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FREQUENCY OF ANTI- Toxocara spp. ANTIBODIES IN INDIVIDUALS ATTENDED BY THE CENTRO DE SALUD FAMILIAR AND ENVIRONMENTAL CONTAMINATION WITH Toxocara canis EGGS IN DOG FECES, IN THE COASTAL NIEBLA TOWN, CHILE

SUMMARY

The frequency of anti-Toxocara spp. antibodies in individuals attended by the Centro de Salud Familiar in the coastal Niebla town, Chile, was related to the host and to environmental factors. IgG anti- Toxocara antibodies were detected with a commercial ELISA kit (SCIMEDX Corporation, USA). Samples with undetermined absorbance values were subjected to an additional ELISA standardized by the Instituto de Salud Pública, Chilean Health Ministry, a commercial ELISA (NOVATEC, Germany), and a commercial Western blot kit (LDBio Diagnostics, France). Hematological exams were performed using an automated blood counter and blood smears. Dog feces were collected from the ground along the main road in Niebla, including rural and urban locations. Ninety (25.4%) of the 355 examined individuals were positive by the ELISA test. The frequency of anti-Toxocara antibodies and the infection risk were significantly higher (p < 0.05) among those individuals ≥ 40 years old with respect to the 20-39 years old group, in individuals from rural locations, those who did not have a safe drinking water supply in the house or who presented blood eosinophilia. The proportion of positive samples of dog feces and the mean number of Toxocara canis eggs/g of feces in urban and rural areas were similar (p > 0.05).

KEYWORDS:
Seroprevalence; Human toxocariasis; Environmental contamination; Eosinophilia

INTRODUCTION

Toxocariasis is a neglected worldwide distributed zoonosis caused by the third-stage larva (L3) of Toxocara canis and Toxocara cati nematodes whose definitive hosts are the domestic dog and cat, respectively. Eggs eliminated by T. canis females are expelled with the dog feces. The infective L3 larvae develop in eggs in the soil between 12 °C and 32 °C, with a relative humidity close to 85%. Eggs are viable for years and are found in 6.6% to 95% of soil samples from different countries11. Rubinsky-Elefant G, Hirata CE, Yamamoto JH, Ferreira MU. Human toxocariasis: diagnosis, worldwide seroprevalences and clinical expression of the systemic and ocular forms. Ann Trop Med Parasitol. 2010;104:3-23..

Transmission occurs predominantly by ingestion of infective eggs present in soil (onicophagy, geophagy) or less frequently by consumption of contaminated raw vegetables, fruits or water. Other possible route of Toxocara transmission is the ingestion of larvae from undercooked tissues of paratenic hosts (birds, ruminants or pigs). Human can also be infected through the direct contact with eggs containing infective larvae present in dog hair22. Overgaauw PA, van Knapen F. Veterinary and public health aspects of Toxocara spp. Vet Parasitol. 2013;193:398-403.. Hatched L3 larvae penetrate the intestinal mucosa and enter the mesenteric vessels to reach the liver, lungs, heart, eyes, and the central nervous system, inducing the formation of granulomas33. Barriga OO. A critical look at the importance, prevalence and control of toxocariasis and the possibilities of immunological control. Vet Parasitol . 1988;29:195-234..

Diagnosis of human toxocariasis is based on clinical, epidemiological, and serological test data; the latter mainly through the detection of anti- T. canis/T. cati antibodies by the enzyme linked immunosorbent assay (ELISA)1. The combined use of ELISA to detect IgG, with detection of excretion-secretion antigens and Western blot assays constitute a good diagnostic option due to their sensibilities and specificities; even when the application of these tests do not differentiate between an active disease and a past infection44. Fillaux J, Magnaval JF. Laboratory diagnosis of human toxocariasis. Vet Parasitol . 2013;193:327-36..

Different clinical forms are described for human toxocariasis: visceral larva migrans (VLM), ocular larva migrans (OLM), neurological toxocariasis (NT) and covert or common toxocariasis55. Fan CK, Liao CW, Cheng YC. Factors affecting disease manifestation of toxocarosis in humans: genetics and environment. Vet Parasitol . 2013;193:342-52.,66. Smith H, Noordin R. Diagnostic limitations and future trends in the serodiagnosis of human toxocariasis. In: Holland CV, Smith HV, editors. Toxocara: the enigmatic parasite. Wallingford: CABI; 2006. p.89-112.. In Chile, OLM has been identified in 31 patients with ages ranging from 4 to 45 years old77. Sapunar J, Verdaguer J, Zenteno J, Zenteno E. Larva migrans ocular por Toxocara: analisis de 31 casos. Parasitol Día. 1989;13:21-33.. In addition, one out of 175 children with positive serology also develops retinal granuloma and visual loss88. Sánchez JE, López JP, González M, Villaseca E, Manieu D, Roizen A, et al. Detección de lesiones oculares en niños seropositivos para Toxocara canis. Rev Chil Infectol. 2011;28:431-4.. VLM has been described in 129 children with serological evidence associated with lung, hepatic, ocular, neurological or skin problems99. Noemí I, Schuh W, Herskovic P, Ríos E, Cerva L, Torres MT, et al. Larva migrans visceral en niños. Rev Chil Pediatr. 1984;55:244-8.,1010. Noemí I, Viovy A, Cerva JL, Gottlieb B, Roncone E, Quera R, et al. Perfil clínico de la toxocariasis en pediatría. Parasitol Día . 1992;16:91-7.. In addition, a case of NT associated with high eosinophilia and positive serology was diagnosed in a 61 year old man1111. Ardiles A, Chanqueo L, Reyes V, Araya L. Toxocariasis en adulto manifestada como síndrome hipereosinofílico con compromiso neurológico predominante: caso clínico. Rev Med Chil. 2001;129:780-5..

