Original Article

Prevalence of Toxocara Species Eggs in the Soil of Public Parks in Hamedan City, Western Iran

Background

Toxocariasis caused by the larval stage of Toxocara canis and Toxocara cati in humans is a neglected infection and one of the most widespread zoonotic disease with public health and socioeconomic importance worldwide (1,2). Upon ingestion of embryonated eggs, the larvae are released from the eggs in the small intestine, penetrate the intestinal wall, and migrate to liver, lungs, and other organ systems causing visceral larva migrans (VLM), ocular larva migrans (OLM), neurotoxocariasis (NT), and covert or common toxocariasis (CT) (3). Visceral toxocariasis is a febrile disease particularly affecting children in their first decade of life due to eating soil, mouthing of objects, playing in sandboxes or playgrounds contaminated with faeces of dogs and cats, and/or their poor understanding of hygiene (4). Toxocara infection is caused mainly by the accidental ingestion of the infective eggs of Toxocara spp. through contaminated soil, water, fruit, or vegetables. It can also be caused by the ingestion of the encapsulated third-stage larvae present in raw/undercooked meat and/or organs from paratenic or transport hosts, such as rabbits, ruminants, and poultry (5). Another mode of transmission is reported to be human contact with dogs or cats, as embryonated eggs could attach to their fur (6).

On a worldwide scale, 20%–40% of dogs and cats with parasitic worm burdens have T. canisor T. cati (7), and national surveys on humans have reported the prevalence of antibodies against T. canis ranging from 1.6 to 81% in different countries (1). In Iran, Toxocara and Toxascaris spp. are among the most frequently observed parasites with a pooled prevalence of 32.6% in dogs, 24.2% in cats, 69.4% in red foxes and 23.3% in golden jackals, and it has been estimated that 9.3% of the general population have antibodies against T. canis (8). The environmental contamination with Toxocara eggs, because of the infected carnivores defecating in playgrounds, sandpits, gardens, parks, and beaches, is one of the major causes of human toxocariasis (7). Several studies have investigated contamination of soil of public areas in different regions of the world and the estimated prevalence rates in the different WHO regions ranged from 13% to 35% (9). According to the published reports, 18% of soil samples from the Middle East and North Africa were contaminated with Toxocara spp. (range: 11%–24%) (9). In Iran, a recent meta-analysis article reported that 16% of soil samples from public areas are contaminated with the eggs of Toxocara spp. (10). Considering (i) notable prevalence of toxocariasis is in both stray and owned dogs (11,12) and cats (first author’s personal experience), (ii) presence of antibodies against T. canis in blood sera of 8.8% of children in the urban and rural areas of Hamedan (13), and (iii) the public health importance of contamination of parks with Toxocara spp. eggs, this study aimed to examine soil samples from different public parks of the city for the presence of Toxocara eggs.

Methods

Study Area

Hamedan city (34° 48′ 0″ N, 48° 31′ 12″ E) is the capital of Hamedan province in the west of Iran with around 600 000 inhabitants. It has a cold semi-arid climate with an annual rainfall of 318 mm and an annual average temperature of 11.3°C. In the city, there are 130 public parks under different categories such as pocket, neighborhood, regional, district, and city parks with various sizes distributed in four districts (14).

During April and May 2019, a total of 120 soil samples were collected from 20 district and city parks with an overall area of 551 241 m². Public parks namely Aramgah-e Bu-Ali Sina, Mardom (also known as Luna), Abbas Abad, Aramgah-e Baba Taher, Eram, Namaz, Bagh-e Irani, Moadarres, Etemadieh, Koodak, Shahrvand, Parvaz, Narges, Maryam, Madar, Shokri Pour, Banovan, Bagh-e-Nazari, Chamran and Banafsheh (Figure 1) are distributed in all four city districts. These parks are crowded all year round, along with children’s playgrounds and camping sites.

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Figure 1.

Location of Sampled Sites.

Figure 1.

Location of Sampled Sites.

