First Report of Toxoplasma gondii Infection in Common Quails ( Coturnix coturnix ) Intended for Human Consumption in Three Provinces of Northeastern China

Abstract

Common quails are nutritious food and are also used as medicine in some parts of the world. Until now, no information on Toxoplasma gondii infection in common quails intended for human consumption in China is available. Therefore, this study was carried out to determine the prevalence of T. gondii infection in common quails in six cities from Shandong, Liaoning, and Jilin provinces, China. Out of 620 common quails examined, 59 (9.52%) were seropositive for T. gondii by the modified agglutination test. T. gondii infection in male and female common quails was 8.10% and 10.71%, respectively. The highest prevalence (13.10%) was detected in a group of common quails from Rizhao of Shandong province, followed by common quails from Yantai of Shandong province (13.04%) and the lowest prevalence (5.56%) was detected in a group of common quails from Shenyang of Liaoning province. The results of this survey revealed the presence of T. gondii infection in common quails in China, indicating that common quails are a potential source for transmission of T. gondii to humans, therefore, posing a potential public health concern. To our knowledge, this is the first report of T. gondii infection in common quails in China.

Introduction

Toxoplasmosis is one of the most common zoonoses worldwide, which is caused by the protozoan parasite Toxoplasma gondii (Dubey 2010a). Humans are mainly infected by oral ingestion of undercooked meat containing tissue cysts or oocysts from the environment contaminated with infected cat feces, such as soil, foods, and water (Elmore et al. 2010). Moreover, congenital and organ transplant can also cause T. gondii infection. It can induce serious illnesses in the fetus during congenital infection and can be fatal to immunocompromised patients, especially in acquired immunodeficiency syndrome patients (Montoya and Liesenfeld 2004, Zhou et al. 2011). T. gondii can infect almost all warm-blooded animals, including birds, and some cold-blooded animals (Dubey 2010a, Sanders et al. 2015, Nasiri et al. 2016). Although high prevalence of toxoplasmosis has been reported for several species of wild and domestic birds in China, information on exposure of common quails to T. gondii is still lacking in China.

Common quail (Coturnix coturnix), one of the smallest members of the order Galliformes, is nutritious food consumed by humans and is also used as medicine in some parts of the world. The world quails breeding stock is about 1 billion and nearly 200 million common quails are reared in China (Huang et al. 2005). China has become the world's superpower in common quails breeding and the meat of quail is not only widely consumed by local residents but is also transported to neighboring countries, such as Korea (Chen 2009). Moreover, previous study showed that T. gondii infection could cause death in quails with severe apathy, dyspnea, and diarrhea (Casagrande et al. 2015). Unfortunately, there is no information about the prevalence of T. gondii infection in common quails in China. Thus, this study was conducted to provide information about T. gondii infection in common quails in China for the first time.

Materials and Methods

Ethics statement

This study was approved by the Animal Ethics Committee of Jilin Agricultural University (approval no. JAUAEC2014-012). Birds from which serum samples were collected were handled in accordance with the Animal Ethics Procedures and Guidelines of the People's Republic of China.

Collection and preparation of serum samples

A total of 620 blood samples were collected between January and November 2015 from common quails in six cities from Shandong, Liaoning, and Jilin provinces, China (Table 1). All adult bird samples from barbecue restaurants were collected by a human by selecting the restaurants sampled, and one blood sample was collected from heart of each bird by local veterinary practitioners, and the blood was taken postmortem. Handling of common quails was performed in strict compliance with the Animal Ethics Procedures and Guidelines of the People's Republic of China. Blood samples were left overnight at room temperature to allow clotting and were centrifuged at 3000 g for 10 min. The sera were collected in Eppendorf tubes and stored at 4°C for 24–72 h. The sera were transported in an ice box to the College of Animal Science and Technology, Jilin Agricultural University, Changchun, Jilin Province, where they were kept at −20°C until tested. Information about species, location of the farms, and gender were acquired from farm administrators.

Table 1.

Seroprevalence of Toxoplasma gondii Infection in Common Quails in China by the MAT

		No. of sera samples with MAT titers of
Variable	Category	1:5	1:10	1:20	1:40	1:80	1:160	1:320	No. tested	No. positive	Prevalence (%) (95% CI)	p
Location	Changchun	2	0	1	2	1	1	0	116	7	6.03 (1.70–10.37)	0.170
	Shenyang	1	1	1	1	1	0	0	90	5	5.56 (0.82–10.29)
	Dalian	2	1	1	1	0	0	0	78	5	6.41 (0.97–11.85)
	Weihai	5	3	4	3	1	2	1	160	19	11.88 (6.86–16.89)
	Yantai	2	3	2	3	1	1	0	92	12	13.04 (6.16–19.93)
	Rizhao	1	6	3	1	2	0	0	84	11	13.10 (5.88–20.31)
Gender	Male	3	3	5	6	4	2	0	284	23	8.10 (4.93–11.27)	0.269
	Female	10	11	7	3	2	2	1	336	36	10.71 (7.41–14.02)
Total		13	14	12	9	6	4	1	620	59	9.52 (7.21–11.83)

MAT, modified agglutination test.