Transmission and risk factors of toxocariasis vary between different geographical localities, and they have been associated with poverty, low education level, and lack of control or treatment of definitive hosts. All the above mentioned factors favor contamination which is reinforced by environmental conditions (light, temperature, humidity, pH, vegetation), and also the development, survival and availability of parasite eggs1212. Macpherson CN. The epidemiology and public health importance of toxocariasis: a zoonosis of global importance. Int J Parasitol. 2013;43:999-1008.. Seroprevalence of human toxocariasis varies between 1.6% and 92.8% in different countries1. Great variability are also described, from 3.7% and 40% among localities of a same country1313. Chieffi PP, Santos SV, Queiroz ML, Lescano SA. Human toxocariasis: contribution by Brazilian researchers. Rev Inst Med Trop Sao Paulo. 2009;51:301-8.. In Chile, seroprevalence varies between 1.3% and 15.6% in blood donors1414. Herskovic P, Astorga B. Toxocariasis humana en Chile. Rev Med Chil . 1985;113:18-21.,1515. Navarrete N, Rojas E. Seroprevalencia de toxocarosis en donantes de sangre. Arch Med Vet. 1998;30:153-6.. Toxocara canis and T. cati prevalences are from 10.7% to 19%1616. Torres P, Franjola R, Pérez J, Auad S, Hermosilla C, Flores L, et al. Geohelmintosis intestinales en el hombre y animales domésticos de sectores ribereños de la cuenca del río Valdivia, Chile. Bol Chil Parasitol. 1995;50:57-66.,1717. Torres P, Hauser M, Santibañez J, Marín F, Gesche W, Montefusco A. Búsqueda de Diphyllobothrium y otros parásitos intestinales en la población humana y carnívoros domésticos del sector del Lago Calafquén, Chile Bol Chil Parasitol . 1980;35:55-61.,1818. Torres P, Ramos M, Carrasco L, Neumann M, Franjola R, Navarrete N. Protozoos, helmintos y artrópodos del perro doméstico en la ciudad de Valdivia, Chile. Bol Chil Parasitol . 1974;29:18-23. and 65.1% to 70%1616. Torres P, Franjola R, Pérez J, Auad S, Hermosilla C, Flores L, et al. Geohelmintosis intestinales en el hombre y animales domésticos de sectores ribereños de la cuenca del río Valdivia, Chile. Bol Chil Parasitol. 1995;50:57-66.,1919. Torres P, Hott A, Boehmwald H. Protozoos, helmintos y artrópodos en gatos de la ciudad de Valdivia y su importancia para el hombre. Arch Med Vet . 1972;4:20-9. in dogs and cats, respectively, in the region of Valdivia.

