TY - JOUR
AU - Fan,, Chia-Kwung
AB - Abstract Background Human toxocariasis is a neglected zoonotic disease and its impact on human health is underestimated. Studies investigating the occurrence of toxocariasis in pregnancy are very scarce in Nigeria. This study investigated the seroprevalence of Toxocara spp. antibodies as well as the possible risk factors in pregnant women who routinely attended an antenatal clinic in a university hospital in Ile-Ife, Osun state. Methods Blood samples were collected from 413 participating pregnant women between October 2017 and February 2018. Epidemiological data were obtained through a structured questionnaire. The sera were screened for anti-Toxocara IgG antibodies by western blot technique based on Toxocara canis larval excretory-secretory antigens, targeting low molecular weight bands of 24-35 kDa, specifically for T. canis infection. Results The overall seroprevalence was 92.49% (382/413). There was no significant difference in the seroprevalence rate of Toxocara spp. infection between pregnant women aged ≤30 y and those aged >30 y (91.63 vs 93.33%; OR 1.28, 95% CI 0.61 to 2.67, p=0.511). The seroprevalence rate increased with the number of miscarriages but there was no statistical significance (p>0.05). Moreover, no significant associations were found between Toxocara spp. seropositivity and other studied risk factors (p>0.05). Conclusion The high seroprevalence of Toxocara spp. in pregnant Nigerian women needs comprehensive health education regarding personal hygiene and how to avoid exposure to this parasite infection. Nigeria, pregnant women, seroprevalence, toxocariasis, western blot Introduction Toxocariasis is a zoonotic disease that occurs in tropical and temperate countries, especially in communities with a low level of hygiene and with poor sanitation.1 The disease is caused by dog and cat nematodes, Toxocara canis and T. cati, respectively, both of which reside in the lumen of the definitive host.2 Humans acquire this infection through accidental ingestion of infective Toxocara spp. eggs in contaminated food or water, which is the primary route of infection. Other routes of infection include consumption of undercooked infected organs such as chicken and cow livers with encapsulated larvae.3,4 The ingested Toxocara eggs hatch into larvae in the small intestine and migrate into various internal organs thus resulting in damage to several tissues in systemic inflammatory responses, showing a wide range of symptoms.5 Helminth infections in pregnancy may cause maternal anemia,6 susceptibility to inflammatory diseases and can possibly promote fatal immune responses with long-term effects.7 Previous studies reported that helminth infections result in low birthweight babies and infant mortality.8 Studies have also reported that toxocariasis greatly increases the risk of giving birth to a baby with clinical manifestations of intrauterine infection, promoting homeostatic disorder and formation of long-term pathology in babies with intrauterine infection.9 In addition, toxocariasis can also cause increased infertility and premature deliveries.9 Furthermore, congenital transmission of Toxocara spp. has been reported in neonates.10 In a study from Argentina, a case of congenital Toxocara infection was reported in a neonate with retinopathy and blood eosinophilia whose mother was seropositive for Toxocara spp.11 Vertical transmission of T. canis and T. cati in the definitive hosts (dogs and cats)12 and T. canis larvae in paratenic hosts such as in BALB/c mice13 demonstrates the migratory ability and tropism of the larvae of this parasite during pregnancy or lactation, reinforcing the importance of performing studies in this area in humans in view of the risk of