Emerging Infectious Diseases
[Volume 5 No.1 / January - February 1999]

Suggested Citation



Dispatches

Preventing Zoonotic Diseases in Immunocompromised Persons: The Role of
Physicians and Veterinarians

Sara Grant and Christopher W. Olsen
University of Wisconsin, Madison, Wisconsin, USA

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      We surveyed physicians and veterinarians in Wisconsin about the
      risk for and prevention of zoonotic diseases in
      immunocompromised persons. We found that physicians and
      veterinarians hold significantly different views about the
      risks posed by certain infectious agents and species of animals
      and communicate very little about zoonotic issues; moreover,
      physicians believe that veterinarians should be involved in
      many aspects of zoonotic disease prevention, including patient
      education.

The bond between humans and animals has been recognized for many years, and
pet ownership has been associated with both emotional and health benefits
(1-4). However, pet ownership may also pose health risks through the
zoonotic transmission of infectious diseases, especially in the
immunocompromised (5). Animal-associated pathogens of concern to
immunocompromised persons include Toxoplasma gondii, Cryptosporidium spp.,
Salmonella spp., Campylobacter spp., Giardia lamblia, Rhodococcus equi,
Bartonella spp., Mycobacterium marinum, Bordetella bronchiseptica,
Chlamydia psittaci, and zoophilic dermatophytes (2,6). However, with the
exception of Bartonella henselae and zoophilic dermatophytes, infections in
humans are more commonly acquired from sources other than pets, and the
infectious disease risk from owning pets is considered low (2,7).
Nonetheless, HIV-infected persons may still be advised not to own pets (8).

Since human medicine often does not delve deeply into the role of animals
in the transmission of zoonotic agents (7,9) and veterinary medicine does
not cover the clinical aspects of human disease, zoonotic disease control
requires involvement of both physicians and veterinarians. We examined how
frequently physicians and veterinarians encounter zoonotic diseases, what
role physicians think veterinarians should play in zoonotic disease
prevention, how often physicians and veterinarians communicate about
zoonoses issues, and what physicians and veterinarians perceive as the
disease risk of immunocompromised persons from pets.

Our sample populations were drawn from membership lists of the Wisconsin
Veterinary Medical Association (WVMA) and the State Medical Society of
Wisconsin (excluding retired practitioners). Veterinarians (n = 526) were
chosen by a systematic sampling of every third name on the WVMA membership
list. Since veterinarians in all types of practice may encounter zoonotic
problems, sampling was not stratified by specialty. Physicians (n=698) were
chosen by specialty most likely to involve both zoonotic diseases and
immunocompromised patients (all physicians who listed infectious disease [n
= 38] or hematology/oncology [n = 103] as specialties), as well as randomly
selected cohorts of pediatricians (n = 100), and general internal medicine
physicians (n = 500). Duplicate names were removed.

Each participant was mailed a cover letter; a number-coded, postage-paid
return envelope; and a physician- or veterinarian-specific survey.
Nonresponders received a second survey 3 weeks after the first. For
questions with a response scale of 1 to 5, the sample size was large enough
for a 2-sample Z-test to statistically compare mean responses between
physicians and veterinarians. Additionally, responses were analyzed by
veterinary practice type and physician specialty. Statistically significant
differences in responses by specialty are noted in the text. A 2-sample
Z-test employing the standard large sample approximation to binomial data
was used to compare the proportions of responses by physicians and
veterinarians to the question about zoonotic pathogens of concern to
immunocompromised patients.

Surveys were completed by 327 veterinarians and 322 physicians (overall
response rate of 53%). Responses from veterinarians were as follows: 142
(43%) small-animal practice, 65 (20%) large-animal practice, 98 (30%)
mixed-animal practice, and 22 (7%) exotic-animal practice. The distribution
of respondents by practice type is very similar to the distribution by
practice type across the State of Wisconsin (46% small animal, 19% large
animal, 35% mixed, and 0.3% exotic [data courtesy of M. Mardock, Wisconsin
Veterinary Medical Association]), except for an overrepresentation of
exotic-animal practitioners. Nationally, 8% of veterinarians are in large
animal practice exclusively, 29% in mixed practice, 58% in small animal
practice and 5% "other" (data from the Veterinary Economics Statistics
Brochure of the AVMA, September 1998). The distribution of responses from
physicians included 24 (7%) in infectious diseases, 48 (15%) in
hematology/oncology, 53 (16%) in pediatrics and 197 (61%) in general
internal medicine (including 16 who specifically categorized themselves as
pulmonologists and 11 as rheumatologists). Among our random selection of
pediatricians and general internists, the respondent ratio of 3.7
internists for every 1 pediatrician is slightly higher than the statewide
ratio of 2.5 (Wisconsin physician data courtesy of M. O'Brien, State
Medical Society of Wisconsin) and the national ratio of 2.0 (10).

