Risk factors for ocular toxoplasmosis among uveitis patients in Kinshasa, DR Congo

Abstract

Objective

To identify the risk factors associated with ocular toxoplasmosis (OT) in a cohort of Congolese patients with uveitis.

Methods and analysis

A cross-sectional study was conducted between March 2020 and July 2021 in two ophthalmic clinics in Kinshasa. Patients with a diagnosis of uveitis were enrolled in the study. Each patient underwent an interview, an ophthalmological examination and serology testing. Logistic regression was performed to identify risk factors for OT.

Results

212 patients were included in the study with a mean age at presentation of 42.1±15.9 years (limits: 8–74 years) and a sex ratio of 1.1:1. OT concerned 96 patients (45.3%). The age of the patients below 60 years (p=0.001, OR=9.75 CI 95% 2.51 to37.80)), the consumption of cat meat (p=0.01, OR=2.65 CI 95% 1.18 to 5.96)) and undercooked meat (p=0.044, OR=2.30 CI 95% 1.02 to 5.21)) and living in rural area (p=0.021, OR=11.4 (CI 95% 1.45 to 89.84])) were identified as risk factors for OT.

Conclusion

OT affects more young people. It is associated with dietary habits. Informing and educating the population is necessary to avoid infection.

WHAT IS ALREADY KNOWN ON THIS TOPIC

• Toxoplasmosis is the leading aetiology of infectious posterior uveitis worldwide. The pathology is more frequent in tropical areas. Depending on the region, different sociodemographic and environmental factors influence the occurrence of ocular toxoplasmosis.

WHAT THIS STUDY ADDS

• This study is first carried out on patients with ocular toxoplasmosis in Central Africa. This study shows that young people were more affected, and eating habits (domestic cats) were the risk factor for the disease, in this part of the world.

HOW THIS STUDY MIGHT AFFECT RESEARCH, PRACTICE OR POLICY

• The results of this study support the view that information and education of the population to avoid some risky eating behaviours would help to reduce the prevalence of the pathology in the region.

Introduction

Toxoplasma gondii is an obligate intracellular protozoan and the causative agent of toxoplasmosis, one of the most prevalent parasitic infections that affect humans and other warm-blooded animals.^1–3 It is estimated that approximately one-third of the human population worldwide has the parasite.^{2 3}

Humans are infected by ingesting sporulated oocysts in raw or undercooked meat, contact with cat faeces from the soil, and consuming contaminated food or water.^{1 3} Other rare transmission causes included transplacental transmission to the fetus, blood transfusion and organ transplant from infected donors.^{1 4}

The prevalence of human Toxoplasma infection varies in different parts of the world, it can range from 10% to 50% in temperate developed countries to over 80% in developing countries of the tropics.⁵ The infection is more prevalent in a warm and humid climate and is lower in cold regions, probably due to the poor survival of the oocyst stage of the parasite under freezing conditions.1 3 4 6 Low seroprevalence has been reported in South East Asia, North America and Europe, whereas high seroprevalence is observed in Latin America and tropical African countries.⁷ Central Africa has the highest reported prevalence rates, and the Democratic Republic of Congo (DRC) has the highest rate among these countries.^{8 9}

The most common clinical manifestation of toxoplasmosis involves the eye in the form of retinochoroiditis¹⁰; it is the leading cause of infectious posterior uveitis in non-immunocompromised individuals worldwide.^{6 11 12} Although ocular toxoplasmosis (OT) results from both congenital and acquired infections, eye disease acquired after birth is much more common than congenital infection.^{6 11–13} OT may occur immediately or long after the initial infection or during reactivation.³ The disability-adjusted life years calculated for toxoplasmosis (both congenital and postnatally acquired) were equivalent to that of tuberculosis.¹⁰ When the disease is acquired after birth, retinochoroiditis accounts for almost the entire burden.¹⁰

OT is considered a significant cause of uveitis in Africa, but a few studies describe the epidemiology of the disease on this continent.¹⁰ In DRC, toxoplasmosis is the patients’ most common aetiology of uveitis.¹⁴