complications it poses during pregnancy (abortion and impaired fetal growth). Transmammary infection was confirmed in 73.9% of BALB/c mice nursed by infected females and the presence of larvae in the brains of the offspring was investigated.14 Entrapped Toxocara larvae in the body were able to cause chronic inflammation and were transmitted into the fetus by placenta or mammary as conducted in a murine model.13–16 Although a few studies have been conducted in some developed countries to investigate the occurrence of toxocariasis among pregnant women, no such study has been conducted in Nigeria. In addition, there is a paucity of information regarding the risk of Toxocara spp. infection to the mother and the fetus during pregnancy. This study investigates the seroprevalence of Toxocara spp. antibodies in pregnant women who attended the Obafemi Awolowo University Teaching Hospitals Complex (OAUTHC) for their routine antenatal clinic and also determines the risk factors associated with Toxocara spp. infection. Materials and methods Study area OAUTHC is a tertiary hospital situated in Ile-Ife, a peri-urban community, in Osun state, southwest Nigeria. It is located within a latitude of 07°30´ and 07°31´N and within a longitude of 4°33´ and 3°34´E. OAUTHC is among the first generation of teaching hospitals established by the federal government of Nigeria. By virtue of its location and the inadequate healthcare facilities in neighboring communities, the hospital also serves as a referral center. Study population A cross-sectional study was conducted on the seroprevalence of Toxocara spp. among 413 pregnant women who attended the Obstetrics and Gynecology unit of the OAUTHC, Ile-Ife, Osun state, Nigeria, between October 2017 and March 2018 for their routine antenatal clinic. The study population comprised pregnant women from Ile-Ife and neighboring communities who registered with the tertiary institution for their routine antenatal clinic. Sample size determination The sample size was calculated using the formula given below at 95% CI level=1.96, an expected prevalence of 50% (since no seroprevalence study has previously been conducted among pregnant women) and 5% marginal error. $$ \mathrm{N}=\frac{{\mathrm{Z}}^2.\mathrm{p}.\left(1\hbox{-} \mathrm{p}\right)}{{\mathrm{d}}^2} $$$$ where n is the sample size, Z is the degree of confidence (=1.96), P is the expected prevalence (=0.5) and d is the maximum tolerated error (=0.05). The sample size was increased by 5% to account for attrition=403. Participation of the pregnant women A meeting was organized to address the pregnant women and inform them about the purpose of the study. They were invited to participate in the study after receiving an explanation of the detailed procedure to be followed. The inclusion criteria for participation included signing an informed consent form, which included authorization to collect 5 ml of a blood sample during routine prenatal care and also being healthy. A structured questionnaire was designed to collect information regarding age, marital status, occupation, educational status, knowledge of toxocariasis, obstetric history (history of abortion, premature birth history, number of pregnancies) and general lifestyle (living with pets, type of food eaten). Collection of serum samples A 5 ml blood sample was drawn from each pregnant woman during routine prenatal care into a plain, clean blood collection tube by trained medical laboratory technicians. Serum samples were separated by centrifuging at 3000 rpm for 5 min. The sera were collected with Eppendorf tubes and stored at -200C until they were analyzed. Preparation of T. canis larval excretory-secretory antigens Adult female T. canis worms were collected from the stools of