If you’ve ever had food poisoning, you know how unpleasant the symptoms can be. Did you know dogs can get food poisoning too? One of the most common causes in dogs and humans is Campylobacter. However, some recent findings have revealed that Campy infections in both species might not be as simple as we thought.
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What are Campylobacter and Campylobacteriosis?
Campylobacter is a Gram-negative rod-shaped bacterium. It is found in the guts of many domestic and wild animals as normal (commensal bacteria). However, they are also quite hardy and can survive for weeks or months in water. Some of the most common species include C. Jejuni, C. upsaliensis and C. helveticus.
In humans, campylobacteriosis, the disease caused by a Campylobacter infection, is one of the most common causes of food poisoning worldwide, with almost 250,000 cases confirmed (the actual number is likely higher) in Europe annually. Though the vast majority of people recover if they are healthy individuals it does kill hundreds every year. It mainly causes vomiting, diarrhoea, a fever and a headache, though more serious gastrointestinal symptoms do occur. There are also rare cases where it causes neurological disease, which we will get on to later.
How Do Humans Get Campylobacteriosis?
As stated above, most Campylobacter species are found in the gastrointestinal tracts of animals. Humans acquire Campylobacter via the faecal-oral route, or ingesting faeces from animals. This makes campylobacteriosis a zoonotic disease.
By far the most common source is from infected poultry
During processing of meat like chicken, the meat can become contaminated with the gut contents of the birds, including Campylobacter. This remains on the raw meat from the factory, to the shop and all the way home. If the meat is improperly cooked, the meat contaminates the home, or the person performs unhygienic practices like washing the meat, there is a high risk that Campylobacter on the meat makes its way into a human and causes campylobacteriosis.
Other sources of infection include contamination from other meat products, and drinking contaminated unpasteurised (raw) milk.
There have also been associations with drinking contaminated water or swimming in infected waters
This is particularly prescient at the moment with the UK’s widespread sewage contamination scandals. We also know that contact with wild animals and pets increase the risk too, especially owners of kittens and puppies – there has been at least one proven case where a young girl received a C. jejuni infection from a new puppy, and multiple outbreaks of the disease in the USA have been linked to puppies from a pet shop chain.
Studies have also shown that dogs fed a raw meat-based diet are more likely to shed pathogenic bacteria
And yes, this includes Campylobacter, which can increase the risk of people catching campylobacteriosis. Worryingly, some of the Campylobacter excreted by dogs has been multi-drug resistant, meaning it is harder to kill using antibiotics – the outbreaks in the USA linked to pet shops were multi-drug resistant Campylobacter.
In summary, while the majority of infections are from contaminated poultry, owning dogs does increase the risk of a campylobacteriosis infection in humans.
What is Campylobacteriosis in Dogs?
Dogs often have commensal Campylobacter (mainly C. upsaliensis) as part of their normal intestinal flora. This means that the majority of dogs have Campy at all times, yet do not become sick – the bigger risk is the zoonotic spread to humans
However, in certain cases, the bacteria can become pathogenic and cause disease. This mostly occurs in very young dogs, very old dogs, or those with a weakened immune system. It can also be seen alongside other pathogens, like coronavirus, rotavirus, roundworms and Salmonella as a mixed infection. As above, some studies have found evidence of Campylobacter in some raw foods, particularly those that have not been frozen, which may increase the risk of already vulnerable dogs getting campylobacteriosis.
Most dogs with campylobacteriosis have mild watery diarrhoea. Mucous can sometimes be seen. Dogs may also have abdominal pain, lethargy and a temperature.
Identifying infections of Campylobacter in dogs can be difficult because it is a normal bacteria for many dogs – looking at faeces under the microscope or utilising PCR to find Campy DNA can help with diagnosis. Often the disease is self-limiting, meaning no treatment is needed, though antibiotics like erythromycin or tylosin may be needed for severe infections. Other supportive treatment, like pre- and pro-biotics, bland food, binding agents and pain relief can help with the symptoms.
Campylobacteriosis and Neurological Disease
There is a rare neurological disease called Guillain-Barré syndrome (GBS) sometimes associated with campylobacteriosis. In simple terms, the body’s own immune system attacks the nerve cells, resulting in numbness, tingling and pain in the early stages, progressing to weakness of the arms and legs, and sometimes head. A quarter of people develop weakness of the respiratory muscles and respiratory failure, and some experience heart issues, with around 7.5% of cases being fatal. Many cases are self-limiting and people return to normal, though this can take months or years. Around 1/3 of people have permanent nerve damage.
Two-thirds of those with GBS had an infection before the onset of symptoms, and around 30% are linked to Campylobacter jejuni (although some cases have been linked to C. upsaliensis). There have also been links to other bacterial and viral infections, including COVID-19, following surgery, some drugs and some vaccines. Is it believed that all these conditions create a normal immune response to fight off infection or process a drug, but the immune response also happens to cross-react with the nerve cells as well, resulting in their damage and GBS.
Thankfully, the condition remains rare, at only 1-2 in 100,000 people per year.
GBS Syndrome in Dogs?
As far back as 1954, there have been cases of dogs with ‘coonhound paralysis’, a disease that showed very similar symptoms to GBS – since it occurred in dogs 1-2 weeks after a bite from a raccoon, it was associated with this. More recently, the disease has been further investigated, and is now called Acute Polyradiculoneuritis (APN) or Idiopathic Polyradiculoneuritis – from studies, we know that the nerve cells are attacked by the immune system, resulting in paresis, paralysis and respiratory impairment if severe. It seems to be more common in smaller dogs, but does affect all breeds.
