Prevalence of helminth ova in soil samples from public places in Shiraz

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H. Motazedian,¹ D. Mehrabani,² S.H.R. Tabatabaee,³ A. Pakniat¹ and M. Tavalali¹

ABSTRACT To determine the prevalence of helminth eggs in public places and children’s playgrounds, 112 soil samples were collected in 26 sites in Shiraz, southern Islamic Republic of Iran, during September 2002–September 2003. Toxocara cati ova were found in 7 (6.3%) samples, 2 had Ascaris lumbricoides ova, 3 had larvae morphologically similar to Strongyloides stercoralis. Coccidia oocysts were also observed in 4 samples. No contamination was observed during the dry season.

Prévalence des œufs d’helminthes dans des échantillons de sol prélevés dans des lieux publics à Chiraz

RÉSUMÉ Afin de déterminer la prévalence des œufs d’helminthes dans des lieux publics et des aires de jeux pour enfants, 112 échantillons de sol ont été prélevés sur 26 sites à Chiraz (sud de la République islamique d’Iran) entre septembre 2002 et septembre 2003. Des œufs de Toxocara cati ont été trouvés dans 7 échantillons (6,3 %), 2 échantillons avaient des œufs d’Ascaris lumbricoides, 3 avaient des larves morphologiquement similaires à celles de Strongyloides stercoralis. Des oocytes de coccidies ont été également observés dans 4 échantillons. Aucune contamination n’a été notée pendant la saison sèche.

¹Department of Parasitology and Mycology, School of Medicine; ³School of Public Health, Shiraz University of Medical Sciences, Shiraz, Islamic Republic of Iran (Correspondence to H. Motazedian: This email address is being protected from spambots. You need JavaScript enabled to view it.).
²Razi Vaccine and Serum Research Institute, Shiraz University, Shiraz, Islamic Republic of Iran.
Received: 28/06/04; accepted: 24/11/04
EMHJ, 2006, 12(5): 562-565

Introduction

Toxocara cati and T. canis are cosmopolitan parasites of cats and dogs and have been most commonly incriminated as the cause of visceral larvae migrans and ocular larvae migrans [1–3]. Direct contact with animals that harbour adult Toxocara worms is unlikely to give rise to infection in humans; the ova must undergo a period of development in the environment before they can become infective [1].

Previous reports have noted the presence of Toxocara in stray cats, stray dogs and primary-school children in Shiraz [2–4]; in addition, Toxoplasma oocysts were found in stray cats and antibody response to Toxoplasma in primary-school children [5,6]. These findings indicate that contact with soil in public places is a potential source of contamination. Stray dogs and cats roam freely in residential areas and public places in Shiraz, and the soil in these places is easily contaminated with their faeces.

As there is a large population of stray dogs and cats in Shiraz and no studies have been made on the extent of contamination of the environment with helminth eggs, this study was undertaken to determine the prevalence of helminth eggs in public places and playgrounds.

Methods

From September 2002 to September 2003, 112 soil samples were collected by cluster random sampling from the uppermost centimetre (15 × 12 cm2) of soil in 26 public places and children’s playgrounds in 4 regions of Shiraz, Southern Iran. Sampling was carried out in all 4 seasons of the year.

Selection of collecting areas was confined to 4 divisions, south-western (region 1), north-western (region 4), south-eastern (region 3) and north-eastern (region 2) Shiraz. These are the divisions used by the Education and Culture Organization of Shiraz.

The samples were first washed with running tap water, using a set of 3 sieves of mesh width 250 µm, 120 µm and 30 µm. The residue remaining in the 30 µm sieve was flushed into a 250 mL graduated cylinder. The liquid was decanted after 15 minutes sedimentation then the sediment was transferred to a centrifuge tube, shaken with saline solution (specific gravity 1.19) and concentrated by zinc sulfate centrifugation–flotation (centrifugation for 5 minutes at 2500 rpm), and then identified microscopically. All samples were processed twice and recorded as positive if eggs or larvae were found at least once.

Results

Table 1 shows the distribution of soil samples from 26 sites in Shiraz. Helminth eggs were recovered from 12 of the 112 soil samples. The results during the whole year and the wet (autumn/winter) seasons are also summarized in Table 1. No contamination was observed during the dry season.

Eggs of T. cati were recovered from 7 samples (Table 1), Ascaris lumbricoides ova from 2 and larvae morphologically similar to Strongyloides stercoralis from 3. In addition, 4 samples contained oocysts of coccidia.

The burden of T. cati ova during the wet season and the whole year is shown in Table 1. The highest contamination rate was in downtown public places in the 3rd (22.2%) and the 4th (20.0%) regions. No contamination was observed during the dry season.

Discussion

Toxocara cati eggs were recovered from 6.3% of soil samples tested. Earlier studies in Shiraz indicated an infection rate of 52.8% in stray cats [2] and 2.9% in stray dogs [4]; around 25% of sera samples from primary-school children were positive for Toxocara [5]. In other studies, 10.78% of stray cats were infected and seropositivity for Toxoplasma gondi was 23.39% in primary-school children [3,6].

Our findings indicate that there is a possibility of human infection from the environment in public places and playgrounds in Shiraz. Embryonated ova can remain viable for a considerable length of time in soil [1]. Small children are considered at risk from geohelminth contamination because of their lifestyle and their playing environment, especially those children with a history of pica [7]. Public parks, particularly playgrounds, may be an important source of contamination [8].

Our findings on the prevalence of T. cati eggs corroborate those of other researchers: contamination with Toxocara eggs is widespread in the soil in public places [9–11].

The high prevalence of T. cati ova in the soil samples from downtown parks in the 3rd and 4th regions of Shiraz is evidence that stray dogs and cats were infected and defecate in these areas. These findings are consistent with the parasite burden in children and stray cats in these areas [2,5]. The presence of Toxocara eggs and larvae in these places emphasizes the risk to children who play there of visceral larvae migrans. Similar findings have been reported previously from Iraq and Jordan [12,13].

As humans are the final host for Ascaris lumbricoides, the presence of this parasite probably reflects the lack of public latrines. The study demonstrates that the soil in public places and playgrounds in Shiraz is a potential source of contamination. Despite the high temperatures prevalent in Shiraz in summer, clearly identifiable ova were present in many of the specimens collected. The results are of public health importance for this area. Because of the mild temperatures in winter and spring, people often spend their time in public places, especially at night.

For this reason, preventive measures should be implemented. These could include health education of the public, hygienic waste disposal, good personal hygiene practices, control of stray dogs and cats and exclusion of dogs and cats from public places and children’s playgrounds by fencing.

Acknowledgements

We would like to thank the Office of the Vice Chancellor for Research of Shiraz University of Medical Sciences for financial support and the Centre for Development of Clinical Research for typing and editorial assistance.

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