Zoonoses and Public Health
ORIGINAL ARTICLE
Prevalence of IgG Antibodies to Toxoplasma gondii in Veterinary and Undergraduate Students at Virginia Tech, Blacksburg, Virginia A. C. Rosypal1, A. E. Houk2, A. M. Zajac2 and D. S. Lindsay2,3 1 2 3
Department of Natural Sciences and Mathematics, Johnson C. Smith University, Charlotte, NC, USA Department of Biomedical Sciences and Pathology, Virginia-Maryland College of Veterinary Medicine, Virginia Tech, Blacksburg, VA, USA Virginia Tech Faculty of Health Sciences, Virginia Tech, Blacksburg, VA, USA
Impacts
• We examined the prevalence of Toxoplasma gondii antibodies in veterinary
• •
students (high exposure) and undergraduate students (normal exposure) for antibodies to T. gondii and found that antibodies were more prevalent in veterinary students than undergraduates, but the difference was not significant (P > 0.05). Age was a significant (P < 0.05) risk factor, but gender, cat ownership and meat consumption were not (P > 0.05). Our findings do not indicate that veterinary students have a higher prevalence of antibodies to T. gondii than undergraduate students and it supports recent studies that indicate the overall prevalence of T. gondii is decreasing in humans in the United States.
Keywords: Cats; meat; Toxoplasma gondii; veterinary students; undergraduate students Correspondence: D. Lindsay. Department of Biomedical Sciences and Pathology, Virginia-Maryland College of Veterinary Medicine, Virginia Tech, Blacksburg, VA 24061, USA. Tel.: +540 231 6032; Fax: +540 231 3426; E-mail: [email protected] This study was conducted in the Department of Biomedical Sciences and Pathobiology, Virginia-Maryland College of Veterinary Medicine, Center for Molecular Medicine and Infectious Diseases, 1410 Prices Fork Road, Virginia Tech, Blacksburg, VA 24061, USA Received for publication September 5, 2014 doi: 10.1111/zph.12184
Summary Toxoplasma gondii is a globally distributed parasitic protozoan that infects humans and other warm-blooded vertebrates. Felids are the only definitive host for T. gondii, and they excrete oocysts in their faeces. The national prevalence in humans is declining in the United States. This zoonotic organism is of particular interest due to its importance in pregnant women, in individuals with altered immune systems, and in reactivated ocular infections. Exposure to the parasite in humans is usually associated with consumption of raw or undercooked meat or by accidental ingestion of oocysts. It was hypothesized that veterinary students would have a greater chance at exposure to the parasite than an average population of undergraduate students due to increased contact with cats who are infected. A commercially available ELISA was used to examine serum samples from 336 students (252 veterinary students and 84 undergraduate students) at Virginia Polytechnic Institute and State University and the Virginia-Maryland Regional College of Veterinary Medicine for serum IgG antibodies to T. gondii antigen. The prevalence of T. gondii in these subjects was 5.6% in veterinary school students (n = 252) and 2.4% in undergraduates (n = 84). There was no significant difference (P > 0.05) in the prevalence of T. gondii antibodies in veterinary versus undergraduate students. The overall prevalence of 4.8% in all students in this study reflects the continuing decline of antibodies to T. gondii in humans in the United States.