People with OT experimented with worse vision-related quality of life.¹⁵ Retinal toxoplasmosis is recognised as a significant cause of blindness in many parts of the world.^{4 16} Overall, 24% of patients with OT developed legal blindness in one eye, generally from retinitis and subsequent scarring within the macula, retinal detachment or optic atrophy.¹⁷

The prevalence of OT in a population is dependent on the overall prevalence of infection in the population.⁶ Due to the severity and irreversibility of ocular lesions caused by T. gondii, knowledge about this infection’s social and epidemiological factors is essential to apply adequate intervention for prevention.¹⁸ Therefore, the prevention of toxoplasmosis is primarily directed toward health education related to avoiding personal exposure to the parasite.³

This study aimed to identify the risk factors associated with OT in a cohort of Congolese patients with uveitis.

Methods

Study population

A cross-sectional study was conducted between March 2020 and July 2021 in two ophthalmic clinics in Kinshasa (DR Congo): the Ophthalmic Center of Masina and the Ophthalmology Department of Saint Joseph Hospital. Patients who received a consultation diagnosed with uveitis were invited to participate in the study. The diagnosis of OT was based on clinical criteria^{16 19} in patient with positive Toxoplasma serology; and negative serology ruled out the diagnosis. Patients with active and cicatricial OT were included in the study. All included individuals provided written informed consent to participate in the study, following a full explanation of the study protocol. Children were allowed to participate in the study if consent was obtained from a parent or legal guardian.

Ophthalmological examination

The same ophthalmologist performed a complete ophthalmic examination.

Visual acuity was measured using a Snellen chart at a distance of 6 m. Biomicroscopy was performed with a slit lamp (Zeiss, Germany). A measure of IOP was made with a Goldmann tonometer. A fundus examination by indirect ophthalmoscopy (Slit lamp Zeiss, Germany and external lens of 78 diopters, Volk, Mentor, Ohio) after dilatation with a drop of tropicamide 1% (Mydriaticum, Théa, Milano, Italy) was performed for each patient.

Serological tests

All participants were sampled for serological analysis. First, 10 mL of the peripheral blood sample was obtained and centrifuged on the day of collection; the resulting serum supernatant was stored at −20°C until the test could be performed. Then, serology testing was performed in each patient by enzyme-linked fluorescent assay (ELFA, Biomerieux, France) using the Vidas R Toxo IgG II (TXG). The ELFA was performed with automated equipment (Mini Vidas, Biomerieux, France). Samples were considered positive for IgG antibodies when ≥8 IU/mL, indeterminate from ≥4 to <8 IU/mL and negative when <4 IU/mL.

Questionnaire

Each patient underwent an interview to obtain details associated with toxoplasmosis. In addition, questionnaires about general demography data, including age, medical history, and epidemiological and sociodemographic characteristics, were applied.

Risk factors assessed in the questionnaire included: age; place of residence, socioeconomic status, contact with soil, consumption of raw or undercooked food; intake of unfiltered and/or unboiled water, contact with cats and type of occupation. In addition, patients’ professions were grouped into two categories, those presenting the most significant risk of contact with the parasites (breeders, farmers, cultivators, agronomists, etc) and the others.

Variables of interest to determine a household’s socioeconomic situation were: the components of household amenities (possession of a refrigerator, a freezer, a stove, a motorcycle, a motorcar, a radio, a mobile phone, a bed, a mattress, chairs and a solar panel), the occupancy status of the dwelling (renter or owner), kind of toilet used, the existence of shared bathroom with other households, type of energy source, the primary type of fuel used for the household cooking, main roof material, primary material of pavement. The Wealth Index, a summary measure of socioeconomic status, was computed using the standard principal component analysis of household amenities ownership.

Statistical analysis

A participant database was established and validated in Microsoft Excel (Microsoft Corp., Redmond, Washington). Results are expressed as mean (min–max) for continuous variables and N (%) for categorical variables. Differences in proportions were analysed using the χ² test. A logistic regression model was used to identify the risk factors associated with OT, including sex, age, wealth index, eating habits, type of drinking water, and living environment. SPSS V.25 (SPSS IBM, Chicago, USA) statistical program was used to perform analysis. P values <0.05 were considered statistically significant.

