This is a comprehensive article on zoonotic diseases and how to reduce infection. It is based upon a study by three scientists which has been published on the Internet but to see it you need to pay. The study is entitled: “Reducing the Risk of Pet-associated Zoonotic Infections”.
I will refer to the domestic cat more than other pets in this article. Other pets include: dogs, fish, birds, amphibians, reptiles rodents and rabbits.
Before discussing the risks in some detail, everyone who has looked after a pet has to agree that the risk of acquiring a disease from your pet is small. That is a general statement and it applies most frequently to people who have a good immune system (immunocompetent). If the risk was not small then pets like cats and dogs would not be so popular. An obvious statement but one that is worth making. In addition, there are known health and emotional benefits to pet ownership. The benefits and the small risk equate to high popularity in pet ownership.
Surveys of patients and epidemiological (patterns, causes and effects of diseases) studies on this topic indicate that the occurrence of pet-associated disease is low. This article therefore is probably more to do with pet owners who have suppressed immune systems for one reason or another.
Pets, however, can serve as a source of zoonotic pathogens (disease producing agents). Close contact with pets in the form of a pet sleeping in bed with the owner or face licking occurs in about 75% of households. Surveys indicate that the general public and people who are at a higher than normal for pet-associated disease are unaware of the risks associated with close contact with their pet. Neither are they aware of ways to reduce that risk. A study indicates that 77% of households in which a person lives, who has just received a cancer diagnosis, acquired a high-risk pet. Cancer makes the patient immunocompromised.
Here lies the first problem perhaps, which is that general practitioners (GPs) practising human medicine do not routinely discuss with their clients whether they are in close contact with their pet and neither do they discuss zoonotic diseases with patients. This applies whether the patient is immunocompetent or not.
Apparently, we don’t know how common it is to get a human disease which has been caused by a pet. However, contact with your pet is a risk factor for many diseases. Further, although pets don’t normally directly transmit arthropod-borne diseases, pets do bring the vectors for these diseases into close proximity of people i.e. ticks and fleas. Arthropods are animals who have an exoskeleton.
How are pet-associated infections transmitted and who is most at risk?
The study states that companion animals are a potential source of more than 70 human diseases. They also say that this is an underestimate. This figure does not apply to cats, let me stress. It must be an overall figure encompassing all companion animals. In this article I am referring to pets in general. People can acquire a zoonotic infection via scratches and bites, direct contact with the skin or mucous membranes. There can also be contact with animal saliva, body fluids and secretions, urine and ingestion of animal faeces. In addition there is inhalation of droplets in the air which are infectious.
The risk of getting a disease from your companion animal varies and is dependent upon the species of pet, the age of the person and the health of their immune system and how people manage their housing. Children under the age of five years and adults over the age of 65 years of age and patients who are immunocompromised and women who are pregnant are at increased risk from zoonotic diseases. They may have a more severe disease as a result and the symptoms may last for a longer time and there may be complications.
Children have an incomplete immune system and elderly people have a waning immune response. In addition, there might be a temporary hormone-induced immune suppression during pregnancy. Further, diseases such as cancer can result in immunodeficiencies. Also, some people may have poor hygiene together with more frequent close contact with their companion animals.
Certain pet-associated pathogens are of the greatest concern. With respect to cats and dogs, the diseases which are of the most concern are:
- Bartonella species: the incidence is low but the study states that it is likely to be under diagnosed while the severity is low to high. This is cat scratch fever. Symptoms can be a fever and you will see redness in inflamed areas of the skin. High-risk patients may have more severe symptoms such as lesions on the skin, liver or spleen.
- Brucella canis: this is dog specific and the incidences rare with moderate severity.
- Campylobacter jejuni: this relates to dogs and cats and possibly other species. The incidence is high and the severity is low. The symptoms are diarrhoea, vomiting and fever. In high-risk patients there might be septicaemia. The infection is passed in the faeces of the cat or dog. Young dogs and cats are more likely to shed this bacteria than adults. A recent adoption of a kitten or puppy is linked to the highest risk of transmission.
- Bacteria which is resistant to drugs: companion animal owners have a six-fold greater risk for colonisation than people who don’t own pets. People with a compromised immune system are more likely to be infected with Clostridium difficile than people with good immune systems. Dogs visiting healthcare facilities for people (I presume these are therapy working dogs for the benefit of the patients) were five times more likely to be infected with Clostridium difficile and Staphylococcus aureus than other dogs. Although people are the reservoir for these multi drug-resistant bacteria companion animals are a secondary source for human infection.
- Salmonella species: this bacteria is most often associated with pets other than cats and dogs such as amphibians, reptiles and exotic animals. Reptiles and amphibians are thought to be responsible for 11% of all salmonella infections amongst patients under 21 years of age. Direct contact with the animal is not required for transmission. Handling animal foods can also result in becoming infected with salmonella.
- Pasteurella multocida key sources are dogs and cats. Incidence of this bacterial diseases is moderate and the severity moderate.
- Tuberculosis – there is a page on this on PoC.
- Cryptosporidium species and Giarda duodenalis: this parasitic disease infects dogs and cats and possibly birds. The incidence is moderate and the severity moderate. Symptoms are diarrhoea, weight loss and chronic diarrhoea in high-risk patients. This parasite is found in both animals and people. There has been recorded incidences of zoonotic transmission. Transmission is through faeces.
