This is a rather interesting article. Although this study was conducted in Thailand, there is mention of studies in London, Spain, Italy and Japan within this article.

http://findarticles.com/p/articles/mi_qa3855/is_200403/ai_n9377621

FREQUENCY RATE OF TOXOCARA SPECIES CONTAMINATION IN SOIL SAMPLES FROM PUBLIC YARDS IN A URBAN AREA "PAYATHAI", BANGKOK, THAILAND, THE

Revista do Instituto de Medicina Tropical de Sao Paulo,  Mar/Apr 2004  by Wiwanitkit, Viroj, Waenlor, Weerachit

SUMMARY

Toxocara species are most common roundworms of Canidae and Felidae. Human toxocariasis develops by ingesting of embryonated eggs in contaminated soil. There is no previous report of Toxocara contamination in the soil samples from the public areas in Bangkok. For this reason our study have been carried out to examine the frequency of Toxocara eggs in public yards in Bangkok, Thailand. A total of 175 sand and clay samples were collected and examined for parasite eggs. According to this study, Toxocara eggs were detected from 10 (5.71%) of 175 soil samples. The high rate of contamination in this study implies the importance of the control of this possible zoonotic disease: control of abandon of dogs and cats, is still necessary.

Toxocara species are most common roundworms of Canidae and Felidae. Both T. canis and T. call arc considered the causative agents of human toxocariasis2. T. cams is well-known by its unique transmission mode, transplaccntal migration, in the definite host. The infection rates arc very high in dogs. Human toxocariasis develops by ingesting of cmbryonatcd eggs in contaminated soil.

From the reviewed literature we have found that, in Japan, the frequency rate of Toxocara eggs in sandpits in public parks ranged from 19.2 to 68.8%5 and 63.3%4. In London, GILLRSPIE et al. also reported the contamination of sandpits in parks and gardens with Tarocam canis was 6.3%2. In Spain, more than 67% of parks and 1.24% of soil samples were contaminated. In Italy, the contaminated soil with Toxocara spp. of urban and suburban area was 63.6%1.

There is no previous report of Toxocara contamination in the soil samples from the public areas in Bangkok. For this reason our study have been carried out to examine the frequency of Tatocam eggs in public yards in Payathai Subdistrict, Bangkok, Thailand. The surveyed area was about 0.5 acre. A total of 175 sand and clay samples were collected on grid from sandpits in the public yards surrounding the building. At each site, the top - soil sample, less than 2 cm depth, in an area of approximately 1 ft^sup 2^ was dug up.

All 175 samples were examined for parasite eggs according to the method reported by UGA & KATAOKA5. Briefly, a fresh soil sample of 2 g per each place was taken to the laboratory. About 2 g of powdery and wet sand was suspended in about 3 ml of aqua solution for 10 minutes. After the precipitation, the precipitant was then removed onto a microscopic slide, covered by coverslip, and examined for parasite eggs or oocysts.

According to this study, Toxocara eggs were detected from 10 (5.71%) of 175 soil samples. Of these ten positive samples, five were the Toxocara cam's and the others were Toxocara call. The density of infection for each sample was one egg per field (X400). The contamination rate in this area compared to above reported was lower. Since the setting of this study is in the capital in Thailand where the promotion of sanitation has been continuously done, the low frequency can be expected. However, we still detect the contamination hence the control of this possible zoonotic disease, control of abandon of dogs and cats, is still necessary. The study of the infection in the population in this study area is planned for our future study.