Introduction Toxoplasma gondii is an important zoonotic parasite that is capable of causing clinical disease in humans and other © 2015 Blackwell Verlag GmbH
animals that are exposed to infective stages of the parasite. Members of the cat family (Felidae) are the only definitive hosts for T. gondii, and they excrete environmentally resistant oocysts in their faeces. Human infections usually occur 1
T. gondii in Veterinary and Undergraduate Students
by ingestion of oocysts in contaminated food and drink or by ingestion of tissue cysts in undercooked meat. Infections by blood transfusion and organ transplantation occur occasionally (Jones et al., 2007). Human T. gondii infections are typically asymptomatic in adults, but T. gondii may cause severe neurological and ocular disease in congenitally infected and in immunosuppressed individuals (Jones et al., 2007). Latent T. gondii infections have recently been recognized to adversely impact human health (Webster et al., 2013). Infected adults may develop toxoplasmic encephalitis, retinochoroiditis and pulmonitis (Elmore et al., 2010). Chronic infection with T. gondii may also be associated with behavioural changes and mental illness (Jones et al., 2007; Webster et al., 2013; Flegr et al., 2014.) The prevalence of T. gondii in the United States is declining (Jones et al., 2014). Studies conducted through the National Health and Nutrition Examination Survey (NHNES) indicated that the T. gondii prevalence among Americans aged 6–49 years old decreased from 14.1% (1988–1994) to 9.0% (1999–2004) (Jones et al., 2001, 2009, 2014). It is currently reported to be 6.7% (2009–2010) in the most recent NHNES (Jones et al., 2014). Risk factors for human T. gondii infections in the United States include exposure to kittens and consumption of certain raw or undercooked foods (Jones et al., 2009). It has also been shown that infection rates are higher among people who are over 12 years of age (Jones et al., 2001). Previous studies suggest that veterinarians, veterinary personnel and veterinary students may have a higher risk of T. gondii infection because they frequently interact with cats (Zimmerman, 1976; Shuhaiber et al., 2003). Veterinary students are continuously exposed to cats due to the nature of their education. The purpose of this study was to investigate the seroprevalence of and risk factors for T. gondii exposure in veterinary students and undergraduate students. This study hypothesized that infection rates would be higher among veterinary students due to their increased contact with cats that may be infected with T. gondii. Undergraduate students (non-veterinary) were also tested for antibodies to T. gondii. Undergraduate students were expected to reflect the prevalence of exposure to T. gondii in college age students in the United States. Materials and Methods Source of samples and questionnaire This study was approved by the Institutional Review Board, Office of Research Compliance, Virginia Tech, Blacksburg, Virginia, USA. Students enrolled in the Veterinary Parasitology course or the undergraduate Introduction to Parasitology course offered for credit at Virginia Tech from 2002 to 2006 were given the opportunity to donate blood samples for T. gondii testing. Most of the subjects were originally from the south-eastern United States. Subjects 2
A. C. Rosypal et al.
completed an accompanying survey in which they were asked to indicate their age at the time of the study, sex, whether or not they ate meat, frequency of rare or medium-rare meat consumption, and history of cat ownership. Only subjects who completed at least one item on the survey were tested for T. gondii antibodies. IgG ELISA Serum samples were examined using a commercially available ELISA (Toxoplasma gondii IgG ELISA Kit; Abnovaâ Corporation, Taiwan) using the procedures provided by the manufacturer which were based on the findings of Voller et al. (1976), Lin et al. (1980), Turune et al. (1983) and Roller et al. (1987). Serum samples were diluted 1/40 in sample buffer and 100 ll was used in the ELISA. Once completed, the ELISA plate was read at 450 nm on a Spectra max 340PC spectrophotometer (Molecular Devices, Sunnyvale, CA, USA) with a microwell reader. Statistical analysis Results were calculated based on wavelengths of each well calculated by the plate reader. Data were then transferred onto a Microsoft Excel spreadsheet, and the averages of the controls and calibrators were taken from the