Wednesday, July 13, 2016

Health risks of being licked by a dog - why we need a one health approach

Capnocytophaga canimorsus, lick, dog, lick of death
Could a lick from a dog be life-threatening?

A recent case report in the British Medical Journal describes a rare and very scary disease in an older lady following a lick from her beloved Italian greyhound. News stories relating to this case have been bouncing around the internet so I thought I’d a) provide the link direct to the case report (always better to get it from the horse’s mouth - click the BMJ link above) and b) add my two cents.

The case describes a 70 year old woman, with some comorbidities (hypothyroidism, epilepsy and transient ischaemic attacks), who seemed fine until she was chatting to a relative on the phone.

Her speech began to slur. The relative, who was on the ball, called an ambulance. When they arrived the patient was slumped over the phone in a reduced state of consciousness.

She was admitted to hospital and they found hyponatraemia (low sodium) which was thought to induce the seizures. She seemed stable until day 4 when she became very confused, developed headache, diarrhoea and rigors, and later developed disseminated intravascular coagulation (DIC), deranged liver function and respiratory failure necessitating ventilation.

Blood cultures revealed Capnocytophaga canimorsus, a gram negative anaerobe associated with dog bites and scratches. The patient had not been bitten or scratched by her dog. But other studies have suggested that 60 per cent of cases were associated with a dog bite and 24 per cent associated with a scratch. 

The owner admitted she had been licked by her dog, so the authors conclude that the source of the infection was the owner’s own dog, via a lick, on the grounds that Capnocytophaga canimorsus was isolated from that patient and that it is a zoonotic organism. My understanding is that this conclusion is based on findings that C canimorsus colonises the mouths of dogs and cats.

And according to human microbiology specialists I’ve spoken to, that assumption about the source of the infective organism is probably correct.

So, what does it tell us? This case highlights a rare but serious potential complication of being licked by a dog. Those people without spleens and alcoholics are at a higher risk of sepsis, as are the elderly. All of us should be cautious.

Of course what is missing here is discussion about the dog1. As a veterinarian I’d have liked to have seen the organism isolated from the dog’s oral cavity, if just for the sake of completeness, and some discussion of its dental condition as well as diet. Could any steps be taken to reduce ongoing risk of exposure, if indeed the dog was the source? Is Capnocytophagia responsible for some of the rare cases of sepsis in companion animals?

Was the dental and periodontal health of the dog assessed? What measures could be taken to reduce the risk of exposure, apart from avoiding being licked by the dog? A recent UK study found that 9.3 per cent of dogs suffered from periodontal disease2. What we don’t know is whether regular dental scaling may reduce carriage of C canimorsus.

Another question, perhaps to be answered by veterinarians, is whether the patient’s comorbidities contributed to the licking by the dog? Companion animals may alter behaviour in response to owners, and may engage in licking or biting as an attempt to rouse owners with a reduced state of consciousness3.  In fact, licking behaviour was performed by 50 per cent of seizure response dogs when owners suffered seizures4. (It is important to note that while licking may be detrimental, seizure response dogs can save lives – in the previous study, one dog brought the cordless phone, another rolled the owner, who had a history of aspiration pneumonia, onto their side, and yet another turned off the electric wheelchair as several accidents had occurred during seizures).

Human animal interactions are complex, involving mutual benefit as well as potential risks to both parties. As a veterinarian I am occasionally asked by owners who suspect they have a zoonotic disease to euthanase the animal in question so that the risk is eliminated. For this reason I feel there is an ethical imperative to confirm the source of infection where possible.

Veterinary investigation of the role of the dog in this case with a veterinarian may help illuminate and reduce animal-based risk factors. This is an example of one of those cases where a One Health approach could potentially help humans and animals.

1. Speare R, Mendez D, Judd J, et al. Willingness to Consult a Veterinarian on Physician's Advice for Zoonotic Diseases: A Formal Role for Veterinarians in Medicine? Plos One 2015;10(8):8.
2. O'Neill DG, Church DB, McGreevy PD, et al. Prevalence of Disorders Recorded in Dogs Attending Primary-Care Veterinary Practices in England. Plos One 2014;9(3):16.
3. Seligman WH, Manuel A. The cat and the nap. Medical Journal of Australia 2014;200(4):229-29.

4. Kirton A, Winter A, Wirrell E, et al. Seizure response dogs: Evaluation of a formal training program. Epilepsy Behav 2008;13(3):499-504.