Warm and wet weather creates ideal conditions for spread of
Toxocara spp. roundworms and other canine soil-transmitted helminths
Dog parks provide an ideal urban space where dogs and their owners can exercise, play and socialise in a safe environment. These parks can however also increase the risk of exposure to infectious and parasitic agents including canine soil-transmitted helminths which are endemic to Australia, such as roundworms, hookworms, whipworms and Strongyloides spp. A recent study showed that almost half (42.6%) of all dog parks across Australia were contaminated with at least one species of canine soil-transmitted helminth, with on average more than 1 in 10 faecal samples (12.7%) testing positive.1 Climate (higher average rainfall and temperature) and socioeconomic factors (lower socioeconomic indices score) were shown to be associated with a greater risk of contamination. A consideration of these parasites is important as they impact not only animal health and wellbeing but also potentially human health, with many also being zoonotic.
Recent wet weather across the country and the forecast of an unusually warm winter by the Bureau of Meteorology may increase the risk of exposure of dogs and people to canine soil-transmitted helminths. Worm larvae develop more quickly in warm and wet conditions and can survive for longer periods of time. Additionally, heavy rain can result in the spread of worm eggs and larvae across the park, rather than having them found in or immediately next to deposited faeces.
Toxocariasis
Toxocariasis is an infection in humans caused by the larvae of Toxocara spp. roundworms. It is a clinically significant zoonosis, yet it remains a persistent problem in dogs and cats worldwide despite readily available and effective anthelmintics. Three species of roundworm are known to infest dogs and cats: Toxocara canis (canine only), T. cati(feline only) and Toxascaris leonina (canine and feline). Toxocara canis and T. cati are the most clinically significant species due to their zoonotic potential and capacity to cause disease in dogs and cats.2
A major challenge in preventing zoonotic Toxocara infections is the ability of roundworm eggs to survive for years in the environment. Human infections occur through the accidental ingestion of eggs from contaminated soil (gardens, sandpits and parks), or on unwashed hands, objects or raw vegetables.3,4 Studies from all over the world have demonstrated high rates (13-35%) of soil contamination with Toxocara spp. eggs in public places such as sandpits, parks, playgrounds and beaches.5 These worms can also infect a range of other animals such as chickens and cattle and the ingestion of raw or undercooked meat is another potential source of transmission. While roundworm cannot complete maturation in humans, developing larvae can migrate through the body and result in signs of disease.
In humans, Toxocara larvae can penetrate the intestinal mucosa and migrate to the liver, lungs and other organ systems (e.g., skeletal muscle, heart, brain and eyes). Migrating larvae are attacked by host immune responses, resulting in local inflammation. A number of clinical syndromes are recognised as being caused by Toxocara infection: visceral larva migrans, ocular larva migrans, covert or common toxocariasis, and neurotoxocariasis.6,7 In addition to more overt clinical manifestations, studies have also shown that infection with roundworm can be positively associated with asthma and epilepsy in children.6 Additionally, a recent, large national study in the United States reported a strong association between serologically confirmed infection with Toxocara spp. and diminished cognitive function in children aged 6-16 years in the general population.8 This relationship was independent of factors such as socioeconomic status, ethnicity, gender and rural residence. There is also evidence linking infection with Toxocara with neurodegenerative conditions in older individuals, including Parkinson’s disease and dementia, although more rigorous studies are needed to fully understand the significance of these associations.6
Whilst severe consequences of human toxocariasis such as blindness are fortunately rare, infection is likely common and is potentially linked to a growing body of evidence of clinical and subclinical effects. A recent meta-analysis of published data estimated that seven per cent of Australians are seropositive for Toxocara antibodies, indicating current or prior infection.9
It is likely that community awareness of the zoonotic potential of Toxocara is low. Knowledge of the risks can be a driving force for owner behaviour change and veterinarians play a crucial role in driving owner compliance for control measures such as regular anthelmintic treatment. The Australian Veterinary Association policy on the role of veterinarians in the management of zoonotic disease states, “Veterinarians should have knowledge of common and locally endemic zoonoses and their clinical impact on both animals and humans, actively educating all clients in strategies to minimize the risk of infection”.10 For Toxocara roundworms, such strategies would include:
- Prompt disposal of dog faeces on a daily basis
- Protecting playgrounds, garden areas and covering sandpits
- Ensuring good hygiene practices, washing hands after handling pets and prior to eating
- Preventing children from ingesting soil and faeces
- Deworming pets monthly
- Limit pet’s access to potential paratenic hosts (e.g., rodents)
Dr Vito Colella, a parasitologist from the University of Melbourne commented, “The effect of weather on infection of animals and humans has been studied throughout the world. Optimal rainfall, humidity, and temperature have all been shown to be associated with an increased risk of human infection with Toxocara roundworms. Given the record-breaking wet weather we have seen recently, it is important that pet owners are aware of the risk and how to manage it. To help minimise the risk roundworms pose to people, infectious disease experts recommend promptly picking up and disposing of pet faeces, hand washing after interacting with potentially contaminated soil and objects and deworming dogs monthly with appropriate products. This is important for all dog owners, but particularly so for those with young children who we know are at greatest risk.”
