12 December 2018
Andrew Masterson
Andrew Masterson is a former editor of Cosmos.
Habitat shrinkage due to climate change will increase the number of Americans killed or injured by big animals such as bears or lynxes – but far more people will still end up in hospital after encounters with bed bugs, lice, snakes, scorpions, centipedes and dogs.
That’s the take-home message from the largest ever analysis of animal-caused injuries in the US, published in the journal Trauma Surgery & Acute Care Open.
A team of researchers led by Joseph Forrester from Stanford University in California looked at nationwide emergency department admissions between 2010 and 2014, combing through all entries logged under classifications relating to encounters with animals.
The results, note the writers, indicate that “the morbidity, mortality, and healthcare cost due to animal encounters in the USA is considerable”.
During the four-year period, 6,457,534 people presented to emergency departments around the country as a result of animal-associated injuries.
By far the biggest single proportion – some 41% – went to hospital following injuries caused by “non-venomous arthropods”. These include bed bugs, lice, mosquitoes, cockroaches and ticks.
Some 26% of admissions – about 1,658,300 – were the result of dog bites, while bites by hornets, wasps and bees comprised the third-largest cohort, at 812,000.
Being savaged by a bear or wolf – or racoon, for that matter – was so uncommon as to be statistically insignificant.
Most of the animal impacts were mild, or, at least, acute. Only 3% of cases were taken from emergency and placed in a ward – with the biggest proportion of those, some 24%, being the result of bites by venomous snakes or lizards.
Across the database, only 1162 people – or 0.02% of emergency department visitors – ended up dying from their encounter.
More sobering, however, is the discovery that of those who did die, the largest proportion – some 24% – did so as a result of being bitten, or scratched, or punctured, by non-venomous arthropods. On another scale, the odds of dying from an animal bite were highest among those unfortunate enough to be injured by a rat.
Based on those figures, it might be reasonable to assume that the odds of being harmed by an animal are highest among those who live in accommodation that is also occupied by vermin and insect pests – in other words, among vulnerable communities.
It is an observation backed up Forrester and colleagues.
“More patients were in the lowest 25% household income for their zip code,” they write.
“Bites from venomous snakes and lizards, spiders and other venomous arthropods tended to occur among patients with a lower household income.”
The healthcare cost associated with animal injuries over the period was estimated at about $6 billion, not including lost work income or take-home medicines, leading the researchers to describe the situation as a “considerable public health issue”.
And the matter is only set to worsen, they conclude. For one thing, injuries caused by large wild animals, to date negligible, are likely to scale up.
“Injuries due to mountain lions, bears, alligators, and venomous snakes among other wild animals attract considerable media attention and are associated with dramatic morbidity and mortality,” they write.
“As available habitat for these animals increasingly overlaps with human development and recreational activities, it is expected encounters with these animals may increase and could result in increased animal-related injuries.”
However, they add, climate change and consequent habitat alteration is also likely to increase injuries caused by venomous and non-venomous arthropods, which are already “considerably more frequent”.
This, they warn, “may be more likely to result in a greater economic and healthcare burden than other more dramatic, but less common, animal encounters in the future.
“Given that venomous and non-venomous arthropod injuries occurred more frequently among persons in the lower income quartile, increases in arthropod-related injury may disproportionately affect persons more influenced by cost of healthcare and lost wages.”