With approximately 74.8 million owned in the United States and 38% of US households having at least one, dogs truly are man's best friend.  And rightfully so, as the benefits of owning a pet are many, including decreased risks for stress and cardiovascular disease, as well as increased heart attack survival rates and improved psychological and physical well-being.   Among children, owning a pet has been associated with reduced risk of asthma and allergies, and improved social skills, self-esteem, and empathy.  But what most dogs owners don't realize is the potential dogs have to spread zoonotic diseases (a disease transmitted between animals and humans), and not just rabies, but parasites and pathogens such as roundworm, Q fever, brucellosis, and leptospirosis.  Even more, novel canine zoonotic diseases continue to emerge. 

Canine zoonoses can be spread by:

• direct contact
• oral route of transmission (e.g. eating with contaminated hands)
• a fomite (object contaminated with an infectious disease that can then be transmitted, e.g. door knob)
• aerosol/respiratory transmission
• vector-borne (e.g. ticks and fleas)

Recently canine influenza virus and canine respiratory coronavirus appeared on the scene. Historically influenza and corona viruses in other species have been transmitted to humans (e.g. swine influenza virus and SARS), so the possibility of these newly discovered canine respiratory viruses causing human infections is not farfetched.  Most notably of late is the discovery of a canine hepatitis C virus.   

Hepatitis C virus (HCV) infections are often asymptomatic but the virus can establish a chronic infection with significant long-term effects on the liver, such as cirrhosis (scarring of the liver). The virus persists in the liver in about 85% of those infected.  HCV is a blood-borne pathogen, and no vaccine is available.  HCV has been around for more than 20 years, but the virus's origins remained unclear because a similar virus had not been identified in animals. 

That all changed following a report by Kapoor et al (2011) recently published in PNAS.  [1]  They discovered a canine homolog of HCV, dubbed canine hepacivirus (CHV), which is closely related to HCV.  Interestingly, CHV is a respiratory illness in dogs, with low virus titers found in the liver.  The authors were unsure whether CHV is hepatotropic (ability of the virus to replicate in the liver).  They estimate the 2 viruses diverged in the past 500-1000 years, after canine domestication.  In the scientific research world, this discovery provides a promising animal model in which to study the pathogenesis and treatment of HCV.  This discovery also gives nod to the zoonotic transmission of viruses between dogs and humans.  It is possible HCV emerged from human infections with CHV.   Though yet to be studied, human infections of the canine hepatitis C virus via respiratory transmission may be occurring.  The implications for human hepatitis infections are vast but unknown at this point.  What this discovery does, on the heels of the emergence of canine influenza and canine respiratory coronavirus, is bring awareness to the potential of man's best friend to transmit diseases to their owners.

Unfortunately, dog owners are unaware of these risks, as no one is effectively communicating the potential risks to them.  In a 2008 random telephone survey conducted in Texas [2], while 98% of respondents knew they could get rabies from a dog, regardless of dog ownership, only 54% knew worms could be transmitted from dogs to humans.  So whose responsibility it is to educate dog owners?  Should a physician ask his/her patients about their pets and know what diseases those pets could carry?  Or should a veterinarian know the health status of the pet owners to know if they are at higher risk of infection with a zoonotic disease? 

The problem lies in a division between disciplines and a lack of communication among physicians and veterinarians.  In a survey of over 600 physicians and veterinarians, 67% of the physicians never discussed zoonotic diseases with their immunocompromised patients, which is extremely important as immunocompromised people are at higher risk of zoonotic disease infections.  Physicians reported they did not feel comfortable advising patients about zoonotic disease risks and felt veterinarians should play an equal or greater role.  However, veterinarians rarely  knew the health status of clients, and patients did not view their veterinarians as a source of information about zoonoses. [3]  Among immunocompromised pet owners,  only 10% of AIDS patients in Florida were informed by their physicians of zoonotic disease risks.  Another survey found 45% of HIV patients owned pets, and 60% of them were advised not to keep them.  But rather than advising at-risk groups to get rid of pets, there needs to be awareness and prevention education that allows them to maintain that bond with their pet because of the wealth of benefits pet ownership brings.

There is a public health disconnect for which a multidisciplinary collaboration to educate physicians, veterinarians, and dog owners could greatly impact the health of dogs and their owners.  Practical, commonsense actions - including hand washing, cleaning animal areas, and keeping dogs healthy - can protect dog owners, but far too often, these safeguards are commonly overlooked.  Physicians may not always consider zoonotic infections in medical differential diagnoses, so they should be encouraged to give special consideration of zoonotic infections for at-risk populations.  Rarely are canine zoonoses life-threatening.  They are often self-limiting and readily treatable, if not completely subclinical.  Certain groups at higher risk for infection include infants, young children (less than 5 years old), pregnant women, the elderly, and those with immunocompromising diseases.   Of course owners can continue to play with and hug their adored furry friend, but an educated dog owner is a safer dog owner. 

1. Kapoor, A., et al., Characterization of a canine homolog of hepatitis C virus. Proc Natl Acad Sci U S A, 2011. 108(28): p. 11608-13.

2. Bingham, G.M., C.M. Budke, and M.R. Slater, Knowledge and perceptions of dog-associated zoonoses: Brazos County, Texas, USA. Prev Vet Med, 2009.

3. Grant, S. and C.W. Olsen, Preventing zoonotic diseases in immunocompromised persons: the role of physicians and veterinarians. Emerg Infect Dis, 1999. 5(1): p. 159-63.