Environmental contamination with Toxocara eggs: a quantitative approach to estimate the relative contributions of dogs, cats and foxes, and to assess the efficacy of advised interventions in dogs

Abstract

BackgroundEnvironmental contamination with Toxocara eggs is considered the main source of human toxocariasis. The contribution of different groups of hosts to this contamination is largely unknown. Current deworming advices focus mainly on dogs. However, controversy exists about blind deworming regimens for >6-month-old dogs, as most of them do not actually shed Toxocara eggs. We aim to estimate the contribution of different non-juvenile hosts to the environmental Toxocara egg contamination and to assess the effects of different Toxocara-reducing interventions for dogs.MethodsA stochastic model was developed to quantify the relative contribution to the environmental contamination with Toxocara eggs of household dogs, household cats, stray cats, and foxes, all older than 6 months in areas with varying urbanization degrees. The model was built upon an existing model developed by Morgan et al. (2013). We used both original and published data on host density, prevalence and intensity of infection, coprophagic behaviour, faeces disposal by owners, and cats’ outdoor access. Scenario analyses were performed to assess the expected reduction in dogs’ egg output according to different deworming regimens and faeces clean-up compliances. Estimates referred to the Netherlands, a country free of stray dogs.ResultsHousehold dogs accounted for 39 % of the overall egg output of >6-month-old hosts in the Netherlands, followed by stray cats (27 %), household cats (19 %), and foxes (15 %). In urban areas, egg output was dominated by stray cats (81 %). Intervention scenarios revealed that only with a high compliance (90 %) to the four times a year deworming advice, dogs’ contribution would drop from 39 to 28 %. Alternatively, when 50 % of owners would always remove their dogs’ faeces, dogs’ contribution would drop to 20 %.ConclusionAmong final hosts of Toxocara older than 6 months, dogs are the main contributors to the environmental egg contamination, though cats in total (i.e. both owned and stray) transcend this contribution. A higher than expected compliance to deworming advice is necessary to reduce dogs’ egg output meaningfully. Actions focusing solely on household dogs and cats are unlikely to sufficiently reduce environmental contamination with eggs, as stray cats and foxes are also important contributors.

Prevalence and risk factors for patent Toxocara infections in cats and cat owners’ attitude towards deworming

“…In the Netherlands, the number of household cats exceeds the number of household dogs (HAS den Bosch and Utrecht University 2015) and, while there are no stray dogs, there is a large stray cat population (Neijenhuis and van Niekerk 2015). This, combined with the typical feline defaecation behaviour, leads to cats being responsible for a substantial contribution to the environmental contamination with Toxocara eggs and possibly the occurrence of toxocariasis in humans (Nijsse et al 2015). Therefore, the public health relevance of T. cati should not be underestimated (Fisher 2003).…”

“…Stray cats probably spend even more time unattended outside, exposed to the same factors, but are likely lacking any preventative veterinary care. Therefore, their contribution to environmental contamination with Toxocara eggs is assumed to be considerable (Fisher 2003; Morgan et al 2013; Nijsse et al 2015). …”

“…cats, dogs, and foxes, cats have been estimated to be responsible for a considerable, if not the largest, portion of Toxocara spp. eggs contaminating the environment (Morgan et al 2013; Nijsse et al 2015). With the aim of reducing environmental contamination with Toxocara eggs, the guidelines of the European Scientific Counsel Companion Animal Parasites (ESCCAP) state that all adult cats should be dewormed at least four times a year to prevent patent T. cati infections (ESCCAP 2010).…”

Contamination by parasites of zoonotic importance in fecal samples from Florianópolis Beaches, Santa Catarina State, Brazil

“…These eggs remain viable in the environment for lengthy periods due to the consistency of their outer cuticle, exposing the human population to the risk of infection and disease development (NIJSSE et al, 2015).…”

Prevalence of gastrointestinal helminth parasites of zoonotic significance in dogs and cats in lower Northern Thailand

“…Humans can be infected via contact with a dog or cat or via contamination of infective stages in food or water [20, 35]. Worldwide, there is a significant variation in the prevalence of gastrointestinal zoonotic helminths in dogs and cats [19, 24].…”