puppies that had been treated with mebendazole. Eggs were harvested from the anterior third of the uteri of females; they were cultured as described by Bowman, Mika-Grieve and Grieve.17 The eggs were stirred in 1% (w/v) sodium hypochlorite solution and then left for 5 min at room temperature. Next, they were then centrifuged at 2000x g for 5 min. The eggs were then washed twice with distilled water and once with 2% formalin. They were resuspended in 2% formalin and then placed in a 250 ml Erlenmeyer flask. In the flask, an additional 2% formalin was added to give a 1 cm-deep layer of liquid. The flask was sealed with parafilm and left at room temperature for 4–6 wk, with gentle weekly agitation, after which the suspended eggs containing third stage larvae were stored at 4°C until use. Figure 1 Open in new tabDownload slide Immunoblotting results of positive sera from samples nos. 93 and 95–97 showing IgG antibodies (Abs) reactive low molecular weight bands at 30–35 kD specifically related to toxocariasis. Sera IgG Abs from sample nos. 91, 92 and 94 did not show reactive low molecular weight bands and were negative for Toxocara spp. infection. Pos. Ctrl, positive control serum; WB, western blot. Figure 1 Open in new tabDownload slide Immunoblotting results of positive sera from samples nos. 93 and 95–97 showing IgG antibodies (Abs) reactive low molecular weight bands at 30–35 kD specifically related to toxocariasis. Sera IgG Abs from sample nos. 91, 92 and 94 did not show reactive low molecular weight bands and were negative for Toxocara spp. infection. Pos. Ctrl, positive control serum; WB, western blot. Table 1 Seropositivity (IgG) for Toxocara spp. according to sociodemographic factors of pregnant women (n=413). Variable . Infection rate . . No. . % . OR . 95% CI . p-value . Age group, y ≦30 (n=203) 186 91.63 1.00 0.511 >30 (n=210) 196 93.33 1.28 0.61 to 2.67 Educational level of subjects Primary/Secondary (n=84) 76 90.48 1.00 0.434 Tertiary (n=329) 306 93.01 1.40 0.60 to 3.25 Educational level of subjects' husbands Primary/Secondary (n=62) 58 93.55 1.00 0.733 Tertiary (n=351) 324 92.31 0.83 0.28 to 2.45 Job classification of subjects Unskilled (n=152) 140 92.11 1.00 0.819 Skilled (n=261) 242 92.72 1.09 0.51 to 2.32 Job classification of subjects' husbands Unskilled (n=131) 125 95.42 1.00 0.131 Skilled (n=282) 257 91.13 0.49 0.20 to 1.23 Knowing that the disease is transmitted from dog to man No (n=127) 120 94.49 1.00 0.309 Yes (n=286) 262 91.61 0.64 0.27 to 1.52 Knowledge of toxocariasis No (n=397) 367 92.44 1.00 0.846 Yes (n=16) 15 93.75 1.23 0.16 to 9.60 Variable . Infection rate . . No. . % . OR . 95% CI . p-value . Age group, y ≦30 (n=203) 186 91.63 1.00 0.511 >30 (n=210) 196 93.33 1.28 0.61 to 2.67 Educational level of subjects Primary/Secondary (n=84) 76 90.48 1.00 0.434 Tertiary (n=329) 306 93.01 1.40 0.60 to 3.25 Educational level of subjects' husbands Primary/Secondary (n=62) 58 93.55 1.00 0.733 Tertiary (n=351) 324 92.31 0.83 0.28 to 2.45 Job classification of subjects Unskilled (n=152) 140 92.11 1.00 0.819 Skilled (n=261) 242 92.72 1.09 0.51 to 2.32 Job classification of subjects' husbands Unskilled (n=131) 125 95.42 1.00 0.131 Skilled (n=282) 257 91.13 0.49 0.20 to 1.23 Knowing that the disease is transmitted from dog to man No (n=127) 120 94.49 1.00 0.309 Yes (n=286) 262 91.61 0.64 0.27 to 1.52 Knowledge of toxocariasis No (n=397) 367 92.44 1.00 0.846 Yes (n=16) 15 93.75 1.23 0.16 to 9.60 Open in new tab Table 1 Seropositivity (IgG) for Toxocara spp. according to sociodemographic factors of pregnant women (n=413). Variable . Infection rate . . No. . % . OR . 