Patient and public involvement

Patients and the public were not involved in the design, conduct, analysis or writing of the manuscript.

Results

General characteristics of the population

The number of consultations per year during our study period was 42 743 patients, including 371 cases of uveitis. The frequency of uveitis was 0.9%. We excluded patients lost to follow-up after the initial consultation. Our study involved 212 patients who agreed to participate. One hundred and thirteen patients (53.3%) were men. The mean age at presentation was 42.1±15.9 years (limits: 8–74 years), and patients aged between 20 to 40 years were the most represented (42%). The majority of patients had a secondary education level (57.5%). Patients with a median wealth index represented 36.8% of the population. Nine patients (4.2%) lived in rural areas outside the city of Kinshasa. Anti-Toxoplasma serology was positive in 86.3% of patients. Among the aetiologies of uveitis, OT concerned 96 patients (45.3%) (table 1). Among the 96 cases of toxoplasmosis, 24 patients (25%) had cicatricial OT. Other clinical characteristics of patients with OT have been previously described.²⁰

Table 1.

General characteristics of the population

	Frequency (%)
Sex
Male	113 (53.3)
Female	99 (46.7)
Age (years)
<20	17 (8)
20–40	89 (42)
41–60	78 (36.8)
>60	28 (13.2)
Education
None/elementary	13 (6.1)
Secondary	122 (57.5)
Tertiary	77 (36.3)
Wealth
Lowest tertile	71 (33.5)
Middle tertile	78 (36.8)
Highest tertile	63 (29.7)
Place of residence
Urban	203 (95.8)
Rural	9 (4.2)
Toxoplasma serology
Positive	183 (86.3)
Negative	29 (13.7)
Ocular toxoplasmosis
Yes	96 (45.3)
No	116 (54.7)

Characteristic differences according to serology and OT

Patients with a positive T. gondii serology were younger than those with negative serology (P=0.01) (table 2). Patients with positive serology had more contact with cats. They consumed more cat, pork, and sheep meat and untreated water, compared with those with negative serology, but this difference was not statistically significant (P≥0.05). All patients living in rural areas had positive serology (table 2). Patients with OT were younger (P<0.001) and consumed more cat meat (P=0.002) and undercooked meat (P=0.009), compared with those with other types of uveitis. In rural areas, seven out of nine patients with positive serology have OT (77.8%), while in the urban area, 89 out of the 174 patients developed OT (51.1%), showing statistically significant differences (P=0.04) (table 2).

Table 2.

