Skip to main content Accessibility help
×
Home

Information:

  • Access
  • Cited by 5

Actions:

      • Send article to Kindle

        To send this article to your Kindle, first ensure no-reply@cambridge.org is added to your Approved Personal Document E-mail List under your Personal Document Settings on the Manage Your Content and Devices page of your Amazon account. Then enter the ‘name’ part of your Kindle email address below. Find out more about sending to your Kindle. Find out more about sending to your Kindle.

        Note you can select to send to either the @free.kindle.com or @kindle.com variations. ‘@free.kindle.com’ emails are free but can only be sent to your device when it is connected to wi-fi. ‘@kindle.com’ emails can be delivered even when you are not connected to wi-fi, but note that service fees apply.

        Find out more about the Kindle Personal Document Service.

        Seroepidemiology of Toxoplasma gondii infection in Bai and Han ethnic groups in southwestern China
        Available formats
        ×

        Send article to Dropbox

        To send this article to your Dropbox account, please select one or more formats and confirm that you agree to abide by our usage policies. If this is the first time you use this feature, you will be asked to authorise Cambridge Core to connect with your <service> account. Find out more about sending content to Dropbox.

        Seroepidemiology of Toxoplasma gondii infection in Bai and Han ethnic groups in southwestern China
        Available formats
        ×

        Send article to Google Drive

        To send this article to your Google Drive account, please select one or more formats and confirm that you agree to abide by our usage policies. If this is the first time you use this feature, you will be asked to authorise Cambridge Core to connect with your <service> account. Find out more about sending content to Google Drive.

        Seroepidemiology of Toxoplasma gondii infection in Bai and Han ethnic groups in southwestern China
        Available formats
        ×
Export citation

Summary

Eating raw pork and/or liver is a custom of the Bai ethnic group in China. Most people living in Dali Bai Autonomous Prefecture, Yunnan Province, southwestern China are of Bai ethnicity. Little is known of the seroprevalence of Toxoplasma gondii in Bai and Han ethnic populations in this region. In the present survey, a total of 555 and 595 blood samples were obtained from Bai and Han ethnic groups in Dali urban and rural areas, respectively. Enzyme-linked immunosorbent assay was performed to examine T. gondii IgG antibodies. Total positive rate of anti-T. gondii IgG in Bai and Han groups in this region was 21·6% (248/1150). The total seroprevalence of T. gondii was significantly higher in the Bai ethnic group (32·3%, 179/555) than in the Han ethnic group (11·6%, 69/595) (P < 0·01). The results of statistical analysis indicated that there was no significant difference between cat feeding/non-cat feeding groups in the Bai ethnic group, the most important risk factor was consumption of raw pork and/or liver for the Bai group, but feeding a cat may be the main route of T. gondii infection for the Han group. Therefore, it is essential to implement integrated strategies to prevent and control T. gondii infection in this unique region of the world.

INTRODUCTION

Toxoplasma gondii can infect a wide range of hosts including wild mammals, birds, livestock, poultry and human beings, leading to zoonotic toxoplasmosis. Most T. gondii infections in immunocompetent individuals are asymptomatic; however, blindness and mental retardation can occur in congenitally infected children [13], and the occurrence of toxoplasmosis in immunocompromised hosts may cause severe diseases or even death.

The prevalence of human toxoplasmosis ranges from 4% in Korea to 92% in Brazil [4], and a mean prevalence of 7·9% has been estimated in China [5]. The different T. gondii prevalences may be due to different factors including sample size, age, occupation, serological techniques, and living customs and habits. Earlier studies indicated that the seroprevalence of T. gondii in slaughter pigs in Yunnan Province in China was 22·28% [6], and the genotype was Toxo DB#9 [7], representing a widespread lineage from pigs, cats, and human patients in China. Dali Bai Autonomous Prefecture is located in the west of Yunnan Province, where 26 ethnic groups live, with the main ethnic groups being of Bai and Han ethnicity. The Bai ethnic group has the habit of consuming raw or undercooked animal meat and/or organs, which may represent a route of T. gondii transmission to humans, and thus stimulated the aims of the present study, which were to investigate T. gondii seroepidemiology and analyse the epidemiological correlation between T. gondii infection and risk factors in Bai and Han populations.