wavelength readings. The averages of the positive and negative controls were determined by dividing the average of the cut-off calibrator readings. The average was determined for individual samples by dividing by the average for the cut-off calibrator which gave a Toxo G Index (TGI) that was used to interpret whether the individual sample had IgG antibodies to T. gondii. A positive result was considered a TGI of 1.00 or greater and indicated a prior exposure to T. gondii. A negative result was considered a TGI 0.05) between the number of T. gondii-positive males compared to T. gondii-positive females. The average age of all females tested was 24.1 years. The average ages of T. gondii antibody positive and antibody negative females were statistically different (P < 0.05) being 27.9 years (95% CI: 22.3–33.5) and 24.0 years (95% CI: 23.5–24.4), respectively. For males, the average age was 24.8 years with the average age for positive males being 30.6 years (95% CI: 16.3–44.9), and the average age for antibody negative males was 24.4 years (95% CI: 23.2–25.7). There was no significant difference (P > 0.05) between age and antibody status within males. Cat ownership was reported for 283 (84.2%) (95% CI: 80.0–87.7) of all 336 subjects and 330 (98.2%) (95% CI: 96.1–99.2) reported a history of eating meat. Of the 16 T. gondii-positive subjects, 15 (93.8%) (95% CI: 71.7–98.9) owned cats and 15 (93.8%) (95% CI: 71.7–98.9) ate meat. We found no significant (P > 0.05) differences in T. gondii antibody status and cat ownership nor did we find any significant differences in the eating of meat and the prevalence of T. gondii antibody positive samples. Discussion The overall seroprevalence in students of 4.8% determined in this study is less than the T. gondii national average of 6.7% reported for the general population of the United States in the most recent national survey (Jones et al., 2014). Antibodies to T. gondii were only detected in 5.6% of veterinary students, which is also lower than the most recent survey of Americans aged 6–49 years of 6.7% (Jones et al., 2014). This suggests that increased contact with cats © 2015 Blackwell Verlag GmbH
T. gondii in Veterinary and Undergraduate Students
through veterinary work does not expose veterinary students to T. gondii at a higher rate than the general population. Sengbush and Sengbush (1976) found that a population of 60 veterinary workers (12 small animal veterinarians and 48 small animal technicians) did not have a higher anti-T. gondii antibody prevalence than did 60 college students. Zimmerman (1976) found that 20.4% of 142 veterinary students were positive for antibodies to T. gondii. No significant differences (P > 0.05) in prevalence were found based on age, sex, meat eating or animal contact (Zimmerman, 1976) in these veterinary students; however, no control population was used for comparison. Shuhaiber et al. (2003) examined sera collected from 110 veterinarians from Canada attending a national veterinary meeting and found that 18 (16.8%) were positive. They also found that 2 (6.5%) of 31 veterinary technicians attending the veterinary meeting were positive for antibodies to T. gondii (Shuhaiber et al., 2003). The total prevalence of antibodies in these 141 subjects was 14.2% (95 CI; 8.4–19.9%) and they concluded that their study indicated that exposure to cats does not appear to increase their risk of contracting T. gondii infection (Shuhaiber et al., 2003). In the present study, age was the only risk factor to have a significant impact on seropositive status in tested students and those who were older were more likely to have T. gondii antibodies. A previous study reported that infection rates are higher among people who are over 12 years of age (Jones et al., 2001). Results from this study indicated that 2.4% of undergraduate students were seropositive for T. gondii, which is lower than the national average despite all subjects being over 12 years old. Neither the veterinary students nor the undergraduate students, who were all over 12 years old, showed increased T. gondii exposure despite their chance of being exposed to T. gondii over a longer time period compared to adolescent age people. Interacting with cats may increase the chance of T. gondii infection in humans by exposure to oocysts in cat faeces. In the present study, 84.2% of all subjects owned a cat at some point during their lives and 15 of 16 (93.8%) of T. gondii-positive students had a