First Report of Toxoplasma gondii Infection in Tuberculosis Patients in China

Abstract

In recent years, coinfection of tuberculosis (TB) and parasitosis in humans is an emerging problem in coendemic areas, which has been increasingly highlighted in developing countries. However, there is limited information about the prevalence of Toxoplasma gondii infection in TB patients. Therefore, through a case–control study, 924 TB patients hospitalized for diacrisis or treatment in northeastern and eastern China, and 924 control subjects from the general population of the same region matched with gender, age, and residence were examined for the presence of IgG and IgM antibodies to T. gondii and associated sociodemographic and behavioral characteristics in a population of TB patients. Seroprevalence of IgG antibodies to T. gondii in TB patients (122/924, 13.2%) was significantly higher than control subjects (90/924, 9.7%) (p = 0.019), and 26 (2.8%) TB patients and 19 (2.1%) controls were positive for anti-T. gondii IgM antibodies (p = 0.291), respectively. Multivariate analysis showed that T. gondii infection was associated with keeping cats at home, presence of stray cats, and consumption of raw/undercooked meat. The present study first revealed the seroprevalence of T. gondii infection in TB patients in China. Moreover, parasitological surveys should be regularly carried out among TB patients, aiming to prevent the possibility of severe toxoplasmosis.

Introduction

T oxoplasma gondii, an important protozoan parasite, can infect nearly all warm-blooded animals, including birds and humans (Dubey 2010, Zhou et al. 2011). Until now, nearly one-third of the human population in the world has been infected by T. gondii (Montoya and Liesenfeld 2004). Humans are infected mainly through consuming undercooked or raw meat containing tissue cysts from an infected intermediate host, as well as unwashed vegetables and fruits or drinking water contaminated with T. gondii oocysts (Dubey 2010).

Although primary infection is generally asymptomatic, it may be a severe threat to immunocompromised patients' lives. Generally, primary infections will subsequently develop into chronic infections. In the chronic infection stage, T. gondii will persist in tissue cysts (Montoya and Liesenfeld 2004). Chronic infections are usually difficult to be found and probably persist indefinitely throughout the whole life, but T. gondii will be reactivated as a result of heavy immunosuppression (Montoya and Liesenfeld 2004, Markovich et al. 2014).

Tuberculosis (TB) is also an important public healthcare problem and remains a main cause of morbidity and mortality all over the world (Dheda et al. 2014, Babu and Nutman 2016). In recent years, many studies have suggested that parasitic infection may also enhance the vulnerability to TB (Resende et al. 2007, Babu et al. 2009, George et al. 2013). Coinfection of TB and parasitic diseases in humans is a crucial public problem in coendemic areas in developing countries (Li et al. 2014). However, epidemiological studies on the association of infection with T. gondii and TB have not been performed in China. Therefore, we first performed a case–control study in China to determine the seroprevalence of T. gondii infection among TB patients and investigate sociodemographic and behavioral characteristics associated with T. gondii seropositivity in these patients.

Materials and Methods

Study sites

The study was carried out in Heilongjiang, Jilin, and Shandong provinces in China. Heilongjiang Province (43°26′–53°33′ N, 121°11′–135°05′ E), located in the most northeastern part of China, has a typical temperate continental monsoon climate. Jilin Province (40°50′–46°19′ N, 121°38′–131°19′ E), located in the central part of northeast China, is hinterland of Northeast Asia as well and the climate is similar with Heilongjiang Province. Shandong province (34°23′–38°24′ N, 114°48′–122°42′ E), located in the east of China, with temperate zone monsoon climate, has the second largest population and is the third largest economic province of China.

Study design and population

Through a case–control study, we detected T. gondii seroprevalence and identified risk factors and possible contamination routes of T. gondii infection in TB patients and control subjects in Heilongjiang, Jilin, and Shandong provinces, China from May 2014 to July 2016. All patients were included in the study based on the following criteria for inclusion: (1) TB patients; (2) aged at least 10 years old; and (3) who accepted to participate in the study. During the study period, 924 patients hospitalized for diacrisis or treatment was invited to participate in the study. As control groups, 924 patients who matched with TB patients by age, gender, and residence were included in the study. Serum samples were obtained from the general population of Heilongjiang, Jilin, and Shandong provinces, China.

Sociodemographic and behavioral data

Sociodemographic data, including age, gender, birth place, and residence were recorded from all participants. Behavioral data included presence of stray cats, keeping cats at home, consumption of raw/undercooked meat, consumption of raw vegetables and fruits, and source of drinking water. These variables were selected based on literature. TB patients and control subjects were invited to provide veridical information and they were informed that data were used in a confidential manner.