- Toxocara species (roundworm): the higher risk of getting this disease is in young children because there is a higher risk that they will ingest dog or cat faeces containing ova. Most companion animals are regularly dewormed. Roundworm larvae require 2 to 3 weeks after being eliminated to become infective. The time at which there is the highest risk of exposure to this parasite is after contact with soil contaminated with faeces from stray animals which are not dewormed. This is likely to take place in sandboxes, gardens or playing fields.
- Toxoplasma gondii: I’ve discussed this at length in other pages. Is a high profile disease much discussed on other websites. Cats serve as the definitive host and it is passed in faeces. However, the truth of the matter is that by far the greater risk to people is in handling food.
- Cutaneous larva migran (hook worms): the incidences low to high depending on the location. Severity is low.
- Echinococcus species:in dogs and cats but the instances rare and the severity high.
- The disease include the well-known ringworm. It is uncommon in people with good immune systems but infections can occur more readily in immunocompromised patients.
- Rabies: this is another very well-known disease which has also been discussed extensively on this website.
How can pet-associated infections be prevented?
For patients with healthy immune systems the risks are slight and therefore “general hand hygiene” (washing your hands thoroughly) after activities which present a higher than average risk is likely to be adequate.
Bites and scratches causing infections are the greatest risk for people. About 4.5 million American citizens are bitten by dogs annually. Bites occur more commonly in people under the age of 14. Dog bites account for 17% of admissions to hospitals which are animal related. Dog bites are also responsible for a quarter of all emergency department “treat-and-release” visits.
To avoid bites and scratches people need to be educated about cat and dog behaviour and when a bite or scratch may occur i.e. when stressed, startled or threatened. People need to be knowledgeable about how to handle companion animals. This is all about how people deal with adopting and understanding their chosen companion animal and educating their children.
People with a compromised or as yet not fully developed immune system, which includes young children under five years of age and older adults over 65 years of age and pregnant women plus people with illnesses reducing immune function, are at an increased risk as mentioned. It appears, or this research study indicates that these people are treated no different from people with good immune systems when advised by veterinarians and/or general practitioners (GPs for humans). There are recommendations in respect of companion animal ownership and contact with these animals.
Below are suggestions for reducing transmission of zoonotic diseases from companion animals to people who are considered to be a higher risk of receiving these diseases (I’ve limited this list to cats and dogs and avoided recommendations regarding exclusively reptiles and amphibians for example):
- children should be supervised when they wash their hands if there are less than five years of age and adults should wash their hands after handling animals.
- The skin should be protected from direct contact with animal faeces. This can be done by wearing household cleaning gloves or using a plastic bag when cleaning up.
- Contact with “animal-derived pet treats” should be avoided.
- If bitten or scratched the area should be washed immediately.
- Companion animals should not be allowed to lick open wounds, medical devices or cuts. Pets should also be discouraged from licking young children’s faces and people with compromised immune systems.
- When not in use playground sandboxes should be covered.
- In households where there are very young children or immunocompromised patients, is suggested that dogs and cats less than six months of age should not be adopted. In fact, they go so far as to say that people should avoid acquiring a cat of less than one year of age.
- Avoid contact with pets with diarrhoea.
- Caution should be exercised when playing with cats to minimise scratches and bites in play. If a cat’s claws have not been worn down in outdoor use then it is recommended that they are trimmed but declawing is not recommended.
- When adopting a new companion animal they say that mature animals from established sellers are a lower risk than other animals.
- When visiting households or other places where there are companion animals the same precaution should be taken there as you would take in your own home.
- People who work with animals such as veterinarians and shelter employees should adjust their work practices to minimise contact with animals when they have been diagnosed with suppressed immune systems.
- Therapy dogs and cats are very beneficial to patients in hospitals but the recommendation is to consider limiting contact with these animals presumably on the basis that patients in hospital have or are likely to have suppressed immune systems.
- Companion animals should be cared for in a way which maintains their health thereby producing the possibility of contracting these diseases.
- Keeping cats indoors, cleaning litter boxes daily, wearing kitchen gloves during cleaning and washing hands routinely or help to maintain a healthy environment.
- Litter boxes should be kept away from kitchens and other areas where there is food preparation or eating.
- Dogs should be confined when suitable and walking should be on a leash to prevent the dog from hunting and eating garbage.
- Companion dogs and cats should only be fed with high-quality canned or dry commercial food (not my recommendation except for occasional grazing). If the food is home prepared it should be well cooked. Dairy-based products should be pasteurised.
- Cats should not have access to surface water or toilet bowls.
- Transmission of pathogens through reproductive tract secretions should be reduced by spaying and neutering.
- Cleaning and disinfecting animal contact services with household bleach is the best way. Household bleach is the most effective killer of viruses which infect cats.
- Companion animal bedding should be laundered regularly.
- Veterinarian should be consulted as soon as possible when a pet falls ill.
The role of veterinarians and physicians
The study suggests that there should be better discussion between veterinarian and general practitioner in order to cross-reference what they’re doing. Perhaps the doctors don’t take the risk sufficiently seriously. For example, physicians could obtain a history of contact with pets or other animals in order to provide a better diagnosis. Follow-up should be done to check for newly acquired pets. Doctors should enquire about the type of companion animal with which his patient has contact, whether the animal is healthy or ill and what the patient does in relation to preventing zoonotic diseases.
Veterinarians perhaps could assist more in providing advice on all aspects of zoonotic disease risk reduction by offering information on pet husbandry and preventative health measures.
The study source
This study upon which this article is based is I believe a review of numerous other studies with reference to an extensive list of resources therefore it is comprehensive. As mentioned, I have précised the study somewhat to limit it or to focus on aspects relating to cats and dogs and primarily cats.