Although some risk factors have been identified for toxocariasis, there is still much inconsistent information11. Rubinsky-Elefant G, Hirata CE, Yamamoto JH, Ferreira MU. Human toxocariasis: diagnosis, worldwide seroprevalences and clinical expression of the systemic and ocular forms. Ann Trop Med Parasitol. 2010;104:3-23.. For example, there is a wide age range leading to the conclusion that there is a higher prevalence in some age groups2020. Anaruma Filho F, Chieffi PP, Correa CR, Camargo ED, Silveira EP, Aranha JJ, et al. Human toxocariasis: a seroepidemiological survey in the municipality of Campinas (SP), Brazil. Rev Inst Med Trop Sao Paulo . 2002;44:303-7.,2121. Cancrini G, Bartolini A, Zaffaroni E, Guglielmetti P, Gamboa H, Nicoletti A, et al. Seroprevalence of Toxocara canis-IgG antibodies in two rural Bolivian communities. Parassitologia. 1998;40:473-5.. In other studies, no association between seroprevalence and age has been found2020. Anaruma Filho F, Chieffi PP, Correa CR, Camargo ED, Silveira EP, Aranha JJ, et al. Human toxocariasis: a seroepidemiological survey in the municipality of Campinas (SP), Brazil. Rev Inst Med Trop Sao Paulo . 2002;44:303-7.,2222. Chiodo P, Basualdo J, Ciarmela L, Pezzani B, Apezteguía M, Minvielle M. Related factors to human toxocariasis in a rural community of ArgentinaMem Inst Oswaldo Cruz. 2006;101:397-400.. Gender does not seem to be a factor associated with human toxocariasis2323. Dogan N, Dinleyici EC, Bor O, Töz SO, Ozbel Y. Seroepidemiological survey for Toxocara canis infection in the northwestern part of Turkey. Turkiye Parazitol Derg. 2007;31:288-91.. However, some authors report the opposite2424. Roldán WR, Espinoza YA, Huapaya PE, Huiza AF, Sevilla CR, Jiménez S. Frequency of human toxocariasis in a rural population from Cajamarca, Peru determined by DOT-ELISA test. Rev Inst Med Trop Sao Paulo . 2009;51:67-71.. Toxocariasis tends to be more prevalent in rural areas than in urban ones2323. Dogan N, Dinleyici EC, Bor O, Töz SO, Ozbel Y. Seroepidemiological survey for Toxocara canis infection in the northwestern part of Turkey. Turkiye Parazitol Derg. 2007;31:288-91.,2525. Herrmann N, Glickman LT, Schantz PM, Weston MG, Domansk LM. Seroprevalence of zoonotic toxocariasis in the United States: 1971-1973. Am J Epidemiol. 1985;122:890-6.. Higher eroprevalences have been associated with the tenancy of dogs and cats2626. Chieffi PP, Ueda M, Camargo ED, de Souza AM, Leopoldo e Silva C, Villa Nova A, et al. Contacto domiciliar e profissional com cães como fatores de risco para infecção humana por larvas de Toxocara. Rev Inst Med Trop Sao Paulo . 1988;30:379-82., particularly regarding veterinarians and those in charge of pets2727. Altcheh J, Nallar N, Conca M, Biancard M, Freilij H. Toxocariasis: aspectos clínicos y de laboratorio en 54 pacientes. An Pediatr (Barc). 2003;58:425-31.. Other authors have not found this association2828. Roldán WH, Espinoza YA, Atúncar A, Ortega E, Martínez A, Saravia M. Frequency of eosinophilia and risk factors and their association with Toxocara infection in schoolchildren during a health survey in the north of Lima, Perú. Rev Inst Med Trop Sao Paulo . 2008;50:273-8.. Some reports associate poor sanitation with higher seroprevalences of toxocariasis2020. Anaruma Filho F, Chieffi PP, Correa CR, Camargo ED, Silveira EP, Aranha JJ, et al. Human toxocariasis: a seroepidemiological survey in the municipality of Campinas (SP), Brazil. Rev Inst Med Trop Sao Paulo . 2002;44:303-7.. Several authors either associate2424. Roldán WR, Espinoza YA, Huapaya PE, Huiza AF, Sevilla CR, Jiménez S. Frequency of human toxocariasis in a rural population from Cajamarca, Peru determined by DOT-ELISA test. Rev Inst Med Trop Sao Paulo . 2009;51:67-71.,2727. Altcheh J, Nallar N, Conca M, Biancard M, Freilij H. Toxocariasis: aspectos clínicos y de laboratorio en 54 pacientes. An Pediatr (Barc). 2003;58:425-31. or do not associate2222. Chiodo P, Basualdo J, Ciarmela L, Pezzani B, Apezteguía M, Minvielle M. Related factors to human toxocariasis in a rural community of ArgentinaMem Inst Oswaldo Cruz. 2006;101:397-400. higher seroprevalences with eosinophilia. In the same way, leukocytosis has been associated2828. Roldán WH, Espinoza YA, Atúncar A, Ortega E, Martínez A, Saravia M. Frequency of eosinophilia and risk factors and their association with Toxocara infection in schoolchildren during a health survey in the north of Lima, Perú. Rev Inst Med Trop Sao Paulo . 2008;50:273-8. or not2020. Anaruma Filho F, Chieffi PP, Correa CR, Camargo ED, Silveira EP, Aranha JJ, et al. Human toxocariasis: a seroepidemiological survey in the municipality of Campinas (SP), Brazil. Rev Inst Med Trop Sao Paulo . 2002;44:303-7. with higher seroprevalences. Hemoglobin values have not apparently been associated with VLM and OLM2727. Altcheh J, Nallar N, Conca M, Biancard M, Freilij H. Toxocariasis: aspectos clínicos y de laboratorio en 54 pacientes. An Pediatr (Barc). 2003;58:425-31.,1010. Noemí I, Viovy A, Cerva JL, Gottlieb B, Roncone E, Quera R, et al. Perfil clínico de la toxocariasis en pediatría. Parasitol Día . 1992;16:91-7..

The aim of this study is to determine the frequency of anti-Toxocara spp. antibodies in individuals attended by the Centro de salud familiar in the coastal Niebla town and associate it with clinical, laboratory and environmental data, including the detection of Toxocara eggs in dog feces.