95% CI . p-value . Age group, y ≦30 (n=203) 186 91.63 1.00 0.511 >30 (n=210) 196 93.33 1.28 0.61 to 2.67 Educational level of subjects Primary/Secondary (n=84) 76 90.48 1.00 0.434 Tertiary (n=329) 306 93.01 1.40 0.60 to 3.25 Educational level of subjects' husbands Primary/Secondary (n=62) 58 93.55 1.00 0.733 Tertiary (n=351) 324 92.31 0.83 0.28 to 2.45 Job classification of subjects Unskilled (n=152) 140 92.11 1.00 0.819 Skilled (n=261) 242 92.72 1.09 0.51 to 2.32 Job classification of subjects' husbands Unskilled (n=131) 125 95.42 1.00 0.131 Skilled (n=282) 257 91.13 0.49 0.20 to 1.23 Knowing that the disease is transmitted from dog to man No (n=127) 120 94.49 1.00 0.309 Yes (n=286) 262 91.61 0.64 0.27 to 1.52 Knowledge of toxocariasis No (n=397) 367 92.44 1.00 0.846 Yes (n=16) 15 93.75 1.23 0.16 to 9.60 Variable . Infection rate . . No. . % . OR . 95% CI . p-value . Age group, y ≦30 (n=203) 186 91.63 1.00 0.511 >30 (n=210) 196 93.33 1.28 0.61 to 2.67 Educational level of subjects Primary/Secondary (n=84) 76 90.48 1.00 0.434 Tertiary (n=329) 306 93.01 1.40 0.60 to 3.25 Educational level of subjects' husbands Primary/Secondary (n=62) 58 93.55 1.00 0.733 Tertiary (n=351) 324 92.31 0.83 0.28 to 2.45 Job classification of subjects Unskilled (n=152) 140 92.11 1.00 0.819 Skilled (n=261) 242 92.72 1.09 0.51 to 2.32 Job classification of subjects' husbands Unskilled (n=131) 125 95.42 1.00 0.131 Skilled (n=282) 257 91.13 0.49 0.20 to 1.23 Knowing that the disease is transmitted from dog to man No (n=127) 120 94.49 1.00 0.309 Yes (n=286) 262 91.61 0.64 0.27 to 1.52 Knowledge of toxocariasis No (n=397) 367 92.44 1.00 0.846 Yes (n=16) 15 93.75 1.23 0.16 to 9.60 Open in new tab Table 2 Seropositivity (IgG) for Toxocara spp. according to environmental risk factors and the history of miscarriage in pregnant women (n=413). Variable . Infection rate . . No. . % . OR . 95% CI . p-value . Contact with dogs No (n=368) 340 92.39 1.00 0.821 Yes (n=45) 42 93.33 1.15 0.34 to 3.96 Contact with cats No (n=398) 369 92.71 1.00 0.391 Yes (n=15) 13 86.67 0.51 0.11 to 2.37 Consumption of undercooked meat No (n=84) 79 94.05 1.00 0.546 Yes (n=329) 303 92.10 0.74 0.27 to 1.98 Consumption of frozen meat No (n=44) 42 95.45 1.00 0.437 Yes (n=369) 340 92.14 0.56 0.13 to 2.42 Drinking unboiled water No (n=217) 204 94.01 1.00 0.222 Yes (n=196) 178 90.82 0.63 0.30 to 1.32 Eating raw vegetables No (n=115) 108 93.91 1.00 0.498 Yes (n=298) 274 91.95 0.74 0.31 to 1.77 History of miscarriage No (n=267) 245 91.76 1.00 0.446 Yes (n=146) 137 93.84 1.37 0.61 to 3.05 No. of miscarriages 0 (n=264) 242 91.67 1.00 0.608 0.376 1 (n=104) 97 93.27 1.26 0.52 to 3.04 ≧2 (n=45) 43 95.56 1.95 0.44 to 8.62 Trimester First/second (n=166) 154 92.77 1.00 0.861 Third (n=247) 228 92.31 0.94 0.44 to 1.98 Variable . Infection rate . . No. . % . OR . 95% CI . p-value . Contact with dogs No (n=368) 340 92.39 1.00 0.821 Yes (n=45) 42 93.33 1.15 0.34 to 3.96 Contact with cats No (n=398) 369 92.71 1.00 0.391 Yes (n=15) 13 86.67 0.51 0.11 to 2.37 Consumption of undercooked meat No (n=84) 79 94.05 1.00 0.546 Yes (n=329) 303 92.10 0.74 0.27 to 1.98 Consumption of frozen meat No (n=44) 42 95.45 1.00 0.437 Yes (n=369) 340 92.14 0.56 0.13 to 2.42 Drinking unboiled water No (n=217) 204 94.01 1.00 0.222 Yes (n=196) 178 90.82 0.63 0.30 to 1.32 Eating raw vegetables No (n=115) 108 93.91 1.00 0.498 Yes (n=298) 274 91.95 0.74 0.31 to 1.77 History of miscarriage No (n=267) 245 91.76 1.00 0.446 Yes (n=146) 137 93.84 1.37 0.61 to 3.05 No. of miscarriages 0 (n=264) 242 91.67 1.00 0.608 0.376 1 (n=104) 97 93.27 1.26 0.52 to 3.04 ≧2 (n=45) 43 95.56 1.95 0.44 to 8.62 Trimester First/second (n=166) 154 92.77 1.00 0.861 Third (n=247) 228 92.31 0.94 0.44 to 1.98 Open in new tab Table 2 Seropositivity (IgG) for Toxocara spp. according to environmental risk factors and the history of miscarriage in pregnant women (n=413). Variable . Infection rate . . No. . % . OR . 