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

Abstract

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.

Toxocara contamination of park soils in the UK: are we underestimating the public health risk?

“…The role of dogs as the predominant source of Toxocara contamination in public parks is further supported by Airs and colleagues' observation of positive correlations between perceived levels of dog fouling and Toxocara egg presence and density. 9 Moreover, this finding suggests a link between the deposition of faeces from infected dogs in public environments and the risk of zoonotic exposure.…”

“…In research summarised on p 33 of this issue of Vet Record, Airs and colleagues have sought to address this data gap by assessing soil samples from 142 parks and recreational grounds across the UK and Ireland for Toxocara egg contamination. 9 Having recovered eggs using an adapted faecal flotation technique, enumerated and morphologically characterised them, they also speciated representative eggs by speciesspecific PCR and sequencing. In addition, they also asked the people who collected the samples to comment on the relative condition of the park and the levels of dog fouling they observed.…”

“…Toxocara-type eggs were found in 86.6 per cent of the parks sampled, with an average egg density of 2.1 eggs per 50 g of topsoil. 9 Parks where Toxocara-positive samples were recorded were widely distributed across the UK and Ireland, indicating a high risk of members of the public coming into contact with eggs. This represents a widespread and persistent hazard to public health, with eggs potentially remaining viable for several years in the soil.…”

“…Although only a small number of eggs in Airs and colleagues' study were suitable for molecular characterisation, sequencing confirmed all to be T canis. 9 In urban environments, dogs would be expected to be a greater contributor of T canis eggs than foxes. This is because although foxes have a high prevalence of T canis infection, fox population density is much lower in urban settings (<10 per km 2 ) than that of pet dogs (>100 per km 2 ).…”

Toxocarosis in humans: how much of a problem is it in the UK?

“…In another study, five soil samples were taken from each of 142 parks and recreational grounds across England, Wales, Scotland, Northern Ireland and the Ireland 40. Samples were processed sequentially, starting with one sample per park.…”