MATERIALS AND METHODS

Study area and human participants

The coastal area of Niebla (Fig. 1), located 15 km from the city of Valdivia (39°48'30''S and 73°14'30''W), has a population of 2,202 and 1,376 inhabitants in the urban and rural areas, respectively2929. Chile. Instituto Nacional de Estadísticas. Censo 2002 : síntesis de resultados. [cited 2016 Mar 15]. Available from: Available from: http://www.ine.cl/cd2002/sintesiscensal.pdf
http://www.ine.cl/cd2002/sintesiscensal....
. The zone has a mean annual temperature of 12 °C and a relative humidity of 88.7%. The study considered individuals who attended the Centro de Salud Familiar (CESFAM) in Niebla to perform a complete blood count, between September 2011 and January 2012. The study was approved by the Ethics Committee in Research, Valdivia Health Service, and Chilean Health Ministry. Recruited people consented in performing the ELISA test for toxocariasis. From the total of 490 people invited to participate in the study, 355 agreed and completed a survey containing their names, age, area where they lived (urban or rural), the ownership of pets (dogs or cats), if they had a yard or a garden, vegetables in the garden, and type of water supply in the house. The 355 participants are representative of people living in urban and rural areas of the Niebla coast who have a limited access to laboratory tests such as the ELISA to detect anti-Toxocara antibodies due to the high cost. All the participants received the ELISA results. The reasons for requesting the blood count were recorded using the Omega 300 system. The distribution of the study participants according to age, gender, and location is shown in Table 1. The age of participants varied from 9 months to 90 years old.

Fig. 1
Route of dog feces collection from the ground and rural and urban sectors in the Niebla coastal locality, Chile.

Table 1
Seropositivity of IgG anti-Toxocara spp. antibodies according to host and environmental factors, in 355 people attended at Centro de la Salud Familiar in the coastal locality of Niebla, Chile

Laboratory methods in humans

A blood sample from each person was obtained through venous puncture. Samples collected in EDTA tubes were used to prepare blood smears stained with May Grunwald-Giemsa, and analyzed by a hematological counter (Sysmex XT-1800i, Kobe, Japan) at the Central Laboratory of the Hospital Base in Valdivia. Results were obtained using the OMEGA 3000 information system at the Hematological Unit of the School of Medicine, Austral University of Chile. Anemia was determined according to hemoglobin values3030. Ruiz-Argüelles G, Ruiz Reyes G, Ruiz Delgado G. Interpretación de la citometría hemática. Índices y parámetros eritrocíticos. Definición de anemia. In: Ruiz-Argüelles G, editor. Fundamentos de hematología. 4ª ed. México: Médica Panamericana; 2009.. Eosinophilia was considered when the number of eosinophils surpassed 4% of the total white cell count, in most cases when it exceeded 500cells/µL3131. Vives Corrons J, Aguilar Bascompte JL. Manual de técnicas de laboratorio en hematología. 3ª ed. Barcelona: Masson; 2006.. Afterwards, EDTA samples were centrifuged at 1,200 g for 10 min; plasma samples were kept frozen in Eppendorf tubes at -20°C.

IgG anti-Toxocara canis/cati antibodies were detected by means of an ELISA kit (SCIMEDX Corporation, New Jersey, USA) at the Instituto de Salud Pública (ISP), Chilean Health Ministry. The ISP validated the kit using the Clinical and Laboratory Standard Institute guides N° EP12-A23232. Clinical and Laboratory Standards Institute. User protocol for evaluation of qualitative test performance: approved guideline. 2ª ed. Pennsylvania: CLSI; 2008. (EP12-A2) and EP15-A23333. Clinical and Laboratory Standards Institute. Verificación del desempeño de la precisión y veracidad por el usuario. 2ª ed. Pennsylvania: CLSI; 2005. (EP15-A2). The obtained sensitivity of 91.7% and the specificity of 80% fulfilled the verification requirements recommended by the manufacturer (sensitivity of 93.3% and specificity of 87.5%). To determine the specificity, the commercial kit was applied to serum samples with confirmed diagnosis of hydatidosis, fasciolosis, trichinellosis, cisticercosis, and autoimmune diseases. Absorbance readings, A462 > 0.350 OD units were considered as positive reactions, while A462 < 0.350 OD units and A462 = 0.250-0.350 OD units were considered as negative and undetermined reactions, respectively. At ISP, undetermined samples underwent additional serological testing: an "in house" standardized anti-IgG ELISA (ISP) and a commercial anti-IgG ELISA (NOVATEC, Dietzenbach, Germany). The positive samples had the results confirmed by a commercial Western blot kit (LDBio Diagnostics, Lyon, France). Samples presenting with two or more polypeptide bands of lower molecular weight (40, 30, 25, and 14 kDA), were considered as positive. The "in house" IgG ELISA assay was evaluated with respect to sensitivity, specificity and precision parameters using the Clinical and Laboratory Standard Institute Guides (CLSI), EP12-A23232. Clinical and Laboratory Standards Institute. User protocol for evaluation of qualitative test performance: approved guideline. 2ª ed. Pennsylvania: CLSI; 2008. (EP12-A2) and EP15-A23333. Clinical and Laboratory Standards Institute. Verificación del desempeño de la precisión y veracidad por el usuario. 2ª ed. Pennsylvania: CLSI; 2005. (EP15-A2).