95% CI . p-value . Contact with dogs No (n=368) 340 92.39 1.00 0.821 Yes (n=45) 42 93.33 1.15 0.34 to 3.96 Contact with cats No (n=398) 369 92.71 1.00 0.391 Yes (n=15) 13 86.67 0.51 0.11 to 2.37 Consumption of undercooked meat No (n=84) 79 94.05 1.00 0.546 Yes (n=329) 303 92.10 0.74 0.27 to 1.98 Consumption of frozen meat No (n=44) 42 95.45 1.00 0.437 Yes (n=369) 340 92.14 0.56 0.13 to 2.42 Drinking unboiled water No (n=217) 204 94.01 1.00 0.222 Yes (n=196) 178 90.82 0.63 0.30 to 1.32 Eating raw vegetables No (n=115) 108 93.91 1.00 0.498 Yes (n=298) 274 91.95 0.74 0.31 to 1.77 History of miscarriage No (n=267) 245 91.76 1.00 0.446 Yes (n=146) 137 93.84 1.37 0.61 to 3.05 No. of miscarriages 0 (n=264) 242 91.67 1.00 0.608 0.376 1 (n=104) 97 93.27 1.26 0.52 to 3.04 ≧2 (n=45) 43 95.56 1.95 0.44 to 8.62 Trimester First/second (n=166) 154 92.77 1.00 0.861 Third (n=247) 228 92.31 0.94 0.44 to 1.98 Variable . Infection rate . . No. . % . OR . 95% CI . p-value . Contact with dogs No (n=368) 340 92.39 1.00 0.821 Yes (n=45) 42 93.33 1.15 0.34 to 3.96 Contact with cats No (n=398) 369 92.71 1.00 0.391 Yes (n=15) 13 86.67 0.51 0.11 to 2.37 Consumption of undercooked meat No (n=84) 79 94.05 1.00 0.546 Yes (n=329) 303 92.10 0.74 0.27 to 1.98 Consumption of frozen meat No (n=44) 42 95.45 1.00 0.437 Yes (n=369) 340 92.14 0.56 0.13 to 2.42 Drinking unboiled water No (n=217) 204 94.01 1.00 0.222 Yes (n=196) 178 90.82 0.63 0.30 to 1.32 Eating raw vegetables No (n=115) 108 93.91 1.00 0.498 Yes (n=298) 274 91.95 0.74 0.31 to 1.77 History of miscarriage No (n=267) 245 91.76 1.00 0.446 Yes (n=146) 137 93.84 1.37 0.61 to 3.05 No. of miscarriages 0 (n=264) 242 91.67 1.00 0.608 0.376 1 (n=104) 97 93.27 1.26 0.52 to 3.04 ≧2 (n=45) 43 95.56 1.95 0.44 to 8.62 Trimester First/second (n=166) 154 92.77 1.00 0.861 Third (n=247) 228 92.31 0.94 0.44 to 1.98 Open in new tab The embryonated eggs were then hatched under aseptic conditions, as reported by Fan et al.18 The eggs were washed with sterile phosphate buffered saline (PBS) then resuspended in sterile 1% (w/v) sodium hydrochloride and incubated in an atmosphere containing 5% CO2 for 30 min at 37°C. They were then washed again in sterile PBS (containing three antibiotics: 100 IU penicillin, 250 ug streptomycin and 25 ug nystatin/ml nystatin; Biochrom GmbH, Berlin, Germany) several times. Motile larvae were collected using modified Baermann apparatus and were kept in an atmosphere containing 5% CO2 for 12 h at 37°C. The larvae were transferred to a 50 ml tissue culture flask containing fresh RPMI-1640 medium (category no. F1235, Biochrom GmbH) with antibiotics to produce 104 larvae/ml. Then the larvae were incubated again in 5% CO2 at 37°C. The supernatant medium in each culture contained the excretory-secretory antigens of the larvae (TcES). This was collected weekly for 3–4 wk. The samples were pooled then centrifuged to precipitate the debris. The resulting supernatant was sterilized by filtration through a membrane with 0.2 μm pores and then dialyzed against PBS at 4°C for 12 h. The protein content of the dialysate was estimated before the dialysate was concentrated by lyophilization and stored at -80°C until use.18 Western blot analysis The TcES were used to test the serum samples for Toxocara-specific IgG antibody, as described by Fan et al.18 The TcES (9 μg/slab) were separated by 12.5% sodium-dodecyl sulphate polyacrylamide-gel electrophoresis. They were transferred onto strips of nitrocellulose membrane in a semiblotter. The membrane strips were then incubated with sera and diluted 1:64 before a western lightning kit was employed to detect any immunoreactions. Any pregnant woman whose serum reacted with any of the low molecular