Sampling and Detection of Helminths Eggs

From each park, four to ten soil samples were taken based on the area of the parks i.e., separate samples were collected from every 50 steps. Soil samples of approximately 200 g were collected at a depth of 3 cm, stored in plastic bags, and taken to the laboratory. For detection of ova, soil samples were dried overnight at room temperature and passed through a 150 μm mesh sieve. Exactly 2 g of powdery soil was subjected to a normal sucrose flotation method (15). Light microscopic examinations were carried out by trained personnel and photomicrographs were taken from positive samples. Eggs were counted and classified according to their developmental stage i.e., non-developed, 2-cell to tadpole stage, and larvated eggs (16).

Results

Fourteen out of 120 samples (11.67%) collected from 10 public parks out of 20 in Hamedan (50.0%) were contaminated with Toxocara spp. eggs.

The ratio of the number of positive specimens to the total number of collected soil samples from each park ranged from 12.5% to 50.0%.

The eggs were spherical to subspherical, measuring approximately 75–85 μm in diameter with a thick shell, an alveolar external layer (thimble-like), and a smooth internal layer as already described (7). All three developmental stages of Toxocara spp. eggs i.e., non-developed (n=2; 14.30%), developing stages (n=6; 42.85%), and larvated eggs (n=6; 42.85%) were observed (Figure 2). Furthermore, in two public parks, Trichuris spp. eggs were found in the soils.

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Figure 2.

Different Stages of Toxocara spp. Eggs in Soil Samples; (a) Non-developed Egg, (b) Dividing Egg, (c) Larvated Egg.

Figure 2.

Different Stages of Toxocara spp. Eggs in Soil Samples; (a) Non-developed Egg, (b) Dividing Egg, (c) Larvated Egg.

Discussion

In this study, 11.67% of soil samples were contaminated with eggs of Toxocara spp. Several studies in different cities of Iran have reported contamination rates ranging between 4 and 63.3% in public areas. All of the studies except two are based on light microscopy examination of soil specimens (Table 1). Furthermore, in the present study, 50.0% of the public parks were found to be contaminated with Toxocara spp. eggs. In similar studies different rates were reported i.e., 80% in Piranshahr (32), 77.77% in Zanjan (42), 76.7% and 14.7% in Tabriz (27,29), 75% in Isfahan (37), 61.2% in Abadan (24), 50% in Ilam (33), 36.4% in Karaj (39), 34.1% in Ardabil (28), 31.25% in Larestan (21), 26.66% in Arak (38), 23.2% in Tehran (36), 22.2% in Khorram Abad (15), 15% in Shiraz (18), and 3.9% in Urmia (26). It has been shown that Toxocara eggs in public places are prevalent in regions with a high relative humidity, which are located at high longitudes and low latitudes (2). However, as sampling seasons and soil examination methods are different, it is not possible to reach a clear conclusion on the contamination of public areas in different localities of the country. A countrywide survey at one time period and a single method is suggested.

In the present study, the molecular examination was not performed to define the distribution pattern of Toxocara species in soil samples; however, there are two studies in Iran in which PCR followed by sequencing were used for this purpose. In Ahavz, 28.0% and 5.7% of the soil samples contained eggs of T. cati and T. canis, respectively (22). And, in Shiraz, 15.3% and 0.7% of soil samples were contaminated with T. cati and T. canis (19). There are controversies in the literature concerning Toxocara spp. in human patients. Some authors state that most cases of human toxocariasis have been associated with parasitism caused by T. canis (44), while some others believe that T. cati has been underestimated and as cats have more access to places where children go, T. catishould be considered responsible for the majority of larva migranscases (7). In Iran, since the first report of larva migrans in 1976 (45), more than 25 confirmed cases of human toxocariasis including VLM, OLM, and NT have been documented as reviewed in a previous study (3). However, the species of Toxocara infecting patients in the country has not been investigated so far. In human populations, serologic tests are commonly used for diagnosis of toxocariasis; however, the problems of cross-reactivity in polyparasitism and indistinguishability between T. canis and T. cati (or possibly T. malayensis) still exist (2). Species-specific diagnostic tools are required to support future epidemiological investigations. Moreover, surgeons should be encouraged to send the freshly removed worm body for molecular identification.