Fecal dog samples collection and laboratory methods

In March 2012, samples of dog feces were collected from the ground along the main road in Niebla, including about 9 km of rural and urban locations (Fig.1). Samples were collected, manually, using double polyethylene bags by two people through a visual inspection of the main road path. At the laboratory, each sample was weighed, homogenized and kept at 4 °C. Five grams were taken from each sample and fixed in 10 mL of formol-saline to perform the qualitative Telemann modified method (TMM) in combination with a floating method (FM) which uses 70 g of zinc sulphate in 100 mL of distilled water1919. Torres P, Hott A, Boehmwald H. Protozoos, helmintos y artrópodos en gatos de la ciudad de Valdivia y su importancia para el hombre. Arch Med Vet . 1972;4:20-9.. The combination of TPM and FM offers a greater efficacy in the detection of Toxocara spp. eggs, in comparison with the techniques applied independently1818. Torres P, Ramos M, Carrasco L, Neumann M, Franjola R, Navarrete N. Protozoos, helmintos y artrópodos del perro doméstico en la ciudad de Valdivia, Chile. Bol Chil Parasitol . 1974;29:18-23.. Regarding the Knight et al. quantitative method (KM)3434. Knight WB, Hiatt RA, Claine BL, Ritchie LS. A modification of the formol-ether concentration technique for increased sensitivity in detecting Schistosoma mansoni eggs. Am J Trop Med Hyg. 1976;25:818-23., feces from homogenized samples were added to a conical calibrated centrifuge tube containing 7 mL of formol-saline to complete 8 mL. To find T. canis eggs using the combined TMM and FM method, two microscopic preparations of the sediment and one preparation of FM were examined. For the KM, all the sediment was examined in microscopic preparations3434. Knight WB, Hiatt RA, Claine BL, Ritchie LS. A modification of the formol-ether concentration technique for increased sensitivity in detecting Schistosoma mansoni eggs. Am J Trop Med Hyg. 1976;25:818-23.. All preparations using 22 x 22 mm cover glass were examined under a light microscope (100 x). Results of the KM method were expressed as the number of eggs/g of feces.

Statistical analysis

Seroprevalence corresponds to the number of seropositive people/number of people examined x 100.To compare the seroprevalences, the Pearson´s chi-square with the Yates´s correction was applied. When pairs of samples presented expected frequencies < 5, the Fisher´s exact test was used3535. Zar JH. Biostatistical analysis. 4th ed. Upper Saddle River: Prentice-Hall; 1999.. The U Mann-Whitney test was used to compare the eggs mean/g of feces3535. Zar JH. Biostatistical analysis. 4th ed. Upper Saddle River: Prentice-Hall; 1999.. For all the tests, results were considered significant at p < 0.05. Odds ratios (OR) and 95% confidence intervals (CI) were calculated with the free software "VassarStat available at http://vassarstats.net/textbook/index.html. When odds ratios and confidence intervals values were >1 they were considered significant.

RESULTS

Ninety (25.4%) of the 355 participants were positive for IgG anti-Toxocara spp. antibodies by the ELISA test; their location is shown in Figure 1. Twenty serum samples were undetermined but 15 of them proved definitively to be positive when the three additional tests were performed. The proportion of individuals with anti-Toxocara spp. antibodies was significantly higher (p < 0.05) in people of different age groups, in all the individuals living in rural areas and among those who did not have a safe drinking water supply in the house (Table 1).

Younger age groups (≤ 40 years old) did not show statistical significant differences (p > 0.05) (Table 1). However, the proportion of individuals with anti-Toxocara spp. antibodies was significantly lower (p < 0.05) in the age group of 20-39 years old with respect to the age group ≥ 40 years old (Table 2). The risk for those ≥ 40 years old was significantly increased (OR 2.23; 95% CI: 1.18 - 4.21) with respect to those with 20-39 years old (Table 1). The infection risk was higher for individuals living in rural areas (OR 1.68; 95% CI: 1.04 - 2.73) and among those who did not have safe drinking water supplies (OR 1.86; 95% CI: 1.09 - 3.17). The proportion of people with anti-Toxocara spp. antibodies of different genders did not show significant differences (p > 0.05) and the risk did not show significant association (OR 0.71; 95% CI: 0.43 - 1.17) (Table 1).

The existence of a yard, garden or vegetables in the garden of the house of the people surveyed as well as the ownership of dogs or cats was not associated with a significantly higher seroprevalence or risk (Table 2). The same was true for the proportion of environmental samples of dog feces with Toxocara eggs and their eggs mean/g feces from rural and urban areas (Table 2).

Table 2
Proportion of dog feces positive for Toxocara eggs collected from the ground and the mean of the number/g of sample in rural and urban areas in the coastal locality of Niebla, Chile

The frequency of anti-Toxocara spp. antibodies was significantly higher (p < 0.05) among individuals with relative or absolute eosinophilia. However, in individuals with or without anemia or leukocytosis it was similar (p > 0.05) (Table 1). The risk was significantly higher for those individuals with relative eosinophilia (OR 2.64; 95% CI: 1.53 - 4.54).

There was no significant difference between the most frequent reasons (health control, diabetes, dyslipidemia and high blood pressure) for requesting a blood count and the Toxocara positivity and negativity (p > 0.05) (Table 1). Also, the infection risk did not show a significant association among individuals who performed the blood exam for health control due to diabetes, dyslipidemia and high blood pressure (Table 1).