weight bands of 24, 28, 30 or 35 kDa was regarded as seropositive.1 Statistical analysis Data were collected and entered into Microsoft Excel (Microsoft Corp., Redmond, WA, USA) and later transferred to SAS version 9.3 (SAS Institute, Cary, NC, USA). Univariate analysis was used to assess the associations of T. canis infection seropositivity with various sociodemographic and environmental risk factors. Crude ORs with their 95% CIs were computed and p<0.05 was considered to be significant. Results A total of 413 pregnant women who visited OAUTHC for antenatal follow-up were examined for anti-Toxocara IgG antibodies. The mean age of the 413 pregnant women who participated in the study was 31.1 (20–43) y. Almost half of the pregnant women (210, 50.8%) were in the age range of 30-34 y. More than half of the pregnant women (59.8%) were in the third trimester of pregnancy. Participants’ serum that reacted with any of the low molecular weight bands of 24, 28, 30 or 35 kDa was considered seropositive (Figure 1) and the overall seroprevalence of Toxocara spp. infection among the pregnant women was 92.49% (382/413). The majority of the seropositive pregnant women (93.33%) were aged ≥30 y. Moreover, no significant differences were observed in the seroprevalence rate according to the age, educational level, occupation or toxocariasis knowledge of the pregnant women (Table 1). Table 2 shows that out of 16 (3.9%) of the pregnant women who claimed to have knowledge of human toxocariasis, only one (0.06%) was seronegative for Toxocara spp. infection. Questionnaire survey analysis revealed that 3.6% (15/413) and 10.9% (45/413) of the pregnant women had contact with cats and dogs, respectively. Approximately 93.33% and 86.67% of those who had contact with dogs and cats, respectively, were seropositive for Toxocara spp.; however, the differences were not statistically significant (p>0.05). Moreover, there was a progressive increase in the seroprevalence rate with increasing numbers of abortions or miscarriages; however, there was no significant difference between the groups (p=0.608, p=0.376, respectively) (Table 2). The results also show that there were no significant associations between Toxocara spp. seropositivity and the consumption of undercooked or frozen meat, drinking unboiled water or the consumption of raw vegetables among participants (p>0.05). In addition, statistical analysis showed no significant risk factors for Toxocara spp. seropositivity among the pregnant women who participated in this study (p>0.05). Discussion This study investigated the seroprevalence of sera anti-Toxocara IgG antibodies among pregnant women in Ile-Ife and environs who attended an antenatal clinic in the university hospital in Nigeria. In most laboratories, TcES-ELISA is the most commonly used technique for detecting T. canis infection in humans.19,20 This technique has a sensitivity of 78% and a specificity of 92% at a threshold titer set at 1:32.1,21 However, due to polyparasitism, which is common in endemic communities in most tropical countries, the specificity is too low to be relied upon. Hence, western blot technique was used to diagnose human toxocariasis in the studied population.1 The overall seroprevalence of Toxocara spp. infection among the pregnant women in this study was very high (92.5%). The high seroprevalence value recorded in this study is an indication that the studied population, a high risk group, are frequently exposed to the parasite. In a review study conducted on toxocariasis by Fakhri et al.,22 a high rate of soil contamination with Toxocara spp. eggs with a mean rate of 24% (ranging from 7–47%) was reported for Nigeria, which might also explain the high seroprevalence recorded in the studied