The survey results indicate that veterinarians (Table 1) encounter zoonotic
diseases in their practices or discuss them with their clients more
frequently (p < 0.00001) than physicians (Table 2). Among veterinarians,
small-animal practitioners encounter zoonoses more frequently than
veterinarians as a whole (mean = 2.80, p = 0.05), and large-animal
veterinarians less frequently (mean = 3.41, p = 0.001). Among physicians,
infectious disease specialists encounter zoonoses more frequently than the
overall population of physician respondents (mean = 3.44, p = 0.001), but
these specialists still encounter zoonoses problems less frequently than
veterinarians (p = 0.05).

 Table 1. Survey of veterinarians

 ------------------------------------------------------------------------------
 Questions                                  Responses
 ------------------------------------------------------------------------------
 How often do you encounter or discuss
 zoonotic diseases in your patient
 population?
      1=Several times/day;
      2=Daily; 3=Weekly;               
      4=Occasionally; 5=Never         X = 3.02(sup a) (0.05)(sup b)

 How often do physicians contact you
 for advice on the animal aspects of
 transmission and risks of zoonotic
 diseases?
      1=Several times/week;
      2=Several times/month;
      3=Several times/year;
      4=Rarely; 5=Never                   X = 4.30 (0.04)
 How often do you contact physicians
 regarding a zoonotic disease?
      1=Several times/week;
      2=Several times/month;
      3=Several times/year;
      4=Rarely; 5=Never                   X = 4.21 (0.04)
 If you know that a client is
 immunocompromised, do you offer
 consultation on zoonotic disease
 prevention?
      - Yes                                   n=96(sup c)

      - No                                       n=9
      - The situation has never
      arisen						 n=205
 How much risk to immunocompromised
 patients is associated with owning or
 having contact with the following
 animals?
      1=Highest risk to 5=Lowest
      risk

           - Reptile                   	X = 2.28 (0.09)

           - Bird                      	X = 2.49 (0.07)
           - Kitten (<6 months of age)    X = 2.81 (0.07)
           - Puppy (<6 months of age)     X = 3.02 (0.07)

           - Farm animals              	X = 3.05 (0.07)

           - Cat                       	X = 3.28 (0.06)

           - Dog                       	X = 3.86 (0.06)
 ------------------------------------------------------------------------------
 (sup a)Mean of all respondents.
 (sup b)Standard error of the mean.
 (sup c)Absolute number of veterinarians answering "yes", "no" or "the situation has
 never arisen".

When physicians were asked (on a scale of 1 to 5 with 1 = very comfortable
and 5 = not comfortable) how comfortable they felt about advising patients
on the role of animals in the transmission of zoonotic agents and
associated risks, with the exception of infectious disease specialists
(whose mean comfort level = 1.92 was significantly [p < 0.0001] better than
that of the overall population of physicians), they responded that they
were not very comfortable in this role (mean = 3.69, Table 2); moreover,
physicians indicated that veterinarians should play an equal or greater
role in advising patients about zoonotic diseases (Table 2). In particular,
they suggested that veterinarians should be involved not only in
controlling zoonotic disease pathogens in animals, but also in providing
information for patients and physicians (Table 2). However, the survey
demonstrated a nearly complete lack of communication between physicians and
veterinarians about zoonotic disease issues (Tables 1,2). In addition,
patients themselves do not appear to view veterinarians as a source of
zoonotic disease information. Of 310 veterinarians, 96 indicated that they
offer special consultation about additional steps for zoonotic disease
prevention if they are aware of the fact that a client is
immunocompromised; however, for 205 of 310 respondents, the client's health
was never discussed (Table 1).

 Table 2. Survey of physicians

 ------------------------------------------------------------------------------
 Questions                                 Responses
 ------------------------------------------------------------------------------
 How often do you encounter or
 discuss zoonotic diseases in your
 patient population?
      1=Several times/day;
      2=Daily; 3=Weekly;              
      4=Occasionally; 5=Never		     X = 4.16(sup a) (0.03)(sup b)

 How comfortable do you feel in
 advising patients specifically on
 the animal aspects of transmission
 and the risks for zoonotic diseases?
      1=Very comfortable to
      5=Not 						X = 3.69 (0.05)
 Should veterinarians be involved in
 advising clients about the potential
 for zoonotic disease?
      1=Veterinarian should have
      primary responsibility;
      3=Responsibility should be
      equal; 5= Physician should
      have primary
      responsibility                  		X = 2.77 (0.05)
 How involved should veterinarians be
 in the following areas in reducing
 transmission of zoonotic disease
 agents to immunocompromised
 patients, providing that client
 confidentiality is maintained?
      1=Very involved to 5=Not
      involved