Patient characteristics according to serology and ocular toxoplasmosis

	Serology		P value	Ocular toxoplasmosis		P value
	Positive	Negative		Yes	No
Sex			0.55			0.43
Male	99 (54.1%)	14 (48.3%)		54 (56.2%)	59 (50.9%)
Female	84 (45.9%)	15 (51.7%)		42 (43.8%)	57 (49.1%)
Mean age±SD (years)	41.0±15.8	48.9±15.2	0.01	35.9±14.5	47.2±15.3	<0.001
Age (years)			0.27			<0.001
<20	16 (8.7%)	1 (3.4%)		12 (12.5%)	5 (4.3%)
20–40	80 (43.7%)	9 (31%)		51 (53.1%)	38 (32.7%)
41–60	65 (35.5%)	13 (44.8%)		30 (31.3%)	48 (41.4%)
>60	22 (12%)	6 (20.7%)		3 (3.1%)	25 (21.6%)
Education			0.53			0.15
None/elementary	10 (5.5%)	3 (10.3%)		4 (4.2%)	9 (7.8%)
Secondary	105 (57.4%)	17 (58.6%)		51 (53.1%)	71 (61.2%)
Tertiary	68 (37.1%)	3 (31%)		41 (42.7%)	36 (31%)
Place of residence			0.22			0.04
Urban	174 (95.1)	29 (100)		89 (92.7)	114 (98.3)
Rural	9 (4.9)	0 (0)		7 (7.3)	2 (1.7)
Wealth			0.95			0.86
Lowest tertile	62 (33.9%)	9 (31%)		32 (33.3%)	39 (33.6%)
Middle tertile	67 (36.6%)	11 (38%)		37 (38.5%)	41 (35.3%)
Highest tertile	54 (29.5%)	9 (31%)		27 (28.2%)	36 (31%)
Presence of cat in the environment			0.63			0.11
Yes	78 (42.6%)	11 (37.9%)		46 (47.9%)	43 (37.1%)
No	105 (57.4%)	18 (62.1%)		50 (52.1%)	73 (62.9%)
Eating domestic cats			0.05			0.002
Yes	49 (26.8%)	3 (10.3%)		33 (34.4%)	19 (16.4%)
No	134 (73.2%)	26 (89.7%)		63 (65.6%)	97 (83.6%)
Eating porks			0.20			0.13
Yes	161 (88%)	23 (79.3%)		87 (90.6%)	97 (83.6%)
No	22 (12%)	6 (20.7%)		9 (9.4%)	19 (16.4%)
Eating lambs			0.33			0.88
Yes	11 (61.2%)	15 (51.7%)		57 (59.4%)	70 (60.3%)
No	71 (38.8%)	14 (48.3%)		39 (40.6%)	46 (39.7%)
Eating undercooked meat			0.86			0.009
Yes	34 (18.6)	5 (17.2%)		25 (26%)	14 (12.1%)
No	149 (81.4%)	24 (82.8%)		71 (74%)	102 (87.9%)
Eating raw vegetables			0.36			0.18
Yes	60 (32.8%)	12 (41.4%)		28 (29.2%)	44 (37.9%)
No	123 (67.2%)	17 (58.6%)		68 (70.8%)	72 (62.1%)
Drink treated water			0.76			0.26
Yes	62 (33.9%)	9 (31%)		36 (37.5%)	35 (30.2%)
No	121 (66.1%)	20 (69%)		60 (62.5%)	81 (69.8%)
High-risk profession			0.24			0.39
Yes	9 (4.9%)	3 (10.3%)		4 (4.2%)	8 (6.9%)
No	174 (95.1%)	26 (89.7%)		92 (95.8%)	108 (93.1%)

Values in bold are those less than 0.05

Risk factors for OT among patients

After analysis by logistic regression, the age of the patients below 60 years (P=0.001, OR=9.75 (CI 95% 2.51 to 37.80)), the consumption of cat meat (P=0.01, OR=2.65 (CI 95% 1.18 to 5.96)) and undercooked meat (P=0.044, OR=2.30 (CI 95% 1.02 to 5.21)) and living in a rural area (P=0.021, OR=11.42 (CI 95% 1.45 to 89.84)) were identified as risk factors for OT (table 3).

Table 3.

Risk factors for ocular toxoplasmosis among patients with uveitis

Risk factors	OR (95% CI)	P value
Age >60 years
No	9.75 (2.51 to 37.80)	0.001
Eating domestic cats
Yes	2.65 (1.18 to 5.96)	0.01
Eating undercooked meat
Yes	2.30 (1.02 to 5.21)	0.04
Living in rural area
Yes	11.42 (1.45 to 89.84)	0.02

Discussion

Worldwide several studies were carried out to determine the seroprevalence of T. gondii infection in the general population. Most authors have studied the infection among pregnant women.^{8 21–23} The seroprevalence of the infection varies greatly depending on the region. In Europe, the seroprevalence of toxoplasmosis varies between 10% in the north to over 50% in the south.^{6 21 23} In the USA, the seroprevalence varies around 11%. It is higher in South America, between 44% and 77%, with Brazil being the most affected country in the region.²³ In Asia, seroprevalence varies between 10% and 60%, with countries like China and India having the lowest rates while the Middle East is the most affected.²³ In Africa, there is a geographical trend of decreasing seroprevalence from the northern to the southern and from the western to the eastern regions of the continent.²⁴ Central Africa has the highest reported prevalence rates of infectious diseases; the DRC has the highest rate among these countries.⁸ A study conducted in Kinshasa in 2014; by Doudou et al found a high seroprevalence of the infection in 80.3% of pregnant women tested.⁹

There are few studies on seroprevalence and risk factors for toxoplasmosis in ophthalmology patients^{18 25–27} (table 4). In our series, we found a high seroprevalence of toxoplasmosis of 86%; it is higher than that found in the general population by Doudou et al.⁹ This could partly explain why toxoplasmosis is the first aetiology of uveitis in the DRC.¹⁴

Table 4.