Serological examination

The serum samples of common quails were tested for T. gondii antibodies by the modified agglutination test (MAT) as described previously (Dubey and Desmonts 1987, Cong et al. 2012, 2014, Lou et al. 2015, Zheng et al. 2016). The Toxoplasma MAT antigen was provided by the Laboratoire de Parasitologie-Mycologie, Centre National de Référence de la Toxoplasmose, Centre de Ressources Biologiques Toxoplasma, Hôpital Maison Blanche, Reims Cédex, France. The pig serum with the titers greater than 1:200 was used as positive control (Lanzhou Veterinary Research Institute, Chinese Academy of Agricultural Sciences, Lanzhou, China). In brief, sera were added to the “U” bottom of 96-well microtiter plates and diluted twofold starting from 1:5 to 1:640. Bird sera with MAT titers of 1:5 or higher were considered positive for T. gondii antibodies based on a previous study (Dubey 2010a), those sera with doubtful reactions were retested, and positive and negative controls were included in each test.

Statistical analysis

Differences in the seroprevalence of T. gondii-infected common quails among different variables including location and gender were analyzed using a Chi-square test by SAS (Statistical Analysis System, Version 8.0). A logistic regression model was built by forward inclusion of response variables (location and gender) and T. gondii seropositive or negative status as outcome variable. Significant variables (p < 0.05) were kept in the model.

Results and Discussion

Of 620 common quail serum samples, 59 (9.52%, 95% confidence intervals [CI] 7.21–11.83) were tested T. gondii-positive by MAT, with titers of 1:5 (n = 13), 1:10 (n = 14), 1:20 (n = 12), 1:40 (n = 9), 1:80 (n = 6), 1:160 (n = 4), and 1:320 (n = 1) (Table 1). Positive common quails were found in all six regions with prevalences varying from 5.56% to 13.10%. The highest prevalence (13.10%) was detected in a group of common quails from Rizhao of Shandong province, followed by common quails from Yantai of Shandong province (13.04%), and the lowest prevalence (5.56%) was detected in a group of common quails from Shenyang of Liaoning province. Moreover, T. gondii prevalence in male and female common quails was 8.10% (23/284) and 10.71% (36/336), respectively.

Considering the geographical conditions, common quails from northeast China (Changchun, Shenyang, and Dalian) have a lower infection rate to T. gondii than those from eastern China (Weihai, Yantai, and Rizhao) (OR = 0.446; 95% CI: 0.248–0.802; p = 0.006). The reason behind that might be the droughty and rainless climate there, and the drying under low humidity and high temperature was deleterious for the oocysts (Dubey, 2010b). So possibly that is the major cause for the lower T. gondii prevalence of common quails in the northeast of China. In the present study, common quails from eastern China were more easily infected with T. gondii than those from northeastern China. This phenomenon might be associated with the water and food contaminated with oocysts, which was the most likely explanation for quails becoming infected.

In this study, MAT was chosen to detect T. gondii antibodies in the examined common quails because it is considered a sensitive and specific method for detecting T. gondii antibodies in avian species. Moreover, numerous reports and data on isolation of viable T. gondii from birds were available with the MAT, using isolation of the parasite as a standard (Dubey 2010a, b). Although most of the infected common quails examined in this study had low titers and the cutoff titer of MAT for positive infection in birds was not confirmed, however, occasionally viable T. gondii has been isolated from poultry with a MAT titer of only 1:5 (Dubey 2002, 2010b, Dubey et al. 2004). Thus, in this study, we stated all titers (Table 1).

Humans can acquire T. gondii infection from domestic, wild, or companion animals (Montoya and Liesenfeld 2004, Dubey 2010a, Elmore et al. 2010, Zhou et al. 2011). Quail eggs and meat are important food products in China. Although there is no direct evidence demonstrating that humans can be infected with T. gondii by consuming eggs, T. gondii strains have been isolated from the eggs of the domestic fowl (Pande et al. 1961, Simitch et al. 1966). Moreover, animal meat is an important source of T. gondii infection for human populations. Thus, the significance of common quails in the prevalence of T. gondii should be paid more attention because they could serve as sources for T. gondii infection in humans who may be infected with T. gondii by consumption of undercooked or raw meat of infected quails.

Conclusions

This study revealed T. gondii seroprevalence (9.52%) in common quails in China for the first time. This finding raises public health concern of T. gondii infection in common quails as a potential source for human infection. Therefore, it is important to execute integrated control strategies and measures to prevent and control T. gondii infection in common quails in China.

Footnotes

Acknowledgments

This work was supported by grants from the Key Scientific and Technological Project of Jilin Province (grant no. 20140204068NY) and China Postdoctoral Science Foundation (grant no. 2016M602145). Prof Xing-Quan Zhu of Lanzhou Veterinary Research Institute, Chinese Academy of Agricultural Sciences, is thanked for copyediting and improving the English of the article.

Author Disclosure Statement

No competing financial interests exist.

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