Zoonosis is the term used to describe diseases that can be passed from animals to people. I think in general people are aware that this can happen, but we don’t believe people realize the vast number of zoonoses actually out there. In many circumstances these diseases seem foreign or far away, but the reality is there are several of these that have the potential to be in your back garden, or even your home. The purpose of this is not to overwhelm pet owners, but to make people aware of these potential risks so that we can prevent problems before they arise.
Let’s start by reviewing some parasites that humans can contract from their pets:
Roundworms in dogs and cats are one of our most common parasites. These species can however, if introduced to the human GI tract by kisses from your furry family member, can develop and migrate to other organ systems and cause issues.
Similar to their roundworm counterparts, hookworms also don’t mind infecting people. These pesky creatures are known to cause the condition visceral larval migrans (larvae migrate to other organs in the body like the brain or the eye) and cutaneous larval migrans (larvae migrate just under the skin). This can cause serious consequences especially in young children.
Most tapeworms tend to be species specific, i.e. they prefer one main host like a dog or a cow. That being said, the flea spread tapeworm Dipylidium can infect humans and mature in the gut. Additionally, immature Taenia spp. tapeworm life stages can be found in raw or undercooked meat, meaning if you or your pet consumes these, risk for tapeworm infection is possible.
One to note in this category is the species Echinococcus. This nasty tapeworm is the culprit behind hydatid cyst disease. While the dog is it’s preferred host, both humans and sheep can act as intermediate hosts and develop potentially life threatening cysts within the body full of immature tapeworms.
Dogs and cats can develop infestations with two major types of mites, including Demodex and Sarcoptes. While Demodex spp. Are not contagious, humans may become infected by Sarcoptes mites, leading to itching and severe skin irritation.
This is most commonly recognized as a tick borne disease, however the symptoms are caused by a bacteria called Borrelia burgdorferi. Borrelia can cause severe clinical signs in ourselves and our pets.
Cat scratch fever is actually caused by a bacteria. This can cause infected cats to develop fever and other signs, and can be transmitted to humans via cat scratch.
Salmonella, E. coli, and Campylobacter:
These are all bacteria that are not only a potential risk of causing GI problems if they infect humans/pets consuming raw or undercooked meats, but they can also be spread via the feces of pet bird species (including chickens).
Rocky Mountain Spotted Fever:
Similar to lyme disease, RMSF is also spread by ticks and is caused by the bacteria Rickettsia rickettsii. This can cause rash, fever, headache, lethargy, etc. and can be serious. While uncommon in the UK, travellers coming back from Europe should be aware of ticks abroad.
Leptospirosis spp. are a group of bacteria that are spread via the urine of affected animals, including dogs. If urine of an infected animal gets into the mucus membranes of another (eyes, mouth, nose) then clinical disease may occur. Signs of leptospirosis infection in dogs are typically general including lethargy, vomiting, fever, increased drinking or urination, and decreased appetite. Elevations in kidney or liver values on bloodwork are a concern as these organs are the target. Leptospirosis is currently uncommon in the UK, but is being diagnosed and is a disease you don’t want to get to know. *See later note on vaccinations in dogs*
The causative agent of Q fever, Coxiella is shed in urine, feces, milk, and birth fluid of ruminants (sheep primarily) and can then be spread to humans to cause a range of signs including fever, cough, vomiting, diarrhea, and lethargy.
Dermatophytosis, better known as ringworm, is a fungal infection of the top layers of the skin. Canine and feline dermatophytosis is extremely common, especially in shelter/rescue scenarios because of large animals in close proximity. Puppies and kittens are often the source in humans soon after adoption. Ringworm can be spread between animals and to humans via direct contact or by contaminated surfaces.
While most species of this protozoal organism tend to be species specific in terms of who they like to infect, it’s important to keep in mind that people can technically still become infected with Giardia from their pet. Giardia is a faecal “parasite” that comes from the faeces of another infected animal. More commonly people and pets become infected from the same contaminated water source containing faecal material while out hiking or camping. This is a common cause of vomiting and diarrhea in pets.
Many people have heard of Toxoplasma but don’t realize it. This is the organism that causes people to warn pregnant women to not scoop the litter box. Toxoplasma is transferred via cat faeces. Cats may show clinical signs of illness including neurologic problems, but they can also pass oocysts asymptomatically. If this parasite makes its way into humans, problems with the fetus in pregnant women may arise. A good excuse to make your non-pregnant partner scoop the box!
While this list is nowhere near exhaustive, (think many, many more), it does list some of the more common diseases we see, especially those parasites that like to infest our companion animals. This reminds us why regular targeted parasite prevention is extremely important. It helps keep not only our pets safe, but ourselves and our families healthy too. Checking with a vet to ensure your pet is appropriately vaccinated is equally essential, particularly in the case of leptospirosis. Vaccination will not prevent exposure, but it will lessen the likelihood of developing severe disease as well as hopefully decrease the amount of bacteria shed. Not all zoonotic diseases can be kept at bay with parasite prevention or vaccination, which is why education and good personal hygiene associated (hand washing) with animal handling is a must.
Making sure your pet is appropriately wormed and vaccinated for your/their lifestyle and location is an ESSENTIAL part of keeping our community healthy; pet and owners alike!
For more information on significant parasites and zoonotic diseases, check out the following resources:
European Scientific Council for Companion Animal Parasites
European Centre for Disease Prevention and Control
Dr. Kirsten Ronngren, DVM MRCVS