Flotation and adherence characteristics of Toxocara canis and T. cati and a reliable method for recovering Toxocara eggs from soil

WormWatch: Park soil surveillance reveals extensive Toxocara contamination across the UK and Ireland

BACKGROUND

Toxocarosis is a globally distributed zoonotic disease, but sources of infection are not well documented over large geographical scales. To determine levels of environmental contamination, soil from 142 parks and recreational areas across the UK and Ireland was assessed for the presence of Toxocara.

METHODS

Toxocara ova (eggs) were isolated from soil samples by sieving and flotation and then enumerated. Individual eggs were isolated and imaged, and a subset was characterised by species-specific PCR and Sanger sequencing.

RESULTS

Characteristic Toxocara-type eggs were found in 86.6% of parks, with an average of 2.1 eggs per 50 g of topsoil. Representative eggs were confirmed as Toxocara canis by Sanger sequencing, with many eggs containing developed larvae, hence being viable and potentially infective. Positive samples were more common, and egg density was higher, in parks with greater perceived levels of dog fouling.

LIMITATIONS

Samples were collected at a single timepoint and with limited spatial mapping within parks. Further study is needed to discern spatiotemporal differences within parks and recreational areas.

CONCLUSION

Toxocara is widespread in soil in public parks, indicating a need for further efforts to reduce egg shedding from pet dogs. Standardised methods and large-scale surveys are required to evaluate risk factors for egg presence and the impact of interventions.

Potentials and challenges in the isolation and detection of ascarid eggs in complex environmental matrices

Ascarid infections constitute a major concern for both human and animal health risk assessment. Although being effectively transmitted by soil, water and contaminated food, reliable detection of ascarid eggs in environmental media often remains challenging. However, contamination of the environment with ascarid ova has gained more attention as a decisive part of proper risk assessment in recent years. Due to various factors, such as sample matrices, dissociation detergents and flotation solutions, defined and standardised protocols for the isolation of eggs from complex environmental matrices are difficult to establish and therefore limited. Thus, this study reviews common techniques used for the recovery of ascarid eggs from environmental media with special emphasis on sampling strategies, purification procedures and microscopic as well as molecular detection of egg contamination. Despite various advancements, mainly in the field of molecular methods leading to more reliable and sensitive detection, it can be concluded that there is still a need for unified guidelines for sampling and recovery of ascarid eggs derived from complex environmental matrices.

The Role of Nile Tilapia (Oreochromis niloticus) in the Life Cycle of Toxocara spp

The present study aimed to experimentally assess Nile tilapia as potential paratenic host of Toxocara spp. A total of 15 Nile tilapia (Oreochromis niloticus) were fed with 300 embryonated Toxocara canis eggs by oral gavage, while five others of the control group received distilled water. The fish were individually analyzed at 16, 24, 48, 72, and 240 h after inoculation. Water contamination was assessed, and tissue migration by liver, gastrointestinal tract (GIT), eyes, and central nervous system. A murine model was used as the paratenic host for egg infectivity assessment. Eggs and larvae were found in plastic tank water and fish GIT, ranging from 23 to 86% per fish. Eggs and larvae were recovered from the tank water (76.3%) and fish GIT (23.7%). The counting of eggs and larvae observed was negatively correlated with number of eggs and larvae in the water tank (rho = -0.698, p = 0.003). Shedding of embryonated eggs was first detected at 16 and up to 240 h, with significant egg and larvae yield decrease on water-shedding (p = 0.001) and in the GIT (p = 0.007). Although no T. canis larva was recovered in fish tissues, egg infectivity after fish GIT transit was experimentally confirmed by mice assessment. In conclusion, despite shedding viable embryonated eggs through the gastrointestinal tract, tilapias may not play a role as a suitable paratenic hosts for Toxocara spp., posing low risk of zoonotic transmission by fish meat consumption.

Soil Contamination with Toxocara Eggs in Public Schools in Rural Areas of Southern Thailand

Soil is considered the primary source of Toxocara transmission to humans, especially children. The status of soil contamination with Toxocara eggs in southern Thailand is unknown. This study aimed at estimating the soil contamination with Toxocara eggs in public schools in Nakhon Si Thammarat province in southern Thailand. Soil samples were collected from 12 public schools between August and September 2017. At each site, ten soil samples were collected from the following five types of locations: (1) playgrounds, (2) football fields, (3) sidewalks, (4) schoolyards, and (5) areas around cafeterias. In total, 120 samples were examined for Toxocara eggs with a modified flotation method using a sucrose solution. Toxocara eggs were detected in 8 (66.7%) of the 12 studied public schools. Of the 120 soil samples, 22 (18.3%; 95% CI: 11.9, 26.4) were contaminated with Toxocara eggs. The highest levels of Toxocara egg contamination were observed in playgrounds (41.7%; 95% CI: 22.1, 63.4), followed by football fields (20.8%; 95% CI: 7.1, 42.2), sidewalks (12.5%; 95% CI: 2.7, 32.4), and schoolyards (12.5%; 95% CI: 2.7, 32.4). There were significant differences in the distribution of Toxocara eggs across location types (p < 0.05). The findings demonstrated that the soil samples from public schools were contaminated with Toxocara eggs. Playgrounds were the most heavily contaminated locations. Teaching children proper handwashing steps and discouraging geophagia should be implemented to reduce the distribution of Toxocara and limit future Toxocara infections.