Seroprevalence of Toxoplasma infection and risk factors in studies on patients in ophthalmology

Authors	Country/year	Population	N	Age X±SD (years)	Sex ratio	Prevalence of infection	Risk factors of infection	Risk factors of OT
Samudio	Paraguay/2015	Patients of the retina department	80	53±20	0.8	84%	Not washing vegetables with sodium hypochlorite eat the meat of wild animals	Not studied
Gomez-Marín	Colombia/2012	Military personnel	500	Median=2520–36 38	–	80%	Drinking lake or river water Consumption of wild animals	Not studied
Mendes	Brazil/2014	Uveitis patients of ophthalmology department	159	Non-spécifié	0.9	73%	Age 31–40 years	Not studied
Fereira	Brazil/2014	Patients of eye clinics	349	56.9±17.0	1.1	74.5%	Presence of cats or dogs consumption of raw or undercooked meat	Age level of schooling
Gomez-Marín	Colombia/2021	The population of two urban districts	161	Median=50 years	0.4	69.5%	Drinking untreated water	No risk factors found
Ukamaka	Nigeria/2016	Patients of ophthalmology department	138	Non-spécifié	0.8	Not specified	Not studied	Exposure to cats Poorly cooked meat Unfiltered water Cataract surgery
Emem	Nigeria/2021	Livestock farmers and raw meat handlers	339	34.8±11.6	0.8	55.8%	Not specified	Age 31–50 years female gender
Abu	Ghana/2016	The population of three communities	390	47±20.3	0.4	85 %	Sanitary conditions contact with soil contact with cat source of drinking water	Older age
This study	RD Congo/2022	Uveitis patients	212	42.1±15.9	1.1	86.3%	No risk factors found	Age <60 years Eating cats and undercooked meat Living in rural area

OT, ocular toxoplasmosis.

The main factors associated with the significant variability in the distribution of T. gondii infection among geographical regions are socioeconomic, environmental and cultural differences as well as those related to the living and eating habits of the residents of a given area.^{5 28 29}

In our series, we studied the impact of several factors (sociodemographic, environmental and dietary habits) on Toxoplasma infection.

None of these factors showed a statistically significant influence on the serology of the patients. The study carried out in Kinshasa by Doudou et al on pregnant women also failed to identify risk factors significantly associated with Toxoplasma infection.⁹ Other studies carried out in populations with high seroprevalence also failed to identify risk factors associated with Toxoplasma gondii infection.^{30 31} The high prevalence of the infection in the study populations can be the cause.

Like us, Ferreira et al in Brazil did not note any association between Toxoplasma infection and patients’ age, socioeconomic level and level of education.²⁵ However, in their series, infection was associated with the following risk factors: the presence of cats or dogs and consumption of raw or undercooked meat²⁵ (table 4). In Paraguay, Samudio et al found their patients’ dietary habits as risk factors.²⁷ (table 4). Another Brazilian study identified the age of patients between 31 and 40 years as a risk factor in their series.¹⁸ In Colombia, in a population-based study carried out in two urban districts, drinking untreated water was a risk factor for Toxoplasma gondii infection.³² In addition, in this country, soldiers operating in the jungle, drinking unboiled and chlorine-untreated water and eating wild animal meat had a higher prevalence of ³³Toxoplasma infection (table 4). Finally, in a population-based study, in Ghana, sanitary conditions, contact with soil and cat, and source of drinking water were the risk factors identified for Toxoplasma infection³⁴ (table 4).

In our series, OT affected 45% of patients who consulted for uveitis during the study period. In Brazil, OT is responsible for 43% of uveitis cases.³⁵

The following risk factors were identified as associated with OT in our patients: the age of patients below 60 years (P=0.001, OR=9.75 (CI 95% 2.51 to 37.80)), the consumption of cat meat (P=0.01, OR=2.65 (CI 95% 1.18 to 5.96) and undercooked meat (P=0.044, OR=2.30 (CI 95% 1.02 to 5.21)) and living in a rural area (P=0.021, OR=11.4 (CI 95% 1.45 to 89.84)).