MATERIALS AND METHODS

Serum samples

A total of 555 and 595 blood samples were collected from Bai and Han groups in Dali urban and rural areas, respectively, by medically trained staff. The individuals' occupation and name were not available because of confidentiality. The information including age, sex, ethnicity, education, consumption of raw pork and/or liver and cat feeding information were obtained through questionnaires and recorded during the sample collection (March–December 2013). Blood was collected by venepuncture in plain tubes and centrifuged to remove blood cells. All sera were stored at −20°C after deactivation of complement at 56°C for 30 min before use. This study was approved by the Ethics Committee of Dali University.

Serological tests

All the serum samples were tested for T. gondii IgG antibodies using a commercially available enzyme-linked immunosorbent assay (ELISA) kit (Haitai Co. Ltd, China) according to the manufacturer's instructions. Positive and negative serum controls were included in every plate. The absorbance was measured at 450 nm using an ELISA reader (Bio-Tek ELISA × 808, USA). All samples were run in triplicate.

Statistical analysis

Between the two ethnic groups, the χ 2 test was used to analyse T. gondii prevalence relating to cat feeding (or not), level of education and various degrees of consumption of raw pork and/or liver by the subjects using SPSS software (release 16.0 standard version, SPSS Inc., USA). For all data, the variation in T. gondii seroprevalence (y) of humans of different ethnic groups (x1), sex (x2), cat-feeding behaviour (x3), education (x4), raw pork and/or liver consumption (x5) and age group (x6) was analysed by χ 2 test. Using multivariable regression analysis, each of these variables was included in the Binary Logit Model as an independent variable. The differences were considered as statistically significant between or among levels within factors and interactions when the probability (P) value was <0·05. Odds ratios (OR) with 95% confidence intervals (CI) were calculated by multivariate analysis using logistic regression.

RESULTS

The age and sex distribution of T. gondii seropositivity in Bai and Han ethnic groups are summarized in Table 1. In total, 248 (21·6%) of the 1150 serum samples were anti-Toxoplasma IgG positive. The overall seroprevalence of T. gondii was higher in the Bai group (32·3%, 179/555) than in the Han group (11·6%, 69/595) (P < 0·01). Within the Bai group, seroprevalence was significantly higher in males (37·8%) than in females (27·4%), but this difference was not significant between males (10·2%) and females (12·4%) within the Han group (P = 0·414). The infection risk was higher in males than in females in the Bai group (P = 0·008, OR 5·346, 95% CI 3·25–8·8). These results confirmed the highly significant difference in seroprevalence of both males and females between Bai and Han ethnic groups (P < 0·01).

Table 1. Age and sex distribution of Toxoplasma gondii seroprevalence in Bai and Han ethnic groups, Yunnan Province, southwestern China

OR, Odds ratio; CI, confidence interval.

P was estimated using the χ 2 test.

* P < 0·001, OR 5·346, 95% CI 3·25–8·8.

P < 0·001, OR 2·654, 95% CI 1·777–3·962.

P < 0·001, OR 3·629, 95% CI 2·668–4·936.

As shown in Table 1, the T. gondii seroprevalence in the <18 years age group was lower than other age groups in both Bai and Han populations. In the Han group, the seropositivity of T. gondii was 0% in the 1–18 years age group, 6·8% in the 18–40 years age group, 16·8% in the 41–65 years age group, and 15·9% in the >65 years age group. For the Bai group, the seroprevalence was also 0% in <18 years age group, but seroprevalence was significantly higher in the 18–40 years age group (34·1%, P < 0·001), 41–65 years group (33·1%, P < 0·001), and >65 years group (29·8%, P = 0·013) in the Bai group than in the Han group.

The results of characteristics of study subjects and risk factors associated with the seropositivity of T. gondii in Bai and Han groups are detailed in Table 2. The subjects were categorized into four education groups: primary school, junior high school, senior middle school and college. There was no significant difference in T. gondii seroprevalence within the Bai group of different education levels (P = 0·144), but the infection risk decreased with increasing level of education in the Han group, and the difference was significant (P = 0·01).

