High Toxocara Egg Contamination Found in Areas of Pennsylvania Parks

A study on the level of Toxocara egg contamination of several parks in Montgomery County, Pennsylvania, found that the highest amounts of contamination were in areas that could contain food droppings or animal waste. The research comes from 13-year-old Devyn Stek, a student at St. Teresa of Calcutta School in Schwenksville, Pennsylvania, who conducted an environmental surveillance study for the school’s science fair. Her research on Toxocara eggs was analyzed further by Misoo Ellison, PhD, and presented in a poster abstract session at ID Week 2018 in San Francisco, California.

Toxocara spp. is a parasite known as roundworm. The most common reservoirs are dogs who can harbor T canis, and cats, who may carry T cati; however, other animals and humans can also be reservoirs for the parasite.

Ingestion of eggs by humans can result in an infection called toxocariasis. Most infections have no symptoms and will go away without treatment, but severe infections can cause weight loss, fever and fatigue, and it is possible for the larvae to migrate to organs and stop development. Once ingested, the worms can move throughout the body, including under the skin, and in rare cases into the eye which can result in blindness.

Children are more frequently infected with toxocariasis (~30% in 6-11-year-olds) than adults (14%) and there is a higher likelihood of hand-to-mouth transmission from contaminated soil.

To perform the study, 6 parks were identified in Montgomery County and 6 soil samples were taken from each park for a total of 36 samples. Two tablespoons of dried and sifted soil were added to a glass then covered with 1/4 cup of a sugar floatation solution which was stirred for 30 seconds. After an hour, the supernatant was transferred to a 20 mL tube and cap and left untouched overnight.

The following day, Miss Stek added 3 drops of surface fluid onto a glass slide and cover and analyzed the sample 400x total magnification, and the number of Toxocara eggs in each sample were counted.

Results indicate that 35 of 36 samples tested positive for Toxocara eggs. The parks and samples varied in their levels of contamination of Toxocara eggs.

The smallest samples (0 and 2 eggs) were collected from Sanatoga Park. The largest samples were collected from Pottstown Memorial Park [52 eggs in the picnic pavilion] and Heather Place Park [56 eggs in the tree grove]. These parks also had the highest averages, Pottstown Memorial Park (18.2 eggs [95% confidence interval (CI): 4.1, 32.1]) and Heather Place Park (18.5 eggs [95% CI: 3.5, 23.5]) and very similar average number of eggs (χ²=0.02 < 3.84).

Furthermore, Miss Stek indicated that “the average number of eggs from Sanatoga Park (2.5 eggs [95% CI: 1.0, 4.0]), Gerald Richards Park (4.0 eggs [95% CI: 3.8, 6.2]), and Althouse Arboretum (4.7 eggs [95% CI: 3.3, 6.1]) were significantly lower than Manderach Park (11.7 eggs [95% CI: 9.6, 13.8]). Sanatoga, Gerald Richards, and Heather Place had similar average number of eggs (χ²=3.97 < 5.99).”

Some limitations of the study include that the investigation did not differentiate between T canis and T cati due to their similar characteristics and that Toxocara eggs counted in the study could be other types of roundworm eggs that appear similar.

Toxocara eggs were found in every park that was tested. Although the number of eggs per sample varied, samples with the highest amounts were found in areas that could contain food droppings or animal waste.

Miss Stek was the youngest researcher to ever present at ID Week.