history of cat ownership. Jones et al. (2009) showed that exposure to cats is a risk factor for human T. gondii infections in the United States. However, it is difficult to separate contact with or interacting with cats and cat ownership because of the cosmopolitan presence of cats. Additionally, outdoor cats can contaminate the environment of individuals that do not own cats. Although most (93.8%) of the T. gondii-positive subjects in the present study owned cats, 83.8% (268 cat owners of 320 T. gondii negative subjects) of the students without antibodies to T. gondii also had a history of cat ownership. Ingestion of tissue cysts in undercooked meat is a common route of T. gondii transmission in humans. Answers 3
T. gondii in Veterinary and Undergraduate Students
to the survey in the present study indicated that 330 of 336 (98.2%) of subjects ate meat and 15 of 16 (93.8%) of students with antibodies to T. gondii consumed meat. The extent of meat as a source of T. gondii infection in the United States is unclear (Dubey and Jones, 2008); however, a European study found consumption of insufficiently cooked meat to be a major risk factor (Cook et al., 2000). The results indicate that the prevalence of T. gondii in veterinary students and undergraduate students is actually lower than the national average and does not indicate that they have a higher risk of coming into contact with T. gondii than the normal population. Cat ownership was 93.8% of positive subjects and supports cats being a risk factor. We must reject our hypotheses that veterinary students would have a higher prevalence of antibodies to T. gondii due to exposure to cats. This research shows a continuing decline in T. gondii prevalence in the United States and agrees with recent national surveys of the United States population. Acknowledgements We thank Drs. Sheila M. Mitchell, David Goodwin and Carly Jordan for assistance with sample collection for this project. We thank Sade Moore and Nancy Tenpenny for conducting ELISA tests. This experiment is supported in part by the Office of Research and Graduate Studies, Virginia-Maryland Regional College of Veterinary Medicine, Virginia Tech, Blacksburg, Virginia, USA. References Brown, L. D., T. T. Cai, and A. DasGupta, 2001: Interval estimation for a proportion. Stat. Sci. 16, 101–133. Cook, A. J. C., R. E. Gilbert, W. Buffolano, J. Zufferey, E. Petersen, P. A. Jenum, W. Foulon, A. E. Semprini, and D. T. Dunn, 2000: Sources of Toxoplasma infection in pregnant women: European multicenter case–control study. Br. Med. J. 321, 142–147. Dubey, J. P., and J. L. Jones, 2008: Toxoplasma gondii infection in humans and animals in the United States. Int. J. Parasitol. 38, 1257–1278. Elmore, S. A., J. L. Jones, P. A. Conrad, S. Patton, D. S. Lindsay, and J. P. Dubey, 2010: Toxoplasma gondii: epidemiology, feline clinical aspects, and prevention. Trends Parasitol. 26, 190–196.
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Flegr, J., J. Prandota, M. Sovickova, and Z. H. Israili, 2014: Toxoplasmosis – a global threat. Correlation of latent toxoplasmosis with specific disease burden in a set of 88 countries. PLoS ONE 9, e90203. Jones, J. L., D. Kruszon-Moran, M. Wilson, G. McQuillan, T. Navin, and J. B. McAuley, 2001: Toxoplasma gondii infection in the United States: seroprevalence and risk factors. Am. J. Epidemiol. 154, 357–365. Jones, J. L., D. Kruszon-Moran, K. Sanders-Lewis, and M. Wilson, 2007: Toxoplasma gondii infection in the United States, 1994–2004, decline from the prior decade. Am. J. Trop. Med. Hyg. 77, 405–410. Jones, J. L., V. Dargelas, J. Roberts, C. Press, J. S. Remington, and J. G. Montoya, 2009: Risk factors for Toxoplasma gondii infection in the United States. Clin. Infect. Dis. 49, 878–884. Jones, J. L., D. Kruszon-Moran, H. M. Rivera, C. Price, and P. P. Wilkins, 2014: Toxoplasma gondii seroprevalence in the United States 2009–2010 and comparison with the past two decades. Am. J. Trop. Med. Hyg. 90, 1135–1139. Lin, T. M., S. P. Halbert, and G. R. O’Connor, 1980: Standardized quantitative enzyme-linked immunoassay for antibodies to Toxoplasma gondii. J. Clin. Microbiol. 11, 275–681. Roller, A., A. Bartlett, and D. E. Bidwell, 1987: Enzyme immunoassay with special reference ELISA technique. J. Clin. Pathol. 31, 507–520. Sengbush, H. G., and L. A. Sengbush, 1976: Toxoplasma antibody prevalence in veterinary personnel and a selected population not exposed to cats. Am. J. Epidemiol. 