It is generally believed that only dogs and cats play role in the contamination of the environment. However, it has been shown that snails have roles in the epidemiology of toxocariasis (46). In a study in an open space in Buenos Aires, Argentina, 20% of Rumina decollatawere infected with the third larval stage (L3) of Toxocara cati(46). A clinical trial on experimental infection of dogs/cats with infected snails will clarify the role of snails in toxocarosis of carnivores. Furthermore, the snail-to-snail transmission of nematodes larvae has been described as a novel route (47). It would be valuable to study whether or not “intermediesis” occurs for Toxocara species.

In most of the discussions, stray and pet cats and dogs are mentioned to be responsible for contamination of the environment but several species of wild canids (e.g. red fox, golden jackal, and wolf) and wild felids (e.g. lynx) are definitive hosts of T. canis and T. cati (48). It is suggested that foxes can be considered as the primary source of Toxocara spp. eggs in the environment because of the high prevalence of patent infections and a total absence of any anthelmintic treatment (49). Phylogenetic analyses of Toxocara spp. recovered from wild canids and felids are required to clarify the role of wild carnivores in contamination of the urban environments via their movements in borders of the cities and their potential to infect stray dogs and cats.

Conclusions

This study provides the first information about the contamination of public areas with Toxocara spp. in Hamedan province and calls for an increased general awareness of public health risk. Parents and pet-owners should get informed about the hazards of toxocariasis by medical and veterinary practitioners. Moreover, the media and science communicators should educate the society on prevention strategies to minimize the risks of zoonotic transmission. Further studies in the province especially with the aid of molecular-based studies for the identification of parasite species are suggested.

Conflict of Interests

The authors declare that they have no conflict of interests.

Acknowledgments

Authors would like to thank the staff of Laboratory of Parasitology, Faculty of Veterinary Sciences, Bu-Ali Sina University for their assistance.

Ethical Approval

Not applicable.

Authors’ Contributions

Conceptualization: AS, MZi; methodology: AS, ST, SN, SF, MZe; original draft preparation: AS; review and editing: MZi; funding acquisition: AS. All authors read and approved the final manuscript.

Funding/Support

This study was supported by the Bu-Ali Sina University, Hamedan, Iran [Grant Number 1/1/28864].