Table 2. Characteristics of study subjects and risk factors associated with the seropositivity of Toxoplasma gondii in Bai and Han ethnic groups, Yunnan Province, southwestern China

OR, Odds ratio; CI, confidence interval; Ref., used as the reference group.

* Estimated using the χ 2 test.

Consumption of raw pork and/or liver was divided into the following categories: never, occasionally (<6 times a year), not often (>6 to <12 times a year), often (⩾12 times a year). In contrast to the ‘never’ group, our statistical analysis showed that the increasing frequency of consumption of raw pork and/or liver is related to high T. gondii seroprevalence in both Bai and Han ethnic groups (P < 0·001). The ratio of people who ate raw pork and/or liver in the Bai group was far greater than in the Han group, but there was no significant difference in the ‘often’ group between the two ethnic populations (P = 0·257), and the seropositivity was 59% and 50% in Bai and Han ethnic groups, respectively.

There was no significant difference in T. gondii seroprevalence between cat feeding (33·3%) or non-cat feeding (32·1%) groups in the Bai groups. By contrast, cat feeding (or not) was significantly associated with T. gondii infection in the Han group (P < 0·001), and the seroprevalence was significantly higher in the cat-feeding group (34·3%, 35/102) than in the non-cat-feeding group (6·9%, 34/493).

The effects of ethnicity, sex, cat feeding, education level, consumption of raw pork and age group associated with T. gondii seropositivity in the present study were analysed using univariate analyses. Optimized by Fisher's scoring technique, forward stepwise logistic regression analysis was conducted to evaluate the risks of multiple variables relating to T. gondii infection. In the final model, two variables had effects on the infectious disease, described by the equation y = 4·12−1·52x3−x5. Not feeding a cat and consuming less raw meat had negative effects on the risk of T. gondii infection, for which the ORs were 0·22 (95% CI 0·134–0·355) and 0·37 (95% CI 0·315–0·428), respectively.

DISCUSSION

In China, T. gondii infection has not been given high priority owing to the limited knowledge of the route of transmission to humans, e.g. the infection risk of the well known food named ‘Heige’ (fresh pork or liver) in many restaurants in Yunnan Province. Therefore, the local cuisine including ‘Heige’ in Dali Bai Autonomous Prefecture, Yunnan Province may represent a potential risk of T. gondii infection, especially for the Bai group which has the habit of eating raw pork and/or liver. Significantly, this potential risk has led to 21·6% anti-T. gondii IgG positivity in Dali Bai Autonomous Prefecture, which is higher than that in northeast and the south of China (12·3%) [8], and it is also much higher than the national average (7·9%) [5]. Although a previous study reported that the T. gondii seroprevalence was 25·4%, 25·3%, 17·1% and 16·7% in Miao, Buyi, Mongol and Zhuang ethnic groups, respectively [5], our study, focusing on the Bai ethnic group, showed the highest seroprevalence of 32·3%.

Some previous reports indicated that the seropositivity of T. gondii was related to age [9, 10]. Consistent with these studies, the present study showed highly significant differences in T. gondii seropositivity in the different age groups (18–45, 45–65, >65 years) in the two ethnic populations. For subjects aged <18 years, there were a limited number of samples in this study, thus the data were inconclusive.

As the definitive hosts for T. gondii, cats play a key role in transmitting T. gondii due to their ability to pass oocysts in their faeces [11, 12]. In China, it has been shown that excretion of T. gondii oocysts in the environment by cats leads to the increased possibility of human infection [12]. The present study showed 33·3% (22/66) and 34·3% (35/102) seropositivity of T. gondii in Bai and Han ethnic groups, respectively, who feed cats. Although there was no significant difference in T. gondii seropositivity between the Bai groups that feed/do not feed a cat, a significant difference was found in T. gondii seropositivity between Han groups that feed cats and those that do not.

