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VETcpd - Parasitology
ova (Overgaauw and Van Knapen 2013, Wright et al. 2016).The eggs when first shed are unembryonated (Figure 3.)
and are not infective. Progression to the infective embryonated stage is required for infection so fresh faeces do not
present a zoonotic risk. Once Toxocara
spp. eggs develop to the infective stage in the environment then they represent a zoonotic risk that can lead to debilitation, blindness and increased risks of chronic conditions such as asthma, epilepsy and dermatitis if eggs are ingested (Overgaauw and Van Knapen 2013).
Although dogs may be infected by ingesting embryonated eggs, the most important route of canine infection is trans-placental. As a result, prevalence
of infection in pups born to untreated dams can reach close to 100%. Dogs may also become infected by trans-mammary infection or consuming paratenic hosts such as rodents.The latter is more important in T.cati transmission where
the feline host frequently hunts and trans- placental transmission does not occur. Trans-mammary infection ensures high prevalence in puppies and kittens without anthelmintic intervention (Figure 4).
Although it
people can be infected by eating the undercooked meat of paratenic hosts such as wild game, the most common route
of human infection is by the ingestion
of embryonated eggs. It was originally thought that T.canis alone was the source of human infection by this route but
there is now strong evidence to suggest that T.cati is significantly involved as well (Fisher 2003). Zoonotic infection through oral ingestion of embryonated eggs can occur through accidental or deliberate consumption of contaminated soil, fruit and vegetables or through transfer of
eggs from the coats of pets.The basis of toxocarosis control is therefore reducing environmental contamination with ova. Routine use of preventative anthelmintics is just one component of reducing toxocarosis risk. Other control measures include:
1. Minimising environmental contamination with cat and dog faeces UK county councils are taking the threat of dog fouling increasingly seriously but cat faecal contamination with Toxocara
ova also needs to be considered to reduce human exposure overall. Covering sand pits when not in use to prevent faecal contamination from cats will help to avoid children playing in these areas being exposed to ova. In addition, cleaning
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Figure 4: Toxocara canis life cycle (courtesy Bayer) Subscribers
has been pro
posed that
outdoor toys before allowing children months significantly reduces Toxocara
Only
to play with them will help to reduce
spp. ova shedding (Wright & Wolfe
2007) and there is no evidence that less frequent deworming frequencies will
have any effect on egg output.Therefore, this frequency should be a minimum recommendation in dogs and cats. Use of a monthly anthelmintic will reduce egg output by over 90% and whether this is necessary will depend on the pet’s lifestyle increasing zoonotic risk, such as puppies, kittens, those hunting, in contact with young children or immune suppressed individuals. T.canis and T.cati are both susceptible to a wide range of licensed anthelmintics such as benzimadazoles
(e.g. Fenbendazole), macrocyclic
lactones (moxidectin, milbeycine oxime, eprinomectin), pyrantel and emodepside.
Fleas
Cat fleas can live on a wide variety of mammalian hosts including cats, dogs, rabbits and wildlife such as foxes and hedgehogs (Clark et al. 2018).They are also well suited to living in the humidity and temperatures maintained in most UK homes with 95% of a typical flea infestation existing in the home as eggs, larvae and pupae.This combination of factors leads to increased flea challenge
exposure. Reduction in the number of
stray cats through neutering and rehoming
programs will also help to reduce the
numbers of untreated cats contributing to
environmental contamination.Veterinary
practices are often already directly or
indirectly supporting cat charities in neutering and rehoming, and reduction of human toxocarosis is a significant health benefit from development of these partnerships.
2. Hand hygiene
Washing hands, particularly before preparing and handling food, will help block transmission of a number of different faecal-oral parasites including Toxocara spp.
3. Washing of fruit and vegetables intended for raw consumption Produce from gardens and allotments can easily be contaminated with cat faeces and as a result should be washed before consumption.
These measures will not however, prevent exposure to Toxocara eggs on their own and routine deworming of cats and dogs is also required to minimise exposure.
It has been demonstrated that use of an effective anthelmintic every three