References

1. Ma G, Holland CV, Wang T, Hofmann A, Fan CK, Maizels RM. Human toxocariasis. Lancet Infect Dis 2018; 18(1):e14-e24. doi: 10.1016/s1473-3099(17)30331-6 [Crossref] [ Google Scholar]
2. Rostami A, Ma G, Wang T, Koehler AV, Hofmann A, Chang BCH. Human toxocariasis-a look at a neglected disease through an epidemiological ‘prism’. Infect Genet Evol 2019; 74:104002. doi: 10.1016/j.meegid.2019.104002 [Crossref] [ Google Scholar]
3. Zibaei M, Sadjjadi SM. Trend of toxocariasis in Iran: a review on human and animal dimensions. Iran J Vet Res 2017; 18(4):233-42. [ Google Scholar]
4. Macpherson CN. The epidemiology and public health importance of toxocariasis: a zoonosis of global importance. Int J Parasitol 2013; 43(12-13):999-1008. doi: 10.1016/j.ijpara.2013.07.004 [Crossref] [ Google Scholar]
5. Zibaei M, Sadjjadi SM, Maraghi S. The occurrence of Toxocara species in naturally infected broiler chickens revealed by molecular approaches. J Helminthol 2017; 91(5):633-6. doi: 10.1017/s0022149x16000559 [Crossref] [ Google Scholar]
6. Bakhshani A, Maleki M, Haghparast A, Parande Shirvan S, Borji H. A survey on Toxocara cati eggs on the hair of stray cats: a potential risk factor for human toxocariasis in Northeastern Iran. Comp Immunol Microbiol Infect Dis 2019; 64:10-3. doi: 10.1016/j.cimid.2019.02.002 [Crossref] [ Google Scholar]
7. Beugnet F, Halos L, Guillot J. Textbook of Clinical Parasitology in Dogs and Cats. Zaragoza, Spain: Servet Publishing; 2018.
8. Vafae Eslahi A, Badri M, Khorshidi A, Majidiani H, Hooshmand E, Hosseini H. Prevalence of Toxocara and Toxascaris infection among human and animals in Iran with meta-analysis approach. BMC Infect Dis 2020; 20(1):20. doi: 10.1186/s12879-020-4759-8 [Crossref] [ Google Scholar]
9. Fakhri Y, Gasser RB, Rostami A, Fan CK, Ghasemi SM, Javanian M. Toxocara eggs in public places worldwide-a systematic review and meta-analysis. Environ Pollut 2018; 242(Pt B):1467-75. doi: 10.1016/j.envpol.2018.07.087 [Crossref] [ Google Scholar]
10. Maleki B, Khorshidi A, Gorgipour M, Mirzapour A, Majidiani H, Foroutan M. Prevalence of Toxocara spp eggs in soil of public areas in Iran: a systematic review and meta-analysis. Alexandria Med J 2018; 54(2):97-101. doi: 10.1016/j.ajme.2017.06.001 [Crossref] [ Google Scholar]
11. Sardarian K, Maghsood AH, Ghiasian SA, Zahirnia AH. Prevalence of zoonotic intestinal parasites in household and stray dogs in rural areas of Hamadan, Western Iran. Trop Biomed 2015; 32(2):240-6. [ Google Scholar]
12. Fallah M. Toxocara canis: infection of stray dogs and visceral larva migrans hazard in Hamadan. Avicenna J Clin Med 1995; 2(2):18-22. [ Google Scholar]
13. Fallah M, Azimi A, Taherkhani H. Seroprevalence of toxocariasis in children aged 1-9 years in western Islamic Republic of Iran, 2003. East Mediterr Health J 2007; 13(5):1073-7. doi: 10.26719/2007.13.5.1073 [Crossref] [ Google Scholar]
14. Municipality of Hamedan. Annual Statistics Book of the Year 1397. Available from: http://announce.hamedan.ir/AttachFiles/AnnDocs1326-dfsn.zip.
15. Zibaei M, Abdollahpour F, Birjandi M, Firoozeh F. Soil contamination with Toxocara spp eggs in the public parks from three areas of Khorram Abad, Iran. Nepal Med Coll J 2010; 12(2):63-5. [ Google Scholar]
16. Abou-El-Naga IF. Developmental stages and viability of Toxocara canis eggs outside the host. Biomedica 2018; 38(2):189-97. doi: 10.7705/biomedica.v38i0.3684 [Crossref] [ Google Scholar]
17. Motazedian H, Mehrabani D, Tabatabaee SH, Pakniat A, Tavalali M. Prevalence of helminth ova in soil samples from public places in Shiraz. East Mediterr Health J 2006; 12(5):562-5. [ Google Scholar]
