Letter to the Editor

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

Sir,

We read with great interest the article by Motazedian et al. entitled “Prevalence of helminth ova in soil samples from public places in Shiraz published in the Eastern Mediterranean Health Journal, 2006, 12(5):562–5” [1]. On the basis of their findings, the authors reported Toxocara cati ova in 7 (6.3%) soil samples after examination by light microscopy. However the methodology was not clearly described to understand how T. cati were differentiated from other Toxocara species, which is difficult using light microscopy. Therefore, we have some concerns about the methodological aspects of the study and the conclusions drawn.

Several studies have indicated that light microscopy is unable to differentiate Toxocara eggs isolated from soil specimens by size [2–4] and light microscopy is not helpful in the differentiation of T. canis and T. cati eggs [5]. Furthermore, the differentiation of T. canis and T. cati eggs on the basis of morphological features is difficult and inconclusive. Uga et al. [5] concluded that 89% of T. canis and 67% of T. cati eggs could be differentiated morphologically by considering the shape and size of the pits and their surrounding albuminous elevation using simple light microscopy. Reliable methods for identifying species of embryos from soil-isolated eggs during routine environmental studies are equally difficult or lacking. Therefore, given the small sample size in Motazedian et al.’s study, it would not have the power to detect contamination by T. cati eggs in soil samples. Although as indicated above, egg size alone is not helpful in such studies and not a good criterion for the differentiation of T. canis and T. cati eggs, the authors do not appear to have measured this to use in conjunction with other criteria.

Moreover, both T. cati and T. canis have been reported from cats and dogs in Shiraz [4,6]; so, it is possible to find both T. cati and T. canis eggs from soil in this region. Thus, without reliable methods for differentiation of the species, it is difficult to conclude with certainty that the isolated ova are T. cati.

To date several studies have been carried out to differentiate Toxocara spp. eggs using electron microscopy approaches rather than light microscopy [7–9], which is a superior technique.

On the bases of these observations, it can be argued that the conclusions reported by the authors are not entirely supported by their results.

References

1. Motazedian H et al. Prevalence of helminth ova in soil samples from public places in Shiraz. Eastern Mediterranean health journal, 2006, 12(5):562–5.
2. Uga S et al. Differentiation of Toxocara canis and Toxocara cati eggs by light and scanning electron microscopy. Veterinary parasitology, 2000, 92:287–94.
3. Fogt-Wyrwas R, Jarosz W, Mizgajska-Wiktor H. Utilizing a polymerase chain reaction method for the detection of Toxocara canis and T. cati eggs in soil. Journal of helminthology, 2007, 81:75–8.
4. Sadjjadi SM et al. Prevalence and intensity of infestation with Toxocara cati in stray cats in Shiraz, Iran. Veterinarski arhiv, 2001, 71:149–57.
5. Uga S et al. Prevalence of Toxocara species eggs in the sandpits of public parks in Hyogo prefecture, Japan. Japanese journal of parasitology, 1989, 38:280–4.
6. Mehrabani D, Sadjjadi SM, Oryan A. Prevalence of gastrointestinal parasites in stray dogs in Shiraz, Southern Iran. Journal of applied animal research, 2002, 22:157–60.
7. Tenora F, Stanek M, Wiger AR. [Scanning electron microscopy of eggs of parasitic Ascaridata parasites of Carnivora]. Acta Universitatis Agriculturae, Facultas Agronomica, Brno, 1983, 31:187–90 [in Norwegian].
8. Ubelaker JE, Allison VF. Scanning electron microscopy of the eggs of Ascaris lumbricoides, A. suum, Toxocara canis and T. mystax. Journal of parasitology, 1975, 61:802–7.
9. Zyngier FR. Scanning electron microscopy of Toxocara canis eggs. Revista do Instituto de Medicina Tropical de Sao Paulo, 1975, 17:269–71.

M. Zibaei* and S.M. Sadjjadi

Department of Parasitology and Mycology, School of Medicine, Shiraz University of Medical Sciences, Shiraz, Islamic Republic of Iran(This email address is being protected from spambots. You need JavaScript enabled to view it.) (This email address is being protected from spambots. You need JavaScript enabled to view it.)

*Present address: Department of Parasitology and Mycology, Lorestan School of Medicine, Lorestan University of Medical Sciences,Khorramabad, Islamic Republic of Iran

Dr Motazedian and colleagues were invited to respond to this letter, but they did not do so.

EMHJ, 2010, 16(5):580