from the same supplier.

Feeding raw meat to pets has increased in popularity because of improved availability and the belief it has health benefits. However, raw pet foods could cause human illness if tainted products are handled or via secondary transfer from contact with contaminated surfaces.

A review of exposures to raw pet food among more than 2,000 STEC cases from January 2013 to December 2017 found handling raw pet food was reported for 12 patients. Nine were infected with STEC O157:H7 and three with serogroups O76:H19, O113:H4 and O146:H21.

A team of scientists in the Netherlands also tested for the presence of zoonotic bacterial and parasitic pathogens in raw meat-based pet foods across different brands in 2018, and found E. coli O157:H7 in 23%, Listeria monocytogenes in 54% and Salmonella in 20% of the samples.

In a two-year study spanning from October 2010 through July 2012, the FDA Center for Veterinary Medicine (CVM) screened over 1,000 samples of pet food for bacteria that can cause foodborne illnesses.

Many of the analysed raw pet foods contained Listeria monocytogenes. Of the 196 raw pet food samples analyzed, 15 were positive for Salmonella and 32 were positive for L. monocytogenes.

Clinically healthy companion animals can carry Salmonella, Listeria and Campylobacter. Raw meat-based diets may be a possible source of bacterial infections by Salmonella and certain E. coli strains, and, if transmitted through the intestines, pose a zoonotic risk for human beings.

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*Shigatoxin-producing E. coli (STEC) is a group of bacteria that cause human disease. They are characterized by the presence of shigatoxin-producing genes. STEC O157:H7 is a major public health concern because of the potential severity of the disease. Symptoms can range from mild diarrhea to abdominal cramps to vomiting and severe bloody diarrhea. In 5-15% of cases, a serious complication, the so-called haemolytic uraemic syndrome (HUS) may develop. The risk of developing HUS is age- and sex-dependent; most common in children under 5 years of age, and may cause acute renal failure. Although HUS is extremely rare, it can be fatal, especially in infants, young children, and the elderly.

Antimicrobial resistance (AMR) transmitted in dog food

Scientists from the University of Porto analysed (dry, raw, pet) dog foods in 2021, and Enterococcus species of bacteria were found in more than a half of the samples. More than a third of the enterococci strains demonstrated resistance to multiple antibiotics, and in excess of 20% were resistant to linezolid, a “last-resort” antibiotic that is used when all other treatment options have failed.

The researchers said the trend for feeding dogs raw food might be fuelling the spread of antibiotic resistant-bacteria.

Drug-resistant infections kill an estimated 700,000 people a year globally and, with the figure projected to rise to 10 million by 2050 if no action is taken, the World Health Organization (WHO) classes antibiotic resistance as one of the greatest public health threats facing humanity. Yet among microbiological hazards, “… antibiotic-resistant bacteria (ARB) and genes with public health impact remain scarcely studied among pet food,” the scientists stated.

DCM (dilated cardiomyopathy) in dogs eating certain „grain-free” pet foods

In July 2018, the FDA announced that it had begun investigating reports of canine dilated cardiomyopathy (DCM) in dogs. DCM is a special disease of a dog’s heart muscle and results in an enlarged heart. As the heart and its chambers become dilated, it becomes harder for the heart to pump, and heart valves may leak, which can lead to a buildup of fluid in the chest and abdomen — congestive heart failure. Dilated cardiomyopathy is recognized as a genetic condition in dogs, typically in large or giant breeds, such as the Golden Retriever, but it had also occurred in other breeds in increasing numbers.

Between January 1, 2014 and July 31, 2020, the FDA received more than 1100 case reports of diagnosed dilated cardiomyopathy in dogs. More than 280 of those dogs were reported to have died. Of the approximately 20 cat reports, there were approximately 13 cat deaths.

FDA announced first in 2018, that consumption of grain-free pet foods may be associated with the occurrence of the disease. A majority of the dogs diagnosed with non-hereditary DCM had received a diet rich in pulses and legumes. FDA also named 16 pet food brands in 2019 summer, presumably linked to the disease cases of dogs. Although legumes had been used in pet food for many years, data showed their increased presence in grain-free products. However, cases were both linked to consumption of grain-free or grain-containing diets. After many years of investigation, there is no convincing evidence that these special diets are unsafe.

Update

In a more recent Canadian study published in May, 8 beagle dogs were fed traditional and high-lentil and high-pea grain-free diets for 28 days. The beagle was chosen because its susceptibility to DCM was not previously known. The authors observed DCM-like changes in dogs fed high pea-containing foods. The condition of the dogs starts to improve if they return to their traditional diet.

The FDA says the adverse event numbers do not yet supply sufficient data to establish a causal relationship with reported products. No pet food has been recalled and no further public updates are planned until meaningful new scientific information can be shared.

