Humans and their pets help parasitic worms spread around the world

Of the nearly 400 parasitic worm species that have been recorded in humans, almost 50% have been found in a diversity of wildlife including domestic animals, according to new research led by Griffith University.

Published in scientific journal Global Change Biology, the research found as much as 49% of parasites such as tapeworms, roundworms and flukes not only exist in humans but more than 500 wildlife species including primates, rodents, deer, cattle, kangaroos, and wild carnivores.

Of those parasites — more formally known as helminths — 45% are also found in domestic animals such as dogs, cats, cows, pigs, and black and brown rats.

The international research team, hailing from Australia, Spain and France, included Griffith Environmental Futures Research Institute scientists Dr Konstans Wells and Professor Hamish McCallum.

Using a global database of humans, domestic animals and wildlife species infected with such parasites, the team used a model-based analysis to predict which attributes had the greatest impact on creating conditions for parasites to cross between species.

They examined a range of factors affecting parasite spillover between mammalian species including diet — which was found to be the major factor of whether a wildlife species shares parasitic worms with humans — as well as geography (moderate impact) and climate and habitat (lower impact).

The researchers discovered that wildlife with a vegetation diet (e.g. cows and deer) and carnivores such as dogs, wolves and foxes are the most likely animals to share parasites with humans.

Notably, insectivore species such as bats, which are known to share a range of viruses with humans, are not as likely to share helminth infections with humans.

“Complete separation of domestic animals from wildlife is not feasible, but as individuals we can reduce such interactions for our personal benefits.”

The researchers also found the risk of parasite spillover has likely been exacerbated by the onset of globalisation as humans have increased their presence and mobility around the world.

According to figures from the World Health Organisation, more than 800 million people are in need of treatment for parasitic worms — and the risk of transmission will continue to grow as a result of future changes to the global distribution of species.

Also affecting transmission risk are factors including the proximity in which humans and animals are living, and the likelihood that they will eventually engage in predator-prey relationships.

The physical closeness between humans and domestic animals in particular — and their shared encroachment on wildlife habitats — is also thought to broaden the diversity of parasite transmission pathways and thus the range of parasites exchanged between humans, domestic animals and wildlife species.

“Control measures that minimise the interactions of humans and domestic animals with wildlife are necessary if we want to reduce the risk of parasite spillover,” Dr Wells said.

“Complete separation of domestic animals from wildlife is not feasible, but as individuals we can reduce such interactions for our personal benefits, and region stakeholders can use preventative measures to reduce parasite spillover in our neighbourhood.”