Sample collection and serological assay

Before the sample collection, all participants have been told about the purpose and procedures of the study, and sign consents. Volunteers/guardians provided informed consent on behalf of all children participants. All volunteers agreed to provide their sera. Blood samples (5 mL) were taken from the elbow vein of each participant using a plain tube. Serum samples were separated by centrifuging at 3000 rpm for 10 min. Sera were collected in Eppendorf tubes and then stored at 4°C for 24–72 h and kept at −20°C until used. The commercially available enzyme immunoassay kits (Demeditec Diagnostics GmbH, Germany) were used to detect the presence of IgG and IgM antibodies in T. gondii (Cong et al. 2015, Meng et al. 2015) following the manufacturer's instructions. Positive and negative controls were included in every plate.

Statistical analyses

The SAS 9.1 software package was used to analyze the present results. For comparison of the frequencies among the groups, the Mantel–Haenszel test, and when indicated the Fisher exact test, were used. Bivariate and multivariate analyses were used to assess the association between the characteristics of the subjects and T. gondii infection. Variables were included in the multivariate analysis if they had a p-value of ≤0.25 in the bivariate analysis (Mickey and Greenland 1989). Adjusted odds ratio (OR) and 95% confidence interval were calculated by multivariate analysis. A p-value <0.05 was considered statistically significant.

Ethical consideration

This study was approved before its commencement by the Ethics Committees of the Weihaiwei People's Hospital, Changchun Infectious Disease Hospital, Affiliated Hospital of Medical College of Qingdao University, and Prevention and Treatment of Infectious Disease Hospital in Heilongjiang province.

Results

Anti-T. gondii IgG antibodies were detected in 122 (13.2%) of 924 TB patients and in 90 (9.7%) of 924 control subjects (p = 0.019), respectively. Twenty-six (2.8%) TB patients and 19 (2.1%) controls were positive for anti-T. gondii IgM antibodies (p = 0.291). A total of 119 (12.9%) TB patients were positive for IgG antibodies compared with 85 (9.2%) in control patients. Twenty-one (2.3%) TB patients and 14 (1.5%) controls were positive for IgM antibodies only, whereas 0.5% (5/924) TB patients and 0.5% (5/924) controls were positive for both IgG and IgM antibodies. Bivariate analysis of sociodemographic and risk factors for TB patients identified some factors with a p-value <0.25 that may be related to infection (Table 1). Three factors were found to be significantly associated with T. gondii infection in multivariable analysis (Table 2): keeping cats at home, presence of stray cats, and consumption of raw/undercooked meat.

Table 1.

Bivariate Analysis of Sociodemographic and Behavioral Data and Infection with Toxoplasma gondii in Tuberculosis Patients and Control Subjects

	Tuberculosis patients				Control subjects
	Prevalence of Toxoplasma gondii infection				Prevalence of T. gondii infection				Tuberculosis patients vs. control subjects
Characteristic	No. of tested	No. of positive	%	p	No. of tested	No. of positive	%	p	p
Age group (years)
<30	233	33	14.2	0.653	301	25	8.3	0.012	0.031
30–44	161	24	14.9		224	19	8.5		0.048
45–59	307	47	15.3		220	30	13.6		0.592
≥60	223	39	17.5		179	30	16.8		0.847
Gender
Male	579	90	15.5	0.941	575	64	11.1	0.877	0.028
Female	345	53	15.4	0.941	349	40	11.5	0.877	0.132
Residence place
Heilongjiang	303	45	14.9	0.764	303	31	10.2	0.553	0.086
Jilin	309	50	16.2		309	33	10.7		0.045
Shandong	312	44	14.1		312	40	12.8		0.639
Residence area
Urban	430	65	15.1	0.778	414	34	8.2	0.008	0.002
Suburban or rural	494	78	15.8	0.778	510	70	13.7	0.008	0.356
Socioeconomic level
Low	606	101	16.7	0.167	544	63	11.6	0.708	0.014
Medium	318	42	13.2	0.167	380	41	10.8	0.708	0.326
Cats at home
Yes	192	53	27.6	<0.001	187	36	19.3	<0.001	0.055
No	732	90	12.3	<0.001	737	68	9.2	<0.001	0.058
Presence of stray cats
Yes	253	65	25.7	<0.001	289	34	11.8	0.741	<0.001
No	671	78	11.6	<0.001	635	70	11.0	0.741	0.732
Consumption of raw/undercooked meat
Yes	331	62	18.7	0.041	322	40	12.4	0.412	0.026
No	593	81	13.7	0.041	602	64	10.6	0.412	0.109
Consumption of raw vegetables and fruits
Yes	318	44	13.8	0.318	308	31	10.1	0.418	0.151
No	606	99	16.3	0.318	616	73	11.9	0.418	0.024
Source of drinking water
Tap	602	86	14.3	0.171	634	62	9.8	0.036	0.015
Well + river	322	57	17.7	0.171	290	42	14.5	0.036	0.280

Table 2.