103, 595–597. Shuhaiber, S., G. Koren, R. Boskovic, T. R. Einarson, O. P. Soldin, and A. Einarson, 2003: Seroprevalence of Toxoplasma gondii infection among veterinary staff in Ontario, Canada (2002): implications for teratogenic risk. BMC Infect. Dis. 3, 8. Turune, H. J., P. O. Leinikke, and K. M. Saari, 1983: Demonstration of intraocular synthesis of immunoglobulin G Toxoplasma antibodies for specific diagnosis of toxoplasmic chorioretinitis by enzyme immunoassay. J. Clin. Microbiol. 17, 988–992. Voller, A., D. E. Bidwell, A. Bartlett, D. G. Flick, M. Perkins, and B. Oladshin, 1976: A microplate enzyme-immunoassay for Toxoplasma antibodies. J. Clin. Pathol. 29, 50–153. Webster, J. P., M. Kaushik, G. C. Bristow, and G. A. McConkey, 2013: Toxoplasma gondii infection, from predation to schizophrenia: can animal behaviour help us understand human behaviour? J. Exp. Biol. 216, 99–112. Zimmerman, W. J., 1976: Prevalence of Toxoplasma gondii antibodies among veterinary college staff and students, Iowa State University. Public Health Rep. 91, 526–532.
© 2015 Blackwell Verlag GmbH
ORIGINAL ARTICLE
Prevalence of IgG Antibodies to Toxoplasma gondii in Veterinary and Undergraduate Students at Virginia Tech, Blacksburg, Virginia A. C. Rosypal1, A. E. Houk2, A. M. Zajac2 and D. S. Lindsay2,3 1 2 3
Department of Natural Sciences and Mathematics, Johnson C. Smith University, Charlotte, NC, USA Department of Biomedical Sciences and Pathology, Virginia-Maryland College of Veterinary Medicine, Virginia Tech, Blacksburg, VA, USA Virginia Tech Faculty of Health Sciences, Virginia Tech, Blacksburg, VA, USA
Impacts
• We examined the prevalence of Toxoplasma gondii antibodies in veterinary
• •
students (high exposure) and undergraduate students (normal exposure) for antibodies to T. gondii and found that antibodies were more prevalent in veterinary students than undergraduates, but the difference was not significant (P > 0.05). Age was a significant (P < 0.05) risk factor, but gender, cat ownership and meat consumption were not (P > 0.05). Our findings do not indicate that veterinary students have a higher prevalence of antibodies to T. gondii than undergraduate students and it supports recent studies that indicate the overall prevalence of T. gondii is decreasing in humans in the United States.
Keywords: Cats; meat; Toxoplasma gondii; veterinary students; undergraduate students Correspondence: D. Lindsay. Department of Biomedical Sciences and Pathology, Virginia-Maryland College of Veterinary Medicine, Virginia Tech, Blacksburg, VA 24061, USA. Tel.: +540 231 6032; Fax: +540 231 3426; E-mail: [email protected] This study was conducted in the Department of Biomedical Sciences and Pathobiology, Virginia-Maryland College of Veterinary Medicine, Center for Molecular Medicine and Infectious Diseases, 1410 Prices Fork Road, Virginia Tech, Blacksburg, VA 24061, USA Received for publication September 5, 2014 doi: 10.1111/zph.12184
Summary Toxoplasma gondii is a globally distributed parasitic protozoan that infects humans and other warm-blooded vertebrates. Felids are the only definitive host for T. gondii, and they excrete oocysts in their faeces. The national prevalence in humans is declining in the United States. This zoonotic organism is of particular interest due to its importance in pregnant women, in individuals with altered immune systems, and in reactivated ocular infections. Exposure to the parasite in humans is usually associated with consumption of raw or undercooked meat or by accidental ingestion of oocysts. It was hypothesized that veterinary students would have a greater chance at exposure to the parasite than an average population of undergraduate students due to increased contact with cats who are infected. A commercially available ELISA was used to examine serum samples from 336 students (252 veterinary students and 84 undergraduate students) at Virginia Polytechnic Institute and State University and the Virginia-Maryland Regional College of Veterinary Medicine for serum IgG antibodies to T. gondii antigen. The prevalence of T. gondii in these subjects was 5.6% in veterinary school students (n = 252) and 2.4% in undergraduates (n = 84). There was no significant difference (P > 0.05) in the prevalence of T. gondii antibodies in veterinary versus undergraduate students. The overall prevalence of 4.8% in all students in this study reflects the continuing decline of antibodies to T. gondii in humans in the United States.