DISCUSSION

The frequency of anti-Toxocara spp. antibodies in individuals attended by the Centro de Salud Familiar in Niebla surpassed the values estimated by Herskovic & Astorga1414. Herskovic P, Astorga B. Toxocariasis humana en Chile. Rev Med Chil . 1985;113:18-21. in blood donors from three regions in Chile (1.3% to 15.6%); in the population of Robinson Crusoe Island (3.8%)3636. Astorga B, Briceño E, Jorquera H, Herskovic P. Perfil parasitológico en habitantes de la Isla Robinson Crusoe. Parasitol Día . 1988;12:176-81., and in blood donors (5.3%) from the city of Valdivia1515. Navarrete N, Rojas E. Seroprevalencia de toxocarosis en donantes de sangre. Arch Med Vet. 1998;30:153-6..

In a review of toxocariasis in Latin America3737. Delgado O, Rodriguez-Morales AJ. Aspectos clínico-epidemiológicos de la toxocariasis: una enfermedad desatendida en Venezuela y América Latina. Bol Malariol Salud Amb. 2009;49:1-33., the seroprevalence in the human populations of different age groups varied between 22.1% and 31.6% in Argentina, 27% and 42% in Bolivia, 47.5% in Colombia, 5.2% in Cuba, 7.3% and 27.9% in Peru, 6.5% in Puerto Rico, and 34.9% in indigenous populations in Venezuela.

The similarity of Toxocara spp. infection in the two younger age groups and the significant higher frequency of anti- Toxocara spp. antibodies and the higher risk for individuals ≥ 40 years old with respect to the 20-39 years old group suggests that L3 larvae remain in the tissues, and that recurrent reinfections maintain the level of circulating antibodies in the affected population. The survival of the parasite in the tissues is also favored by the mechanisms that L3 larvae use to evade the immunological response3838. Maizels RM. Toxocara canis: molecular basis of immune recognition and evasion. Vet Parasitol . 2013;193:365-74.. In Valdivia, Navarrete & Rojas1515. Navarrete N, Rojas E. Seroprevalencia de toxocarosis en donantes de sangre. Arch Med Vet. 1998;30:153-6. did not find significant differences in the seroprevalence of different age groups of blood donors. In Colombia, Agudelo et al.3939. Agudelo C, Villarreal E, Cáceres E, López C, Eljach J, Ramírez N, et al. Human and dogs Toxocara canis infection in a poor neighborhood in Bogotá. Mem Inst Oswaldo Cruz 1990;85:75-8. found higher seroprevalences in age groups from 10-39 in a population of age varying from months to 70 years old. Rubinsky-Elefant et al.4040. Rubinsky-Elefant G, da Silva-Nunes M, Malafronte RS, Muniz PT, Ferreira MU. Human toxocariasis in rural Brazilian Amazonia: seroprevalence, risk factors, and spatial distribution. Am J Trop Med Hyg . 2008;79:93-8. found a higher seroprevalence in people from 5 to 14 years old in comparison with those from 15 to 90 years old in the Amazonian region of Brazil. In Bolivia2121. Cancrini G, Bartolini A, Zaffaroni E, Guglielmetti P, Gamboa H, Nicoletti A, et al. Seroprevalence of Toxocara canis-IgG antibodies in two rural Bolivian communities. Parassitologia. 1998;40:473-5. and Brazil2020. Anaruma Filho F, Chieffi PP, Correa CR, Camargo ED, Silveira EP, Aranha JJ, et al. Human toxocariasis: a seroepidemiological survey in the municipality of Campinas (SP), Brazil. Rev Inst Med Trop Sao Paulo . 2002;44:303-7. seroprevalence was similar in different age groups, in populations from two to 85 and from 3 months to 80 years old, respectively.

In Niebla, the frequency of anti-Toxocara spp. antibodies and the infection risk was similar in different gender groups. These data is in agreement with those from other Chilean authors1515. Navarrete N, Rojas E. Seroprevalencia de toxocarosis en donantes de sangre. Arch Med Vet. 1998;30:153-6. and in other countries2121. Cancrini G, Bartolini A, Zaffaroni E, Guglielmetti P, Gamboa H, Nicoletti A, et al. Seroprevalence of Toxocara canis-IgG antibodies in two rural Bolivian communities. Parassitologia. 1998;40:473-5.,2323. Dogan N, Dinleyici EC, Bor O, Töz SO, Ozbel Y. Seroepidemiological survey for Toxocara canis infection in the northwestern part of Turkey. Turkiye Parazitol Derg. 2007;31:288-91.,4141. Teixeira CR, Chieffi PP, Lescano SA, de Melo Silva EO, Fux B, Cury MC. Frequency and risk factors for toxocariasis in children from a pediatric outpatient center in southeastern Brazil. Rev Inst Med Trop Sao Paulo . 2006;48:251-5.. However, some other studies reported higher seroprevalences in males11. Rubinsky-Elefant G, Hirata CE, Yamamoto JH, Ferreira MU. Human toxocariasis: diagnosis, worldwide seroprevalences and clinical expression of the systemic and ocular forms. Ann Trop Med Parasitol. 2010;104:3-23.,2424. Roldán WR, Espinoza YA, Huapaya PE, Huiza AF, Sevilla CR, Jiménez S. Frequency of human toxocariasis in a rural population from Cajamarca, Peru determined by DOT-ELISA test. Rev Inst Med Trop Sao Paulo . 2009;51:67-71. than in females3939. Agudelo C, Villarreal E, Cáceres E, López C, Eljach J, Ramírez N, et al. Human and dogs Toxocara canis infection in a poor neighborhood in Bogotá. Mem Inst Oswaldo Cruz 1990;85:75-8.. The latter has been associated with a more intense exposure due to working activities2424. Roldán WR, Espinoza YA, Huapaya PE, Huiza AF, Sevilla CR, Jiménez S. Frequency of human toxocariasis in a rural population from Cajamarca, Peru determined by DOT-ELISA test. Rev Inst Med Trop Sao Paulo . 2009;51:67-71. in those with more contact with soil, working in agriculture or cattle rising.

