A nation of animal lovers
It is estimated that 57% of households in Canada have one or more pets with cats being most popular (7.9 million) closely followed by dogs (5.9 million). There is a trend for the more exotic pet such as snakes, reptiles, amphibians, hedgehogs and even pigs. Then of course there are the more common pets such as fish along with the pocket pets (mice, hamsters, rats, rabbits).
There are several reasons why people keep pets with the most obvious being as a companion, reducing stress and teaching children to have a caring nature. However, the negative aspects of pet ownership beyond being woken up with the sun or coming home to find a deposit on your floor, is the potential of contracting pathogens that could lead to potential fatal conditions.
Is pathogen acquisition from pets such a big issue?
Zoonotic pathogen transfer was known even before the pioneering work of Robert Koch. Historically, the most significant zoonotic pathogens was the plague, bovine tuberculosis and anthrax. Thankfully, pathogens acquired from pets don’t result in epidemics but certainly can lead to acute or chronic conditions some of which are fatal. Still, from the outset it is important to note that most pathogens are transferred between people and zoonotic routes account for 14% of infections with only a small fraction of that attributed to household pets. This may make some think that there is no problem and a fuss about nothing. However, the reality is that most of homes with pets have persons who can be considered susceptible to the 70 pathogen types associated with pets. Specifically, the very young (<5 years old), pregnant, elderly and immunocompromised.
From our feline friends
There are a diverse range of parasites, fungi, bacteria and viruses that can be acquired then passed on by cats. One of the most notable are the enteric protozoan, Toxoplasma gondii, Giardia and Cryptosporidium. Toxoplasma is of most significance given that the pathogen results in birth defects in pregnant women. The other parasites cause gastroenteritis type symptoms that can persist and reoccur. Cats can also transmit cowpox and ironically is a more significant source of the virus compared to cattle. However, cowpox is very rare in North America but has been encountered in the UK.
Bartonellosis, (Cat Scratch Disease) caused by Bartonella, can be transmitted to humans via bites or scratches and results in swelling of the lymph nodes along with headaches and fatigue. Felines are also carriers of more commonly encountered pathogens such as Salmonella, Campylobacter, Clostridium perfringens and C. difficile.
What we can get from Lassie?
There are some common pathogens transmitted by both cats and dogs (for example, Salmonella, Campylobacter, Giardia). In addition, dogs carry ticks that can transfer the pathogen Borrelia burgdorferi to humans potentially resulting in lyme disease- a condition characterized by fever, rash and paralysis. In a similar manner, humans can contract Rickettsia from dogs harboring fleas carrying the pathogen. Our Canine friends also have been identified as a significant source so Methicillin Resistant Staphylococcus aureus (MRSA) that can lead to difficult to treat skin infections.
There is a strong association between the transmission of Salmonella and Campylobacter from birds. Indeed, there have been several high profile Salmonella outbreaks linked to pet chicks. Other less known diseases transmitted includes the fungus Cytococcsis that can cause respiratory disease in humans. The transmission of Mycobacterium avium from birds to humans is less clear although can result in abdominal pain along with fatigue.
Pocket pets, hedgehogs, reptiles, amphibians and fish
Pocket pets cover a range of small mammals such as mice, hamsters, gerbils, rats, guinea pigs and rabbits. Salmonella has been recovered from mice and rats, in addition to hedgehogs that were implicated in an outbreak back in 2013. Apart from Salmonella, there is a link of lymphocytic choriomeningitis virus (LCMV). The virus is thought to be transmitted primarily by mice and causes an influenza-like condition in humans. As with many pathogens, the infectious dose and outcomes largely depend on host susceptibility. In the case of LCMV the most susceptible are the young and pregnant women. LCMV can be transmitted to the fetus in pregnant women but the condition is normally non-fatal although can lead to long term neurological problems.
Reptiles and amphibians have the most press when it comes to transmission of Salmonella. The major villains identified are turtle and frogs that in addition to be asymptomatic carriers of Salmonella are also likely to be handled by the young. Even the humble goldfish has been identified as a source of Salmonella including virulent serovars such as paratyphi.
So what is the most dangerous pet from a zoonotic transfer standpoint?
This is a tough question to answer but there are obvious top candidates for the honor. In terms of pathogen carriage, cats would top the list although it should be noted there are multiple factors to consider. Specifically, young cats and dogs are known to shed pathogens to a greater extent than older animals. Those animals that have access to the outdoors or provided raw meat feed are more likely to carry more pathogens. Aggressive animals that bite or scratch can also be regarded as an added risk factor. Then there are the owner related factors. For example, are susceptible people in the household? do pets lick faces of people during petting? are ill pets quarantined and have they got access to high risk areas such as kitchens? Finally, do people wash their hands after handling pets? This is relevant given that hand washing after handling pets reduced transmission of MRSA by 75%.
In summary, it would be wrong to consider our pets as the Grim Reaper and that we have to don a hazmat suit to handle them. Yet there is the potential to acquire pathogens (and visa versa) but this can be minimized by taking precautions such as hand washing.
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