Introduction Toxoplasma gondii is an important zoonotic parasite that is capable of causing clinical disease in humans and other © 2015 Blackwell Verlag GmbH
animals that are exposed to infective stages of the parasite. Members of the cat family (Felidae) are the only definitive hosts for T. gondii, and they excrete environmentally resistant oocysts in their faeces. Human infections usually occur 1
T. gondii in Veterinary and Undergraduate Students
by ingestion of oocysts in contaminated food and drink or by ingestion of tissue cysts in undercooked meat. Infections by blood transfusion and organ transplantation occur occasionally (Jones et al., 2007). Human T. gondii infections are typically asymptomatic in adults, but T. gondii may cause severe neurological and ocular disease in congenitally infected and in immunosuppressed individuals (Jones et al., 2007). Latent T. gondii infections have recently been recognized to adversely impact human health (Webster et al., 2013). Infected adults may develop toxoplasmic encephalitis, retinochoroiditis and pulmonitis (Elmore et al., 2010). Chronic infection with T. gondii may also be associated with behavioural changes and mental illness (Jones et al., 2007; Webster et al., 2013; Flegr et al., 2014.) The prevalence of T. gondii in the United States is declining (Jones et al., 2014). Studies conducted through the National Health and Nutrition Examination Survey (NHNES) indicated that the T. gondii prevalence among Americans aged 6–49 years old decreased from 14.1% (1988–1994) to 9.0% (1999–2004) (Jones et al., 2001, 2009, 2014). It is currently reported to be 6.7% (2009–2010) in the most recent NHNES (Jones et al., 2014). Risk factors for human T. gondii infections in the United States include exposure to kittens and consumption of certain raw or undercooked foods (Jones et al., 2009). It has also been shown that infection rates are higher among people who are over 12 years of age (Jones et al., 2001). Previous studies suggest that veterinarians, veterinary personnel and veterinary students may have a higher risk of T. gondii infection because they frequently interact with cats (Zimmerman, 1976; Shuhaiber et al., 2003). Veterinary students are continuously exposed to cats due to the nature of their education. The purpose of this study was to investigate the seroprevalence of and risk factors for T. gondii exposure in veterinary students and undergraduate students. This study hypothesized that infection rates would be higher among veterinary students due to their increased contact with cats that may be infected with T. gondii. Undergraduate students (non-veterinary) were also tested for antibodies to T. gondii. Undergraduate students were expected to reflect the prevalence of exposure to T. gondii in college age students in the United States. Materials and Methods Source of samples and questionnaire This study was approved by the Institutional Review Board, Office of Research Compliance, Virginia Tech, Blacksburg, Virginia, USA. Students enrolled in the Veterinary Parasitology course or the undergraduate Introduction to Parasitology course offered for credit at Virginia Tech from 2002 to 2006 were given the opportunity to donate blood samples for T. gondii testing. Most of the subjects were originally from the south-eastern United States. Subjects 2