Multivariate Analysis of Characteristics of the Tuberculosis Patients and Their Association with Toxoplasma gondii Infection

Characteristic ^a	Adjusted odds ratio ^b	95% confidence interval	p
Socioeconomic level	1.246	0.859–1.860	0.234
Cats at home	2.616	1.777–3.851	<0.001
Presence of stray cats	2.450	1.695–3.541	<0.001
Consumption of raw/undercooked meat	1.507	1.050–2.164	0.026
Source of drinking water	1.203	0.833–1.738	0.324

The variables included were those with a p < 0.25 obtained in the bivariate analysis.

Adjusted by age and the rest of characteristics included in this table.

Discussion

As the second leading cause of death, TB may claim 1.4 million lives each year all over the world (WHO 2012). It is estimated that nearly one-third of the world's population is infected with TB (Board and Suzuki 2016), and 5–10% of all untreated. In that case, these untreated individuals will develop into an active TB disease (CDC 2012). For a long time, many researchers have turned to identify diseases that may induce decreased immunity and heightened sensitivity to TB. HIV has attracted a lot of attention, and other chronic illnesses such as diabetes mellitus also receive some attention. However, far less focus has been placed on another more common source of potential immune system vulnerability globally, namely parasites. In our case–control study, the results revealed a higher seroprevalence of anti-T. gondii IgG antibodies in TB patients (13.2%) compared with the control subjects (9.7%), with a statistically significant difference (p = 0.019). This difference may be explained by the speculation that immunity of TB patients are low, which makes them more sensitive to this parasite. This may be the main reason for the high seropositivity in TB patients.

In the present study, T. gondii infection was found to be significantly associated with the presence of domestic cats at home, indicating that it was a risk factor. This result is consistent with studies reported from France (Baril et al. 1999) and China (Liu et al. 2009). However, many other studies reported an opposite view that there was no association between T. gondii infection and the presence of domestic cats at home (Baril et al. 1999, Gebremedhin et al. 2013, Mwambe et al. 2013). Indeed, accidental contact with or ownership of cats may not be a risk factor, but the risk of infection to an appreciable level may be caused by frequent exposure to feline feces or no measures of protection. In recent years, the number of pet cats and dogs rose sharply in China. However, the inspection and quarantine measures were inadequate. These phenomena could increase the chances of infection with animal diseases such as T. gondii. Thus, the environment is more likely to be polluted by T. gondii oocysts. Meanwhile, humans have more chance to be infected and it was expected that the prevalence would be higher.

It is known that humans can infect T. gondii through ingesting tissue cysts in undercooked or raw meat from an infected intermediate host, or by ingesting the oocysts from unwashed vegetables and fruits, or drinking water contaminated by the feces excreted by infected cats (Daryani et al. 2014, Krueger et al. 2014, Cong et al. 2015). Analogously, the present study found that consumption of raw/undercooked meat was significantly associated with T. gondii seropositivity (adjusted OR = 1.507; 95% confidence interval: 1.050–2.164; p = 0.026). In China, an increasing number of people like to eat raw/undercooked meat such as fish, beef, etc. Therefore, it is necessary to publicize the knowledge of disease prevention, especially emphasizing the important role played by cats in the transmission of T. gondii and the association between T. gondii infection and behavioral characteristics.

Usually, it is difficult to diagnose toxoplasmosis in patients due to lack of specific symptoms and signs (Nimir et al. 2013). Moreover, pulmonary toxoplasmosis was clinically misdiagnosed as pulmonary TB at times (Ma et al. 2001, Gong and Yan 2002, Yang et al. 2007). Coinfection of TB and toxoplasmosis has been found in some clinical cases (Schroeder et al. 1984, Guneratne et al. 2011, Hwang et al. 2012), and also in a study of a series of coinfected patients in Egypt (Mashaly et al. 2017), which suggested that the severity of pulmonary TB could actually be increased by toxoplasmosis coinfection. Therefore, doctors should be more careful with these TB patients in the clinical diagnosis. Moreover, parasitological surveys should be regularly implemented among TB patients, aiming to prevent the possibility of severe toxoplasmosis.

Conclusions

Through a case–control study, the present study first revealed that infection with T. gondii in TB patients is common in northeastern and eastern China. Moreover, we determined the risk factors among Chinese TB patients referred for testing, including keeping cats at home, presence of stray cats, and consumption of raw/undercooked meat. The risk factors determined may help in establishing toxoplasmosis prevention programs therefore reducing toxoplasmosis in China, and the screening of TB patients would aid in vigilant diagnosis and timely treatment, decreasing complications in this sensitive group of patients.

Footnotes

Authors Disclosure Statement

No competing financial interests exist.

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