Results suggest that the level of contamination and the risk of transmission of human toxocariasis in rural and urban areas would be similar since the proportion of positive dog feces samples, taken directly from the soil, and the eggs mean/g of feces did not present significant differences between these areas. Nevertheless, the frequency of anti-Toxocara spp. antibodies and the risk of infection were higher in individuals from rural areas. Gawor et al.4242. Gawor J, Borecka A, Zarnowska H, Marczynska M, Dobosz S. Environmental and personal risk factors for toxocariasis in children with diagnosed disease in urban and rural areas of central Poland. Vet Parasitol . 2008;155:217-22. concluded that in Poland, the proportion of soil samples from rural and urban homes contaminated with Toxocara eggs was similar. The proportion of dog feces samples with Toxocara eggs was similar (13.5%) to previous data from the city of Valdivia 1616. Torres P, Franjola R, Pérez J, Auad S, Hermosilla C, Flores L, et al. Geohelmintosis intestinales en el hombre y animales domésticos de sectores ribereños de la cuenca del río Valdivia, Chile. Bol Chil Parasitol. 1995;50:57-66.,1717. Torres P, Hauser M, Santibañez J, Marín F, Gesche W, Montefusco A. Búsqueda de Diphyllobothrium y otros parásitos intestinales en la población humana y carnívoros domésticos del sector del Lago Calafquén, Chile Bol Chil Parasitol . 1980;35:55-61.,1818. Torres P, Ramos M, Carrasco L, Neumann M, Franjola R, Navarrete N. Protozoos, helmintos y artrópodos del perro doméstico en la ciudad de Valdivia, Chile. Bol Chil Parasitol . 1974;29:18-23.,4343. Oberg C, Franjola R, Leyán V. Helmintos del perro doméstico (Canis familiaris), en la ciudad de Valdivia, Chile. Bol Chil Parasitol . 1979;34:21-6.. In Brazil, Negri et al.4444. Negri EC, Santarém VA, Rubinsky-Elefant G, Giuffrida R. Anti-Toxocara spp. antibodies in an adult healthy population: serosurvey and risk factors in Southeast Brazil. Asian Pac J Trop Biomed. 2013;3:211-6. did not find significant differences in the seroprevalence of people from rural or urban areas. Studies in the U.S.A.2525. Herrmann N, Glickman LT, Schantz PM, Weston MG, Domansk LM. Seroprevalence of zoonotic toxocariasis in the United States: 1971-1973. Am J Epidemiol. 1985;122:890-6., and Turkey2323. Dogan N, Dinleyici EC, Bor O, Töz SO, Ozbel Y. Seroepidemiological survey for Toxocara canis infection in the northwestern part of Turkey. Turkiye Parazitol Derg. 2007;31:288-91. showed that seroprevalences of human toxocariasis were significantly higher in rural areas.

The existence of a yard, garden or vegetable in the garden, in the house, as well as having pets was not associated with seropositivity and infection risk in individuals of Niebla. Roldán et al.2828. Roldán WH, Espinoza YA, Atúncar A, Ortega E, Martínez A, Saravia M. Frequency of eosinophilia and risk factors and their association with Toxocara infection in schoolchildren during a health survey in the north of Lima, Perú. Rev Inst Med Trop Sao Paulo . 2008;50:273-8. reported an association between individuals that were seropositive for Toxocara and the existence of gardens. Other studies in Brazil20 and Colombia3939. Agudelo C, Villarreal E, Cáceres E, López C, Eljach J, Ramírez N, et al. Human and dogs Toxocara canis infection in a poor neighborhood in Bogotá. Mem Inst Oswaldo Cruz 1990;85:75-8. have shown that there is no association between seroprevalence and having pets. However, there are also studies that have shown the opposite in Argentina2222. Chiodo P, Basualdo J, Ciarmela L, Pezzani B, Apezteguía M, Minvielle M. Related factors to human toxocariasis in a rural community of ArgentinaMem Inst Oswaldo Cruz. 2006;101:397-400., Brazil2626. Chieffi PP, Ueda M, Camargo ED, de Souza AM, Leopoldo e Silva C, Villa Nova A, et al. Contacto domiciliar e profissional com cães como fatores de risco para infecção humana por larvas de Toxocara. Rev Inst Med Trop Sao Paulo . 1988;30:379-82., Chile4545. Triviño X, Bedregal P, Torres M, Canales M, Alvarado C, Hernández R. Toxocarosis en Chile: serie clínica en un centro de pediatría ambulatoria. Parasitol Día . 1999;23:113-7., Colombia4646. Mendoza Meza DL, Lozano Socarras S, Jaimes MB. Exposición al parásito Toxocara canis en un población escolar de la comuna 7 del distrito de Santa Marta, Colombia. Duazary. 2010;7:183-90., and Peru2424. Roldán WR, Espinoza YA, Huapaya PE, Huiza AF, Sevilla CR, Jiménez S. Frequency of human toxocariasis in a rural population from Cajamarca, Peru determined by DOT-ELISA test. Rev Inst Med Trop Sao Paulo . 2009;51:67-71..