Previous studies have indicated that level of education was associated with T. gondii infection [1315]. Similarly, our study showed that T. gondii seroprevalence was significantly different in Han ethnic populations of different educational levels, showing that the proportion of subjects who have college education had lower T. gondii prevalence than others, although there was no significant difference in the Bai ethnic group for different education levels.

CONCLUSION

The present study revealed for the first time that human infection with T. gondii is common in Bai and Han ethnic groups in Dali Bai Autonomous Prefecture, Yunnan Province, southwestern China. The overall T. gondii seroprevalence in the Bai ethnic group was 32·3%, Eating raw pork and/or liver was the most important risk related to T. gondii infection in the Bai ethnic group. Cat feeding and raw meat consumption had positive effects on the risk of T. gondii in both Bai and Han ethnic groups in this area. Improved food habits and hygiene practices should be promoted to reduce the prevalence of T. gondii infection in humans in this unique region of the world.

ACKNOWLEDGEMENTS

Project support was provided, in part, by the State Key Laboratory of Veterinary Etiological Biology, Lanzhou Veterinary Research Institute, Chinese Academy of Agricultural Sciences (grant no. SKLVEB2013KFKT011), the Specialized Research Fund for the Doctoral Program of Dali University (grant no. KYBS201217), Application and Development Projects of Dali University (grant no. KYYY201302) and the Science Fund for Creative Research Groups of Gansu Province (grant no. 1210RJIA006).

DECLARATION OF INTEREST

None.

REFERENCES

1. McLeod, R, et al. Why prevent, diagnose and treat congenital toxoplasmosis? Memorias do Instituto Oswaldo Cruz 2009; 104: 320344.
2. Choi, WY, et al. Foodborne outbreaks of human toxoplasmosis. Journal of Infectious Diseases 1997; 175: 12801282.
3. Phan, L, et al. Longitudinal study of new eye lesions in children with toxoplasmosis who were not treated during the first year of life. American Journal of Ophthalmology 2008; 146: 375384.
4. Dubey, JP. Toxoplasmosis of Animals and Humans, 2nd edn. Boca Raton, Florida: CRC Press, 2010, pp. 313.
5. Xu, LQ, et al. A national survey on current status of the important parasitic diseases in human population. Chinese Journal of Parasitology and Parasitic Diseases 2005; 23: 332340.
6. Zou, FC, et al. Seroprevalence of Toxoplasma gondii in pigs in southwestern China. Parasitology International 2009; 58: 306307.
7. Zhou, P, et al. Genetic characterization of Toxoplasma gondii isolates from pigs in southwestern China. Journal of Parasitology 2011; 97: 11931195.
8. Xiao, Y, et al. Seroepidemiology of human Toxoplasma gondii infection in China. BMC Infectious Diseases 2010; 10: 4.
9. Markovich, MP, et al. Seroepidemiology of Toxoplasma gondii infection in the Israeli population. Epidemiology and Infection 2014; 142: 149155.
10. Nowakowska, D, et al. Age-associated prevalence of Toxoplasma gondii in 8281 pregnant women in Poland between 2004 and 2012. Epidemiology and Infection 2014; 142: 656661.
11. Elmore, SA, et al. Toxoplasma gondii: epidemiology, feline clinical aspects, and prevention. Trends in Parasitology 2010; 26: 190196.
12. Du, F, et al. Survey on the contamination of Toxoplasma gondii oocysts in the soil of public parks of Wuhan, China. Veterinary Parasitology 2012; 184: 141146.
13. Jones, JL, et al. Toxoplasma gondii infection in the United States: seroprevalence and risk factors. American Journal of Epidemiology 2001; 154: 357365.
14. Akinbami, AA, et al. Seroprevalence of Toxoplasma gondii antibodies amongst pregnant women at the Lagos State University Teaching Hospital, Nigeria. Nigerian Journal of Postgraduate Medicine 2010; 17: 164167.
15. Babaie, J, et al. Seroprevalence and risk factors for Toxoplasma gondii infection among pregnant women in Northeast Iran. Clinical and Vaccine Immunology 2013; 20: 17711773.