A. C. Rosypal et al.
completed an accompanying survey in which they were asked to indicate their age at the time of the study, sex, whether or not they ate meat, frequency of rare or medium-rare meat consumption, and history of cat ownership. Only subjects who completed at least one item on the survey were tested for T. gondii antibodies. IgG ELISA Serum samples were examined using a commercially available ELISA (Toxoplasma gondii IgG ELISA Kit; Abnovaâ Corporation, Taiwan) using the procedures provided by the manufacturer which were based on the findings of Voller et al. (1976), Lin et al. (1980), Turune et al. (1983) and Roller et al. (1987). Serum samples were diluted 1/40 in sample buffer and 100 ll was used in the ELISA. Once completed, the ELISA plate was read at 450 nm on a Spectra max 340PC spectrophotometer (Molecular Devices, Sunnyvale, CA, USA) with a microwell reader. Statistical analysis Results were calculated based on wavelengths of each well calculated by the plate reader. Data were then transferred onto a Microsoft Excel spreadsheet, and the averages of the controls and calibrators were taken from the wavelength readings. The averages of the positive and negative controls were determined by dividing the average of the cut-off calibrator readings. The average was determined for individual samples by dividing by the average for the cut-off calibrator which gave a Toxo G Index (TGI) that was used to interpret whether the individual sample had IgG antibodies to T. gondii. A positive result was considered a TGI of 1.00 or greater and indicated a prior exposure to T. gondii. A negative result was considered a TGI 0.05) between the number of T. gondii-positive males compared to T. gondii-positive females. The average age of all females tested was 24.1 years. The average ages of T. gondii antibody positive and antibody negative females were statistically different (P < 0.05) being 27.9 years (95% CI: 22.3–33.5) and 24.0 years (95% CI: 23.5–24.4), respectively. For males, the average age was 24.8 years with the average age for positive males being 30.6 years (95% CI: 16.3–44.9), and the average age for antibody negative males was 24.4 years (95% CI: 23.2–25.7). There was no significant difference (P > 0.05) between age and antibody status within males. Cat ownership was reported for 283 (84.2%) (95% CI: 80.0–87.7) of all 336 subjects and 330 (98.2%) (95% CI: 96.1–99.2) reported a history of eating meat. Of the 16 T. gondii-positive subjects, 15 (93.8%) (95% CI: 71.7–98.9) owned cats and 15 (93.8%) (95% CI: 71.7–98.9) ate meat. We found no significant (P > 0.05) differences in T. gondii antibody status and cat ownership nor did we find any significant differences in the eating of meat and the prevalence of T. gondii antibody positive samples. Discussion The overall seroprevalence in students of 4.8% determined in this study is less than the T. gondii national average of 6.7% reported for the general population of the United States in the most recent national survey (Jones et al., 2014). Antibodies to T. gondii were only detected in 5.6% of veterinary students, which is also lower than the most recent survey of Americans aged 6–49 years of 6.7% (Jones et al., 2014). This suggests that increased contact with cats © 2015 Blackwell Verlag GmbH
T. gondii in Veterinary and Undergraduate Students
through veterinary work does not expose veterinary students to T. gondii at a higher rate than the general population. Sengbush and Sengbush (1976) found that a population of 60 veterinary workers (12 small animal veterinarians and 48 small animal technicians) did not have a higher anti-T. gondii antibody prevalence than did 60 college students. Zimmerman (1976) found that 20.4% of 142 veterinary students were positive for antibodies to T. gondii. No significant differences (P > 0.05) in prevalence were found based on age, sex, meat eating or animal contact (Zimmerman, 1976) in these veterinary students; however, no control population was used for comparison. Shuhaiber et al. (2003) examined sera collected from 110 veterinarians from Canada attending a national veterinary meeting and found that 18 (16.8%) were positive. They also found that 2 (6.5%) of 31 veterinary technicians attending the veterinary meeting were positive