By Gemma Ma PhD candidate, Sydney School of Veterinary Science, The University of Sydney
Q fever is an important human disease that is transmitted from animals. Most cases in Australia occur after exposure to farm animals, especially cattle, sheep, and goats. A recent increase in human Q fever cases in northern NSW in people without direct farm animal exposures raised concerns about alternative routes of infection, including from companion animals.
Dogs and cats are a significant part of the home environment and therefore an important consideration for public health. Australia is a pet loving nation; almost two thirds of Australian households have a pet, with 40 percent owning dogs and 27 percent owning cats. Many of our pets are considered important members of our families, enjoying access indoors, sharing outings, even sharing our beds.
When companion animals are considered from the perspective of public health, the conversation rarely goes beyond investigating dogs and cats as the source of zoonotic diseases and parasites. Dogs and cats can transmit diseases and parasites to humans, however, this over-simplifies often complex epidemiological relationships. This is exemplified in findings from our recent research into the role of dogs and cats in Q fever epidemiology, which sheds light on potentially important sources of the disease for humans.
Q fever is an important human disease that is transmitted from animals. Most cases in Australia occur after exposure to farm animals, especially cattle, sheep, and goats. The organism that causes Q fever, the bacterium Coxiella burnetii, multiples to very high numbers in reproductive tissues and is mainly excreted in the placenta and birth fluids. However, because the bacterium is highly stable in the environment – able to survive months, even in very hot and dry conditions – people can become infected without having direct contact with an infected animal.
A recent increase in human Q fever cases in northern NSW in people for whom the source of infection was unknown raised concerns about alternative routes of infection, including from companion animals.
It is reasonably well understood that human cases of Q fever can also occur following contact with both dogs and cats. We know this from a handful of case reports in the literature both from Australia and overseas . As far as we are aware, dogs and cats do not become sick with C. burnetii infections but can pass on the disease to people around the time they give birth to their puppies or kittens. However, the degree of Q fever risk posed by companion animals remains unclear.
This prompted our study. We tested 475 dogs and cats from northern NSW for C. burnetii antibodies, which indicates previous exposure to the bacteria. We also tested for bacterial DNA which might indicate current infection.
We found that a large proportion of the dogs and cats tested had antibodies to C. burnetii, and that this proportion varied significantly by geographic location. Dogs and cats that lived within 150km of a 2015 human Q fever outbreak in northern NSW [3] were more than eight times as likely to have been exposed to the disease than the pets that lived further away.
The exposure to C. burnetii of these pet dogs and cats is likely to have occurred in their homes, backyards, or local neighbourhoods. Pet dogs and cats do not usually accompany their owners to work in abattoirs or in shearing sheds.
Our findings suggest both pets and people in northern NSW acquire Q fever infections from a shared environmental source, challenging assumptions that only people exposed to livestock through their occupation are at risk of Q fever.
“Contact with livestock, both by the pets themselves and by their owners, was not a risk factor for pets being antibody positive.”
This finding agrees with other epidemiological studies, particularly from Europe, which have highlighted the potential for Q fever infections to occur down-wind of intensive livestock production. The bacterium survives in dust and can be spread by wind for up to five kilometres, making it plausible that anyone living in sheep, cattle or goat producing areas, even if they do not have direct contact with animals, is at risk of Q fever infection. This risk is likely to be exacerbated by drought and dust storms and may also be increased by proximity to higher densities of livestock such as along major transport routes.
We found no C. burnetii DNA from any dogs or cats. This suggests that none of the 475 pets had a current infection and therefore did not pose a risk to their human families.
We conclude that people are very unlikely to acquire Q fever from pet dogs or cats. It appears the only time dogs and cats present an important risk of Q fever infection to people is in the days surrounding the birth of puppies and kittens. We therefore recommend that cat and dog breeders be vaccinated against Q fever.
This study highlights the value of considering our canine and feline family members in studying communicable disease epidemiology. It is worth considering what else we might be able to learn about our own health from the other animals that share our homes.
Ma GC, Norris JM, Mathews KO, Chandra S, Šlapeta J, Bosward KL, Ward MP (2020) New insights on the epidemiology of Coxiella burnetii in pet dogs and cats from New South Wales, Australia. Acta Tropica. 205, doi: 10.1016/j.actatropica.2020.105416
First published in June 2020 Intouch PDF.