Recovering of Toxocara canis eggs from samples of experimentally contaminated soil

LETTER TO THE EDITOR

Recovering of Toxocara canis eggs from samples of experimentally contaminated soil

Pedro Paulo Chieffi^I,II; Maisa Leite de Queiroz^I; Fernanda Mehlmann^I; Maria Aparecida Paschoalotti^I; Susana Angelica Zevallos Lescano^II

^IFaculdade de Ciências Médicas da Santa Casa de São Paulo, São Paulo, SP, Brasil

^IIInstituto de Medicina Tropical de São Paulo (LIM 06), São Paulo, SP, Brasil

^{Correspondence to}

São Paulo, October 20, 2008

Dear Sir

Human infections by Toxocara canis or Toxocara cati larvae are frequent and have a cosmopolitan distribution^8,10 resulting, sometimes, in the occurrence of visceral larva migrans syndrome. Ingestion of embryonated Toxocara eggs, present in the superficial layers of the soil, represents the most important way for human infection by these ascarids¹. Therefore, contact with contaminated soil is considered an important risk factor for the occurrence of this particular zoonosis^1,8,10.

Several studies carried out worldwide showed soil contamination by Toxocara eggs with variable positivity rates¹. In Brazil surveys performed in several areas also reported the frequent presence of Toxocara eggs in superficial soil samples of public places^3,4,5,6,7,9 and some found seasonal variations in soil contamination^4,9.

There are reports pointing out better evolution rates for ascarid eggs when present in clayey than in sandy kind of soils. On the other hand, sandy are well aerated and relatively less-adhesive than clayey soils², perhaps facilitating recovering ascarid eggs from soil samples. We tested this assertiveness employing samples of clayey and sandy soils experimentally contaminated with Toxocara canis eggs.

One Petri dish was filled up with 100 grams of sandy soil and other with the same quantity of clayey soil. Both soil samples had been previously sterilized at 150 ºC for 40 minutes and, afterwards, were each one contaminated with 7,000 Toxocara canis eggs obtained from the uterus of dissected females. One week after, all sandy and clayey soil were completely examined by flotation in a saturated zinc sulphate solution and the quantity of recovered eggs showed in the Table 1.

Our results suggest that, despite the referred better evolution rate in clayey soils², Toxocara eggs could be more easily recovered from sandy soils and this should be taken in account for result interpretation of surveys carried out for soil contamination by ascarid eggs.

References

• 1. BARRIGA, O.O. - A critical look at the importance, prevalence and control of toxocariasis and the possibilities of immunological control. Vet. Parasit., 29:195-234,1988.
• 2. BEAVER, P.C. - Biology of soil-transmitted helminths: the massive infection. Hlth Lab. Sci., 12:116-125,1975.
• 3. CAMPOS, D.M.B.; LEÃO, D.A.; ISAC, E. & CALIL, F. - Pesquisa de ovos de Toxocara sp. em localidades públicas da cidade de Goiânia, Goiás. 1. Comparação de métodos de exame. Rev. Pat. trop., 16:7-11,1987.
• 4. CHIEFFI, P.P. & MÜLLER, E.E. - Estudo da variação mensal na contaminação do solo por ovos de Toxocara sp. (Nematoda, Ascaroidea), na zona urbana do município de Londrina, Estado do Paraná, Brasil. Rev. Inst. Adolfo Lutz, 38:13-16,1978.
• 5. COELHO, L.M.P.S.; DINI, C.Y.; MILMAN, M.H.S.A. & OLIVEIRA, S.M. - Toxocara sp. eggs in public squares of Sorocaba, São Paulo State, Brazil. Rev. Inst. Med. trop. S. Paulo, 43:189-191,2001.
• 6. COSTA-CRUZ, J.M.; NUNES, R.S. & BUSO, A.G. - Presença de ovos de Toxocara spp. em praças públicas da cidade de Uberlândia, Minas Gerais, Brasil. Rev. Inst. Med. trop. S. Paulo, 36:39-42,1994.
• 7. GUIMARÃES, A.M.; ALVES, E.G.L.; REZENDE, G.F. & RODRIGUES, M.C. - Ovos de Toxocara sp. e larvas de Ancylostoma sp. em praça pública de Lavras, MG. Rev. Saúde públ. (S. Paulo), 39:293-295,2005.
• 8. OVERGAAUW, P.A.M. - Aspects of Toxocara epidemiology: human toxocarosis. Crit. Rev. Microbiol., 23:215-231,1997.
• 9. QUEIROZ, M.L.; SIMONSEN, M.; PASCHOALOTTI, M.A. & CHIEFFI, P,P. - Frequency of soil contamination by Toxocara canis eggs in the South Region of São Paulo municipality (SP, Brazil) in a 18-month period. Rev. Inst. Med. trop. S. Paulo, 48:317-319,2006.
• 10. SCHANTZ, P.M. - Toxocara larva migrans now. Amer. J. trop. Med. Hyg., 41(suppl. 3):21-34,1989.

Publication Dates

• Publication in this collection
  09 Dec 2008
• Date of issue
  Dec 2008