18. Ghorbani Ranjbary A, Shafie A, Anamipor A, Najy S. Frequency of Toxocara egg in public parks Shiraz/Iran. J Kerman Univ Med Sci 2014; 21(2):174-9. [ Google Scholar]
19. Choobineh M, Mikaeili F, Sadjjadi SM, Ebrahimi S, Iranmanesh S. Molecular characterization of Toxocara spp eggs isolated from public parks and playgrounds in Shiraz, Iran. J Helminthol 2019; 93(3):306-12. doi: 10.1017/s0022149x18000354 [Crossref] [ Google Scholar]
20. Rezanezhad H, Sarvestani A, Armand B, Shadmand E. Soil contamination of public parks, primary schools and kindergartens with Toxocara spp egg in Jahrom city, southern Iran. Pars J Med Sci 2017; 15(1):1-6. doi: 10.29252/jmj.15.1.1 [Crossref] [ Google Scholar]
21. Ebrahimizadeh F, Kiani Z, Sahranavard F, Shookohi G, Abolghazi A. Prevalence of Toxocara egg in the parks soil in Larestan, south of Iran in 2018. Med J Mashhad Univ Med Sci 2018; 61(5):1257-63. doi: 10.22038/mjms.2019.13339 [Crossref] [ Google Scholar]
22. Khademvatan S, Abdizadeh R, Tavalla M. Molecular characterization of Toxocara spp from soil of public areas in Ahvaz southwestern Iran. Acta Trop 2014; 135:50-4. doi: 10.1016/j.actatropica.2014.03.016 [Crossref] [ Google Scholar]
23. Kazemi F, Arjmand R, Fallahizadeh S, Tavalla M. Comparison of the detection of Toxocara spp. in the soils of public parks of Ahvaz (southwest of Iran) by PCR and Loop-Mediated Isothermal Amplification (LAMP). Infect Disord Drug Targets. 2020. 10.2174/1871526520666200715100433
24. Maraghi S, Mazhab-Jafari K, Sadjjadi SM, Latifi SM, Zibaei M. Study on the contamination of Abadan public parks soil with Toxocara spp eggs. J Environ Health Sci Eng 2014; 12:86. doi: 10.1186/2052-336x-12-86 [Crossref] [ Google Scholar]
25. Mazhab-Jafari K, Zibaei M, Maraghi S, Rouhandeh R, Helichi M, Ghafeli-Nejad M. Prevalence of Toxocara eggs in the soil of public parks of Khorramshahr city, southwest Iran. Ann Parasitol 2019; 65(4):351-6. doi: 10.17420/ap6504.220 [Crossref] [ Google Scholar]
26. Tavassoli M, Hadian M, Charesaz S, Javadi S. Toxocara spp eggs in public parks of Urmia city, West Azerbaijan province Iran. Iran J Parasitol 2008; 3(3):24-9. [ Google Scholar]
27. Garedaghi Y, Shabestari-Asl S. Contamination rate of Toxocara spp eggs in the public parks of Tabriz city: a short report. J Rafsanjan Univ Med Sci 2012; 11(2):173-8. [ Google Scholar]
28. Pezeshki A, Haniloo A, Alejafar A, Mohammadi-Ghalehbin B. Detection of Toxocara spp eggs in the soil of public places in and around of Ardabil city, northwestern Iran. Iran J Parasitol 2017; 12(1):136-42. [ Google Scholar]
29. Nematollahi A, Shahbazi P, Nasrollahi N. Contamination of the soil of public parks to Toxocara spp eggs and its relation to toxocariasis in man in Tabriz (Iran). J Zoonotic Dis 2017; 2(1):14-8. [ Google Scholar]
30. Ghashghaei O, Khedri J, Jahangiri-Nasr F, Hashemi SH, Nourollahi Fard SR. Contamination of soil samples of public parks with Toxocara spp eggs in Kermanshah, Iran. İstanbul Univ Vet Fak Derg 2016; 42(1):47-50. doi: 10.16988/iuvfd.2016.73365 [Crossref] [ Google Scholar]
31. Maleki B, Seyyed Tabaee SJ, Tahvildar F, Khorshidi A. Soil contamination of public places with Toxocara spp egg in Kermanshah, Iran, in 2014. Nov Biomed 2016; 4(3):105-9. doi: 10.22037/nbm.v4i3.10488 [Crossref] [ Google Scholar]
32. Yakhchali M, Ebn-Adamnezhad A. A study on Toxocara canis (Ascaridida: Ascaridae) infection in dogs and soil of public parks of Piranshahr city, West Azarbaijan province, Iran. J Vet Res 2014; 69(4):355-62. [ Google Scholar]
33. Viesy S, Abdi J, Rezaei Z, Karimian M. Prevalence of Toxocara spp eggs in soil samples of public parks of Ilam city, Iran. J Clin Diag Res 2020; 14(7):DC23-DC5. [ Google Scholar]