           - General
           maintenance of
           animal health              		X = 1.62 (0.06)
           - Additional
           zoonotic disease
           screening of
           animals                    		X = 1.78 (0.06)
           - Zoonoses
           education for
           patients                   		X = 2.08 (0.06)
           - Consultation
           for physicians             		X = 2.12 (0.06)
 How often do veterinarians contact
 you regarding zoonotic diseases?
      1=Several times/week;
      2=Several times/month;
      3=Several times/year;
      4=Rarely; 5=Never               		 X = 4.74 (0.03)
 How often do you contact
 veterinarians for advice on the
 animal aspects of transmission and
 risks of zoonotic diseases?
      1=Several times/week;
      2=Several times/month;
      3=Several times/year;
      4=Rarely; 5=Never               		X = 4.55 (0.03)
 How much risk to immunocompromised
 patients is associated with owning
 or having contact with the following
 animals?
      1=Highest risk to 5=Lowest
      risk

           - Bird                     		X = 2.37 (0.07)
           - Kitten (<6 months of age)          X = 2.47 (0.08)

           - Cat                      		X = 2.58 (0.07)

           - Reptile                  		X = 2.64 (0.09)

           - Farm animals             		X = 2.94 (0.08)
           - Puppy (<6 months of age)           X = 3.28 (0.08)

           - Dog                      		X = 3.69 (0.06)
 ------------------------------------------------------------------------------
 (sup a)Mean of all respondents.
 (sup b) Standard error of the mean.

In the second portion of the survey, we examined the views of physicians
and veterinarians on the possible disease risks (from specific animals or
pathogens) to immunocompromised persons. Various animals were ranked on a
risk scale of 1 to 5 (1 = highest risk to 5 = lowest risk, with an option
to respond "unsure"). Veterinarians assigned a higher risk than physicians
to reptiles (p = 0.004) and puppies (p = 0.01); physicians assigned a
higher risk than veterinarians to cats (p < 0.00001) and kittens (p =
0.001) (Tables  1,2). Physicians and veterinarians were also asked to list
the two zoonotic pathogens of greatest concern for immunocompromised
persons (Table 3). The two most frequently named pathogens were Salmonella
spp. and Toxoplasma gondii. Within this ranking, Salmonella spp. were
listed more frequently (p = 0.001) by veterinarians than physicians, and
this concern may explain why veterinarians thought that reptiles pose the
greatest risk to the immunocompromised (Table 1). (Because of the high
prevalence in reptiles of Salmonella infection, immunocompromised persons
are advised not to own or handle reptiles [2,11]). In contrast, T. gondii
was listed as a potential disease risk more often by physicians (p =
0.001), which is consistent with physician's concern about
immunocompromised persons owning kittens and cats as pets (Table 2).

 Table 3. Responses of physicians and veterinarians when In summary, our
 asked to "List the two zoonotic pathogens you believe   survey results
 should be of greatest concern for immunocompromised     indicate that
 individuals"                                            physicians and
                                                         veterinarians hold
                                                         very different
 --------------------------------------------------------views about the
 Pathogen              Physicians   Veterinarians        disease risks from
 --------------------------------------------------------certain animals
                                                         and infectious
 Toxoplasma gondii  n(sup a) = 144 n(sup b) = 74(sup c)  agents and
 Salmonella spp.         n = 61        n = 111(sup c)    communicate very
                                                         little about
 Cryptosporidium                                         zoonotic disease
 parvum                  n = 54         n = 86           prevention. The
 Mycobacterium spp.      n = 29         n = 18           perceived risks
                                                         posed by specific
 Chlamydia psittaci      n = 24         n = 31           pathogens raise
 Bartonella spp.         n = 15         n = 10           some questions.
 Histoplasma                            n = 1c           First, for both
 capsulatum              n = 13                          Salmonella spp.
                                                         and T. gondii,
 Giardia lamblia         n = 12         n = 14           contact with pets
 Pasteurella spp.         n = 9         n = 6            is not the only,
                                                         or even the most
 Borrelia burgdorferi     n = 8         n = 6            important, source
 Pneumocystis carinii     n = 8         n = 2            of infection for
 Cytomegalovirus          n = 8       n = 0(sup C)       humans.
                                                         Contaminated foods
 Blastomyces                                             are the most
 dermatitidis             n = 7         n = 9            common vehicle of
 Rabies virus             n = 6         n = 2            Salmonella spp.
                                                         infection (12);
 Campylobacter spp.       n = 5         n = 10           undercooked meat
 Escherichia coli         n = 2        n = 11(sup d)     is also a common
                                                         vehicle of T.
 Streptococcus spp.       n = 1        n = 9(sup d)      gondii infection.