As in humans, early studies showed the causes varied, with a number of experiments inducing neuritis in laboratory animals after injection of various substances. Most interestingly for today, in 1996, chickens were paralysed after being injected with C. jejuni isolated from a human patient with GBS. This was subsequently demonstrated in rats, guinea pigs and rabbits too.
In the last few years, there has been stronger evidence that Campylobacter and nerve damage might be linked
A 2018 study looked into APN in dogs – 27 dogs suffering from APN and 47 healthy dogs had their faeces tested to identify Campylobacter. They found that 13 of the 27 (48%) dogs with APN had Campylobacter in their faeces, though two samples could only identify the bacteria via DNA and not direct culture. This compares to 11/47 (23%) of the healthy dogs having Campylobacter in their faeces. Using their statistical analysis, this meant that APN-positive dogs were 9.4 times likely to have Campylobacter in their faeces when compared to healthy dogs. Most of these were C. upsaliensis.
More interestingly, based on an owner questionnaire and clinical history, 96% of the dogs with APN were fed raw chicken, with the final 4% having daily contact with chickens – only 26% of control dogs ate raw chicken. This meant that owners of dogs with APN were 70.7 times more likely to report their dog was raw fed than the control dogs. When flipped on its head, this may indicate that dogs fed raw chicken were more likely to get APN, though this is a big assumption. They confirmed that many of the APN dogs were small breeds, and noted that these were more likely to be fed raw poultry, when compared to larger dogs that were fed other meats.
A similar study of two dogs, both fed raw poultry for years, which both developed APN, found one was positive for C. jejuni on a faecal test – the latter was not.
Problems with the Studies
Both studies do unfortunately have some flaws that may reduce the reliability of their results. Firstly, the small sample size of 27 and 2 APN-positive dogs respectively, a tiny sample size compared to the overall population of dogs. The latter also did not have any healthy control dogs.
Secondly is the testing for Campylobacter in faeces. As mentioned above, C. spp. are commensal bacteria in dogs, meaning that many healthy dogs will carry the bacteria and not be unwell. Conversely, testing for campylobacteriosis in dogs does not always result in a positive faecal test, due to the way the bacteria shed and the timing of the sampling. This means not finding Campy in the stools does not completely rule out it being a cause of infection, while finding it may not always indicate it is the cause of infection.
Finally, there is the lack of association with APN and finding Campylobacter. We know Campylobacter is linked to GBS in humans, and there have been studies in laboratory animals that cause GBS-like symptoms, but we have no conclusive evidence that Campy causes APN in dogs. Finding Campy in the stools of APN-positive dogs does not prove or disprove that they are linked. The first study’s statistics were significant, as per their methods, but that is still not a conclusive proof that one caused the other.
Does Campylobacter Cause APN?
Based on preliminary evidence, there has been some statistical and incidental evidence that dogs with APN are more likely to have Campylobacter in their faeces compared to healthy dogs. This may indicate that, as in humans, Campylobacteriosis in dogs may result in an immune reaction that causes APN. Dogs fed raw poultry are more likely to have Campylobacter in their stools, meaning they may be more likely to develop APN. However, at this stage, no conclusive link can be proven, leaving the causes of APN in dogs unclear.
Summary:
- Campylobacter is a bacteria that causes food-poisoning in humans
- Campylobacter is a normal gut bacteria in many dogs, though it can occasionally cause gastrointestinal disease
- In humans, Campylobacter can rarely cause a neurological disease called Guillain-Barré syndrome (GBS)
- Campylobacter is a zoonotic disease, and owners of dogs are more likely to get Campylobacteriosis
- Raw meat, particularly poultry, is more likely to harbour Campylobacter
- Dogs that eat raw poultry diets excrete Campylobacter in higher numbers than dogs fed normal diets
- Owners of dogs fed raw poultry thus may be at a higher risk of getting Campylobacteriosis
- Dogs can get a similar disease to GBS called Acute Polyradiculoneuritis (APN)
- Small studies have found dogs with APN are more likely to have Campylobacter in their faeces
- Campylobacter may be one of the causes of APN in dogs
- Thus, dogs fed raw poultry may increase the risk of getting APN
- Further investigation is needed before any conclusive association with Campylobacter and APN can be made
References and further reading:
- Outbreak of Multidrug-resistant Campylobacter Infections Linked to Contact with Pet Store Puppies | CDC
- Multistate Outbreak of Multidrug-Resistant Campylobacter Infections Linked to Contact with Pet Store Puppies
- Occurrence of Campylobacter jejuni in Pets Living with Human Patients Infected with C. jejuni – PMC
- Neonatal Sepsis by Campylobacter jejuni: Genetically Proven Transmission from a Household Puppy | Clinical Infectious Diseases | Oxford Academic
- Raw pet foods: handling and preventing infection – GOV.UK
- Presence of pathogenic bacteria in faeces from dogs fed raw meat-based diets or dry kibble
- Raw Meat-Based Diets in Dogs and Cats – PMC
- Can Raw Dog Food Really Cause Nerve Damage? – Vet Help Direct
- Raw Meat-Based Diets in Dogs and Cats – PMC
- Why raw dog food could be harmful for pets and owners alike
- Acute canine idiopathic polyneuropathy. A Guillain-Barré-like syndrome in dogs
- Neuromuscular Disease – NDSR.
- Manual therapeutic plasma exchange for treatment of a dog with suspected acute canine polyradiculoneuritis | Acta Veterinaria Scandinavica
- Two cases of acute polyradiculoneuritis in dogs consuming a raw poultry diet – PMC
- Investigation of the Role of Campylobacter Infection in Suspected Acute Polyradiculoneuritis in DogsWebmedCentral.com :: Update On Guillain-Barre Syndrome-Like Conditions In Animals
- Is More Expensive Better for Dog Food?
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