Zoonotic diseases

Human Toxocariasis

Human toxocariasis (HT), caused by the dog and cat parasites Toxocara canis/cati, is a significantly underdiagnosed public health issue around the world (Rostami et al., 2019).

It can cause a wide range of diseases, from childhood asthma (Momen et al., 2018), urticaria (Vinas et al. 2020) and neuropsychiatric disorders (Fan, 2020) to decreased cognitive function in children and young adults (Walsh and Haseeb, 2012; Erickson et al., 2015).

However, HT is rarely on a differential list, particularly when clinical signs in children are as nondescript as fever, abdominal pain, nausea and wheezing, and therefore it’s rarely diagnosed (Ma et al., 2018).

How do we become infected?

Humans become infected by ingesting eggs containing infective larvae, for example through eating raw meat or children eating soil.

Larvae penetrate the intestinal wall and are transported to different tissues through the bloodstream (Strube et al., 2013). The persistence of larvae in the brain, eye, liver and muscle can cause a broad range of clinical symptoms that occur most often in children (Despommier, 2003).

There are four distinct syndromes, and these are described in Table 1.

Is it time to update the treatment advice we give?

It’s extremely easy to treat Toxocara, with choices including tasty chews for dogs and spot-on products for cats. Given that the prepatent period of Toxocara spp. is just over a month, worming monthly is the best way to minimise egg shedding in animals.

However, a common advice to worm every three months has been around for decades, and it appears veterinarians are reluctant to update it based on two main objections:

The fact that infection in adults is less common than it is in juveniles should be weighed against the comparatively large ratio of adults to puppies and kittens; this means adults account for a significant proportion of eggs entering the environment (Morgan et al., 2013).

In addition, unnecessary drug exposure and resistance should always be considered when prescribing prophylaxis, but not at the expense of minimising zoonotic risk and safeguarding children’s health (Pennelegion et al., 2020)

Parasites of dogs and cats have large natural reservoirs of infection (refugia) (Pennelegion et al., 2020) that are not exposed to dewormers, such as birds, rodents and feral cats, and of course the numerous pet owners that actively provide refugia for us by not deworming their pets.

Given this, we need to reconsider the argument for not treating monthly to reduce the risk of resistance development. This means we would be deliberately withholding treatment and allowing zoonotic worm eggs to be shed into the environment – a practice that’s difficult to justify on public health grounds.

In addition, treating animals that don’t have infections poses no risk of anthelmintic resistance development, and there are no reports worldwide of resistance in Toxocara spp. (European Scientific Counsel for Companion Animal Parasites, 2020).

Key recommendations

There are several independent, research based advisory groups that provide recommendations for Toxocara treatment in cats and dogs (CAPC, ESCCAP, TroCCAP and ACAZAP)

The European Scientific Counsel for Companion Animal Parasites provides research-based, independent advice to veterinarians and pet owners. It recommends that adult dogs and cats who go outside be wormed at least four times a year, and monthly if they:

are fed raw meat
are working/therapy dogs
are in contact with children under five years (that includes if dogs or cats go near areas where children play such as playgrounds or sandboxes)
live with immunocompromised individuals

Webinar by Professor Eric Morgan

Veterinarians have an important role in protecting public health as well as animal health and there are many ways to reduce environmental contamination from Toxocara. A good source of more information on these is a webinar by Professor Eric Morgan, professor of Veterinary Parasitology at Queen’s University, Belfast.

Human Toxocariasis

Human toxocariasis (HT), caused by the dog and cat parasites Toxocara canis/cati, is a significantly underdiagnosed public health issue around the world (Rostami et al., 2019).

It can cause a wide range of diseases, from childhood asthma (Momen et al., 2018), urticaria (Vinas et al. 2020) and neuropsychiatric disorders (Fan, 2020) to decreased cognitive function in children and young adults (Walsh and Haseeb, 2012; Erickson et al., 2015).

However, HT is rarely on a differential list, particularly when clinical signs in children are as nondescript as fever, abdominal pain, nausea and wheezing, and therefore it’s rarely diagnosed (Ma et al., 2018).

How do we become infected?

Is it time to update the treatment advice we give?

Key recommendations

Webinar by Professor Eric Morgan

Further Reading: Articles by Dr Abi Chase BSc(Hons) BVMS PhD (parasitology)

What's Next?

Digital Tiles - for Facebook, Instagram, websites and eDMs

Short Videos - for clinic screens, social channels, websites

Short Videos

References

Human Toxocariasis

Human toxocariasis (HT), caused by the dog and cat parasites Toxocara canis/cati, is a significantly underdiagnosed public health issue around the world (Rostami et al., 2019).

It can cause a wide range of diseases, from childhood asthma (Momen et al., 2018), urticaria (Vinas et al. 2020) and neuropsychiatric disorders (Fan, 2020) to decreased cognitive function in children and young adults (Walsh and Haseeb, 2012; Erickson et al., 2015).

However, HT is rarely on a differential list, particularly when clinical signs in children are as nondescript as fever, abdominal pain, nausea and wheezing, and therefore it’s rarely diagnosed (Ma et al., 2018).

How do we become infected?

Is it time to update the treatment advice we give?

Key recommendations

Webinar by Professor Eric Morgan

Further Reading: Articles by Dr Abi Chase BSc(Hons) BVMS PhD (parasitology)

What's Next?

Digital Tiles - for Facebook, Instagram, websites and eDMs

Short Videos - for clinic screens, social channels, websites

Digital Tiles for social, web and eDM

Short Videos

References