 Dermatophytes            n = 1        n = 24(sup C)     Up to 25% of lamb
                                                         and pork samples
 "Unsure"                n = 29         n = 9            contain Toxoplasma
 Total number of         n = 259       n = 271           tissue cysts (13).
 participants                                            Therefore,
 responding                                              although cats are
 to this question                                        the definitive
                                                         hosts for T.
 --------------------------------------------------------gondii, cat
 (sup a)Total number of times each agent was listed by   ownership is not
 physicians.                                             associated with an
 (sup b)Total number of times each agent was listed by   increase in
 veterinarians.                                          among HIV-infected                                                        Toxoplasma seroconversion
 (sup c,d) The number of times these organisms were 	   persons (14).
 physicians and veterinarians were significantly         of the infectious   
 different. (sup c)p < 0.001; (sup d)p=0.02 ).           disease agents (e.g., 
 Secondly, a number						   Borrelia burgdorferi,
                                                         Histoplasma capsulatum,
 								         Blastomyces dermatitidis,
and Pneumocystis carinii) listed as zoonotic disease risks by both physicians 
and veterinarians are not truly zoonotic, but rather shared infections. Both 
animals and humans are infected, but animals are not the direct vehicles of 
infection for humans. In addition, cytomegaloviruses of humans and animals are 
not infectious across species. Finally, it is surprising that infection with 
B. henselae, the causative agent of cat scratch disease, which also causes 
bacillary angiomatosis, peliosis hepatis, and other conditions in immunocompromised 
persons, was listed relatively infrequently by both physicians and veterinarians
(Table 3). Exposure to kittens has been clearly implicated as a significant risk 
factor in the epidemiology of B. henselae (15). Both physicians and veterinarians 
need to recognize the role of this pathogen in the zoonotic infection of 
immunocompromised persons and the role of cats in its transmission.

Our finding that 205 of 310 veterinarians never knew a client's
immunocompromised condition is consistent with a previous study in which
only 21% of HIV patients felt most comfortable in asking their veterinarian
about the health risks of pet ownership (16). Through approaches such as
small signs in exam rooms, zoonotic disease brochures in reception areas,
comments in practice newsletters, and affiliation with support groups in
the community, veterinarians can encourage immunocompromised persons to
avail themselves of the diagnostic and preventive measures that can be
provided for zoonotic agents.

Our results suggest that communication between physicians and veterinarians
about zoonotic diseases is largely absent. Enhancing such communication
could help prevent transmission of zoonotic agents. In addition to directly
contacting veterinary practitioners in their community, physicians can also
contact their state health departments for information, since some health
departments have public health veterinarians on staff. Links between the
professions on a broader scale (e.g., through combined veterinary/medical
student training and continuing education) to foster a broader consensus
about zoonotic disease risks and prevention should also be encouraged.

Acknowledgments

We thank Linda Sullivan, George Mejicano, Ken Felz, Barbara Burell, and
Winifred Grant for assistance in designing or distributing the surveys and
Chet Thomas, Rick Nordheim, Brian Aldridge, Sandra Martin, and Tom Tabone
for assisting in data analysis.

      The Geraldine R. Dodge Foundation and the Bernice Barbour Foundation
supported this research.

      Dr. Grant is a staff veterinarian at the New Haven Central Hospital
for Veterinary Medicine in New Haven, Connecticut. She conducted this
research during her studies at the University of Wisconsin School of
Veterinary Medicine.

      Dr. Olsen is an assistant professor of public health at the
University of Wisconsin School of Veterinary Medicine. His research
interests include DNA vaccine development and immunity to influenza viruses
in horses and pigs, as well as the molecular epidemiology of swine
influenza viruses as zoonotic agents.

      Address for correspondence: Christopher W. Olsen, Department of
Pathobiological Sciences, School of Veterinary Medicine, University of
Wisconsin, 2015 Linden Drive West, Madison, WI 53706, USA; fax:
608-263-0438; e-mail: olsenc@svm.vetmed.wisc.edu.

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Emerging Infectious Diseases
National Center for Infectious Diseases
Centers for Disease Control and Prevention
Atlanta, GA

URL: ftp://ftp.cdc.gov/pub/EID/vol5no1/ascii/grant.txt

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