population. Exposure to Toxocara may be through environmental contamination, which is prevalent in peri-urban communities, where stray dogs and cats roam freely releasing their feces containing Toxocara spp. eggs. This is exacerbated by poverty, poor hygiene and the risk of contact with infected dogs.19,23 The high prevalence recorded could also possibly be due to drinking water that might have been contaminated. Although more than half (52.5%) of the pregnant women claimed that they drank boiled water (as revealed by the questionnaire survey), 94.01% of them were still seropositive for Toxocara spp. infection. This might possibly be due to using contaminated vessels for drinking boiled water. The high prevalence could also be due to the fact that the antibody-based study could not differentiate between a recent and a remote infection.24 The high seroprevalence also shows the extent to which the disease (toxocariasis) threatens the health of both the women and that of the fetus. A similarly high seroprevalence of 86.1% was reported among school-aged children from an urban slum community in Nigeria.25 The seroprevalence of Toxocara spp. recorded among the study population was significantly higher than the 21.16% reported among pregnant women in Ilam Province, western Iran,26 7.4% of pregnant women in Brasilia, Brazil,27 6.4% of pregnant women in southern Brazil,28 9.19% of pregnant women in Shandong Province, eastern China,29 4.5% of pregnant women in Russia 9 and 35.3% of pregnant women in the USA.30 Factors that might have contributed to the high seroprevalence include diagnostic procedures, environmental conditions, sampling period, sample sizes, sanitation, water supply and lifestyle of the studied population. Comparing seroprevalence values obtained with the results of previous studies may be difficult because of varying serodiagnostic techniques, cut-off titres and the challenge in associating relationships between titres, infection and clinical disease.23,31 Pregnant women who claimed to have a knowledge of toxocariasis had a higher seroprevalence than those who responded negatively. This may be due to inadequacies in their knowledge of toxocariasis, which might have exposed them to the infection. In addition, they might have not taken cognizance of the need for protection against accidental contraction of the disease. Previous studies have reported that age is one of the most important risk factors for toxocariasis. Gyang et al.25 Gyang et al. reported that the seroprevalence of T. canis infection in school children increased with age. However, some studies reported no association between age and seroprevalence of Toxocara spp.,32–34 which is similar to the findings from this study. Previous researchers have reported that contact with dogs or cats is also an important risk factor for toxocariasis.35–37 Humans can be exposed to Toxocara spp. infection through direct contact with cats and dogs. Previous studies have reported a higher prevalence of T. canis in stray rather than domestic dogs; however, domestic dogs pose a higher risk for human exposure as a result of frequent contact with their owners.36,Toxocara spp. eggs have been recovered from both the feces and the hairs of domestic dogs and cats in previous studies.38–43 Due to the fact that under favorable environmental conditions, Toxocara spp. eggs on the hairs of domestic dogs and cats may become embryonated, direct contact with these animals may increase the risk of humans contracting toxocariasis.36,38 In this study, contact with cats and dogs were not risk factors because there was no association between the seropositivity of Toxocara spp. infection and contact with these animals. Studies have reported that humans can contract Toxocara