for antibodies to T. gondii (Shuhaiber et al., 2003). The total prevalence of antibodies in these 141 subjects was 14.2% (95 CI; 8.4–19.9%) and they concluded that their study indicated that exposure to cats does not appear to increase their risk of contracting T. gondii infection (Shuhaiber et al., 2003). In the present study, age was the only risk factor to have a significant impact on seropositive status in tested students and those who were older were more likely to have T. gondii antibodies. A previous study reported that infection rates are higher among people who are over 12 years of age (Jones et al., 2001). Results from this study indicated that 2.4% of undergraduate students were seropositive for T. gondii, which is lower than the national average despite all subjects being over 12 years old. Neither the veterinary students nor the undergraduate students, who were all over 12 years old, showed increased T. gondii exposure despite their chance of being exposed to T. gondii over a longer time period compared to adolescent age people. Interacting with cats may increase the chance of T. gondii infection in humans by exposure to oocysts in cat faeces. In the present study, 84.2% of all subjects owned a cat at some point during their lives and 15 of 16 (93.8%) of T. gondii-positive students had a history of cat ownership. Jones et al. (2009) showed that exposure to cats is a risk factor for human T. gondii infections in the United States. However, it is difficult to separate contact with or interacting with cats and cat ownership because of the cosmopolitan presence of cats. Additionally, outdoor cats can contaminate the environment of individuals that do not own cats. Although most (93.8%) of the T. gondii-positive subjects in the present study owned cats, 83.8% (268 cat owners of 320 T. gondii negative subjects) of the students without antibodies to T. gondii also had a history of cat ownership. Ingestion of tissue cysts in undercooked meat is a common route of T. gondii transmission in humans. Answers 3
T. gondii in Veterinary and Undergraduate Students
to the survey in the present study indicated that 330 of 336 (98.2%) of subjects ate meat and 15 of 16 (93.8%) of students with antibodies to T. gondii consumed meat. The extent of meat as a source of T. gondii infection in the United States is unclear (Dubey and Jones, 2008); however, a European study found consumption of insufficiently cooked meat to be a major risk factor (Cook et al., 2000). The results indicate that the prevalence of T. gondii in veterinary students and undergraduate students is actually lower than the national average and does not indicate that they have a higher risk of coming into contact with T. gondii than the normal population. Cat ownership was 93.8% of positive subjects and supports cats being a risk factor. We must reject our hypotheses that veterinary students would have a higher prevalence of antibodies to T. gondii due to exposure to cats. This research shows a continuing decline in T. gondii prevalence in the United States and agrees with recent national surveys of the United States population. Acknowledgements We thank Drs. Sheila M. Mitchell, David Goodwin and Carly Jordan for assistance with sample collection for this project. We thank Sade Moore and Nancy Tenpenny for conducting ELISA tests. This experiment is supported in part by the Office of Research and Graduate Studies, Virginia-Maryland Regional College of Veterinary Medicine, Virginia Tech, Blacksburg, Virginia, USA. References Brown, L. D., T. T. Cai, and A. DasGupta, 2001: Interval estimation for a proportion. Stat. Sci. 16, 101–133. Cook, A. J. C., R. E. Gilbert, W. Buffolano, J. Zufferey, E. Petersen, P. A. Jenum, W. Foulon, A. E. Semprini, and D. T. Dunn, 2000: Sources of Toxoplasma infection in pregnant women: European multicenter case–control study. Br. Med. J. 321, 142–147. Dubey, J. P., and J. L. Jones, 2008: Toxoplasma gondii infection in humans and animals in the United States. Int. J. Parasitol. 38, 1257–1278. Elmore, S. A., J. L. Jones, P. A. Conrad, S. Patton, D. S. Lindsay, and J. P. Dubey, 2010: Toxoplasma gondii: epidemiology, feline clinical aspects, and prevention. Trends Parasitol. 26, 190–196.
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