34. Raissi V, Raiesi O, Etemadi S, Firoozeh F, Getso M, Muslim Hadi A. Environmental soil contamination by Toxocara species eggs in public places of Ilam, Iran. Ann Agric Environ Med 2020; 27(1):15-8. doi: 10.26444/aaem/118130 [Crossref] [ Google Scholar]
35. Tavalla M, Oormazdi H, Akhlaghi L, Razmjou E, Moradi Lakeh M, Shojaee S. Prevalence of parasites in soil samples in Tehran public places. Afr J Biotechnol 2012; 11(20):4575-8. doi: 10.5897/ajb11.2522 [Crossref] [ Google Scholar]
36. Khazan H, Khazaei M, Seyyed Tabaee SJ, Mehrabi A. Prevalence of Toxocara spp eggs in public parks in Tehran city, Iran. Iran J Parasitol 2012; 7(3):38-42. [ Google Scholar]
37. Ghomashlooyan M, Falahati M, Mohaghegh MA, Jafari R, Mirzaei F, Kalani H. Soil contamination with Toxocara spp eggs in the public parks of Isfahan city, Central Iran. Asian Pac J Trop Dis 2015; 5:S93-S5. doi: 10.1016/s2222-1808(15)60865-9 [Crossref] [ Google Scholar]
38. Mohamadi S, Eslamirad Z, Hajihossein R, Didehdar M. The study of soil contamination with Toxocara eggs in Arak public parks, 2015. J Arak Univ Med Sci 2016; 18(12):67-73. [ Google Scholar]
39. Zibaei M, Bahadory S, Cardillo N, Khatami AR. Soil contamination with eggs of Toxocara species in public parks of Karaj, Iran. Int J Enteric Pathog 2017; 5(2):45-8. doi: 10.15171/ijep.2017.11 [Crossref] [ Google Scholar]
40. Shirvani G, Abdizadeh R, Manouchehri Naeini K, Mortezaei S, Khaksar M. The study of soil contamination by Toxocara spp eggs in different areas of Chaharmahal and Bakhtiari province, southwest Iran. Int J Epidemiol Res 2019; 6(4):177-81. doi: 10.15171/ijer.2019.31 [Crossref] [ Google Scholar]
41. Raissi V, Saber V, Zibaei M, Bahadory S, Akhlaghi E, Raiesi O. Comparison of the prevalence of Toxocara spp eggs in public parks soils in different seasons, from 2017 to 2018, Tehran province, Iran. Clin Epidemiol Glob Health 2020; 8(2):450-4. doi: 10.1016/j.cegh.2019.10.007 [Crossref] [ Google Scholar]
42. Jafari S, Norouzi R, Barabadi B. Contamination rate of Toxocara spp eggs in the public parks of Zanjan city in 2018: a short report. J Rafsanjan Univ Med Sci 2019; 17(12):1181-8. [ Google Scholar]
43. Berenji F, Movahedi Rudy AG, Fata A, Tavassoli M, Mousavi Bazaz M, Salehi Sangani G. Soil contamination with Toxocara spp eggs in public parks of Mashhad and Khaf, north east of Iran. Iran J Parasitol 2015; 10(2):286-9. [ Google Scholar]
44. Moreira GM, Telmo Pde L, Mendonça M, Moreira AN, McBride AJ, Scaini CJ. Human toxocariasis: current advances in diagnostics, treatment, and interventions. Trends Parasitol 2014; 30(9):456-64. doi: 10.1016/j.pt.2014.07.003 [Crossref] [ Google Scholar]
45. Jamalian R, Samar G, Mowlavi MA. Visceral larva migrans and a case report in Iran. J Med Council Iran 1976; 5(1):36-9. [ Google Scholar]
46. Cardillo N, Prous CG, Krivokapich S, Pittaro M, Ercole M, Perez M. First report of Toxocara cati in the domestic land snail Rumina decollata. Rev Argent Microbiol 2016; 48(3):206-9. doi: 10.1016/j.ram.2016.04.004 [Crossref] [ Google Scholar]
47. Colella V, Giannelli A, Brianti E, Ramos RA, Cantacessi C, Dantas-Torres F. Feline lungworms unlock a novel mode of parasite transmission. Sci Rep 2015; 5:13105. doi: 10.1038/srep13105 [Crossref] [ Google Scholar]
48. Otranto D, Deplazes P. Zoonotic nematodes of wild carnivores. Int J Parasitol Parasites Wildl 2019; 9:370-83. doi: 10.1016/j.ijppaw.2018.12.011 [Crossref] [ Google Scholar]
49. Nijsse R, Overgaauw P, Ploeger H, Mughini-Gras L. Sources of environmental contamination with Toxocara spp: an omnipresent parasite. Adv Parasitol 2020; 109:585-614. doi: 10.1016/bs.apar.2020.01.010 [Crossref] [ Google Scholar]