According to a veterinarian, the following symptoms indicate that a dog is developing heart failure: decreased activity, tiredness, lethargy, coughing, shortness of breath, and decreased appetite. The detection of a protein called BNP in a blood test also proves that the heart muscle is damaged.

Dog owners are advised to avoid pet foods with peas, lentils, chickpeas, potatoes or sweet potatoes in the first 10 ingredients.

Veganism as a new trend

Keeping the companion animals (dogs, cats) on a vegan diet is increasingly popular. Often, pet owners themselves live a vegan diet.

Mars announced in December 2019 that, for environmental reasons, it would produce meat-free foods for dogs and cats. They planned to substitute chicken, beef or rabbit meat with plant-based ingredients with protein content.

Is it really good to give only plant-based food to our pet?

The dog’s closest wild relative, the wolf, also consumes plants. Of the fecal samples from wolves in Yellowstone Park, 74% contained plant material. Domestication of dogs from wolves began much earlier than that of cats, and over time, as they consumed the remains from what humans ate, their bodies became more and more adapted to digesting plant-based food (besides meat and other animal foods, of course). The dog has now acquired a number of genetic changes that make its life different from ancient wolves (e.g., the appearance of the amylase enzyme and the different structure of the maltase enzyme make the digestion of starch more efficient). It tolerates the plant diet well, but only to a certain extent. There are no known benefits of an exclusive plant diet. Prolonged vegan feeding leads to deterioration of its condition and eventually the death of the dog.

The cat, on the other hand, has always remained a carnivore, being kept by man because of its predatory nature. Feeding it with plant food quickly leads to nutrient deficiency and death. For example, cats can only absorb certain vitamins and nutrients from food of animal origin. Cats need practically only protein and fat from food, not carbohydrates. Consumption of the latter leads to obesity and type 2 diabetes.

High content of vitamin D in dog food

Dog foods were recalled in the United States due to elevated levels of vitamin D. Fat soluble vitamins can be easily overdosed by dogs in case of supplementing as most of the quality dog foods are enriched with vitamins.

Many pet owners don’t take this fact into account, and give high amounts of food to their dog. This results in frequent overdoses of fat soluble vitamins. The vitamin is taken up by the liver of the dog, and can’t be quickly eliminated. Overdoses of vitamins A and D are frequent. 

Cat foods linked to feline pancytopenia have been recalled

Since April 2021 there have been over 130 cases of feline pancytopenia in the United Kingdom. Pancytopenia is a very rare condition where the number of blood cells (red, white and platelets) rapidly decrease, causing serious illness, that can often be fatal in cats. Certain dry cat foods have been recalled as a precautionary measure. The link to the diseases could not be proved.

Pet food contaminated with aflatoxins has killed several pets

Pet food heavily contaminated with aflatoxin was recalled in the US in 2020-2021. More than 100 dogs died upon eating from the product. These news were shared on our website.

Severe liver disease and death of dogs in Australia

17 dogs died in severe liver disease in Australia in July 2021. They were suspected to have ingested a toxin called indospicine.

Indospicine is a naturally occurring hepatotoxin (toxin that causes liver damage) found in plant species from the genus Indigofera, which usually grows in outback areas for grazing. Indospicine residues accumulate in the tissues of grazing animals such as cattle, camels and horses, and can persist in tissues for several months after exposure.

Dogs are particularly sensitive to indospicine. Prior to a detection of indospicine in Victorian dogs in 2021, there had also been – albeit in only 2 instances - previously reported cases of consumption of horse or camel meat containing indospicine resulting in the illness and death of dogs.

By 27 September 2021, 68 dogs had been reported ill in this case, and 26 of them died. Indospicine was detected in the dog foods collected from the concerned owners. The analysed pet foods originated from the same knackery.

During the investigations it was found that the property owner of the grazing land in Northern Territory sold 26 free-roaming, semi-domesticated horses in May, which were carried to the knackery in May-June 2021.

Blood samples were taken from 3 horses remaining at the grazing land, which resulted in high levels of indospicine. Indospicine was also detected in 6 of the 7 pet foods analysed. These pet foods contained horse meat, which 2 owners were even unaware of. The risk of indospicine can’t be eliminated by heat treatment.

Deadly disease of dogs in Norway

A mysterious illness spread among dogs in September 2019 in Norway. Approximately 200 dogs had the same symptoms (vomiting, bloody diarrhoea), of which about 25 died. The diseases were reported mainly from around Oslo. Necropsies performed on 10 carcasses had shown serious infection of the intestine. In five cases, abnormally elevated presence of Clostridium perfringens and Providencia alcalifaciens were detected, but neither of them were confirmed as the source of the diseases.

Based on the latest information from 2021, Providencia alcalifaciens was the most likely source of the outbreak, however, this could not be confirmed by epidemiological investigations. Further studies are needed to investigate the disease-causing properties of P. alcalifaciens in dogs. In the meantime, the outbreak has ended.