The Australian Companion Animal Zoonoses Guidelines cover 19 important zoonoses, providing recommendations and strategies to minimise the risk of zoonotic disease transfer from dogs and cats in the veterinary clinic and community setting. To download a copy of the Guidelines, visit Animal Health Academy (www.animalhealthacademy.com.au) by scanning the QR code below[H(RBAS1] . If you don’t already have an account, it is simple to create one using the access code: myAcademy.
NexGard SPECTRA is Australia’s #1 parasite protection brand.† It provides the most complete protection against fleas, ticks, mites, heartworm and intestinal worms, all in one monthly treatment. Using NexGard SPECTRA monthly aligns with the Australian Companion Animal Zoonoses Guidelines which recommend year-round flea control and monthly deworming of all cats and dogs to reduce the risk of zoonotic disease transmission.
Article written and supplied by Boehringer Ingelheim Animal Health
†CEESA International Sales Services MAT Q4 2023
See product label for full claim details and usage instructions.
REFERENCES
1. Massetti, L. et al. (2022) Faecal prevalence, distribution and risk factors associated with canine soil-transmitted helminths contaminating urban parks across Australia. Int J Parasitol, 52, 637–646.
2. Despommier, D. (2003) Toxocariasis: clinical aspects, epidemiology, medical ecology, and molecular aspects. Clin Microbiol Rev, 16, 265–72.
3. Robertson, I. D. & Thompson, R. C. (2002) Enteric parasitic zoonoses of domesticated dogs and cats. Microbes Infect, 4, 867–873.
4. Carvalho, E. A. de A. & Rocha, R. L. (2014) Visceral Larva Migrans Syndromes Associated with Toxocariasis: Epidemiology, Clinical and Laboratory Aspects of Human Toxocariasis. Curr Trop Med Rep, 1, 74–79.
5. Fakhri, Y. et al. (2018) Toxocara eggs in public places worldwide – A systematic review and meta-analysis. Environ Pollut, 242, 1467–1475.
6. Ma, G. et al. (2018) Human toxocariasis. Lancet Infect Dis, 18, e14–e24.
7. Chen, J. et al. (2018) Toxocariasis: a silent threat with a progressive public health impact. Infect Dis Poverty, 7, 59.
8. Walsh, M. G. & Haseeb, M. A. (2012) Reduced cognitive function in children with toxocariasis in a nationally representative sample of the United States. Int J Parasitol, 42, 1159–1163.
9. Rostami, A. et al. (2019) Seroprevalence estimates for toxocariasis in people worldwide: A systematic review and meta-analysis. PLoS Neglected Trop Dis, 13, e0007809.
10. Australian Veterinary Association. The role of veterinarians in the management of zoonotic disease. https://www.ava.com.au/policy-advocacy/policies/professional-practices-for-veterinarians/the-role-of-veterinarians-in-the-management-of-zoonotic-disease/ Accessed 29 May 2024.
[H(RBAS1]Insert QR code below this section that goes to: https://www.animalhealthacademy.com.au/course/view.php?id=1007