spp. infection through eating raw or undercooked flesh containing Toxocara larvae of various paratenic hosts, such as chickens, cows or lambs.3,4,44–46 However, this study did not find any association between eating raw or undercooked meat and the seropositivity of Toxocara spp. infection. Less than half (36.65%) of the seropositive pregnant women with Toxocara spp. infection had miscarriages, however, there was no significant difference between the seropositive and seronegative pregnant women. A similar finding was reported in a study conducted in southern Brazil,28 where no significant association between seropositivity against Toxocara IgG and the occurrence of miscarriages was reported. However, Taylor, O'Connor, Hinson and Smith30 reported a significant association between seropositivity against Toxocara IgG and a history of previous abortions. The statistical analysis neither identified nor established risk factors related to toxocariasis among the pregnant women from the questionnaire, which may be due to the high seroprevalence rate obtained in this study. However, the authors recommend more studies among pregnant women in other parts of the country to identify risk factors which facilitate acquisition of toxocariasis. The high seroprevalence recorded in this study raises serious concerns, hence there is a need for further research to investigate the possibility of congenital transmission of Toxocara spp. to the fetus. Maffrand, Avila-Vázquez, Princich and Alasia11 and the CDC reported and registered congenital infection in human toxocariasis; however, the CDC did not consider the possibility of the parasite being transmitted during pregnancy.47 Experimental studies have provided evidence of vertical transmission of T. canis and T. cati in definitive hosts (dogs and cats).48 Furthermore, T. canis larvae in paratenic hosts have shown the capacity and tropism to migrate during pregnancy,49,50 hence the need to conduct this type of study in humans.13,51 In conclusion, the overall seroprevalence of toxocariasis among the pregnant women studied in this study was very high. This is the first report of a study on Toxocara spp. seroprevalence among pregnant women in Nigeria. There is a need for intensive health education regarding personal hygiene among pregnant women. Authors’ contributions CKF and OS conducted and designed this study; KI, OS and OA designed the study protocol; KA, SA, VG, EH and TN were involved in collecting samples; KI, OS and CKF carried out data curation; TWC and KI carried out statistical analysis; KI, OS and CKF wrote the original draft and were involved in reviewing and editing it. Funding We appreciate the Tertiary Education Trust Fund (TETFUND) for funding this study. The funders had no role in the study design, data collection and analysis, decision to publish or preparation of the manuscript. Competing interests The authors declare that they have no competing interests. Ethical approval The research protocol was submitted to the Ethics and Research Committee of the OAUTHC, Ile-Ife, Osun state, Nigeria. It was reviewed and approved with protocol no. ERC/2017/10/09. Acknowledgements We are grateful to the pregnant women for their participation in the study by providing their blood samples. 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TI - High seroprevalence of Toxocara antibodies in pregnant women attending an antenatal clinic at a university hospital in Ile-Ife, Nigeria
JO - Transactions of The Royal Society of Tropical Medicine and Hygiene
DO - 10.1093/trstmh/trz116
DA - 2020-04-08
UR - https://www.deepdyve.com/lp/oxford-university-press/high-seroprevalence-of-toxocara-antibodies-in-pregnant-women-attending-d6ULvo2V1j
SP - 301
VL - 114
IS - 4
DP - DeepDyve
ER -