Toxocara species environmental contamination of public spaces in New York City

Human toxocariasis has been identified as an under-diagnosed parasitic zoonosis and health disparity of significant public health importance in the United States due to its high seropositivity among socioeconomically disadvantaged groups, and possible links to cognitive and developmental delays. Through microscopy and quantitative PCR, we detected that Toxocara eggs are widespread in New York City public spaces, with evidence of significant levels of contamination in all five boroughs. The Bronx had the highest contamination rate (66.7%), while Manhattan had the lowest contamination rate (29.6%). Moreover, infective eggs were only found in the Bronx playgrounds, with over 70% of eggs recovered in embryonic form and the highest egg burden (p = 0.0365). All other boroughs had eggs in the pre-infectious, unembronyated form. Toxocara cati, the cat roundworm, was the predominant species. These results suggest that feral or untreated cats in New York City represent a significant source of environmental contamination. These findings indicate that human toxocariasis has emerged as an important health disparity in New York City, with ongoing risk of acquiring Toxocara infection in public spaces, especially in poorer neighborhoods. There is a need for reducing environmental Toxocara contamination. Additional rigorous public health interventions should explore further approaches to interrupt transmission to humans.

Toxocara canis and Toxocara cati are helminth worms that infect dogs and cats, respectively. Infected dogs and cats will defecate thousands of Toxocara eggs into the environment. Humans are incidental hosts and are exposed when consuming contaminated soils via the fecal-oral route. After leaving the gastrointestinal tract, the Toxocara larvae will enter the vasculature and can migrate to any major organ system, including lungs, ocular, and central nervous system. Symptoms can range from mild muscle aches to severe asthma, blindness, and encephalitis. Humans are not definitive hosts of the parasite and cannot transmit Toxocara eggs to the environment or other humans. There is a need for research on the sanitary impact of Toxocara for both humans and animals, especially in large urban cities such as New York City. Poverty is also associated with higher rates of toxocariasis, with more contamination in poorer neighborhoods where animal control, deworming of pets, and less sanitary conditions exist. This study aims to understand further the disparity of lower socioeconomic areas having higher rates of contaminated parks and playgrounds, comparing the five boroughs of New York City.

Sources of environmental contamination with Toxocara spp.: An omnipresent parasite

Embryonated Toxocara eggs in the environment are considered to be the most important source of human toxocariasis. These eggs, however, are also a source of infection for the definitive and paratenic hosts. Most available literature focuses on Toxocara canis in dogs, or other canids. There are, however, other Toxocara species with their accompanying definitive hosts. Results from studies that modelled patent infections in dogs, cats and foxes show that although dogs are a very important source for environmental contamination with Toxocara eggs, other sources cannot be ignored. For a good understanding of the relative contributions of different definitive hosts to environmental contamination with Toxocara eggs, computational models should be built and fed with data from different fields of expertise as is discussed in this paper.

Seasonal variation in the prevalence of Toxocara eggs on children's playgrounds in the city of Hanover, Germany

BACKGROUND

Roundworms of the genus Toxocara are worldwide distributed zoonotic parasites of carnivores. Based on case numbers and the potential impact on human health, the Centers for Disease Control and Prevention (CDC) categorised toxocarosis as one of the most important neglected parasitic diseases. As contact with contaminated soil, e.g. in sandpits, is considered the primary transmission route, data on playground contamination are needed to assess infection risk for children. Here, playground contamination rates and their seasonal variation in the city of Hanover, Germany, were investigated.

METHODS

Sand samples were collected monthly over a 12-month period on 46 playgrounds in the city of Hanover, Germany. In total, 1,362 samples were examined for Toxocara eggs and analysed statistically for seasonal influences on potential infection risk.

RESULTS

Contamination rates ranged from 6.5% (3/46) Toxocara positive sandpits in September to 41.3% (19/46) in February, while contamination with infective embryonated eggs varied between 2.2% (1/46) and 23.9% (11/46). Compared to September, the month with the lowest contamination rate, significantly more sandpits were positive for Toxocara eggs from January to August and in October, while the prevalence of infective Toxocara eggs was significantly increased only in January and February. Regarding egg numbers, significantly higher total counts were observed in October and from December to June, while infective egg counts were significantly increased only in January, February and April.

CONCLUSIONS

Compared to data from 1985, contamination rates have dropped from 55.8% to an average of 23.2% in 2011. Even though the observed egg numbers indicate a moderate to low general infection risk, the potential risk to single individuals should not be underestimated, as highly contaminated spots may occur infrequently and independent of season.