The prevalence of toxocariasis and the infection risk in Niebla were higher among individuals that did not have safe drinking water supplies in their homes. This suggests that the water consumed from springs, boreholes or streams are potentially contaminated with Toxocara eggs or that food washed with these water sources could represent a transmission risk, coinciding with a study performed in Colombia4646. Mendoza Meza DL, Lozano Socarras S, Jaimes MB. Exposición al parásito Toxocara canis en un población escolar de la comuna 7 del distrito de Santa Marta, Colombia. Duazary. 2010;7:183-90.. Anaruma-Filho et al.2020. Anaruma Filho F, Chieffi PP, Correa CR, Camargo ED, Silveira EP, Aranha JJ, et al. Human toxocariasis: a seroepidemiological survey in the municipality of Campinas (SP), Brazil. Rev Inst Med Trop Sao Paulo . 2002;44:303-7. concluded that individuals who filtered drinking water before consumption showed a significantly lower frequency of toxocariasis, compared with those who did not treat drinking water.

The frequency of anti-Toxocara spp. antibodies in Niebla was significantly higher in people with eosinophilia, confirming the results obtained in Argentina2222. Chiodo P, Basualdo J, Ciarmela L, Pezzani B, Apezteguía M, Minvielle M. Related factors to human toxocariasis in a rural community of ArgentinaMem Inst Oswaldo Cruz. 2006;101:397-400., Brazil4141. Teixeira CR, Chieffi PP, Lescano SA, de Melo Silva EO, Fux B, Cury MC. Frequency and risk factors for toxocariasis in children from a pediatric outpatient center in southeastern Brazil. Rev Inst Med Trop Sao Paulo . 2006;48:251-5. and Peru2424. Roldán WR, Espinoza YA, Huapaya PE, Huiza AF, Sevilla CR, Jiménez S. Frequency of human toxocariasis in a rural population from Cajamarca, Peru determined by DOT-ELISA test. Rev Inst Med Trop Sao Paulo . 2009;51:67-71.. However, the frequency of antibodies was not associated with the presence of anemia or leukocytosis, corroborating other studies2020. Anaruma Filho F, Chieffi PP, Correa CR, Camargo ED, Silveira EP, Aranha JJ, et al. Human toxocariasis: a seroepidemiological survey in the municipality of Campinas (SP), Brazil. Rev Inst Med Trop Sao Paulo . 2002;44:303-7.,2424. Roldán WR, Espinoza YA, Huapaya PE, Huiza AF, Sevilla CR, Jiménez S. Frequency of human toxocariasis in a rural population from Cajamarca, Peru determined by DOT-ELISA test. Rev Inst Med Trop Sao Paulo . 2009;51:67-71.,2727. Altcheh J, Nallar N, Conca M, Biancard M, Freilij H. Toxocariasis: aspectos clínicos y de laboratorio en 54 pacientes. An Pediatr (Barc). 2003;58:425-31.,4141. Teixeira CR, Chieffi PP, Lescano SA, de Melo Silva EO, Fux B, Cury MC. Frequency and risk factors for toxocariasis in children from a pediatric outpatient center in southeastern Brazil. Rev Inst Med Trop Sao Paulo . 2006;48:251-5..

As a conclusion, the frequency of anti-Toxocara spp. antibodies and the infection risk was significantly higher among individuals ≥ 40 years old with respect to the 29-39 years group, in those living in rural areas, and also among those that did not have safe drinking water supplies at home or who presented blood eosinophilia.

ACKNOWLEDGEMENTS

This research was partially funded by the Parasites Diversity and Zoonosis Transmitted by Aquatic Organisms Program. Dirección de Investigación y Desarrollo (DID N° I2010-02) . Universidad Austral de Chile. The authors are indebted to Claire Evans for the English revision of the manuscript .

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    Teixeira CR, Chieffi PP, Lescano SA, de Melo Silva EO, Fux B, Cury MC. Frequency and risk factors for toxocariasis in children from a pediatric outpatient center in southeastern Brazil. Rev Inst Med Trop Sao Paulo . 2006;48:251-5.
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Publication Dates

  • Publication in this collection
    2016

History

  • Received
    04 Dec 2015
  • Accepted
    15 Mar 2016
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