In Brazil, Ferreira et al, in their clinical study, also found an association between the age of patients and OT. Like us, they note that patients with OT are younger than those with other ocular pathologies.²⁵ A Brazilian population-based study³⁴ found that older age showed no association with the presence of ocular lesions, unlike other studies that reported this variable as a risk factor for OT.^{11 34 36}

In our series, the consumption of undercooked meat would increase by two times (CI 95% 1.05 to 5.2) the risk of presenting OT. Ferreira et al in Brazil²⁵ and Fuh et al in Nigeria²⁶ also found the consumption of undercooked meat as a risk factor for OT in their series. In Ghana, no association was found between the development of OT and the consumption of meat.³⁴ In Colombia, in a recent study, none of the factors studied was associated with ocular lesions in patients with positive Toxoplasma serology.³²

Transmission of human toxoplasmosis occurs mainly through ingesting food-containing cysts of T. gondii; this concerns 42%–61% of all cases, depending on the geographical area.^{2–4 37} T. gondii has been detected in different meats (sheep, pigs, cows, chickens and goats).^{2 37} Oral exposure to T. gondii through food mainly depends on parasite prevalence and people’s food consumption habits.³⁷ However, while consuming raw or undercooked meat was consistently identified as a risk factor, the relative importance of the risk factor and the type of meat associated with it varied among different countries.^{2 37} In addition, consumption habits play a critical role in the transmission of T. gondii by food; the parasite can be inactivated through cooking, freezing and salting.³⁷

In our series, we found the consumption of domestic cat meat as a risk factor which increases by two times (CI 95% 1.14 to 5.4) the risk of OT. In the city of Kinshasa, many young people consume the meat of domestic cats after killing them. Through this practice, they could become infected by coming into contact with cat faeces that contain oocysts. Felids play a leading role in T. gondii epidemiology, as they can spread millions of oocysts, causing substantial environmental contamination.^{36 38} Due to their high abundance, domestic cats are likely the primary source of ecosystem contamination in many areas.⁴

Nine of our patients lived in rural areas and had come to town to manage their ocular pathology. Living in a rural environment increases by 11 times (CI 95% 1.45 to 89.84) the risk of OT in our series. A study conducted in the military in Colombia found a higher risk of Toxoplasma gondii infection among the military operating in the jungle compared with those in the city (P<0.0001, OR=11.4 (CI 95% 3.8 to 34)).³² In this study, the high frequency of Toxoplasma gondii infection was correlated with the consumption of untreated water and wild animals by soldiers operating in the jungle.³² Unfortunately, the small number of patients living in rural areas in our series did not allow us to identify the factors that could explain the higher frequency of OT in this group of patients.

Conclusion

Identifying the risk factors for OT in an area is necessary; because it helps educate the population to avoid exposition to the parasite. We describe the first study on the risk factors of OT in Central Africa. In our series, we noted a high seroprevalence of the infection, higher than that found in most South American studies. The pathology would affect more young people, who constitute the active portion of the population. It would, thus, have a higher impact on the quality of life of the subjects. OT appears to be associated with dietary habits (consumption of cats and undercooked meat), identified as risk factors in our study. The prevention of the pathology will pass through information and education of the population to modify its eating habits to reduce the risk of infection.

Limitations

One of the limitations of this study is that we used a convenience non-probabilistic sample size. This may have prevented the identification of statistically significant potential risk factors. Population-based studies, with a more rigorous methodology, could help to identify other sociodemographic and environmental risk factors for OT. In addition, genetic studies would also be necessary to identify possible risk factors linked to the host or parasite characteristics.

Data availability statement

No data are available.

Ethics statements

Patient consent for publication

Not applicable.

Ethics approval

This study involves human participants and was approved by Ethics Committee of the Medical School of the University of Kinshasa ESP/CE/047/2020. Participants gave informed consent to participate in the study before taking part.