Case-based study of zoonotic disease
CASE STUDIES IN ZOONOSES
J Scott Weese DVM DVSc DipACVIM
Ontario Veterinary College, University of Guelph, Guelph, ON, Canada
Pets play important roles in many peoples’ lives and there is increasing evidence of positive health, emotional and social benefits of pet interaction. Yet, every animal harbours potential zoonotic pathogens, and some degree of zoonotic infection risk is inherent with pet ownership or other pet contact. As it is increasingly apparent that pets are important parts of the family both emotionally and microbiologically, efforts to minimize zoonotic disease risks while maximizing benefits are critical.
Zoonotic pathogen exposure is an ever-present risk in veterinary medicine. Veterinarians play important roles in prevention and control of zoonotic infections. Further, while diagnosis of management of human disease lies within the realm of human medicine, veterinarians can provide important input to ensure that zoonotic infections are considered and to facilitate the physician’s approach to the human patient.
All animals harbour multiple zoonotic pathogens; however, risks posed to people vary. Zoonotic diseases risks are generally low, but risks can be heightened in situations based on the pet (e.g. reptiles), person (e.g. immunocompromised) or interactions (e.g. management practices). Of particular concern is individuals whose immune systems are compromised because of age (i.e. <5 years of age or >65 years of age), physiologic state (e.g. pregnancy), disease or treatment (e.g. immunosuppressive therapy). “Immunocompromised individuals” do no belong to one clear and distinct group, as the degree of compromise can be highly variable between individuals, as well as within the same individual over time. Nonetheless, people with suboptimal immune systems have some elevated degree of infectious disease risk compared to the general population, but may also have the greatest benefits from pet interaction.
To provide optimal guidance for zoonotic diseases, veterinarians must have a broad range of knowledge that includes understanding of the pathogen (e.g. sources, routes of transmission, disease), animal management practices, preventive measures for the animal species and for specific pathogens, and the role of the animal in the household (to help discuss cost-benefit), among other important factors. A consideration of all of these is required to help owners select pets, identify optimal management practices, reduce the risk of zoonotic infection and understand disease risks.
Examples of cases and issues that may be discussed are provided below
A 10 yr old boy is presented to a physician with fever, rash and arthritis. After apparent clinical resolution following symptomatic therapy, the signs recur and the child is referred to an infectious diseases physician. The child has an unremarkable medical history and has had no previous problems. Upon further questioning, it is identified that the family had acquired a pet rat a few weeks prior to the onset of disease. The child had suffered a ‘very minor’ bite and had been licked by the rat. Things to consider include:
What disease(s) might be of concern?
Is this rat a potential source of disease?
What factors may have contributed to disease?
What should be done in this household to investigate the causes?
What should be done to prevent this from recurring?
What information should be provided by the veterinarian as part of this situation?
Whose responsibility is it to provide current or prospective pet owners about zoonotic diseases and infection control practices?
A client brings in their healthy, 4 yr old Pekingese for a wellness examination. The client is chatty and during conversation, she mentions that she had lost her spleen in a car accident a few years earlier:
Is this of concern?
What does the absence of a functional spleen do to the risk of zoonotic infections?
What pathogens are of particularly concern?
Is this information relevant enough to be recorded (and if so, how)?
Are there are recommendations that should be made to the owner?
Does this change your approach to management of this patient?
A pediatric oncologist calls you about a 5 yr old patient that is undergoing chemotherapy for leukemia. The family has 4 cats, 2 indoor and 2 outdoor. All are healthy, according to the information he has, but he has had a discussion with the family about the risks of toxoplasmosis since this child is highly immunocompromised:
What are the concerns regarding toxoplasmosis in this individual?
Are cats an important source of Toxoplasma?
What is the likelihood that these cats pose a risk?
What should be done with the cats?
What should the owners be told?
What else should be considered in this household?